Title:prepa Ration Of W-based Cata Lysts And Its Photoca-Talytic Performance

The burning of fossil energy made environmental pollution and energy shortages increasingly serious.Large reserved,easy accessed,and environmentally friendly solar energy are receiving more and more attention.Semiconductor photocatalytic technology can use solar energy to degrade polhtants,prepare clean energy hydrogen and reduce CO2,etc,which has attracted the attention of more and more researchers.However,at this stage,the wide-bandgap semiconductor catalyst represcnted by TiO2 is not widely used in practice due to its shortcomings such as low utilization rate of photogenerated carriers and weak solar light response.Therefore,there is an urgent need to explore the modification method of photocatalyst in order to meet the challenges of practical needs.In this thesis,a "Z-type heterojunction system" which is similar to photosynthesis is constructed by using W-based catalysts and different semiconductor materials to solve the problem of photo-generated electron-hole reconmbination.In this thesis,organic dye MB was used to degrade the target substance,and its photocatalytic activity was evaluated and then photocatalytic hydrogen production experiments were carried out.The main research contents are as follows:(1)Preparation and properties of WO3/TiO2 composite nanofibers.Ammonium tungstate was used as tungsten source,butyl titante used as titanium source,solvent ethanol(EtOH),N,N-dimethylformamide(DMF)and acetic acid(HAc)were used in a ratio of 5:5:9,the amount of WO3 is 5%.It was used to prepare WO3/TiO2 composite nanofibers by electrospinning.When the calcination temperature was 520℃,the prepared WO3/TiO2(WT)composite nanofibers had good crystallinity and maintain a uniform morphobgy.The crystal form was a mixed crystal of anatase and rutile with a specific area of 51.457 m2/g,the forbidden band width is 3.16 eV.Using Xenon lamp(250 W)as the simulated light source and MB solution as the target degradation product,the degradation rate of WO3/TiO2 composite nanofibers to 20 mg/L MB solution can reach 96.2%in 120 min,while the degradation rate of TiO2 nanofibers only 72%.Under the irradiation condition of 100 W mercury lamp,the hydrogen production rate can reach 107.15 μmol/g/h,which was about 1.5 times higher than that of pure TiO2.(2)Preparation and properties of C and N co-doped WO3/TiO2(C/N-WT).On the basis of preparation of WO3/TiO2 nanofibers,C/N-WT nanocomposite photocatalytic fiber were prepared with urea as C and N source,with 1%urea doping as the best doping amount and 550 ℃ as the optimal calcination temperature.The experimental results showed that the crystal form of C/NWT catalyst does not change after doping two elements.It belongs to the mixed crystal of anatase and rutile,and its crystallinity has improved.Within 90 min,C/N-WT composite photocatalyst under the visible light(Xenon lamp,250 W)with 20 mg/L MB solution as the target degradant,the degradation rate can reach 100%,compared with TiO2,the degradation rate was increased by about 4 times under the condition of 100 W mercury lamp irradiation,the hydrogen production rate was 139.73 μmol/g/h,which was about 1.3 and 1.8 times higher than that of WO3/TiO2 and TiO2,respectively.(3)Preparation and properties of carbon nitride g-C3N4 supported WO3/TiO2(g-C3N4/WT).On the basis of preparation of WO3/TiO2,a composite photocatalyst of g-C3N4/WT was synthesized by one-step hydrothermal method using urea as the source of g-C3N4.It was found that with the increase of g-C3N4,the photocatalytic activity of g-C3N4/WT composites increased first and then decreased,and 5%of g-C3N4 composites had the best photocatalytic activity.When controlling the preparation conditions of g-C3N4/WT(hydrothermal time 4 h,hydrothermal temperature 160 ℃),the degradation rate of 20 mg/L MB solution can reach 100%within 70 min under irradiation with 250 W xenon lamp.Under the irradiation condition of 100 W mercury lamp,the hydrogen production rate of g-C3N4/WT can reach 136.98 μmol/g/h,and the hydrogen production performance of WO3/TiO2 and TiO2 was also improved by about 1.3 and 1.8 times.(4)Preparation and properties of W18O49/g-C3N4 composite catalyst.W18O49/g-C3N4 composite catalyst was prepared by solvothermal method with urea and WC16 as raw materials.The W18O49/g-C3N4 composite catalyst showed that the nano-flower of W18O49 was supported on the g-C3N4 of the sheet,and the W18O49 of the monoclinic phase was chemically bonded to the g-C3N4 of the graphite-like phase.As the compounding amount of W18O49 increases,the degradation efficiency first increases and then decreases.When the composite amount of W18O49 is 40%,The photocatalytic performance W18O49/g-C3N4 was the best.When the hydrothermal temperature was 180 ℃ and the hydrothermal time was 24 h,the degradation rate of 20 mg/L MB reached 100%in 60 min under the irradiation of 250 W xenon lamp.Under the irradiation of 100 W mercury lamp,the hydrogen production rate of W18O49/g-C3N4 was 143.89 μmol/g/h,which was 1.7 times higher than that of pure g-C3N4.