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In this study, electrochemical and analytical techniques are employed to explore the effect of thiosulfate, sulfite, and a mixture of thiosulfate-sulfite in the electrolyte on the gold electrowinning process. The open circuit potential (OCP) analysis showed negative potential shifts from − 0.02 V (in the electrolyte containing Au-TS (E1)) to − 0.21 V, − 0.33 V, and − 0.42 V in the presence of thiosulfate oversupply (electrolyte E2), sulfite (electrolyte E3), and thiosulfate-sulfite mixture (electrolyte E4). The linear sweep voltammetry (LSV) results exhibited − 0.4 V potential shift by the addition of sulfite to the gold-thiosulfate electrolyte, attributing to the formation of Au(S 2 O 3)(SO 3) 2 5- as the most stable gold complex. Based on chronoamperometry (CA) and atomic absorption spectrometer (AAS) results, sulfite could control the kinetics and thermodynamics of gold reduction reactions by minimizing undesired cathodic side reactions such as thiosulfate decomposition or water reduction, resulting in purer gold deposition, elimination of colloidal sulfur, and a more efficient EW process. The presence of thiosulfate accelerated the kinetics of the gold reduction reaction. However, adding sulfite to the electrolyte stabilized the kinetic about 10 times faster. SEM and EDS analysis depicted the morphological changes in the deposited gold layer from different electrolytes during CA, showing that thiosulfate oversupply results in the formation of a greater number of smaller grains by accelerating the nucleation process, while sulfite addition led to the formation of a smoother and more uniform gold layer on the cathode surface. [Display omitted] [ABSTRACT FROM AUTHOR]

The occurrence of the {2 1 0} shape of pyrite crystals has been used as an empirical indicator for gold enrichment in ore deposits. Such indicating, also called 'typomorphism' in ore mineralogy, was conventionally attributed to environmental factors such as sulfur fugacity and temperature and pressure conditions in the ore-forming hydrothermal fluid. Here we show that the crystal-face specific redox reactivity of pyrite is also an important governing potency that drives gold enrichment in the pyrite crystals with particular shapes. This conclusion was drawn from data compiled from chemical analysis of field samples, laboratory testing of gold deposition on natural pyrite crystals, as well as theoretical calculations. Kinetic measurements of gold reductive deposition first revealed the highest precipitation rate on the {2 1 0} faces, particularly when pyrite crystals are enclosed by complex forms containing {2 1 0}. Corroborating with the experimental observations, density functional theory (DFT) calculations further indicated that the {2 1 0} possesses a high adsorption energy for gold, a high energy state of the highest occupied molecular orbital and consequently a low Eh. These results afford evidence supporting the view that the face specific reactivity, an intrinsic property of crystal, plays an important role in the gold concentration in pyrite and the occurrence of specific pyrite shapes. Our findings not only provide a surface chemical view for understanding the empirical prospecting method but also exemplified the significance of crystal face specific-reactivity in understanding crystallographic orientation related geochemical processes. The crystal face specific reactivity may be a critical factor controlling geochemical reactions at mineral-water interface, such as prebiotic synthesis on pyrite surfaces and mineral-water interface controlled kinetic isotope fractionation. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Integrated field and isotopic analysis of Zhengchong gold deposit, Hunan, China. • Orogenic gold deposit formed during Late Ordovician Jiangnan Orogeny. • Four-stage mineralization at temperatures from 400 °C (Stage 1) to 130 °C (Stage 4). • Gold sourced from local metamorphosed sediments and emplaced via fluid boiling. • Boiling driven by hydrostatic-to-lithostatic pressure shifts due to fault release. Abstract The Zhengchong gold deposit is located in the central Jiangnan Orogen Belt, where gold ore occurs mainly as quartz veins, altered slates, and minor breccias hosted by shear zones in the Lengjiaxi Group. Based on its vein crosscutting relationships, mineral assemblages, and paragenetic sequences, mineralization in this deposit is divided into four stages: Stage 1: quartz(Q1)–pyrite stage, Stage 2: quartz(Q2)–pyrite–arsenopyrite stage, Stage 3: quartz(Q3)–pyrite–polymetallic sulfide mineral stage, and Stage 4: quartz(Q4)–carbonate stage. Two types of fluid inclusions have been recognized in the quartz grains: CO 2 -bearing fluid inclusions (C-type) and aqueous fluid inclusions (W-type). Fluid inclusions in hydrothermal quartz yield homogeneous temperatures and salinities of 312–406 °C and 4.65–9.21 wt% NaCl equiv (Stage 1), 252–324 °C and 2.20–8.10 wt% NaCl equiv (Stage 2), 193–296 °C and 2.24–14.04 wt% NaCl equiv (Stage 3), and 127–209 °C and 2.57–6.59 wt% NaCl equiv (Stage 4). The co-occurrence of these inclusion types despite their variable fluid salinities can be explained by fluid boiling during Stages 2 and 3 of mineralization, possibly as a result of episodic pressure decreases linked to fault-valve activity. Laser Raman spectroscopic analysis results reveal that small quantities of CH 4 and N 2 are present in the Stage 2–3 fluid inclusions. Fluid inclusion data and microthermometric results show that the ore fluids were low-salinity and CO 2 -rich, yielding both CO 2 inclusions (C-type) and aqueous inclusions (W-type). The trapping pressures estimated from the C-type inclusions are 80–180 MPa for Stages 2 and 3, yielding gold mineralization depths of ∼7–8 km. The mineralizing fluids had calculated δ18O H2O values ranging from +3.7‰ to +8.2‰ and δD values from −75.2‰ to −61.8‰, indicating derivation mainly from metamorphic fluids. The sulfide minerals yield δ34S values of −8.9 to −0.1‰ and 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb ratios of 17.83–18.12, 15.67–15.76, and 38.03–38.62, respectively, which differ significantly from the isotopic composition of the granodiorite (δ34S = −2.4‰ to +1.0‰; 206Pb/204Pb = 18.57–19.28; 207Pb/204Pb = 15.69–15.76; 208Pb/204Pb = 38.97–40.34). However, the S–Pb isotopic compositions of the sulfide minerals are similar to those of slates of the Lengjiaxi Group in the study area. The Zhengchong gold deposit probably originated from a metamorphic fluid system characterized by low salinity, low density, and CO 2 enrichment with limited admixture of magmatic fluids. Based on similarities to other orogenic gold deposits, we infer that the Zhengchong orebody represents an orogenic gold deposit formed during the Late Ordovician Jiangnan Orogeny caused by collision of the Yangtze and Cathaysia blocks. [ABSTRACT FROM AUTHOR]

