Catalytic Effect Of Au Research Articles

Gas-sensing performance of Au loading Sn0.97Cu0.03O2 and its use on quantifying CO and H2 concentration by BP-temperature modulation method

Based on the temperature modulation, the quantification of CO and H2 is carried out to solve the problem of poor selectivity for metal oxide semiconductor gas sensors. In this work, the effect of the synergistic modification as Cu2+ doping and Au loading of SnO2 gas-sensing material on sensitivity and selectivity of CO and H2 was investigated. The stable resistance value as the static characteristics and the following-up time as the dynamic characteristics were used by an algorithm of BP neural network to establish a model for quantifying CO and H2 concentrations. The result shows that the operating temperature were reduced to 250 °C from 350 °C by Au loading of 3.0 mol%Cu2+ doping SnO2 gas-sensing material, the response value was increased to 58.3 from 9.3 at 1000 ppm of CO, and the selectivity (RCO/RH2) was increased to 1.55 from 0.33 due to the grain size decrease of SnO2 gas-sensing material and the catalytic effect of Au. And these data including the resistance value and the following-up time were used to obtain WijT, Vjq, ΘjT and ΓqT matrices including the weight values wij, vjq and threshold values θj, γq for the model by training through the algorithm of BP neural network the weight values and threshold values matrices, where the relative error of the quantitative results of CO and H2 concentrations was less than 2.0%, which provides a new way for the quantification of mixed gas.

Enhancement of room temperature ethanol sensing behavior of PbS–SnS2 nanocomposite by Au decoration

Resistive-based gas sensors generally work at high temperatures, and this leads to some limitations in their applications in remote areas or low power consumption electronic devices. Realization of room temperature gas sensors can be an excellent strategy to significantly decrease the power consumption of these kinds of gas sensors. Herein, we prepared pristine and Au-decorated PbS–SnS2 nanocomposite for ethanol sensing at room temperature. In order to find the optimal amount of Au-decoration, different amounts of Au (0.5, 1, and 1.5 wt%) were added to PbS–SnS2 nanocomposite. Based on the ethanol sensing studies, it was found that the sensor with 1 wt% Au had the highest sensing performance towards ethanol. The optimal gas sensor showed the highest response to ethanol gas, and fast sensor dynamics (less than 80 s) at room temperature. Enhanced sensing capacity of the optimized gas sensor was related to the formation of Au-metal sulfide heterojunctions and catalytic effect of Au towards ethanol. This research demonstrates the promising effects of noble metal decoration on metal sulfides for room temperate sensing applications and can be extended to similar systems.

Au(I)-catalyzed cycloaddition pathways of non-terminal propargyl substrates

Novel chiral menthol-based pyridyl nitrone ligands were synthesized and Au(I) coordination of the ligands gave chiral Au(I)–nitrone complexes. 1H NMR studies of the gold(I) coordination experiments with nitrone ligands afforded a convenient method for monitoring complex formation. The catalytic effect of Au(I)–nitrone complexes, shown to tune catalytic systems to produce uncommon products, was evaluated in [2 + 2 + 2] cyclotrimerization and [2 + 4] cyclodimerization reactions of non-terminal propargyl acetals. Alternative gold(I)-catalyzed [2 + 2], [2 + 4] and [3 + 4] cycloaddition reaction pathways of non-terminal propargyl acetals with imine substrates gave a diverse range of N-heterocyclic products. The present screening study demonstrates the potential and the versatility of non-terminal propargyl acetals in gold(I)-catalyzed cycloaddition reactions.

Low power-consumption CO gas sensors based on Au-functionalized SnO2-ZnO core-shell nanowires

We report a novel self-heated CO gas sensor based on Au-functionalized networked SnO2-ZnO core-shell nanowires. Increasing the applied voltage particularly enhanced the sensing response due to the self-heating effect within the sensor, and the sensors exhibited good performance without the need for an external heater. The power consumption at 3 and 20 V was estimated to be 11.3 nW and 8.3 μW, respectively. In a sensor with the optimal ZnO shell thickness of 80 nm, the responses for 50 ppm CO were 1.17 and 1.62 at 3 and 20 V, respectively. Also, the important role of ZnO-ZnO homojunctions in the self-heating of the sensor was demonstrated by increasing the ZnO shell thickness, which led to an increase in the sensor response. Furthermore, the optimized sensor exhibited outstanding selectivity toward CO gas. The optimized ZnO shell, the catalytic effect of Au, and the Joule effect contributed to the good, selective response toward CO gas with low power consumption. Since low power consumption is a fundamental requirement for wireless sensors and sensor arrays, this sensor with very low power consumption is a promising choice for such applications.

