Study On The Surface And Interface Regulation And Photocatalytic Performance Of Metal Organic Framework Materials And Their Derivative

Energy crisis and environmental pollution are the two major problems of the society today,which greatly endanger the sustainable development of human beings and need to be solved urgently.It is well known that sunlight is the most abundant and cleanest energy resource on Earth,however,its diffuse and intermittent nature makes it difficult to be used continuously as an energy source.Among the various technologies of solar energy utilization,photocatalysis is considered to be a green and environmentally friendly technology.On one hand,it can convert solar energy into other types of chemical energy;On the other hand,it can also decompose and mineralize organic pollutants in the water environment.Nevertheless,the realization of photocatalytic processes requires stable,efficient and economical semiconductor photocatalysts.In recent years,metal-organic frameworks（MOFs）materials and their derivatives have been developed due to their unique morphologies,designable structures and functions,good chemical stability,high catalytic activity and easy preparation,has received extensive attention in the field of photocatalysis.However,the fast recombination of photogenerated electrons and holes,slow charge transfer,and severe photocorrosion greatly hinder the further improvement of the photocatalytic efficiency of MOFs and their derivatives.Regarding the issue above,the purpose of this thesis is to shorten the migration distance of charges,improve the kinetic rate of electron transfer and accelerate the separation efficiency of electrons and holes based on surface interface regulation technologies（such as electronic structure regulation,defect design and construction of heterojunctions,etc.）.The main research contents are as follows:（1）Efficient electron transfer between photosensitizers and catalysts is an important factor to achieve high catalytic activity.In this chapter,by introducing different numbers of-F groups into the ligands of MIL-101（Fe）,the efficient regulation of its electronic structure is achieved.The high electronegativity of the fluorine-containing group can lead to a decrease in the electron density of the iron active center in the MIL-101 and an increase in the electrode potential,which makes it easier to accept the photoelectrons generated by the photosensitizer（Ru（bpy）₃Cl₂·6H₂O）.The favorable charge transport channel facilitates the electronic connection between the photosensitizer and MIL-101（Fe）,enabling efficient modulation of the photocatalytic activity.Compared with pristine MIL-101（Fe）,both0.25MIL-101-F and 0.25MIL-101-F,F exhibited faster electron transfer rate and higher photocatalytic CO₂-to-CO reduction performance,the CO generation rate of the latter is 2.8 times and 3 times that of the former,respectively.In addition,the electronic structure modulation of this ligand fluorination can also be used to improve the photocatalytic CO₂-to-CO reduction performance of MIL-53（Fe）and MIL-88（Fe）,indicating that our proposed electronic structure modulation strategy has the advantages of good versatility.This work tunes the electronic structure of the catalyst through ligand fluorination,thereby facilitating the efficient electron transfer between the photosensitizer and the catalyst,providing a general strategy for enhancing the photocatalytic performance of MOFs.（2）The poor intrinsic activity limits the practical application of hematite（α-Fe₂O₃）in photo-Fenton-like systems,and surface structure engineering is considered as one of the effective methods to tune the photo-Fenton-like catalytic performance ofα-Fe₂O₃.Therefore,it is crucial to understand how the surface structure ofα-Fe₂O₃-based photocatalysts affects their catalytic activity at the nanoscale.In this chapter,α-Fe₂O₃materials were synthesized using benzimidazole-modified Fe-MOFs as templates.By controlling the amounts of benzimidazole introduced,on one hand,the morphology ofα-Fe₂O₃（sphere,octahedron,spindle and rod）can be regulated.On the other hand,during the calcination process,the nitrogen atoms in the benzimidazole can extract the oxygen atoms in the lattice or the surface hydroxyl groups ofα-Fe₂O₃in the form of"NO_x",generating oxygen vacancy defects with controllable concentration on the surface ofα-Fe₂O₃,thereby greatly increasing its active sites(Fe²⁺and oxygen vacancies)for photo-Fenton-like catalysis.The experimental and theoretical calculation results show that the rod-shapedα-Fe₂O₃ with the largest concentration of oxygen vacancies exhibits the highest methylene blue degradation activity with an apparent reaction rate constant of 0.08 min^-1.The enhanced photocatalytic activity can be attributed to the synergistic effect of large specific surface area,high Fe²⁺and oxygen vacancy concentrations.This work provides a novel strategy for rationally tuning the surface structure of semiconductor materials to develop high-performance photocatalysts.（3）Electron transfer kinetics between semiconductor heterojunction interfaces is an important factor determining the photocatalytic performance,but its precise regulation remains a great challenge.In this chapter,a series of sensitized semiconductor heterojunctions consisting of monodisperse CdS quantum dots（QDs）with controllable sizes range of 2.2～6.5 nm and cadmium tetrakis（4-carboxyphenyl）porphyrin（Cd-TCPP）nanosheets are constructed through partial sulfidation strategy.The in situ resultant CdS/Cd-TCPP composites exhibit size-dependent photocatalytic hydrogen evolution reaction（HER）activitywith the highest activity of 3150μmol·h^-1·g^-1 obtained at a medium CdS QD size of 4.8 nm.It is demonstrated that the interfacial electron transfer rate and the corresponding photocatalytic HER activity can be regulated by tuning the CdS QD size that determines the conduction band position of CdS relative to Cd-TCPP.The larger size of CdS QDs has a lower conduction band position,which increases the driving force of electron transfer between the heterojunction interfaces,and thus is more favorable for receiving injected electrons from Cd-TCPP.This work provides a promising strategy for rationally tuning the electron transfer rate at the heterojunction interface to develop high-performance photocatalysts.