Construction of S-scheme heterojunction within Sn QDs/TiO2@N, O-containing biochar composite photocatalyst for efficient removal of dye and antibiotic

Semiconductor titanium dioxide (TiO ₂) has garnered significant attention in photocatalysis field, but the wide bandgap and fast recombination of photogenerated electron-hole pairs severely hamper its extensive application. Herein, we present a novel biomass-assisted strategy to construct S-scheme heterojunction tin quantum dots-modified titanium dioxide@nitrogen, oxygen-containing biochar composite photocatalyst (Sn QDs/TiO ₂@biochar). The influence of pyrolysis temperature, biomass amount, and Sn content on adsorptive and UV-/Vis-photocatalytic performance of Sn QDs/TiO ₂@biochar were systematically optimized. The optimally-prepared catalyst displays a full light absorptive response feature and improved adsorptive and UV-/Vis-photocatalytic performance in the removal of high concentration methylene dye and tetracycline hydrochloride. The excellent performance of Sn QDs/TiO ₂@biochar is attributed to the enhanced synergic effects among many factors, such as multi-functions of each component, series size quantum effects of Sn QDs, heterojunctions, especially S-scheme heterojunction between Sn QDs and TiO ₂. Furthermore, a plausible photocatalytic mechanism was proposed. This study may provide a simple and sustainable approach for constructing environmentally friendly, cost-effective, and high-performance photocatalysts.