Electrocatalytic activity of a novel titanium-supported nanoporous gold catalyst for glucose oxidation

A novel Ti-supported gold catalyst (nanoAu/Ti) with a nanoporous 3D texture has been fabricated using a hydrothermal method. Au particles were stably deposited on the Ti surface from the mixture of aqueous tetrachlororoauric acid and polyethylene glycol at 180 °C. Voltammetry (CV) and chronoamperometry were used to characterize the nanoAu/Ti electrode and assess its electroactivity towards glucose oxidation. Compared to polycrystalline Au, the nanoAu/Ti electrode shows similar CV profiles in alkaline solution. However, in an alkaline solution containing 10 mM glucose, the nanoAu/Ti electrode presents much higher anodic current densities and a more negative onset potential (ca. ?0.75 V) for glucose oxidation than a bulk Au electrode. Analysis for Tafel plot of the nanoAu/Ti electrode shows that electro-oxidation of glucose takes place via a one-electron rate-determining step. Results indicate a high and (relatively) stable electrocatalytic activity of the nanoAu/Ti for glucose oxidation.     

Electrocatalytic activity of bimetallic platinum-gold catalysts fabricated based on nanoporous gold

A tiny amount of Pt was deposited in a quasi-two-dimensional form onto the nanoporous gold (NPG) substrate through a simple immersion-electrodeposition (IE) method, forming nanostructured bimetallic Pt-Au catalysts. Such Pt-Au nanostructures have much higher structural stability than the bare NPG; moreover, they exhibit better catalytic activity and stronger poison resistance than commercial Pt-Ru catalysts because of the synergistic effect of the bimetallic compositions.     

Silver UPD ultra-thin film modified nanoporous gold electrode with applications in the electrochemical detection of chloride

Nanoporous noble metals are usually expected to exhibit much higher surface areas than smooth ones, making them of particular importance in many electrochemical applications. This paper describes a simple electrochemical method to modify a nanoporous Au (NPG) surface by using an under potentially deposited (UPD) Ag adlayer. The NPG electrode was obtained by the dealloying of Zn from Au_xZn_1−x in a 40-60 mol% zinc chloride-1-ethyl-3-methylimidazolium chloride (ZnCl₂-EMIC) ionic liquid. The Ag UPD modified nanoporous gold (NPG/Ag(UPD)) electrode possessed dual properties, including an intrinsic high surface area from the nanoporous structure and the characteristics of the Ag UPD adlayer. The potential utility of using NPG/Ag(UPD) for sensors was demonstrated by its excellent sensitivity and selectivity in the electrochemical determination of chloride ions. An atomic scale metal monolayer obtained in the UPD process was selected as a sensing agent. The long-term storability and operational stability of the electrode were strongly demonstrated. Specifically, two couples of redox waves at ∼552 mV and ∼272 mV, respectively, were observed in the cyclic voltammograms (CVs) of the NPG/Ag(UPD) after the adsorption of chloride ions. The first couple of redox waves was related to the UPD and silver stripping and the second couple of redox waves was induced by the adsorption of Cl⁻. The Cl⁻ adsorption process on the NPG/Ag(UPD) electrode followed the transient Langmuir adsorption kinetic model. The ratio of the integrated charges for these two anodic stripping peaks was selectively used to determine dilute chloride ion levels. The calibration curve was linear in the Cl⁻ concentration range of 0.5-30.0 μM.     

Electrochemiluminescence immunoassay at a nanoporous gold leaf electrode and using CdTe quantun dots as labels

An electrochemiluminescence-based immunoassay using quantum dots (QDs) as labels for the carcinoembryonic antigen (CEA) was developed using an electrode modified with leafs of nanoporous gold. CEA was initially immobilized on the electrode via a sandwich immunoreaction, and then CdTe quantum dots capped with thioglycolic acid were used to label the second antibody. The intensity of the ECL of the QDs reflects the quantity of CEA immobilized on the electrode. Thus, in the presence of dithiopersulfate as the coreactant, the ECL serves as the signal for the determination of CEA. The intensity of the electroluminescence (ECL) of the electrode was about 5.5-fold higher than that obtained with a bare gold electrode. The relation between ECL intensity and CEA concentration is linear in the range from 0.05 to 200?ng.mL^-1, and the detection limit is 0.01?ng.mL^-1. The method has the advantages of high sensitivity, good reproducibility and long-term stability, and paves a new avenue for applying quantum dots in ECL-based bioassays.

Electrodeposition of tubular-rod structure gold nanowires using nanoporous anodic alumina oxide as template

One-dimensional tubular-rod structure gold nanowires have been prepared using electrodeposition method at constant current mode with confined nanochannels of porous anodic aluminum oxide template. The reduction mechanism of gold ions and formation process of tubular-rod structure gold nanowires are studied. Electron microscopy results show that the tubular-rod structure gold nanowires transform to solid nanorods when the electrodeposition time is long enough. The tubular-rod structure gold nanowires have an average diameter of 180 nm, which coincide with the diameter of the template used. X-ray diffraction results confirm that the tubular-rod structure gold nanowires are crystalline structure.     

