The Preparation Of Supported Ta And V-based Photocatalysts And Research On Their CO₂ Reduction Properties

The extensive use of non-renewable fossil energy has led to energy shortage and increased CO₂concentration in the air,which has brought about a series of environmental problems.Photocatalytic technology directly utilizes the inexhaustible solar energy to convert CO₂ into renewable fuels such as CO,CH₄,CH₃OH and so on.It provides a green way to solve the above problems.H₂SrTa₂O₇?HST?has a layered perovskite structure and it can make the photoelectrons-holes distributed in different space positions,which can effectively inhibit carrier recombination and improve photocatalytic activity.Ag,Pd,Au and Cu₂O cocatalysts can be used as electron traps to capture photogenerated electrons,further promoting the separation of photoinduced charges in HST,thus improving the photocatalytic reaction efficiency.A photocatalytic material with appropriate conduction band potential can be obtained by preparing Bi_xY_?1-x?VO₄ solid solution with adjustable band structure.The charge separation of the photocatalyst can be promoted by the supporting of the cocatalysts,so as to improve its photocatalytic activity.In order to overcome the problem of low specific surface area of Bi_xY_?1-x?VO₄ solid solution,we tried to prepare Bi_0.5Y_0.5VO₄ solid solution photocatalyst?HT-BYV?with large specific surface area by hard template method.The main contents and conclusions of this paper are as follows:?1?HST photocatalyst was prepared by solid-state and ion-exchange method.Ag,Pd,Au and Cu₂O cocatalysts were loaded on the surface of HST by photodeposition method.The effect of cocatalysts on the performance of HST in photocatalytic reduction of CO₂ and its mechanism were studied.The results showed that the photocatalytic activity of the supported samples were generally improved,and the evolution rates of CO and H₂ on the samples were significantly different.The results of PL,LSV and activity test show that the photocatalytic activity of HST can be improved by effectively separating the photogenerated carriers of HST.Each sample has different evolution activity of CO and H₂ due to CO and H₂ have different evolution overpotentials in the samples.Pd/HST samples showed high photocatalytic activity for CO and H₂:the formation rates of CO and H₂ were 0.28?mol·g^-1·h^-1 and 16.5?mol·g^-1·h^-1,respectively.This is because CO and H₂ have the lower evolution overpotential on Pd/HST samples.?2?Bi_xY_1-xVO₄?x=0,0.1,0.3,0.5,0.6,1.0?photocatalysts were prepared by solid-state method.The samples were characterized and their properties were tested.The results showed that Bi_xY_1-xVO₄ formed solid solution with the structure of tetragonal phase of YVO₄ in the range of x=0.1-0.5.The substitution of Bi for Y in YVO₄ lattice can effectively reduce the conduction band position and thus the band gap of Bi_xY_1-xVO₄ solid solution.The results of activity test showed that only CO was produced on the photocatalyst and the photocatalytic activity of Bi_0.5Y_0.5VO₄?BYV?was the highest.The rate of CO formation of BYV is 0.07?mol·g^-1·h^-1.In order to further improve the photocatalytic activity of BYV,Au and Cu cocatalysts were loaded on the surface of BYV.The results of characterization and performance test show that the loading of Au and Cu promotes the charge separation ability of BYV and reduces the overpotential of CO evolution,thus further improving the photocatalytic activity of BYV.The photocatalytic activity of Au/BYV is the highest when Au cocatalyst is loaded at 1.0 wt%,reaching 0.25?mol·g^-1·h^-1,which is 3.5 times of that of BYV.The activity of photocatalytic reduction of CO₂ of BYV was further enhanced after loading of Cu species.When the loading of Cu species was 3.0 wt%,the rate of CO evolution on Cu/BYV reached 0.32?mol·g^-1·h^-1,which is 1.28 times of that of 1.0 wt%Au/BYV.Cu species as a cocatalyst can not only promote the activity of photocatalytic CO₂ reduction,but also effectively reduce the cost of the catalyst.?3?The BYV solid solution photocatalyst with large specific surface area was prepared by hard template method using SiO₂ as template.The results of characterization and performance test show that the particle size of HT-BYV sample is smaller and the specific surface area is larger than that of bulk BYV.However,the photocatalytic activity of HT-BYV is lower than that of BYV,which may be due to the fact that Na⁺on the surface of HT-BYV occupies the active site,thus inhibiting the adsorption of CO₂.