Preparation And Photocatalytic Properties Of Functionalized Semiconductor Metal Oxides

Environmental pollution and the lack of green and clean energy are some serious problems facing the world at present.Photocatalytic technology based on semiconductor is one of the feasible measures to solve environmental pollution and energy shortage by utilizing abundant and clean solar energy.TiO₂ and WO₃,as the most common wide-gap n-type semiconductors,are widely used in various fields of photocatalysis due to the low cost and simple preparation,such as organic matter degradation,water decomposition to produce hydrogen and oxygen,carbon dioxide reduction,etc.However,because of the low utilization efficiency of sunlight and the rapid recombination of photo-generated electron hole pairs,the photocatalytic performance of pure TiO₂ and WO₃ is not ideal.Therefore,it is the focus of this study to adopt different strategies to improve the photocatalytic performance of n-type semiconductor（TiO₂ and WO₃）.The main research contents include the following aspects:（1）Cu₂O/TiO₂（P25）composite composed of TiO₂（P25）nanoparticles and Cu₂O was synthesized by a one-pot hydrothermal method.The evolution process of Cu₂O nanoparticles was studied by hydrothermal experiments under different reaction conditions,which indicated that the reaction temperature and time have important effects on the morphology of the nanoparticles.Cu₂O/TiO₂（P25）（60 wt%）has excellent photocatalytic performance for hydrogen production,the hydrogen production rate is up to 2.55 mmol g^-1 h^-1,which is 41.46and 3.88 times that of Cu₂O and TiO₂（P25）,respectively.A series of experimental characterization showed that the improved photocatalytic performance of the composite was attributed to the formation of Cu₂O/TiO₂（P25）p-n heterojunction,which effectively separated the electron hole pair and improved the electron transfer rate,the visible and ultraviolet light had a synergistic effect on the photocatalyst.（2）Two-dimensional ultrathin WO_3-x nanosheets with oxygen rich defects were prepared by inert atmosphere calcination method.Then,noble metal single atom Au modified WO_3-xnanosheets with oxygen rich defects(Au₁-WO_3-x)were successfully prepared by photodeposition.The results of XPS,UV-vis-NIR and EPR experiments confirmed that the introduction of Au was more conducive to the maintenance of oxygen vacancies in photocatalytic reactions.Under atmospheric pressure,room temperature and visible light irradiation,the selectivity of Au₁-WO_3-x photocatalytic selective oxidation of toluene to benzaldehyde is 96%,the yield is 1631.61μmol g^-1 h^-1,which is 4.7 times that of pure WO_3-x.The effect of interfacial synergism between metal sites and oxygen-containing semiconductor on selective photocatalytic oxidation of toluene was studied by HAADF-STEM,EXAFS,PL and EPR.（3）Two-dimensional ultrathin WO_3-x-C₃N₄ nanosheets were fabricated by a simple electrostatic self-assembly method.Zeta potential results exhibit that WO_3-x and C₃N₄ have opposite surface charges,which is beneficial to the stability of the composite structure and charge transfer.The photocatalytic performance of toluene oxidation was evaluated by measuring the photocatalytic performance of different photocatalyst materials.The prepared10%WO_3-x-C₃N₄ composite greatly improved the photocatalytic oxidation activity of toluene to benzaldehyde under ultraviolet and visible light.The yield of benzaldehyde within 6 hours is 2738.55μmol g^-1 h^-1,and the selectivity is 96%,which is 6.6 and 3.3 times of WO_3-x and C₃N₄,respectively.The improvement of photocatalytic performance is mainly due to the successful construction of two-dimensional nano-heterojunction and the abundance of oxygen vacancies which are conducive to the separation and migration of photoinduced carriers.