Electrochemical detection of hydrazine using a highly sensitive nanoporous gold electrode

A facile alloy–dealloy technique performed in aqueous media was employed to prepare a nanoporous gold (NPG) electrode that demonstrated extremely high sensitivity toward hydrazine oxidation. An Ag_∼60Au_∼40 alloy was electrodeposited at a constant potential on sequentially Cr- and Au-deposited indium tin oxide (Au/Cr/ITO) from a bath that contained sulfuric acid, thiourea, HAuCl₄·3H₂O, and AgNO₃. The dealloying step was performed in concentrated HNO₃, where Ag in the alloy was selectively oxidized to leave the NPG structure. The NPG electrode was employed to study the hydrazine oxidation in basic phosphate buffer solution (PBS), and the results were compared with those obtained using the gold nanoparticle (AuNP)-modified ITO (AuNP/ITO) electrode. The NPG electrode demonstrated an unusual surface-confined behavior, which probably resulted from the thin-layer characteristics of the nano-pores. Hydrazine was detected by hydrodynamic chronoamperometry (HCA) at +0.2 V (vs. Ag/AgCl). The steady-state oxidative current exhibited a linear dependence on the hydrazine concentration in the concentration range of 5.00 nM–2.05 mM, and the detection limit was 4.37 nM (σ = 3). This detection limit is the lower than the detection limits reported in the current literature concerning the electrochemical detection of hydrazine. The NPG electrode indeed demonstrates greater stability after hydrazine detection than the AuNP/ITO electrode.     

Truncated ditetragonal gold prisms as nanofacet activators of catalytic platinum

We report a facile, seed-mediated method to synthesize nanoscale gold truncated ditetragonal nanoprisms (TDPs) enclosed by 12 high-index {310} facets. The method leads to the formation of nanoparticles with high size and shape monodispersity and allows for easy surfactant removal. The dependence of particle shape on the synergetic contribution of metallic ions, halide ions, and surfactant adsorbates during synthesis is described. The resulting high-index nanoparticle facets were demonstrated as efficient activators of a supported catalytic material (platinum). A Pt monolayer deposited onto the Au TDP nanofacets with sharp electrochemical signatures exhibits an enhanced catalytic activity.     

Correlation between catalytic activity and surface ligands of monolayer protected gold nanoparticles

Gold nanoparticles (GNPs) are known to be a very good catalyst. Also, the anchoring of GNPs with stabilizing ligands is essential for surface modification, tuning of size and shapes, and to prevent from aggregation in suspension. But the effect of ligand on the catalytic property of ligand-capped GNP is yet to be explored in detail. In this paper, we perform an in-depth study of effect of ligands on the catalytic activity of monolayer protected GNPs. For this study, a series of different ligand functionalized GNPs in suspension as well as functionalized GNPs' thin film on glass substrate are prepared and used as catalysts in two model reactions, viz. borohydride reduction of 4-nitrophenol and redox reaction between potassium ferricyanide and sodium thiosulfate. The functionalization of GNPs with any ligand reduces its virgin catalytic activity, no matter whether the GNPs are suspended or supported as thin film. An increase in alkyl chain length of alkanethiols and alkylamines ligands and their graft density to the surface of GNP reduces its catalytic activity. Interestingly, the capping of GNPs with 11-mercaptoundecanoic acid and 11-mercaptoundecanol ligands completely destroys its catalytic activity. The effect of anchoring group of ligand molecules on the catalytic activity of ligand-protected GNPs is also discussed.     

Facile synthesis and excellent catalytic activity of gold nanoparticles on graphene oxide

For the first time,Au nanoparticles on graphene oxide（GO-AuNPs） were successfully fabricated without applying any additional reductants,just by the redox reaction between AuCl₄^-1 and GO.Their structure was characterized by transmission electron microscopy and X-ray powder diffraction.The results show that flower-like AuNPs were successfully dispersed on GO surface.Importantly,they showed a high catalytic activity for the Suzuki-Miyaura coupling reaction in an aqueous medium.     

金团簇二十面体结构融合过程中其催化活性的演变

近年来,由有机配体保护的原子精确金属团簇在合成方面已取得了重要进展,其独特的原子结构对一些化学反应产生独特的催化效果.原子精确的团簇催化剂明显不同于纳米颗粒催化剂和单原子催化剂,是一种关联均相和多相的、原子数目确定、尺寸均一、结构精确的新型催化剂.从原子尺度上精确构筑团簇催化剂,探究亚纳米尺度的微观结构对催化性能的影响...     

