| With the development of China’s economy, a large number of light industries have sprang up. Dyes are synthetic organic compounds that are increasingly being produced and used as colorant in many industries, including textile, leather, paper, etc. Most of the dyes are toxic and carcinogenic compounds. They are recalcitrant and stable in the receiving environment, posing a serious threat to environment and human health. To protect humans and the receiving ecosystem from contamination, the dyes must be eliminated from the dye-contained wastewaters before being released into the environment. Hence, searching for novel, cost effective, and efficient methods for removal of dyes is very important. To treating the organic pollutants in water, many studies have focused on the adsorption and photocatalytic technology Recently. Based on the above viewpoints, Cr2WO6 was proposed as a good adsorbent and Ag2 Cr O4 also was studied as a photocatalyst. The performance of the materials were optimized by changing the technological factors.(1) Cr2WO6 nanocrystallites were successfully synthesized by hydrothermal assisted calcination using Na2WO4·2H2O as tungsten source and Cr(NO3)3·9H2O as chromium source. The phase composition, element content, thermal conversion characteristics, morphology, specific surface area, surface electrical properties and optical properties of the as-prepared samples were characterized by X-ray diffraction, energy dispersive spectrometer, scanning electron microscopy, thermogravimetry-differential scanning calorimetry, transmission electron microscopy, N2-sorption BET surface area, UV-vis diffuse reflectance spectroscopy and the Zeta potential analyzer. The influence of p H values, hydrothermal time, hydrothermal temperature, Cr3+/WO42- ratio of mole, as well as the heat treatment temperature and time on the phases, morphologies and properties of Cr2WO6 nanocrystalline was discussed. Results show that crystal growth of Cr2WO6 needs higher activation energy. When the precursor p H value varies within the range of 1~7, pure phase Cr2WO6 nanocrystalline with poor crystalline could be obtained by hydrothermal method, while amorphous precipitate was obtained with the p H value of 7~13. In order to get well crystallization Cr2WO6 crystal, hydrothermal product must be calcined under 650°C for 2h. Compared with solid state reaction, we found that the hydrothermal process providing an effective method to prepare Cr2WO6 nanocrystals. Photocatalytic degradation of methylene blue show that the photocatalytic activity of Cr2WO6 nanocrystal was poor under ultraviolet light, indicating that Cr2WO6 nanocrystal is not suitable for photocatalyst. However, it is found that the as-prepared Cr2WO6 sample possesses highly negatively charged surface in aqueous media. The preferential adsorption of cation dye is depends upon the surface charge of adsorbent and the type of dyes. Therefore, we report the preferential adsorption of MB dye on Cr2WO6 nanoparticles which prepared by hydrothermal assisted method in this paper. The hydrothermal assisted Cr2WO6 nanocrystallites in our research may provide good potential as adsorbent material for organic wastewater treatment applications.(2) The influence of different methods on the phases, morphologies and photocatalytic properties of Ag2 Cr O4 crystalline was discussed. Results show that the sample prepared by precipitation method exhibits the highest photocatalytic efficiency on the degradation of rhodamine B(Rh B) under visible-light irradiation. The enhanced photocatalytic activity could be ascribed to the smaller particle size and larger surface area. Based on this result, the influence of various process factors on the structures and photocatalytic properties of Ag2 Cr O4 crystalline was investigated. Results show that the best reaction precursor concentration is 0.05mol/L. The p H value played an important role on the phase and photocatalytic properties of Ag2 Cr O4 crystalline. The pure phase Ag2 Cr O4 crystalline was obtained with the precursor p H value of 1~7. The Ag2 Cr O4 samples prepared at p H value of 1 had obviously enhanced photocatalytic activity in Rh B degradation. The influences of different templates(PVP and SDBS) on the phase composition, morphologies and optical performances of the products were investigated. Results show that rod-like Ag2 Cr O4 nanocrystallines are prepared using PVP as template, while the Ag2 Cr O4 nanoparticles are prepared using SDBS as template. Different templates have different effects on the structure, size and optical properties of the products. The photocatalytic activity was increased with the increase of the specific surface area of Ag2 Cr O4 nanocrystallines. |
