Synthesis of a BiVO4/SnS2/Bi2S3 ternary heterojunction via ion exchange: Experimental and DFT study on the synergistic photocatalysis for Cr(VI) reduction and tetracycline degradation

In response to the rising severity of co-pollution from heavy metal ions and organic antibiotics in water, creating efficient synergistic removal technologies has become a critical research direction in environmental catalysis. In this study, a BiVO 4 /SnS 2 /Bi 2 S 3 ternary heterojunction photocatalyst with a broad spectral response was successfully constructed through a hierarchical construction strategy, using a hydrothermally synthesized BiVO 4 /SnS 2 binary heterojunction as the precursor, followed by in-situ growth of narrow-bandgap Bi 2 S 3 nanoparticles via a room-temperature ion exchange method. Characterization results from XRD, TEM and XPS confirmed that SnS 2 nanosheets and Bi 2 S 3 nanoparticles were distributed on the BiVO 4 surface, forming a tightly contacted heterojunction interface. The sequential introduction of SnS 2 and Bi 2 S 3 significantly increased the specific surface area of the material (to 14.723 m 2 /g). Optical performance tests demonstrated that the ternary heterojunction exhibited substantially enhanced visible light absorption, with the bandgap narrowing to 2.21 eV. Electrochemical tests revealed a significant reduction in the interfacial charge transfer resistance and a marked improvement in the charge carrier separation efficiency. Photocatalytic performance evaluation indicated that under simulated solar irradiation, BV/SN/BS(1 h) achieved a Cr(VI) reduction rate constant (0.07032 min −1 ) over 15 times higher than that of pure BiVO 4 and a TC degradation rate constant (0.00520 min −1 ) approximately 1.3 times higher. In the Cr(VI)-TC combined system, a significant synergistic degradation effect was observed, with the Cr(VI) reduction rate constant further increasing to 0.09252 min −1 and the TC degradation rate constant rising to 0.01471 min −1 . Notably, EPR tests did not detect •O 2 − or •OH radicals. DFT calculations combined with experimental characterization revealed the formation of a type-II heterojunction among BiVO 4 , SnS 2 and Bi 2 S 3 , in which electrons and holes migrate in opposite directions, achieving efficient charge carrier separation. Cr(VI) and TC act as mutual sacrificial agents during the reaction process, further enhancing the photocatalytic efficiency. This study provides a novel material construction strategy and theoretical basis for designing efficient photocatalytic systems aimed at the synergistic degradation of heavy metal-organic pollutants from complex water bodies.