Sensing behavior to ppm-level gases and synergistic sensing mechanism in metal-functionalized rGO-loaded ZnO nanofibers

Noble metal-functionalized, reduced graphene oxide (rGO)-loaded metal oxides are a new class of ternary composites that combine the advantages of each component, resulting in exceptional materials. But, there are few reports on their use as gas sensors. This paper reports the gas sensing behavior of Au or Pd-functionalized rGO-loaded ZnO nanofibers (NFs) synthesized by using a combination of facile, cost-effective sol-gel and electrospinning methods. An examination of the gas sensing properties revealed that Au-functionalized NFs have a very high response to CO gas. In particular, the gas response (Ra/Rg) to 1ppm of CO was as high as 23.5, whereas Pd-functionalized NFs showed a high response to C6H6 gas (11.8 to 1ppmC6H6). The presence of rGO/ZnO heterointerfaces, the catalytic effect of Au and Pd nanoparticles (NPs), and the high surface area of NFs were the main factors that contributed to the strong response of the Au or Pd-functionalized rGO-loaded ZnO NFs sensors. These results show that the combination of noble metals, such as Au or Pd NPs, with rGO and ZnO can impart new gas sensing functionality that is potentially useful for CO or C6H6 sensing applications, respectively.

Hydrogen sensors based on gold nanoclusters assembled onto ZnO nanostructures at low operating temperature

In this work, the hydrogen (H2) sensor performance of gold nanoclusters (Au NCs) assembled onto zinc oxide (ZnO) nanostructures films were investigated and compared to ZnO nanostructures films. ZnO nanostructures were prepared by thermal oxidation of zinc films on glass substrate at different oxidation temperatures. Au NCs were assembled onto obtained ZnO nanostructures via photoreduction of HAuCl4 solution. The morphology of ZnO nanostructures were comprised of short rods branched into their ZnO bases. The diameters of cylindrical ZnO nanostructures increased approximately 50 to 90 nm upon increasing the oxidation temperatures. The morphology of Au NCs assembled onto ZnO nanostructures exhibited growth to encapsulate individual ZnO nanostructures as cluster−like with dimensions less than 100–150 nm. The amount of Au NCs assembly was proportion to crystallinity and materials’ stoichiometry of ZnO nanostructures. H2 sensor performance of the films were investigated at different operating temperature in the range of 150–450 °C. It was found that optimum operating temperatures of Au NCs assembled ZnO nanostructures films were 200 °C in all cases less than that 350 °C of pure ZnO nanostructures. Au NCs assembled ZnO nanostructures films had still high H2 sensor response at operating temperature of 150 °C. Furthermore, the sensor response of Au NCs assembled ZnO nanostructures seems to have higher than those ZnO nanostructures and their sensor response was directly proportion to amount of Au NCs. Accordingly, the enhancement of sensor response can be explained in terms of the reaction rate constant (kOxy) by considering the catalytic effect of Au. These results can be further explored for H2 safety sensor in fuel cell due to the demand of high H2 response at the low operating temperature.

