Preparation Of TiOF₂ And TOF₂/TiOF₂ Catalysts And Their Photocatalytic Activity

The problem of water environment and ecological pollution caused by dye wastewater has attracted widespread attention.Dyestuff wastewater has the characteristics of large amount of water,high concentration,heavy color,serious toxicity and poor biodegradability,and the traditional biological or chemical method is not suitable for treating dye wastewater.As a new advanced oxidation technology,photocatalytic oxidation technology has become one of the most promising sewage treatment technologies due to its strong redox ability,stable chemical properties,simple reaction conditions,low energy consumption and no secondary pollution.Because only ultraviolet light can be used,photocatalytic technology using titanium dioxide as a catalyst can be limited in practical applications.Therefore,the development of sunlight-responsive photocatalysts that can effectively utilize sunlight has attracted more and more attention from researchers.In recent years,a few studies have shown that titanium oxyfluoride(TiOF2)as a new narrow-bandgap solar response photocatalyst can be applied to the degradation of organic pollutants,photolysis of water and other fields,but its degradation performance needs to be further improved.In addition,the existing preparation of TiOF2 generally requires hydrothermal or high-temperature preparation,the process is complex and the energy consumption is high,which is not conducive to large-scale preparation.In this dissertation,the TiOF2 catalysts with good visible light photocatalytic performance at low temperature were prepared.With butyl titanate as the titanium source and hydrofluoric acid as the fluorine source,TiOF2 was prepared by sol-gel method and hydrothermal method,respectively.In order to enhance its photocatalytic performance,we have creatively prepared TiO2/TiOF2 composite photocatalyst by one-step hydrothermal method and hydroxylated it to prepare OH-TiO2/TiOF2.The photocatalytic activity of the sample was investigated with methylene blue dye wastewater as the target pollutant.The samples were characterized by XRD,SEM,UV-Vis DRS,FT-IR,PL.The mechanism of photocatalytic activity of the samples was discussed.The mechanism of one-step preparation of TiO2/TiOF2 composite photocatalysts was also discussed.The results show:(1)The TiO2 nano-particles prepared by the sol-gel method are spherical in shape,while the TiOF2 prepared by the hydrothermal method is cubic.The flower globular morphology has not been reported in the literature.Compared with the data,the prepared TiOF2 catalysts have excellent photocatalytic properties.The reaction time has an important influence on the crystal phase and morphology of the sample as well as the photoelectric recombination rate,thus affecting its photocatalytic performance.(2)A one-step hydrothermal method was used to prepare TiO2/TiOF2 composite photocatalyst with different amounts of hydrofluoric acid and different reaction times with butyl titanate and hydrofluoric acid as titanium source and fluorine source.This method has not been seen yet in literature reports.The amount of hydrofluoric acid and the hydrothermal time control the crystal structure and morphology,and seriously affect the surface hydroxyl radicals,associated hydrogen bonds and the sample’s response to visible light.When the amount of hydrofluoric acid was 10mL and the hydrothermal reaction time was 120min,a mixed crystal structure in which both TiO2 and TiOF2 exist simultaneously is formed.When the composite ratio of the two crystals was(TiO2/TiOF2)=0.55,the solar light and visible light photocatalytic activity of this sample was the best,and far better than single-phase TiOF2 and similar materials reported in the current literature.Its excellent photocatalytic properties attributed to its mixed crystal structure which reduces the bandgap of the material and enhances its visible light performance.(3)Hydrothermal alkali washing method was used to prepare OH-TiO2/TiOF2 photocatalyst with sodium hydroxide as the hydroxyl source,which improved the performance of TiO2/TiOF2 composite photocatalyst.The use of alkali washing with sodium hydroxide for improving the performance of TiO2/TiOF2 composites has not been reported in the literature.Hydroxylation can change crystal structure,morphology and the ratio of TiO2 to TiOF2.Compared with TiO2/TiOF2,the photocatalytic activity of OH-TiO2/TiOF2 photocatalyst is obviously improved.Due to the rich hydroxyl radical,particle size decreases specific surface area and more oxygen vacancies.