Peroxymonosulfate enhanced photocatalytic decomposition of silver-cyanide complexes using g-C3N4 nanosheets with simultaneous recovery of silver

Abstract

Due to the complicated chemical nature and toxicity of noble metal-cyanide complexes, the appropriate treatment of wastewaters contaminated with such pollutants is challenging. In this study, the simultaneous decomposition of Ag-cyanide and recovery of precious Ag from Ag-cyanide aqueous solution was investigated using a synergistic peroxymonosulfate (PMS)/g-C3N4 nanosheets system under visible light (λ > 400 nm). The combination of g-C3N4 (1.0 g/L) and PMS (0.5 mM) resulted in higher Ag-cyanide (0.45 mM) decomposition under visible light and Ag recovery efficiencies (74% and 68%, respectively) compared with single PMS oxidation or g-C3N4 photocatalytic oxidation within 150 min. Ag species deposited on g-C3N4 in the form of metallic Ag° and Ag2O may also further improve the decomposition of Ag-cyanide complexes. Ag species deposited on g-C3N4 can enhance the separation of electron/hole charges of the photoactive g-C3N4. Quenching of reactive oxygen species (ROS) experiments and electron spin resonance (ESR) analysis showed the generation of SO4·−, OH, O2−, 1O2 and e- species in this system, among them O2−, 1O2, and e- were the most active species for the decomposition of Ag-cyanide complexes.