Au Doping Research Articles

Understanding the promotional effect of Au on Pt/WO3 in hydrogenolysis of glycerol to 1,3-propanediol

Pt/Au/WO3 bimetallic catalysts were prepared by impregnation of Pt onto preformed Au/WO3, obtained by a hexadecyl trmethyl ammonium bromide (CTAB)-assisted one-pot synthesis method. The resulting Pt/Au/WO3 catalysts exhibited remarkable synergistic effects for selective hydrogenolysis of glycerol to 1,3-propanediol. The characterization results showed that doping of Au promoted the reduction of both Pt and W at low temperatures and uniform dispersion of Pt on the WO3 support. Furthermore, more low-valence Pt species were produced on the WO3 surface after introduction of Au. These changes in electronic properties resulted in enhancement of both glycerol conversion and selectivity for 1,3-propanediol.

Photocatalytic Properties of Titanium Dioxide Thin Films Doped with Noble Metals (Ag, Au, Pd, and Pt)

Sol‐gel grown TiO2 thin films are deposited on glass substrates by spin‐coating, using noble metals (M = Ag, Au, Pd, and Pt) for doping. The films are thermally treated at 500 °C, to obtain the anatase phase. The film properties are characterized by field‐emission scanning electron microscopy (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDX), X‐ray diffraction (XRD), Raman spectroscopy, profilometry, and UV/VIS/NIR spectroscopy. FE‐SEM images and EDX measurements show the presence of dopant elements in the metallic form. XRD and Raman measurements show the presence of the anatase phase for pure and doped samples. Optical measurements show the optical band gap decreases for Au and Pt doping, while it shows little change for Ag and Pd doping, compared to pure TiO2. The photocatalytic activity of all films is evaluated by measuring the rate of decolorization of methylene blue (MB) under UV irradiation. The normalization of the rate of degradation of MB according to the film thickness shows significant photocatalytic activity of all films with the following order Pt‐TiO2 > Pd‐TiO2 > Au‐TiO2 > Ag‐TiO2 > pure TiO2.

Effect of Au doping on the Magnetic Properties of Fe3O4 NPs Prepared via Photolysis and co-Precipitation Methods

Effect of Au doping on the Magnetic Properties of Fe3O4 NPs Prepared via Photolysis and co-Precipitation Methods

Au-doped ZnO sol-gel thin films: An experimental investigation on physical and photoluminescence properties

Undoped and Au-doped ZnO thin films were prepared on glass substrates by sol-gel process and dip-coating technique. The effects of Au concentration (10–30 at%) on structural, morphological and optical properties of the ZnO films were studied using X-ray diffraction (XRD), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), UV–Vis–NIR spectrometry, Hall-effect measurements and photoluminescence (PL) spectroscopy. XRD results show that all films crystallized in a hexagonal wurtzite structure and are highly c-axis oriented. The crystal quality of the films is found to decrease with the increase in Au doping. A weak diffraction peak related to Au cubic phase is also observed at Au concentration higher than 10 at%. The Raman studies confirmed that the film's crystallinity degraded with increasing Au content. FE-SEM micrographs and AFM images show that both morphology and surface roughness are affected by the Au doping concentration. UV–Vis–NIR optical spectra reveal that increasing Au doping into ZnO films enhances their transparency. Photoluminescence measurements at room temperature put into evidence the presence of two intense bands at 373.6 and 385 nm in the UV spectra and four very weak emission bands in the visible spectral range. All the visible emissions are found to increase with Au content. The emission at 373.6 is maximal for the film doped at 20 at%, whereas the one at 385 nm reaches its maximum intensity in the film doped at 10 at%.

