Visible-light-assisted peroxydisulfate activation over Ag6Si2O7/Cu(II)-modified palygorskite composite for the effective degradation of organic pollutants by radical and nonradical pathways

Photoassisted persulfate activation (PPA) is highly efficient oxidation process, but the eligible catalysts are scarce. Herein, a visible-light-responsive Ag₆Si₂O₇ was anchored on Cu(II)-exchanged attapulgite (Cu-Pal) via a facile precipitation-deposition method to construct a novel PDS activator. The synthesized catalyst was systemically analyzed by a series of characterization techniques. The results revealed that Ag₆Si₂O₇ nanoparticles were evenly dispersed on Cu-Pal to form heterojunction. 16%-Ag₆Si₂O₇/Cu-Pal, an optimal catalyst exhibited excellent catalytic performance and stability in the visible-light-assisted PDS activation for AR18 degradation. The influences of reaction parameters on this process were investigated. Under the optimal conditions ([catalyst] = 1.0 g L^-1, [PDS] = 3.9 mM, pH_i = 5.1), 50 mg L^-1 of AR18 was completely degraded within 30 min. More importantly, quenching experiments and EPR tests revealed that besides the common SO₄^•- and •OH, ¹O₂ and O₂^•- were generated as main reactive oxygen species in the PPA by 16%-Ag₆Si₂O₇/Cu-Pal. Moreover, it was found that surface hydroxyl groups of the catalyst and copper species incorporated in Pal could significantly influence PDS activation and ROS generation. Based on these results, together with PDS decomposition, fluorescent probe analysis, and XPS analysis of the used catalyst, the possible mechanisms of the PPA by 16%-Ag₆Si₂O₇/Cu-Pal were proposed. Finally, the versatility and practicability of the established PPA process were verified by degrading other organic contaminants and testing effects of the coexisting anions and water matrices on AR18 degradation. This study may provide new insights for designing and developing the efficient heterogeneous catalysis for wastewater treatment via persulfate-based AOP.