Synthesis of Ag/TiO2 photocatalysts via direct photodeposition of silver from industrial electroplating wastewater

Silver-containing wastewater from cyanide-based electroplating processes represents both an environmental burden and an underutilized resource. Conventional silver recovery methods often generate intermediate products that require further refining before reuse. This study demonstrates a proof-of-concept waste-to-material strategy in which real silver-containing electroplating wastewater was used directly as the Ag source for photodeposition onto TiO 2 , without adding high-purity silver precursors. Structural analyses confirmed the formation of Ag-modified TiO 2 with increase Ag nanoparticle sizes from 5.29 ± 3.49 to 13.19 ± 5.60 nm, corresponding to Ag contents of 0.82, 3.54, and 8.69 wt% for Ag/TiO 2 -1, Ag/TiO 2 -2, and Ag/TiO 2 -3, respectively. Ag incorporation also reduced the apparent bandgap from 3.14 eV for pristine TiO 2 to 2.96 eV for Ag/TiO 2 -3. Under UV irradiation, all photocatalysts achieved a substantial decrease in Staphylococcus aureus viability (99.9%) at 1 mg/mL, while Ag/TiO 2 -3 showed the strongest antibacterial activity at the lowest tested concentration of 0.1 mg/mL. Consequently, Ag/TiO₂-3 was identified as the optimal composite and chosen for further mechanistic studies. These studies indicated a non-lytic killing pathway driven by enhanced intracellular reactive oxygen species generation and membrane permeabilization. This work demonstrates the feasibility of converting silver-containing industrial wastewater into functional Ag/TiO 2 photocatalysts and support broader strategies for environmental remediation.