Au Concentration Research Articles

220 keV Ag ion irradiation-induced surface plasmon resonance shift of gold nanoparticles in fullerene C60 matrix

The effect of 220 keV Ag ion beam irradiation on the optical and structural properties of thermally co-deposited Au-C60 nanocomposite thin films on a quartz substrate is investigated by irradiating samples at different doses. To determine the exact gold (Au) concentration in the film and thickness of the film, Rutherford Backscattering Spectrometry (RBS) was utilized on the as-deposited film. The Surface Plasmon Resonance (SPR) of Au nanoparticles embedded into the fullerene C60 matrix was seen at 721 nm in the as-deposited sample. A ∼34 nm redshift in SPR wavelength was obtained at a dose of 1 × 1014 ions/cm2 which was mainly due to the increase in the size of Au nanoparticles with irradiation. At higher doses, a blue shift of ~67 nm was obtained at a dose of 1 × 1016 ions/cm2 which was due to the transformation of fullerene C60 matrix into amorphous carbon with a much lower dielectric constant at higher doses. The progressive transformation of fullerene C60 into amorphous carbon with increasing doses was confirmed by Raman spectroscopy. The size of Au nanoparticles in the highest dose irradiated sample was found to be ∼3.9 nm by High-Resolution Transmission Electron Microscopy (HRTEM) bright-field measurements. The size modifications of nanoparticles and SPR wavelength tuning of these nanoparticles are very much needed to use them in organic solar cell.

A novel benzothiazole modified chitosan with excellent adsorption capacity for Au(III) in aqueous solutions

A novel benzothiazole modified chitosan (BCS) with excellent Au(III) adsorption performance and selectivity was prepared as adsorbents. The structure and morphology of the adsorbents were characterized by FTIR, SEM, XRD and XPS. The adsorption property of the adsorbents for Au(III) were investigated under different reaction time, initial concentration of Au(III), temperature, pH and coexisting ions. The maximum adsorption capacity of BCS for Au(III) was 1072.22 mg/g at 298 K and optimal pH = 4, which was better than that of other adsorbents reported in literature. The adsorption kinetics and isotherm models fit the pseudo-second-order and Langmuir equations. This shows that the adsorption process of Au(III) is a monolayer chemical adsorption. The adsorption process can proceed spontaneously and belong to the endothermic reaction according to the thermodynamic results. The excellent adsorption performance is mainly attributed to the ion exchange and chelation of the nitrogen, sulfur and oxygen groups on the adsorbent with gold ions. Significantly, BCS has excellent selectivity toward Au(III) and remarkable recycle performance. With the high adsorption capacity, excellent selectivity and outstanding reusability, the BCS adsorbent could be a promising candidate to adsorb Au(III) from wastewater.

Carbonation of Neoproterozoic mantle section and formation of gold-bearing listvenite in the Northern Nubian Shield

