Showing papers in "Journal of Physical Chemistry B in 2001"
TL;DR: In this article, a fitting technique combines using accurate ab initio data as the target, choosing an efficient fitting subspace of the whole potential energy surface, and determining weights for each of the fitting points based on magnitudes of the potential energy gradient.
Abstract: We present results of improving the OPLS-AA force field for peptides by means of refitting the key Fourier torsional coefficients. The fitting technique combines using accurate ab initio data as the target, choosing an efficient fitting subspace of the whole potential-energy surface, and determining weights for each of the fitting points based on magnitudes of the potential-energy gradient. The average energy RMS deviation from the LMP2/cc-pVTZ(-f)//HF/6-31G** data is reduced by ca. 40% from 0.81 to 0.47 kcal/mol as a result of the fitting for the electrostatically uncharged dipeptides. Transferability of the parameters is demonstrated by using the same alanine dipeptide-fitted backbone torsional parameters for all of the other dipeptides (with the appropriate side-chain refitting) and the alanine tetrapeptide. Parameters of nonbonded interactions have also been refitted for the sulfur-containing dipeptides (cysteine and methionine), and the validity of the new Coulombic charges and the van der Waals σ's ...
3,516 citations
TL;DR: Gold nanorods with aspect ratios of 4.6 ± 1.2, 13 ± 2, and 18 ± 2.5 are prepared by a seeding growth approach in the presence of an aqueous miceller template.
Abstract: Gold nanorods with aspect ratios of 4.6 ± 1.2, 13 ± 2, and 18 ± 2.5 (all with 16 ± 3 nm short axis) are prepared by a seeding growth approach in the presence of an aqueous miceller template. Citrate-capped 3.5 nm diameter gold particles, prepared by the reduction of HAuCl4 with borohydride, are used as the seed. The aspect ratio of the nanorods is controlled by varying the ratio of seed to metal salt. The long rods are isolated from spherical particles by centrifugation.
2,428 citations
TL;DR: The use of localized surface plasmon resonance (LSPR) spectroscopy to probe the size-tunable optical properties of Ag nanoparticles and their sensitivity to the local, external dielectric environment (viz., the nanoenvironment) is discussed in this article.
Abstract: Nanosphere lithography (NSL) is an inexpensive, simple to implement, inherently parallel, high throughput, materials general nanofabrication technique capable of producing an unexpectedly large variety of nanoparticle structures and well-ordered 2D nanoparticle arrays. This article describes our recent efforts to broaden the scope of NSL to include strategies for the fabrication of several new nanoparticle structural motifs and their characterization by atomic force microscopy. NSL has also been demonstrated to be well-suited to the synthesis of size-tunable noble metal nanoparticles in the 20−1000 nm range. This characteristic of NSL has been especially valuable for investigating the fascinating richness of behavior manifested in size-dependent nanoparticle optics. The use of localized surface plasmon resonance (LSPR) spectroscopy to probe the size-tunable optical properties of Ag nanoparticles and their sensitivity to the local, external dielectric environment (viz., the nanoenvironment) is discussed in...
2,422 citations
TL;DR: In this paper, the synthesis of water-soluble semiconductor nanoparticles and their properties are described and discussed and the properties of the resulting nanocrystals are discussed and characterized.
Abstract: We describe the synthesis of water-soluble semiconductor nanoparticles and discuss and characterize their properties. Hydrophobic CdSe/ZnS core/shell nanocrystals with a core size between 2 and 5 nm are embedded in a siloxane shell and functionalized with thiol and/or amine groups. Structural characterization by AFM indicates that the siloxane shell is 1−5 nm thick, yielding final particle sizes of 6−17 nm, depending on the initial CdSe core size. The silica coating does not significantly modify the optical properties of the nanocrystals. Their fluorescence emission is about 32−35 nm fwhm and can be tuned from blue to red with quantum yields up to 18%, mainly determined by the quantum yield of the underlying CdSe/ZnS nanocrystals. Silanized nanocrystals exhibit enhanced photochemical stability over organic fluorophores. They also display high stability in buffers at physiological conditions (>150 mM NaCl). The introduction of functionalized groups onto the siloxane surface would permit the conjugation of ...
