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ChemPhysChem - published by Wiley
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ZnO nanorod arrays are a very eligible option as electron acceptor material in hybrid solar cells, owing to their favorable electrical properties and abundance of available, easy, and low-cost synthesis methods. To become truly effective in this field, a major prerequisite is the ability to tune the nanorod dimensions towards optimal compatibility with electron-donating absorber materials. In this work, a water-based seeding and growth procedure is used to synthesize ZnO nanorods. The nanorod diameter is tuned either by modifying the zinc concentration of the seeding solution or by changing the concentration of the hydrothermal growth solution. The consequences of this morphological tailoring in the performance of hybrid solar cells are investigated, which leads to a new record efficiency of 0.82?% for hydrothermally grown ZnO nanorods of size 300?nm in combination with poly(3-hexylthiophene-2,5-diyl) (P3HT). This improvement is attributed to a combined effect of nanorod diameter and orientation, and possibly to a better alignment of the P3HT backbone resulting in improved charge transport.Connecting rods: The consequences of morphological tailoring in the performance of hybrid solar cells are investigated (see picture), which leads to a new record efficiency of 0.82?% for hydrothermally grown ZnO nanorods in combination with poly(3-hexylthiophene-2,5-diyl) (P3HT). This improvement is attributed to a combined effect of nanorod diameter and orientation, and to a better alignment of the P3HT backbone resulting in improved charge transport.
On p. 2051 W. Deng et al. study acene-modified triphenylamine dyes and they predict that TPA-AC3 with an anthracene moiety shows a balance of energetic and spectroscopic parameters, and is promising for dye-sensitized solar cells.
Recent advances have expanded the application of STED microscopy to various topics from cell biology to material science. On p. 1986, A. Kraegeloh et al. introduce the working principle and discuss new techniques and their usage for structural and functional analyses.
Although gas-filled nanoscale bubbles that are stable for days to months have been identified on different solid surfaces, current theories predict that they should not exist at all. This special section is dedicated to this interesting phenomenon. James R. T. Seddon and Joost H. Weijs are kindly acknowledged for compiling this image.
An improved ability to manipulate nanoscale objects could spur the field of nanotechnology. Optical tweezers offer the compelling advantage that manipulation is performed in a non-invasive manner. However, traditional optical tweezers based on laser beams focused with microscope lenses face limitations due to the diffraction limit, which states that conventional lenses can focus light to spots no smaller than roughly half the wavelength. This has motivated recent work on optical trapping based on the sub-wavelength field distributions of surface plasmon nanostructures. This approach offers the benefits of higher precision and resolution, and the possibility of large-scale parallelization. Herein, we discuss the fundamentals of optical manipulation using surface plasmon resonance structures. We describe two important issues in plasmonic trapping: optical design and thermal management strategies. Finally, we describe a surface plasmon nanostructure, consisting of a gold nanopillar that takes these issues into consideration. It is shown to enable the trapping and rotation (manual and passive) of nanoparticles. Methods by which this concept can be extended are discussed.Conventional optical tweezers, in which lasers are focused with microscope objectives, are limited in the trapping force they can exert on an object for a given laser power. In this Concept, the authors review the fundamentals of optical tweezers and describe an optical nanotweezer (see picture) that exceeds the performance limitations of conventional tweezers while avoiding thermal effects with a heat-sinking approach.
Steady-state and time-resolved fluorescence behavior of coumarin?153 (C153) is investigated in a series of 1-ethyl-3-methylimidazolium alkylsulfate ([C2mim][CnOSO3]) ionic liquids differing only in the length of the linear alkyl chain (n=4, 6, and 8) in the anion. The aim of the present study is to understand the role of alkyl chain length in solute rotation and solvation dynamics of C153 in these ionic liquids. The blueshift observed in the steady-state absorption and emission maxima of C153 on going from the C4OSO3 to the C8OSO3 system indicates increasing nonpolar character of the microenvironment of the solute with increasing length of the alkyl side chain of the anion of the ionic liquids. The average solvation time is also found to increase on changing the substituent from butyl to octyl, and this is attributed to the increase in the bulk viscosity of the ILs. A steady blueshift of the time-zero maximum of the fluorescence spectrum with increasing alkyl chain length also indicates that the probe molecule experiences a less polar environment in the early part of the dynamics. Rotational dynamics of C153 are also analyzed by using the Stokes–Einstein–Debye (SED), Gierer–Wirtz (GW), and Dote–Kivelson–Schwartz (DKS) theories. Analyses of the results seem to suggest decoupling of the rotational motion of the probe from solvent viscosity.Blueshifts in steady-state absorption and emission maxima of coumarin?153 on going from 1-ethyl-3-methylimidazolium (EMIM) butyl- through hexyl- to octylsulfate ionic liquids (BSU, HSU, OSU, respectively; see picture) indicates increasing nonpolar character of the microenvironment of the solute with increasing length of the alkyl side chain of the anion.
Two new NIR-absorbing BODIPY dyes, each bearing two pyridinium groups, are synthesized and their DNA-binding affinities and DNA photocleavage abilities examined in depth. While one BODIPY dye photocleaves DNA mainly through singlet oxygen, the other photocleaves DNA through both singlet oxygen and hydroxyl radical. To the best of our knowledge, this is the first example of a hydroxyl radical being involved in the photodynamic behavior of BODIPY-type dyes. EPR experiments confirm the ability of these and several related BODIPYs to generate superoxide anion radical and hydroxyl radical. This finding may shed light on the mechanism of BODIPY-based photodynamic therapy (PDT) and open a new avenue for development of more efficient BODIPY-type PDT agents.New photocleavage mechanism: New cationic BODIPY dye 6 is found, for the first time, to be able to generate singlet oxygen (1O2), superoxide anion radical (O2.?) and hydroxyl radical (.OH) simultaneously on irradiation (??600?nm). Both 1O2 and .OH participate in photocleavage of DNA by this BODIPY dye.
Photoresponsive polymeric films fabricated by a facile electrostatic self-assembly technique are utilized to switch protein adsorption by light irradiation. The introduction of SiO2 nanoparticles on the substrate results in a large reversible change of both wettability and protein adsorption.
Good connections: A graphene–CdSe quantum dot (QD) nanocomposite is prepared through a one-step hydrothermal method using graphene oxide (GO), Cd(CH3COO)2, Na2SeSO3, and aminoethanethiol (AET). The bifunctional AET acts not only as a covalent linker but also as a reductant to transform GO into graphene. The photoactive graphene–QD nanocomposite exhibits a significantly higher photocurrent compared to the QDs, GO or the graphene substrate under illumination.
Camera-based fluorescence correlation spectroscopy (FCS) approaches allow the measurement of thousands of contiguous points yielding excellent statistics and details of sample structure. Imaging total internal reflection FCS (ITIR-FCS) provides these measurements on lipid membranes. Herein, we determine the influence of the point spread function (PSF) of the optical system, the laser power used, and the time resolution of the camera on the accuracy of diffusion coefficient and concentration measurements. We demonstrate that the PSF can be accurately determined by ITIR-FCS and that the laser power and time resolution can be varied over a wide range with limited influence on the measurement of the diffusion coefficient whereas the concentration measurements are sensitive to changes in the measurement parameters. One advantage of ITIR-FCS is that the measurement of the PSF has to be performed only once for a given optical setup, in contrast to confocal FCS in which calibrations have to be performed at least once per measurement day. Using optimized experimental conditions we provide diffusion coefficients for over ten different lipid membranes consisting of one, two and three constituents, measured in over 200000 individual correlation functions. Using software binning and thus the inherent advantage of ITIR-FCS of providing multiple observation areas in a single measurement we test the FCS diffusion law and show how they can be complemented by the local information provided by the difference in cross-correlation functions (?CCF). With the determination of the PSF by ITIR-FCS and the optimization of measurement conditions ITIR-FCS becomes a calibration-free method. This allows us to provide measurements of absolute diffusion coefficients for bilayers with different compositions, which were stable over many different bilayer preparations over a time of at least one year, using a single PSF calibration.A new method to determine the point spread function (PSF, see picture) based on the autocorrelation functions obtained from camera-based fluorescence correlation spectroscopy (FCS) measurements is proposed. Using this correct value for the PSF, the authors report diffusion coefficients of a number of supported lipid bilayers on glass, demonstrate the spatial organization of these model membranes, and provide limits on the laser power and time resolution in camera-based FCS.
Graphene, the thinnest two-dimensional material in nature, has abundant distinctive properties, such as ultrahigh carrier mobility, superior thermal conductivity, very high surface-to-volume ratio, anomalous quantum Hall effect, and so on. Laterally confined, thin, and long strips of graphene, namely, graphene nanoribbons (GNRs), can open the bandgap in the semimetal and give it the potential to replace silicon in future electronics. Great efforts are devoted to achieving high-quality GNRs with narrow widths and smooth edges. This minireview reports the latest progress in experimental and theoretical studies on GNR synthesis. Different methods of GNR synthesis—unzipping of carbon nanotubes (CNTs), cutting of graphene, and the direct synthesis of GNRs—are discussed, and their advantages and disadvantages are compared in detail. Current challenges and the prospects in this rapidly developing field are also addressed.Making ribbons: Synthetic methods for graphene nanoribbons, including unzipping of carbon nanotubes, lithographic patterning and plasma etching of graphene, cutting of graphene sheets by metal nanoparticles or oxidation, and chemical synthesis (see picture), are reviewed from both experimental and theoretical viewpoints, and advantages and disadvantages of these methods are compared.
Magnetic and luminescent bifunctional divalent europium nanocrystals (Eu2+ NCs) are a promising class of novel advanced materials that have various applications in magneto-optic devices, catalysis, bioimaging, and solar cells. In the past few decades, much work has been carried out to study the synthesis, properties, and applications of Eu2+ NCs. The aim of this Minireview is to present the progress in preparing Eu2+ NCs based on the reported research, by describing the advantages and disadvantages of the synthesis methods. The morphologies and size are controlled through adjusting the experimental conditions. Eu2+ NCs show superior magnetic and luminescence properties simultaneously. Self-assembly and doping with other ions are important routes to improve their magnetic and luminescence properties. Their applications in magneto-optic devices are discussed. Some difficulties and challenges in the fabrication of Eu2+ NCs are discussed, such as water-soluble Eu2+ NCs and tunable luminescence in the whole visible region.Under control: Divalent europium nanocrystals (Eu2+ NCs) are a promising class of novel advanced materials that have various applications in magneto-optic devices, catalysis, bioimaging, and solar cells. This Minireview presents the progress in preparing Eu2+ NCs (see picture). Some difficulties and challenges in Eu2+ NC fabrication are discussed, such as water-soluble Eu2+ NCs and tunable luminescence in the whole visible region.
