Tuned S-Scheme Cu₂S_TiO₂_WO₃ Heterostructure Photocatalyst toward S-Metolachlor (S-MCh) Herbicide Removal

A dual S-scheme Cu₂S_TiO₂_WO₃ heterostructure was constructed by sol-gel method using a two-step procedure. Due to the synthesis parameters and annealing treatment the heterostructure 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 Cu₂S, anatase TiO₂ and monoclinic WO₃ with crystallite sizes varying from 65.2 Å for Cu₂S 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, Cu₂S_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.