Synthesis And Photocatalytic Performance Of Two-dimensional BiVO₄ Nanocomposite Materials

As a kind of visible-light catalyst, monoclinic BiVO4 (m-BiV04) with the band gap of 2.4-2.5eV is non-toxic, low-cost and stability against photocorrosion. Therefore, m-BiVO4 has been comprehensively investigated over the past two decades. At present, m-BiVO4 has been considered as a potentially suitable visible light-driven photocatalyst for pollutant decomposition and water splitting. However, the application of m-BiV04 in the field of photocatalysis research has been limited owing to its poor adsorptive performance and low separation efficiency of electron-hole pairs. Therefore, the improvement of photocatalytic activity of m-BiVO4 has been the subject of numerous studies. To enhance the photocatalytic efficiency of m-BiVO4 in the visible light region, many attempts have been explored, such as synthesis of BiVO4 with special morphologies, surface modification or doping. Since the photocatalytic activity is influenced with a certain extent by the surface area of catalysts, it is advisable to modify the m-Bi VO4 after the morphology optimization for the sake of a higher efficient photocatalyst.In this thesis, we have firstly prepared BiVO4 nanosheets by adjusting the concentration of precursors, pH, hydrothermal treatment time and hydrothermal treatment temperature. And then the prepared BiVO4 nanosheets are composited with graphene or graphene loaded with noble metal. The photocatalytic activity of BiVO4-based composites has been examined by liquid-phase degradation of dyes. Simultaneously, the properties of as-prepared samples, such as crystal phase, morphology, photoresponse, specific surface area and elementary composition et al., have been characterized by a series of techniques, including X-ray diffraction (XRD), UV-vis diffuse reflectance spectra (DRS), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), nitrogen adsorption-desorption, photoluminescence spectra (PL), Raman spectra, X-ray photoelectron spectra (XPS), and electrochemical analysis. The main results and conclusions obtained from the present research are as follows:1. we have synthesized BiVO4-GR nanocomposites via a facile hydrothermal method. And the prepared BiV04-GR composites show a higher photocatalytic activity than that of blank-BiV04 nanosheets, which contributes to the synergistic effect between the BiVO4 nanosheets and the graphene sheets. The 2-D GR sheets are able to promote transfer of the photogenerated electrons from semiconductor BiVO4 nanosheets, thus inhibiting the recombination of photogenerated electron-hole pairs and resulting in the improved photoactivity of BiVO4 nanosheets-GR composites toward degradation of dyes under visible light irradiation.2. Ternary BiVO4 nanosheets-GR-Pd composites have been prepared by the hydrothermal treatment of Pd-modified graphene oxide (GO) and BiV04 nanosheets. The ternary BiV04-GR-Pd features intimate interfacial contact with spatially and intimately cross-linked sheet structure, which exhibits remarkably higher photocatalytic activity than binary BiVO4 nanosheets-GR composites under visible light. Our findings highlight the importance of interfacial composition optimization on boosting the photogenerated charge carriers separation and transfer across the interfacial domain and thus photoactivity of 2D semiconductor-2D graphene composites.