Preparation,Characterization And Photocatalytic Performance Of Nanocrystalline Metal Boride Coupled With TiO₂

With the rapid development of modern industry and economy,environmental pollution and energy shortage have become two major problems that threaten the survival of human beings.Especially,the increasingly serious discharge of organic dye industry wastewater has threatened human life and health.Semiconductor photocatalysis technology converts renewable solar energy into chemical energy,and the resulting photogenerated carriers can effectively degrade organic pollutants into water and carbon dioxide,which provides a green and sustainable way to degrade organic pollutants.Titanium dioxide（TiO₂）stands out among many photocatalysts because of its low fabrication cost,high photochemical stability,simple preparation process,and non-toxicity that can be industrialized on a large scale.However,this material has a high photogenerated carrier complexation rate and low photocatalytic efficiency in the photocatalytic process.Therefore,to improve the photocatalytic activity of TiO₂,this thesis systematically investigates the compound physical phase,microstructure,and the separation and transport properties of photogenerated carriers for the first time by using nano-metal borides as co-catalysts and compounding with nano-TiO₂,thereby reveal the mechanism of photocatalytic activity enhancement.The main research contents of this thesis are as follows:（1）Firstly,the sol-gel method was used with tetrabutyl titanate as the titanium source,and add a certain amount of inhibitors such as hydrochloric acid and glacial acetic acid in the solution mixing stage to adjust the p H value and to form the sol-gel by condensation reaction.Subsequently,the obtained colloids were aged,dried,and calcined to produce single-phase TiO₂powder with an average particle size of 20 nm.The photocatalytic performance was systematically tested with rhodamine B and tetracycline as the degradation targets.The results showed that the degradation rates of self-made TiO₂for rhodamine B and tetracycline were 92%and 83%,respectively,both of which were higher than the commercial TiO₂（P25）powder degradation rates of 64%and 66%.（2）To further improve the nano-TiO₂photocatalytic activity,TaB₂@TiO₂composites were prepared by doping with different mass percentages of tantalum diboride nanoparticles（TaB₂）in the solution mixing stage for compounding.The results of photocurrent,impedance,and fluorescence lifetime tests showed that the sample with 3%doping（TT3）had the highest photocurrent,the lowest impedance,and the longest fluorescence lifetime,indicating a significant improvement in the separation of photogenerated carriers.The photocatalytic test results demonstrated that the composite increased the degradation rates of rhodamine B and tetracycline to100%and 90%,respectively,and the degradation rates were 1.73 and 1.23times higher than those of pure TiO₂.The results of first-principles calculations show that the composite interface and TaB₂both have good electrical conductivity,moreover,the TaB₂Fermi energy level is lower than the TiO₂conduction band,which enables the photogenerated carriers to be separated and transported effectively and thereby enhances the photocatalytic activity.（3）Considering the nano rare earth lanthanum hexaboride（LaB₆）has a strong surface plasmon resonance effect in the near infrared region,its surface generates strong local electric field and hot electrons.These properties provide excellent conditions for reducing photogenerated carrier complexation in photocatalytic reactions.Therefore,this thesis proceeds to investigate the phases,microstructure and photocatalytic performance of nano-LaB₆and TiO₂composites.It was found that the sample with 5%LaB₆doping（TL5）had the highest photocurrent,the lowest impedance and the longest fluorescence lifetime.Meanwhile,the composite had the best photocatalytic activity with 96%and 92%degradation rates of rhodamine B and tetracycline,respectively,which were better than those of self-made TiO₂and commercial P25.In summary,we selected nanoborides with different photocatalytic enhancement mechanisms as co-catalysts in this paper,and systematically studied the series of composites microstructures,electronic structures and photocatalytic ability of organic degradation of,and obtained excellent photocatalytic composites.It provides a new idea for preparation and modification of novel,high-efficiency multifunctional heterojunction photocatalytic composites.