Morphology-controlled Preparation And Photocatalytic Performance Of Bismuth-based Oxometalates

Semiconductor photocatalysis has attracted immense interest over recent decades and has been applied to eliminate the organic pollutants in an environmentally friendly manner, either in water or air. As an ef?cient and commercially cheap photocatalyst, titanium dioxide(Ti O2) has been intensively studied. However, Ti O2 possesses a wide band gap of 3.2 e V, allowing the material harvest UV light, which accounts for 5% of the incoming solar energy. Moreover, the photogenerated electrons and holes of Ti O2 can recombine rapidly, which results in the low quantum efficiency. It is still a challenge to engineer a robust, cheap and stable photocatalyst that exhibits wide visible-light response. Besides the study on Ti O2 modi?cation, a great deal of effort has been made to develop non-Ti O2-based photocatalysts with visible light response, in which bismuth-based oxometalates or oxononmetalates has attracted much attention due to its special electronic structure. In the present work, we focus on development of new and efficient bismuth-based photocatalysts, such as bismuth titanate(Bi12Ti O20) and bismuth oxyhalide(Bi OBr), by one-step hydrothermal treatment. The relationship between reaction conditions and the crystal phase and morphology of the photocatalysts was investigated, and the photocatalytic activity was evaluated through photocatalytic degradation of typical organic pollutant, the the degradation mechanism was proposed.1. Single-crystalline bismuth titanates(Bi12Ti O20) with the cubic phase and various morphologies(flower-, belt-, tetrahedral-like) were controllably fabricated by using a mild template-free hydrothermal process. The samples were fully characterized by X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM), transmission electron microscopy(TEM), high-resolution TEM, nitrogen porosimetry measurement, UV-vis diffuse reflectance spectroscopy(DRS), and X-ray photoelectron spectroscopy(XPS). The influence of the solvent and the concentration of NO3? in the reaction system on the crystallinity and morphology of the Bi12 Ti O20 samples was investigated in detail. Bi12 Ti O20 crystals were used as the sunlight-driven photocatalysts to degrade aqueous dye methyl orange(MO) and p-nitrophenol(PNP), and the influence of Bi12 Ti O20 morphology on the photocatalytic activity was discussed. Finally, the recyclability of Bi12 Ti O20 was evaluated through three consecutive runs.2. A series of hierarchical Bi12 Ti O20–graphene nanoarchitectures(Bi12Ti O20–GR) with GR loadings from 1% to 10% are fabricated by a single-step solvothermal treatment technique, and the intimate interfacial contact between flexible GR sheets and flower-like Bi12 Ti O20 nanocrystals is observed in the Bi12 Ti O20–GR composites. As a novel composite photocatalyst, Bi12 Ti O20–GR with GR loading of 2% possesses the highest simulated sunlight photocatalytic activity towards the degradation of two typical organic pollutants, methyl orange(MO) and p-nitrophenol(PNP). Furthermore, the separation and transportation of the photogenerated carriers in the simulated sunlight-irradiating Bi12 Ti O20–GR system is studied, meanwhile, the active species(hVB+, O2?- and ?OH) generated in the Bi12 Ti O20–GR-photocatalyzed PNP degradation system are identified by free radical and hole scavenging experiments. Based on the experimental and theoretical results, the mechanism of photocatalytic degradation of PNP in the simulated sunlight-irradiating Bi12 Ti O20–GR system are proposed. Based on the detection of intermediate products, we deduce the degradation pathway of PNP.3. Hydrothermal/solvothermal method was used to achieve various Bi OBr materials with different micro-morphology, including Bi OBr nanosheets, Bi OBr microflowers assembled by nanosheets, Bi OBr microspheres, and sphere-ike Bi OBr microflowers. The samples were fully characterized by X-ray diffraction(XRD), field emission scanning electron microscopy(FESEM), UV-vis diffuse reflectance spectroscopy(DRS), and nitrogen porosimetry measurement. Through photocatalytic degradation of p-nitrophenol(PNP) under simulated sunlight(320 nm < ??< 680 nm) and visible-light(400 nm < ??< 680 nm) irradiation, the photocatalytic activities of various Bi OBr sample were compared, the photocatalytic activity ranks in the order of sphere-ike Bi OBr microflowers > Bi OBr microspheres > Bi OBr microflowers > Bi OBr nanosheets, the micro-morphology of Bi OBr signi?cantly affect its photocatalytic activity. In addition, a series of Pt-doped Bi OBr sample with 1wt% Pt loading was synthesized by an in situ photodeposition method. After deposition with Pt nanoparticles, Pt-Bi OBr microspheres exhibited the highest photocatalytic activity towards PNP degradation. The synergistic effect of mesoporous structure of Bi OBr microspheres and surface plasma resonance(SPR) originated from Pt nanoparticles gives a positive influence on improving the photocatalytic activity. Furthermore, tetrabromobisphenol-A(TBBPA) was used to further evaluate the simulated sunlight and visible-light photocatalytic activity of Pt(1%)-Bi OBr microspheres, and the results were compared with Degussa P25. The photoelectrochemistry and the free radical and hole scavenging experiments was conducted to study the mechanism of photocatalytic degradation of PNP in the visible-light-irradiating Pt(1%)-Bi OBr system. Based on the analysis of intermediate products during the photocatalytic TBBPA degradation, we deduce the degradation pathway of PNP over Pt(1%)-Bi OBr.