Construction of S-scheme heterojunction based on an organic hybrid silver tin selenide with strong affinity to Cr(VI) for efficient photocatalytic Cr (VI) reduction

Owing to the open-framework structures and the affinity of protonated organic amines to Cr(VI) oxyanions, the immense potential of organic hybrid metal chalcogenides for photocatalytic Cr(VI) reduction deserves attention. However, the photocatalytic Cr(VI) reduction properties of such materials are rarely explored, thus more efforts need to be given to advance the research. Herein, we synthesized an organic hybrid silver tin selenide [CH3NH3]2[H3O]Ag5Sn4Se12 center dot C2H5OH (MSTS), whose structure featured a three-dimensional framework with regular open channels, where the protonated [CH3NH3]+ and [H3O]+ cations were located. After the MSTS bulk crystals were ultrasonically crushed into nanoparticles, PEDOT was coated on the surface of the MSTS nanoparticles, and MSTS@PEDOT-x (x = 40, 60, 80) composites were obtained. The in situ irradiated XPS, EPR tests, DFT calculations, and radical trapping experiments proved the S-scheme heterojunction formed between MSTS and PEDOT. The S-scheme heterojunction consumed the holes from MSTS, but saved the electrons with high reduction ability to reduce Cr(VI). Consequently, MSTS@PEDOT-x showed outstanding photocatalytic performance for Cr(VI) reduction. Particularly, MSTS@PEDOT-60 took only 16 min to completely reduce Cr(VI) (100 mg/L), giving an extremely high Cr(VI) conversion rate of 375 mg/(g center dot h), which was superior to most of the reported photocatalysts. Moreover, MSTS@PEDOT-60 possessed excellent anti-interference ability and cycling stability. In addition, MSTS@PEDOT-60 can maintain high photocatalytic efficiency under sunlight during most hours of the daytime. Our research presents new perspectives on the design of the photocatalysts based on organic hybrid metal chalcogenides for Cr(VI) reduction.