Assay of multiple serum tumor markers such as carcinoembryonic antigen (CEA), cytokeratin 19 fragment antigen (CYFRA21-1), and neuron specific enolase (NSE), is important for the early diagnosis of lung cancer. Dickkopf-1 (DKK1), a novel serological and histochemical biomarker, was recently reported to be preferentially expressed in lung cancer. Four target proteins were sandwiched by capture antibodies attached to microarrays and detection antibodies carried on modified gold nanoparticles. Optical signals generated by the sandwich structures were amplified by gold deposition with HAuCl 4 and H 2 O 2 , and were observable by microscopy or the naked eye. The four tumor markers were subsequently measured in 106 lung cancer patients and 42 healthy persons. The assay was capable of detecting multiple biomarkers in serum sample at concentration of <1 ng mL −1 in 1 h. Combined detection of the four tumor markers highly improved the sensitivity (to 87.74%) for diagnosis of lung cancer compared with sensitivity of single markers. A rapid, highly sensitive co-detection method for multiple biomarkers based on gold nanoparticles and microarrays was developed. In clinical use, it would be expected to improve the early diagnosis of lung cancer. [ABSTRACT FROM AUTHOR]

Titanium dioxide based nanotubes (TN) were synthesized through hydrothermal synthesis route followed by acid washing under ambient conditions. The as-prepared TN with high specific surface area and titanate layered structure were subsequently functionalized with titanium (IV) peroxo groups (TNp) and gold (TN/Au) to examine an influence of non-metal/metal presence in the CWPO of aqueous methyl orange (MO) solution under ambient conditions. The obtained results showed higher activity and mineralization extent of MO over TNp catalyst in comparison to TN/Au at ambient conditions. The 50 ppm MO solution containing 2 g/L of TNp catalyst and stoichiometric amount of hydrogen peroxide was purified up to 68% of TOC during 4 h of CWPO process. As far as TN/Au is concerned, high TOC removal (83%) was only witnessed when the CWPO process was conducted at elevated temperatures (T = 80 °C). Moreover, comparing the simplicity of the synthesis routes and catalytic activities of obtained solids, the metal-free catalyst showed greater potential for the degradation of MO solution under ambient conditions without deprivation of its activity, as demonstrated in successive 4-cycle oxidation runs conducted in the presence of a surplus amount of H 2 O 2 . [ABSTRACT FROM AUTHOR]