1,285 citations
TL;DR: In this article, the authors report on the inexpensive fabrication of large three-dimensional and highly oriented porous microrod array of n-type ZnO semiconductor with a unique designed architecture consisting of well-defined, length-tailored, monodisperse, perpendicularly oriented single-crystalline hexagonal rods, grown directly onto poly crystalstalline, single-cell, or amorphous substrates.
Abstract: We are reporting here on the inexpensive fabrication of large three-dimensional and highly oriented porous microrod array of n-type ZnO semiconductor with a unique designed architecture consisting of well-defined, length-tailored, monodisperse, perpendicularly oriented single-crystalline hexagonal rods, grown directly onto polycrystalline, single-crystalline, or amorphous substrates, from an aqueous solution of zinc salt at low temperature.
942 citations
TL;DR: In this paper, thermal properties, density, self-diffusion coefficient of the anions and cations, viscosity, and ionic conductivity were measured for these ionic liquids in wide temperature ranges.
Abstract: Room-temperature ionic liquids, 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIBF4), 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (EMITFSI), 1-butylpyridinium tetrafluoroborate (BPBF4), and 1-butylpyridinium bis(trifluoromethylsulfonyl)imide (BPTFSI), were prepared and characterized The thermal property, density, self-diffusion coefficient of the anions and cations, viscosity, and ionic conductivity were measured for these ionic liquids in wide temperature ranges A pulsed-gradient spin−echo NMR method was used to independently measure self-diffusion coefficients of the anions (19F NMR) and the cations (1H NMR) The results indicate that the cations diffuse almost equally to the anion in EMIBF4 and BPBF4, whereas they diffuse faster than the anion in EMITFSI and BPTFSI The summation of the cationic and anionic diffusion coefficients for each ionic liquid follows the order EMITFSI > EMIBF4 > BPTFSI > BPBF4, under an isothermal condition The order of the magnitude of the diffusion coe
935 citations
TL;DR: In this article, the authors studied the high pressure phase behavior of CO2 with six ionic liquids: 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1n-octyl, 3-methyl, and 3-methyl-3methyloridazolate ([emim][EtSO4]), and N-butlypyridinium tetrafluoroborate ([N-bupy][BF4]).
Abstract: This work presents the high-pressure phase behavior of CO2 with six ionic liquids: 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1-n-octyl-3-methylimidazolium hexafluorophosphate ([C8-mim][PF6]), 1-n-octyl-3-methylimidazolium tetrafluoroborate ([C8-mim][BF4]), 1-n-butyl-3-methylimidazolium nitrate ([bmim][NO3]), 1-ethyl-3-methylimidazolium ethyl sulfate ([emim][EtSO4]), and N-butylpyridinium tetrafluoroborate ([N-bupy][BF4]). We explored the effect of systematically changing the anionic and cationic components of the ionic liquid on the CO2−ionic liquid phase behavior. For all of the ionic liquids tested, large quantities of CO2 dissolved in the ionic liquid phase, but no appreciable amount of ionic liquid solubilized in the CO2 phase. In addition, the liquid phase volume expansion with the introduction of even large amounts of CO2 is negligible, in dramatic contrast to the large volume expansion observed for neutral organic liquids. Our results seek to elucidate the underlying physica...
917 citations
TL;DR: In this paper, a tetraoctylammonium bromide (TOAB)-capped metal nanoparticles on TiO2 films improved the photocurrent generation and induced a shift in the apparent flat band potential.
Abstract: Noble metal particles of Au, Pt, and Ir were deposited on nanostructured TiO2 film using an electrophoretic approach. The nanocomposite films were characterized by UV-absorption and atomic force microscopy (AFM). The deposition of tetraoctylammonium bromide (TOAB)-capped metal nanoparticles on TiO2 films improved the photocurrent generation and induced a shift in the apparent flat band potential. The TiO2 films modified with TOAB-capped metal nanoparticles were less prone to the electron scavenging by the oxygen in solution. Improved photoelectrochemical performance of semiconductor−metal composite film is attributed to the shift in quasi-Fermi level of the composite to more negative potentials. Continuous irradiation of the composite films over a long period causes photocurrent to decrease as the semiconductor−metal interface undergoes chemical changes. The role of semiconductor−metal composite films in improving the rate of photocatalytic degradation of an azo dye is also discussed.
