Study On Preparation And Dye Photodegradation Properties Of Tungsten Oxide Based Photocatalyst

Photocatalytic technology, which uses the unlimited solar without introducing additional influence to effectively remove pollutants with high toxicity in low concentration and difficult to deal with, has been considered as the most effective way for treatment of environmental pollution. Tungsten trioxide, one of the earliest investigated photocatalyst, has been widely applied in photocatalytic O2 evolution, photoelectrochemical cell and photocatalytic pollutant removal, due to the properties of environmental friendly and excellent stability. In this dissertation, a series of tungsten trioxides with different crystal structure and microstructure have been synthesized via liquid phase method and their modification have also been carried out. The relationship between the crystal structure, microstructure, optical charge carrier separation and their photocatalytic performance has been systematically studied. Based on the aforementioned research contents, The mainly research work have been carried out as follows:Hexagonal tungsten trioxide with ultra-thin nanosheet has been synthesized via hydrothermal method. The thickness of as-prepared ultra-thin nansheet is about 5 nm. Based on the experiment results and analysis, we conclude that urea plays an critical role in crystal structure and morphology of tungsten trioxide, in which the hydrolysis of urea slows down the growth rate of tungsten trioxide. On the other hand, NH4+ and CO32- derived from the hydrolysis of urea which can ensure the formation of hexagonal phase and ultra-thin nanosheet. Compared with hexagonal tungsten trioxide nanowire and nanorod, the as-prepared hexagonal tungsten trioxide ultrathin nanosheet displays superior photocatalytic activity. 86.6 % of Rh B has been eliminated after 240 min.Cubic tungsten trioxide hemihydrate has been synthesized via solvothermal method by regulating the amount of acetone and urea. The size of as-prepared sample is from 120 nm to 180 nm. Urea and acetone play an adjusting role in the p H of reaction system on cystal structure, and the urea, acetone and intermediate also play a role in the crystal structure and morphology. In addition, it is found that the crystal water of cubic tungsten trioxide hemihydrate has an important effect on photocatalytic property and the reason has been discussed. The photocatalytic activity degradates when crystal water of as-prepared sample has been removed. While, the photocatalytic activity has been recovered when crystal water has been added again. The investigation on the photocatalytic activity of cubic tungsten trioxide hemihydrate showed that 99 % Rh B has been eliminated after 220 min.Orthorhombic hydrate tungsten trioxide flower-like hierarchical structure has been synthesized via solvothermal method by regulating the amount of acetone. Compared with the morphology of orthorhombic hydrate tungsten trioxide thorn sphere（synthesized without adding acetone）,（020） facet of orthorhombic tungsten trioxide hydrate can be reserved by acetone adsorption, and the flower-like hierarchical structure has been obtained. The morphology of flower-like hierarchical structure has been influenced by the amount of acetone, due to the change of saturation vapour pressure in reaction system. In addition, the visible-light absorption of sample has been improved by the increment of acetone. Flower-like hierarchical structure tungsten trioxide hydrate displays superior photocatalytic performance than thorn sphere tungsten trioxide hydrate. 88.5 % of Rh B has been eliminated after 240 min.The interstitial carbon doping orthorhombic tungsten trioxide hydrate has been synthesized via a room temperature liquid phase method. The carbon doping position has been studied, and the carbon is doped into the interstitial position. SAED and HRTEM display the lattice defect and distortion induced by the carbon doping, which may increases local dipole of sample. In addition, the optical property and theoretical calculation of carbon doped sample have been studied. It is found that the carbon doping narrowed the Eg, improved visible-light absorption and a new level formed above the valence band. PL spectra show the recombination of photo-generated carriers is suppressed by carbon doping. In addition, the photocatalytic performance of carbon doped samples decrease with the increment of carbon doping. However, the photocatalytic activity of all carbon doped samples are higher than that of the undoped one.The all tungsten based Z-scheme composite photocatalyst（composed of WO₃·0.33H₂ O and Pb WO₄） has been synthesized via a liquid phase ion-exchange method. The crystal phase and composition of the composite have been determined by XRD and Raman measurement. Orthorhombic tungsten trioxide hydrate has been formed by ion exchange process and structural rearrangement occurs on the surface of lead tungstate, which is proved. The ion exchange position can be understood by HRTEM investigation. It is found that ion exchange occurs at the end of（110） facet of lead tungstate. The composites exhibit much higher photocatalytic activities than that of individual hydrated tungsten trioxide and lead tungstate. The apparent photodegradation rate constants of Rh B over composites are more than 6 to 8 times higher than that of two monomer components. Based on the results of photocatalytic mechanism and photodeposition Pt experiments, it indicates that the excellent photocatalytic activity of composite photocatalyst is due to the advantage of Zscheme configuration., almost all of Rh B has been eliminated after 40 min and 82 % MO can be eliminated after 60 min, respectively.