The surface modification of Ag nanoparticles supported on reduced graphene oxide (RGO) with a small amount of Au and the activity of Au-modified Ag/RGO (Au–Ag/RGO) catalysts for the electrooxidation of glycerol have been investigated. The deposition of Au on Ag/RGO nanocomposites was performed electrochemically, and the Au–Ag/RGO catalysts with Au:Ag atomic ratios in a range from 1:303 to 1:43 were prepared. The characterization of catalysts reveals a partial coverage of the Ag nanoparticle surface by Au adatoms. Cyclic voltammetric measurements indicate that the Au–Ag/RGO catalysts show almost the same activity as Au/RGO in terms of the geometric surface area of glassy carbon substrates for glycerol oxidation in alkaline solution, while Ag/RGO shows no catalytic activity. The Au–Ag/RGO catalysts have great advantages over Au/RGO in terms of the Au mass specific activity. A significant improvement in the catalytic activity of Ag/RGO by the deposition of a small amount of Au and a high utilization of Au are achieved, and the result is of significance for preparing highly active catalysts at low cost by using less expensive metal and active metal. [ABSTRACT FROM AUTHOR]

Europium(III) oxide nanoparticles were prepared using a hydrothermal method. Gold was deposited by a photo-assisted deposition method. Europium(III) oxide and gold deposited europium(III) oxide were characterized using different techniques. The results demonstrated that gold was present as a metallic gold, and it was well-dispersed on the europium(III) oxide surface. The photocatalytic activity of europium(III) oxide and gold deposited europium(III) oxide was measured by the degradation of atrazine using visible light irradiation. The photocatalytic activity of gold deposited europium(III) oxide is higher than that of europium(III) oxide. This finding can be attributed to the synergic effect between europium(III) oxide and gold. Moreover, the results revealed that an increase in the weight percent of gold increases the photocatalytic activity of europium(III) oxide, and the most active photocatalyst is 0.20 wt % gold deposited europium(III) oxide. The photocatalyst of 0.20 wt % gold deposited europium(III) oxide has high photocatalytic stability and can be reused five times without a decrease in photocatalytic activity. [ABSTRACT FROM AUTHOR]

The partial surface modification of reduced graphene oxide-supported Pt nanoparticles with a small amount of Au and the electrooxidation of ethylene glycol and glycerol on Au-modified Pt nanoparticles/reduced graphene oxide (Au/Pt/RGO) catalysts have been investigated. The deposition of Au on Pt/RGO was performed electrochemically, and Au/Pt/RGO catalysts with the Au:Pt atomic ratio of 1:74, 1:41 and 1:20 were prepared. The characterization of catalysts showed the coverage from 4 to 17% of the Pt surfaces by Au adatoms. The Au/Pt/RGO catalysts have the property reflecting the features of both Pt and Au, but behave more similar to Pt/RGO in ethylene glycol oxidation and to Au/RGO in glycerol oxidation. Furthermore, the Au/Pt/RGO catalysts exhibit higher activity than Pt/RGO and Au/RGO in the two reactions. The significant change in the activity of Pt/RGO by the surface modification with a small amount of Au and the different performances of Au/Pt/RGO in the oxidation of ethylene glycol and glycerol are of significance for practical application and theoretical investigation. [ABSTRACT FROM AUTHOR]

Highlights: [•] Gold nanoparticles are deposited onto carbon monoliths. [•] Gold is reduced by the own carbon material. [•] Two different materials are prepared with different gold concentrations. [•] Materials are characterized by different techniques XPS, ICP, SEM-EDX, FE-SEM. [•] Heat treatment led to changes in gold particle morphology. [ABSTRACT FROM AUTHOR]

