Effect Of Au Loading Research Articles

Photosynthesis of Au/TiO2 nanoparticles for photocatalytic gold recovery from industrial gold-cyanide plating wastewater

A series of Aux/TiO2 nanoparticles (NPs) with different gold loadings (x = 0.1–1.0 wt%) was synthesized by the photodeposition and then employed as photocatalysts to recover precious component from the industrial gold-cyanide plating wastewater. Effects of Au loading, catalyst dosage and types of hole scavenger on the photocatalytic gold recovery were investigated under ultraviolet–visible (UV–Vis) light irradiation at room temperature. It was found that different Au loadings tuned the light absorption capacity of the synthesized photocatalysts and enhanced the photocatalytic activity in comparison with the bare TiO2 NPs. The addition of CH3OH, C2H5OH, C3H8O, and Na2S2O3 as a hole scavenger significantly promoted the photocatalytic activity of the gold recovery, while the H2O2 did not. Among different hole scavengers employed in this work, the CH3OH exhibited the highest capability to promote the photocatalytic gold recovery. In summary, the Au0.5/TiO2 NPs exhibited the best photocatalytic activity to completely recover gold ions within 30 min at the catalyst dosage of 0.5 g/L, light intensity of 3.20 mW/cm2 in the presence of 20 vol% CH3OH as hole scavenger. The photocatalytic activity slightly decreased after the 5th cycle of recovery process, indicating its high reusability.

Evaluation of Au/γ-Al2O3 nanocatalyst for plasma-catalytic decomposition of toluene

The emission of toluene into the atmosphere can seriously affect the environmental quality and endanger human health. A dielectric barrier discharge reactor filled with a small amount of Au nanocatalysts was used to decompose toluene in He and O2 gases mixtures at room temperature and atmospheric pressure. Normally, the oxidation of toluene using Au nanocatalysts suffers from low reaction activity and facile catalyst deactivation. Herein, the effects of Au loading, calcination time and calcination temperature were systematically investigated. It was found that 0.1 wt%Au/γ-Al2O3 calcined at 300 °C for 5 h can keep an average size around 6 nm with good dispersion on γ-Al2O3 surface and display the best catalytic performance. Moreover, the influences of energy density, gas flow rate, toluene concentration and O2 concentration on toluene degradation using 0.1 wt%Au/γ-Al2O3 were evaluated. It showed the best catalytic performance of near 100% conversion for toluene degradation under the reaction conditions of the energy density was 20 J/L, the gas flow rate was 300 mL/min, the concentration of toluene was 376 mg/m3 and the oxygen content was 10%. Combining experimental results and theoretical calculations, the values of reaction constant k were 8.6 × 10−5, 3.53 × 10−5 and 3.09 × 10−5 m6/(mol*J), when O2 concentration, power or flow rate changed, respectively. Therefore, O2 concentration has the greatest effect on toluene decomposition compared to other factors in the presence of Au/γ-Al2O3.

Au nanoparticles decorated sulfonated graphene-TiO2 nanocomposite for sunlight driven photocatalytic degradation of recalcitrant compound

Au nanoparticles decorated with sulfonated graphene-TiO2 nanocomposites at varying Au concentrations were prepared by hydrothermal method followed by a polyol reduction process. The structural, optical and morphological properties of the prepared photocatalyst were studied using XRD, XPS, Raman, FTIR, UV-DRS, PL and HRTEM. The results reveal that with the increasing loading of Au nanoparticles the band gap of the nanocomposite decreases, and also exhibits reduction in the electron hole pair recombination rate. The results of spectroscopic and microscopic analysis confirm the presence of Au nanoparticles and sulfonated graphene in the composite photocatalyst. The photocatalytic activity of the nanocomposite was investigated by examining the removal of Methyl Orange, Rhodamine B and recalcitrant compound p-nitrophenol under sunlight irradiation. The effect of Au loading on composite shows an increase in photocatalytic activity up to threshold value of 2 mM beyond which it decreases. At this composition, Au decorated sulfonated graphene-TiO2 composites catalyst exhibit 3.2 fold higher photocatalytic performance compared to pristine TiO2 system. The improved photocatalytic performance is attributed to the synergistic effect of increased interfacial electron transfer between composite, decreased recombination rate of photoexcited electrons and holes, and the plasmonic effect of Au nanoparticles.

