Probing the deactivation and regeneration of ZnIn2S4 in photocatalytic degradation of tetracycline

ZnIn₂S₄ (noted as ZIS) has great potential in tetracycline degradation due to its suitable band gap structure and great light absorption capability. However, its serious photo-corrosion results in the deactivation of photocatalytic activity. In this work, we try our best to probe the deactivation and regeneration of ZnIn₂S₄ in photocatalytic degradation of tetracycline. EPR, XPS, and PL results reveal that the deactivation mechanism of ZIS is due to the breakage of Zn-S bonds which results in excessive sulfur vacancies. After choosing Na₂S as regenerant, the degradation rate in second cycle increased from 57.4 % to 88.1 % and improved from 30.3 % to 76.8 % in third cycle. Ab initio molecular dynamics simulations (AIMD) and density functional theory (DFT) calculations are further conducted for the regeneration mechanism. These results confirm that the negatively charged ions (HS⁻ and OH⁻ ions) produced by hydrolysis of the Na₂S are attracted to the positively charged sulfur vacancies, promoting the re-bonding of Zn-S bonds and thereby relieve excessive sulfur vacancies. This work not only provides a detailed discussion of performance deactivation caused by photo-corrosion of ZnIn₂S₄ but also offers new insights into the regeneration mechanism of ZnIn₂S₄.