897 citations
TL;DR: In this paper, a multistage purification method has been investigated for extracting the Fe metal catalyst and non-SWNT carbon from nanotubes produced by the HiPco process.
Abstract: A purification method is given for extracting the Fe metal catalyst and non-SWNT carbon from nanotubes produced by the HiPco process.1,2 A multistage purification method has been investigated. Sample purity is documented by ESEM, TEM, TGA, Raman and UV-vis−near-IR spectroscopy. Metal catalyzed oxidation at low temperature has been shown to selectively remove non-SWNT carbon and permit extraction of iron with concentrated HCl. Prolonged catalyzed oxidation has been found to preferentially remove smaller diameter tubes. The onset of oxidation of purified smaller diameter HiPco SWNTs is also found to be approximately 100 °C lower than for purified larger diameter tubes produced in the laser-oven process.
816 citations
TL;DR: A new version of the DelPhi program, which provides numerical solutions to the nonlinear Poisson−Boltzmann (PB) equation, is reported in this paper, which can divide space into multiple regions containing...
Abstract: A new version of the DelPhi program, which provides numerical solutions to the nonlinear Poisson−Boltzmann (PB) equation, is reported. The program can divide space into multiple regions containing ...
806 citations
TL;DR: In this article, the diameters of single-walled carbon nanotubes are determined by their diameters in the cores of catalytic nanoparticles with diameters between 1−2 nm and 3−5 nm.
Abstract: Discrete catalytic nanoparticles with diameters in the range of 1−2 nm and 3−5 nm respectively are obtained by placing controllable numbers of metal atoms into the cores of apoferritin, and used for growth of single-walled carbon nanotube (SWNTs) on substrates by chemical vapor deposition (CVD). Atomic force microscopy (AFM), transmission electron microscopy (TEM), and micro-Raman spectroscopy are used to characterize isolated nanotubes grown from the discrete nanoparticles. The characterizations, carried out at single-tube and single-particle level, obtain clear evidence that the diameters of nanotubes are determined by the diameters of catalytic nanoparticles. With nanoparticles placed on ultrathin alumina membranes, isolated SWNTs are grown and directly examined by transmission electron microscopy. For the first time, both ends of an as-grown single-walled nanotube are imaged by TEM, leading to a microscopic picture of nanotube growth mechanism. It is shown that controlling the structures of catalytic ...
TL;DR: When asked to explain the importance of the discovery of conducting polymers, I offer two basic answers: first they did not (could not?) exist, and second, that they offer a unique combination of properties not available from any other known materials.
Abstract: When asked to explain the importance of the discovery of conducting polymers, I offer two basic answers: First, they did not (could not?) exist; and second, that they offer a unique combination of properties not available from any other known materials. The first is an intellectual challenge; the second expresses a promise for utility in a wide variety of applications.
TL;DR: In this article, the photoinduced surface wettability conversion reactions of ZnO and TiO2 thin films were investigated by means of water contact angle measurement and X-ray photoelectron spectroscopy.
Abstract: The photoinduced surface wettability conversion reactions of ZnO and TiO2 thin films were investigated by means of water contact angle measurement and X-ray photoelectron spectroscopy. Before ultraviolet (UV) illumination, ZnO and TiO2 films exhibited water contact angles of ∼109 and ∼54°, respectively. UV illumination turned both surfaces to highly hydrophilic with water contact angles smaller than 10°. Storage in the dark reconverted the highly hydrophilic films to their original states. Reversible surface wettability conversion reactions were achieved by alternate UV illumination and storage in the dark on both the films. The similar behaviors of wettability conversion observed on ZnO and TiO2 surfaces suggest that they follow a similar conversion mechanism. Preferential adsorption of water molecules on the photogenerated surface defective sites is ascribed to the formation of highly hydrophilic ZnO and TiO2 surfaces. Achievement of highly hydrophilic ZnO and TiO2 surfaces by high-temperature annealing...
