The Mechanism Research Of The Surface Defects And Hydrophobic Synergistic Regulation On The Effect Of TiO₂ Photocatalytic Nitrogen Fixation Synthesize Ammonia Performance

With the rapid increase of world population and the acceleration of industrialization,humanity is facing enormous challenges such as energy crisis,environmental pollution,and food shortage.Ammonia is an important chemical raw material and non-carbon energy carrier,and is an important raw material for the fertilizer industry,polymer chemical industry,explosives industry,and basic organic chemical industry.With the increasing demand for ammonia by humans,biological nitrogen fixation ammonia synthesis are far from meeting human needs.At present,the Haber-Bosch ammonia synthesis process,which is mainly used in industry,can produce a large amount of ammonia under high temperature,high pressure,and the presence of catalysts,but it also brings huge energy consumption and excessive greenhouse gas emissions.It can be seen that the development of green and low energy consumption synthetic ammonia technology is of great significance in alleviating energy crises and protecting the ecological environment.Semiconductor photocatalytic technology is a green technology that utilizes solar energy to drive chemical reactions,providing a new choice for low-cost,low energy consumption,and low pollution ammonia synthesis.TiO₂ has unique advantages such as simple synthesis process,non-toxicity,stable chemical properties,and low price.It has always been a star catalyst in the field of photocatalysis,and has been widely used in fields such as photocatalytic pollutant removal,water decomposition for hydrogen production,and carbon dioxide reduction.Due to the narrow response range of TiO₂ to solar spectrum and the short lifespan of photogenerated charge carriers,especially the low adsorption and activation ability of pure TiO₂ surface for nitrogen,the efficiency of photocatalytic nitrogen fixation synthesize ammonia is low.This dissertation focuses on two key scientific issues in the field of photocatalytic nitrogen fixation synthesize ammonia,namely,how to improve the activation ability of TiO₂for nitrogen-nitrogen triple bonds and the degree of nitrogen adsorption on its surface.The mechanism of the synergistic regulation of surface defects and hydrophobicity on the performance of TiO₂ photocatalytic nitrogen fixation synthesize ammonia is systematically studied.The main research content includes the following four parts:1.Defect construction and fluorine surface modification to improve the photocatalytic nitrogen fixation synthesize ammonia performance of TiO₂:Firstly,oxygen vacancies（Vo）were introduced onto the surface of TiO₂ by solid-state thermal reduction method.Defective TiO₂（Vo-TiO₂）was synthesized by optimizing reaction temperature,thermal reduction time,and sodium borohydride addition amount.The influence of Vo on the band structure and photogenerated carrier lifespan of TiO₂ was investigated through a series of characterization methods such as DRS and photoelectrochemical testing,combined with theoretical calculations.By regulating the amount of fluorine modification on the surface of Vo-TiO₂,the influence of fluorine surface modification on the hydrophobicity and photocatalytic nitrogen fixation performance of the catalyst was investigated.The experimental results show that the photocatalysis nitrogen fixation synthesize ammonia efficiency of F-Vo-TiO₂,which is rich in defects and modified with fluorine,can reach 206μmol·g^-1·h^-1,which is about 9 times that of pure TiO₂(23μmol·g^-1·h^-1).2.Defect construction and alkyl acid surface modification to improve the photocatalytic nitrogen fixation synthesize ammonia performance of TiO₂:Based on the use of solid-phase thermal reduction method to obtain surface rich oxygen vacancies in Vo-TiO₂.A series of C_x-Vo-TiO₂ modified with alkyl acids of different carbon chain lengths,such as acetic acid,valeric acid,octanoic acid,undecanonic acid,and tetradecanoic acid,were synthesized by surface modification of Vo-TiO₂.The influence of alkyl acid carbon chain length on the hydrophobicity of Vo-TiO₂ and the performance of photocatalytic nitrogen fixation synthesize ammonia was investigated.The results indicate that alkyl acid modification can improve the hydrophobicity and hydrophilicity of Vo-TiO₂ surface,effectively inhibiting hydrogen evolution reaction.Among them,the photocatalytic nitrogen fixation efficiency C₈-Vo-TiO₂ modified with octanoic acid can reach 392μmol·g^-1·h^-1,which is about 17 times that of pure TiO₂.3.Defect construction and bipyridine derivative surface