Study On Photocatalytic Property And Mechanism Of Bismuth-Based Materials Modified By Organic Small Molecule Surface

With the rapid development of the global economy,energy shortages and environmental pollution have become increasingly prominent,which gradually become the constraint of the world economy,and restrict the progress and development of human society.For the sustainable and healthy development of the world economy,all countries have vigorously developed green environmental protection technologies.In 1972,Fujishima,a Japanese scientist,discovered that nano-sized titanium dioxide could split water to clean energy hydrogen under light conditions for the first time.Subsequently,in the following decades,photocatalytic technology has rapidly become a research hotspot around the world due to its green environmental protection and direct use of solar light and other advantages.However,the development of semiconductor photocatalytic technology has been constrained by two factors,namely the narrow light response range and low quantum yield,which limits its practical industrial applications.Therefore,in order to solve these two problems,researchers have made many attempts.On the one hand,more new efficient photocatalysts are explored to improve the photocatalytic performance of semiconductor materials.Among them,bismuth based semiconductor has been widely studied due to its unique structure and excellent photocatalytic activity.On the other hand,scientists have explored a series of modification methods to maximize the performance of photocatalysts.The surface modification of-inorganic semiconductor by organic molecule is one of the effective methods to improve the photocatalytic activity of semiconductor.First,the modification of semiconductor by organic small molecules is based on molecular level,and organic molecules can be evenly dispersed on the surface of the material,resulting in a large contact area.Secondly,organic molecules and inorganic semiconductors are connected by chemical bonds,which is beneficial to the transmission of photogenic electrons and holes.Finally,organic molecules can be used to expand the absorption range of semiconductor photocatalytic materials and regulate their energy band structures.Therefore,this paper mainly uses small organic molecules to modify the surface of bismuth-based materials,thereby improve the photocatalytic activity of bismuth-based materials,and explore the synergistic mechanism between organic molecules and inorganic semiconductors.In the first chapter,we briefly introduced the research background of semiconductor photocatalysis technology,including its basic principle,application,research progress,restriction factors and modification methods.Then,several bismuth-based photocatalytic materials were introduced.In view of the narrow range of light response and low quantum yield of bismuth-based materials,a new idea of surface modification of bismuth-based materials by organic small molecules is proposed.Finally,the research significance and the outline of this thesis were summarized.In the second chapter,we investigated the synergistic mechanism between the small molecule mercaptobenzoic acid and BiOBr.First,BiOBr and 4CBT-BiOBr were synthesized by hydrothermal method.Next,the mott-schottky test and the kelvin probe force microscope(KPFM)test confirmed that the small molecule modification changed the interface electronic structure of the BiOBr,and also proved the existence of the polar interface in 4CBT-BiOBr.Subsequently,we verified the existence of a huge exciton effect in BiOBr through fluorescence spectrum(PF)and low-temperature phosphorescence spectrum(PH),and preliminarily proved that the polar interface electric field generated by modification of small molecule can induce the dissociation of exciton in BiOBr.To further confirm this conclusion,we verified the decrease of excitons and the increase of free carriers in 4CBT-BiOBr through reactive oxygen species(ROS)test and electron spin resonance(ESR).Finally,we conclude that small molecule modification can promote exciton dissociation,increase photogenerated carriers,and improve photocatalytic activity of the BiOBr.In the third chapter,we used small organic molecules-pyridine to modify the surface of BiOBr,BiOCOOH,Bi2O3,Bi2O2CO3,and investigated the effect of pyridine modification on the photocatalytic activity of these materials.By degrading RhB under full light,we found that the photocatalytic performance of BiOCOOH was significantly improved after pyridine modification,while the photocatalytic performance of other bismuth-based materials was not.Through further analysis,we found that pyridine reacted with bismuth nitrate to generate a new substance,bismuth pyridinium.Next,XRD,SEM,TGA,and FI-IR revealed that its crystal structure is similar to that of BiOCOOH,consisting of a staggered arrangement of the[Bi2O2]2+cationic layer and a pyridine layer,However,they are two different substances,and the photocatalytic and photoelectric properties of bismuth pyridinium are significantly higher than BiOCOOH.In the fourth chapter,we briefly summarized the main research content of this thesis,then analyzed and discussed the innovations and deficiencies of this paper,and looked forward to the next step.