Much effort has been devoted to investigating the unusual properties of the ? electrons in Möbius cyclacenes, which are localized in a special region. However, the localized ? electrons are a disadvantage for applications in optoelectronics, because intramolecular charge transfer is limited. This raises the question of how the intramolecular charge transfer of a Möbius cyclacene with clearly localized ? electrons can be enhanced. To this end, [8]Möbius cyclacene ([8]MC) is used as a conjugated bridge in a donor–?-conjugated bridge–acceptor (D–?–A) system, and NH2-6-[8]MC-10-NO2 exhibits a fascinating spiral charge-transfer transition character that results in a significant difference in dipole moments ?? between the ground state and the crucial excited state. The ?? value of 6.832?D for NH2-6-[8]MC-10-NO2 is clearly larger than that of 0.209?D for [8]MC. Correspondingly, the first hyperpolarizability of NH2-6-[8]MC-10-NO2 of 12?467?a.u. is dramatically larger than that of 261?a.u. for [8]MC. Thus, constructing a D–?–A framework is an effective strategy to induce greater spiral intramolecular charge transfer in MC although the ? electrons are localized in a special region. This new insight into the properties of ? electrons in Möbius cyclacenes may provide valuable information for their applications in optoelectronics.Spiral ? bridge: [8]Möbius cyclacene is used as a one-sided ?-conjugated bridge in a donor–?–acceptor framework to induce large intramolecular electron transfer. For example, NH2-6-[8]MC-10-NO2 (see picture) shows dramatic enhancement of the first hyperpolarizability ?0, because the difference in dipole moments ?? between the ground and the crucial excited states is significantly increased.
Natural orbital functional theory (NOFT) is used for the first time in the analysis of different types of chemical bonds. Concretely, the Piris natural orbital functional PNOF5 is used. It provides a localization scheme that yields an orbital picture which agrees very well with the empirical valence shell electron pair repulsion theory (VSEPR) and Bent’s rule, as well as with other theoretical pictures provided by valence bond (VB) or linear combination of atomic orbitals–molecular orbital (LCAO-MO) methods. In this context, PNOF5 provides a novel tool for chemical bond analysis. In this work, PNOF5 is applied to selected molecules that have ionic, polar covalent, covalent, multiple (? and ?), 3c–2e, and 3c–4e bonds.A localized orbital picture which agrees with chemical intuition is provided by Piris natural orbital functional in its fifth implementation (PNOF5). As an example, PNOF5 valence orbitals of ethane, ethylene, and acetylene, along with their corresponding diagonal Lagrange multipliers in Hartrees and occupation numbers in parenthesis, are shown in the picture.
The structural characteristics of fully-hydrogenated carbon and boron nitride mono- and multilayer slabs, together with nanotubes derived from the slabs, are investigated mainly by means of periodic local second-order Møller–Plesset perturbation (LMP2) calculations and the results are compared with Hartree–Fock (HF), density functional theory (DFT), and dispersion function-augmented DFT (DFT-D) obtained ones. The investigated systems are structurally analogous to (111) and (110) slabs of diamond, where the hydrogenated (111) slab of diamond corresponds to the experimentally known graphane. Multilayering of monolayers and nanotubes is energetically favorable at the LMP2 level for both C and BN, while HF and DFT are not able to reproduce this behavior for CH systems. The work highlights the importance of utilizing methods capable of properly describing weak interactions in the investigation of dispersively-bound systems such as the multilayered graphanes and the corresponding nanotubes.Layer-up: Quantum chemical methods are used to investigate the structural characteristics of fully-hydrogenated monolayers and nanotubes of both C and BN, placing particular emphasis on the potential of the nanostructures to form multilayered structures analogous to graphite and h-BN. The energetic preference of the nanostructures for existing as multilayered structures (see picture) is demonstrated.
Thermodynamic parameters obtained from studying the micellization of amphiphilic p-sulfonatocalix[n]arenes were correlated with the alkyl chain length and with the number of monomeric units (n) in the calix[n]arene structure. The micellization Gibbs free energy (?${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$) becomes more negative upon increasing the alkyl chain length of the p-sulfonatocalix[4]arene. This is in agreement with the trend generally observed for other surfactants. However, the ?${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ value for transferring one CH2 group from the bulk aqueous medium to the micelle [?${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$(CH2)] is lower than the value generally observed for single-chain surfactants, suggesting the existence of intramolecular interactions between the alkyl chains of the free unimers. On the other hand, the critical micelle concentration (cmc; per alkyl chain unit) increased with the increasing number of monomeric units. These results are explained on the basis of the conformation adopted by the calixarene in the bulk solution. The calix[4]arene derivatives are preorganized into the cone conformation, which is favorable for the formation of globular aggregates. The calix[6]arene and calix[8]arene derivatives do not adopt cone conformations. Changing these conformations to the more favorable cone conformer in the aggregates implies an energetic cost that contributes to making ?${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$ less efficient. In the case of the calix[6]arene derivative this energetic cost is enthalpic, whereas in the case of the octamer it is both enthalpic and entropic. Both the ?${G{{{\rm o}\hfill \atop {\rm M}\hfill}}}$(CH2) value and the change in heat capacity (?C${{\rm p}{{{\rm o}\hfill \atop {\rm M}\hfill}}}$) seem to indicate that for the cone calix[4]arene derivatives all alkyl chains are solvated by the same hydration shell, whereas in the case of the highly flexible calix[8]arene derivative each alkyl chain is individually hydrated.Stand out from the crowd: A microcalorimetric study on the aggregation of amphiphilic calix[n]arenes provided detailed information about the hydration of the hydrophobic alkyl chain in this special class of surfactants and supported previous observations of preorganization effects contributing to the free energy of micellization in these amphiphiles (see picture).
A low temperature route to crystalline titania nanostructures in thin films is presented. The synthesis is performed by the combination of sol-gel processes, using a novel precursor for this kind of application, an ethylene glycol-modified titanate (EGMT), and the structure templating by micro-phase separation of a di-block copolymer. Different temperatures around 100?°C are investigated. The nanostructure morphology is examined with scanning electron microscopy, whereas the crystal structure and thin film compositions are examined by scattering methods. Optoelectronic measurements reveal the band-gap energies and sub-band states of the titania films. An optimum titania thin film is created at temperatures not higher than 90?°C, regarding sponge-like morphology with pore sizes of 25–30?nm, porosity of up to 71?% near the sample surface, and crystallinity of titania in the rutile phase. The low temperature during synthesis is of high importance for photovoltaic applications and renders the resulting titania films interesting for future energy solutions.Less is more: A low temperature route to crystalline titania nanostructures is presented. Deliberate tailoring of the nanostructures obtained from an ethylene glycol-modified titanate precursor on large sample areas is achieved by combining sol-gel chemistry with a block-copolymer template. Annealing at 90?°C only leads to a well-defined crystalline titania network structure, as probed with scanning electron microscopy (see picture).
Model structures of 1,3,5-triarylbenzenes with a substituted benzene core linked to thienyl or 3,4-ethylenedioxythienyl (EDOT) terminal groups are studied by electrochemical and in situ ESR/UV/Vis/NIR spectroelectrochemical techniques. Oxidative polymerization of the monomers results in CC coupling of the thiophene moieties in the 5-position, forming dimeric structures with bithiophene linkers as the first step. Both the doubly charged protonated dimer and the new dimer formed after proton release are studied in detail for 2,4,6-tris[2-(3,4-ethylenedioxythienyl)]-1-methoxybenzene. Quite high stability of the doubly charged ? dimer formed on oxidation with unusual redox behavior at the electrode is observed. Density functional calculations of the molecular structure as well as spectroscopic and electronic properties of charged states in 1,3,5-triarylbenzene derivatives in the monomeric, dimeric, and oligomeric form are presented. The complex spectroelectrochemical response of a thin solid film formed on the electrode surface upon potentiodynamic polymerization indicates the existence of different charge states of oligomeric structures within the solid matrix.Redox-active, cross-linked, hyperbranched polymers: On oxidative polymerization of various 1,3,5-trithienylbenzenes with methoxy-substituted benzene cores, CC coupling of the thienyl substituents leads to a variety of oligomeric structures, as revealed inter alia by cyclic voltammetry (see picture; C green, H gray, O red, S yellow).
Fast and fancy: Lithium that was originally disordered within the structure of the perovskite Li0.18Sr0.66Ti0.5Nb0.5O3 can be induced into ordering within the yellow region of the unit cell by low temperatures and treatment with n-butyl-lithium. The fast kinetics of lithium insertion, in connection with a color change, make this nontoxic, air-stable material a suitable candidate for use in electrochromic systems or lithium-storage batteries.
A theoretical treatment of a Schottky barrier dynamic response is developed on the basis of a general model of a semiconductor with thickness comparable in length to the space charge region width. It is shown that, when the space charge region approaches the metal/semiconductor interface, the electric field at this interface, induced by the charge accumulated on the metal, becomes significant with respect to the electric field induced by the charge accumulated on the semiconductor. Under this condition, the total capacitance of the Schottky barrier becomes independent of the polarization potential and tends to the value ?/L, like in a pure dielectric insulator. The term thin film is intended to be with respect to the screening length, which is a function of the volumetric charge density. In amorphous materials the transition potential at which the semiconducting to insulating behaviour is observed is dependent on the frequency. An approximated analytical solution for the capacitance of the junction is calculated. The model for finite thickness semiconductors is successfully applied to the study of anodic Nb2O5, formed in phosphate buffer 0.5?M aqueous solution up to different formation potentials (namely 5, 10 and 20?V vs. Ag/AgCl). The finite thickness semiconductor model permits extrapolation to a general behaviour of the oxide in a wide range of frequencies, potentials and thicknesses, and identification of the electron transfer between adsorbed surface species and the conduction band of Nb2O5 at potentials near to the flat band value.The other side counts: The charge accumulated on the metal/semiconductor (M/SC) junction interfaced with electrolyte (El) gives rise to an induced bound charge density, ?, which influences the ac response of the semiconductor in solution (see picture).
In recent years, an enormous amount of research has been devoted to the study of photosensitive materials from both fundamental and practical viewpoints, due to their wide applications in photocatalytic[1–3] and optoelectronic devices,[4,?5] ultraviolet (UV) photodetectors,[6–9] photoswitch microdevices,[10,?11] light-emitting diodes,[12,?13] photovoltaic devices,[14–16] and photoelectrochemical cells.[17] Metal oxides, such as ZnO, TiO2, SnO2, and NiO have been the most investigated photosensitive materials.[3,?6–8,?18–21] To enhance and take full advantage of their photosensitivity, functionalizing their surface with a polymer that has a high light absorption ability has become one of the widely used methods.[1–12,?22–24] For example, Z.?L. Wang et?al. reported that the UV photocurrent of a ZnO nanobelt-based sensor was enhanced by close to five orders of magnitude after functionalizing its surface with polystyrene sulfate which has a high UV absorption ability.[25] T. Sasaki et?al. reported the assembly of a TiO2 nanoparticle film with poly(3,4-ethylenedioxythiophene) and poly(4-styrene sulfonate) (PEDOT-PSS) through layer-by-layer fabrication in the nanometer scale. The electric conductivity of the TiO2 composite films could be tuned by UV and visible (Vis) light.[22] Thus, sunlight or photon energy can be used and transformed to electrical energy by UV-photosensitive metal oxides after their surfaces have been functionalized with a dye that has a high Vis absorption ability. To date, most of the dye-sensitized solar cells are based on the surface functionalization of UV-photosensitive metal oxides by dyes.[26–28] However, to the best of our knowledge, all of the reports on surface functionalization enhanced only the UV photosensitivity of the metal oxide. In other words, this method has been used exclusively to enhance the UV photocurrent in metal oxides that already have UV-photosensitive properties, but not to induce UV photocurrent in metal oxides that have no UV-photosensitive properties. In fact, to the best of our knowledge, there are no surface-functionalizing reports on inducing UV or Vis photocurrent in metal oxides that have no UV- or Vis-photosensitive properties.No longer silent: A surface-functionalization method with well-matched energy levels is presented to induce UV or Vis photoresponse in semiconducting materials (see picture) that provide only weak photoresponse prior to the treatment or are completely silent. UV and Vis photoresponses of the metal oxides, Bi2O3 and V2O5, have been realized for the first time through the functionalization of their surfaces with polyaniline.
