The Preparations Of Mofs Compostite Materials And The Research Of Its Photocatalytic Performance

In recent years,the environmental pollution caused by the rapid development of industry has attracted much attention.Semiconductor photocatalysis technology has broad development prospects in the water environment treatment.Metal-organic frameworks（MOFs）have become one of research hotspot of photocatalysis due to their high porosity,large specific surface area,and adjustable pore size.In this thesis,several MOFs-based composite photocatalysts were prepared,characterized by a variety of technical means,and their composition,microstructure and optical properties were characterized.Their photocatalytic degradation performance on organic dyes in aqueous solutions were tested,and the photocatalytic mechanism was discussed.The main contents are as follows:1.At first,g-C₃N₄ nanosheets（HCN）were obtained by chemical exfoliation method.Then,a round-the-clock catalyst of high-performance ZIF-8/HCN composite was synthesized by the liquid phase diffusion method.The experiments at dark show that 20%ZIF-8/HCN has a degradation effect on MB,superoxide radicals（·O₂^-）is used to degrade MB as the main reactive species.The photocatalytic results show that under visible light,the degradation rate constant of 20%ZIF-8/HCN to MB is 0.05941 min^-1,which is 2.25 times and 12.8 times that of ZIF-8and HCN alone,respectively.Free radical quenching experiments show that under visible light,both holes（h⁺）and·O₂^-are used to degrade MB as the main reactive species.The photocatalytic activity of the composite comes from the narrow band gap width,the synergistic effect of light and heat,the heterojunction formed between HCN and ZIF-8,and the rapid separation of photogenerated electrons and holes.In addition,the stability experiment shows that the composite material has good cycle stability and reusability.2.Using precipitation method to prepare CdS nanoparticles,and then uniformly load the CdS nanoparticles on the surface of MIL-53（Al）by stirring at room temperature to form a new CdS/MIL-53（Al）composite photocatalyst.Characterization results show that the introduction of CdS nanoparticles not only have no significant impact on the original structure and morphology of MIL-53（Al）,but also solve the problem of easy agglomeration and photo-corrosion of CdS nanoparticles.Moreover,it extends the range of light absorbed from the ultraviolet region to the visible light region.The photocatalytic performance test results show that under visible light,the degradation rate constant of 50%CdS/MIL-53（Al）to methyl orange（MO）in water is 0.08086 min^-1,which is 8 times that of CdS alone.Free radical quenching experiments show that the main reactive species to degrade MO are h⁺and·O₂^-.The composite material exhibits excellent photocatalytic degradation properties due to the heterojunction formed between CdS and MIL-53（Al）and the high separation efficiency of photogenerated carriers.In addition,the cycle stability of 50%CdS/MIL-53（Al）composites was also studied.Experiments show that the introduction of the sacrificial agent sodium sulfite can effectively inhibit the photo-corrosion effect of CdS.Thereby further improving the stability of the photocatalyst.3.UiO-66 was prepared by solvothermal method at first,and then UiO-66/BiOI composite was synthesized by co-precipitation method.Various characterization methods show that the introduction of UiO-66can effectively reduce the photo-generated electron-hole recombination rate.The photocatalytic performance test results show that 20%UiO-66/BiOI removes MO under the synergistic effect of adsorption and photocatalysis.When used as an adsorbent,it exhibits a strong adsorption capacity for MO due to the large specific surface area of UiO-66 in the composite,thereby promoting the photocatalytic process.When used as a photocatalyst,the degradation rate of MO in water by 20%UiO-66/BiOI is 0.04011 min^-1,which is 1.91 times that of BiOI alone.Free radical quenching experiments show that h⁺and·O₂^-act together as the main reactive species in the degradation of MO.The composite material exhibits excellent photocatalytic degradation properties,which can be derived from the heterojunction formed between BiOI and UiO-66 and high separation efficiency of photogenerated carriers.