Construction of magnetic Fe₃O₄-BiOBr/Graphene aerogel and Cr(VI) wastewater purification

In order to improve the photogenerated electron-hole separation and recycling ability of single semiconductor powder material, based on the functionally synergistic effect, magnetic graphene aerogel (Fe₃O₄-BiOBr/graphene) modified by Fe₃O₄-BiOBr had been facilely prepared by one-step hydrothermal process by dispersing Fe₃O₄-BiOBr composite in aqueous solution of graphene oxide containing lysine. The Fe₃O₄-BiOBr composite was synthesized in non-miscible solvent system under room-temperature, in which nano Fe₃O₄, firstly prepared by co-precipitation method using Fe³⁺/Fe²⁺ salt under the action of ammonia water with a certain concentration, was dispersed in n-octane containing hexadecyl trimethyl ammonium bromide (CTAB) for providing Br^–, interacting with an aqueous solution containing bismuth nitrate and citric acid adding drop by drop. The crystal structure, morphology and catalytic activity of the samples were characterized by XRD, Raman, XPS, SEM, TEM, and UV-Vis spectra. Fe₃O₄-BiOBr/graphene composites, in which spherical Fe₃O₄ with a size of 10-25 nm are evenly embedded in layered BiOBr flakes, and they interact with graphene, overall, have showed a sphere-sheet-cavity structure. Fe₃O₄-BiOBr/graphene composites have favorable visible light absorption efficiency and Cr(VI) photocatalytic activity. The photocatalytic activity of Cr(VI) could achieve about 100% within 30 min, which is higher than that of single magnetic Fe₃O₄. This phenomenon maybe origin from the introduction of Fe₃O₄-BiOBr heterostructure and conductive graphene as well as their good interfacial interaction within them, effectively promoting the separation efficiency of photogenerated electrons and holes between Fe₃O₄-BiOBr/graphene composite.