Search Results (10)

Electroless silver (Ag) plating has emerged as a simple yet effective surface modification technique, garnering significant attention in consumer electronics and composite materials. This study systematically investigates the influence of glucose dosage on the microstructural refinement of Ag coatings deposited from silver–ammonia solutions onto iron (Fe) particles while also evaluating the oxidation resistance of Ag-plated particles through thermogravimetric analysis. Optimal results were achieved at a silver nitrate concentration of 0.02 mol/L and a glucose concentration of 0.05 mol/L, producing Fe particles with a uniform and dense silver coating featuring an average Ag grain size of 76 nm. The moderate excess glucose played a dual role: facilitating Ag⁺ ion reduction while simultaneously inhibiting the growth of Ag atomic clusters, thereby ensuring microstructural refinement of the silver layer. Notably, the Ag-plated particles demonstrated superior oxidation resistance compared to their uncoated counterparts. These findings highlight the significance of fine-grained electroless Ag plating in developing high-temperature conductive metal particles and optimizing interfacial structures in composite materials. Full article

In this study, MoS₂ nanosheets have been prepared and treated ultrasonically with silver ammonia solutions. The MoS₂/Ag precursor was reduced using dopamine (DA) as reducing and linking agent at room temperature, and it was subjected to a hydrothermal treatment to produce MoS₂/Ag nanocomposites (denoted as MoAg). The MoAg samples were functionalized with N-oleoylethanolamine to improve dispersion in the base oil component of additives. Use of the functionalized MoAg (denoted as Fc-MoAg) as a lubricant additive for steel balls resulted in effective friction reduction and anti-wear. This work avoids ion exchange during exfoliation, and the Ag⁺ has been reduced to nano-silver particles by dopamine to enlarge the layer spaces of MoS₂. Taking the case of lubrication with base oil containing Fc-Mo_0.6Ag₁₅, the wear scar diameters and coefficients of friction of the steel balls were 0.428 and 0.098 mm, respectively, which were about three-fifths base oil. In addition, MoS₂/Cu and MoS₂/Ni nanocomposites were synthesized and the tribological properties associated with steel/steel balls assessed. The results demonstrate that all MoS₂/metal composites exhibit enhanced tribological behavior in the steel/steel pair tests. Both nanocomposite synergy and the tribofilm containing sulfide, oxide, carbide, and other compounds play important roles in achieving reduced friction and improved anti-wear. The friction and wear properties of base oil containing Fc-MoAg and commercial additives were evaluated using a four-ball wear tester with steel/steel, steel/zirconia and zirconia/zirconia pairs. The base oil containing Fc-MoAg delivered smaller coefficients of friction (COFs) and/or scarring groove depths than those observed with the use of pure base oil and base oil containing commercial additives. Full article

Polyacrylic acid (PAA) chains were used to decorate the surface of multi-walled carbon nanotubes (MWCNTs) via in situ free radical polymerization, and sulfonated chitosan (SCS) was synthesized via a simple and environmental method. Silver-ammonia ions were introduced as the fixative with PAA-MWCNTs as the basic framework, and SCS was used to decorate the surface, thereby obtaining PAA-MWCNTs-Ag-SCS. The modified electrode exhibited excellent cyclic voltammogram (CV) stability after 100 cycles of scanning. According to differential pulse voltammetry (DPV), the peak current value was approximately 250 μA, exhibiting outstanding sensitivity to phenylglycinamide (Pen) enantiomers. The peak current ratio of D-Pen to L-Pen reached 2.16, showing excellent selectivity. The detection limit (DL) was calculated as 0.015 mM and 0.036 mM for L-Pen and D-Pen, respectively, using the signal-to-noise ratio (S/N = 3). This study provides a new idea for the construction of a chiral-sensing platform with outstanding sensitivity, superior stability, and excellent recognition efficiency. Full article