The ultramafic rocks of Gabal Balamhindit are exposed as conspicuous ridges in the south Eastern Desert of Egypt, Northern Nubian Shield. These rocks include extensively to completely serpentinized harzburgites and dunites, which are listvenitized along faults and shear zones. The relict primary minerals of these serpentinized peridotites are represented by olivine, orthopyroxene and Cr-spinel, whereas serpentine minerals, amphiboles and chlorite are secondary phases. The listvenite is composed essentially of quartz and carbonates, with relics of serpentine minerals and Cr-spinel. The carbonate minerals include magnesite, dolomite, breunnerite and calcite. A characteristic feature of listvenite is the presence of rhythmic banding of quartz and carbonate minerals and presence of fuchsite. Mineral chemistry of primary minerals revealed that the Fo content of olivine, Mg# of orthopyroxene and Cr# of Cr-spinel in serpentinized dunite are higher than those of corresponding minerals in the serpentinized harzburgite. The composition of primary minerals in both serpentinized dunite and harzburgite (olivine Fo = 90–92; orthopyroxene Mg# = 0.91–0.93; Cr-spinel with Cr# of 0.61–0.72 and TiO2 content of 0.04–0.2 wt%) and whole-rock geochemical characteristics (Mg# = 0.91–0.92; low TiO2 content of values <0.04 wt%) are consistent with depleted mantle protolith, typically associated with supra-subduction zone environments, and more specifically with fore-arc settings. The examined serpentinized peridotite represents mantle residue that experienced different degrees of partial melting (33–40%). The restriction of listvenization to shear zones and presence of relics of mesh-textured serpentine and Cr-spinel with ferritchromite rims in the listvenite reflect formation through replacement of ultramafic rocks during ophiolite obduction in the Arabian-Nubian Shield. Schistosity and deformation fabrics in the listvenite imply that initial listvenitization took place at conditions similar to those where serpentinization of primary ultramafic precursors occurred. The Balamhindit listvenite has variable contents of fluid mobile elements such as As (127–164 ppm), Sb (8–18 ppm), Sr (88–162 ppm) and Pb (193–276 ppm), with presence of native gold. Compared to listvenites, serpentinites contain less amounts of these elements (4–9 ppm As, 0.26–1.02 ppm Sb, 4–10 ppm Sr and 0.27–1.27 ppm Pb). The wide distribution of listvenites along the suture zones favor a metamorphic source of the fluids during the accretionary tectonics. The listvenitization process concentrated gold in listvenite compared to the low-grade Au concentration in the host serpentinite. The Au content in listvenite samples shows positive correlation with the metals Zn, As, Cu, Ag and Pb, suggesting a common source. The listvenites of Gabal Balamhindit are auriferous, with gold content up to 3 ppm, suggesting that the listvenites of the Arabian-Nubian Shield (ANS) are potential target for gold exploration.

Mineral-scale variation in the trace metal and sulfur isotope composition of pyrite: implications for metal and sulfur sources in mafic VMS deposits

The link between metal enrichment and the addition of a magmatic volatile phase in volcanogenic massive sulfide deposits and actively forming seafloor massive sulfide deposits remains poorly characterized. This is especially true when considering how metal, sulfur and fluid flux change with time. In this study, we combine in situ sulfur isotope (δ34S; n = 31) measurements with trace metal chemistry of pyrite (n = 143) from the Mala VMS deposit, Troodos, Cyprus. The aim of our study is to assess the links between volatile influx and metal enrichment and establish how, or indeed if, this is preserved at the scale of individual mineral grains. We classify pyrite based on texture into colloform, granular, disseminated and massive varieties. The trace metal content of different pyrite textures is highly variable and relates to fluid temperature and secondary reworking that are influenced by the location of the sample within the mound. The sulfur isotope composition of pyrite at Mala ranges from − 17.1 to 7.5‰ (n = 31), with a range of − 10.9 to 2.5‰ within a single pyrite crystal. This variation is attributed to changes in the relative proportion of sulfur sourced from (i) SO2 disproportionation, (ii) thermochemical sulfate reduction, (iii) the leaching of igneous sulfur/sulfide and (iv) bacterial sulfate reduction. Our data shows that there is no correlation between δ34S values and the concentration of volatile elements (Te, Se) and Au in pyrite at Mala indicating that remobilization of trace metals occurred within the mound.

Pretreatment of low-grade shredded dust e-waste to enhance silver recovery through biocyanidation by Pseudomonas balearica SAE1.

The online version contains supplementary material available at 10.1007/s13205-021-02977-4.

Optimization of the Composition of PdAuCu Ternary Alloy Nanoparticles for Plasmonic Hydrogen Sensing

Alloying is a long-standing central strategy in materials science for the tailoring and optimization of bulk material properties, which more recently has started to find application also in engineered nanomaterials and nanostructures used in, among other, nanoplasmonic hydrogen sensors. Specifically, alloying Pd nanoparticles to form binaries and ternaries with the coinage metals Au and Cu has proven efficient to mitigate hysteresis in the sensor response, improve response and recovery times, boost sensitivity in the low hydrogen concentration sensing range, and reduce the detrimental impact of carbon monoxide poisoning. However, when surveying the corresponding studies, it is clear that there is a trade-off between the sensitivity enhancement and the CO-poisoning resistance effects provided by Au and Cu alloyants, respectively. Therefore, in this work, we systematically screen the impact of the Au and Cu concentration in PdAuCu ternary alloy nanoparticles used for plasmonic hydrogen sensing, to obtain a champion system with maximized sensitivity and CO-poisoning resistance based on an evaluation using the stringent ISO 26142 test protocol. As the main results, we find that the best hysteresis-free and sensitive response combined with deactivation resistance to 500 ppm CO in synthetic air is obtained for the Pd65Au25Cu10 ternary alloy system, which also exhibits good long-term stability during operation under severe CO poisoning conditions.

