Photocatalytic mechanism and performance of a novel wool flake-BiFeO3 nanosheet-TiO2 (wool-BFO-TiO2) core-shell structured composite photocatalyst.

In this study, BiFeO3 (BFO) nanosheets ground from BFO particles were first incorporated with wool pallets to construct the sandwich-like wool-BFO composites using the vibration-assisted ball milling technique in freezing condition. The wool-BFO composites were then loaded with a thick layer of TiO2 nanoparticles to prepare the core-shell structured wool-BFO-TiO2 composites using the hydrothermal synthesis process. The microstructure of the core-shell wool-BFO-TiO2 composites and its photocatalytic applications were systematically examined by using a series of characterization methods. The trapping experiments and electron spin resonance (ESR) spectra were also employed to judge the active radical species like superoxide radical (O2-), singlet oxygen (1O2), hole (h+), and hydroxyl radical (OH) by using benzoquinone (BQ), furfuryl alcohol (FFA), ethylenediamine tetraacetic acid (EDTA), and tert-butanol (TBA) as the scavengers, respectively. The photodegradation performance of the wool-BFO-TiO2 composites was measured using more resistant methyl orange (MO) dye as the pollutant model. In comparison with the wool-TiO2 or wool-BFO composites, the superior photocatalytic properties of the wool-BFO-TiO2 composites under visible light irradiation were attributed to the presence of mesopores and macropores, the large specific surface area, and the intimate interface between wool-BFO composites and TiO2 nanoparticles, 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 photo-generated electrons and holes pairs. The wool-BFO-TiO2 composites could be used for the repeatedly photodegradation of organic pollutants, while be recycled easily by using a magnet. The active radical species of the wool-BFO-TiO2 composites were O2- and 1O2 rather than OH and h+, which were involved in the photodegradation of MO dye under visible light irradiation.