| Photocatalytic technology has many excellent properties such as lower energy consumption, lower cost, none secondary pollution, the profound and lower temperature of reaction, purify thoroughly and can directly using solar energy as light source to drive the reaction, so it become a kind of green environmental treatment technology. Currently, as a kind of typical simple oxide, Bi2WO6 materials has been researched due to a narrow band-gap and the better visible-light response ability, study on the Bi2WO6 material is helpful to improve the utilization efficiency of the solar energy, thus improving the visible-light photocatalytic performance, it has application value in the development of new energy and environmental purification. To further improve the visible-light catalytic properties of Bi2WO6 material, different synthesis methods and various modification methods have been studied by researchers, such as ion doping, composited semiconductor, immobilized load, adding surface active agent, etc. However, biomass resources in which nature and the human environment exist are rich and varied, the adsorption ability of biomass carbon heating by biomass resources was very strong, the specific surface area and pore structure were also developed, it has broad application prospects in the field of energy and environment. As a result, combined the excellent properties of the biomass carbon and Bi2WO6, the preparation of composite materials using carbon and semiconductor has sufficient reference in the aspect of improving photocatalytic activity, provides richer theory and practice verification for this paper.Microwave-assisted hydrothermal synthesis method was used in this topic, Bi2WO6-C composite materials with visible-light response was prepared using different biomass resources as raw materials. The influence factors that include the addition amount of biomass carbon, synthesis paths, pH value, reaction temperature and time were studied. The photocatalytic activities that pure Bi2WO6 and Bi2WO6-C composite material were compared and analyzed, the mechanism of photocatalytic reaction was discussed. At the same time, different surfactants were added in the reaction system to prepare Bi2WO6-C composite material, in order to make the microscopic morphology and crystal structure of products were controlled regularly. The main content of this paper was summarized as follows:1. Bi2WO6-C composite materials were prepared successfully by one-step microwave hydrothermal synthesis method using different biomass (glucose, starch, cotton, oil, bamboo charcoal) as carbon source, together with Bi(NO3)3·5H2O and Na2WO4·2H2O as raw materials. Results indicate that the morphology structure of Bi2WO6-C has been great influenced by different biomass carbon. The morphologies of Bi2WO6-C products are relatively uniform when using cotton and glucose as carbon source, with three-dimensional layered structure that stack for each other, and presents better photocatalytic activity. After 240min visible-light irradiation, the degradation efficiency of RhB were reached 92% and 90.8% respectively. There may be two reasons for it:Firstly, compared with the pure Bi2WO6 samples, Bi2WO6-C samples which prepared by different biomass carbon have uniform absorption ability in visible area, indicates that the spectral response range of products were expanded when using biomass carbon, the absorption of visible-light was enhanced. Secondly, Bi2WO6-C composite materials which prepared by cotton and glucose as carbon source, the arc radius of sample that after irradiation is significantly less than the light before that measured by EIS Nyquist. Results show that the separation rate of electron-hole is larger when Bi2WO6-C composite material was used as photocatalyst, the transmission of carriers on the surface is faster. The photocurrent result analyzed the photocurrent of products which prepared by cotton and glucose is the largest, the effective carriers mobility and the separation of electrons-holes may promote the photocatalytic reaction and the improvement of photocatalytic activity. Therefore, preparation the composite photocatalytic materials using the combination of biomass carbon and Bi2WO6 is feasible in enhancing the photocatalytic properties.2. The preparation and photocatalytic properties of Bi2WO6-C composite materials using cotton as carbon sources was further studied. Influencing factors such as different pH, different reaction temperature, different reaction time, different amount of cotton and the mechanism of photocatalytic reaction process were detailly discussed. Results indicate that the better crystal and photocatalytic stability of Bi2WO6-C based on cotton can be obtained under the condition of the pH value is 7, reaction 60min in 200℃, amount of cotton is 6.09%. With three-dimensional layered structure that stack for each other, presents the stronger visible-light absorption ability, the forbidden band is 2.61eV, the electron mobility is enhanced, specific surface area is the largest, it could provide more active site for photocatalytic reaction, the adsorption capacity in the dark reaction stage is the strongest. ESR deeply analyzed the mechanism of photocatalytic reaction process of Bi2WO6-C based on cotton.3. The preparation and photocatalytic properties of Bi2WO6-C composite materials using glucose as carbon sources was further studied on the basis of the previous chapter content. Several influencing factors such as using one-step or two-step methods, different calcination temperature, addition amount of glucose and reaction system pH value were mainly discussed. The differences between pure Bi2WO6 and Bi2WO6-C on structure and properties were compared thoroughly, and the mechanism of photocatalytic reaction of Bi2WO6-C was discussed on the preliminary. Research shows that using one-step synthesis route, precursor solution pH=7, the molar ratio of glucose, Bi(NO3)3 and Na2WO4 for 1:10:5, microwave hydrothermal reaction 60min 200℃, and the condition of 300℃ calcination process, the product based on glucose presents better photocatalytic activity. It can be attributed to the materials with microstructure of porous structure, better crystallization degree, smaller optical band gap (2.691eV), larger specific surface area (25.1m2/g) and effective carrier transmission ability, thus the response range of light absorption was enlarged, the contact area between catalyst and organic pollutants was increased, the active site of the reaction became larger.At the same time, the structure and photocatalytic performance of pure Bi2WO6 and Bi2WO6-C composite material were compared deeply. Results show that the carbon in which Bi2WO6-C exist is in the form of amorphous. There was an intense interfacial interaction between carbon and Bi2WO6. The mechanism of photocatalytic reaction speculates that the separation of electrons-holes was effectively promoted through the introduction of biomass carbon, the transmission of carrier on the surface of Bi2WO6 was improved. ESR confirmed that in the process of photocatalytic reaction, more of the oxidation of free radicals could be produced in Bi2WO6-C material under the same UV radiation, thus its photocatalytic activity was improved.4. Preliminary explored using pomelo peel as biomass carbon source, preparation and morphology control of Bi2WO6-C composite by adding different surfactants were studied, and its structure and performance were discussed. Results show that the crystallization of Bi2WO6-C based pomelo peel is good after adding CTAB, it is a beautiful hydrangea shape, and it is helpful to form of adsorption storage space due to the holes of rich morphological rules that the formation of density of flake cross growth. On the optical properties, absorption capacity of the product in visible-light area is the strongest by adding CTAB, there exists uniform absorption phenomenon, its Optical band-gap is 2.65 eV, and the peak intensity of PL under the light excitation is the weakest, indicates that the composite efficiency of internal electronic-hole of material under the light excitation is the smallest, the efficiency degradation of RhB reached 96.9% after visible-light irradiation in 180min, the repeatability and stability of product could be better. So using CTAB as surfactant, the Bi2WO6-C composite material based on pomelo peel presents significant photocatalytic activity, it could provide a reference for the related or similar research in the future. |
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