SnO2/SnS2 heterojunctions anchored on biochar through the −C=Sn-bonds: ∙CO2 – cooperation with e⁻ to effectively convert Cr(VI)

Highlights: • SnO₂/SnS₂ heterojunctions were anchored on biochar via the −C=Sn-bonds were prepared. • The −C=Sn-bonds effectively modulated the separation of photo-induced carriers. • Oxalate activated by the −C=Sn-bonds was effectively converted to ∙CO₂⁻ • The synergistic effect of e⁻ and ∙CO₂⁻ resulted in the rapid consumption of Cr(VI). • The system exhibited an ideal reusability with removal efficiency. -- Abstract: Controlling the migration behavior of photogenerated carriers by designing the microstructure of materials remains a significant challenge. In this work, the solvothermal method was used to fabricate a SnO₂/SnS₂ heterojunction anchored on biochar through −C=Sn#-bonds between biochar and SnS₂, as demonstrated by X-ray photoelectron spectroscopy characterization. DFT calculations further confirmed −C=Sn-bonds can shorten theoretical band gap of SnS₂@biochar from 1.01 eV to 0.66 eV and provide a pathway for swift electron migration, which can effectively modulate the separation of photo-induced carriers and promote the generation of e⁻ and h⁺. Additionally, the oxalate activated by −C=Sn-bonds can effectively capture h⁺ and produce abundant ∙CO₂⁻ free radicals. When the obtained composites were used as photocatalysts, Cr(VI) was thoroughly reduced by the SnO₂/SnS₂@biochar composite with a molar ratio of SnO₂ and SnS₂ of 2 within 20 min under visible light irradiation when oxalate was 1.0 mM (CSO-2/H₂C₂O₄-1). Furthermore, CSO-2/H₂C₂O₄-1 exhibited excellent reusability, and the degradation efficiency of Cr(VI) remained above 91.71% after five cycles. The remarkable photocatalytic properties can be ascribed to the synergistic effects of e⁻ and ∙CO₂⁻. This work proposes a new strategy for the preparation of an applied photocatalyst with a high separation rate of photoinduced carriers.