Preparation And Properties Of Vanadate And Their Composite Photocatalyst

In recent years, using solar power to solve the energy source shortage and environmental pollution problems have attracted extensive attention. Degradation of organic pollutants, which are harmful to human health has gradually become the focus of scientific research in today’s scientific world. Because these organic pollutants and emission sources are different, the biodegradation of these organic pollutants is usually very slow and regular management are mostly ineffective. In this regard, the photocatalytic technology, especially with the semiconductor photocatalytic system appears to be the most appealing mean than the more conventional chemical oxidation methods for decomposition of toxic compounds. Photocatalytic degradation of environmental contaminants has been studied in the past two or three decades. Besides traditional TiO2, hundreds of photocatalysts were developed over the past decades,such as Ag3PO4, BiVO4, BiOBr. However, limited absorption in the visible light range and high recombined rate of the excited electrons and holes are still two basic problems in photocatalytic research. To solve these problems, lots of methods have been developed. This thesis focused on the synthesis of novel vanadate semiconductor materials(AgVO3 and BiVO4) with different morphologies and further design of visible-light-driven plasmonic photocatalyst AgVO3@AgBr@Ag and Ag-AgBr/BiVO4. The RhB removal performance under visible light irradiation of as-prepared samples is determined by their photocatalytic activity. Based on that, the preparation, structure and properties of the photocatalysts were studied by modern testing methods. Meanwhile, the photocatalytic reaction kinetics was investigated. The component and crystal growth mechanism of the photocatalysts were explorated. The research work of this thesis could be described as follows:(1) Hydrothermal preparation of AgVO3 nanobelts and studies of photocatalytic activity of AgVO3 nanobeltsThe AgVO3 nanobelt crystals were prepared with Bi(NO3)3 and NH4VO3 as starting materials through the hydrothermal method. And the relationship between the crystal type of the AgVO3 and its photocatalytic properties was further studied. We carried out the experiments of the RhB removal performance as a test to demonstrate the visible light photoactivity of the AgVO3 nanobelt. The results indicate that crystal structure of the as-obtained AgVO3 is monoclinic structure. The thickness of as-obtained AgVO3 is 30-50 nm, the width is 100-400 nm, the length is 10-100μm. The catalyst show high efficiency for the degradation of Rhodamine B(RhB) under visible light irradiation(>420).(2) Fabrication of Visible-light-induced Ag/AgBr/AgVO3 nanostructures and their photocatalytic propertiesThe precursor AgVO3 nanobelts were prepared by hydrothermal method. Through the ion exchange reaction the Ag/AgBr/AgVO3 nanobelts heterostructures were fabricated by reacting the above AgVO3 nanobelt crystals with CTAB aqueous solutions at room temperature. The prepared AgBr microspheres irradiated under sunlight were reduced, and next a certain amount of silver and Ag/AgBr nanoparticles are uniformly on the surface of AgVO3 nanobelts. AgBr@Ag size of the AgVO3@AgBr@Ag nanobelts with different molar ratios of AgVO3 to CTAB are discussed. The photocatalytic property was evaluated by photodegradation of RhB under visible light irradiation. In addition, we discussed the formation mechanism of the composite photocatalyst. Ag/AgBr/AgVO3 nanostructures had high photocatalytic activity under visible light, and the degradation was 70% in 2min. The as-prepared Ag/AgBr/AgVO3 exhibited superior photocatalytic performance, possessing the surface plasmon resonance(SPR) of noble metal nanoparticles and double VL active components(AgBr, AgVO3).(3) Hydrothermal synthesis and photocatalytic activity of novel semiconductor photocatalyst leaf-like BiVO4 nanocrystalThe leaf-like BiVO4 nanocrystal were synthesized by the hydrothermal method using Bi(NO3)3 and NH4VO3 as starting materials and with NaOH to adjust pH. The nanocrystals were characterized by many modern characterization methods, such as XRD, SEM and UV-DRS. The results indicate that the morphology of leaf-shaped BiVO4 is 60~70 nm in thickness and 70~100 μm in lateral size. The photocatalytic performance for Rhodamine B degradation was also investigated for leaf-like BiVO4 under the visible light irradiation. The possible growth mechanism of leaf-like BiVO4 nanocrystal was investigated.(4) Controllable Synthesis, structures and photocatalytic performance of photocatalyst Ag-AgBr/BiVO4 nanojunctionAg-AgBr/BiVO4 nanojunction has been facilely prepared by the deposition-precipitation method with surfactant and subsequent light-driven route. As a low-cost and efficient visible light-driven photocatalyst, BiVO4 is chosen as an ideal support. Cetyltrimethylammonium bromide(CTAB) were used as both of the surfactant, template-directing reagent and the Br source. The Photocatalyst was characterized by many modern characterization methods, such as XRD, SEM, TEM and UV-DRS. The photocatalytic property was evaluated by photodegradation of RhB under visible light irradiation. The obtained Ag-AgBr/BiVO4 photocatalyst shows excellent visible-light-driven photocatalytic performance. It can decompose Rhodamine B(RhB) within 14 min under visible-light irradiation. Meanwhile, compared with other VLD(visible light-driven) photocatalysts such as Ag-AgBr, Ag-TiO2 and AgBr-Ag-TiO2 composite, the amount of Ag needed and the cost decreases significantly. Moreover, the possible photocatalytic mechanism of the Ag-AgBr/BiVO4 nanojunction was investigated.(5) Synthesis and Photocatalytic Activity of shuttlelike Bismuth VanadatesThe shuttle-like BiVO4 nanocrystal were synthesized by the hydrothermal method using Bi(NO3)3 and NH4VO3 as starting materials. The phase structures of the BiVO4 samples were observed by X-ray diffraction(XRD), which indicated that the as-prepared samples possessed monoclinic cells. The photocatalytic performance of as-prepared BiVO4 photocatalysts for Rhodamine B degradation was also investigated for shuttle-like BiVO4 under the visible light irradiation(λ>420nm). A possible photocatalytic mechanism of shuttle-like BiVO4 nanocrystal was proposed.