Photocatalytic mechanism and performance of a novel wool flake–BiFeO3 nanosheet–TiO2 core–shell-structured composite photocatalyst

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.