An unexpected possible role of base in asymmetric catalytic hydrogenations of ketones. Synthesis and characterization of several key catalytic intermediates

The dihydrogen compound trans-[Ru((R)-BINAP)(H)(eta2-H2)((R,R)-dpen)]+ (2', BINAP = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl, dpen = 1,2-diphenylethylenediamine) is a proposed intermediate in asymmetric ketone hydrogenations. It quickly reacts at -80 degrees C with 1 equiv of the base KOtBu in 2-PrOH-d8/CH2Cl2-d2 under H2 to generate trans-Ru((R)-BINAP)(H)(2-PrO)((R,R)-dpen) (4). The alkoxide 4 does not react with H2 after hours under ambient conditions. Addition of 1 equiv of KOtBu to 4 produces a hydrogen bonded species 10 that reacts readily with H2 at -80 degrees C to generate the dihydride catalytic intermediate trans-[Ru((R)-BINAP)(H)2((R,R)-dpen)] (3'). Addition of 1 equiv of ((CH3)3Si)2NK to the alkoxide 4 produces the amide catalytic intermediate 5. Compound 5 reacts reversibly with H2 to generate 3'.     

CuNaY分子筛的制备及其催化甲醇氧化羰基化

采用多种铜盐溶液与NaY分子筛离子交换制备了CuNaY催化剂,通过加入氨水提高溶液pH值以及高温活化,显著提高了该催化剂对甲醇氧化羰基化合成碳酸二甲酯的反应活性。不同的铜盐水溶液交换制备的CuNaY催化剂催化活性不同,添加氨水将溶液pH值调节为11后,离子交换制备的CuNaY催化剂的催化活性和DMC选择性明显升高且趋于一致。经元素分析、XRD、XPS和H₂-TPR表征可知,加入氨水可促进Cu²⁺离子交换的进行,提高CuNaY催化剂中Cu的交换量,催化剂中约75%的Cu²⁺定位于分子筛的超笼中。     

Catalysis by supported gold: correlation between catalytic activity for CO oxidation and oxidation states of gold

X-ray absorption near-edge spectra and temperature-programmed oxidation and reduction data demonstrate that Au(I) and Au(0) are both present in working MgO-supported gold catalysts for CO oxidation. EXAFS data indicate gold clusters with essentially the same average diameter (about 30 A) in each catalyst sample. Thus, the results provide no evidence of an effect of gold cluster size on the catalytic activity, but both the catalytic activity and the surface concentration of Au(I) were found to decrease with increasing CO partial pressure (as Au(0) was increasingly formed), demonstrating that the catalytic sites incorporate Au(I).     

High catalytic activity of ultrafine nanoporous palladium for electro-oxidation of methanol, ethanol, and formic acid

Nanoporous palladium (NPPd) with ultrafine ligament size of 3–6 nm was fabricated by dealloying of an Al–Pd alloy in an alkaline solution. Electrochemical measurements indicate that NPPd exhibits significantly high electrochemical active specific surface area (23 m² g⁻¹), and high catalytic activity for electro-oxidation of methanol, ethanol, and formic acid. Mass activities can reach 149, 148, 262 mA mg⁻¹ for the oxidation of methanol, ethanol and formic acid, respectively. Moreover, superior steady-state activities can be observed for all the electro-oxidation processes. NPPd will be a promising candidate for the anode catalyst for direct alcohol or formic acid fuel cells.     

Chemiluminescence detection of label-free C-reactive protein based on catalytic activity of gold nanoparticles

A novel, quantitative analytical method for measuring C-reactive protein (CRP) levels in human serum has been developed based on the catalytic activity of gold nanoparticles (GNPs) and luminol-H₂O₂ chemiluminescence (CL). The CL intensity in the presence of CRP and its ligand, O-phosphorylethanolamine (PEA), was greatly enhanced due to the aggregation of GNPs after the addition of 0.5 M NaCl. Any pretreatment steps, such as covalent functionalization of GNPs, addition of antibodies, or labeling of CRP, were not needed for CL detection. The CL enhancement was linearly proportional to CRP concentration in the range of 1.88 fM to 1.925 pM. The detection limit of CRP in serum samples was estimated to be as low as 1.88 fM. The detection sensitivity was increased more than 164 times of magnitude over that of the conventional, enzyme-linked immunosorbent assay (ELISA) method. This proposed GNP-based CL detection method offers the advantages of simplicity, rapidity, and sensitivity.     

银改性硅藻土材料捕集烯烃的研究

银改性硅藻土作为烯烃捕集材料已用于多维气相色谱分析汽油组分，烯烃捕集容量与硅藻土的比表面积和AgNO3负载量有关。采用X射线衍射(XRD)测定不同载银量的材料中晶相AgNO3的衍射强度，得到AgNO3在硅藻土表面单分子层最大分散量。实验结果与密置单层模型计算的AgNO3最大分散量接近，与色谱法测定结果相吻合。热分析结果表明：捕集材料在使用过程中具有良好的稳定性；吸附的烯烃可以定量回收。