Exposure to acidic and alkaline pHs results in an ionic imbalance. Cellular responses involved in osmoregulation in silver catfish exposed to different pHs (5.5, 7.5, and 9.0) for 24 h were evaluated. The gills and kidney were collected to measure Na⁺/K⁺-ATPase (NKA) and H⁺-ATPase (V-ATPase) activities and to evaluate the expression of ion transporter-related genes: NKA (atp1a1), H⁺-ATPases (atp6v0a1b, atp6v0a2a, atp6v0a2b), Na⁺/H⁺ antiporter (slc9a3), K⁺/Cl⁻ symporters (slc12a4, slc12a6, slc12a7a, slc12a7b), Na⁺/K⁺/2Cl⁻ symporter (slc12a2), and ammonium transporter Rh type b (rhbg). The gills presented greater responses to pH changes than the kidney. The pH alterations changed the atp1a1 gene expression and NKA activity, whereas the H⁺-ATPase activity increased in the gills in alkaline water, probably to maintain ionic balance. The slc9a3 and slc12a2 genes play more prominent roles in the ion uptake at acidic pH than H⁺-ATPase. The slc12a7a was the only isoform of this transporter affected by pH. The rhbg is apparently related to ammonia excretion through the gills and kidney (minor scale). Exposure to alkaline pH seems to be battled by impairment of NKA and H⁺-ATPase activities in the gills, whereas the expression of some ion transporters in silver catfish changes during both acidic and alkaline pHs. Full article

In recent years, with the excavation of an increasing amount of gold and silver artifacts, there has been an urgent need to optimize the formulations and methods of metallographic etching. Herein, a kinetic control study is performed to investigate the mechanisms leading to poor results when etching ancient gold materials with aqua regia, i.e., when secondary AgCl impurities form during the etching of the sample surface. To this end, a concentrated ammonia and sodium thiosulfate solution is used to dissolve AgCl impurities and obtain high-quality metallographic images of ancient gold materials using a coordination reaction to generate stable free-state coordination ions from Ag⁺. On this basis, a ferric chloride + sodium thiosulfate method is proposed to optimize the formulation of the etchant for ancient silver materials. The formulation is efficient, safe and easy to handle, and solves the problems of the easy failure of the commonly used etchant of ammonia + hydrogen peroxide and the complicated preparation process of acidified potassium dichromate while maintaining the long-term stability of the etched Ag–Cu alloy samples. Full article

The leaching behaviors of gold and silver from a complex sulfide concentrate in copper-tartrate-thiosulfate solutions were investigated in this paper. Experimental parameters, including temperature, initial pulp pH, and concentration of copper, tartrate, and thiosulfate, were systematically studied. The copper-tartrate-thiosulfate leaching system exhibits promising performance in dealing with the complex sulfide concentrate. Thiosulfate consumption could be greatly reduced due to the in-situ generation of thiosulfate derived from sulfur or disulfide ions. Increasing the temperature and concentrations of copper, tartrate, and thiosulfate can promote gold leaching. A low tartrate content and a moderate increase in temperature and copper and thiosulfate concentrations can accelerate silver leaching, but a higher temperature or copper content may depress silver extraction. A suitable pulp pH is critical for gold and silver leaching in copper-tartrate-thiosulfate solutions. An extraction of 74.50% Au and 36.33% Ag was obtained with the direct leaching of the concentrate, while the percentages can be significantly increased up to 82.60% and 70.38%, respectively, when leaching the calcine following the oxidative roasting pretreatment. The recycling of leaching solutions demonstrates that a suitable free tartrate content is of great significance in maintaining the stability of the novel system. As an alternative to the traditional cyanide or copper-ammonia-thiosulfate leaching processes, the copper-tartrate-thiosulfate leaching system provides an environmentally friendly, nontoxic, and relatively low-cost method for gold and silver leaching from ores or concentrates. Full article

