Design And Application Of Bismuth Based Compound/MOFs Composite Photocatalytic Materials

Environmental and energy issues have been the focus of human attention since entering the21st century.Therefore,the effective use of renewable energy for environmental governance to promote the sustainable development of human society has not only become an important strategic goal implemented by all countries in the world,but also become the focus of current scientific researchers.After more than 40 years of development,semiconductor photocatalytic technology,which can effectively use solar energy,has gradually shown its incomparable advantages in pollution-free treatment,especially in water pollution treatment.Metal-organic framework materials（MOFs）have the characteristics of large specific surface area,high porosity and adjustable structure,and also have the characteristics of semiconductor can be excited by light.In recent years,MOFs have made outstanding achievements in hydrogen production,carbon dioxide reduction,nitrogen fixation and pollutant degradation.Bismuth based semiconductor has become a hot material in photocatalysis because of its advantages in pollutant degradation.At the same time,bismuth series is a photocatalytic material with abundant reserves,no irritation and good stability in nature.However,the single bismuth based material has the disadvantages of easy recombination of photogenerated electrons and holes and low efficiency of electron hole separation.Therefore,the combination of MOFs and bismuth-based photogenerated can solve the shortcomings of poor optical absorption and easy recombination of bismuth-based photogenerated electron holes,so that they can complement each other.Therefore,this paper designed a series of composite photocatalytic materials based on MOFs and bismuth compounds and studied their photocatalytic performance in water pollution treatment,and also studied their mechanism.The specific research contents are as follows:（1）A series of BiOI/MIL-121（Al）hybrid photocatalysts has been prepared by a facile hydrothermal method.Two-dimensional BiOI sheets are intimately anchored on rod-like MIL-121due to the electrostatic and coordination effects between Bi³⁺and carboxyl.The BiOI/MIL-121（Al）hybrid exhibits favorable performances for visible-light-driven degradation of tetracycline.The degradation performance of the optimal sample BiOI/MIL-121-20 is more than twice as that of pure BiOI.Apart from the close contacts between BiOI and MIL-121,the hydrogen bond induced by carboxyl in MIL-121 promotes the adsorption of tetracycline,which is also conducive to the photocatalytic degradation process.Moreover,results show that photo-induced holes and superoxide radicals are both the main active species for the photocatalytic degradation of tetracycline over BiOI/MIL-121 composites.This work would inspire the materials design with specific functional groups for efficient（photo）catalytic reaction.（2）Antibiotics are only a small part of water pollution,and the actual pollution is often a complex pollution system containing both toxic metal ions and antibiotics.Therefore,in Chapter2,a flower-like MIL-125-NH₂@BiOI composite photocatalyst was prepared by solvothermal method,which was used for photocatalytic removal of Cr（VI）/tetracycline mixed pollutants at the same time under visible light.The strong interaction between amino in MIL-125-NH₂ and Bi³⁺of BiOI promotes the formation of this unique inlaid structure and enables the favorable contact between MIL-125-NH₂ and BiOI,thus accelerating the transfer of charge carriers.Remarkably,MIL-125-NH₂@BiOI displays a superior activity compared with that of two monomers for the photocatalytic reduction of Cr（VI）and degradation of tetracycline.More significantly,the photocatalytic efficiency can be further boosted in the coexistence of Cr（VI）and tetracycline,which is 1.8 and 1.6 times that of single Cr（VI）and tetracycline,respectively.The synergistic effect between Cr（VI）reduction and tetracycline oxidative degradation can further facilitate the separation of photo-induced electrons and holes,resulting in the improved efficiencies in the Cr（VI）/tetracycline coexistent environment.This work sheds light on that MOF-based photocatalysts possess huge potential for practical environmental remediation.（3）There are not only toxic metals and antibiotics in complex polluted water,but also phenols and toxic metals in complex polluted water.Therefore,the next work was to fix the oxygen-rich vacancy Bi₂Mo O₆ uniformly on MIL-121 by solvothermal and low-temperature thermal reduction methods to remove the complex polluted water containing phenols and toxic metals.Profiting from the efficient light capture and rich electron traps triggered by oxygen vacancies,and the intimate interface contact and intrinsic heterostructure,strikingly enhanced separation and transportation of photo-excited charge carriers were achieved.For photocatalytic Cr（VI）reduction and 2-nitrophenol oxidation under visible light,Bi₂Mo O₆/MIL-121 with rich oxygen-vacancies（Vo-BMO/M）performed much higher activities than those of Bi₂Mo O₆,MIL-121 and Bi₂Mo O₆/MIL-121 without oxygen-vacancies.Specifically,the capacities over Vo-BMO/M are 4.8,7.1 and 1.4 folds those of the above three counterparts for Cr（VI）reduction,or6.1,5.4 and 1.2 folds for 2-nitrophenol oxidation,respectively.More encouragingly,the corresponding efficiencies would be further ameliorated in the coexistent environment of Cr（VI）and 2-nitrophenol thanks to the timely consumption of photo-excited electrons and holes,which ulteriorly expedites their spatial separation.It is expected that this study could enlighten the treatment of complicated environmental pollution and the elaborate design of（photo）catalysts.