TL;DR: In this article, the transferable potentials for phase equilibria-united atom (TraPPE-UA) force field for hydrocarbons is extended to primary, secondary, and tertiary alcohols by introducing the following (pseudo-)atoms: common hydroxyl O and H for all alcohols, α-CH3, α -CH2, α −CH, and α-C for methanol, primary and secondary alcohols respectively, and the Lennard−Jones well depth and size parameters for the new interaction sites were determined by fitting to the
Abstract: The transferable potentials for phase equilibria-united atom (TraPPE-UA) force field for hydrocarbons is extended to primary, secondary, and tertiary alcohols by introducing the following (pseudo-)atoms: common hydroxyl O and H for all alcohols, α-CH3, α-CH2, α-CH, and α-C for methanol, primary, secondary, and tertiary alcohols, respectively. In the TraPPE-UA force field, the nonbonded interactions of these sites are governed by Lennard−Jones 12−6 potentials and Coulombic interactions of fixed partial charges. The values of these partial charges were borrowed from the optimized potentials for liquid simulations-united atom (OPLS−UA) force field [Jorgensen, W. L. J. Phys. Chem. 1986, 90, 1276]. The Lennard−Jones well depth and size parameters for the new interaction sites were determined by fitting to the single-component vapor−liquid-phase equilibria of a few selected model compounds. Although the well-depth parameters for the α-carbons could be taken directly from the TraPPE-UA parameters for the corres...
TL;DR: In this article, the methods of obtaining various mesostructures made of nanocrystals are described, and collective optical, magnetic, and transport properties are demonstrated by applying a magnetic field during the deposition process.
Abstract: In this feature article, the methods of obtaining various mesostructures made of nanocrystals are described. With silver and silver sulfide, the nanocrystals are able to self organize in 2D and 3D super lattices to form “supra” crystals. With cobalt and ferrites nanocrystals, it has been possible to make ribbons, dots, or labyrinths. These mesostructures present new physical properties differing from those of the isolated nanocrystal and from those of the bulk phase. Collective optical, magnetic, and transport properties are demonstrated. By applying a magnetic field during the deposition process of nanocrystals, the easy axes of the particles are oriented along the direction of the applied field, inducing again the collective magnetic properties.
TL;DR: In this article, the authors presented the vapor−liquid equilibrium and the liquid-liquid equilibrium phase behavior and associated thermodynamic properties of water with three ionic liquids: 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1n-octyl-1methylorideamideamidazolateamide (C8mim]), and 1-nc-3methylamideamidemidazoline tetrafluoroborate ([C 8mim][
Abstract: This work presents the vapor−liquid equilibrium and the liquid−liquid equilibrium phase behavior and associated thermodynamic properties of water with three ionic liquids: 1-n-butyl-3-methylimidazolium hexafluorophosphate ([bmim][PF6]), 1-n-octyl-3-methylimidazolium hexafluorophosphate ([C8mim][PF6]), and 1-n-octyl-3-methylimidazolium tetrafluoroborate ([C8mim][BF4]). Although water stable, these compounds are hygroscopic, so the uptake of water vapor is an important issue. Due to the negligible volatility of ionic liquids, we were able to measure vapor−liquid equilibrium using a gravimetric microbalance, which was designed to measure adsorption on solids. The Henry's law constants range from 0.033 to 0.45 bar, with infinite dilution activity coefficients ranging from slight positive deviations from Raoult's law to as high as 8.62. The enthalpies and entropies of absorption are similar to those for the absorption of water into alcohols. In addition, we present water/ionic liquid liquid−liquid equilibria,...
TL;DR: In this article, the femtosecond optical response of noble metal nanoparticles and its connection to the ultrafast electron dynamics are discussed in light of the results of high-sensitivity femtocond pump−probe experiments.
Abstract: The femtosecond optical response of noble metal nanoparticles and its connection to the ultrafast electron dynamics are discussed in light of the results of high-sensitivity femtosecond pump−probe experiments. The physical origins of the nonlinear responses in the vicinity of the surface plasmon resonance and interband transition threshold are analyzed using extension of the theoretical models used in the bulk materials. These responses contain information on the electron interaction processes (electron−electron and electron−phonon scattering) that can thus be directly investigated in the time domain. Their size and environment dependences are discussed, and the results are compared to the ones in the bulk materials. Time-resolved techniques also permit direct study of the vibrational modes of metal nanoparticles and, in particular, the determination of their damping, which is a sensitive probe of the nature of the surrounding matrix and of the interface quality.
