Knowledge Management System Of Institute of process engineering,CAS
中国为钒产业大国，含钒矿物储量与钒产品产量均居于世界首位，但目前钒系产品的生产和应用均以大宗钒产品为主。为满足中国钒产业可持续发展的重要需求，亟需开发高附加值的含钒产品并拓展其应用领域。光催化是同时利用光与催化剂对化学反应进行支持或提速的过程，可用于污染物降解、水分解制氢等。钒酸铋（BiVO4）是一种在可见光照射下具有光催化活性的材料，因而本论文选择了该含钒化合物为研究对象，通过材料结构设计和制备工艺研究，提高其在可见光照射下的光催化响应性能和循环使用性能，以探索其在光催化领域实际应用的可能性。首先，制备了具有不同晶体结构、尺寸、形貌的BiVO4材料，其中单斜BiVO4（m-BiVO4）纳米微球和一维m-BiVO4纳米棒在可见光照射下显示出对亚甲基蓝（MB）较好的降解效果。随后，设计并制备了BiVO4/石墨相氮化碳（g-C3N4）复合材料和BiVO4 /还原氧化石墨烯（rGO）核壳复合材料，促进了光生电子转移和电子-空穴分离，提高了对亚甲基蓝的降解速率，显示出优异的循环稳定性。最后，以碳布和碳纤维作为光催化剂支撑材料，制备了具有高负载量的催化材料，解决了光催化材料循环使用时的分离问题。本论文主要在以下几个方面取得了创新性成果：（1）通过共沉淀、溶胶-凝胶、溶剂热等方法制备了BiVO4材料。其中，通过溶剂热法制备得到的直径为1.5-2 μm的m-BiVO4中空微球具有较高的光催化性能（MB降解率为~84%）。合成机理的研究表明，局部奥斯瓦尔德熟化和化学诱导的自转化机制可能是中空微球形成的主要驱动力。通过调整尿素的添加量，可以调控m-BiVO4中空微球的尺寸、比表面积、中空结构，并影响其光催化性能。（2）通过调节溶剂种类和比例、前驱体浓度、反应温度等参数，采用水热法制备了两种不同的BiVO4样品。以水为溶剂，在pH=2、180 ?C的条件下，经12小时反应，制备得到了BiVO4纳米微球，其在可见光照射下、4小时内可将MB降解96%，但循环3次后降解率就衰减至89%。以水和乙醇按3:1比例作为混合溶剂，在pH=4、180 ?C的条件下，经过24小时制备得到了一维m-BiVO4纳米棒，其在可见光照射下、30分钟内可以将MB降解97%，3次循环后对MB的降解率稳定在95%。（3）为了进一步提高光催化活性和循环性能，设计并制备了m-BiVO4/g-C3N4复合材料，其中g-C3N4纳米片沉积在m-BiVO纳米板表面上。该m-BiVO4/g-C3N4异质结复合材料的在可见光照射下、25分钟内可以将MB降解98%以上（是g-C3N4的2.4倍、m-BiVO4纳米片的1.2倍），且8次循环后对MB的降解率仍稳定在95%。（4）采用乙醇、水、乙酸比例为3:1:1的溶剂，在180 ?C下经10小时反应，创新性制备了BiVO4/g-C3N4与BiVO4/rGO复合材料。可能由于BiVO4与g-C3N4不完全成键，导致BiVO4/g-C3N4复合材料光催化活性略差（84%，MB）。相比而言，rGO的电导性使BiVO4/rGO核壳复合材料具有优越的电子耦合性能，复合材料形成的3D网络有利于光生电子-空穴的分离，因而，该复合材料在可见光照射下对MB有较高的降解率（98%）且循环性能良好。（5）为了解决光催化材料循环使用时的分离难题，引入碳布和碳纤维作为光催化剂的支撑材料。在碳布上覆盖BiVO4/rGO复合材料，可以制备得到BiVO4/rGO@碳布材料，但3次循环后BiVO4/rGO复合材料开始从碳布上掉落。为此，设计了以尿素为粘结剂、乙二胺四乙酸（EDTA）为模板的溶剂热法，制备得到了具有较高m-BiVO4负载量的m-BiVO4@碳纤维光催化材料，解决了光催化材料循环使用时的分离问题。;China is a major country of vanadium industry in the world. Both the amount of vanadium bearing minerals and the output of vanadium products of China are in the first place in the world. However, manufacture and application of the vanadium products mainly focus on the bulk products in China at present. In order to satisfy the important requirement of sustainable development of Chinese vanadium industry, the vanadium bearing products with high added value should be exploited as well as the application field of these vanadium products also need to be expanded. Photocatalysis is a procedure where light and catalysts are concurrently used to support or speed up a chemical reaction, which can be used for the degradation of pollutions and water splitting. Bismuth vanadate (BiVO4) can be active in visible light irradiation, so this vanadium bearing compound is selected as a photocatalyst candidate in present work.The microstructure is designed as well as the preparation process are studied in order to improve the photocatalytic and recycling performance under visible light irradiation for application in the photocatalytic field. Under visible light irradiation, monoclinic bismuth vanadate (m-BiVO4) sphere and nanoribbon express outstanding photocatalytic activities for the degradation of methylene blue (MB) among the synthesized BiVO4 samples with different crystal structures, crystal sizes and morphologies. Graphitic carbon nitride (g-C3N4) and reduced graphene oxide (rGO) are added in BiVO4 to form heterostructure systems, respectively. The BiVO4/g-C3N4 and BiVO4/rGO composite demonstrate faster charge transfer and improved separation of photogenerated charge carriers. Consequently, the photocatalytic activities including degradation rate, degradation speed and durability are enhanced. For the practical application, the reusability problem of BiVO4 based photocatalysts is solved by introduction of carbon fibre and carbon cloth as supporting materials. The main achievements and innovative progresses are exhibited as follow:(1) BiVO4 samples are synthesized through the co-precipitation method, sol-gel method and solvothermal/hydrothermal method (with and without surfactants), respectively. In three methods, only the m-BiVO4 hollow microspheres (1.5~2 μm in diameter) fabricated by hydrothermal method achieve high photocatalytic degradation activity of ~84%. Localized Ostwald ripening and chemically induced self-transformation mechanism are the main driving force for the formation of hollow spheres. The average crystallite size, speci?c surface area, hollow interior structure and photocatalytic degradation activity of these BiVO4 hollow spheres could be tuned by altering the amount of urea.