Labelling of human Wharton's jelly-derived mesenchymal stem cells with gold nanorods by biomimicry method.

Mesenchymal stem cell (MSC)-based cell therapy can provide opportunities for the treatment of various diseases. However, when used in vivo, these cells should be labelled and monitored by a non-invasive method during delivery to the desired locations within the body. This study describes a biomimicry method that effectively labels human Wharton's jelly-derived MSCs (hWJ-MSCs) with a photoacoustics (PA) contrast agent, gold nanorods (GNRs), without the need for transfection agents (TAs). In this method for cell labelling, the hWJ-MSCs were co-incubated with non-adherent cells isolated from fresh umbilical cord for 2 days immediately before incubation with GNRs. Next, hWJ-MSCs were labelled with the GNRs at a concentration of approximately 1010 nanorads/mL (NR/mL) followed by transmission electron microscopy (TEM) and inductively coupled plasma mass spectroscopy (ICP-MS) to verify their labelling effectiveness. The GNRs-labelled MSCs prepared by this method had an intracellular gold (Au) concentration of 3.4 ± 0.4pg/cell, which is an acceptable amount for cell labelling.

Coupling between bulk thermal defects and surface segregation dynamics

Surface segregation is a phenomenon that depends on the delicate interplay between thermodynamic driving forces and kinetic obstacles, for which elevated temperature is often needed to enhance the atom mobility and reach equilibrium. Using the classic system of ${\mathrm{Cu}}_{3}\mathrm{Au}(100)$ under nonisothermal conditions, herein, we show an adatom process underlying transient surface segregation dynamics through the temperature-change-driven creation and annihilation of thermal vacancies in the bulk and the resulting bulk-surface mass exchanges. This is demonstrated by monitoring the surface composition evolution of ${\mathrm{Cu}}_{3}\mathrm{Au}(100)$ with temperature changes between 250 and $500{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$, showing that the increase in temperature decreases monotonically the surface Au concentration as a result of the transfer of more Cu than Au from the bulk to the surface to form Cu-rich clusters of adatoms. Such a bulk thermal defect effect is expected to be universal in inducing the disparity in the bulk-surface mass exchanges of dissimilar atoms in multicomponent materials because of the inherent differences in the vacancy formation energies of the constituent atoms.

Preparation of Gd-Au Dendrimer-Entrapped Gold Nanoparticles-Folic Acid Nanoparticles and Its Application in Computed Tomography/Magnetic Resonance Imaging Dual-Modality Diagnosis of Abdominal Tumors

ABSTRACTThe development of nanomaterials, especially the development of multi-modality imaging nanoprobe technology has become a reality for tumor imaging diagnosis. In this study, the gadolinium ion chelating agent (2,2′,2′′-(10-(2-(2, 5-dioxopyrrolidin-1-oxyl)-2 oxoethyl)-1, 4, 7, 10-tetraazacyclododecane-1, 4, 7-tri)triacetic acid) (DOTA-NHS) and polyethylene glycol (PEG)-modified targeting ligand PEG-folic acid (FA) were grafted onto the PEG-modified fifth-generation polyamide-amine dendrimer (P5-NH2), which were undertaken as standards to wrap gold nanoparticles. Then, remaining amino group was acetylated to acquire Gd–Au DENPS-FA nanoparticles. Biocompatibility and cytotoxicity of nanoparticles were analyzed while characterizing them. The cases with unidentified tumors (mass diameter &gt;4.5 cm) of abdominal or pelvic origin were selected and used for clinical study of computed tomography (CT)/magnetic resonance imaging (MRI) dual-modality abdominal tumors. In the test, average particle size of Gd-Au DENPs-FA nanoparticles was 4.2 nm, and they had good water solubility and stability in aqueous solution. When concentration of Au+ nanoparticles increased, the cell morphology remained normal, only a small number of round cells appeared, and the cell activity remained above 80%. GD-Au DENPs-FA nanoparticles had a good targeting specificity for KB cells with high folate receptor expression. During 6–24 hours of injection, the signal at the tumor site of the patient was enhanced markedly, namely the targeted gold nanoparticles were bound to the tumor tissue and the metabolic rate was slow. Based on this material, CT/MRI imaging could be performed in the patient’s body and further used for the early diagnosis of abdominal tumors.