Abstract: Highly ordered titanium dioxide nanotube (≈100–200nm pore diameter) arrays, were formed on a titanium foil by anodising at a cell voltage of 60V, in two stages. The nanotube arrays were over-coated with nanoparticulate gold using physical vapour deposition (PVD) sputtering resulting in a well dispersed coating. The electrodes were used to study the oxidation of 20×10−3 moldm−3 borohydride ions in 3moldm−3 NaOH, at 298K, by cyclic voltammetry. The gold-coated titanium oxide nanotube array electrodes provided higher electrical charge per unit mass of gold and unit area that a gold nanoparticle deposit on carbon and gold adsorbed on hydrothermally synthesised titanate nanotubes offering a reliable and low cost technique to produce a high surface area anode for a direct borohydride fuel cell. [Copyright &y& Elsevier]

Abstract: Electrodeposition of Au on 3-D porous graphite (PG) at different pH values was investigated through an electrogenerative process in 3hours of operation of the system. In the pH range between 1 and 3, the deposition efficiency was highest. However, with concerns regarding passivation and corrosion, the optimum pH was 3. The Au particles were spontaneously deposited on the PG surface in metallic form. Electrogenerative deposition of Au on the PG surface can provide a free energy of −1021kJmol−1 and a simple, fast and clean method to prepare electrocatalysts. In this study, oxidation of glucose is reported as a potential application by the as prepared Au/PG electrocatalyst. [Copyright &y& Elsevier]

Abstract: In this study, new xanthine biosensors, XO/Au/PVF/Pt and XO/Pt/PVF/Pt, based on electroless deposition of gold(Au) and platinum(Pt) nanoparticles on polyvinylferrocene(PVF) coated Pt electrode for detection of xanthine were presented. The amperometric responses of the enzyme electrodes were measured at the constant potential, which was due to the electrooxidation of enzymatically produced H2O2. Compared with XO/PVF/Pt electrode, XO/Au/PVF/Pt and XO/Pt/PVF/Pt exhibited excellent electrocatalytic activity towards the oxidation of the analyte. Effect of Au and Pt nanoparticles was investigated by monitoring the response currents at the different deposition times and the different concentrations of KAuCl4 and PtBr2. Under the optimal conditions, the calibration curves of XO/Au/PVF/Pt and XO/Pt/PVF/Pt were obtained over the range of 2.5×10−3 to 0.56mM and 2.0×10−3 to 0.66mM, respectively. The detection limits were 7.5×10−4 mM for XO/Au/PVF/Pt and 6.0×10−4 mM for XO/Pt/PVF/Pt. The effects of interferents, the operational and the storage stabilities of the biosensors and the applicabilities of the proposed biosensors to the drug samples analysis were also evaluated. [Copyright &y& Elsevier]

Abstract: Static ToF-SIMS was used to evaluate the effect of gold condensation as a sample treatment prior to analysis. The experiments were carried out with a model molecular layer (Triacontane M =422.4Da), upon atomic (In+) and polyatomic (Bi3 +) projectile bombardment. The results indicate that the effect of molecular ion yield improvement using gold metallization exists only under atomic projectile impact. While the quasi-molecular ion (M+Au)+ signal can become two orders of magnitude larger than that of the deprotonated molecular ion from the pristine sample under In+ bombardment, it barely reaches the initial intensity of (M−H)+ when Bi3 + projectiles are used. The differences observed for mono- and polyatomic primary ion bombardment might be explained by differences in near-surface energy deposition, which influences the sputtering and ionization processes. [Copyright &y& Elsevier]

Abstract: The main purpose of this research is to show the effects of solvent nature, partial charge distribution and polarity index, on the preparation of uniform silane self-assembly monolayers. Octadecyltrichlorosilane (OTS) on silicon wafers was chosen as a case study. Contrary to what was thought before, dipole moment data are not enough and one needs accompanying data on partial charge distribution and polarity index to predict the best solvent for a uniform self-assembled monolayer (SAM). Results can be applied to other monolayer-solvent systems. [Copyright &y& Elsevier]