Fully Ordered and Trace Au‐Doped Intermetallic PdFe Catalyst with Extra High Activity and Durability toward Oxygen Reduction Reaction

AbstractDeveloping Pt‐free catalysts with high activity and durability is considered as an essential step for cost reduction and real commercialization of fuel cells. Previous Pt‐free catalysts are either lack of activity and/or insufficient in durability. Here we report the first synthesis of a carbon‐supported PdFe catalyst with a fully ordered intermetallic structure by controlling the atomic ratio of Pd and Fe and high‐temperature annealing for structural ordering. This intermetallic catalyst is then doped with a trace amount of Au (atomic ratio of Au/Pd: 1/50) mainly in the surface region of the ordered lattice. Such an Au‐doped intermetallic PdFe catalyst is finally demonstrated to possess a comparable catalytic activity and much better durability for oxygen reduction reaction than the commercial catalyst of Pt/C. For example, the half‐wave potential of the Au‐PdFe catalyst decreases at a rate 9 times slower than that of Pt/C catalyst after potential cycling under harsh electrochemical conditions. The excellent activity and durability of this new catalyst is attributed to the ordered structure of PdFe particles and the protective effect of the surface Au doping. This study provides a new strategy to developing Pt‐free catalysts, lowering the production cost, and accelerating the practical application of fuel cells.

Au doping effects in ZrO<sub>2</sub>-based resistance random access memory based on first-principles calculations

Oxygen vacancy plays the critical role for resistive switching in transition metal oxide resistive random access memory (RRAM). First principles calculation was performed to investigate the band structure, density of states, the oxygen vacancy formation energy and the migration barriers energy of pure ZrO2 and Au doped ZrO2, and we analyzed the impact of Au doping in ZrO2-based RRAM. It was found that the localized impurity band at the Fermi level appeared in forbidden band and the band gap was significantly reduced in Au doped ZrO2, which improved the conductivity of ZrO2. By doping Au in ZrO2, the formation energy and the migration barriers energy of oxygen vacancy were significantly reduced, indicating that it was beneficial to the formation and migration of oxygen vacancy and decreased the forming voltage and the set voltage of ZrO2-based RRAM. The electron localization function was used to study the [001] direction oxygen vacancy cluster of ZrO2 supercell with an Au doped element. The results showed that the oxygen vacancy around the impurity formed an ordered conductive filament in the [001] direction.

First-principles study of Cu adsorption on vacancy-defected/Au-doped graphene

To enhance the interaction between Cu and graphene in graphene reinforced Cu matrix composites, the first principles calculation was carried out to study the adsorption of Cu atoms on graphene. P-type doping and n-type doping were formed, respectively, on vacancy-defected and Au-doped graphene based on band structure analysis, and this was verified by subsequent investigation on density of states. A computation on charge transfer confirmed that p-type doping could promote the electron transport between Cu and graphene, while n-type doping would prevent it. In addition, adsorption energy and Mulliken population analysis revealed that both vacancy defects and Au doping could improve the stability of the Cu–graphene system. The research conducted in this paper provides useful guidance for the preparation of Cu/graphene composites.

Stability, structural and electronic properties of ternary Pd Au Ag clusters (x + y + z = 7): A theoretical study

Abstract Full range of Au and Ag doped Pd clusters, PdxAuyAgz with x + y + z = 7 in their ground states, are studied using the density functional theory (DFT) at TPSSTPSS method with SDD pseudopotential. The average interatomic distance, chemical order, charge distribution, binding energy, mixing energy, finite difference energy, vertical ionization potential, electron affinity and HOMO-LUMO gap of the ternary clusters are evaluated as a function of the whole concentration range, from which the mutual influences of Au and Ag dopants on the properties of Pd cluster are predicted and analyzed.

A Novel Redox Precipitation to Synthesize Au-Doped α-MnO2 with High Dispersion toward Low-Temperature Oxidation of Formaldehyde.

A novel method of redox precipitation was applied for the first time to synthesize a Au-doped α-MnO2 catalyst with high dispersion of the Au species. Au nanoparticles (NPs) can be downsized into approximate single atoms by this method, thereby realizing highly efficient utilization of Au element as well as satisfying low-temperature oxidation of formaldehyde (HCHO). Under catalysis of the optimal 0.25% Au/α-MnO2 catalyst, a polluted stream containing 500 ppm HCHO can be completely cleaned at 75 °C with the condition of a weight hourly space velocity (WHSV) of 60000 mL/(g h). Meanwhile, the catalyst retains good activity for removal of low-concentration HCHO (about 1 ppm) at ambient temperature with a high WHSV, and exhibits a high tolerance to water and long-term stability. Our characterization of Au/α-MnO2 and catalytic performance tests clearly demonstrate that the proper amount of Au doping facilitates formation of surface vacancy oxygen, lattice oxygen, and charged Au species as an active site, which are all beneficial to catalytic oxidation of HCHO. The oxidation of HCHO over Au-doped α-MnO2 catalyst obeys the Mars-van Krevelen mechanism as evidenced by in situ diffuse reflectance infrared Fourier transform spectroscopy.

