A general approach to mesoporous metal oxide microspheres loaded with noble metal nanoparticles

Catalytic microspheres: A general approach is demonstrated for the facile preparation of mesoporous metal oxide microspheres loaded with noble metal nanoparticles (see TEM image in the picture). Among 18 oxide/noble metal catalysts, TiO(2)/0.1?mol?% Pd microspheres showed the highest turnover frequency in NaBH(4) reduction of 4-nitrophenol (see picture).     

Photoinduced cathodic deposition of CdTe nanoparticles on polycrystalline gold substrate

A combination of photocathodic stripping and precipitation was used to prepare CdTe nanoparticles (size range: 30–60 nm) that were immobilized on a polycrystalline Au substrate. Thus visible light irradiation of a Te modified Au surface generated Te²⁻ species in situ followed by interfacial reaction with added Cd²⁺ ions in 0.1 M Na₂SO₄ electrolyte. The resultant CdTe compound semiconductor deposited as nanosized particles uniformly dispersed on the Au substrate surface. This approach to CdTe nanoparticle deposition was monitored by a combination of electrochemical methods (voltammetry, chronoamperometry) and quartz crystal microgravimetry in the “dark” and under illumination. The synthesized CdTe nanoparticles were characterized by scanning electron microscopy and energy dispersive X-ray analyses and laser Raman spectroscopy.     

Toposelective electrochemical desorption of thiol SAMs from neighboring polycrystalline gold surfaces

We describe a method for the selective desorption of thiol self-assembled monolayers from gold surfaces having micrometer-scale separations on a substrate. In an electrolyte solution, the electrical resistance between the adjacent areas can be much lower than the resistance between a surface and the counter electrode. Also, both reductive and oxidative thiol desorption may occur. Therefore, the potentials of the surfaces must be independently controlled with a multichannel potentiostat and operating windows for a given thiol/electrolyte system must be established. In this study operating windows were established for 1-dodecanethiol-based SAMs in phosphate buffer, phosphate-buffered saline, and sodium hydroxide solution, and selective SAM removal was successfully performed in a four-electrode configuration.     

Nucleation of gold nanoparticles on latex particle surfaces

Gold particles were nucleated on functionalized (i.e., sulfonate or imidazole groups) latex particle surfaces. Gold ions were associated with the functional groups present on the surface of the latex particles by metal‐ligand formation and were then reduced to nucleate gold particles on the particle surface. The use of imidazole groups favored the metal‐ligand formation more effectively compared with sulfonic acid groups, so gold nucleation was investigated on the surface of imidazole‐functionalized model latex particles. The desorption of gold atoms or their surface migration first occurred during the reduction process and then gold nanoparticles were nucleated. The utilization of strong reductants, such as NaBH₄ and dimethylamine borane (DMAB) under mildly acidic conditions (i.e., pH 4) led to the deprotonation of imidazole‐rich polymer chains present on the surface of the model latex particles followed by deswelling of hydrophilic polymer surface layers. As a result, well‐dispersed gold nanoparticles were embedded in the hydrophilic polymer surface. On the other hand, the use of weak reductants led to the formation of localized gold aggregates on the surface of the latex particles. The removal of residual styrene monomer is very important because gold ions can be coordinated with the vinyl groups present in styrene monomer and would then be reduced by nucleophilic water addition. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 912–925, 2008     

Preexponential factors for hydrogen desorption from single crystal metal surfaces

Partition functions for adsorbed hydrogen atoms have been evaluated for Ni(100), Ni(111), Pd(111) and Pt(111) surfaces. These account for the relative order of magnituted of the preexponential factors for associative desorption, ν_d, including the abnormally low value for the Pt(111)/H system. Furthermore application of transition state theory yields numbers for ν_d which are in good agreement with experimental data.     