(2) Two different types of m-BiVO4 are synthesized via hydrothermal method under different experimental parameters including solvent, pH value, precursor, temperature, et al. By using water as a solvent, the m-BiVO4 spheres consisted of nano-particles were synthesized in the condition of pH=2 at 180 ?C after 12 hour, which yield an efficient photocatalytic activity as up to 96% in 4 hours against the degradation of MB under visible light irradiation. However, the degradation rate decreased to 89 % after 3 cycles. By using water and ethanol as a mixture solvent (H2O:C2H5OH = 3:1), the uniform m-BiVO4 nanoribbons possessing well-defined 1-D architectures were further synthesized under pH=2 at 180 °C after 24 hours. The obtained m-BiVO4 nanoribbons show efficient photocatalytic activities up to 97% in 30 minutes against the degradation of MB under visible light irradiation. The photocatalytic activities of m-BiVO4 nanoribbons also remains stable up to 95 % after 3 cycles illustrating a good recyclability, which might be attributed to the higher surface area and better crystallinity.(3) g-C3N4 nanosheets are grafted on the surface of m-BiVO4, in order to further improve the photocatalytic and recyclable performance. Employing the water as solvent, g-C3N4 nanosheets are well dispersed on the nanoplates surface of m-BiVO4 at 100 ?C after 12 hours. The photocatalytic activities of the BiVO4/g-C3N4 composite against the degradation of MB under visible light is 98% within 25 min, which is about 2.4 and 1.2 times of the pure g-C3N4 and m-BiVO4, respectively. This BiVO4/ g-C3N4 heterostructure material also shows outstanding durability that is ~95% degradation efficiency of MB even after eight consecutive cycles. (4) By using solvent of C2H5OH: H2O:CH3COOH (3:1:1), new type core shell heterostructure materials of BiVO4/g-C3N4 and BiVO4/rGO are synthesized at 180 ?C after 10 hours. Due to the incompletely binding between BiVO4 and g-C3N4, BiVO4/ g-C3N4 composite shows a lower photocatalytic activity of 84% against the degradation of MB. Comparatively speaking, the photoactivity of BiVO4/rGO composite upon visible light irradiation is enhanced by yielding superior electronic coupling because of the electron conductivity of rGO. In the BiVO4/rGO composite, the enhanced separation of photogenerated charge carriers in 3D networks results in superior photocatalytic activities of MB decomposition up to 98% with great reusability. (5) In order to solve the drainage problem during washing after each photodegradation cycle, carbon fibre and carbon cloth are introduced as supporting materials for photocatalysts. After coating on carbon cloth, the obtained samples (BiVO4/rGO@carbon cloth) show stable degradation efficiency of ~95% for MB after 2 cycles. But BiVO4/rGO composites start to separate from the surface of carbon cloth after the 3rd cycle. To solve this problem, m-BiVO4@carbon fibre material is obtained by a new hydrothermal condition with usage of urea as binder and ethylenediaminetetraacetic acid (EDTA) as surfactant. The immobilization of m-BiVO4 hollow microspheres photocatalyst on the surface of CF do not reduce the visible light absorption capability with comparison to that of pure m-BiVO4. Moreover, the m-BiVO4@carbon fibre composite shows an enhanced reusability up to 92% after 3 consecutive cycles. Because of the strong mobility of BiVO4 with carbon fibre, the BiVO4@carbon fibre with high activity and reusability can be a good solution for the drainage problem.
|TOHEED AHMED. 钒酸铋基光催化材料的设计、制备以及光催化性能研究[D]. 中国科学院大学,2018.|
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