Studies On Strategies For Improving The Photo (Electro) Catalytic Activity Of Nano-semiconductors And Mechanism Insight

As the global environmental and energetic problems become more serious,semiconductor based photo?electro?catalytic techniques has attracted tremendous attention in the fields of pollution degradation,water splitting and CO₂ reduction,etc.However,the low photo?electro?catalytic activities restrict their practical application in industry.Comprehensively the poor photogenerated charge separation is the key factor affecting the performances of photocatalysts.Therefore,it's of theoretical and practical significance to develop facile and effective modification strategies for semiconductor photocatalysts to realize the targeted modulation of electrons and holes thereby improve the efficiency of photogenerated charge separation,meanwhile revealing the process mechanism.In this thesis,several typical inorganic semiconductors,such as CuO,Bi₂WO₆,BiOBr and BiOCl,are chosen as the model photocatalysts.Aiming at the limited reduction ability of the narrow band-gap semiconductors with positive conduction band?CB?position and the fast charge recombination,we have developed the modification strategy of coupling with wide band-gap ones.Aiming at the weak adsorption of photocatalysts surface with oxygen in the photocatalytic organic degradation,the surface phosphate modification strategy has been developed.Aiming at the bottleneck of O₂ evolution by photogenerated holes photo?electro?catalytic in the water splitting,the co-modification strategy with graphene and phosphate has been proposed.Through the above strategies developed in this thesis,we have realized the modulation of photogenerated electrons and holes and then enhanced the photo?electro?catalytic performances.Moreover,the mechanismsoftheimprovedphotogeneratedchargeseparationand photo?electro?catalytic performances have revealed by advanced techniques.The main content of this thesis includes four parts:?1?The effect of TiO₂ coupling to CuO nanoplates in the photo?electro?catalytic water reduction has explored.Firstly,we have prepared CuO nanoplates via hydrothermal method.Then TiO₂ nanoparticles have been coupled on CuO nanoplates by the wet chemical method to prepare TiO₂/CuO nanocomposites.Our results show that the introduction of TiO₂ can effectively accept and utilize the visible light photogenerated electronstoenhancethechargeseparationandthentopromotethe photo?electro?catalytic activity of water reduction.?2?The effect of SnO₂ coupling to nanostructured Bi₂WO₆ in photocatalytic degrading 2,4-DCP has explored.Nanostructured Bi₂WO₆ with large surface area have been synthesized by the hydrothermal method,and then SnO₂ nanoparticles with different amounts were coupled to form SnO₂/Bi₂WO₆ nanocomposites.These nanocomposites were utilized for photocatalytic degradation of 2,4-dichlorophenol?2,4-DCP?.Our results show that a proper amount of SnO₂ coupling can obviously improve the photocatalytic activities of Bi₂WO₆,attributing to SnO₂ can effectively accept and utilize the visible light photogenerated electrons to enhance the charge separation.Besides,SnO₂ coupling can also available to that of Fe₂O₃ by the same strategy,further demonstrating that SnO₂ is a more ideal electron platform compared with TiO₂?3?The effect of phosphate modification to the surface O₂ adsorption and photocatalytic oxidation activity on Bi OBr has explored.Impregnation-calcination method has been applied to modify BiOBr nanoplates with phosphate on BiOBr.As indicated by the experimental results,proper-amount modification of phosphate could effectively improve the photocatalytic degradation of organic pollutants in gas phase and liquid phase under visible light,which can attribute to the affinity of BiOBr surface with O₂ then facilitate the capture of O₂ by the photogenerated electrons,and then improve the charge separation.?4?The effect of reduced graphene oxide?RGO?and phosphate co-modification to the photo?electro?catalytic activity of water oxidation on BiOCl has explored.Firstly,BiOCl has been prepared and then coupled with RGO by the hydrothermal method to prepare RGO/BiOCl nanocomposites.Finally,the composites were modified with different amount of phosphate.Our results show that appropriate amount of RGO modification can greatly promote the photo?electro?catalytic activities,including water oxidation and degradation of methyl orange.While a proper phosphate modification can further improve the photo?electro?catalytic activities and stability of BiOCl.This enhancement can be attributed to the promoting of photogenerated electrons transfer and separation by RGO,and the phosphate groups could form the negative field in the aqueous system to induce the immigration of photogenerated holes to the surface of catalyst thin film,which has realized the bilateral modulation of photogenerated electron and holes to enhance the charge separation.Additionally,the unstable Cl-could be replaced by the phosphate group resulting in the formation of Cl vacancy which may be the recombining site of photogenerated carrier,thus stability of BiOCl is improved.Furthermore,this strategy of bilateral modulation of photogenerated electron and holes can also be extended to BiOBr material.