Photoinduced electron transfer between chlorophyll a and gold nanoparticles

Excited-state interactions between chlorophyll a (Chla) and gold nanoparticles have been studied. The emission intensity of Chla is quenched by gold nanoparticles. The dominant process for this quenching has been attributed to the process of photoinduced electron transfer from excited Chla to gold nanoparticles, although because of a small overlap between fluorescence of Chla and absorption of gold nanoparticles, the energy-transfer process cannot be ruled out. Photoinduced electron-transfer mechanism is supported by the electrochemical modulation of fluorescence of Chla. In absence of an applied bias, Chla cast on gold film, as a result of electron transfer, exhibits a very weak fluorescence. However, upon negatively charging the gold nanocore by external bias, an increase in fluorescence intensity is observed. The negatively charged gold nanoparticles create a barrier and suppress the electron-transfer process from excited Chla to gold nanoparticles, resulting in an increase in radiative process. Nanosecond laser flash experiments of Chla in the presence of gold nanoparticles and fullerene (C60) have demonstrated that Au nanoparticles, besides accepting electrons, can also mediate or shuttle electrons to another acceptor. Taking advantage of these properties of gold nanoparticles, a photoelectrochemical cell based on Chla and gold nanoparticles is constructed. A superior performance of this cell compared to that without the gold film is due to the beneficial role of gold nanoparticles in accepting and shuttling the photogenerated electrons in Chla to the collecting electrode, leading to an enhancement in charge separation efficiency.     

Water-gas-shift reaction on metal nanoparticles and surfaces

Density functional theory was employed to investigate the water-gas-shift reaction (WGS, CO+H2O-->H2+CO2) on Au29 and Cu29 nanoparticles seen with scanning tunneling microscopy in model AuCeO2(111) and CuCeO2(111) catalysts. Au(100) and Cu(100) surfaces were also included for comparison. According to the calculations of the authors, the WGS on these systems operate via either redox or associative carboxyl mechanism, while the rate-limiting step is the same, water dissociation. The WGS activity decreases in a sequence: Cu29>Cu(100)>Au29>Au(100), which agrees well with the experimental observations. Both nanoparticles are more active than their parent bulk surfaces. The nanoscale promotion on the WGS activity is associated with the low-coordinated corner and the edge sites as well as the fluxionality of the particles, which makes the nanoparticles more active than the flat surfaces for breaking the O-H bond. In addition, the role of the oxide support during the WGS was addressed by comparing the activity seen in the calculations of the authors for the Au29 and Cu29 nanoparticles and activity reported for XCeO2(111) and XZnO(000i)(X=Cu or Au) surfaces.     

Self-assembly of lysozyme on the surfaces of gold nanoparticles

The interaction of lysozyme(Lys) and gold nanoparticles was investigated via UV-vis absorption and resonance light-scattering method.There are some changes of the plasmon absorption and resonance light-scattering of gold nanoparticles that were observed via the addition of Lys.The normalized plasmon absorption and resonance light-scattering intensity with gold nanoparticles were both linear wilh 1-20 nmol/L Lys.A simple model about the component of the gold nanoparticles and Lys complex was established and the calculated result was fitted well in their concentration ratio.Furthermore,the activity analysis of Lys showed that the interaction was weak and nondestructive.     

Organometallic chemistry and catalysis on gold metal surfaces

As in transition metal complexes, CN-R ligands adsorbed on powdered gold undergo attack by amines to give putative diaminocarbene groups on the gold surface. This reaction forms the basis for the discovery of a gold metal-catalyzed reaction of CN-R, primary amines (R′NH₂) and O₂ to give carbodiimides (R′-NCN-R). An analogous reaction of CO, RNH₂, and O₂ gives isocyanates (R-NCO), which react with additional amine to give urea (RNH)₂CO products. The gold-catalyzed reaction of CN-R with secondary amines (HNR′₂) and O₂ gives mixed ureas RNH(CO)NR′₂. In another type of gold-catalyzed reaction, secondary amines HN(CH₂R)₂ react with O₂ to undergo dehydrogenation to the imine product, RCHN(CH₂R). Of special interest is the high catalytic activity of gold powder, which is otherwise well-known for its poor catalytic properties.     

纳米银粒子负载的多孔氧化锆材料的研究

采用液相浸渍移植及后续热处理工艺,把贵金属Ag成功地负载到多孔ZrO2材料中。产物用XRD,HRTEM,EDS,FT-IR,XPS及UV-vis等多种手段进行表征。结果表明,热处理对Ag粒子在多孔材料中的分散性具有重要的影响。在合适温度下,银的团簇粒子可以均匀地分散在多孔材料的孔道中,并产生明显的光吸收增强等主客体效应;随着温度的升高,银粒子倾向于向孔的外表面扩散。     

Preparation and electrocatalytic properties of gold nanoparticles loaded carbon nanotubes

Here, we report a new method of preparation of gold nanoparticles loaded carbon nanotubes (Au/CNTs) and the eleltrocatalystic properties of the obtained Au/CNTs as composite catalyst. This method shows advantages as it is easy to wash sodium citrate and the particle size of Au nanoparticles could by controlled by pH.     