modification to improve the photocatalytic nitrogen fixation synthesize ammonia performance of TiO₂:Based on the use of solid-phase thermal reduction method to obtain Vo-TiO₂ with abundant oxygen vacancies on the surface,a series of bipyridine derivatives with hydrophobic properties such as dbbpy,dmbpy,dcbpy,dcebpy were used to modify Vo-TiO₂,and a series of bipyridine derivatives with different substituent types and positions modified Vo-TiO₂ were synthesized.The influence of substituent types and positions in bipyridine derivatives on the hydrophobicity of Vo-TiO₂ was investigated through the variation of contact angle.The influence of substituent types and positions of bipyridine derivatives on the spectral response and photogenerated carrier lifespan of Vo-TiO₂ was investigated through photoluminescence and photoelectric performance tests.Theoretical calculations were used to investigate the coordination mode and binding energy of bipyridine derivatives with TiO₂.At the same time,the contribution of defect construction and surface modification of different bipyridine derivatives to the improvement of photocatalytic ammonia synthesis performance was explored.The experimental results indicate that the contribution of different substituent types of bipyridine derivatives to the prolongation of photogenerated carrier lifespan is different,and the position of substituents mainly affects the hydrophobicity of the sample,which can lead to differences in the performance of photocatalytic ammonia synthesis.The photocatalytic ammonia synthesis efficiency of 2,2-bipyridyl-6,6-dicarboxylic acid modified Vo-TiO₂（6-dcbpy-Vo-TiO₂）can reach 310μmol·g^-1·h^-1,which is about 13 times that of pure TiO₂.4.In-situ construction of defects and heterojunction by high pressure rotary shear to collaborative improve the photocatalytic nitrogen fixation synthesize ammonia performance of TiO₂:The TiO₂ with different defect amounts and phase transition degrees（TiO₂-XR）was obtained using high-pressure rotary shear technology,and the effects of pressure,shear force,and other conditions on the phase transition degree and defect amounts of TiO₂ were investigated.The effects of high-pressure rotary shear on the physical properties of TiO₂ such as grain size,specific surface area,and pore size were investigated through XRD,TEM,specific surface area,and pore size analyzer.The influencing mechanism of defects and heterojunctions constructed through high-pressure rotary shear technology on the spectral response characteristics of TiO₂,the sites and modes of adsorption and activation of nitrogen,carrier interface transport separation,and the efficiency of photocatalytic nitrogen fixation synthesize ammonia were systematically investigated.The experimental results show that the TiO₂-800R obtained using high-pressure rotary shear technology can achieve a photocatalytic nitrogen fixation synthesize ammonia efficiency of 198μmol·g^-1·h^-1,which is 12.4 times higher than that of pure TiO₂ samples.In addition,the effects of surface modification with fluorine,linear alkyl acids,and bipyridine derivatives combined with high-pressure rotary shear technology on improving the efficiency of TiO₂ photocatalytic nitrogen fixation synthesize ammonia were also investigated.After surface modification of TiO₂-800R,the photocatalytic nitrogen fixation synthesize ammonia activity is further improved,with F-TiO₂-800R,C₈-TiO₂-800R,and 6-dcbpy-TiO₂-800R being 277μmol·g^-1·h^-1,492μmol·g^-1·h^-1,and 381μmol·g^-1·h^-1,respectively.In summary,this dissertation obtained TiO₂ with different defect amounts through solid-phase thermal reduction and high-pressure rotary shear techniques,expanding the spectral response range and achieving the activation of nitrogen-nitrogen triple bonds.The effective adsorption of nitrogen at the three-phase contact interface was enhanced through hydrophobic regulation strategies such as fluorine modification,alkyl acid modification,and bipyridine derivative modification.The TiO₂ phase transition caused by high-pressure rotary shear treatment has resulted in the in-situ construction of heterojunction,promoting the separation and transport of photogenerated charge carriers,and prolonging the lifespan of photogenerated charge carriers.The synergistic regulation of surface defects and surface hydrophobicity effectively improves the efficiency of TiO₂ photocatalytic nitrogen fixation synthesize ammonia.This work plays an important leading role in further developing new TiO₂ based composite photocatalysts,improving their photocatalytic performance,and expanding their application scope in the field of photocatalysis.