Photocatalytic mechanism and performance of a novel wool flake-BiFeO₃nanosheet-TiO₂core-shell-structured composite...

In this study, BiFeO₃(BFO) nanosheets ground from BFO particles were first incorporated with wool flakes to construct sandwich-like wool-BFO composites using the vibration-assisted ball milling technique in freezing conditions. The wool-BFO composites were then loaded with a thick layer of TiO₂nanoparticles to prepare the core-shell-structured wool-BFO-TiO₂composites using a hydrothermal synthesis process. The microstructure of the core-shell wool-BFO-TiO₂composites and its photocatalytic applications were systematically examined using a series of characterization methods. Trapping experiments and electron spin resonance spectra were also employed to judge the active radical species like superoxide radicals (·O₂^-), singlet oxygen (¹O₂), holes (h⁺), and hydroxyl radicals (·OH) using benzoquinone, furfuryl alcohol, ethylenediamine tetraacetic acid, and tert-butanol as the scavengers, respectively. The photodegradation performance of the wool-BFO-TiO₂composites was measured using more resistant methyl orange (MO) dye as the pollutant model. In comparison with the wool-TiO₂or wool-BFO composites, the superior photocatalytic properties of the wool-BFO-TiO₂composites under visible light irradiation were attributed to the presence of mesopores and macropores, the large specific surface area and intimate interface between wool-BFO composites and TiO₂nanoparticles, the coexistence of Fe³⁺, Fe²⁺, Bi³⁺, Bi^(3-x)+, Ti⁴⁺, and Ti³⁺species, and the strong visible light harvesting, thus leading to the fast separation of photogenerated electron-hole pairs. The wool-BFO-TiO₂composites could be used for the repeated photodegradation of organic pollutants and be recycled easily using a magnet. The active radical species of the wool-BFO-TiO₂composites were ·O₂^-and¹O₂rather than ·OH and h⁺, which were involved in the photodegradation of MO dye under visible light irradiation.