Hierarchical S-Scheme Heterostructure of CdIn2S4@UiO-66-NH2 toward Synchronously Boosting Photocatalytic Removal of Cr(VI) and Tetracycline

Developing highly efficient photocatalysts toward synchronously removing heavy metals and organic pollutants is still a serious challenge. Herein, we depict hierarchical S-scheme heterostructured photocatalysts prepared via in situ anchoring UiO-66-NH2 nanoparticles onto the CdIn2S4 porous microsphere structures assembled with numerous nanosheets. In the mixed system of Cr(VI) and tetracycline (TC), the optimal photocatalyst (CIS@U66N-30) shows remarkable photocatalytic activities toward the synchronous removal of Cr(VI) (97.26%) and TC (close to 100% of) under visible-light irradiation for 60 min, being the best removal rates among those of the reported photocatalysts, and sustains the outstanding stability and reusability. Its reaction rate constants of Cr(VI) reduction and TC degradation are about 2.06 and 1.58 folds that in the single Cr(VI) and TC systems, respectively. The enhanced photocatalytic activities of CIS@U66N-30 mainly result from the following synergism: (1) its hierarchical structure offers abundant active sites, and the S-scheme migration mechanism of charge carriers in the heterostructure accelerates the separation and migration of the useful photoinduced electrons and holes with the high redox capability; (2) Cr(VI) and TC can serve as the electron scavenger for TC oxidation degradation and the hole and •OH scavenger for Cr(VI) reduction, respectively, further enhancing the separation and utilization efficiency of photoinduced electrons and holes. Besides, the possible TC degradation pathway and plausible S-scheme photocatalytic mechanism over CIS@U66N-30 for the concurrent elimination of Cr(VI) and TC are proposed.