Photogenerated Carriers Regulation Of MIL(Ti) And UiO Series Metal-Organic Frameworks And Study Of Their Photocatalytic Properties

Energy shortage and environmental pollution are the two major problems facing mankind and have become the main factors restricting social development.Photocatalysis is a green environmental protection technology,which converts solar energy into other types of chemical energy by the photocatalytic reaction over semiconductor materials.It holds huge prospect in the application of energy conversion and environmental protection,and has attracted wide attention.Among many photocatalytic materials,MOFs,as a new type of porous coordination polymer,are formed by the combination of metal nodes and organic ligands through coordination bonds.Due to their advantages of large surface area,adjustable structure and function,more exposed reactive sites due to the porous structure and abundant transport channels for reactants/products,make MOFs hold great potential in the field of photocatalysis.The photocatalytic decomposition of water,CO2 conversion,pollutant degradation and organic matter conversion have been extensively studied.Although a large number of studies have shown that MOFs-based photocatalysts are good photocatalytic materials,the photocatalytic activity of MOFs is limited by the poor photocarrier separation efficiency and poor charge transfer rate,which hinder their practical application.Therefore,according to the structural characteristics of MOFs and application requirements,structure design and function adjustment of MOFs are carried out to improve charge carrier separation and improve its photocatalytic activity,which is of great significance for the realization of industrial application.So,in this paper we aim to regulate the electron distribution,improve carrier separation efficiency and mobility,and ultimately obtain highly active energy conversion photocatalyst.In addition,based on the research experience of MOFs in our research group over the years,we modify the highly stable MOFs(MIL and UiO series)to improve their photocatalytic activity by introducing cocatalysts and electron-deficient boron-containing molecules.The details are as follows:In chapter 1,the synthesis strategy and application of MOFs materials are summarized.Secondly,the advantages,application and shortcomings of MOFs in the application of photocatalysis are analyzed.Then,the modification strategies of MOFs to overcome their shortcomings in photocatalysis are summarized.Finally,the significance and research content of this thesis are introduced.In chapter 2,Ti3C2@MIL-NH2 composite is synthesized by using cocatalyst strategy to realize carrier regulation of MIL-NH2,and its photocatalytic hydrogen production performance is studied.On the one hand,Ti3C2 MXene is used as Ti source to in-situ grow and anchor MILNH2,and as the support material to achieve effective dispersion of MIL-NH2 nanoparticles.On the other hand,it can be used as a cocatalyst to promote the carrier separation and transport of MIL-NH2 based on the excellent electronic conductivity of Ti3C2 MXene.X-ray photoelectron spectroscopy(XPS),Fourier transform infrared spectroscopy(FTIR)and electron paramagnetic resonance spectroscopy(EPR)under dark conditions indicate that N of NH2 in MIL-NH2 is coordinated with Ti3+of Ti3C2 surface to form N-Ti bond.It provides a new path for electron transfer from MIL-NH2 to Ti3C2.This strategy significantly improves the electron conductivity and carrier separation efficiency and mobility of Ti3C2@MIL-NH2,and therefore,endows Ti3C2@MIL-NH2 excellent photocatalytic activity.This work provides a new idea for preparing MOFs materials and improving their photocatalytic activity.In chapter 3,the electron-deficient boron-containing 4-carboxybenzoic acid molecule is introduce into UiO-66 to replace the traditional terephthalic acid ligand,to construct a novel boron-containing UiO-66-B with UiO-66 topology to achieve carrier regulation and study its photocatalytic production of H2O2 by promoting 02 reduction.In the photocatalytic process,boron element can regulate the electron distribution by extracting electrons to realize the carrier regulation and promote the carrier separation and transfer of UiO-66-B.In addition,the electron deficiency of boron makes it easy to bond with the lone pair electron of O2 molecule and promotes the adsorption and transformation of O2,which makes UiO-66-B exhibits excellent photocatalytic production of H2O2 by promoting O2 reduction.This work systematically studies the role of boron in photocatalytic production of H2O2 by promoting O2 reduction,and has certain enlightenment on how to improve the photocatalytic activity of MOFs materials.In chapter 4,the strategy of introducing electron-deficient boron-containing molecule is further used to introduce 4’-(carboxyl)biphenyl 4-boric acid into UiO-67 to construct a novel boron-containing UiO-67-B,and study its photocatalytic performance of CO2 cycloaddition with epoxides.The introduction of boron-containing molecule not only promote the carrier separation and transport of UiO-67-B,but also avoid the adsorption competition between CO2 and epoxide in the cycloaddition reaction by the chemical adsorption of CO2 molecules as the Lewis acid site,which significantly improves the photocatalytic activity of UiO-67-B.This work further reveals the potential application of boron element in enhancing MOFs activity and provides a new way for photocatalytic CO2 fixation and conversion.In chapter 5,Pt species(Pt(0),Pt(Ⅱ)and Pt(Ⅳ))with different valence states are deposited on Zr-based UiO-67-B by introducing cocatalyst strategy to achieve carrier regulation,and the role of Pt with different valence states in photocatalytic H2O2 formation and decomposition is systematically investigated.It is found that the Cl in[PtCl4]2-coordination with H of Zr-OH in UiO-67-B to form Cl-H bond,which promotes the carrier separation and transport of UiO-67B,and exhibits excellent photocatalytic production of H2O2 by promoting O2 reduction.In addition,Cl-H bond effectively inhibits the decomposition of H2O2 by avoiding the interaction between H2O2 and UiO-67-B.This work enriches the understanding of different valence Pt species in photocatalytic reactions,especially the effects on the formation and decomposition of H2O2,and provides a new strategy for designing photocatalysts with good H2O2 yield.In chapter 6,we summarize the research contents and innovation points of this paper.Besides,the shortcomings are analyzed,and the future work is prospected.