Preparation And Properties Of Lanthanum Molybdate Based Photocatalyst

In recent years,the energy crisis and environmental pollution have become one of the urgent issues to be solved in today's society.Semiconductor photocatalytic technology is considered to be the most ideal treatment method because of its advantages of energy saving,low cost,mild reaction conditions and no secondary pollution.However,the development of an efficient,stable,and practical semiconductor photocatalyst still faces serious challenges.This is mainly due to the fact that most of the catalysts have lower carrier mobility and higher recombination probability in the photocatalytic process.Therefore,under the premise of satisfying the thermodynamics required for semiconductor photocatalytic reaction,the improvement of photogenerated carrier dynamics is the key to improve its catalytic performance.In this paper,Bi₂MoO₆ is used as a research object with a wide response range under visible light.Moreover,the kinetic behavior of the photo-generated carriers of the catalyst is regulated by a series of modification means to improve its photocatalytic performance.The Fe³⁺ doped Bi₂MoO₆ photocatalyst was prepared by solvothermal method.After doping,the sample showed excellent photocatalytic properties in nitrogen fixation,reduction of Cr??? and degradation of organic pollutants.The theoretical calculation and experimental results of DFT show that the photocatalytic performance of the doped modified sample is mainly attributed to the fact that the surface work function of Bi₂MoO₆ can be significantly reduced after Fe³⁺ ion doping,and the migration of photogenerated carriers to the surface is promoted.Moreover,doping can construct Fe³⁺/Fe²⁺ redox channels on the surface of the material,and promote the photocatalytic reaction as an active site for N₂ reduction.Therefore,compared with the pure phase Bi₂MoO₆,the photocatalyzed nitrogen fixation activity of the doped sample showed a 3.7-fold increase and showed higher stability and selectivity.The PO₄^3--doped,atomic-thick Bi₂MoO₆ ultra-thin nanosheet photocatalyst was prepared by a solvothermal process with sodium phosphate and a surfactant.By analyzing the effects of different doping amounts on the phot ocatalytic activity of the samples,the Bi₂MoO₆ photocatalyst exhibited excellent photocatalytic nitrogen fixation and reduced Cr???activity when the doping amount was 3.0%.The results of DFT theoretical calculations and experiments show that the atomic-scale thickness of Bi₂MoO₆ nanosheet structure can greatly shorten the distance of photogenerated carriers transported to the surface,thereby promoting their effective separation;and introducing PO₄^3-anion groups into the crystal of Bi₂MoO₆ will cause lattice distortion,resulting in oxygen vacancies in the Mo-O octahedron and exposure of Mo ions that promote nitrogen adsorption and activation.In addition,the surface work function of Bi₂MoO₆ is also reduced by doping to promote the migration of photogenerated carriers to the surface.Therefore,compared with the pure phase Bi₂MoO₆,the nitrogen fixation activity of the sample after the doping showed an increase of about 4.1 times.The C₃N₄ ultra-thin nanosheets were prepared by thermal etching,and further mixed with Bi₂MoO₆ ultrathin nanosheets to construct C₃N₄/Bi₂MoO₆ Van der Waals heterojunction photocatalyst.The HSO-C₃N₄ photocatalyst was prepared by surface modification of C₃N₄ with a sulfonic acid group.The C₃N₄ ultra-thin nanosheet was modified by sulfonic acid group,and further combined with Bi₂MoO₆ to form a sulfonic acid group bridged C₃N₄/Bi₂MoO₆ composite photocatalyst.The samples showed excellent photocatalytic performance.The C₃N₄/Bi₂MoO₆ Van der Waals heterojunction photocatalyst has a strong electron coupling effect between the semiconductors,which effectively improves the separation efficiency of the photo-generated carriers and promotes the photocatalytic activity.The reason for the improvement of the photocatalytic performance of the HSO-C₃N₄ sample is attributed to the fact that the sulfonic acid group is an electron withdrawing group,which can induce the migration of photogenerated carriers to the catalyst surface,thereby promoting the transport and separation of photogenerated carriers.In the sulfonate-bridged C₃N₄-Bi₂MoO₆ composite photocatalyst,the formation of a photo-transfer carrier transfer channel between the two semiconductors by the sulfonic acid group can promote the transfer of carriers between the catalysts,thereby improving Transmission and separation of photogenerated carriers.The QDs self-decorating Bi₂MoO₆/BCN ternary composite photocatalyst was successfully constructed by solvothermal method.The mechanism of quantum dots generation and the effect of different BCN introduction on photocatalytic performance were systematically analyzed.The sample showed the best photocatalytic activity when the solvothermal temperature was 180? and the BCN was introduced at 5%.Analysis of photoelectrochemistry and time-resolved fluorescence spectroscopy was performed to analyze the dynamic behavior of photogenerated carriers.In the homojunction of quantum dot self-modification,photogenerated carriers are more easily transferred due to the existence of lattice matching and band matching.The introduction of BCN further promotes the transfer and separation of photogenerated carriers.Therefore,the photocatalytic reduction of Cr performance of this sample showed an increase of approximately 7.14,2.28,and 1.66 times compared to BCN,BMO,and BMO?Q?.