Scalable synthesis of submicron spherical silver powders mediated by sulfate ions: Dual-function protection mechanism for morphology control and simplified wastewater treatment

Conventional silver powder production routes, which reduce silver nitrate solution in the presence of a polymer protective agent, complicate subsequent powder cleaning and wastewater treatment. This study proposes a sulfate-based inorganic protective agent (utilizing Ag 2 SO 4 precursor replacement) that serves dual functions: morphology stabilization and wastewater treatment simplification. This innovation enables the environmentally friendly preparation of sub-micron spherical silver powder. The effects of peristaltic pump flow rate, pH value, temperature, concentration ratio of oxidant to reducing agent on the particle size and morphology of silver powder were systematically investigated. The resulting silver powder exhibited an average particle size of 0.64 ± 0.05 μm and excellent thermal stability (weight loss rate < 0.50 % up to 1000 °C). Mechanistic analysis via combined XRD, Zeta potential measurements, and density functional theory (DFT) calculations revealed that SO 4 2− preferentially adsorbs on Ag(111) facet via chemisorption. Moreover, the production wastewater can be directly treated biochemically after calcium oxide precipitation and air-stripping treatment. Furthermore, the scale-up experiment (single yield 50.0 g) showed that the performance of the experimental product was consistent with the lab-scale results, indicating that the process has good reproducibility.