Enhanced NO2-Sensing Properties of Au-Loaded Porous In2O3 Gas Sensors at Low Operating Temperatures

NO2-sensing properties of semiconductor gas sensors using porous In2O3 powders loaded with and without 0.5 wt% Au (Au/In2O3 and In2O3 sensors, respectively) were examined in wet air (70% relative humidity at 25 °C). In addition, the effects of Au loading on the increased NO2 response were discussed on the basis of NO2 adsorption/desorption properties on the oxide surface. The NO2 response of the Au/In2O3 sensor monotonically increased with a decrease in the operating temperature, and the Au/In2O3 sensor showed higher NO2 responses than those of the In2O3 sensor at a temperature of 100 °C or lower. In addition, the response time of the Au/In2O3 sensor was much shorter than that of the In2O3 sensor at 30 °C. The analysis based on the Freundlich adsorption mechanism suggested that the Au loading increased the adsorption strength of NO2 on the In2O3 surface. Moreover, the Au loading was also quite effective in decreasing the baseline resistance of the In2O3 sensor in wet air (i.e., increasing the number of free electrons in the In2O3), which resulted in an increase in the number of negatively charged NO2 species on the In2O3 surface. The Au/In2O3 sensor showed high response to the low concentration of NO2 (ratio of resistance in target gas to that in air: ca. 133 to 0.1 ppm) and excellent NO2 selectivity against CO and ethanol, especially at 100 °C.

Effects of Au loading on the enhancement of photoelectrochemical activities of the Au@ZnO nano-heteroarchitecture

The nano-heteroarchitecture of Au@ZnO evidencing the surface attachment without chemical reaction at the interface delivered enhanced PEC activities by facilitating the injection of hot electrons from the SP state into the conduction band of ZnO.

Photocatalytic hydrogen production by water splitting over Au/Al-SrTiO3

Visible light water splitting activity of Au-Al/SrTiO3 was tested in this work. Al/SrTiO3 was synthesized via solid state reaction while Au loading was done with homogenous deposition precipitation method. The effects of Au loading and Al doping were investigated in 10, 20 and 30% aqueous solutions of methanol, ethanol, and isopropyl alcohol. The methanol was performed better over 0.25%Au-1.0%Al/SrTiO3 at 20% alcohol concentration while the isopropyl alcohol resulted in better performance over the same catalyst at 30% concentration; the latter was also the best result obtained in this work with the hydrogen evolution rate of 347 μmol/h.gcat. Ethanol showed lower performance than other two alcohols. It was found from UV–vis analysis that Al doping increased the band energy of SrTiO3. XRD and XPS analyses clearly showed that the dominant structure was SrTiO3 in all samples. Au was found to be generally loaded as 30–40 nm particles by SEM.

Increased Affinity of Small Gold Particles for Glycerol Oxidation over Au/TiO2 Probed by NMR Relaxation Methods

The aerobic oxidation of glycerol in aqueous solution over Au/TiO2 catalysts has been studied, and the effect of Au loading by wet impregnation, in the range 0.5–5% Au, has been assessed. Low metal loading favors the deposition of smaller particles, whereas higher loadings lead to the formation of much larger gold particles, as revealed by scanning transmission electron microscopy (STEM) analysis. Reaction studies show that a higher metal loading has a detrimental effect on the catalyst activity, which decreases significantly as the Au load increases. In addition to reaction studies, 1H NMR T1/T2 relaxation time measurements have been used to assess the effect of metal loading and particle size on the adsorption properties of glycerol (reactant) and water (solvent) within the catalyst. The NMR results show that the adsorption properties of glycerol relative to water as a function of the Au loading have a similar trend to that observed for the reactivity, with glycerol exhibiting a higher surface affinity ...

