Fluorinated-TiO₂/Mn_0.2Cd_0.8S S-Scheme Heterojunction with Rich Sulfur Vacancies for Photocatalytic Hydrogen Production

The quick recombination of photogenerated carriers and the high surface reaction barrier are two important aspects influencing photocatalytic hydrogen generation. In this paper, a sulfur vacancy-modified two-dimensional (2D) fluorinated-TiO₂ nanosheet/Mn_0.2Cd_0.8S (F-TiO₂/MCS) S-scheme heterojunction was synthesized by a simple hydrothermal method to accelerate photogenerated electron transfer. The formation of an S-scheme heterojunction between MCS nanoflowers and 2D F-TiO₂ enhances the efficacy of photocatalytic hydrogen generation by facilitating the separation of photogenerated electron-hole pairs. Meanwhile, the sulfur vacancies of F-TiO₂/MCS change the local electronic structure of the heterojunction surface by capturing photogenerated electrons, resulting in a photocatalytic hydrogen evolution rate for F-TiO₂/MCS of 3197 μmol g^-1 h^-1, which is 4.42 times greater than that of the pure MCS. Experimental measurements and density functional theory (DFT) calculations show that the mutual synergy between the S-scheme heterojunction and the sulfur vacancies not only provides abundant H₂ adsorption active sites but also promotes interfacial charge separation and migration, which improves the photocatalytic performance of the F-TiO₂/MCS composite. This work holds significance for the photocatalytic hydrogen production of sulfur vacancy-modified S-scheme heterojunctions.