Can Cu₂ZnSnS₄ nanoparticles be used as heterogeneous catalysts for sulfadiazine degradation?

As a quaternary copper-based semiconductor, Cu₂ZnSnS₄ (CZTS) is drawing growing attention and is anticipated as a promising photocatalyst, thanks to its large absorption coefficient, exceptional photostability, and theoretical power conversion efficiency. However, CZTS has never been used as an activator of H₂O₂ for the degradation of refractory organic pollutants. In this study, the synthesis of CZTS nanoparticles obtained with diverse morphologies and crystallinities using solvents of deionized water (CZTS-W) and ethylene glycol (CZTS-EG) was examined in the activation of H₂O₂ to degrade sulfadiazine (SDZ). The results revealed that CZTS coupled with H₂O₂ could be an effective system for the degradation of SDZ. Compared to CZTS-EG, CZTS-W presented higher reusability in consecutive cycles with negligible leaching of copper. Reactive oxygen species quenching tests and electron paramagnetic resonance analyses illustrated that •O₂^-, •OH, and ¹O₂ contributed to the degradation of SDZ, and ¹O₂ prevailed over •O₂^- and •OH. The mechanistic investigation showed that efficient degradation could be associated to the effective recycling of Cu(II)/Cu(I) and low-valent/high-valent sulfur. Also, the degradation pathways of SDZ have been proposed through the detection of intermediate products. This study manifests that CZTS synthesized using deionized water is encouraging for the elimination of organic pollutants.