Gold-modified indium tin oxide as a transparent window in optoelectronic diagnostics of electrochemically active biofilms

Microbial electrochemical technologies (METs) are one of the emerging green bioenergy domains that are utilizing microorganisms for wastewater treatment or electrosynthesis. Real-time monitoring of bioprocess during operation is a prerequisite for understanding and further improving bioenergy harvesting. Optical methods are powerful tools for this, but require transparent, highly conductive and biocompatible electrodes. Whereas indium tin oxide (ITO) is a well-known transparent conductive oxide, it is a non-ideal platform for biofilm growth. Here, a straightforward approach of surface modification of ITO anodes with gold (Au) is demonstrated, to enhance direct microbial biofilm cultivation on their surface and to improve the produced current densities. The trade-off between the electrode transmittance (critical for the underlying integrated sensors) and the enhanced growth of biofilms (crucial for direct monitoring) is studied. Au-modified ITO electrodes show a faster and reproducible biofilm growth with three times higher maximum current densities and about 6.9 times thicker biofilms compared to their unmodified ITO counterparts. The electrochemical analysis confirms the enhanced performance and the reversibility of the ITO/Au electrodes. The catalytic effect of Au on the ITO surface seems to be the key factor of the observed performance improvement since the changes in the electrode conductivity and their surface wettability are relatively small and in the range of ITO. An integrated platform for the ITO/Au transparent electrode with light-emitting diodes was fabricated and its feasibility for optical biofilm thickness monitoring is demonstrated. Such transparent electrodes with embedded catalytic metals can serve as multifunctional windows for biofilm diagnostic microchips.

Direct Synthesis of Indium Nanotubes from Indium Metal Source

Metallic indium (In) nanotubes were prepared by direct thermal evaporation of an In metal source. In metal was heated in an Ar atmosphere at a high temperature, and after certain period of heating the system was allowed to cool to room temperature in normal atmosphere during which the nanotubes were formed. Growth of the nanotubes was initiated by the catalytic effect of Au, whereas the low melting point of the In metal was found to be responsible for the formation of the hollow core of the nanotubes. The samples were characterized by X-ray diffraction, scanning and transmission electron microscopy, and energy dispersive analysis of X-ray.

Highly selective flow injection spectrophotometric determination of gold based on its catalytic effect on the oxidation of variamine blue by potassium iodate in aqueous N, N-dimethylformamide medium

A highly selective and simple flow injection method is reported for the determination of Au(III) in jewel samples. The method is based on the catalytic effect of Au(III) on the oxidation of 4-amino-4′-methoxydiphenylamine hydrochloride (Variamine Blue B base, VB) by KIO 3. The colored reaction product was monitored spectrophotometrically at 546 nm. A volume fraction of 40% N, N-dimethylformamide (DMF) greatly enhances the selectivity of the method. The chemical (pH and concentrations of reagents) and instrumental variables (sample injection volume, reagents flow rates, reaction coil length) affecting the determination were studied and optimized. Under the selected values, the analyte could be determined in the range of 0.1–12.0 mg L −1 ( r = 0.9997), at a sampling rate of 120 h −1. The proposed assay was precise ( s r = 0.8% at 5.0 mg L −1 Au(III), n = 12) and adequately sensitive with a 3 σ limit of detection of 0.03 mg L −1. The method was successfully applied to the analysis of jewel samples. The obtained results were favorably compared to flame atomic absorption spectrometry (FAAS) used as a reference method.

Metal/GaN reaction chemistry and their electrical properties

AbstractWe investigated the reaction chemistry of metal contacts to GaN during annealing using X‐ray photoelectron spectroscopy (XPS). GaN decomposition was estimated, using XPS, to occur in N2 annealed Ni‐alloy contacts at 550 °C. The reaction was greatly accelerated by the catalytic effect of Au and Pt. The decomposition was correlated with the rapid degradation of electrical properties during annealing. The results suggest that high‐temperature applications may be critically limited by the degradation of metal contacts especially due to activated Ni reactivity in Ni‐alloyed contacts. Meanwhile, the thermal stability of Ni/Au contact greatly improves by suppressing the activated Ni reactivity, which is able to be obtained by forming preferential Ni–O bonding through annealing in air. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Photochronometric determination of traces of gold(III)

A method for the determination of traces of gold is based on the catalytic effect of Au(III) on the reduction of Ag(I) with Fe(II). The time elapsing from the addition of the Fe(II) solution to the appearance of a certain precipitation (determined photometrically) is measured and the Au content is read from a calibration curve. Interferences are caused by halogen and cyanide ions and by oxidizing agents. 45 ng of Au could be determined with a maximum error of 2.5 ng.