Maximizing the synergistic effect of PdAu catalysts on TiO2(1 0 1) for robust CO2 reduction: A DFT study

To provide insight into how to realize maximization of the synergistic effect of supported PdAu catalysts, we have performed first-principles calculations for CO2 reduction over PdAu/TiO2(1 0 1). The results indicate that introducing a secondary metal (Au) to supported Pd catalyst and controlling Au concentration can affect the binding energy of reactants and also alter the dominant reaction pathway. The energetically preferred path for CO2 reduction on Pd8-xAux/TiO2 changes from the formate pathway (referred to as the “CO2 HYD” pathway) (x = 0–3) to the reverse water-gas shift and CO hydrogenation (“RWGS + CO HYD”) pathway (x = 4–6). Notably, the CO2 reduction activity shows a volcano trend as a function of the binding energy of the initial reactant CO2* in the “CO2 HYD” pathway or the adsorption energy difference between CHO* and CO* in the “RWGS + CO HYD” pathway. In addition, there is a component-dependent relationship between the water-promotion-effect and the nanoalloy structure. This work proposes fundamental insights into the effect of nanoalloy composition and water promotion in maximizing the synergy of PdAu catalysts for CO2 reduction, providing facile descriptors for the activity of reaction pathways, and offering important guidance for rational design of supported nanoalloy catalysts.

Platinum-group elements and gold distribution in ores of the Haftcheshmeh porphyry Cu-Mo-Au deposit, NW Iran

The Haftcheshmeh porphyry Cu-Mo-Au deposit is located in the Arasbaran metallogenic belt, northwest Iran, with mineralization occurring mainly in gabbro-diorite and granodiorite porphyry. Pyrite and chalcopyrite are the most abundant sulfides that occur as disseminated and veinlet type ores in the potassic alteration zone. Platinum-group elements (PGEs), Au, and Cu concentrations of selected pyrite- and chalcopyrite-bearing samples were analyzed using in situ LA-ICP-MS and bulk rock Lead Fire Assay. Relatively high contents of PGEs and other precious elements are present in sulfide minerals, especially in pyrite that is the principal carrier of these elements in the deposit. Palladium is the most abundant of the PGEs in the sulfides. The contents of Pd are systematically higher than Pt in this deposit, consistent with other porphyry deposits, although Os, Rh, and Ir abundances are in general equal to or below the limits of detection in pyrite and chalcopyrite. The most important factors related to potential PGEs and chalcophile elements enrichment in the Haftcheshmeh deposit is the oxidized mafic endmember components of source magmas, i.e., high ƒO2 conditions, possibly with a semi-metal collector melt involved, and the high saline magmatic hydrothermal fractionation process. All these mechanisms seem to have enhanced the concentration of PGEs, Au, and other chalcophile metals. PGEs and other chalcophile elements were transported by exsolved high-T, saline magmatic hydrothermal fluids and then low T reaction and reduction to enhance saturation of sulfide phases during mineralization associated with potassic alteration.

Fabrication of gold-immobilized quantum dots/silica core–shell nanoparticles and their multimodal imaging properties

