Indium surface gradient doped ZnS for efficient photodegradation under visible-light irradiation

ZnS generally exhibits poor photocatalytic activity due to its wide bandgap and rapid carrier recombination. In this work, indium surface gradient doped ZnS was successfully synthesized through a chemical vapor strategy (In₂O₃ served as the evaporation source). Indium surface doping not only expanded the absorption edge to the visible-light region by forming impurity levels, but also efficiently enhanced carrier separation and transfer ability (much superior to In element bulk doping). In addition, it resulted in a more negative conduction band position, which was conducive to the generation of superoxide radicals as the main active species through reduction reactions. Thereby, the optimal indium surface gradient doped ZnS achieved a degradation rate of ∼70% for levofloxacin within 1 h under visible-light irradiation, which was ∼3.3 times that of indium bulk doped ZnS. It also exhibited good dye degradation activity, and its degradation pathway for levofloxacin was also investigated. It is hoped that this work can provide a new perspective for the design of surface-doped photocatalysts.