Showing papers in "Journal of Physical Chemistry B in 2002"
TL;DR: In this article, a photoactive molecule (e.g., pyrene) is added to a metal nanoparticle to enhance the photochemical activity and render the organic−inorganic hybrid nanoassemblies suitable for light harvesting and optoelectronic applications.
Abstract: Unique electronic and chemical properties of metal nanoparticles have drawn the attention of chemists, physicists, biologists, and engineers who wish to use them for the development of new generation nanodevices. Metal nanoparticles such as gold and silver show noticeable photoactivity under UV−visible irradiation as is evident from the photoinduced fusion and fragmentation processes. Binding a photoactive molecule (e.g., pyrene) to metal nanoparticle enhances the photochemical activity and renders the organic−inorganic hybrid nanoassemblies suitable for light-harvesting and optoelectronic applications. The nature of charge-transfer interaction of fluorophore with gold surface dictates the pathways with which the excited-state deactivates. Obtaining insight into energy and electron-transfer processes is important to improve the charge separation efficiencies in metal−fluorophore nanoassemblies and photocatalytic activity of metal−semiconductor composites.
1,870 citations
TL;DR: In this article, photostable thiol-capped CdTe nanocrystals were synthesized using post-preparative size-selective precipitation and selective photochemical etching.
Abstract: New approaches to synthesize photostable thiol-capped CdTe nanocrystals are reported. Post-preparative size-selective precipitation and selective photochemical etching have been developed as methods providing an increase of photoluminescence quantum efficiency of the nanocrystals of up to 40%. Some advantages of thiol-capping in comparison to conventional organometallic syntheses of quantum dots are discussed.
1,500 citations
TL;DR: In this article, the evaporation of a sessile droplet with a pinned contact line was investigated experimentally, by analytic theory and by computation using the finite element method (FEM).
Abstract: The evaporation of a sessile droplet with a pinned contact line is investigated experimentally, by analytic theory and by computation using the finite element method (FEM). Because of the low value of R2/Dtf = cv(1 − H)/ρ = 1.4 × 10-5, where R is the contact-line radius, D is the water vapor diffusivity, cv is the saturated water vapor concentration, H is the relative humidity, and ρ is the liquid water density, the evaporation can be considered as a quasi-steady-state process. Hence, the vapor concentration distribution above the droplet satisfies the Laplace equation but with a time-varying droplet surface. It is found both theoretically and experimentally that the net evaporation rate from the droplet remains almost constant with time for a small initial contact angle (θ < 40°), even though the evaporation flux becomes more strongly singular at the edge of the droplet as the contact angle decreases during evaporation. We also measured the critical contact angle at which the contact line starts to reced...
1,302 citations
TL;DR: In this paper, a surface-enhanced Raman scattering (SERS) was discovered which impacted on surface science and spectroscopy because of its extremely high surface sensitivity, but SERS had not developed as many people had hoped to be a powerful surface diagnostic technique that can be widely used because of some obstacles.
Abstract: In the mid-1970s, surface-enhanced Raman scattering (SERS) was discovered which impacted on surface science and spectroscopy because of its extremely high surface sensitivity. However, SERS had not developed as many people had hoped to be a powerful surface diagnostic technique that can be widely used because of some obstacles. For example, only three noble metals Au, Ag, and Cu could provide large enhancement, severely limiting the widespread applications involving other metallic materials of both fundamental and practical importance. In this article, emphasis is put on the recent work of our group to directly generate SERS on net transition metals (e.g., Pt, Ru, Rh, Pd, Fe, Co, Ni, and their alloys) by developing various roughening procedures and optimizing the performance of the confocal Raman microscope. An approach of replacing the randomly roughened surface with ordered nanorod arrays of transition metals is introduced as a promising class of highly SERS-active substrates. The surface enhancement fa...
1,250 citations
TL;DR: In this paper, the small signal ac impedance of electron diffusion and recombination in a spatially restricted situation with application in systems such as porous TiO2 nanostructured photoelectrodes and intrinsically conducting polymers is analyzed.