This work describes the fabrication of quantum dot (QD)/silica (SiO2) core–shell particles immobilized with Au nanoparticles and the evaluation of their abilities in fluorescence and x-ray computed tomography (CT) imaging. The QD nanoparticles were coated with silica shells by a sol-gel method using tetraethyl orthosilicate (QD/SiO2). Reduction of Au3+ in a citrate aqueous solution gave an Au nanoparticle colloidal solution. (3-Mercaptopropyl)trimethoxysilane thiolated the QD/SiO2 particle surface (QD/SiO2/SH). Immobilization of the Au nanoparticles on the QD/SiO2/SH particle surface was performed with the addition of the Au nanoparticle colloidal solution to the QD/SiO2/SH nanoparticle colloidal solution (QD/SiO2/SH/Au). Surface-PEGylated QD/SiO2/SH/Au particles were fabricated using thiol-terminated polyethylene glycol (PEG) (QD/SiO2/SH/Au/PEG). The QD/SiO2/SH/Au/PEG nanoparticle colloidal solution was imaged by fluorescence and x-ray CT imaging techniques. The CT value per unit concentration of Au (M) for the QD/SiO2/SH/Au/PEG nanoparticle colloidal solution was 1.5 × 104 HU/M. The QD/SiO2/SH/Au/PEG nanoparticle colloidal solution was injected into the tail vein of a mouse and circulated in the blood, although some QD/SiO2/SH/Au/PEG nanoparticles were trapped and remained in the liver and spleen.

Abstract P-8:Fe2O3-SiO2-Au Core-Shell Nanoparticles for Theranostics

Background: Core-shell nanoparticles (NPs) Fe3O4-SiO2 covered with Au grains due to their unique magnetic, biological, optical and mechanical properties are promising nanostructured material especially in biomedical field. Magnetic core allows controlling the position of NPs, SiO2 shell makes them biocompatible and decrease magnetostatic interactions between them, and Au NPs on the surface allow creating additional matrix around them and using such systems as controlled nanocontainers in tasks of drug delivery, magnetic resonance imaging and target cancer cell therapy. Methods: Inner magnetic core of the NPs was synthesized using polyol method, a 3-step process which resulting in magnetite NPs with hydrophilic surface. Shell was made by covering Fe3O4 particles in surfactant and growing SiO2 on top of them by sol-gel method. Covering core-shell NPs with 3.5 nm Au seed grains using monosilane and their further growth to control diameter. Structural properties were studied using TEM and Dual Beam SEM. Magnetic properties were investigated using LakeShore VSM 7400 magnetometer. Results: Two samples with different concentration of Au NPs were investigated. SEM observations show that core-shell Fe3O4-SiO2 are spherical with average diameter of 200 nm and Au NPs with diameter of 15 nm are evenly dispersed on their surface. Magnetic measurements showed that different concentration of Au NPs results in different coercive forces of the sample. Decreasing the temperature to 77 K showed up to 6 times increase of coercive force and slight increase in magnetization. Conclusion: Biocompatible magnetic nanoparticles are critical advances in biomedical applications. In this work, we studied the morphology of the samples, demonstrated the change of coercive force of NPs with different Au concentration and investigated their magnetic properties in low temperatures.

Full Factorial Design for Gold Recovery from Industrial Solutions.

Gold is one of the precious metals with multiple uses, whose deposits are much smaller than the global production needs. Therefore, extracting maximum gold quantities from industrial diluted solutions is a must. Am-L-GA is a new material, obtained by an Amberlite XAD7-type commercial resin, functionalized through saturation with L-glutamic acid, whose adsorption capacity has been proved to be higher than those of other materials utilized for gold adsorption. In this context, this article presents the results of a factorial design experiment for optimizing the gold recovery from residual solutions resulting from the electronics industry using Am-L-GA. Firstly, the material was characterized using atomic force microscopy (AFM), to emphasize the material’s characteristics, essential for the adsorption quality. Then, the study showed that among the parameters taken into account in the analysis (pH, temperature, initial gold concentration, and contact time), the initial gold concentration in the solution plays a determinant role in the removal process and the contact time has a slightly positive effect, whereas the pH and temperature do not influence the adsorption capacity. The maximum adsorption capacity of 29.27 mg/L was obtained by optimizing the adsorption process, with the control factors having the following values: contact time ~106 min, initial Au(III) concentration of ~164 mg/L, pH = 4, and temperature of 25 °C. It is highlighted that the factorial design method is an excellent instrument to determine the effects of different factors influencing the adsorption process. The method can be applied for any adsorption process if it is necessary to reduce the number of experiments, to diminish the resources or time consumption, or for expanding the investigation domain above the experimental limits.

