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.