Defects-engineering of magnetic γ-Fe2O3 ultrathin nanosheets/mesoporous black TiO2 hollow sphere heterojunctions for efficient charge separation and the solar-driven photocatalytic mechanism of tetracycline degradation

Defect-engineered magnetic γ-Fe2O3 ultrathin nanosheets/mesoporous black TiO2 hollow sphere heterojunctions (γ-Fe2O3/b-TiO2) are fabricated by a metal-ion intervened hydrothermal technique and high-temperature hydrogenation, which exhibit wide-spectrum response and magnetic separation. The specific surface area, pore size and pore volume of the resultant γ-Fe2O3/b-TiO2 with hollow structure are ∼63 m2 g−1, 10.5 nm and 0.14 cm3 g−1, respectively. After surface hydrogenation, α-Fe2O3 nanosheets are converted to γ-Fe2O3 ultrathin nanosheets (∼6 nm) combined with the formation of surface defects. The ultrathin nanosheet structure facilitates the surface engineering and also favors the diffusion and transportation of photogenerated charge carriers. The apparent rate constant (k) of defect-engineered γ-Fe2O3/b-TiO2 photocatalytic degradation biotoxic tetracycline is ∼3 times higher than that of α-Fe2O3/b-TiO2 under AM 1.5 irradiation. The enhancement is attributed to the introduction of narrow bandgap unit-cell-thick γ-Fe2O3 nanosheets, the hollow structure and the defect engineering, which are beneficial to solar-light-harvesting and rapid electron transport, and spatial separation of photogenerated charge carriers. The photocatalytic degradation mechanism is also proposed. The novel magnetic γ-Fe2O3/b-TiO2 heterojunction is a promising photocatalyst for recovering the domestic sewage in environment.