Industries such as mining, cokemaking, (petro)chemical and electroplating produce effluents that contain free cyanide (fCN = HCN + CN⁻). Currently, fCN is mainly removed by (physico)chemical methods or by biotreatment with activated sludge. Cyanide hydratases (CynHs) (EC 4.2.1.66), which convert fCN to the much less toxic formamide, have been considered for a mild approach to wastewater decyanation. However, few data are available to evaluate the application potential of CynHs. In this study, we used a new CynH from Exidia glandulosa (protein KZV92691.1 designated NitEg by us), which was overproduced in Escherichia coli. The purified NitEg was highly active for fCN with 784 U/mg protein, k_cat 927/s and k_cat/K_M 42/s/mM. It exhibited optimal activities at pH approximately 6–9 and 40–45 °C. It was quite stable in this pH range, and retained approximately 40% activity at 37 °C after 1 day. Silver and copper ions (1 mM) decreased its activity by 30–40%. The removal of 98–100% fCN was achieved for 0.6–100 mM fCN. Moreover, thiocyanate, sulfide, ammonia or phenol added in amounts typical of industrial effluents did not significantly reduce the fCN conversion, while electroplating effluents may need to be diluted due to high fCN and metal content. The ease of preparation of NitEg, its high specific activity, robustness and long shelf life make it a promising biocatalyst for the detoxification of fCN. Full article

The reaction of ammoniacal AgNO₃ solution (or aq. solution of [Ag(NH₃)₂]NO₃) with aq. NaClO₄ resulted in [Ag(NH₃)₂]ClO₄ (compound 1). Detailed spectroscopic (correlation analysis, IR, Raman, and UV) analyses were performed on [Ag(NH₃)₂]ClO₄. The temperature and enthalpy of phase change for compound 1 were determined to be 225.7 K and 103.04 kJ/mol, respectively. We found the thermal decomposition of [Ag(NH₃)₂]ClO₄ involves a solid-phase quasi-intramolecular redox reaction between the perchlorate anion and ammonia ligand, resulting in lower valence chlorine oxyacid (chlorite, chlorate) components. We did not detect thermal ammonia loss during the formation of AgClO₄. However, a redox reaction between the ammonia and perchlorate ion resulted in intermediates containing chlorate/chlorite, which disproportionated (either in the solid phase or in aqueous solutions after the dissolution of these decomposition intermediates in water) into AgCl and silver perchlorate. We propose that the solid phase AgCl-AgClO₄ mixture eutectically melts, and the resulting AgClO₄ decomposes in this melt into AgCl and O₂. Thus, the final product of decomposition is AgCl, N₂, and H₂O. The intermediate (chlorite, chlorate) phases were identified by IR, XPS, and titrimetric methods. Full article

Plasmas with dense concentrations of reactive species such as hydrated electrons and hydroxyl radicals are generated from focusing intense femtosecond laser pulses into aqueous media. These radical species can reduce metal ions such as Au³⁺ to form metal nanoparticles (NPs). However, the formation of H₂O₂ by the recombination of hydroxyl radicals inhibits the reduction of Ag⁺ through back-oxidation. This work has explored the control of hydroxyl radical chemistry in a femtosecond laser-generated plasma through the addition of liquid ammonia. The irradiation of liquid ammonia solutions resulted in a reaction between NH₃ and OH·, forming peroxynitrite and ONOO⁻, and significantly reducing the amount of H₂O₂ generated. Varying the liquid ammonia concentration controlled the Ag⁺ reduction rate, forming 12.7 ± 4.9 nm silver nanoparticles at the optimal ammonia concentration. The photochemical mechanisms underlying peroxynitrite formation and Ag⁺ reduction are discussed. Full article

Three different routes were used to infiltrate the pores of anodic porous alumina templates with silver nanoparticles, selected as an example of a bioactive agent. The three methods present a continuous grading from more physical to more chemical character, starting from ex situ filling of the pores with pre-existing particles, moving on to in situ formation of particles in the pores by bare calcination and ending with in situ calcination following specific chemical reactions. The resulting presence of silver inside the pores was assessed by means of energy dispersive X-ray spectroscopy and X-ray diffraction. The number and the size of nanoparticles were evaluated by scanning electron microscopy of functionalized alumina cross-sections, followed by image analysis. It appears that the best functionalization results are obtained with the in situ chemical procedure, based on the prior formation of silver ion complex by means of ammonia, followed by reduction with an excess amount of acetaldehyde. Elution of the silver content from the chemically functionalized alumina into phosphate buffer saline has also been examined, demonstrating a sustained release of silver over time, up to 15 h. Full article