Abstract: This paper analyzes the small signal ac impedance of electron diffusion and recombination in a spatially restricted situation with application in systems such as porous TiO2 nanostructured photoelectrodes and intrinsically conducting polymers. It is shown that the diffusion−recombination model with the main types of boundary conditions assumes a finite set of possible behaviors in the frequency domain, which are classified according to relevant physical parameters. There are four possible cases: (i) the impedance of finite diffusion with reflecting boundary, (ii) the impedance of finite diffusion with absorbing boundary, (iii) the impedance of diffusion-reaction in semiinfinite space or Gerischer impedance, and (iv) the impedance that combines Warburg response at high frequency and a reaction arc at low frequency. The generality of the approach is discussed in terms of the spatial distribution of the electrochemical potential or quasi-Fermi level and also in terms of the transmission line representation....
1,199 citations
TL;DR: In this article, a comparative study of the oxygen reduction reaction on two carbon-supported Pt-based alloy catalysts in aqueous acidic electrolyte at low temperature is presented.
Abstract: We describe a comparative study of the oxygen reduction reaction on two carbon-supported Pt-based alloy catalysts in aqueous acidic electrolyte at low temperature. Both alloys have the bulk compositions of 50 and 75 at. % Pt, with the alloying elements being Ni and Co. Comparison is made to a pure Pt catalyst on the same carbon support, Vulcan XC-72, having the same metal loading (20 wt %) and nominally the same particle size (4 ± 2 nm). High-resolution electron microscopy was used to determine the size and shape of the particles as well as the particle size distribution on all catalysts. Electrochemical measurements were performed using the thin-film rotating ring−disk electrode method in 0.1 M HClO4 at 20−60 °C. Hydrogen adsorption pseudocapacitance was used to determine the number of Pt surface atoms and to estimate the surface composition of the alloy catalysts. Kinetic analysis in comparison to pure Pt revealed a small activity enhancement (per Pt surface atom) of ca. 1.5 for the 25 at. % Ni and Co c...
903 citations
TL;DR: In this paper, the solubility of nine different gases in 1-n-butyl-3-methylimidazolium hexafluorophosphate was investigated.
Abstract: This work presents the solubility of nine different gases in 1-n-butyl-3-methylimidazolium hexafluorophosphate. The gases considered include carbon dioxide, ethylene, ethane, methane, argon, oxygen, carbon monoxide, hydrogen, and nitrogen. We also report the associated Henry's constants and enthalpies and entropies of absorption. We found carbon dioxide to have the highest solubility and strongest interactions with the ionic liquid, followed by ethylene and ethane. Argon and oxygen had very low solubilities and immeasurably weak interactions. Carbon monoxide, hydrogen, and nitrogen all had solubilities below the detection limit of our apparatus. Our results suggest that the mass transfer of gases into ionic liquids likely will be an important issue for reactions involving these gases. We also determined that ionic liquids show good potential for use as a gas-separation medium.
896 citations
TL;DR: In this article, the size-dependent absorption cross section of CdSe nanocrystal quantum dots was measured and compared to simple theoretical models of light scattering from light-absorbing small particles.
Abstract: The linear absorption cross section is a crucial parameter to the design of nanocrystal quantum dot devices and to the interpretation of spectroscopic data. We measure and report the size-dependent absorption cross section of CdSe nanocrystal quantum dots. We compare the results for absorption far above the band edge, where the quantum dot density of states may be approximated as a continuum, to simple theoretical models of light scattering from light-absorbing small particles. Excellent agreement with theory is found for dilute dispersions in hexane. We find that for absorption at 350 nm the per particle absorption cross section Cabs (in cm2) for CdSe is Cabs = (5.501 × 105)a3 cm-1, where a is the particle radius in cm. The absorption cross section is observed to be largely insensitive to the solvent refractive index. Detailed modeling of the effect of the ligand shell may be necessary to understand the lack of sensitivity of the absorption properties of nanocrystal quantum dots to the refractive index o...
832 citations
TL;DR: In this article, a nearly monodisperse iron nanoclusters have been used to define the diameters of carbon nanotubes grown by chemical vapor deposition (CVD).
Abstract: Nearly monodisperse iron nanoclusters have been used to define the diameters of carbon nanotubes grown by chemical vapor deposition (CVD). Iron nanoparticles with average diameters of 3, 9, and 13 nm were used to grow carbon nanotubes with average diameters of 3, 7, and 12 nm, respectively. Transmission electron microscopy studies of the nanotubes show that the as-grown nanotubes are single-walled carbon nanotubes (SWNTs) or thin multiwalled carbon nanotubes (MWNTs) with 2 or 3 layers. Investigations of the growth conditions also demonstrate that the supply of carbon reactant is critical for enabling the growth of large diameter nanotubes from large iron nanoclusters, and that the growth temperature is especially important for achieving high-quality large diameter nanotubes. The implications of these results and possible applications of the nanotubes are discussed.
