The In-situ Growth Of Coatings On Inorganic Fibers By Hydrothermal Process And Their Photocatalytic Performance

BiVO4 and Bi2MoO6 as narrow band gap ternary semiconductors, exhibit good photocatalytic activity under visible light. However, the powdery photocatalysts are severely limited in their industrial application due to such shortcomings as easy agglomeration and difficult separation. Nevertheless, supported photocatalysts can overcome the above disadvantages and extend their application scope. In this thesis, the carbon fibers with BiVO4 coating (BiVO4/CFs) and carbon fibers with Bi2MoO6 coating (Bi2MoO6/CFs) are prepared respectively by direct hydrothermal method, EDTA-assisted hydrothermal method, and EG-assisted solvothermal method. The products are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-visible diffuse reflectance spectroscopy (UV-Vis DRS), and their photocatalytic performance evaluated under visible light.The research contents mainly include the following three aspects:(1) visible-light-driven photocatalyst BiVO4/CFs are prepared by a direct hydrothermal process. The samples exhibit good photocatalytic activity under visible light due to their perfect crystallization, homogeneous coating and small particle size.The effects of pH value and hydrothermal time on the morphology, crystallinity and photocatalytic property of samples are investigated. The results show that, moderate acidic conditions favor the formation of monoclinic phase BiVO4, but strong acidic condition suppresses the formation of crystal nucleus and their growth, and greatly reduces the amount of loaded BiV04 on carbon fiber surface at the same time. BiVO4 coating can not be formed when hydrothermal time is shorter than 2h, while excessively thick BiVO4 coatings with agglomerated BiVO4 particles are formed when it longer than 16 h, and thick coatings are easier to fall off and unfavorable to their application. Therefore, the optimal process conditions for synthesizing BiVO4/CFs photocatalyst should be that hydrothermal temperature is at 180℃, hydrothermal pH= 3,and hydrothermal time 8 h.(2) visible-light-driven photocatalyst BiVO4/CFs are also prepared by EDTA-assisted hydrothermal process. The samples exhibit good photocatalytic activity under visible light due to their perfect crystallization, lamellar morphology and homogeneous coating.The effects of pH value and hydrothermal time on the morphology, crystallinity, and photocatalytic property of samples are investigated. The results show that, the amount of loaded BiVO4 and its crystallinity in BiVO4/CFs sample increase with the prolonging of hydrothermal time. Meanwhile, hydrothermal pH values mainly affect the microstructure of BiVO4 crystallites. When pH value is equal to 1, massive nucleus of BiVO4 are formed. With the increase of pH value, when pH value is equal to 2, the nucleus numbers reduces. The lamellar morphology of BiVO4 crystallites can be obtained, and homogeneous BiV04 coating prepared on carbon fiber surface. When hydrothermal pH= 3, the nucleus numbers continually decrease. At the same time, the lamellar BiV04 crystallites are thinner and thinner in thickness, but the amount of loaded BiV04 decreases. Thus, optimal process conditions for preparation of BiVO4/CFs is that hydrothermal time is 5 h, hydrothermal temperature 180℃, and hydrothermal pH=2.(3) visible-light-driven photocatalyst Bi2MoO6/CFs are prepared by EG-assisted solvothermal process. The samples exhibit good photocatalytic activity under visible light due to their perfect crystallization, nanosheet morphology, and homogeneous coating.The effects of solvent types, reactant concentration, solvothermal time and solvothermal temperature on the morphology, crystallinity, and photocatalytic property of samples are investigated. The results show that, methanol as a solvent is more favorable for Bi2MoO6 crystallization than ethanol; reactant concentration should not be too high, Bi2MoO6 coating with nanosheet morphology can be formed using 5 mmol/L of Bi(NO)3 and Na2MoO4 mixed solution; and crystallinity and surface morphology of BiaMoO6/CFs samples are also affected by solvothermal temperature and time. When the temperature reaches 160℃, pure tetragonal phase of Bi2MoO6 can be obtained. With the increasing of solvothermal temperature, crystallinity of Bi2MoO6/CFs sample is gradually improved, meanwhile, Bi2MoO6 morphology changes from flake to granular shape. Similarly, prolonging solvothermal time also enhances their crystallinity, and Bi2MoO6 morphology transforms from the flake to granules.