Construction of a recyclable dual-responsive TiO2-based photocatalyst modified with ZnIn2S4 nanosheets and zinc phthalocyanine for Cr(VI) reduction under visible light

This study synthesized a recyclable dual-responsive core–shell photocatalyst Fe 3 O 4 @SiO 2 @TiO 2 @ZnIn 2 S 4 /ZnPc   (FSTZP) used for hexavalent chromium (Cr   (VI)) reduction. Core-shell Fe 3 O 4 @SiO 2 @TiO 2   (FST) was prepared and modified with ZnIn 2 S 4 and zinc-tetra   ( N -carbonylacrylic)   aminephthalocyanine (ZnPc) to obtain FSTZP and characterized by XRD, XPS, SEM, HRTEM and UV–vis DRS. In FSTZP, ZnIn 2 S 4 could provide more adsorption active sites and promote charge-carrier separation; ZnPc would efficiently use visible light to transfer energy. Both of ZnIn 2 S 4 and ZnPc in FSTZP could improve the light-harvesting resulting in excellent photocatalytic performance of FSTZP towards Cr   (VI) reduction and pollutant degradation. The highest reduction efficiency of Cr   (VI) by FSTZP   (0.3 g/L) was up to 96.4% in 60 min at pH = 6. The removal efficiencies of Rhodamine B (RhB), Methylene blue (MB), Methyl Orange   (MO) and Tetracycline hydrochloride   (TC•HCl) by FSTZP   (0.3 g/L) under visible light were 99%, 99%, 95% and 86% in 40 min at pH = 6. Meanwhile, almost all of Cr   (VI) and organic molecules in the coexistence system could be removed by FSTZP under visible light. FSTZP also presented the adsorption property and the mechanism of dual-responsive FSTZP for Cr   (VI) reduction and organic pollutants removal was explored. Moreover, as an efficient photocatalyst, FSTZP still maintained stability after reused for fourth photocatalytic cycle by magnetic recovery. This study was devoted to develop an efficient photocatalyst suitable for removing Cr   (VI) and organic pollutants.