Catalyzed radical polymerization of styrene vapor on nanoparticle surfaces and the incorporation of metal and metal oxide nanoparticles within polystyrene polymers

We present a novel approach to polymerize olefin vapors on the surfaces of metallic and semiconductor nanoparticles. In this approach, a free radical initiator such as AIBN is dissolved in a volatile solvent such as acetone. Selected nanoparticles (prepared separately using the laser vaporization-controlled condensation method) are used to form initiator-coated nanoparticles placed on a glass substrate. The olefin (styrene) vapor is polymerized by the thermally activated initiator on the nanoparticle surfaces. Our approach also provides structural and mechanistic information on the early stages of catalyzed gas-phase polymerization, which can be used to correlate the gas-phase structural properties with the bulk properties and the performance of the polymer nanocomposites. This correlation is the key step in controlling the properties of the polymer nanocomposites. Our results clearly demonstrate the success of this method in preparing polymer coated nanoparticles for a variety of interesting applications. The precise control of the chemical functionality, thickness, and morphology of the polymer film and the size, size distribution, and properties of the core nanoparticles (photoluminescence, magnetic) may lead to major technological breakthroughs in a variety of applications including drug delivery, ultrasensitive detectors, and chemical and biological sensors.     

Photoinduced elimination of senescent microglia cells in vivo by chiral gold nanoparticles

Parkinson''s disease (PD) is an age-related neurodegenerative disease, and the removal of senescent cells has been proved to be beneficial for improving age-associated pathologies in neurodegeneration disease. In this study, chiral gold nanoparticles (NPs) with different helical directions were synthesized to selectively induce the apoptosis of senescent cells under light illumination. By modifying anti-B2MG and anti-DCR2 antibodies, senescent microglia cells could be cleared by chiral NPs without damaging the activities of normal cells under illumination. Notably, l-P⁺ NPs exhibited about a 2-fold higher elimination efficiency than d-P⁻ NPs for senescent microglia cells. Mechanistic studies revealed that the clearance of senescent cells was mediated by the activation of the Fas signaling pathway. The in vivo injection of chiral NPs successfully confirmed that the elimination of senescent microglia cells in the brain could further alleviate the symptoms of PD mice in which the alpha-synuclein (α-syn) in cerebrospinal fluid (CFS) decreased from 83.83 ± 4.76 ng mL⁻¹ to 8.66 ± 1.79 ng mL⁻¹ after two months of treatment. Our findings suggest a potential strategy to selectively eliminate senescent cells using chiral nanomaterials and offer a promising strategy for alleviating PD.

The apoptosis pathways of senescent microglia cells induced by chiral NPs under the irradiation of 808 nm laser in the brain of PD mice.     

Hybrid films prepared from latex particles incorporating metal oxide nanoparticles

Metal oxide (ZrO₂) nanoparticle-dispersed polymer films (hybrid latex films) were prepared from polymer particles incorporating ZrO₂ nanoparticles (hybrid latex dispersion). The hybrid latex dispersions were synthesized by miniemulsion polymerization. The resulting films were transparent, and they derived their properties from the ZrO₂ nanoparticles. The refractive indexes of the films increased with the ZrO₂ content. Surface-modified ZrO₂ nanoparticles were dispersed successfully in a polymer matrix containing phosphoric acid groups, which interacts with the surfaces of the ZrO₂ nanoparticles and increases the compatibility between the polymer and ZrO₂.     