Methane Dissociation on Bimetallic AuNi3, Au2Ni2 and Au3Ni Clusters‐A DFT Study

AbstractThe effect of gold atom for the dissociation of methane on tetrahedral bimetallic AuxNiy (x+y=4; x,y=1‐3) clusters are introduced using density functional theory method. The binding energy and HOMO‐LUMO gap fluctuate with odd‐even number of gold atoms. The clusters, AuNi3 and Au3Ni, containing odd number of doped gold atoms, which causes open shell configuration, are exceptionally stable and highly resistance to carbon deposition, whereas closed shell Au2Ni2 cluster is less stable. As the number of doped Au atom increases in the clusters, adsorption or binding energy of methane increases. The dissociation of methane is a four elementary steps process, and first step of dissociation, CH4→CH3, is not the rate determining step, and thermodynamically favorable at room temperature and pressure for the clusters due to adsorption. Whereas, the dissociation of CH→C, coke formation step 4, is the rate determining step due to highest energy barrier for all the clusters. The calculated activation energies for the rate determining step are 0.92 eV, 0.41 eV and 1.64 eV for AuNi3, Au2Ni2 and Au3Ni clusters, respectively. In addition, the dissociation temperature for all the intermediates, e. g., CH3, CH2 and CH are 450 K(CH3 and CH2) and 650 K(CH) on AuNi3 cluster; 450 K(CH3) and 550 K(CH2 and CH) on Au2Ni2 cluster; and 650 K(CH3), 750 K(CH2) and 950 K(CH) on Au3Ni cluster. Thus, the coke resistivity decreases as Au3Ni >AuNi3>Au2Ni2 and corresponding coke resistance temperatures are 950 K, 650 K and 550 K, respectively. The charge tranfer to the clusters during adsorption is negative, and is positive in the dissociation steps. Thus, the number of doped gold atom not only influences the stability of bimetallic Au−Ni clusters, but also their reactivity towards methane, which can provide some new insight for the design of coke resistant catalysts for methane reforming.

Role of oxygen vacancies in Ag/Au doped CeO2 nanoparticles for fast photocatalysis

Efficiency of oxide semiconductors for photocatalytic degradation of organic pollutants is highly dependent on their morphology, particle size, electron-hole recombination and oxygen vacancies. Doping of cations modifies the phase composition and induces oxygen vacancies needed for faster photocatalytic degradation of organic contaminants. Here, thioglycerol capped undoped and noble metal (Ag and Au) doped sub-10 nm sized CeO2 nanoparticles (NPs) have been successfully synthesized at natural pH by co-precipitation method and were used as photocatalyst for degradation of rhodamine blue dye (RhB) in an aqueous medium under UV–Visible (UV–Vis.) irradiations without the addition of any external reagent. Photocatalytic studies revealed that among undoped and doped (Ag/Au) CeO2 NPs, 2.0 at% Ag and 0.4 at% Au doping concentrations are optimum to demonstrate superior degradation efficiency. Degradation time was reduced further when RhB dye has been degraded with optimum doped NPs synthesized at higher pH. Moreover, gold doped NPs have shown better photocatalytic efficacy as compared to silver doped NPs. With the help of various characterizations, a possible degradation mechanism has been proposed which shows the effect of generation of oxygen vacancies owing to the doping of Ag and Au on photodegradation process.

Evolution of electronic and vibrational properties of M@Xn (M = Ag, Au, X = Ge, Si, n = 10, 12, 14) clusters: a density functional modeling

Evolution of electronic and vibrational properties of M@Xn (M = Ag, Au, X = Ge, Si, n = 10, 12, 14) nanoclusters is investigated by using first-principle density functional theory (DFT)-based calculations with effective core potentials. To explain the thermodynamic and chemical stability of the ground state cluster in each size, variation of different thermodynamic and chemical parameters, like, binding energy (BE), HOMO–LUMO gap (ΔE), vertical ionization potential (VIP) and vertical electron affinity (VEA) was studied with the variation of the size of the clusters for emphasizing the differences and similarities in the clusters. It is found that Au doping in Ge and Si cages prefers endohedral position, whereas Ag prefers to take the position at the surface of the cages. In addition, IR and Raman spectra of the clusters are also studied to understand the vibrational nature of the stable clusters. At the end, present theoretical results are compared with existing experimental data. Theoretical knowledge of the thermodynamic, chemical and vibrational properties of these specific ground state structures is important for understanding its potential application in the field of optoelectronic science.