Abstract: The preparations and performances of the novel amperometric biosensors for glucose based on immobilized glucose oxidase (GOD) on modified Pt electrodes are described. Two types of modified electrodes for the enzyme immobilization were used in this study, polyvinylferrocene (PVF) coated Pt electrode and gold deposited PVF coated Pt electrode. A simple method for the immobilization of GOD enzyme on the modified electrodes was described. The enzyme electrodes developed in this study were called as PVF-GOD enzyme electrode and PVF-Au-GOD enzyme electrode, respectively. The amperometric responses of the enzyme electrodes were measured at constant potential, which was due to the electrooxidation of enzymatically produced H2O2. The electrocatalytic effects of the polymer, PVF, and the gold particles towards the electrooxidation of the enzymatically generated H2O2 offers sensitive and selective monitoring of glucose. The biosensor based on PVF-Au-GOD electrode has 6.6 times larger maximum current, 3.8 times higher sensitivity and 1.6 times larger linear working portion than those of the biosensor based on PVF-GOD electrode. The effects of the applied potential, the thickness of the polymeric film, the amount of the immobilized enzyme, pH, the amount of the deposited Au, temperature and substrate concentration on the responses of the biosensors were investigated. The optimum pH was found to be pH 7.4 at 25°C. Finally the effects of interferents, stability of the biosensors and applicability to serum analysis of the biosensor were also investigated. [Copyright &y& Elsevier]

In the present study, copper cementation was evaluated as a method for the recovery of gold from thiosulfate leach solutions. It was found that it is possible to achieve appreciable cementation rates of gold onto a copper substrate. The presence of 0.4 M ammonia had a positive effect on cementation, shifting the reaction from the chemical reaction control regime to the diffusion control regime. This effect is explained by the shift in the anodic reaction, copper oxidation, as ammonia was added. Electrochemical studies of the cathodic reaction, gold deposition, were also carried out. It was found that a high overpotential is required to deposit gold onto a gold substrate. However, the presence of copper, either as metallic copper or as Cu(I) thiosulfate, dramatically enhances the gold deposition half reaction. Without this enhancement, the cementation reaction would occur at a very low rate. [Copyright &y& Elsevier]

• TOF-SIMS with gold deposition was proposed as a novel method for quantification. • This method makes it possible to compare the amount of organic additives among different matrix polymers. • This method has a potentiality for the quantification independent of matrices. • Its application to not only additives on polymers but also to other fields such as adhesion or tribology can be realized. A novel method for the quantification of organic additives on polymer surfaces was investigated using time-of-flight secondary ion mass spectrometry (TOF-SIMS) with gold deposition. Pentaerythritol tetrakis (3- (3,5-di- tert -butyl-4-hydroxyphenyl) propionate and tris (2,4-di- tert -butylphenyl) phosphite were used as typical organic additives, and polystyrene (PS), polymethyl methacrylate (PMMA) and polyethylene terephthalate (PET) were used as typical polymers for this investigation. Gold deposition on polymer film surfaces containing various concentrations of additives made TOF-SIMS analysis possible for quantitative evaluation of the additives from negative ion mass spectra among the different matrices. This method is expected to be expanded to the absolute quantification of organic materials on polymer surfaces, not only with respect to additives on polymers but also for other fields such as adhesion or tribology. [ABSTRACT FROM AUTHOR]

• A robust, simple, reliable and multiple-targeted colorimetric immunoassay platform. • Detection of CVD protein biomarkers in serum with high specificity. • Dual signal amplification based on gold deposition for colorimetric immunoassay. Multiplexed detection of increased CRP and IL-6 levels in serum could warn the risk of Cardiovascular Disease (CVD) in clinical diagnosis. Herein, we report a robust, simple, reliable and multiple-targeted colorimetric immunoassay platform for the detection of CVD protein biomarkers in serum with high specificity. With dual signal amplification involving in AuNPs probes via ssDNA hybridization and AuNPs initiated gold deposition, this colorimetric immunoassay achieves a limit of detection (LOD) of 326 pg/mL for CRP and a LOD of 8 pg/mL for IL-6 simultaneously. In addition, this assay exhibited high specificity and selectivity when challenged with different interfering proteins. Clinical feasibility is evaluated by utilizing this assay in clinical serum samples of CVD patients and the experimental results show a good consistency with ELSIA kit. Importantly, this immunoassay shows several advantages such as simple operation, less time-consuming, multiplex, reliability and no requirement of labelled reagents and expensive equipment, which demonstrates its potential utility in clinical diagnostics for CVD. [ABSTRACT FROM AUTHOR]