Spray-assisted layer-by-layer assembly is applied to the fabrication of functional thin film composites based on colloidal semiconductor nanocrystals (see picture). The technique is capable of handling various material combinations, yielding varying functional architectures. Light-emitting devices, including those of all-inorganic design, are generated in order to demonstrate the potential applicability and versatility of this approach.
Fullerene peapods have opened the possibility of studying reactions in a confined space (see picture) that might lead to materials which under other conditions would be impossible to synthesize. Progress has been made, but there are more challenges are ahead.
This work shows that colloidal stability and aggregation kinetics of hydrophobic polystyrene (PS) nanospheres are extremely sensitive to the nature of the salt used to coagulate them. Three PS latices and four aggregating electrolytes, which all share the same cation (Na+) but have various anions located at different positions in the classical Hofmeister series depending on their kosmotropic or chaotropic character, are used. The present study focuses on analyzing different aggregating parameters, such as critical coagulation concentrations (CCC), cluster size distributions (CSD), initial kinetic constants K11, and fractal dimensions of the aggregates df. While aggregation induced by SO42? and Cl? behaved according to the predictions of the classical Derjaguin–Landau–Verwey–Overbeek theory, important discrepancies are found with NO3?, which become dramatic when using SCN?. These discrepancies among the anions were far more significant when they acted as counterions rather than as co-ions. While SO42? and Cl? trigger fast diffusion-limited aggregation, SCN? gives rise to a stationary cluster size distribution in a few aggregation times when working with cationic PS particles. Clear differences are found among all analyzed parameters (CCC, CSD, K11, and df), and the experimental findings show that particles aggregate in potential wells whose depth is controlled by the chaotropic character of the anion. This paper presents new experimental evidence that may help to understand the microscopic origin of Hofmeister effects, as the observations are consistent with appealing theoretical models developed in the last few years.Aggregation kinetics of a polystyrene latex is detected by means of changes in the intensity of light scattered at 5°. The salt concentration was always constant, set at 600?mM (see picture), but the nature of the anions was changed: NaCl (blue triangles), NaNO3 (cyan circles), NaSCN (green squares), and Na2SO4 (red stars).
The conformational distributions of N-acetyl-L-cysteine (NALC) in aqueous solutions at several representative pH values are investigated using vibrational absorption (VA), UV/Vis, and vibrational circular dichroism (VCD) spectroscopy, together with DFT and molecular dynamics (MD) simulations. The experimental VA and UV/Vis spectra of NALC in water are obtained under strongly acid, neutral, and strongly basic conditions, as well as the VCD spectrum at pH?7 in D2O. Extensive searches are carried out to locate the most stable conformers of the protonated, neutral, deprotonated, and doubly deprotonated NALC species at the B3LYP/6-311++G(d,p) level. The inclusion of the polarizable continuum model (PCM) modifies the geometries and the relative stabilities of the conformers noticeably. The simulated PCM VA spectra show significantly better agreement with the experimental data than the gas-phase ones, thus allowing assignment of the conformational distributions and dominant species under each experimental condition. To further properly account for the discrepancies noted between the experimental and simulated VCD spectra, PCM and the explicit solvent model are utilized. MD simulations are used to aid the modelling of the NALC–(water)N clusters. The geometry optimization, harmonic frequency calculations, and VA and VCD intensities are computed for the NALC–(water)3,4 clusters at the B3LYP/6-311++G(d,p) level without and with the PCM. The inclusion of both explicit and implicit solvation models at the same time provides a decisively better agreement between theory and experiment and therefore conclusive information about the conformational distributions of NALC in water and hydrogen-bonding interactions between NALC and water molecules.Role models:N-Acetylcysteine is investigated in aqueous solutions of different pH values using vibrational absorption and vibrational circular dichroism spectroscopy in combination with ab initio and molecular dynamics calculations. Implicit and explicit solvation models, the latter based on small water-solvated clusters (see picture), are systematically evaluated to derive detailed conformational distributions.
Large scale for small size: We report a large-scale synthetic method to produce uniform and ultra-small-sized Ag nanoparticles (see picture) with good productivity. This method is simple and efficient. It produces Ag nanoparticles within 20?min by heating a reaction mixture containing only three chemicals. The size of the nanoparticles is controlled by varying the heating rate.
Atom transfer radical polymerization (ATRP) was initially developed in the mid-1990s, and with continued refinement and use has led to significant discoveries in new materials. However, metal contamination of the polymer product is an issue that has proven detrimental to widespread industrial application of ATRP. The laboratories of K. Matyjaszewski have made significant progress towards removing this impediment, leading the development of “activators regenerated by electron transfer” ATRP (ARGET ATRP) and electrochemically mediated ATRP (eATRP) technologies. These variants of ATRP allow polymers to be produced with great molecular weight and functionality control but at significantly reduced catalyst concentrations, typically at parts per million levels. This Concept examines these polymerizations in terms of their mechanism and outcomes, and is aimed at giving the reader an overview of recent developments in the field of ATRP.Less is better: Atom transfer radical polymerization (ATRP) is examined in terms of recent developments in activators regenerated by electron transfer (ARGET) ATRP and electrochemically mediated ATRP (eATRP), techniques that significantly reduce metal catalyst concentrations.
We review our recent efforts utilizing poly(N-isopropylacrylamide)-co-acrylic acid (pNIPAm-co-AAc) microgels and their assemblies for the removal of an azo-dye molecule, 4-(2-Hyrodxy-1-napthylazo) benzenesulfonic acid sodium salt (Orange?II), from aqueous solutions. First, the ability of dispersed, single microgels to remove Orange?II from aqueous solutions at room temperature is discussed.[1] Uptake efficiency (i.e., the amount of Orange?II removed from water) increased with AAc composition in the microgels, yielding a maximum uptake efficiency of 29.5?% for pNIPAm microgels with 10?% AAc. Assemblies of microgels (aggregates) were also investigated for their removal efficiency, which yielded a maximum uptake efficiency of 44.1?% at room temperature.[2] Removal efficiencies for the microgels and their aggregates were also monitored at elevated temperatures, and a maximum of 56.6?% removal efficiency was achieved for unaggregated microgels, while aggregates were able to remove 73.1?% Orange?II. To further explore the impact of the microgel system’s structure on function, we investigated the role microgel size in the aggregates plays on the uptake efficiency. Initial observations showed that the aggregates composed of microgels with large diameter yielded improved uptake efficiency over the aggregates composed of small diameter microgels. Langmuir sorption isotherms were fit to the data for the dye removal by the unaggregated and aggregated microgels, which showed good fits in all cases.Water contamination is a global epidemic, and new, more effective water-remediation approaches need to be devised. In this Concept, the authors review basic water-remediation approaches with a focus on water remediation using poly(N-isopropylacrylamide)-based microgels and their assemblies.
A simple and useful thermodynamic approach to the prediction of reactions taking place during thermal treatment of layers of multinary semiconductor compounds on different substrates has been developed. The method, which uses the extensive information for the possible binary compounds to assess the stability of multinary phases, is illustrated with the examples of Cu(In,Ga)Se2 and Cu2ZnSnSe4 as well as other less-studied ternary and quaternary semiconductors that have the potential for use as absorbers in photovoltaic devices.The solar-cell materials Cu2ZnSnSe4 and Cu(In,Ga)Se2 (CZTS and CIGS) are taken as a case study to show how thermal stability at surfaces and interfaces can be predicted and rationalized. The authors describe how the annealing conditions can be controlled to maximize the stability—and therefore the quality—of the material.
CuO/ZnO nanocomposites were synthesized on Al2O3 substrates by a hybrid plasma-assisted approach, combining the initial growth of ZnO columnar arrays by plasma-enhanced chemical vapor deposition (PE-CVD) and subsequent radio frequency (RF) sputtering of copper, followed by final annealing in air. Chemical, morphological, and structural analyses revealed the formation of high-purity nanosystems, characterized by a controllable dispersion of CuO particles into ZnO matrices. The high surface-to-volume ratio of the obtained materials, along with intimate CuO/ZnO intermixing, resulted in the efficient detection of various oxidizing and reducing gases (such as O3, CH3CH2OH, and H2). The obtained data are critically discussed and interrelated with the chemical and physical properties of the nanocomposites.Trapped in the array: High-purity p-type CuO/n-type ZnO nanocomposites were prepared by Cu sputtering on columnar ZnO arrays obtained by plasma-enhanced chemical vapor deposition, followed by annealing in air. Preliminary gas-sensing tests revealed very attractive responses, along with the possibility of discriminating between oxidizing and reducing species.
Anodically grown WO3 photoelectrodes prepared in an N-methylformamide (NMF) electrolyte have been investigated with the aim of exploring the effects induced by anodization time and water concentration in the electrochemical bath on the properties of the resulting photoanodes. An n-type WO3 semiconductor is one of the most promising photoanodes for hydrogen production from water splitting and the electrochemical anodization of tungsten allows very good photoelectrodes, which are characterized by a low charge-transfer resistance and an increased spectral response in the visible region, to be obtained. These photoanodes were investigated by a combination of steady state and transient photoelectrochemical techniques and a correlation between photocurrent produced, morphology, and charge transport has been evaluated.Light capture: Anodically grown WO3 electrodes show interesting properties displaying both a partial visible absorption and good charge-transport abilities. They exhibit typical crystalline oxide nanostructures and they reach 70?% of photon-to-current conversion in 1?M H2SO4 at 1.5?V versus SCE under illumination (see picture).
The general case of a heterogeneous electron-transfer reaction is realized by ultrafast electron transfer from a light-absorbing molecule to a wide continuum of electronic acceptor states, realizing the so-called wide band limit. Experimental data obtained for perylene dye/TiO2 systems confirm the predictions of fully quantum mechanical model calculations of the dynamics. The energy distribution of the injected electron shows an energy loss due to excitations of high-energy (quantum) vibrational modes in the ionized perylene moiety. The electron-transfer mechanism is non-adiabatic and the reaction is ultrafast, for example, with a time constant of 9?fs for the COOH anchor-bridge group. The underlying strong coupling of the electronic states to high-energy vibrational modes is a characteristic feature of sensitizer molecules.Electron-transfer reaction dynamics at electrodes (see picture) have a long history of both theoretical modeling and experimental efforts to test such theories with contributions by many researchers. This Minireview reports on the most recent fundamental experimental data which have solved some of the long-standing issues and opened up the field to further experimental and theoretical progress.
