| In recent years,photocatalytic technology,a green advanced oxidation technique has attracted much attention due to its low cost,simple operation and absence of secondary pollution because of the intensification of energy crisis and environmental pollution.And it has been applied in a wide range of fields including photodegradation of organic contaminators in wastewater,hydrogen production from water splitting and CO2 conversion to renewable fuels.As the core of photocatalytic technology,the research of photocatalysts have been the focus of research scholars,and it is committed to the development of photocatalysts that are simple and easy to obtain,green,non-toxic,stable and superior performance.In this paper,the perovskite-structured bismuth tungstate?Bi2WO6?material was the focus of research,and metal?titanium?-organic frameworks?Ti-MOFs?,a type of materials with large specific surface area and highly porous nanostructure was introduced during the synthesis of Bi2WO6 photocatalyst to further improve the catalytic performance of the composite photocatalyst.A variety of characterization methods were applied to analyze the composition,structure,morphology,optical and electrochemical properties of the composites,and all research data were integrated to explore possible photocatalytic mechanisms.1.In this paper,white MIL-125?Ti?material powder was synthesized via solvothermal method,and it was successfully introduced into MIL-125?Ti?/Bi2WO6composite with different MIL-125?Ti?content during the preparation of Bi2WO6photocatalyst.SEM,TEM and Mapping results showed that the Bi2WO6 nanosheets were uniformly distributed on the surface of MIL-125?Ti?plate material.The photocatalytic performance of MIL-125?Ti?/Bi2WO6 composites was evaluated by the degradation of TC under visible light irradiation.The results showed that the photocatalytic performance of MIL-125?Ti?/Bi2WO6 composites was significantly higher than that of the monomeric Bi2WO6,of which 5 wt%MIL-125?Ti?/Bi2WO6exhibited the best photocatalytic activity.It was found that the specific surface area of MIL-125?Ti?/Bi2WO6 composite was larger than Bi2WO6 monomer material,providing more active sites.DRS characterization results indicated that the MIL-125?Ti?/Bi2WO6 composite broadens its absorption range of solar light and is beneficial for absorbing more energy.Electrochemical characterization showed that MIL-125?Ti?/Bi2WO6 composites displayed higher photogenerated carrier generation and separation efficiency and lower recombination efficiency,further improved the photocatalytic performance.The results of free radicals trapping experiments and ESR analysis indicated that·O2-and h+were the main active species during the photocatalytic process,and further explored the possible mechanism within the photocatalytic degradation process.2.On the basis of the previous chapter,NH2-MIL-125?Ti?,MIL-125?Ti?material with amino group introduced,was prapered and then combined with Bi2WO6monomer material to synthesize NH2-MIL-125?Ti?/Bi2WO6 composites via hydrothermal method.By inducing the growth of amino groups on MIL-125?Ti?to form NH2-MIL-125?Ti?,a ligand-metal charge transfer band?LMCT?from the amino group to the metal node can be constructed.The photoexcitation is initialized by delocalizing the?-electron at the site of O2-in the 2-aminoterephthalate?ATA?group,and the band is formed by further transferring the electron to the Ti-oxo cluster with the formation of Ti3+by reducing Ti4+.In addition,the absorption of visible light increased,thereby improving the photocatalytic performance.Therefore,the NH2-MIL-125?Ti?/Bi2WO6 composite displayed a broadly broadened light absorption range detected by DRS.The photocatalytic activity of NH2-MIL-125?Ti?/Bi2WO6composites was evaluated by photocatalytic degradation of tetracycline?TC?and rhodamine B?RhB?.Furthermore,the structure,morphology,optical properties and photocatalytic properties of the composites were also studied.The relationship between structure and performance was analyzed in detail and possible photocatalytic mechanism was proposed based on the experimental results.3.In photocatalytic applications,morphological control in nanostructures and microstructures plays a key role.In order to further study the photocatalytic performance of the MOFs/Bi2WO6 composites,the combination of aminated NH2-MIL-125?Ti?and modified Bi2WO6 material would be employed to explore the enhencement of photocatalytic performance.The modification method adopted the regulation of the morphology of the Bi2WO6 material by adjusting the pH value during the reaction,and generated a flower-shaped spherical Bi2WO6 material assembled by nanosheets.NH2-MIL-125?Ti?/S-Bi2WO6 composites were obtained by simple hydrothermal route and the morphology of the composites did not change significantly compared to pure S-Bi2WO6,which was observed by SEM,TEM,Mapping and other characterization methods.It was found by BET and DRS characterization that the specific surface area and the light response range of composites were increased.Electrochemical analysis showed that the separation efficiency of photogenerated electrons-hole pairs increased as well as the recombination efficiency decreased under the visible light illumination,which promoted the photocatalytic activity greatly.Photocatalytic degradation experiment was carried out by employing tetracycline hydrochloride?TC?as the target pollutant under visible light to evaluate the photocatalytic performance of the prepared photocatalysts.Results showed that the photocatalytic performance of NH2-MIL-125?Ti?/S-Bi2WO6 composites was significantly enhanced compared to monomer materials,and the optinmal amount of NH2-MIL-125?Ti?was 5 wt%.Finally,ESR and free radicals trapping experiments were carried out to verify that the major active species were superoxide radicals?·O2-?and holes?h+?.The possible photocatalytic mechanism was speculated based on all the experimental results and characterization analysis. |
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