Adsorption behavior of CO2 on pristine and doped phosphorenes: A dispersion corrected DFT study

The density functional theory (DFT) method was used to study the adsorption of CO2 molecules on pristine and doped phosphorenes. Twenty dopants were considered during this study: Fe, Co, Ni, Ti, Cu, Au, Ag, Ca, Cr, Pd, Pt, V, Sr, Mn, B, C, N, O, Si, Ge, Se, and S. Two initial configurations of CO2 on the pristine and doped phosphorenes were also studied. The results for adsorption energy, isosurface of electron density difference, partial density of states, and charge transferring analysis indicated that pristine phosphorene had a very weak interaction with CO2. Some of transition metallic dopants, namely Fe, Co, Ti, Ni, Cr, and V, significantly improved the interactions between phosphorenes and CO2. Some other metallic dopants, however, namely Au, Ag, Pd, and Pt, and nonmetallic dopants, namely Ge, Si, Se, S, N, C, B, and O had negligible effect on the interactions between CO2 and phosphorene. Cr, Fe, Ti and V-doped phosphorenes had the potential to enhance CO2 adsorption with a particular CO2 configuration. The role of charge donor or acceptor changed between CO2 and (V- Cr-, Fe-, and Ti-) doped phosphorenes when the initial CO2 configuration changed. Thus, the use of transition metallic dopants was an effective way to enhance the interactions between CO2 and phosphorene. In particular, (V- Cr-, Fe-, and Ti-) doped phosphorenes showed the potential to sense or capture CO2 molecules.

Synthesis of Two-Electron Bimetallic Cu-Ag and Cu-Au Clusters by using [Cu13 (S2 CNn Bu2 )6 (C≡CPh)4 ]+ as a Template.

Atomically precise Cu-rich bimetallic superatom clusters have been synthesized by adopting a galvanic exchange strategy. [Cu@Cu12 (S2 CNn Bu2 )6 (C≡CPh)4 ][CuCl2 ] (1) was used as a template to generate compositionally uniform clusters [M@Cu12 (S2 CNn Bu2 )6 (C≡CPh)4 ][CuCl2 ], where M=Ag (2), Au (3). Structures of 1, 2 and 3 were determined by single crystal X-ray diffraction and the results were supported by ESI-MS. The anatomies of clusters 1-3 are very similar, with a centred cuboctahedral cationic core that is surrounded by six di-butyldithiocarbamate (dtc) and four phenylacetylide ligands. The doped Ag and Au atoms were found to preferentially occupy the centre of the 13-atom cuboctahedral core. Experimental and theoretical analyses of the synthesized clusters revealed that both Ag and Au doping result in significant changes in cluster stability, optical characteristics and enhancement in luminescence properties.

Gold fillings unravel the vacancy role in the phase transition of GeTe

Phase change memory (PCM) is an important candidate for future memory devices. The crystalline phase of PCM materials contains abundant intrinsic vacancies, which plays an important role in the rapid phase transition upon memory switching. However, few experimental efforts have been invested to study these invisible entities. In this work, Au dopants are alloyed into the crystalline GeTe to fill the intrinsic Ge vacancies so that the role of these vacancies in the amorphization of GeTe can be indirectly studied. As a result, the reduction of Ge vacancies induced by Au dopants hampers the amorphization of GeTe as the activation energy of this process becomes higher. This is because the vacancy-interrupted lattice can be “repaired” by Au dopants with the recovery of bond connectivity. Our results demonstrate the importance of vacancies in the phase transition of chalcogenides, and we employ the percolation theory to explain the impact of these intrinsic defects on this vacancy-ridden crystal quantitatively. Specifically, the threshold of amorphization increases with the decrease in vacancies. The understanding of the vacancy effect sheds light on the long-standing puzzle of the mechanism of ultra-fast phase transition in PCMs. It also paves the way for designing low-power-consumption electronic devices by reducing the threshold of amorphization in chalcogenides.

