Defects-engineering of magnetic gamma-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 gamma-Fe2O3 ultrathin nanosheets/mesoporous black TiO2 hollow sphere heterojunctions (gamma-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 gamma-Fe2O3/b-TiO2 with hollow structure are similar to 63 m(2) g(-1), 10.5 nm and 0.14 cm(3) g(-1), respectively. After surface hydrogenation, alpha-Fe2O3 nanosheets are converted to gamma-Fe2O3 ultrathin nanosheets (similar to 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 gamma-Fe2O3/b-TiO2 photocatalytic degradation biotoxic tetracycline is similar to 3 times higher than that of alpha-Fe2O3/b-TiO2 under AM 1.5 irradiation. The enhancement is attributed to the introduction of narrow bandgap unit-cell-thick gamma-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 gamma-Fe2O3/b-TiO2 heterojunction is a promising photocatalyst for recovering the domestic sewage in environment.