Preparation Modification And Investigation Of Nitrogen Fixation On Cerium And Bismuth Based Photocatalytic Materials

Owe to the energy depletion and environmental pollutant crisis,it is a crucial point of scientific research in 21^th century to develop the novel clean energy.Comparing to the industrial ammonia synthesis with complicated operation,intensive energy consumption and centralized production mode,the photocatalysis technology for nitrogen fixation can transform N₂ in air and water to ammonia driven by solar energy.It is promising to be the new ammonia synthesis method because of the green and non-pollution feature of photocatalytic process.However,the catalysts in photocatalytic systems have not yet satisfied the demands of ammonia yield and rate in the application.Modifying the compositions and structures of catalysts can introduce active sites on the surface,to activate N₂ molecules and improve ammonia yield.Bismuth-based and cerium-based materials arouse the interests in photocatalysis field,owing to the special natures of these two elements.Herein,bismuth-based and cerium-based materials were rationally modified through the elaborate design of medification strategies and synthetic approaches.The structural change of modified catalysts and the corresponding optics and electric properties were investigated in depth using both experiments and theoretical calculations.The relationship between structure and performance,and the formation and reaction mechanism were also discussed and analyzed in detail.Ce O₂/Ce(OH)CO₃ hybrid precursor was successfully prepared with dicyandiamide providing the alkaline and carbon-containing sources.Abnormal cerium ions were preserved through the pyrolysis of carbonates under inert atmosphere.It hinders the formation of crystal structure with the oxygen lack condition and induces the presence of amorphous cerium oxides(A-Ce O_x).Amorphization engineering brings the abundant oxygen vacancies into A-Ce O_x samples.Interestingly,the concentration of oxygen vacancies can be controllably adjusted by changing the carbonates ratio in precursor.Oxygen vacancies with appropriate concentration can promote the adsorption and reduction of N₂ molecules,therefore amorphous A-Ce O_x exhibit better performance of109?mol·g^-1·h^-1for photocatalytic nitrogen fixation.Based on the fact cyclization reaction polyacrylonitrile occurred under heat treatment,cyclic polyacrylonitrile(c-PAN)was introduced into Bi₂WO₆ synthesis process with solvothermal method.Consequently,it is successful to prepare Bi₂WO₆/c-PAN composites,realizing in situ modification by the surficial decoration.c-PAN anchored on the surface of Bi₂WO₆ nanosheets and had the strong interaction with terminal oxygen atoms.It causes the exposed and unsaturated N atoms,which can activate N₂ molecules and weaken N?N triple bonds.This modification of surficial decoration with c-PAN endows Bi₂WO₆ with the performance of 140?mol·g^-1·h^-1 for photocatalytic nitrogen fixation.MOF-76(Ce)materials in micrometer scale were prepared via simple solvothermal method.After further light illumination treatment,nanosized MOF-76(Ce)rods were obtained with a top-down mode.This process of size decline was accompanied by the cracks propagation,leading to the cerium ions with unsaturated coordination state to be exposed on surface,which can provide electrons occupied and unoccupied 4f orbits.They can accept from and donated electrons back to N₂ molecules,promoting N₂ transform to NH₃ on MOF-76(Ce)nanomaterials.The cerium incorporation into Bi-MOF was achieved through the location replacement of metal ions,preparing the nodes mixed Bi(Ce)-MOF successfully.There is no change for the original frameworks structure under a low primary concentration of two metal ions and the small addition amounts of cerium nitrates.The low energy 4f orbits of incorporated cerium ions consists of the energy bands of as-prepared double metal Bi(Ce)-MOF materials,extending the absorbed light towards visible light regions and enhancing photocatalytic performance 342?mol·g^-1·h^-1 for nitrogen fixation.