Firefly luciferase catalyzes a light-emitting reaction in which an excited-state product is formed. Both experimental and theoretical methodologies are used to study this system, and the reactions catalyzed by luciferase are relatively well characterized. However, the mechanism by which an excited-state product is formed is still unknown. This Minireview deals with the current understanding of firefly bioluminescence and chemiluminescence. Thermal decomposition of simple 1,2-dioxetanes is also discussed, due to their role in formation of the excited-state bioluminophore.Efficient bio- and chemiluminescence of firefly oxyluciferin are reviewed. The thermal decomposition of firefly dioxetanones and 1,2-dioxetanes is discussed (see picture), as are their chemiexcitation mechanisms.
Flavin adenine dinucleotide (FAD) and flavin mononucleotide (FMN) are derivatives of riboflavin (RF), a water-soluble vitamin, more commonly known as vitamin B2. Flavins have attracted special attention in the last few years because of the recent discovery of a large number of flavoproteins. In this work, these flavins are used as extrinsic fluorescence markers for probing the microheterogeneous environment of a well-known transport protein, human serum albumin (HSA). Steady-state and time-resolved fluorescence experiments confirm that both FMN and FAD bind to the Sudlow’s site-1 (SS1) binding pocket of HSA, where Trp214 resides. In the case of RF, a fraction of RF molecules binds at the SS1, whereas the major fraction of RF molecules remains unbound or surface bound to the protein. Moreover, flavin(s)–HSA interactions are monitored with the help of isothermal titration calorimetry, which provides free energy, enthalpy, and entropy changes of binding along with the binding constants. The molecular picture of binding interaction between flavins and HSA is well explored by docking and molecular dynamics studies.Where do the flavins bind? The binding interactions of riboflavin (RF), flavin adenine dinucleotide (FAD), and flavin mononucleotide (FMN) with human serum albumin (see picture) are monitored by steady-state and time-resolved fluorescence spectroscopy, isothermal titration calorimetry, and circular dichroism studies. The results are supported by docking and molecular dynamics simulation studies.
A double-zero quantum (DZQ)-refocused INADEQUATE experiment is introduced for J-based NMR correlations under ultra-fast (60?kHz) magic angle spinning (MAS). The experiment records two spectra in the same dataset, a double quantum–single quantum (DQ-SQ) and zero quantum–single quantum (ZQ-SQ) spectrum, whereby the corresponding signals appear at different chemical shifts in ?1. Furthermore, the spin-state selective excitation (S3E) J-decoupling block is incorporated in place of the second refocusing echo of the INADEQUATE scheme, providing an additional gain in sensitivity and resolution. The two sub-spectra acquired in this way can be treated separately by a shearing transformation, producing two diagonal-free single quantum (SQ-SQ)-type spectra, which are subsequently recombined to give an additional sensitivity enhancement, thus offering an improvement greater than a factor of two as compared to the original refocused INADEQUATE experiment. The combined DZQ scheme retains transverse magnetization on the initially polarized (I) spin, which typically exhibits a longer transverse dephasing time (T2?) than its through-bond neighbour (S). By doing so, less magnetization is lost during the refocusing periods in the sequence to give even further gains in sensitivity for the J correlations. The experiment is demonstrated for the correlation between the carbonyl (CO) and alpha (CA) carbons in a microcrystalline sample of fully protonated, [15N,13C]-labelled CuII,?ZnII superoxide dismutase, and its efficiency is discussed with respect to other J-based schemes.Multitasking: The implementation of a new scheme for through-bond correlations in solids is presented, which provides remarkable transfer efficiencies, by simultaneous detection of multiple-quantum coherences, and improved resolution, by integrating a virtual J-decoupling block (see picture). The application to a microcrystalline protein sample is presented.
Silica aerogels possess a variety of unique and remarkable properties, but the mechanisms of silicon alkoxide, Si(OR)4, hydrolyses and oligomerization in the initial stage of sol–gel processes are still not well understood. On the basis of density functional theory calculations at the B3LYP/6-31G(d,p)//B3LYP/6-311++G(d,p) basis set level, the hydrolysis and oligomerization reactions of Si(OR)4 in neutral, acidic, and alkaline solutions were systematically investigated and we found that in acidic solutions the precursor Si(OCH3)4 was inclined to hydrolyze rather than to condense and the hydrolysis processes were energetically more favorable than the neutral ones. In alkaline solutions, the hydrolysis products oligomerize through an SN1 dimerization mechanism and the condensation rates are fast to form denser colloidal aerogels. Our calculations also testify that the subsequent cyclization reactions are energetically unfavorable.Overcoming barriers: The hydrolysis–oligomerization mechanisms of silicon alkoxides in neutral, acidic (see picture), and alkaline solutions were revealed with density functional theory calculations.
Single-molecule force spectroscopy (SMFS) opens new avenues for elucidating the structures and functions of large coiled molecules such as synthetic and biopolymers at the single-molecule level. In addition, some of the features in the force–extension curves (i.e. force spectra) are closely related to primary/secondary structures of the molecules being stretched. For example, the long force plateau in the DNA stretching curve is related to the double-helix structure. These features can be regarded as the force fingerprints of individual macromolecules. These force fingerprints can therefore be used as indicators/criteria of single-molecule manipulation during the measurement of some unknown intra- or intermolecular interactions. By comparing the force spectra of a single polymer chain before and after interaction with other molecules, the mode/strength of such molecular interactions can be derived. This Review focuses on recent advances in AFM-based SMFS studies on molecular interactions in both synthetic and biopolymer systems using a single macromolecular chain as probe, including interactions between nucleic acids and proteins, mechanochemistry of covalent bonds, conformation-regulated enzymatic reactions, adsorption and desorption of biopolymers on a flat surface or from the nanopore of a carbon nanotube, and polymer interactions in the condensed state.Feel the force! Recent advances in single-molecule force spectroscopic studies on inter- and intrapolymer interactions, mechanochemistry of covalent bonds, force-induced acceleration/inhibition of enzymatic reactions, polymer–interface interactions, and polymer interactions in the condensed state, by using the polymer chain as probe, are reviewed. Future opportunities and challenges are discussed.
Bacterial infections remain one of the biggest concerns to our society. Conventional antibiotic treatments showed little effect on the increasing number of antibiotic-resistant bacteria. Advances in synthetic chemistry and nanotechnology have resulted in a new class of nanometer-scale materials with distinguished properties and great potential to be an alternative for antibiotics. In this Minireview, we address the current situation of medical-device-associated infections and the emerging opportunities for antibacterial nanomaterials in preventing these complications. Several important antimicrobial nanomaterials emergent from advances in synthesis chemistry are introduced and their bactericidal mechanisms are analyzed. In addition, concerns regarding the biocompatibility of such materials are also addressed.Nanomaterials to the rescue: Medical-device-associated bacterial infections remain challenges to modern medicine. Several nanomaterials have proven to be effective antibacterial agents (see graphic). The increasing number of antibiotic-resistant bacteria makes such materials valuable tools for fighting infection.
This paper reports on an ATR-FTIR spectroscopic investigation of the CO2 absorption characteristics of a series of heterocyclic diamines: hexahydropyrimidine (HHPY), 2-methyl and 2,2-dimethylhexahydropyrimidine (MHHPY and DMHHPY), hexahydropyridazine (HHPZ), piperazine (PZ) and 2,5- and 2,6-dimethylpiperazine (2,6-DMPZ and 2,5-DMPZ). By using in situ ATR-FTIR the structure–activity relationship of the reaction between heterocyclic diamines and CO2 is probed. PZ forms a hydrolysis-resistant carbamate derivative, while HHPY forms a more labile carbamate species with increased susceptibility to hydrolysis, particularly at higher CO2 loadings (>0.5?mol CO2/mol amine). HHPY exhibits similar reactivity toward CO2 to PZ, but with improved aqueous solubility. The ?-methyl-substituted MHHPY favours HCO3? formation, but MHHPY exhibits comparable CO2 absorption capacity to conventional amines MEA and DEA. MHHPY show improved reactivity compared to the conventional ?-methyl- substituted primary amine 2-amino-2-methyl-1-propanol. DMHHPY is representative of blended amine systems, and its reactivity highlights the advantages of such systems. HHPZ is relatively unreactive towards CO2. The CO2 absorption capacity CA (mol CO2/mol amine) and initial rates of absorption RIA (mol CO2/mol amine min?1) for each reactive diamine are determined: PZ: CA=0.92, RIA=0.045; 2,6-DMPZ: CA=0.86, RIA=0.025; 2,5-DMPZ: CA=0.88, RIA=0.018; HHPY: CA=0.85, RIA=0.032; MHHPY: CA=0.86, RIA=0.018; DMHHPY: CA=1.1, RIA=0.032; and HHPZ: no reaction. Calculations at the B3LYP/6-31+G** and MP2/6-31+G** calculations show that the substitution patterns of the heterocyclic diamines affect carbamate stability, which influences hydrolysis rates.Carbon dioxide fixation by absorption in aqueous solutions of heterocyclic diamines (hexahydropyrimidine, 2-methyl- and 2,2-dimethylhexahydropyrimidine, hexahydropyridazine, piperazine and 2,5- and 2,6-dimethylpiperazine) is studied by ATR-FTIR spectroscopy (see picture).
The recent discovery of Ag@AgX (X=Cl, Br, I) plasmonic photocatalysts motivates us to elucidate the origin of the higher photocatalytic performance compared to commonly used TiO2-based materials. Herein, the electronic structure and effective masses of electrons at the conduction band minimum (CBM) and holes at the valence band maximum (VBM) are studied along different directions in the silver halide for the first time by means of first-principles calculations. It is revealed that the smaller effective mass of electrons at the CBM in silver halides contributes to the higher photocatalytic performance. The remarkable dependence of the effective mass of holes on the direction and the anion of the silver halide explains well the experimental observed morphology and anion dependence of photocatalytic activities of Ag@AgX. The crystal field splitting of the Ag 4d bands in the valance band of silver halides is found to be a main factor leading to the large effective mass of the photogenerated holes and consequently to a weaker transfer ability. A new crystal design and exerting strain along the coordinate axis are proposed as solutions to decrease the effective mass of holes. The present work may be helpful in exploring this novel class of silver halide-based photocatalysts.What?s your weight? The electronic structures and effective masses of electrons and holes in silver halides are studied. The effective mass of holes differs along different directions and with the anion of the silver halide (see picture). The effective mass characteristics of the holes can be used to understand the experimental observed morphology and anion effects on the photocatalytic activities of silver halide-based Ag@AgX (X=Cl, Br, I).