818 citations
TL;DR: Experimental and theoretical studies of nonpolar solute partitioning into water are surveyed and it is noted that the hydrophobic effect is not just due to “water ordering” and not merely due to small size effects of water.
Abstract: Oil and water do not mix. The disaffinity of oil for water, with its unusual temperature dependence, is called the hydrophobic effect. It is important to understand the factors underlying the hydrophobic effect because they appear to play key roles in membrane and micelle formation, protein folding, ligand-protein and protein−protein binding, chromatographic retention, possibly nucleic acid interactions, and the partitioning of drugs, metabolites, and toxins throughout the environment and living systems. Here, we survey experimental and theoretical studies of nonpolar solute partitioning into water. We note that the hydrophobic effect is not just due to “water ordering” and not merely due to small size effects of water. The properties vary substantially with temperature and solute shape. Also, we discuss the limitations of using oil/water partitioning as the basis for some thermodynamic models in chemistry and biology.
800 citations
TL;DR: In this article, the surface composition of polycrystalline bulk alloys of Pt3Ni and Pt3Co was determined via low-energy ion-scattering (LEIS) spectroscopy.
Abstract: The oxygen reduction reaction (ORR) has been studied on polycrystalline Pt3Ni and Pt3Co alloys in acid electrolytes using the rotating ring disk electrode (RRDE) method. Preparation and characterization of alloy surfaces were performed in ultrahigh vacuum (UHV). Clearly defined surface composition was determined via low-energy ion-scattering (LEIS) spectroscopy. Polycrystalline bulk alloys of Pt3Ni and Pt3Co were prepared in UHV having two different surface compositions: one with 75% Pt and the other with 100% Pt. The latter we call a “Pt-skin” structure and is produced by an exchange of Pt and Co in the first two layers. The base voltammetry in 0.1 M HClO4 solution of the 75% Pt alloy surface indicated a decrease of Hupd pseudocapacitance (ca. 30−40 μC/cm2) consistent with the surface composition determined in UHV. With the exception of the “Pt-skin” surface on Pt3Ni, all the alloy electrodes exhibited stable i−E curves with repeated cycling between 0.05 and 1.0 V at all temperatures. Activities of Pt-a...
TL;DR: In this article, the authors showed that the activity of a photocatalyst with antimony and chromium was remarkably higher than that of one with only chromium and that the charge balance was kept by codoping of Sb5+ and Cr3+ ions, resulting in the suppression of formation of Cr6+ ions and oxygen defects in the lattice.
Abstract: TiO2 and SrTiO3 codoped with antimony and chromium showed intense absorption bands in the visible light region and possessed 2.2 and 2.4 eV of energy gaps, respectively. TiO2 codoped with antimony and chromium evolved O2 from an aqueous silver nitrate solution under visible light irradiation, while SrTiO3 codoped with antimony and chromium evolved H2 from an aqueous methanol solution. The activity of TiO2 photocatalyst codoped with antimony and chromium was remarkably higher than that of TiO2 doped with only chromium. It was due to that the charge balance was kept by codoping of Sb5+ and Cr3+ ions, resulting in the suppression of formation of Cr6+ ions and oxygen defects in the lattice which should work as effectively nonradiative recombination centers between photogenerated electrons and holes.
TL;DR: In this paper, the role of Ni as a catalytically enhancing agent in the methanol oxidation process was investigated using cyclic voltammetry, chronoamperometry, X-ray photoelectron spectroscopy, transmission electron microscopy, and Xray diffraction.