Au/uncalcined TS-1 catalysts for direct propene epoxidation with H2 and O2: Effects of Si/Ti molar ratio and Au loading

For direct propene epoxidation with H2/O2, TS-1 with blocked micropores (TS-1-B) is recognized as an attractive support for Au catalysts with enhanced stability and activity by suppressing the deactivation caused by micropore blocking. In this work, as a consecutive effort, effect of Si/Ti molar ratio of TS-1-B on catalytic performance is investigated. It is shown that the optimum Si/Ti molar ratio is 40. In other words, both lower and higher ratios are unfavorable for the formation of propylene oxide, which are possibly attributed to the presence of extra-framework Ti species and the difficult transmission of hydroperoxide species from Au surface to nearby Ti sites, respectively. Based on this, effect of Au loading on catalytic performance is further examined. When the Au loading is 0.13wt%, the catalyst shows not only high PO formation rate of 158gPOh−1kgCat−1 comparable to the reported best activity without adding promoters, but also significantly enhanced stability at 200°C over 30h.

Chemoselective hydrogenation of o-, p- and m-chloronitrobenzene at ambient temperature on Au/Fe2O3 catalysts

Gold nanoparticles deposited on an α-Fe2O3 substrate were prepared by different procedures including the deposition–precipitation in presence of urea or NaOH, and by the traditional wet impregnation followed by calcination. Metal loading and catalyst structures were determined by ICP-MS and XRD analyses while the size and electronic nature of Au nanoparticles were assessed using TEM and XPS. The effect of the catalyst preparation methodology was evaluated in the catalytic hydrogenation of nitrobenzene (NB) carried out in a batch reactor at 25°C and 20bar of H2 pressure. Among the catalysts studied, 1.0%Au/α-Fe2O3 prepared by deposition–precipitation with urea recorded the best performance (TOF=4.6s−1) and a selectivity toward aniline of 92%. The XRD and TEM data pointed out that the active sites are small gold particles (3.8nm) highly dispersed on the substrate surface. Moreover, the effect of Au loading (0.5, 1.0 and 2.0wt.%) was investigated in the hydrogenation reaction of o-, m- and p-chloronitrobenzene (o, m- and p-CNB) to o-, m- and p-chloroaniline (o-, m- and p-CAN) (a batch reactor; T=25°C; P=20bar of H2) over Au/α-Fe2O3 catalysts prepared by deposition–precipitation with urea. Regardless of the CNB isomer, maximum activity was recorded for the catalyst with 0.5wt.% Au loading (m-CNB conversion of 99.7%). At 6h reaction time, the yields of o-CAN, m-CAN and p-CAN were 97, 93.7 and 91.7mol.%, respectively. Catalytic activity decreases in the order: m-CNB>o-CNB>p-CNB, but this sequence does not depend on the Au loading. Other factors such as the electronic properties of Au nanoparticles and steric factors of Cl substitute appear to play a major role in the reaction.

Enhanced acetone sensing performances of hierarchical hollow Au-loaded NiO hybrid structures

Hierarchical hollow Au-loaded NiO hybrid microspheres have been synthesized with good uniformity by a surfactant-free hydrothermal route and subsequent heat treatment. This method requires high concentrations of a nickel precursor (0.2 M) and introduction of a trace amount of Au nanoparticles into the reaction system. The hierarchical hollow Au-loaded NiO hybrid microsphere comprises several nanorods and nanosheets. To demonstrate the usage of such hierarchical hybrid nanomaterials, a gas sensor has been fabricated from the as-synthesized Au-loaded NiO microspheres and investigated for acetone detection. The Au-loaded NiO sensor exhibits significantly improved sensing performances in terms of high sensitivity, low detection limit, better selectivity, rapid response, and good reproducibility in comparison with pure NiO. The effects of Au loading on the acetone-sensing properties of hierarchical NiO microspheres have been investigated.

Selective CO oxidation over promoted Au/γ-Al2O3 catalysts in the presence of CO2 and H2O in the feed

Abstract In this work, the effect of promoter type (Mg, Mn, Ce, Co, Fe and Ni) on selective CO oxidation performance of Au/γ-Al2O3 was studied with the realistic feed stream containing CO2 and H2O. The effects of Au loading, promoter loading, reaction temperature and the feed composition were also investigated. It was found that MgO was the best promoter in the presence of CO2 and H2O, and 1.25 wt.% Mg was sufficient for promotion. The CO conversion decreased with the addition of CO2 while the presence of H2O had some positive effects.

金/酸化チタン触媒上でのプロピレンの反応選択性に対する金担持量効果

金/酸化チタン触媒上でのプロピレンの反応選択性に対する金担持量効果