Methanol was co-adsorbed with oxygen on Ru(0001) under conditions approaching those of real catalysts: at room temperature and at relatively high pressures and exposures, together with a comparative analysis of flat and defective surfaces. To clarify reaction routes, parallel exposures to formaldehyde and oxygen have also been analyzed. It is found that for both mixtures of gases, a new reaction path is activated on defective surfaces, in which methanol is oxidized to formate. Furthermore, at variance with pure methanol adsorption, apart from CO, various intermediates are observed in both flat and defective surfaces. On flat surfaces, formaldehyde and formyl are recognized whereas on defective ones methoxy and formate are detected. A model involving steering effects is presented, which accounts for the activity of surface defects towards the synthesis of formate.The discreet charm of imperfections: A new reaction path emerges during methanol oxidation on Ru(0001) when the surface has a high concentration of surface defects, namely the formation of formate (see graphic).
As indicated by nearly perfect XRD data, but challenged by a two-signal IR spectrum of CO guest molecules, it is confirmed by computer simulations and XPS experiments that the most defect-free SURMOFs contain about 4?% defective Cu sites.Nobody?s perfect: As indicated by nearly perfect XRD data, but challenged by a two-signal IR spectrum of CO guest molecules, it is confirmed by computer simulations and XPS experiments (see picture) that the most defect-free SURMOFs contain about 4?% defective Cu sites.
Gestalt: The (LiHHHLi)+ cation can be looked at in two ways ? as a stabilized linear H3? anion. Or as two LiH molecules stabilizing a proton. It is not certain if this interesting pentatomic cation can be detected, for it is computed to have only marginal stability with respect to decomposition to its only likely escape channel, to a complex of H2 and the LiHLi+ ion.
Solvation at the interphase: A study of the influence of water on the effective acidity of silanol and carboxylic acid groups of propionic acid functionalized SBA-15 reveals that to affect the proton-donating ability of an acidic group at the surface, water should be able to form a solvation shell around that group. As a result, water does not affect the acidity of native SBA-15 but dramatically enhances that of SBA-15 functionalized with propionic acid moieties.
A chiral molecule absorbs preferentially right- or left-handed circularly polarized light in a circular dichroism (CD) measurement. Usually, the chirality of individual molecules is regarded as the origin of the CD signals. However, recently, several reports have suggested that the vortex flow of a solution of an achiral molecule gives rise to a CD signal, which is dependent on the stirring direction. This article introduces types of molecular architecture and material designs that show stir-induced chirality. We also discuss the effects of the molecular structure and alignment in vortex flows on this phenomena, reviewing the related issues.Stir to chirality: Several types of supramolecular structures formed by achiral molecules exhibit chirality in a vortex flow used as a source of physical chirality. This article describes which chemical structures show chirality in stirred solutions and how they affect this phenomenon with reviewing the related studies.
We report an unusual alignment behavior of liquid crystals (LCs) on well-ordered comb-like poly(oxyethylene) surfaces. The homeotropic LC alignments that are observed on as-coated surfaces of the polymers are transformed to the random planar type after annealing treatment, even though the molecular structure of the polymer surface becomes more ordered and the surface energy decreases. Studies of the surface properties, such as molecular structure, morphology, and wettability, reveal that such an unexpected alteration of the LC alignment originates from the density of the alkyl side chains being enhanced by localized packing.Unexpected collapse: Ordered liquid crystals on comb-like polymer surfaces collapse after annealing treatment although molecular alignment is enhanced (see picture). In order to clarify this unusual phenomenon, molecular structure, morphology, and wettability of the polymer surfaces are systematically characterized.
The Bingel–Hirsch reaction consists in the reaction of a bromomalonate with electron-poor ??bonds, for example, of carbon materials, yielding cyclopropane derivatives. The reactive nucleophile is generated in situ from the respective malonate using CBr4 and a base. The resulting cyclopropane moiety links the carbon material’s surface atoms covalently with the functional side groups of the malonate. So far, the reaction was limited to fullerenes and carbon nanotubes. Herein, we report on the first application of this reaction type for the surface modification of diamond nanoparticles. The surface of thermally annealed nanodiamond consists of fullerene-like sp2 carbon atoms which exhibit a similar reactivity as those in the all-sp2 carbon nanomaterials. It was found that the reaction proceeds smoothly and enables the grafting of a large variety of functional groups to the surface of nanodiamond. The generated nucleophiles are also able to react with carbonyl species on the diamond. This reaction pathway enables the grafting of malonates even on oxidized nanodiamond without prior thermal annealing.Functionalized nanodiamond carrying a variety of terminal groups is synthesized by applying the Bingel–Hirsch reaction of bromomalonates with the surface of the diamond nanoparticles.
Localized reactions: Computations of complete conformational ensembles of cyclobutene derivatives coupled to an external constraint validate the key assumption of chemomechanics and show that while the correlation between the constraining force and reaction kinetics depends on multiple factors, including substituents and the size of the molecular moiety, coupling between local restoring force and reactivity does not.
Structures and binding energies for bimetallic clusters consisting of a large variety of atomic species are obtained for all atomic sizes N?40 and all concentrations, using an interatomic potential derived within a quasi-classical description. It is found that increasing the difference between the two types of atoms leads to a gradual disappearance of the well-known homo-atomic geometric magic numbers and the appearance of magic pairs corresponding to the number of atoms of each atomic species in binary nanostructures with higher stability. This change is accompanied by structural transitions and ground-state?isomer inversions, induced by changes in composition or concentration. There is a clear tendency towards phase separation, the core–shell radial segregation being predominant (energetically favored) in this model.Magic clusters: Increasing the difference between the two types of atoms in binary metallic clusters leads to a gradual disappearance of the homo-atomic geometric magic numbers and the appearance of magic pairs corresponding to the number of atoms of each atomic species in binary nanostructures with higher stability (see picture). Changes in composition or concentration induce structural transitions and ground-state?isomer inversions.
A unique direct electrodeposition technique involving very high current densities, high voltages and high electrolyte concentrations is applied for highly selective mass synthesis of stable, isolable, surfactant-free, single-crystalline Bi hexagons on a Cu wire at room temperature. A formation mechanism of the hexagons is proposed. The morphology, phase purity, and crystallinity of the material are well characterized by FESEM, AFM, TEM, SAED, EDX, XRD, and Raman spectroscopy. The thermal stability of the material under intense electron beam and intense laser light irradiation is studied. The chemical stability of elemental Bi in nitric acid shows different dissolution rates for different morphologies. This effect enables a second way for the selective fabrication of Bi hexagons. Bi hexagons can be oxidized exclusively to ?-Bi2O3 hexagons. The Bi hexagons are found to be promising for thermoelectric applications. They are also catalytically active, inducing the reduction of 4-nitrophenol to 4-aminophenol. This electrodeposition methodology has also been demonstrated to be applicable for synthesis of bismuth-based bimetallic hybrid composites for advanced applications.Picky: The selective mass synthesis of stable, isolable, surfactant-free, single-crystalline Bi hexagons (see picture) is demonstrated by forceful electrodeposition on a Cu wire at room temperature by applying high current densities, high voltages and high electrolyte concentrations quite contrary to the usual electrodeposition methodologies. The material is promising for thermoelectric and catalytic applications.
In recent years, the possibility of nanobubbles at the solid–liquid interface has drawn wide attention in the scientific community and industry. Thus the search for evidences for the existence of nanobubbles became a scientific hotspot. To produce interfacial nanobubbles, a systematic experiment, called the temperature difference method, is carried out by replacing low temperature water (LTW) with high temperature water (HTW) at the highly-oriented pyrolytic graphite (HOPG)–water interface. When LTW (4?°C) is mixed with HTW (25–40?°C), nanobubbles are observed by atomic force microscopy (AFM), and their size, density and total volume per square micrometer are measured. Furthermore, pancake-like gas layers and the coexistence of nanobubbles on top of the pancake layers are also observed.Handle with care: Applying the temperature difference method the formation of nanobubbles is observed by atomic force spectroscopy. Their size, density and total volume are characterized and shown to depend on temperature.
Interactions of gold(I) catalysts with alkenes and alkynes are analyzed. Neutral chlorido, and cationic phosphine and N-heterocyclic carbene complexes are studied. High-level ab initio calculations are performed to benchmark the accuracy of popular DFT methods. Donation and backdonation contributions in the bond between the gold fragment and the alkene/alkyne substrate are discussed. These contributions depend on the nature of the gold fragment, but also on the substituents on the alkene/alkyne.Differences in bonding nature between [AuCl(S)] and [Au(PR3)(S)]+/ [Au(NHC)(S)]+ (NHC=N-heterocyclic carbene, S=alkene or alkyne) complexes are studied theoretically for understanding the activity of gold(I) catalysts. For example, the picture shows energies of formation of [AuCl(S)] (A) and [Au(PH3)(S)]+ (B) for various alkenes (S=1–6) and alkynes (S=7–13).
Cheap and safe: The catalytic efficiency of a light-dependent photoenzyme (NADPH: protochlorophyllide oxidoreductase) is investigated as a function of the excitation wavelength (see picture). It becomes evident that “red” photons are more efficiently utilized in enzyme catalysis than “blue” photons. This shows an adaptation of the enzyme activity to the natural light conditions.
A ferrocene–distyryl BODIPY dyad and a ferrocene–distyryl BODIPY–C60 triad are synthesized and characterized. Upon photoexcitation at the distyryl BODIPY unit, these arrays undergo photoinduced electron transfer to form the corresponding charge-separated species. Based on their redox potentials, determined by cyclic voltammetry, the direction of the charge separation and the energies of these states are revealed. Femtosecond transient spectroscopic studies reveal that a fast charge separation (kCS=1.0×1010 s?1) occurs for both the ferrocene–distyryl BODIPY dyad and the ferrocene–distyryl BODIPY–C60 triad, but that a relatively slow charge recombination is observed only for the triad. The lifetime of the charge-separated state is 500 ps. Charge recombination of the dyad and triad leads to population of the triplet excited sate of ferrocene and the ground state, respectively.Promising dyes: The photoinduced electron-transfer properties of a ferrocene–distyryl BODIPY dyad and a ferrocene–distyryl BODIPY–C60 triad (BODIPY: boron dipyrromethene) are studied. The triad undergoes a relatively slow charge recombination, giving a charge-separated state with a lifetime of 500 ps.
Pt–Co alloy nanoparticle networks (NNs) with adjustable composition are synthesized by co-reduction of H2PtCl6 and CoCl2 with NaBH4 in an ethylene glycol assisted cetyltrimethylammonium bromide/water/chloroform system at room temperature. Electrochemical measurements indicate that the as-prepared spongelike Pt–Co NNs exhibit composition-dependent electrocatalytic activities and CO tolerance with better durability toward methanol and formic acid oxidation than commercially available Pt/C catalyst. In particular, Pt3Co NNs show the highest specific activity, while Pt2Co NNs exhibit optimal mass activity among Pt–Co alloy NNs with different composition. These Pt–Co alloy NNs may be promising supportless anode catalysts for the direct methanol and direct formic acid fuel cells.Spongelike networks of Pt–Co alloy nanoparticles with tunable composition (see picture) are synthesized by facile, one-step co-reduction of metal precursors with NaBH4 in a two-phase system at room temperature. These nanoparticle networks (NNs) exhibit high stability and enhanced electrocatalytic activity in methanol and formic acid oxidation compared to commercial Pt/C catalyst.