Abstract: Electrooxidation of methanol in sulfuric acid solution was studied using Pt, Pt/Ni(1:1 and 3:1), Pt/Ru/Ni(5:4:1 and 6:35:05), and Pt/Ru(1:1) alloy nanoparticle catalysts, in relation to methanol oxidation processes in the direct oxidation methanol fuel cell The Pt/Ni and Pt/Ru/Ni alloys showed excellent catalytic activities compared to those of pure Pt and Pt/Ru The role of Ni as a catalytically enhancing agent in the oxidation process was interrogated using cyclic voltammetry, chronoamperometry, X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray diffraction X-ray diffraction data showed alloy formation for all Pt/Ni, Pt/Ru/Ni, and Pt/Ru nanoparticles, whereas X-ray photoelectron spectroscopy confirmed that chemical states of Pt were exclusively metallic The presence of metallic Ni, NiO, Ni(OH)2, NiOOH, metallic Ru, RuO2, and RuO3 was also confirmed We found that the Pt4f binding energies for the Pt/Ni and Pt/Ru/Ni alloy nanoparticles were lower than those for clean Pt na
TL;DR: A high surface area pn-heterojunction between TiO2 and an organic p-type charge transport material (spiro-OMeTAD) was sensitized to visible light using lead sulfide (PbS) quantum dots as mentioned in this paper.
Abstract: A high surface area pn-heterojunction between TiO2 and an organic p-type charge transport material (spiro-OMeTAD) was sensitized to visible light using lead sulfide (PbS) quantum dots. PbS quantum dots were formed in situ on a nanocrystalline TiO2 electrode using chemical bath deposition techniques.1 The organic hole conductor was applied from solution to form the sensitized heterojunction. The structure of the quantum dots was analyzed using HRTEM technique. Ultrafast laser photolysis experiments suggested the initial charge separation to proceed in the subpicosecond time range. Transient absorption laser spectroscopy revealed that interfacial charge recombination of the initially formed charge carriers is much faster than in comparable dye-sensitized systems.2,3 The sensitized heterojunction showed incident photon-to-electron conversion efficiencies (IPCE) of up to 45% and energy conversion efficiencies under simulated sunlight AM1.5 (10 mW/cm2) of 0.49%.
TL;DR: In this article, the authors present results from theoretical studies of aqueous ionic solvation of alkali halides aimed at developing a microscopic description of structure and dynamics at the interface between air and saliency.
Abstract: We present results from theoretical studies of aqueous ionic solvation of alkali halides aimed at developing a microscopic description of structure and dynamics at the interface between air and sal...
TL;DR: In this paper, an all-atom force field is developed using a combination of density functional theory calculations and CHARMM 22 parameter values for the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate.
Abstract: We report the results of a molecular dynamics study of the ionic liquid 1-n-butyl-3-methylimidazolium hexafluorophosphate [bmim][PF6], a widely studied ionic liquid. An all-atom force field is developed using a combination of density functional theory calculations and CHARMM 22 parameter values. Molecular dynamics simulations are carried out in the isothermal−isobaric ensemble at three different temperatures. Quantities computed include infrared frequencies, molar volumes, volume expansivities, isothermal compressibililties, self-diffusivities, cation−anion exchange rates, rotational dynamics, and radial distribution functions. Computed thermodynamic properties are in good agreement with available experimental values.
TL;DR: In this article, surface modification of nanocrystalline metal oxide particles with enediol ligands was found to result in altered optical properties of nanoparticles, and the surface modification results in a red shift of the semiconductor absorption compared to unmodified nanocrystites.
Abstract: Surface modification of nanocrystalline metal oxide particles with enediol ligands was found to result in altered optical properties of nanoparticles. The surface modification results in a red shift of the semiconductor absorption compared to unmodified nanocrystallites. The optical shift is correlated to the dipole moment of the Ti−ligand complexes at the particle surface and decreases with the ligand size. The binding was found to be exclusively characteristic of colloids in the nanocrystalline domain(<20 nm). X-ray near-edge structure measurements at Ti K edge indicate that in this size domain the surface Ti atoms adjust their coordination environment to form undercoordinated sites. These five-coordinated defect sites are the source of novel enhanced and selective reactivity of the nanoparticle toward bidentate ligand binding as observed using IR spectroscopy. Enediol ligands have the optimal geometry for chelating surface Ti atoms, resulting in a five-membered ring coordination complex and restored si...
TL;DR: In this paper, the authors reported a direct examination of chemical enhancement by using an integrated flow injection and ultrasensitive optical imaging/spectroscopy system, where colloidal silver nanoparticles are immobilized on a glass surface inside a microflow device and single-particle SERS signals are observed in real time while the immobilized particles are treated by chemical reagents in the flow cell.
