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