CuS Nanoparticles Trigger Sulfite for Fast Degradation of Organic Dyes under Dark Conditions

CuS nanoparticles (CuS NPs) were synthesized by a simple precipitation method using rice starch water as a capping and reducing agent. The phase composition, morphology, absorbance, chemical bonds, and chemical states of the CuS NPs were investigated systematically and then examined for dye degradation catalytic activity with or without sulfite (SO₃ ^2-) under dark conditions. Herein, we observed two reaction trends after the addition of SO₃ ^2- in a CuS NPs/dye system, first substantially enhanced dye degradation and second greater degradation activity between reaction time interval "t" 0-12 min. The redox cycling of Cu(II)/Cu(I) and oxidized sulfur (SO ^2-) species on the surface of CuS NPs played a major role for the activation of SO₃ ^2- and generation and transformation of a sulfite radical (^•SO₃ ^-) into a sulfate radical (^•SO₄ ^-). Scavenging studies of reactive oxygen species (ROS) revealed that ^•SO₄ ^- was major reactive species involved in dye degradation. Our study showed that SO₃ ^2- acted as a source and CuS NP surface acted as an SO₃ ^2- activating agent for the generation of ^•SO₄ ^-, which degrades the dyes. The activation pathway of SO₃ ^2- and generation pathway of relevant ROS were proposed.