Catalytic performance of iron oxide loaded on electron-rich surfaces of carbon nitride

Carbon nitride(CN) in CN encapsulated Ni/Al_2O_3(denoted as CN/Ni/Al_2O_3) catalyst was evidenced previously as a material in electron-rich state and possessed H2-dissociative adsorption activity due to the electron doping effect from underlying nickel. In this report, iron oxide loaded on the CN/Ni/Al_2O_3 was synthesized and investigated by Fischer-Tropsch(F-T) synthesis to test the special effect of electron-rich support on the catalytic activity of iron oxide. The Fe/CN/Al_2O_3 and CN/Ni/Al_2O_3 samples were accordingly synthesized for comparison. In Fe/CN/Ni/Al_2O_3, the iron oxide was reduced to magnetite by syngas as evidenced by the in-situ XPS measurements and XRD pattern of used catalyst. Compared with Fe/CN/Al_2O_3, more light hydrocarbons over Fe/CN/Ni/Al_2O_3 were observed. It should be understood by the interaction between iron oxide and support mainly due to the effect of electron-rich state and thus enhanced H_2 adsorption ability. In addition, such a novel support facilitated the CO conversion and retarded the water-gas shift reaction and CO2 formation. The new type of adjustment on electronic state should be useful for novel catalyst design.     

Matrix-free laser desorption/ionization of ions landed on plasma-treated metal surfaces

We report new experiments in which laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF-MS) was applied to detection and characterization of gramicidin S and IgG pentapeptide (DSDPR) that were reactively landed on plasma-treated stainless steel surfaces. The distributions of [M + H](+), [M + Na](+) and [M + K](+) ion species in LDI-TOF for gramicidin S and IgG pentapeptide (DSDPR) were found to be markedly different from those in conventional MALDI-TOF spectra of the same samples. LDI-TOF mass spectra showed a strong preference for [M + K](+) adducts even in the presence of a large excess of sodium cations, or following surface treatment with trifluoroacetic acid. Alkali metal cations (K(+) and Cs(+)) can be exchanged in reactively landed peptide samples to provide the corresponding cationized peptide ions by LDI. Multiple charged trypsin cations were reactively landed into a layer of 2-(4-hydroxyphenylazo)benzoic acid and ionized by LDI. The ionization mechanisms for LDI of surface-deposited peptides are briefly discussed. Copyright (c) 2008 John Wiley & Sons, Ltd.     

Laser desorption/ionization mass spectrometry analysis of monolayer-protected gold nanoparticles

Monolayer-protected gold nanoparticles (AuNPs) feature unique surface properties that enable numerous applications. Thus, there is a need for simple, rapid, and accurate methods to confirm the surface structures of these materials. Here, we describe how laser desorption/ionization mass spectrometry (LDI-MS) can be used to characterize AuNPs with neutral, positively, and negatively charged surface functional groups. LDI readily desorbs and ionizes the gold-bound ligands to produce both free thiols and disulfide ions in pure and complex samples. We also find that LDI-MS can provide a semi-quantitative measure of the ligand composition of mixed-monolayer AuNPs by monitoring mixed disulfide ions that are formed. Overall, the LDI-MS approach requires very little sample, provides an accurate measure of the surface ligands, and can be used to monitor AuNPs in complex mixtures.      

UV laser-stimulated resonant desorption from metal surfaces: NO/Ni(100)

NO chemisorbed on a Ni(100) surface at 170 K, has been desorbed with UV laser light (ArF, 193 nm = 6.42 eV) in the energy range of the most intense electronic absorption of the NO/Ni(100) system. The rotational and vibrational state distribution of the desorbing molecules is probed via laser-induced fluorescence. The desorbing molecules are vibrationally and rotationally excited. The rotational distribution is markedly non-Boltzmann. The velocity distributions are narrow and very different for various rotational states. They cannot be fitted to a Maxwell distribution. We believe that these results provide evidence for the resonant nature of the light-absorption-desorption process for NO on a Ni(100) surface.     

Aqueous solvation dynamics at metal oxide surfaces

Broadband transient absorption (TA) spectroscopy, three-pulse photon echo peak shift (3PEPS), and anisotropy decay measurements were used to study the solvation dynamics in bulk water and interfacial water at ZrO(2) surfaces, using Eosin Y as a probe. The 3PEPS results show a multiexponential behavior with two subpicosecond components that are similar in bulk and interfacial water, while a third component of several picoseconds is significantly lengthened at the interface. The bandwidth correlation function from TA spectra exhibits the same behavior, and the TA spectra are well reproduced using the doorway-window picture with the time constants from PEPS. Our results suggest that interfacial water is restricted to a thickness of less than 5 A. Also the high-frequency collective dynamics of water does not seem to be affected by the interface. On the other hand, the increase of the third component may point to a slowing down of diffusional motion at the interface, although other effects, may play a role, which are discussed.