We report the use of an organo-iridium dye conjugated with a water-soluble copolyethylenimine polymer, allowing the hybrid material to be used in combination with thioacid-coated CdTe quantum dots in an aqueous medium. When they are combined, hot carrier cooling observed in the pure quantum-dot case is heavily suppressed indicating fast (ps) electron transfer on a timescale that competes with non-radiative (Auger) relaxation.Fast electron transfer: Picosecond charge transfer between CdTe quantum dots and a novel water-soluble organo-Ir dye is shown. This process allows hot electron transfer from the nanoparticles to the organic component before cooling is complete and before Auger relaxation processes can compete for the carrier’s excess energy. Understanding and controlling fast charge transfer is a key to making improved solar-energy conversion devices.
Fluorescent Ag nanoclusters are of significant interest because they provide the bridge between atomic and nanoparticle behavior in noble metals. Herein, microwave irradiation was originally used for the synthesis of water-soluble fluorescent Ag nanoclusters. As-prepared Ag nanoclusters present red fluorescence emission around 608 nm and a characteristic absorption peak at about 508 nm. Transmission electron microscopy (TEM) shows an average size of 1.6 nm for Ag nanoclusters. The effect of solution pH on the synthesis process and optical properties of Ag nanoclusters was investigated. The pH-dependent present form and adsorption capacity of poly(methacrylic acid, sodium salt) (PMAA) ligands are believed to be the reason for the pH effect.Nuke ?em! A convenient microwave irradiation synthesis method of fluorescent Ag nanoclusters in aqueous solution is reported (see picture). Furthermore, the effect of the solution pH during the synthesis on the optical properties of Ag nanoclusters is investigated.
A cobalt oxide-based oxygen-evolving cocatalyst (Co-Pi) is photodeposited by visible-light irradiation onto nanocrystalline TiO2–polyheptazine (TiO2–PH) hybrid photoelectrodes in a phosphate buffer. The Co-Pi cocatalyst couples effectively to photoholes generated in the surface polyheptazine layer of the TiO2–PH photoanode, as evidenced by complete photooxidation of water to oxygen under visible-light (?>420?nm) irradiation at moderate bias potentials. In addition, the presence of the cocatalyst also reduces significantly the recombination of photogenerated charges, particularly at low bias potentials, which is ascribed to better photooxidation kinetics resulting in lower accumulation of holes. This suggests that further improvements of photoconversion efficiency can be achieved if more effective catalytic sites for water oxidation are introduced to the surface structure of the hybrid photoanodes.A visible difference: TiO2–polyheptazine (TiO2–PH) hybrid photoanodes loaded with photodeposited cobalt oxide-based oxygen-evolving cocatalyst (Co-Pi) exhibit visible-light-driven photooxidation of water to oxygen at moderate bias potentials (see picture).
This paper brings together field emission scanning electron microscopy, single-crystal X-ray diffraction, and density functional electronic structure calculations in both an isolated molecule and a cluster of seven whole and fourteen half molecules of 4,4?-dimethoxybiphenyl to investigate coupled methyl-group rotation (over a barrier) and methoxy-group libration (meaning a rotation from the ground state not all the way to the transition state and back again). The structure of the isolated molecule, determined by the electronic structure calculations, is compared with the structure of the molecule found in the crystal. As the methyl group rotates from its ground state to its transition state, the methoxy group rotates 30° in the isolated molecule and 16° in the cluster. The calculated barriers for this coupled methyl-group rotation and methoxy group libration in the isolated molecule and in the crystal are 12.8 kJ?mol?1 and 10.3 kJ?mol?1 respectively, suggesting that intermolecular interactions in the crystal lower the barrier. These barriers are compared with the value of 11.5±0.5 kJ?mol?1 obtained from solid-state 1H spin-lattice relaxation measurements [P. A. Beckmann and E. Schneider, J. Chem. Phys.2012, 136, 054508.]Can't have one without the other: Coupled methyl-group rotation and methoxy-group libration of 4,4?-dimethoxybiphenyl is investigated by means of field emission scanning electron microscopy, single-crystal X-ray diffraction (see picture), and density functional electronic structure calculations.
Molecular systems where several apparently equivalent charge separation pathways exist upon photoexcitation are presented. They encompass MQn (n?2) architectures, where M is a chromophore and Q an electron transfer quencher (either donor or acceptor), and M–M systems where M acts as both electron donor and acceptor. In all cases, charge separation involves symmetry breaking. The conditions for such process to be operative as well as the origin of the symmetry breaking are discussed.Fearful symmetry: In some molecular systems, two or more apparently equivalent charge separation pathways exist upon photoexcitation (see picture). In all cases, charge separation involves symmetry breaking. The conditions for such process to be operative as well as the origin of the symmetry breaking are discussed.
In principle, the Redfield theory of EPR spectra applies only to fast-rotating complexes with rather small static zero-field splitting (ZFS) terms. However, at sufficiently high frequencies, typically of 35 GHz and above, it predicts values of the central magnetic fields which are surprisingly accurate well beyond its expected applicability range. This remarkable feature is demonstrated by showing that the Redfield EPR spectrum crosses its baseline at the same point as its “exact” simulated counterpart. It is shown that the shift of the central magnetic field with respect to its limiting value in the absence of ZFS terms is often simply proportional to the square of the magnitude of the static ZFS term divided by the spectrometer frequency. This property is used to determine the magnitude of the static ZFS term independently of its fluctuation dynamics and of the presence of the transient ZFS term.Despite their differences, the approximate EPR spectrum predicted by the Redfield formalism and its “exact” counterpart obtained by Monte Carlo (MC) simulation have equal central field values, mainly proportional to the square of the magnitude of the static zero-field splitting term (see picture; dota4?=1,4,7,10-tetraazacyclododecane-N,N?,N??,N???-tetraacetate).
Hydroxyapatite, the main inorganic material in natural bone, has been used widely for orthopaedic applications. Due to size effects and surface phenomena at the nanoscale, nanophase hydroxyapatite possesses unique properties compared to its bulk-phase counterpart. The high surface-to-volume ratio, reactivities, and biomimetic morphologies make nano-hydroxyapatite more favourable in applications such as orthopaedic implant coating or bone substitute filler. Recently, more efforts have been focused on the possibility of combining hydroxyapatite with other drugs and materials for multipurpose applications, such as antimicrobial treatments, osteoporosis treatments and magnetic manipulation. To build more effective nano-hydroxyapatite and composite systems, the particle synthesis processes, chemistry, and toxicity have to be thoroughly investigated. In this Minireview, we report the recent advances in research regarding nano-hydroxyapatite. Synthesis routes and a wide range of applications of hydroxyapatite nanoparticles will be discussed. The Minireview also addresses several challenges concerning the biosafety of the nanoparticles.Biocompatible nanomaterials: Nano-hydroxyapatite materials combine the benefits of nanosized particles with the main organic phase of bone, hydroxyapatite. The advantages of nano-hydroxyapatite are biocompatibility, controlled delivery and capacity to couple with hydrophobic materials. This Minireview discusses the syntheses of nano-hydroxyapatite materials and their applications in the fields of hard tissue repair, drug delivery, antibacterial treatments, magnetic delivery and gene therapy.
Using supercritical fluid CO2 (Sc-CO2) as a medium, PbS nanoparticles can be uniformly deposited on surfaces of various substrates. Sc-CO2 deposition of PbS nanoparticles on carbon-coated copper grids, into small holes in silicon, and formation of uniform PbS nanoparticle films on glass are described. Fluorescence spectra of PbS nanoparticles obtained from the films prepared by the Sc-CO2 method indicate effective energy transfer between PbS nanoparticles of different sizes.Size matters: Uniform PbS nanoparticle films can be deposited on different substrates, including glass in supercritical fluid CO2 for spectroscopic studies of energy transfer between PbS particles of different sizes (the picture shows the apparatus for Sc-CO2 deposition of PbS nanoparticles on glass and the as-formed film).
A hybrid CdSe/ZnS quantum dot and gold nanoparticle dimer is assembled using AFM nanomanipulation. The quantum dot acquires a pronounced polarization dependence on the incident excitation light due to the excitation of localized surface plasmons in the gold nanoparticle (see picture). A large polarization contrast ratio beyond the maximum field enhancement is observed and explained quantitatively.
The three-unit homoaromatic electron-delocalizing nature of the benzo-fused tetra(triptycene)porphyrins (TTPs) with a three-dimensional conjugated model is clarified using density functional theory studies. Due to the electron delocalization, the unidirectional photon-induced current of this kind of TTP molecular skeleton with a highest efficiency of about 90?% in the range between 350 and 500 nm gives them great potential as efficient solar antenna collectors. In addition, their active triptycene cups fused at the central porphyrin core render possible potential application in host–guest chemistry.Three?s a crowd: The three-unit homoaromatic electron-delocalizing nature of the benzo-fused tetra(triptycene)porphyrins with a three-dimensional conjugated model is clarified using density functional theory (see picture). The potential applications of the compounds in the fields of solar antenna collectors and host–guest chemistry are discussed.
Hybrid polymer–nanocrystal photovoltaic (PV) cells have received much attention during the past decade as promising low-cost solar energy harvesting devices, and showed significant progress with power conversion efficiency reaching 5?% recently. This review starts from the introduction of hybrid materials to their application in electronic devices, with particular focus on bulk-heterojunction hybrid polymer–nanocrystal PV devices. The synthesis, surface chemistry, and electronic properties of colloidal inorganic nanocrystals are described. The recent development of hybrid PV devices will be discussed from the perspective of tailoring both inorganic nanocrystals and conjugated polymers, controlling polymer–nanocrystal hybrid morphology, engineering polymer–nanocrystal interface, and optimizing device architecture. Finally, future directions for further advancing hybrid PV technology to potential commercialization are also discussed.Hybrid materials for photovoltaics: The recent development of solution-processed hybrid polymer–nanocrystal photovoltaic cells is reviewed. The tailoring of colloidal nanocrystals and conjugated polymers as well as the manipulation of polymer–nanocrystal interfaces and device architectures are highlighted. The picture shows device structure and J–V characteristics of a hybrid photovoltaic device.
A macroscopic system of single-walled carbon nanotubes (SWNTs) created by a novel DNA/protein complex-assisted assembly is investigated. Due to a point-like nature of connectors, the resulting SWNT aerogel represents a network of self-suspended nanotubes with a record-low density of less than 0.75 mg?cm?3. The assembly method and low density enable a direct comparison of optical properties of nanotubes in solvent and air to surfactant solubilized nanotubes. Optical properties of SWNT gels are investigated using optical absorption, photoluminescence, and Raman spectroscopy. Gelled nanotubes in water and in the low-energy regime behave similar to solubilized nanotubes. In contrast, the photoluminescence of SWNT aerogels exhibits a previously unobserved peak at 1.3 eV that corresponds to a phonon-assisted recombination of photoexcited charges. This new emission pathway is the result of the unique nature of self-suspended nanotubes in aerogel and a reduced phonon decay.Exit through the gel: Optical properties of a novel single-walled carbon nanotube (SWNT) aerogel produced by DNA/protein-guided assembly are investigated (see picture). Their spectra show a previously unobserved photoluminescence emission at 1.32 eV that is assigned to a phonon assisted relaxation.