Abstract: Recent research in several groups has identified a new class of metal colloidal nanoparticles that is able to enhance the efficiencies of surface-enhanced Raman scattering (SERS) by as much as 1014−1015 fold. This enormous enhancement allows single-molecule detection and spectroscopy at room temperature. Previous single-molecule and single-particle studies have yielded important insights into the mechanism of electromagnetic field enhancement, but little is known about the contributions of surface active sites and chemical enhancement. Here we report a direct examination of chemical enhancement by using an integrated flow injection and ultrasensitive optical imaging/spectroscopy system. A key feature is that colloidal silver nanoparticles are immobilized on a glass surface inside a microflow device and that single-particle SERS signals are observed in real time while the immobilized particles are treated by chemical reagents in the flow cell. In situ surface plasmon scattering studies of spatially isolate...
TL;DR: In this article, the authors investigated other methods of preparation of Au/TiO2 catalysts to obtain small gold metal particles (2−3 nm) and a higher Au loading.
Abstract: The best current way to prepare Au/TiO2 catalysts is the method of deposition−precipitation with NaOH (DP NaOH) developed by Haruta and co-workers. With this method, it is possible to obtain small gold metal particles (2−3 nm), but the corresponding gold loading remains rather low (∼3 wt %). The main goal of this work is to investigate other methods of preparation of Au/TiO2 catalysts to obtain small gold metal particles (2−3 nm) and a higher Au loading. It is shown that anion adsorption with AuCl4- (AA) does not produce Au loading higher than 1.5 wt % and the average particle size is not very small (∼4 nm). Cation adsorption with Au(en)23+ (CA) leads to small particles (2 nm) when the solution/support contact time is moderate (1 h), but the Au loading does not exceed 2 wt %. The most promising method of preparation appears to be deposition−precipitation with urea (DP urea). Indeed, samples with gold particles as small as those obtained with DP NaOH (∼2 nm) can be prepared, and all gold in solution is dep...
TL;DR: In this article, the influence of chemical cross-links between a single-walled fullerene nanotube and a polymer matrix on the matrix−nanotube shear strength has been studied using molecular dynamics simulations.
Abstract: The influence of chemical cross-links between a single-walled fullerene nanotube and a polymer matrix on the matrix−nanotube shear strength has been studied using molecular dynamics simulations. A (10,10) nanotube embedded in either a crystalline or amorphous polyethylene matrix is used as a model for a nonbonded interface (in the absence of cross-links). The simulations predict that shear strengths and critical lengths required for load transfer can be enhanced and decreased, respectively, by over an order of magnitude with the formation of cross-links involving less than 1% of the nanotube carbon atoms. At this level of chemical functionalization, calculations also predict that there is a negligible change in tensile modulus for a (10,10) nanotube.
TL;DR: In this article, the 1Se,h−1Pe,h and 1Pe, h−1De,h intraband excitations were identified and assigned to the sub-μs lifetime and near-unity quantum yield.
Abstract: PbSe nanocrystal colloids exhibit a well-defined excitonic structure with the lowest energy exciton tuning from 0.5 to 1 eV, as a function of size. Band-edge fluorescence is observed from 1.2 to 2 μm with a small Stokes shift, sub-μs lifetime, and near-unity quantum yield. Upon pumping at 1.064 μm, the first exciton decay is consistent with radiative relaxation at low pump intensity and with Auger recombination at higher pump intensities. Optically induced absorption is observed at approximately midgap. These transitions exhibit strengths similar to the interband exciton and are size-tunable. They are assigned to the 1Se,h−1Pe,h and 1Pe,h−1De,h intraband excitations. Intraband pump−probe measurements of the 1Se,h−1Pe,h transition reveal a short lifetime and the absence of the phonon bottleneck.
TL;DR: In this article, the luminescence properties of chemically prepared gold nanoclusters, each composed of a 28-atom core and a glutathione (GSH) adsorbate layer consisting of 16 molecules, were investigated.
