Study On Photocatalytic Properties Of Halogen Doped Titanium Dioxide With Long-afterglow Luminescence Composites

With the rapid development of China’s industrialization,environmental pollution is becoming increasingly prominent.The discharge of organic dyes causes water pollution,and volatile organic pollutants also seriously harm people’s health.Compared with other purification technologies,photocatalytic oxidation technology can use active particles,such as hydroxyl radical（-OH）and superoxide radical（O₂^-）,to mineralize organic pollutants into carbon dioxide（CO₂）and water（H₂O）,which is a clean technology.Generally,photocatalytic process mainly includes photoexcitation,pollutant absorption,generation and migration of carriers,degradation of pollutants.However,the duration of illumination is limited.At night,due to the absence of photoexcitation,the photocatalytic reaction will stop and the photocatalyst will lose its ability to degrade.Long-afterglow luminescent materials can store energy under light and slowly release light energy in dark.Therefore,this paper combines the two materials together to develop a photocatalyst that can carry out catalytic degradation in both light and dark environments,realizing the goal of combining the catalytic degradation function of photocatalyst with the energy storage function of long-afterglow luminescent materials.Halogen（F and I）doped TiO₂ is an ideal catalyst due to its simple preparation and good visible light catalytic performance.Sr Al₂O₄:Eu,Dy and Sr₂Mg Si₂O₇:Eu,Dy luminescent materials have been developed and commercialized,which are ideal carriers for composite materials.The specific content of the paper is as follows:1.F-TiO₂ and I-TiO₂ were prepared by sol-gel method and hydrolysis method,respectively.The optimal F doping amount is 5wt.%,and the optimum I doping content is 40wt.%.Then,Sr Al₂O₄:Eu,Dy and Sr₂Mg Si₂O₇:Eu,Dy long-afterglow luminescence were added in the preparation process of the above materials respectively,F-TiO₂/Sr Al₂O₄:Eu,Dy and I-TiO₂/Sr₂Mg Si₂O₇:Eu,Dy composites were prepared.By degrading Rhodamine B,the optimal composite ratio was determined.For F-TiO₂/Sr Al₂O₄:Eu,Dy composite,the optimal composite ratio was 90%of the mass of F-TiO₂;For I-TiO₂/Sr₂Mg Si₂O₇:Eu,Dy composites,the best composite ratio is 30%by mass of I-TiO₂.2.X-ray diffractometer was used to analyze the structure and chemical bond of the composites.The diffraction peaks of halogen doped TiO₂ and long-afterglow luminescence were found in the composites.Scanning electron microscope was used to observe the morphology of the composite.It was found that the halogen-doped TiO₂were spherical particles,which were well combined with the long-afterglow luminescence.The element composition and valence state of the composite were analyzed by X-ray photoelectron spectroscopy.It was found that the composite contains all elements of halogen doped titanium dioxide and long-afterglow luminescence materials.By using UV-Vis diffuse reflectance spectroscopy and photoluminescence spectroscopy,it was found that the composite can utilize the visible light emitted by the long-afterglow luminescent material,and it could realize photocatalysis in dark.3.The effects of different heat treatment processes on the photocatalytic properties of the composites were investigated.For the F-TiO₂/Sr Al₂O₄:Eu,Dy composite,when the sintering temperature is 450℃and the holding time is 1 h,the degradation rate of Rh B reaches 33.7%within 3 h of illumination,and 50.5%in dark within 6 h.For I-TiO₂/Sr₂Mg Si₂O₇:Eu,Dy composite,when the sintering temperature is 400℃and the holding time is 2 h,the degradation rate of Rh B reaches 19.2%in 3 h of illumination,and 30.1%in dark within 6 h.In addition,the degradation of ethanol gas was also explored in the experiment,and it was found that the composite still had photocatalytic degradation ability for volatile organic compounds（VOCs）.