Inorganic anions assisted on crystal transition of polymorphic ZnIn2S4 for enhanced photocatalytic tetracycline hydrochloride degradation and Cr(VI) reduction

A series of polymorphous ZnIn2S4 was successfully synthesized by changing the type of metal precursor and inorganic acid that adjust the pH value of hydrothermal reaction system to 1.0, and the mutual conversion between cubic and hexagonal phase had been triumphantly implemented under controllable conditions. Among them, the addition of acid mainly inhibits the production of In(OH)3, and the inorganic anions affect the crystal structure of the material under the same pH value, including crystal phase and crystal plane, which could be attributed to the electronegativity and polarity between inorganic anions (Cl− > NO3− > SO42−). ZIS-ZnCl2-pHH2SO4 had better photocatalytic performance and stability, the apparent quantum yield reached 18.45%, which the removal rate of tetracycline hydrochloride (HTC) and Cr(VI) reached 95.18% and 99.85% in 120 min, respectively. The relationship between the structure and properties of ZIS-ZnCl2-pHH2SO4 proved that SO42− can make cubic transform hexagonal phase, and promote the (1 0 2) crystal plane of hexagonal phase preferentially grow and expose more active sites, thus improving the photocatalytic activity. This work provides an effective method to construct different crystal structure of ZnIn2S4 with highly exposed active crystal phase.