A series of metal-free acene-modified triphenylamine dyes (benzene to pentacene, denoted as TPA-AC1 to TPA-AC5) are investigated as organic sensitizers for application in dye-sensitized solar cells (DSSCs). A combination of density functional theory (DFT), density functional tight-binding (DFTB), and time-dependent DFT (TDDFT) approaches is employed. The effects of acene units on the spectra and electrochemical properties of the acene-modified TPA organic dyes are demonstrated. The dye/(TiO2)46 anatase nanoparticle systems are also simulated to show the electronic structures at the interface. The results show that from TPA-AC1 to TPA-AC5 with increasing sizes of the acenes, the absorption and fluorescence spectra are systematically broadened and red-shifted, but the oscillator strength and electron injection properties are reduced. The molecular orbital contributions show increasing localization on the bridging acene units from TPA-AC1 to TPA-AC5. From the theoretical examination of some key parameters including free enthalpy related to the electron injection, light-harvesting efficiency, and the shift of semiconductor conduction band, TPA-AC3 with an anthracene moiety demonstrates a balance of the above crucial factors. TPA-AC3 is expected to be a promising dye with desirable energetic and spectroscopic parameters in the DSSC field, which is consistent with recent experimental work. This study is expected to deepen our understanding of TPA-based organic dyes and assist the molecular design of new metal-free dyes for the further optimization of DSSCs.In the balance: The absorption and fluorescence spectra of triphenylamine dyes modified with acenes (benzene to pentacene, TPA-AC1 to TPA-AC5) are broadened and red-shifted with increasing size of acene (see picture), but the oscillator strength and electron injection properties are reduced. TPA-AC3 with an anthracene moiety shows a balance of energetic and spectroscopic parameters, and is promising for dye-sensitized solar cells.
Molecular films obtained by electrochemical reduction of diazoniuim tetrafluoroborate salts [4-carboxybenzene (PhCOOH) and 4-amino-(2,3,5,6-tetrafluoro)-carboxybenzene (PhF4COOH)] on Au substrates and post-functionalization with an osmium pyridil-bipyridine complex are studied by a combination of X-ray photoelectron (XPS) and polarization-modulation infrared reflection absorption spectroscopy (PM-IRRAS). The spectroscopic evidence suggests the formation of NN bonds tethering the complexes to Au. The surface coverage of the azo-bonded osmium complexes strongly depends on the electrode potential. The resulting tethered osmium redox centres were characterized by cyclic voltammetry and impedance spectroscopy. Similar electron transfer-rate constants were measured for both fluorinated and non fluorinated benzene-linked Os complexes.Azo tether: Molecular films obtained by electrochemical reduction of diazonium tetrafluoroborate salts of 4-carboxy benzene and 4-amino-(2,3,5,6-tetrafluoro)-carboxy benzene on Au substrates are studied by a combination of X-ray photoelectron and polarization-modulation infrared reflection absorption spectroscopy. The spectroscopic evidence demonstrates the formation of NN bonds tethering the complexes to Au (see picture).
Single-walled carbon nanotubes (SWCNT) embedded in a non-electroactive polymer are electrochemically characterized. The increasing voltammetric maximums obtained with rising temperature or electrolyte concentration point to a chemical nature of the processes. The chemical kinetic control of the processes is corroborated by its empirical chemical kinetics: the initial reaction rates are obtained from the chronoamperometric responses to potential steps. The activation energy of the reaction includes information about the structural state of the SWCNT before the potential step. Under constant current the potential evolution (chronopotentiometric response) and consumed electrical energy at any time change as a function of (are sensors of) the experimental temperature or the electrolyte concentration. The reactive material, or any device based on this material, senses these working variables, and shows dual and simultaneous actuating–sensing properties.Electrochemical responses from carbon nanotubes (CNT) as a function of different variables are presented and discussed. The results fit those expected from chemical reactions and cannot be explained in terms of a capacitive origin (see picture). The reactive material senses the working conditions and thus shows dual sensing–actuating behaviour.
A series of aluminium complex ions with trifluoromethyl-heteroarylalkenolato (TMHA) ligands are studied by gas-phase infrared multiphoton-dissociation (IRMPD) spectroscopy and computational modelling. The selected series of aluminium TMHA complex ions are promising species for the initial study of intrinsic binding characteristics of AlIII cations in the gas phase as corresponding molecular ions. They are readily available for examination by (+) and (?) electrospray ionization mass spectrometry (ESI-MS) by spraying of [Al3+?(L?)3] solutions. The complex ions under investigation contain trivalent Al3+ cations with two chelating anionic enolate ligands, [Al3+?(L?)2]+, providing insights in the nature of the heteroatom-Al bonds. Additionally, the structure of a deprotonated benzimidazole ligand, L?, and an anionic complex ion of AlIII with two doubly deprotonated benzimidazole ligands, [Al3+?(L2?)2]?, are examined by (?)ESI-IRMPD spectroscopy. Experimental and computational results are highly consistent and allow a reliable identification of the ion structures. In all complex ions examined the planar TMHA ligands are oriented perpendicular to each other around the metal ion, leading to a tetrahedral coordination sphere in which aluminium interacts with the enolate oxygen and heteroaryl nitrogen atoms available in each of the bidentate ligands.Oxygen, but not over all: Experimental and computational results indicate that the coordination sphere built up by the planar trifluoromethyl-heteroarylalkenolato ligands around aluminium(III) is tetrahedral, The first binding site of the bidentate ligands are the negatively charged enolate oxygens, whereas the second binding site is determined by the aromatic character of the heterocycle (see picture).
III–V nanowires have attracted plenty of attention because of their potential outstanding performance in a wide range of applications. However, compared to other III–V nanowires, the synthesis of high quality Sb-based nanowires is less developed, which obstructs the progress towards further applications. In this study we report high quality GaSb and InSb nanowires synthesized by a simple vapor deposition method. Epitaxial growth of nanowires on growth substrates is demonstrated. Te doped GaSb nanowires are achieved through in?situ doping during the vapor deposition process. Electrical measurements of nanowire field-effect transistors show high performance of the synthesized InSb nanowires.GaSb and InSb nanowires: Vapor deposition is used for the synthesis of high quality GaSb and InSb nanowires. Epitaxial growth and doping capability are also demonstrated. The high on-currents of InSb nanowire field-effect transistors qualify nanowires synthesized for electronic applications.
Like Swiss cheese: The fabrication of PEG-modified FITC-labeled magnetic mesoporous silica nanoparticles (F-M-MSN) with three different pore sizes is described (see picture). Based on molecular confinement, the effect of pore size on their dual-modal imaging and drug delivery properties is explored.
Quick and easy: An efficient approach for a direct observation of a thermally induced phase transition of a responsive polymer film on gold surfaces is described (see schematic). Voltammetric measurements show that the peak current and the peak separation for a small redox couple are particularly sensitive to the conformational change of the polymer film and allow its phase transition detection.
Silver bismuth tungstate (AgBiW2O8) nanoparticles were prepared for the first time by solution combustion synthesis by using the corresponding metal nitrates as the precursor and urea as the fuel. These nanoparticles were subsequently modified with Pt catalyst islands using a photocatalytic procedure and used for the photogeneration of syngas (CO+H2). Formic acid was used for this purpose for the in situ generation of CO2 and its subsequent reduction to CO. In the absence of Pt modification, H2 was not obtained in the gas products evolved. These results were compared with those obtained with acetic acid in place of formic acid. The combustion process was simulated by thermogravimetry and the synthesized powder was characterized using transmission electron microscopy, diffuse reflectance UV/Vis spectroscopy, X-ray diffraction, surface area measurements, and X-ray photoelectron spectroscopy. Tauc plots derived from the diffuse reflectance data yielded an optical band gap of 2.74?eV. The photocatalytic activity of these nanoparticles was superior to a sample prepared by solid-state synthesis. Mechanistic aspects are finally presented, as are structural models and electronic calculations, using density functional theory (DFT).Silver bismuth tungstate nanoparticles are prepared by solution combustion synthesis, modified with a Pt co-catalyst, and finally used for the photogeneration of syngas (CO+H2). Formic acid is used to produce CO2 in situ and subsequently reduce it to CO. The photocatalytic activity of these nanoparticles is superior to that of nanoparticles prepared by solid-state synthesis.
A comparative study of benzene oxidation at boron-doped diamond (BDD) and nitrogenated nanocrystalline diamond (NCD) anodes in 0.5?M K2SO4 aqueous solution is conducted by using cyclic voltammetry and electrochemical impedance spectroscopy. It is shown by measurements of differential capacitance and anodic current that during the benzene oxidation at the BDD electrode, adsorption of a reaction intermediate occurs, which partially blocks the electrode surface and lowers the anodic current. At the NCD electrode, benzene is oxidized concurrently with oxygen evolution, a (quinoid) intermediate being adsorbed at the electrode. The adsorption and the electrode surface blocking are reflected in the impedance–frequency and impedance–potential complex-plane plots.It is all about adsorptivity: During benzene oxidation at a boron-doped diamond electrode, adsorption of a reaction intermediate occurs, which partially blocks the electrode surface and lowers the anodic current (see picture, blue curve). However, using a nanocrystalline diamond electrode, benzene is oxidized concurrently with oxygen evolution, and a (quinoid) intermediate is adsorbed at the electrode.
The interplay between halogen bonds and cation–? interactions is investigated by ab initio calculations at the MP2 level of theory. Different energetic effects are observed in the studied complexes in which halogen bonds and cation–? interactions coexist, which can be ascribed to the direction of charge transfer for the two interactions. These effects are analyzed in detail in terms of the structural, energetic, and charge-transfer properties of the complexes. In addition, the quantum theory of atoms in molecules is employed to characterize the interactions and to examine their enhancement and attenuation in terms of the variations in electron density at the bond and cage critical points. Finally, experimental evidence for a combination of the two interactions is obtained from the Cambridge Structural Database.Cooperative or diminutive effects are observed when halogen bonds and cation–? interactions coexist in the same complex, depending on the mutal directions of charge transfer of the two interactions (see picture).
The temperature dependence of nanobubbles was investigated experimentally using atomic force microscopy. By scanning the same area of the surface at temperatures from 51?°C to 25?°C it was possible to track geometrical changes of individual nanobubbles as the temperature was decreased. Interestingly, nanobubbles of the same size react differently to this temperature change; some grow whilst others shrink. This effect cannot be attributed to Ostwald ripening, since the growth and shrinkage of nanobubbles appears to occur in distinct patches on the substrate. The total nanobubble volume per unit area shows a maximum around 33?°C, which is comparable with literature where experiments were carried out with increasing temperature. This underlines the stability of surface nanobubbles.Some like it hot: The temperature dependence of nanobubbles is investigated experimentally using atomic force microscopy. By scanning the same area of the surface at different temperatures, it is possible to track geometrical changes of individual nanobubbles as the temperature is decreased (see picture for the distribution at 45?°C). This underlines the stability of surface nanobubbles.