TL;DR: In this article, the authors report results from molecular dynamics simulations of a series of sodium halide solution/air interfaces and develop a molecular picture of hydrogen bonding in the interfacial region that might be tested by surface sensitive spectroscopic experiments.
Abstract: Most salts raise the surface tension of water. Interpretation of this phenomenon via the Gibbs adsorption equation has led to the commonly held belief that the ions are repelled from the air/solution interface. Here, we report results from molecular dynamics simulations of a series of sodium halide solution/air interfaces. The simulations reproduce the experimentally measured increases in surface tension relative to pure water. Analysis of the structure reveals that the small, nonpolarizable fluoride anion is excluded from the interface, in accord with the traditional picture. However, all of the larger, polarizable halide anions are present at the interface, and bromide and iodide actually have higher concentrations in the interfacial region than in the bulk. On the basis of the simulations we develop a molecular picture of hydrogen bonding in the interfacial region that might be tested by surface sensitive spectroscopic experiments. The novel, microscopic view of the interfacial structure of aqueous sal...
TL;DR: The authors showed that CO preference for low-coordination binding sites on Pt(111) and vicinals to it is not consistent with a host of low-temperature experimental studies.
Abstract: Notwithstanding half a dozen theoretical publications, well-converged density- functional calculations, whether based on a local-density or generalized-gradient exchange-correlation potential, whether all-electron or employing pseudopotentials, underestimate CO's preference for low-coordination binding sites on Pt(111) and vicinals to it. For example, they imply that CO should prefer hollow- to atop-site adsorption on Pt(111), in apparent contradiction to a host of low-temperature experimental studies.
TL;DR: Using femtosecond mid-IR spectroscopy, a series of studies designed to understand how the interfacial electron transfer dynamics depends on the properties of the adsorbates, semiconductors, and their interaction are presented in this paper.
Abstract: Interfacial electron transfer (ET) between semiconductor nanomaterials and molecular adsorbates is an important fundamental process that is relevant to applications of these materials. Using femtosecond midinfrared spectroscopy, we have simultaneously measured the dynamics of injected electrons and adsorbates by directly monitoring the mid-IR absorption of electrons in the semiconductor and the change in adsorbate vibrational spectrum, respectively. We report on a series of studies designed to understand how the interfacial ET dynamics depends on the properties of the adsorbates, semiconductors, and their interaction. In Ru(dcbpy)2(SCN)2 (dcbpy = 2,2‘-bipyridine-4,4‘-dicarboxylate) sensitized TiO2 thin films, 400 nm excitation of the molecule promotes an electron to the metal-to-ligand charge transfer (MLCT) excited state, from which it is injected into TiO2. The injection process was characterized by a fast component, with a time constant of <100 fs, and a slower component that is sensitive to sample con...
TL;DR: In this article, the use of several analytical techniques, including X-ray absorption spectroscopy (XAS), electron microscopy, and electron diffraction, as tools for characterizing the structural dynamics of supported Pt nanoscale particles was described.
Abstract: In this report, we describe the use of several analytical techniques, including X-ray absorption spectroscopy (XAS), electron microscopy, and electron diffraction, as tools for characterizing the structural dynamics of supported Pt nanoscale particles. We examined several carbon-supported samples. Electron microscopy shows that the particles in these samples (S1−S3) have average particle diameters of roughly 20, 40, and 60 A respectively, while electron microdiffraction data for these particles provided evidence of long-ranged ordering in the form of face centered cubic structures. This study highlights the use of advanced synchrotron X-ray absorption spectroscopies (XAS), in particular extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES), as powerful tools for studying the structural habits and dynamics of these prototypical nanoscale materials. Using state-of-the-art methods of measurement and computational modeling, we demonstrate that it is possible to deve...
TL;DR: In this paper, the perovskite-like structure of ATaO3 photocatalysts was investigated for water splitting into H2 and O2 under UV irradiation, and it was shown that the excess alkali in the preparation increased the crystal size of NaTaO3 formed and prevented formation of alkali defects in the powder by volatilization.