The Electronic and Optical Properties of Au Doped Single-Layer Phosphorene

The electronic properties and optical properties of single and double Au-doped phosphorene have been comparatively investigated using the first-principles plane-wave pseudopotential method based on density functional theory. The decrease from direct band gap 0.78 eV to indirect band gap 0.22 and 0.11 eV are observed in the single and double Au-doped phosphorene, respectively. The red shifts of absorbing edge occur in both doped systems, which consequently enhance the absorbing of infrared light in phosphorene. Band gap engineering can, therefore, be used to directly tune the optical absorption of phosphorene system by substitutional Au doping.

Gold doping induced strong enhancement of carbon quantum dots fluorescence and oxygen evolution reaction catalytic activity of amorphous cobalt hydroxide

Au doping leads to tunable and strong enhancement of SCQDs fluorescence and OER activity of amorphous Co(OH)2.

Density Functional Theory Study of the Formaldehyde Catalytic Oxidation Mechanism on a Au-Doped CeO2(111) Surface

Formaldehyde is a harmful and toxic substance. Au-CeO2 catalysts show the excellent formaldehyde catalytic oxidation activity even under ambient temperatures. Here, we present the DFT+U calculations to investigate HCHO oxidation mechanisms and the effects of Au doping and multiple oxygen vacancies. The reaction process of HCHO oxidation mainly consists of the following steps: HCHO adsorption, C–H bond cleavages, CO2 desorption, O2 adsorption, and H2O formation and desorption. The doped Au reduces the energy barriers in C–H bond cleavages on the AuCe1–xO2(111) surface compared with the CeO2(111) surface. Au also leads to the activation of the surface oxygen species and then promotes HCHO adsorption and decreases the formation energies of oxygen vacancies. For HCHO adsorption and oxidation reaction on defective surfaces, catalysts with more oxygen vacancies possess higher adsorption energy and lower activation energy. These results provide deep insights into the effects of Au and multiple oxygen vacancies o...

Determination of gold and cobalt dopants in advanced materials based on tin oxide by slurry sampling high-resolution continuum source graphite furnace atomic absorption spectrometry

A novel approach is developed for the determination of Co and Au dopants in advanced materials based on tin oxide using high-resolution continuum source graphite furnace atomic absorption spectrometry (HR CS GFAAS) with direct slurry sampling. Sodium carboxylmethylcellulose (Na-CMC) is an effective stabilizer for diluted suspensions. Use Na-CMC allows to transfer the analytes into graphite furnace completely and reproducibly. The relative standard deviation obtained by HR CS GFAAS was not higher than 4%. Accuracy was proven by means inductively coupled plasma mass spectrometry (ICP-MS) in solutions after decomposition as a comparative technique. To determine Au and Co in the volume of SnO2, the acid decomposition conditions (HCl, HF) of the samples were suggested by means of an autoclave in a microwave oven.

Enhanced photocatalytic activity of Au-doped Au@ZnO core-shell flower-like nanocomposites

We introduce a simple and low-cost three-step hydrothermal and pulsed laser ablation technique for the fabrication of flower-like pure ZnO nanostructures, Au@ZnO core-shell nanocomposites, and Au@ZnO/Au core-shell nanocomposites doped with various concentrations (5, 10, and 15 wt%) of Au nanoparticles without using surfactants or catalysts to enhance the catalytic performance of ZnO under UV–visible irradiation. The decoration of Au nanoparticles on the surface of ZnO promoted the absorption of visible light due to the surface plasmon resonance of Au. Further, we evaluated the photocatalytic performance of the nanocomposites in the degradation of methylene blue (MB). Our findings revealed that the Au@ZnO/Au core-shell nanocomposites with 5 wt% of doped Au NPs demonstrated the highest photocatalytic activity. In addition, radical-scavenging experiments were conducted to determine the main reactive species formed in the reaction mixture, and accordingly, a plausible photocatalytic reaction mechanism for the enhanced photodegradation of MB is presented.