Abstract: The luminescence properties of chemically prepared gold nanoclusters, each composed of a 28-atom core and a glutathione (GSH) adsorbate layer consisting of 16 molecules, were investigated These clusters show a distinct absorption onset at 13 eV corresponding to the opening of an electronic gap within the conduction band (HOMO-LUMO gap) Here we report on the radiative properties of these molecular-like gold clusters By using a combination of different detectors with sensitivities in the visible to the infrared (20−08 eV), a broad luminescence extending over this entire spectral range was observed Our results further suggest that the luminescence can be separated into two bands with maxima around 15 and 115 eV indicating that radiative recombination between the ground state and two distinctively different excited states takes place The origin of the observed luminescence bands is discussed using a solid state as well as a molecular model for the electronic structure and relaxation of the clusters
TL;DR: In this paper, a metal film over nanosphere (MFON) electrode was developed and characterized to solve the problem of the stability and reproducibility of most SERS-active electrode surfaces.
Abstract: The stability and reproducibility of most SERS-active electrode surfaces are far from ideal. We have focused on this problem by developing and characterizing a metal film over nanosphere (MFON) electrode which solves these shortcomings. Atomic force microscopy (AFM), cyclic voltammetry, and surface-enhanced Raman spectroscopy (SERS) of representative molecules were used to characterize and evaluate the electrochemical and SERS performance of MFON electrodes. Tremendous stability to extremely negative potential excursions is observed for MFON electrodes as compared to standard metal oxidation reduction cycle (MORC) roughened electrodes. Consequently, irreversible loss of SERS intensity at negative potentials is not observed on these MFON electrodes. We conclude that MFON electrodes present a significant advantage over MORC electrodes because SERS enhancement is not lost upon excursion to extremely negative potentials. This work demonstrates that the MFON substrate, while easily prepared and temporally stable, offers unprecedented stability and reproducibility for electrochemical SERS experiments. Furthermore, one can conclude that irreversible loss is not a distinguishing characteristic of electrochemical SERS and consequently cannot be used as evidence to support the chemical enhancement mechanism.
TL;DR: Copper and copper oxides (Cu2O and CuO) have been deposited by evaporation of copper and subsequent oxidizing treatments, on the surface of flat SiO2 and ZrO2 substrates.
Abstract: Copper and copper oxides (Cu2O and CuO) have been deposited by evaporation of copper and subsequent oxidizing treatments, on the surface of flat SiO2 and ZrO2 substrates. Large variations of severa...
TL;DR: In this paper, the orientation relationship between the orthorhombic superlattice and the rutile structured SnO2 was determined to be [001]o || [102]t and (100)o'||'(010)t for the nanowires and sandwiched nanoribbons.
Abstract: Nanowires, sandwiched nanoribbons, and nanotubes of SnO2 are synthesized using elevated temperature synthesis techniques, and their structures are characterized in detail by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). In addition to the normal rutile structured SnO2, it has been possible to form an orthorhombic superlattice-like structure in the present study. The orthorhombic structure can form in a thin nanowire, coexist with the normal rutile structured SnO2 in a sandwiched nanoribbon, or occur in the form of nanotubes. This result is distinct from that for bulk SnO2 where pressures in excess of 150 kbar are required to form the orthorhombic form. The orientation relationship between the orthorhombic SnO2 and the rutile structured SnO2 is determined to be [001]o || [102]t and (100)o || (010)t for the nanowires and sandwiched nanoribbons, and [001]o || [3 ]t and (110)o || (451)t for the nanotubes. Although the growth direction of the rutile structured SnO2 nanowires i...
TL;DR: In this article, the authors used the X-ray back reflection method to determine the crystal orientation of a single crystal in graphite crucibles and showed that the introduction of (111) steps to the basal plane, leading to Cu(S)-[n(100) × (111)] orientations, significantly promoted C2H4 formation and suppressed CH4 formation.
Abstract: Electrochemical reduction of CO2 was studied using single-crystal electrodes, Cu(111), Cu(100), Cu(S)-[n(100) × (111)], and Cu(S)-[n(100) × (110)] at a constant current density 5 mA cm-2 in 0.1 M KHCO3 aqueous solution. Copper single crystals were prepared from 99.999% copper metal in graphite crucibles by the Bridgeman method. The crystal orientation was determined by the X-ray back reflection method. The Cu(111) electrode yields mainly CH4 from CO2, and the Cu(100) favorably gives C2H4. Introduction of (111) steps to Cu(100) basal plane, leading to Cu(S)-[n(100) × (111)] orientations, significantly promoted C2H4 formation and suppressed CH4 formation. The selectivity ratio C2H4/CH4 on Cu(711) (n = 4) amounted to 14, 2 orders of magnitude higher than that on Cu(111).