Carbon atoms are displaced in pre-selected locations of carbon nanotubes by using a focused electron beam in a scanning transmission electron microscope. Sub-nanometer-sized holes are created that change the morphology of double and triple-walled carbon nanotubes and connect the shells in a unique way. By combining in situ transmission electron microscopy experiments with atomistic simulations, we study the bonding between defective shells in the new structures which are reminiscent of the shape of a flute. We demonstrate that in double-walled nanotubes the shells locally merge by forming nanoarches while atoms with dangling bonds can be preserved in triple-walled carbon nanotubes. In the latter system, nanoarches are formed between the inner- and outermost shells, shielding small graphenic islands with open edges between the neighboring shells. Our results indicate that arrays of quantum dots may be produced in carbon nanotubes by spatially localized electron irradiation, generating atoms with dangling bonds that may give rise to localized magnetic moments.Many morphologies: Irradiation with a focused electron beam can be used to puncture carbon nanotubes, and to create defects in pre-defined locations. These defects lead to new structures and morphologies in double- and triple-walled carbon nanotubes, connecting the walls in a unique way.
Ag2S/Ag heterostructure nanoparticles with narrow size distribution are synthesized by a one-pot method at room temperature. The prepared nanohybrids show excellent photocatalytic inactivation of Escherichia coli under UV irradiation.
Surface and bulk nanobubbles are two types of nanoscopic gaseous domain that have recently been discovered in interfacial physics. Both are expected to be unstable to dissolution because of the high internal pressure driving diffusion and the surface tension which squeezes the gas out, but there is a rapidly growing body of experimental evidence that demonstrates both bubble types to be stable. However, the two types of bubbles also differ in many respects: surface nanobubble stability is most probably assisted by the nearby wall, which can repel the water (in the case of hydrophobicity), accept physisorbed gas molecules, and reduce the surface area through which outfluxing can occur; bulk nanobubbles, on the other hand, must stabilise themselves. This is perhaps through ionic shielding, perhaps through diffusive shielding, or perhaps through both. Herein, the features of both bubble types are described individually, their common and disparate features are discussed, and emerging applications are examined.On the bubble: Surface and bulk nanobubbles (see picture) are two types of nanoscopic gaseous domain that occur in interfacial physics. The common and disparate features of both bubble types are described, and their possible stabilising mechanisms and potential applications are examined.
How does your graphene grow? In situ X-ray photoelectron spectroscopy and X-ray diffraction measurements during chemical vapor deposition on Ni catalyst films show that graphene forms both isothermally and by precipitation on cooling (see picture). A coherent graphene growth model is devised and sub-surface dissolved carbon is shown to play an important role.
Suited for heavy stuff: An efficient mesoporous sorbent based on a pure ethylendiamine-bridged polysilsesquioxane is presented. This material, with both a high amine loading and a high surface area, is applied for heavy metal ion removal.
For about a decade, superresolution fluorescence microscopy has been advancing steadily, maturing from the proof-of-principle stage to routine application. Of the various techniques, STED (stimulated emission depletion) microscopy was the first to break the diffraction barrier. Today, it is a prominent and versatile form of superresolution light microscopy. STED microscopy has shed a sharper light on numerous topics in cell biology, but also in material sciences. Both disciplines extend into the nanometer range, making detailed studies of structural and functional relationships difficult or even impossible to achieve using diffraction-limited microscopy. With recent advancements like spectral multiplexing or live-cell imaging, STED microscopy makes nanoscale materials and components of the cell accessible for fluorescence-based investigations. With multicolor superresolution imaging, even the interactions between biological and engineered nanostructures can be studied in detail. This review gives an introduction into the working principle of STED microscopy, provides a detailed overview of recent advancements and new techniques implemented for use with STED microscopy and shows how these have been applied in the life sciences and nanotechnologies.All things bright and beautiful: Superresolution STED microscopy has become a versatile tool for the study of nanoscale objects (see picture), be it cellular components in life sciences or nanoparticles in the material sciences. This review provides insight into the working principle, the latest advances and developments and the applications of STED microscopy.
Nanoscale gas bubbles have surprising stability at water/solid surfaces. Herein, we summarize progress made on investigating gases at the water/solid interfaces on the nanometer scale. The gas states include nanobubbles, micropancakes, multiple gas layers and their coexistence; these were investigated from experimental and theoretical aspects. The stability of nanoscale gas bubbles may be attributed to high inner density, as observed in molecular dynamic simulations and theoretical analysis. Moreover, it was found that there were maximal length scales for stable nanobubbles, namely, 100 nm high and a curvature radius of 2 ?m.Forever blowing (nano)bubbles! Gas states observed at the nanometer scale include nanobubbles, micropancakes, multiple gas layers, and their coexistence (see picture). Molecular dynamic simulations showed that nanoscale gas bubbles may have a high inner density, which could be one reason why nanobubbles are stable at water/solid interfaces.
We introduce a new family of spiked particles resulting from the growth of high aspect ratio gold nanorods. Upon spike growth, elongated beads are obtained with sizes above 300?nm. Interestingly, and in contrast to smooth particles of the same size, these spiked-particles are not only able to sustain localized surface plasmon resonances and consequently enhance Raman signals, but are also big enough to be recognized by standard confocal optical microscopy. These spiked beads have been engineered into thin films to test their surface-enhanced Raman scattering (SERS) enhancing efficiency as a function of the particle density. Such films provide a high level of portability and easiness of use for “in-field” optical ultrasensitive analysis.One to enhance them all: Spiked gold beads are efficient optical enhancers for single-particle SERS ultradetection (see picture), due to the localization of high electric fields at the apex of the tips and the antenna effect displayed by the core.
Plasmonic nanocrystals strongly interact with chiral molecular shells through electric and magnetic fields and in this way acquire new chiro-optical properties. Transfer of chirality from biomolecules to the plasmonic resonances is a collective phenomenon and strongly depends on the geometry of nanostructure. Collective effects in a molecular chiral shell may suppress or enhance plasmonic circular dichroism (CD) depending on the geometry of hybrid nanocrystal. In large chiral plasmonic structures, we identify a new electrodynamic mechanism of plasmonic CD that is qualitatively different to the near-field, dipolar mechanism of the plasmonic chirality described by us previously. Our models also show that anisotropic nanocrystals, such as nanorods or oriented molecular shells, have strongly enhanced CD at the plasmonic frequency. A family of chiral plasmonic nanostructures proposed and modeled here can be used for designing new optical media and chiral sensors.Chirality transfer: In large chiral plasmonic structures, a new electrodynamic mechanism of plasmonic CD that is qualitatively different to near-field, dipolar mechanism of plasmonic chirality is described. The models presented also show that anisotropic nanocrystals have strongly enhanced CD at the plasmonic frequency.
Nanoplates: Hydrogen peroxide is added in a seed-mediated growth process for producing silver nanoplates (see graphic) with not only significantly improved synthetic yield, but also greatly shortened reaction time and much enhanced reproducibility.
The formation mechanism of a nanoscale gas state is studied on inorganic clay surfaces modified with hexamethyldisilazane, which show different contact angles in ethanol–water solutions. As the dissolved oxygen becomes oversaturated due to the decrease in ethanol–water ratio, oxygen nanoscale gas state are formed and stabilized on the hydrophobic surfaces so that the total oxygen content in the suspension is increased compared to the control solution without the particles. However, the total oxygen content in the suspension with hydrophilic surfaces is lower than the control solution without the particles because the hydrophilic particle surfaces destabilize the nanobubbles on the surfaces by spreading and coagulating them into microbubbles that quickly escape from the suspension solution. No significant correlation was observed between the nanobubble formation and the shape or roughness of the surfaces. Our results suggest that a nanoscale gas state can be formed on both hydrophobic and hydrophilic particle surfaces, but that the stability of the surface nanoscale gas state can vary greatly depending on the hydrophobicity of the solid surfaces.The formation mechanism of a nanoscale gas state is studied on modified inorganic clay surfaces (see picture). The results suggest that a nanoscale gas state can be formed on both hydrophobic and hydrophilic particle surfaces, but that the stability of the surface nanoscale gas state can vary greatly depending on the hydrophobicity of the solid surfaces.
Using molecular dynamics, we study the nucleation and stability of bulk nanobubble clusters. We study the formation, growth, and final size of bulk nanobubbles. We find that, as long as the bubble-bubble interspacing is small enough, bulk nanobubbles are stable against dissolution. Simple diffusion calculations provide an excellent match with the simulation results, giving insight into the reason for the stability: nanobubbles in a cluster of bulk nanobubbles protect each other from diffusion by a shielding effect.Small, but tough: Bulk nanobubble clusters can be stable under specific conditions. MD simulations (see picture) of binary mixtures of simple (Lennard-Jones) fluids are used to show this.
We report a facile hydrothermal synthetic route to prepare a class of monodispersed lanthanide-based compound submicrospheres with controllable size, which employs raw lanthanide oxides as starting material, urea as precipitator and poly(N-vinyl-2-pyrrolidone) (PVP) as surfactant. Dependent on the intrinsic properties of respective lanthanide, the resulting products could be in the form of oxide, hydroxide or basic carbonate. These lanthanide hydroxides or basic carbonates can be easily transformed into their corresponding oxides by calcination, retaining the same morphology and size dispersion. The formation mechanism of these lanthanide-based compound submicrospheres is investigated and PVP plays a critical role in forming uniform and well-dispersed products. Furthermore, this method could be extended to a binary system by using two kinds of lanthanide oxides as starting material, resulting in doped-type lanthanide oxide submicrospheres (such as Y2O3:Eu3+). The Y2O3:Eu3+ submicrospheres exhibit nearly uniform spherical morphology and narrow size distribution as well as good water solubility and sharp spectral emission at 610?nm (corresponding to the 5D0–7F2 transition of Eu3+). This makes them attractive materials for applications in fields such as fluorescent lamps, field emission displays (FEDs) or LCDs, or as biomedical labels and molecular probes.Easy! A facile hydrothermal synthetic route is presented to prepare a class of monodispersed lanthanide-based compound submicrospheres with controllable size (see picture). The method only employs raw lanthanide oxides as starting material, urea as precipitator and poly(N-vinyl-2-pyrrolidone) as surfactant.
Jacobus van’t Hoff proposed in 1874 that molecules have three-dimensional structures. A novel reaction microscope employs advanced single-particle imaging detectors that measure the full three-dimensional velocity distribution of correlated electrons and (fragment) ions emitted from an excited molecule. In their Minireview (DOI: 10.1002/cphc.201100107), M.?H.?M. Janssen and co-workers illustrate the wealth of detailed information that can be obtained about the interplay between shaped laser fields, femtosecond dynamics, ionization processes and multichannel pathways in three-dimensional (chiral) molecules.
Posted on 10 May 2011 | 5:59 am
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