Tuned s-scheme cu2 s_tio2 _wo3 heterostructure photocatalyst toward s-metolachlor (S-mch) herbicide removal

Abstract

A dual S-scheme Cu2 S_TiO2 _WO3 heterostructure was constructed by sol–gel method using a two-step procedure. Due to the synthesis parameters and annealing treatment the het-erostructure is characterized by sulfur deficit and oxygen excess allowing the passivation of oxygen vacancies. The photocatalytic activity was evaluated under UV and UV–Vis irradiation scenarios using S-MCh as reference pollutant. The heterostructure is composed on orthorhombic Cu2 S, anatase TiO2 and monoclinic WO3 with crystallite sizes varying from 65.2 Å for Cu2 S to 97.1 Å for WO3. The heterostructure exhibit a dense morphology with pellets and particle-like morphology closely combined in a relatively compact assembly. The surface elemental composition indicate that the heterostructure maintain a similar atomic ratio as established during the synthesis with a slight sulfur deficit due to the annealing treatments. The results indicate that the three-component heterostructure have higher photocatalytic efficiency (61%) comparing with two-component heterostructure or bare components. Moreover, Cu2 S_TiO2 _WO3 exhibit a superior constant rate (0.114 s−1) due to the high concentration of photogenerated charge carriers, efficient charge separation and migration.