Abstract: Alkali tantalate ATaO3 (A = Li, Na, and K) photocatalysts with perovskite-like structure showed activities for water splitting into H2 and O2 under UV irradiation. When the alkali tantalates were prepared in the presence of excess alkali, their activities were increased by 1 to 2 orders of magnitude. Scanning electron microscopy and photoluminescence measurements indicated that the excess alkali in the preparation increased the crystal size of NaTaO3 formed and prevented formation of alkali defects in NaTaO3 powder by volatilization, resulting in an increase in the photocatalytic activity. A LiTaO3 photocatalyst showed the highest activity among the naked alkali tantalate photocatalysts prepared in the presence of excess alkali. On the other hand, the activity of a NaTaO3 photocatalyst was increased by 1 order of magnitude when a NiO cocatalyst was loaded. The NiO(0.05 wt %)/NaTaO3 photocatalyst produced H2 and O2 from pure water with rates of 3.39 and 1.58 mmol h-1, respectively. The apparent quantum yie...
TL;DR: In this paper, gold nanoparticles were produced by laser ablation of a gold metal plate in an aqueous solution of sodium dodecyl sulfate, and the size distribution of the nanoparticles thus produced was measured by an electron microscope and was found to shift to a smaller size with an increase in surfactant concentration.
Abstract: Gold nanoparticles were produced by laser ablation of a gold metal plate in an aqueous solution of sodium dodecyl sulfate. The absorption spectrum of the gold nanoparticles was essentially same as that of gold nanoparticles chemically prepared in a solution. The size distribution of the nanoparticles thus produced was measured by an electron microscope and was found to shift to a smaller size with an increase in surfactant concentration. This behavior is explained in terms of the dynamic formation model. Dependence of the nanoparticle abundance on surfactant concentration in the solution shows that stable gold nanoparticles tend to be formed as the surfactant concentration exceeds 10-5 M. The gold nanoparticles having diameters larger than 5 nm were pulverized into those having diameters of 1−5 nm by a 532-nm laser.
TL;DR: In this paper, the potential of graphite nanofiber supported platinum catalysts as an electrode for fuel cell applications was investigated using the electrochemical oxidation of methanol at 40 °C as a probe reac...
Abstract: The potential of graphite nanofiber supported platinum catalysts as an electrode for fuel cell applications was investigated using the electrochemical oxidation of methanol at 40 °C as a probe reac...
TL;DR: In this paper, a purification method has been developed that provides for the removal of metal catalysts and impurity carbon from laser-oven-grown single-wall carbon nanotube (SWNT) material.
Abstract: A purification method has been developed that provides for the removal of metal catalysts and impurity carbon from laser-oven-grown single-wall carbon nanotube (SWNT) material. The oxidation rate of SWNTs in air at elevated temperatures is correlated to the metal content of the sample. Sample purity is documented with SEM, TEM, electron microprobe analysis, Raman, and UV−vis−near-IR. We also note that the relative intensity of the electronic transitions in the near-infrared to the continuum absorption at 400 nm in the UV serves as a useful monitor of the perturbation of the sidewall π-electron density of SWNTs due to sidewall substitution and/or oxidation.
TL;DR: In this article, a combination of multiwavelength laser excitation Raman scattering spectroscopy and solution-phase visible and near-infrared spectroscopies was used to characterize the library of carbon nanotubes produced in current preparations.
Abstract: Full-length single-walled carbon nanotubes (SWNTs) were rendered soluble in common organic solvents by noncovalent (ionic) functionalization of the carboxylic acid groups present in the purified SWNTs. Atomic force microscopy (AFM) showed that the majority of the SWNTs ropes were exfoliated into small ropes (2−5 nm in diameter) and individual nanotubes with lengths of several micrometers during the dissolution process. The combination of multiwavelength laser excitation Raman scattering spectroscopy and solution-phase visible and near-infrared spectroscopies was used to characterize the library of SWNTs that is produced in current preparations. The average diameter of metallic nanotubes was found by Raman spectroscopy to be smaller than that of semiconducting nanotubes in the various types of full-length SWNT preparations. This observation sheds new light on the mechanism of SWNT formation.
