The Preparation Of Bismuth Vanadate With Different Surface Structure And Its Photocatalytic Performance

As a visible-light responsive photocatalyst,bismuth vanadate oxides?BiVO₄?exhibited good photocatalytic performance in the application of organic pollutants degradation.In this thesis,BiVO₄ with different surface states were prepared by changing the experimental methods,increasing surface defect state and metal ion modification.Their photocatalytic properties were also studied.The prepared samples were characterized by X-ray powder diffraction?XRD?analysis,scanning electron microscopy?SEM?,transmission electron microscopy?TEM?,X-ray photoelectron spectroscopy?XPS?,photoluminescence?PL?spectroscopy and UV-visible diffuse reflectance spectra?DRS?analysis and so on.And the relationship between the surface state and photocatalytic properties of samples with different morphologies was further explored.The main contents of this paper include the following three parts:a)BiVO₄ nanofibers with high specific surface area and high catalytic performance were prepared by a two-step synthesis method.The ethylene glycol?EG?and NaOH solution played an important role on their formation.The BiVO₄ nanofibers prepared by this method had a higher specific surface area than the conventional BiVO₄samples,and the adsorption performance was greatly increased.At the same time,the surface acidic properties of BiVO₄ nanofibers availed the degradation of dyes.In addition,we prepared M_xV_yO_z-BiVO₄ photocatalysts by doping metal ions Mⁿ⁺with high adsorption performance using BiVO₄ nanofiber as the substrate.The experimental results showed that the addition of Ce³⁺inhibited the crystal transformation of bismuth vanadate oxide and improved its photocatalytic activity.b)BiVO₄ photocatalysts with different morphologies and crystal phases were prepared by alkali etching treatment.After treatment of NaOH?low concentration?,the surfaces of the BiVO₄ polyhedrons were slowly etched and became rough.When the NaOH concentration increased to a certain value,the polyhedral BiVO₄ samples completely changed into other phases,such as Bi₂O₃ regular tetrahedrons,Bi₇VO₁₃sheets and rods,and Bi₂₅VO₄₀0 triangle-blocks and cuboids.Particularly,when the concentration of NaOH was 0.1 M,the obtained samples were the composites of the polyhedral BiVO₄ with rough surfaces and the regular tetrahedral Bi₂O₃.And the composites exhibited the best photocatalytic activity in the degradation of several organic pollutants.Through the exploration of the degradation mechanism of composite materials,the results showed that the composite of BiVO₄ and Bi₂O₃greatly increased the transfer rate of photogenerated electron-hole pairs,and then produced highly active species such as h⁺.In addition,bismuth vanadate oxide photocatalysts with different crystalline phases also exhibited antibacterial activity towards Escherichia coli,greatly inhibiting the growth and proliferation of bacteria.The photocatysts would have potential applications in the biological field.c)The monoclinic phase BiVO₄ photocatalysts with nanofibrous,polyhedral,coral and spherical morphologies were prepared to study the influence of different surface states on the photocatalytic performance.The results are as follows:the nanofibrous BiVO₄ had the best adsorption performance for organic matter,due to its high specific surface area.The photocatalytic activities of polyhedral BiVO₄ samples were higher than that of coral and spherical BiVO₄.This was because the separation efficiencies of the photogenerated electron-hole pairs of the polyhedral BiVO₄ samples were higher than that of the coral and spherical samples.The surface hydroxyl groups were tested and found on the surface of BiVO₄ samples by the methods of acid-alkali titrations and Zeta potentials.Furthermore,the number of surface acidic hydroxyl groups on the surface of polyhedral BiVO₄ samples was higher than that on coral and spherical BiVO₄ samples.More surface hydroxyl groups were reacted with holes to form more active species,such as hydroxyl radicals?·OH?,which can effectively degrade organic pollutants in water.This paper aimed to provide basic data and theoretical support for the development of other efficient visible-light response photocatalysts,and these results are of great significance to recognize the photocatalytic mechanism correctly and clearly.