Preparation,Doping Modified And Photocatalytic Performance Research Of Small Size Hollow TiO₂ Nanomaterials

With the development of human society,more and more people are aware of the importance of energy conservation and environmental protection.Photocatalytic degradation technology as a green,environmental repair technology came into being.Photocatalyst plays an important role in photocatalytic technology.Under normal temperature and pressure,titanium dioxide?TiO₂?as the ideal photocatalyst,is exposed to light with a certain wavelength to decompose the organic pollutants into low-toxicity small molecule organic substances or carbon dioxide and water.Hollow TiO₂ nanomaterials have higher specific surface area and photoelectric activity than traditional TiO₂.At present,the commonly used preparation methods of hollow TiO₂are the template method and solvothermal method.Hollow TiO₂ obtained by these two methods usually has a larger diameter more than 100 nm and a small specific surface area.There are many disadvantages of TiO₂,for example,low sunlight utilization rate and high photocharge charge recombination rate.These greatly limit the practical application of TiO₂.In this paper,the photocatalytic properties of hollow TiO₂ were improved by doping.The main research are as follows:?1?Using titanium sulfate as titanium source,the small size hollow TiO₂nanomaterials were successfully prepared by co-precipitation method combined with hydrothermal method.The particle size and wall thickness were about 10-20 nm and2-5 nm respectively.Compared with the traditional preparation method,the process has the following advantages:the template coating and the template removal process are reduced;the obtained product has small particle size,large specific surface area and pure composition;the preparation process does not use organics and has no pollution to the environment.The crystal forms of final product were anatase and bronze?TiO₂?B??.The specific surface area of TiO₂ was about 114 m²/g.In the experiment,methylene blue was used as a degradant to investigate the photocatalytic performance of TiO₂ in two light sources?ultraviolet light and simulated sunlight?.?2?Through non-metal doping,using melamine as doping agent,doping in hydrothermal stage,N-TiO₂ were prepared with different doping amount to investigate the effect of doping N on the photocatalytic performance.The results were as follows:under both light sources,doping N enhanced the photocatalytic performance of samples and the maximum degradation rates were achieved at a molar ratio of N:Ti?1:1?;the degradation rate under UV light?98.57%?was 27.55%higher than TiO₂,and the degradation rate?98.54%?under simulated sunlight was 13.67%higher than TiO₂.The reasons for the increase of TiO₂ photocatalytic activity by doping nitrogen were analyzed by XRD,SEM,TEM,EDS,N₂ adsorption and desorption,UV-vis and other characterization tests.?3?Through metal doping,the typical transition metal-cobalt and rare earth metal-niobium were selected respectively.Using cobalt nitrate and cerium nitrate as dopants,Co-TiO₂ and Ce-TiO₂ were prepared by different doping methods?doping in the coprecipitation stage and doping in the hydrothermal stage?and different doping amount to study the effect of cobalt or cerium doping on the photocatalytic performance.The experimental results showed that doping in the hydrothermal stage was better than the co-precipitation stage.Under UV light:0.5%Co-TiO₂ had the highest degradation rate?82.44%?,which was 11.42%higher than that of pure TiO₂;1%Ce-TiO₂ had the highest degradation rate?95.20%?which was improved 24.18%than pure TiO₂.Under simulated sunlight,the cobalt ion doping reduced the photocatalytic activity of the samples;0.5%Ce-TiO₂ had the highest degradation rate?98.81%?,which was 13.94%higher than pure TiO₂.The reasons for the change of product photocatalytic activity were analyzed by XRD,SEM,TEM,EDS,N₂adsorption and desorption,UV-vis and other characterization tests.?4?Through non-metal and metal Co-doping,using melamine,cobalt nitrate and cerium nitrate as doping agent,doping in hydrothermal stage,N,Co,and Ce multivariable doped hollow TiO₂?N/Co/Ce-TiO₂?nanomaterials were prepared by orthogonal experiment.The orthogonal experimental results showed that the doping amount of Co had the greatest influence on the photocatalytic activity of the sample.Under UV light and simulated sunlight,the degradation rates of Co/Ce/N-TiO₂ were lower than that of single-factor doping,indicating that the doping elements?Co,Ce and N?showed antagonistic effect.