Accelerated charge transfer in well-designed S-scheme Fe@TiO₂/Boron carbon nitride heterostructures for high performance tetracycline removal and selective photo-reduction of CO₂ greenhouse gas into CH₄ fuel

Designing and fabrication of smart hybrid multifunctional materials for energy/fuel production and environmental detoxification is indeed of great significance for sustainable development. Herein, we synthesized a new well-structured S-scheme heterostructure Fe@TiO₂/Boron Carbon nitride (FT/BCN) with high performance tetracycline degradation and selective CO₂ photo-reduction to CH₄. Under visible light irradiation, 96.3% tetracycline was degraded in 60 min using best performing FT30/BCN sample with a high 83.2% total organic carbon removal in 2 h. The tetracycline degradation rate for FT30/BCN composite catalyst was ∼7 times than bare boron carbon nitride (BCN). The impact of reaction parameters as pH, presence of interfering electrolytes, light source and water matrix was also investigated. The FT30/BCN photocatalyst shows dramatic improvement in CO₂ photoreduction as exhibited in 24.7 μmol g⁻¹ h⁻¹ CH₄ and 2.4 μmol g⁻¹ h⁻¹ CO evolutions with optimal 91.1% CH₄ selectivity. Pure BCN shows a poor 39.1% selectivity. Further, effect of alkali activation, CO₂/H₂O feed ratio, reducing agent and light source onto CH₄ production and selectivity was also investigated. The CH₄ evolution and selectivity was improved because of enhanced visible light absorption, high adsorption potential, charge carrier separation and high reducing power of photogenerated electrons induced by an effective S-scheme heterojunction between Fe@TiO₂ and boron carbon nitride. An S-scheme (step-scheme) charge transfer mechanism is here operative both during tetracycline removal and CO₂ reduction. The drug degradation route and photocatalytic mechanism for antibiotic removal and CO₂ reduction was also predicted.