Single-Molecule Fluorescence Images Revealing The Hydrophilic And Hydrophobic Effect Of TiO₂ Particals On Photocatalytic Degradation Mechanism Of Organic Pollutauts

Illegal discharge of industrial wastewater,abuse of antibiotics,pesticides and leakage of organic chemicals will lead to the discharge of organic pollutants into water bodies,causing serious pollution of water environment and affecting human life and health and harmonious development of society.Since most organic pollutants in water are difficult to degrade naturally,their accumulation and transformation in water will cause lasting damage to the environment.Therefore,degradation of organic pollutants in water has become an urgent problem for water pollution control.Photocatalysis technology driven by renewable solar energy is an effective method to degrade organic pollutants in water.In the degradation reaction of organic pollutants mediated by photocatalyst,photocatalyst generates photogenerated electron-hole pairs by absorbing solar energy.Photogenerated electrons with strong reducing capacity and holes with strong oxidizing capacity can react with H₂O and O₂on the surface of catalyst to generate reactive oxygen species（ROS）such as O₂^·-,H₂O₂and·OH.These highly chemically active ROS can react with organic pollutants adsorbed on the surface of the catalyst,resulting in their eventual degradation into H₂O,CO₂,etc.,thus achieving the purpose of organic pollutant degradation.Due to the hydrophilicity and hydrophobicity of the catalyst,the adsorption amounts of H₂O and O₂at the surface interface will be significantly affected,and then the ROS redox path generated by H₂O or O₂at the catalyst interface will be regulated,affecting the efficiency of photocatalytic degradation reaction.Therefore,surface interface hydrophilicity and hydrophobicity become key regulatory factors in ROS generation and transformation process.To investigate the influence of catalyst surface hydrophilicity and hydrophobicity on ROS production and transformation is crucial for accurately understanding the surface interface process of photocatalytic degradation of organic pollutants in water and regulating catalytic reactions.At present,the main research methods aimed at the surface interface catalysis mechanism of catalysts include electron spin resonance（EPR）,chemiluminescence（CL）and UV-visible spectrophotometry（UV-Vis）.Most of the above detection methods are based on the average results of all signals in the reaction system at a certain time.However,the distribution of active sites in different regions of the surface interface of the catalyst is not uniform,and the average results often cover the influence of surface defects,crystal surface effects and heterogeneous microenvironments such as hydrophilicity and hydrophobicity on the catalytic activity of the photocatalyst.The study and cognition of ROS participating in photochemical reaction are limited by the hydrophilic and hydrophobic regulation of photocatalyst surface interface.Single-molecule fluorescence microscopy（SMFM）realizes the resolution of a single molecule by improving the signal-to-noise ratio,and monitors the interface reaction process in real time through fluorescence molecule tracking and imaging.The researchers used the technique to explore the microscopic effects on the reaction mechanism.For example,the effect of hydrophobicity of nanopore on closed catalytic reaction kinetics was studied at the level of single particle and single molecule.The spatial heterogeneity of reaction sites on the surface of a single photocatalyst was studied using SMFM.In addition,researchers have used SMFM to study bimetallic effect,constraint effect and hydrogen spillover effect.SMFM can effectively reveal the catalytic kinetic mechanism at the level of single molecule.In the first chapter of this thesis,the significance and current status of the research on hydrophilicity and hydrophobicity of catalyst surface interface were reviewed,as well as the research progress of surface interface catalytic detection and the analysis of the catalytic reaction process by single molecular fluorescence imaging.The idea of using single molecule fluorescence imaging technique to study the regulation process of surface hydrophilicity and hydrophobicity on catalytic performance was proposed.In Chapter 2,a micron-scale titanium dioxide（TiO₂）photocatalyst with spherical structure was synthesized to achieve the regulation of the surface hydrophilicity and hydrophobicity of TiO₂by ultraviolet（UV,200-400 nm,20 W）irradiation and dark storage,so as to explore the differences of ROS species produced on the surface of TiO₂with different hydrophobicity.Through UV-vis spectroscopy,fluorescence spectroscopy,This thesis analyzes the influence of the photocatalyst surface interface of Hydrophilic TiO₂（TiO₂-Hydrophilic）and Hydrophobic TiO₂（TiO₂-Hydrophobic）on the degradation efficiency of organic pollutants,the number of ROS species generated on the surface and the adsorption type of organic pollutants"phobic".The experimental results show that the TiO₂-Hydrophilic photocatalyst"phobic"generates more·OH on the surface interface,while the surface interface TiO₂-Hydrophilic"phobic"generates more ¹O₂.In Chapter 3,based on the single-molecule fluorescence imaging on the surface of the catalyst TiO₂-Hydrophilic and TiO₂-Hydrophobic,at the single-particle level,we analyze the species differences generated by ROS regulation by different hydrophobic and hydrophobic surface interfaces and the spatial heterogeneity of the active site for ROS generation.At the same time,the adsorption and dissociation rates of fluorescent products on the surface of single particles and the ROS generation rate were analyzed by single molecule fluorescence kinetics,and the molecular mechanism of different hydrophilic and hydrophobic TiO₂catalysts for degradation of organic pollutants was analyzed by combining the results of DFT calculationIn summary,this thesis studied the photocatalytic reaction process regulated by hydrophobicity and hydrophobicity on the surface of catalyst particles through single molecule fluorescence imaging technology,and explained the regulation effect of hydrophobicity and hydrophobicity on photocatalytic degradation of organic pollutants.The establishment of the research method and the information obtained will provide important scientific basis and theoretical guidance for further revealing the surface photochemical process and regulatory mechanism of particles,evaluating catalytic performance and designing catalysts.