TL;DR: In this paper, three catalysts for the electroreduction of oxygen have been prepared by pyrolyzing between 400 and 1000 °C two iron precursors (Fe acetate or Fe porphyrin) adsorbed on a synthetic carbon made from the pyrolys of PTCDA (perylene tetracarboxylic dianhydride) in a H2/NH3/Ar atmosphere.
Abstract: Three catalysts for the electroreduction of oxygen have been prepared by pyrolyzing between 400 and 1000 °C two iron precursors (Fe acetate or Fe porphyrin) adsorbed on a synthetic carbon made from the pyrolysis of PTCDA (perylene tetracarboxylic dianhydride) in a H2/NH3/Ar atmosphere. One Fe loading (0.2 wt %) has been used for the catalyst made from the salt precursor. Two Fe loadings (0.2 and 2.0 wt %) have been used for the catalyst made from the porphyrin precursor. These three catalysts have been analyzed by ToF SIMS and RDE (or GDE) in order to find correlations between ions detected by ToF SIMS and the catalytic activity. These correlations provide information about the number and the structure of the catalytic sites, which are active in these materials. By following the variation of FeNxCy+ ions, it is found that (i) two different catalytic sites exist simultaneously in all catalysts made with the Fe salt or the Fe porphyrin; (ii) one site, named FeN4/C, is at the origin of three families of FeNx...
TL;DR: In this article, a variety of structural and dynamical properties of protein hydration water are reviewed and compared with those of bulk and with corresponding experimental results, which can be traced back to the complexity of the overall protein−solvent energy landscape.
Abstract: The use of molecular dynamics simulation to investigate the properties of hydration water around proteins is outlined. A variety of structural and dynamical properties of the protein hydration water are reviewed and compared with those of bulk and with the corresponding experimental results. In particular, the accessibility to the protein medium, the hydrogen bond networking capability, the residence times, the diffusive mobility, the relaxation behavior, and the inelastic vibrational features of hydration water are analyzed in framework of the peculiar interactions of water at the protein surface. All these features, which can be traced back to the complexity of the overall protein−solvent energy landscape, are discussed in connection with the role played by hydration water in the biological functionality.
TL;DR: A set of polycrystalline TiO2 photocatalysts loaded with various ions of transition metals (Co, Cr, Cu, Fe, Mo, V, and W) were prepared by using the wet impregnation method.
Abstract: A set of polycrystalline TiO2 photocatalysts loaded with various ions of transition metals (Co, Cr, Cu, Fe, Mo, V, and W) were prepared by using the wet impregnation method. The samples were characterized by using some bulk and surface techniques, namely X-ray diffraction, BET specific surface area determination, scanning electron microscopy, point of zero charge determination, and femtosecond pump−probe diffuse reflectance spectroscopy (PP-DRS). The samples were employed as catalysts for 4-nitrophenol photodegradation in aqueous suspension, used as a probe reaction. The characterization results have confirmed the difficulty to find a straightforward correlation between photoactivity and single specific properties of the powders. Diffuse reflectance measurements showed a slight shift in the band gap transition to longer wavelengths and an extension of the absorption in the visible region for almost all the doped samples. SEM observation and EDX measurements indicated a similar morphology for all the parti...
TL;DR: In this article, the authors review the issues guided by experimental studies, from this laboratory, of polar hydration dynamics at the surfaces of two proteins (Subtilisin Carlsberg (SC) and Monellin).
Abstract: The unique features of a macromolecule and water as a solvent make the issue of solvation unconventional, with questions about the static versus dynamic nature of hydration and the physics of orientational and translational diffusion at the boundary. For proteins, the hydration shell that covers the surface is critical to the stability of its structure and function. Dynamically speaking, the residence time of water at the surface is a signature of its mobility and binding. With femtosecond time resolution it is possible to unravel the shortest residence times which are key for the description of the hydration layer, static or dynamic. In this article we review these issues guided by experimental studies, from this laboratory, of polar hydration dynamics at the surfaces of two proteins (Subtilisin Carlsberg (SC) and Monellin). The natural probe tryptophan amino acid was used for the interrogation of the dynamics, and for direct comparison we also studied the behavior in bulk watera complete hydration in 1 ...