Gold dispersion in tropical weathering profiles at the Belikombone gold anomaly (Bétaré Oya gold district), east Cameroon

The distribution of gold in the weathering blanket at the Belikombone gold prospect in east Cameroon provides insights into gold mobility in the secondary environment and in tropical terrains worldwide. Both gridline-controlled sampling of topsoil (surface samples) and sampling of various layers in pits are used and the gold assay for each sample determined by NiS fire assay with ICP-AES finish. One hundred and thirty-two (132) surface samples and a total of 206 samples from 19 exploration pits were analyzed. The results from the topsoil samples show an anomaly with the highest Au concentration at 5.9 mgkg−1. The mineralization corridor follows a NE-SW trend. The horizons within the pits range from sap rock at the base, through saprolite, rubble layer rich in relict quartz material to a ferruginous loose layer at the top although some horizons are missing in some pits. All the layers contain gold and the highest concentration in the sap rock horizon is 3.4 mgkg−1 while the rubble layer has a gold high of 6.1 mgkg−1. The individual soil horizons show no systematic gold trends and given the presence of gold in all layers, the patterns point towards supergene dissolution and redistribution of gold. Gold enrichment within the upper horizons in the weathering blanket is attributed to sequestration by Fe oxides of chemically remobilized gold. However, the high gold content within the sap rock and saprolite layers suggests that migration of gold in the particulate form supersedes chemical gold redistribution. Particulate gold obtained by panning samples from the pits varies in shape from euhedral, elongated to irregular. Electron microprobe analysis on the grains record high contents of gold in the rim zones (90.0 to 99.8 wt%). The cores are relatively rich in Ag (12.6 to 14.2 wt%) while the rims are poor in Ag. The low Ag content in the rims is attributed to the preferential leaching of Ag. The soil pH value in this area varies between 3.6 and 7.3. Under such acidic to near neutral conditions, bisulfide and thiosulfate ions can dissolve and transport Au and Ag to be precipitated under surficial conditions creating authigenic Au haloes especially in the saprolite and sap rock layers. Such pH values together with oxidizing Eh conditions explain the solubility of gold in the area. These results are important for geochemical exploration of gold in tropical terrains, and confirm previous studies.

Au integrated 2D ZnO heterostructures as robust visible light photocatalysts

Integration of semiconducting nanostructures with noble metal nanoparticles are turning highly desirable for cost efficient energy and environmental related applications. From this viewpoint, we report on a facile aqueous synthesis of polymer capped gold (Au) nanoparticles on free standing 2D layered structures of zinc oxide (ZnO) to result with ZnO/Au nanocomposites. Concentration of Au nanoparticles were observed to promote the preferential growth of ZnO along the (002) wurtzite plane. The ZnO/Au structures and their morphological dissemination was noted to be of few. This flake like structure was also noted to be greatly influenced by the concentration of Au in the colloidal blend. Optical band edge transformations noted in the absorption spectra across the lower wavelength region and the shift in surface plasmon resonance (SPR) towards the red region of the visible spectrum signify the improved absorptivity of the heterostructures along the visible spectrum. These heterostructures exhibited remarkable visible light driven photocatalytic activity (99% efficiency) on par with pristine ZnO. The findings also attest this new class of composite structures to open up new openings in diversified solar energy conversion related functions.

Interaction of size-selected Ag-clusters on Au-thin films: a composition study with in-situ XPS analysis at an elevated temperature

In this paper, we describe a novel method of synthesis of bimetallic Ag–Au alloy nanoparticles with an estimated Ag to Au concentration ratio of ∼3:1 by using a gas-aggregation cluster source. The real time chemical changes occurred on the surface of the alloy film during different stages of annealing at an elevated temperature are observed by in-situ x-ray photoelectron spectroscopy analysis. It is found that the concentration of both Ag and Au of the alloy film simultaneously decreases with the increase of the annealing time. The chemical states of the elements present on the surface are analyzed from the HR-XPS data, which are recorded for the dominant elements present on the surface. From the analyses, it is found that a small part of metallic Ag gets oxidized for higher annealing time whereas no trace of oxidation of Au is observed. The surface morphology of the as-deposited and post-annealed alloy films are characterised by FESEM and AFM measurements. Due to thermal diffusion of Ag and Au, resultant narrow size distributions of the bimetallic Ag–Au nanoparticles are observed on the surface. The film morphologies suggest that the evolutions of bimetallic Ag–Au nanoparticles are nearly spherical in shape with an average aspect ratio value of ∼1.5.

