Hydrothermal Synthesis Of Novel Bismuth Vanadate-based Semconductor Photocatalysts And Their Photocatalysis Property

In the past thirty years, researcher pay attention for the nanostructures Ti O2-based semiconductor materials photocatalytic technology due to it widly application in environmental protection for photocatalytic oxidation organic pollutants and photocatalytic reduction inorganic metal ions. The researchers make a depth research on the photocatalytic reaction process and mechanism of nanostructure TiO2-based semiconductor. However, due to the lower utilization of solar energy and the quantum efficiency, TiO2-based photocatalysts are limitted widely used in actual pollutants water treatment. Therefore, a large number of new and highly efficiency visible light responsive phtotcatalysts were developed by the researchers systems investigated, while monoclinic phase BiVO4 is one of the interesting visible light responsive catalysts in recent years. Monoclinic phase BiVO4 have a relative smaller band gap(Eg = 2.4 eV), and the oxidation potential of the valence band is located in the vicinity of 2.4 V. Therefore, monoclinic phase BiVO4 has a ability of oxidizing the contaminants. However, photoexcited electrons from monoclinic phase BiVO4 are not easily captured by oxygen dissolved in the water due to its conduction band edge at 0 V(vs.NHE), and the photoexcited electrons weill accumulate in the surface of the catalyst, which increasing the utilization of the electron and hole recombination probability, resulting in a poor photodegradation contaminants under visible light irradiation. In order to improve the photocatalytic degradation pollutants of BiVO4 efficiency, it is very important to inhibite the photo-generated electron-hole complex. Therefore, we explore a variety of methods to improve the activity of monoclinic phase BiVO4 photocatalytic decomposition of pollutants, which including preparation of high surface area nanostructures doped rare earth ions, compound semiconductor materials. These studies will develop the monoclinic phase BiVO4 photocatalyst on the catalytic decomposition pollutants in a widely application, but also will provide some new ideas for the design and synthesis of novel visible-light responsive catalysts. The main work of this thesis includes the following sections:(1) Different morphologies of monoclinic phase BiVO4 micro- and nanopowders were prepared by hydrothermal synthesis method under controlling the p H value of the reaction solution. The photocatalytic activity of monoclinic BiVO4 micro- and nanopowders for Rhodamine B dye and phenol were investigated under simulated sunlight irradiation. Under simulated solar light irradiation conditions, porous peanut-shaped monoclinic phase BiVO4 nanopowder exhibit stronger photocatalytic activity than other powders, which mainly due to the monoclinic phase BiVO4 sample synthesized at pH = with a larger surface area. In addition, the photocatalytic activity BiVO4 powder effectively enhanced after added in light of H2O2 as an efficient catalytic system electron acceptor.(2) Porous peanut-shaped Nd3+ and Sm3+ doped BiVO4 nanopowders were prepared by a simple hydrothermal synthesis method. Under simulated sunlight irradiation, the photocatalytic activity for Rhodamine B dye of porous Nd3+ and Sm3+ doped BiVO4 nanopowders were investigated by controlling the presence or absence H2O2 in the phtocatalytic reaction system. The results shown that peanut-shaped porous Nd3+ and Sm3+ doped BiVO4 nanopowders exhibit enhanced catalytic activity than pure monoclinic BiVO4 nanopowders under simulated sunlight irradiation. In addition, the porous peanut-shaped Nd3+, Sm3+ doped BiVO4 nanopowders kept the high efficiency photocatalytic activity after several repeated phtocatalytic process in the H2O2/Rhodamine B reaction system under light irradiation conditions.(3) 2% Sm3-doped BiVO4 nanopowders were used to evaluate the catalytic activity for phenol degradation efficiency and Cr(VI) reduced under simulated sunlight irradiation. The results shown that Sm3-doped BiVO4 nanopowders has better catalytic activity than the pure monoclinic BiVO4 nanopowders. After adding H2O2 in the photocatalytic reaction system, the catalytic activity of Sm3-doped BiVO4 nanopowders will effectively enhanced the catalytic efficiency for phenol. Similarly, Sm3+-doped BiVO4 nanopowders also has a better for Cr(VI) catalytic activity under simulated sunlight irradiation. We also explored the Sm3-doped BiVO4 nanopowders photocatalytic activity for Cr(VI) and phenol coexist wastewater treatment in this chapter. The experimental results shown that Sm3+ doped BiVO4 photocatalyst exhibited better photocatalytic activity for Cr(VI) reduction and phenol photocatalytic decomposition than any single one of the pollutant in the Cr(VI) and phenol coexist system. The photocatalytic efficiency have been greatly improved, showing the catalytic oxidation and reduction synergistic effective.(4) Porous structure TiO2/BiVO4 nanocomposite structure were synthesized by a simple hydrothermal method. The results photocatalytic activity found that the sample with 20wt% content of anatase TiO2 TiO2/BiVO4 composite structure has the strongest catalytic activity for rhodamine B dye under simulated sunlight irradiation. The nanocomposite structure of TiO2/BiVO4 will benift for photoexcited electron-hole pairs separated, thus reducing the photo-generated electron-hole pair recombination rate.