TL;DR: In this paper, the optical properties of the resulting thin Au@SiO2 particles have been analyzed as a function of the particle volume fraction, which is controlled through the silica shell thickness, and the surface plasmon peak position in films with volume fractions up to φ > 0.5 is accurately predicted by the Maxwell−Garnett model.
Abstract: Homogeneous films of Au@SiO2 particles have been deposited on glass as a prototype 3D “artificial solid” using the LBL method. The film thickness is controlled by the number of dipping cycles and is measured by AFM. Each cycle results in approximately one monolayer of particles being deposited. The particle films are dense, but disordered. The optical properties of the resulting thin films have been analyzed as a function of the particle volume fraction, which is controlled through the silica shell thickness. We find that the surface plasmon peak position in films with volume fractions up to φ > 0.5 is accurately predicted by the Maxwell−Garnett model. The films exhibit remarkably uniform, transmitted colors and display metallic reflection at low angles of incidence, even at low volume fractions. The films can be annealed at T > 500 K to provide extremely stable, optical films.
TL;DR: In this paper, a self-consistent charge density functional tight binding (SCC-DFTB) method was used to obtain the energy of the triosephosphate isomerase (TIM) catalyzed reactions.
Abstract: A quantum mechanical/molecular mechanical (QM/MM) approach based on an approximate density functional theory, the so-called self-consistent charge density functional tight binding (SCC-DFTB) method, has been implemented in the CHARMM program and tested on a number of systems of biological interest. In the gas phase, SCC-DFTB gives reliable energetics for models of the triosephosphate isomerase (TIM) catalyzed reactions. The rms errors in the energetics compared to B3LYP/6-31+G(d,p) are about 2−4 kcal/mol; this is to be contrasted with AM1, where the corresponding errors are 9−11 kcal/mol. The method also gives accurate vibrational frequencies. For the TIM reactions in the presence of the enzyme, the overall SCC-DFTB/CHARMM results are in somewhat worse agreement with the B3LYP/6-31+G(d,p)/CHARMM values; the rms error in the energies is 5.4 kcal/mol. Single-point B3LYP/CHARMM energies at the SCC-DFTB/CHARMM optimized structures were found to be very similar to the full B3LYP/CHARMM values. The relative sta...
TL;DR: In this paper, a vanadium-doped, supported TiO2 photocatalyst is presented which is quite active using visible (396−450 nm) light, and the oxidation of ethanol over this catalyst was studied using 13C solid-state NMR methods that demonstrated that this catalyst photooxidizes ethanol to produce mostly carbon dioxide with small amounts of acetaldehyde, formic acid, and carbon monoxide under visible irradiation.
Abstract: A vanadium-doped, supported TiO2 photocatalyst is presented which is quite active using visible (396−450 nm) light. The oxidation of ethanol over this catalyst was studied using 13C solid-state NMR methods that demonstrated that this catalyst photooxidizes ethanol to produce mostly carbon dioxide with small amounts of acetaldehyde, formic acid, and carbon monoxide under visible irradiation. Under UV irradiation, the catalyst has comparable activity and product distribution as a similarly prepared TiO2 thin-film monolayer catalyst.
TL;DR: In this paper, the process of Fermi level equilibration in 5 nm ZnO quantum dot−metal nano-junctions has been monitored using changes to both the surface plasmon band of the metal island and the sharp exciton band in the nanocrystals following photoinduced electron accumulation.
Abstract: The process of Fermi level equilibration in 5 nm ZnO quantum dot−metal nanojunctions has been monitored using changes to both the surface plasmon band of the metal island and the sharp exciton band of the ZnO nanocrystals following photoinduced electron accumulation. In the cases of silver, copper, and gold islands, excess electrons reside on both the quantum dot and the metal, whereas for Pt islands, the excess electrons reside exclusively on the Pt island. Electrons are transferred rapidly from Pt to the solvent ethanol, preventing accumulation on the quantum dots. The combination of exciton bleaching and surface plasmon shifts provides a simple way of probing the efficiency of small metal islands as redox catalysts on semiconductor particles.