Photoluminescence enhancement of single-layer graphene quantum dots by the surface plasmon resonance of Au nanocubes

Highly photoluminescent single-layer graphene quantum dots around Au nanocubes (SLGQDs/Au) were synthesized using a simple method. The SLGQDs were synthesized using a low-cost hydrothermal method from glucose as a precursor. The atomic force microscopy analysis proved that the average thickness of the GQDs is lower than 4 Å, meaning that the GQDs are single-layer dots. The novel cubic shape of the SLGQDs/Au nanocomposites was confirmed by field-emission scanning electron microscopy and Transmission electron microscopy. Structural characterization was performed by X-ray diffraction, energy-dispersive X-ray spectroscopy and Raman spectroscopy. Photoluminescence (PL) spectroscopy revealed that the obtained SLGQDs/Au nanocomposite has a higher PL emission peak intensity than that of the SLGQDs, which is due to the surface plasmon resonance of Au nanocubes at 530 nm, revealed in the UV–Vis absorption spectra. Finally, the effect of Au concentration on the PL emission peak intensity of the SLGQDs was studied, and the quantum yield of the optimum sample was measured and discussed.

Facile sol-gel method derived Au nanoparticles decoration nickel ferrites thin films: Effect on optical and magnetic properties

Noble metal Au nanoparticles (Au NPs) decoration nickel ferrite (hereafter abbreviated as NFA-x, x = 0, 0.04, 0.08 and 0.12) thin films were synthesized on quartz and Pt/Ti/SiO2/Si substrates by a facile sol-gel method. The structural, optical and magnetic performances of NFA-x thin films have been investigated. The XRD patterns revealed the formation of cubic spinel ferrite structure. The SEM analysis indicated that NFA-x thin films were dense and uniform, which also confirm that crystalline size decreased with increasing of Au content. A remarkable surface plasmon resonance (SPR) features has been observed in NFA-0.12 films. The optical band gap of NFA-x thin films decreased with increasing Au concentration. In addition, our results revealed that the magnetism was highly depending on the Au concentration. The saturation magnetization remarkable decreased then sharply increased with increasing of Au content, which is attributed to Au NPs decoration effect. However, the coercive field and squareness ration showed increasing trend with increasing of Au concentration. Our work suggests that Au nanoparticles decoration nickel ferrites thin films have promising applications in multifunctional materials field.

An Application for Thermodynamic Calculation of AuxAg1 – x-Fluid Equilibria: Super-Pure Native Gold in Woxi Au–Sb–W Deposit, Western Hunan, China

The native gold in the Woxi Au–Sb–W deposit is characterized by remarkably high purities (99.9%), called as super-pure native gold. The deposit can thus be used as the suitable application example for analyzing ore-forming conditions by using the thermodynamic calculation of AuxAg1 – x-fluid equilibria. According to experimental results of minerals and fluid inclusions, some physicochemical conditions are assumed in the thermodynamic calculation of the fluids equilibrated with Au–Ag solid solutions of XAu = 0.999. Calculated results in log fO2-pH diagrams show dissolved gold and silver concentrations, as well as stability fields of pyrite and sericite associated with the super-pure native gold. On the other hand, LA-ICP-MS analysis indicates that both Au and Ag concentration are determined in the fluid inclusions of scheelite, showing varied Au/Ag ratios with different homogenization temperatures. The calculated results assumed by different data of inclusions in scheelite, indicate two fluid inclusions showing higher homogenization temperatures (303°C and 356°C) and higher Au/Ag ratios are possible for precipitation of the super-pure native gold coexisting with pyrite and sericite, whereas one fluid inclusion showing a lower homogenization temperature (198°C) and a lower Au/Ag ratio is impossible for the super-pure native gold. Therefore, the super-pure native gold in the Woxi deposit was probably formed by the hydrothermal fluid with higher Au/Ag ratios and high temperatures in the mineralization stage of scheelite.