| At present, semiconductor of titanium dioxide, as the benchmark of wide band gap photocatalyst, has many technical problems. Such as poor solar energy utilization and low quantum efficiency have directly affected the photocatalytic activity and seriously limited the utilization of industrialization. To solve these problems, visible light photocatalysts which have performances with high efficient solar energy utilization and high quantum efficiency is becoming a hot issue in current research.As novel visible light response photocatalyst, bismuth vandate (BiV04) have attracted much attention. Futher study of the relationship between photocatalytic activities, crystalline phase, particle size and morphology will have great significance with the development of this wide spectral response material.In this paper, BiVO4 samples were all synthesized via hydrothermal method and effects of hydrothermal synthesis conditions on physicochemical properties, morphology and photocatalytic activities under visible light irradiation were investigated systematically. Phase transform mechanism during the process of synthesis was discussed simultaneously. Grapheme oxide (GO) was used as a carbon source to modify the surface of BiVO4 samples which were named as C/BVO. Efficiency in the separation of photogenerated electron-hole pairs can be facilitated after modification, the surface of C/BVO samples contains rich oxygen functional groups. The composition, structure, morphology and surface states of catalysts were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectrum (FT-IR) and raman spectroscopy (Raman). The photoresponse, possible mechanism of photocatalytic degradation were investigated by UV-vis diffuse reflectance spectra (DRS), detection of active species in photocatalytic degradation process.The main conclusions obtained from these studies are as follows:(1) By controlling different Bi:V molar ratio of the raw material, different morphologies of BiVO4 samples were obtained. Such as package balls with 2-3μm in diameter, sheet materials with 300-500 nm in width size. After liquid phase activity tests, the best photocatalytic activity sample was selected. And the optimal hydrothermal preparation condition is Bi:V=4:1,180℃, holding for 48 h.(2) The phase transform process from tetragonal zircon structure (z-t) to monoclinic sheelite structure (s-m) was investigated by XRD and DRS. The crystal phase transition mechanism of sheet materials was put forward. The conclusion of s-m phase has better photocatalysis activity has been confirmed once again.(3) Using GO as carbon source, the surface modification was studied for the both two phases of BiVO4. By testing the liquid-phase photocatalytic degradation of 10 ppm Rhodamine B (RhB) over these samples, it is interesting to find that after carbon modification, the z-t phase samples’photocatalytic activity was promoted by 7.6 times, the s-m phase samples’ photocatalytic activity was enhanced by 1.4 times as well. Through a series of active species capture experiments, the results indicated that O2·- was the key active species in the photocatalytic process.The features and innovations of this paper are as follows:① This is a novel report on exploring the phase transformation mechanism of bismuth vanadate by using sheet morphology. ② We had firstly tried to investigate the influence of different BiVO4 phases was modified by carbon which using GO as the carbon source. After the modification, C/BVO samples’ photocatalytic performance was improves significantly. |
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