This paper, written by researchers from Wuhan University of Technology and others, discusses BiOX (X = Cl, Br, I) nanostructures: Mannitol-mediated microwave synthesis, visible light photocatalytic performance, and Cr(VI) removal capacity. The paper is published in an important journal < Journal of Colloid and Interface Science >. IF：5.091.

In recent years, the research work of microwave chemical instrument used in the synthesis of materials has become a hot direction of scientific research, which has been paid great attention to by many scholars!

A facile microwave irradiation method has been successfully developed for the controllable fabrication of BiOX (X = Cl, Br, I) nanostructures in mannitol solution. The morphology and size of BiOX nanostructures could be readily tailored by adjusting the amount of halide, reaction precursor, and mannitol concentration. Mannitol molecule acts as both a capping agent and a cohesive agent in the formation of BiOX nanostructures. A possible two-stage formation mechanism was discussed based on the morphology evolution of BiOI nanostructures obtained in mannitol solution with different concentrations. The as-synthesized BiOX nanostructures exhibit much higher photocatalytic activities than that of commercial TiO2. In particular, flower-like BiOX hierarchical nanostructures display the best photocatalytic performance, which is mainly ascribed to their unique hierarchical structure, high BET surface area, and large band gap. Moreover, BiOX nanostructures also demonstrate superior Cr(VI) removal capacity. The Cr(VI) adsorption behavior was also analyzed by the Langmuir and Freundlich adsorption isotherms.

In summary, BiOX (X = Cl, Br, I) nanostructures have been successfully synthesized via a facile and rapid microwave irradiation method in mannitol solution. The sizes, morphologies, and struc- tures of BiOX nanostructures could be easily controlled by varying the amount of halide, reaction precursor, and mannitol concentration. Mannitol plays a critical role in the modulating, the formation and assembly of BiOX nanostructures, which serves as not only a capping agent but also a cohesive agent. A possible two-stage formation mechanism was discussed based on the morphology evolution of BiOI nanostructures under different mannitol concentrations. The obtained BiOX nanostructures exhibit shapeassociated improved photocatalytic performance for RhB degradation under visible light irradiation. Flower-like BiOX hierarchical nanostructures show the highest photocatalytic activity, which is mainly ascribed to their unique hierarchical structure, wide band gap, and large BET surface area. In addition, the as-synthesized BiOX nanostructures also exhibit remarkable Cr(VI) removal capacities. This work not only demonstrates a facile and fast pathway to fabricate BiOX nanostructures, but also provides a new approach for the controllable synthesis of bismuth-containing nanostructures with tunable sizes, morphologies and structures. Moreover, their excellent photocatalytic activities and heavy metal Cr(VI) removal capacities should be significantly valuable for further practical application in water treatment.

In a typical synthesis, 0.485 g (1 mmol) bismuth nitride (Bi(NO3)3_5H2O) was dissolved into 30 mL mannitol solution (0.1 M), which contained 0.058 g NaCl (1 mmol). After sonication for several minutes, the mixture was heated to 110 _C within 3 min and then kept at this temperature for 27 min by a microwave reactor with a microwave irradiation power of 500W (XH-300A, Beijing Xianghu Technology Co., Ltd.). After microwave treatment, the mixture was cooled down to room temperature naturally. A white precipitate was collected by centrifugation and washed with deionized water and ethanol for six times. Finally, the product was dried in a desiccator for a few days for further characterization (SC1). Other BiOX samples were also prepared under identical conditions by changing the amount of halide, reaction precursor (KBr, KI, CTAC, CTAB), and mannitol concentration. The detailed experimental parameters are listed in Table 1.