Study On The Growth Mechanism Of Cerium Carbonate Crystals Simulated By AIMD

The physical and chemical properties such as different sizes,morphologies and dispersibility of cerium oxide determine its application in ultraviolet absorption,glass additives,catalytic oxidation and other related fields.Due to the inheritance of morphology,the morphology of precursor Ce₂（CO₃）₃crystal can be controlled.So in this thesis,Ce₂（CO₃）₃crystal as the research object,in order to reduce the experimental cost,the means of computer simulation.Density functional theory（DFT）combined with ab initio molecular dynamics（AIMD）was used to simulate the influence of CTAB on the nucleation and growth of Ce₂（CO₃）₃crystals,so as to reveal the regulation mechanism of CTAB on the crystallization of cerium compounds.The main results are as follows:The interaction and bonding stability of soft template CTAB with Ce³⁺in three different cerium salt systems（nitrate,sulfate,chloride）were studied by density functional theory.Studies have shown that only Br^-in CTAB interacts with Ce³⁺and forms Ce-Br bond in the water environment under different cerium salt systems.The bond stability of Ce—Br bond formed by Ce³⁺and Br^-in CTAB is that the order of ICOHP is:ICOHP _{nitric acid system}<ICOHP _{sulfuric acid system}<ICOHP _{chlorination system}.It is proved that the template CTAB has a good ability to regulate the nucleation stage of Ce₂（CO₃）₃crystal in nitric acid system.Ab initio molecular dynamics（AIMD）and density functional theory（DFT）were used to calculate and simulate the bond formation between Ce³⁺and surrounding atoms in three different cerium salt systems with different Ce³⁺concentrations（6:3:2）and different cerium salt systems after adding precipitantsCO₃^2-.When the concentration of Ce³⁺is 3,the bonding probability between Ce³⁺and surrounding atoms is high and the bonding distance is stable.The stability of Ce—O bond formed by Ce andCO₃^2-in nitric acid system is the strongest,which indicates that it is easier to prepare Ce₂（CO₃）₃precipitation with nitric acid system as cerium source in the process of preparing Ce₂（CO₃）₃crystal.By analyzing the electronic structure,COHP and ICOHP,the adsorption of CTAB on Ce₂（CO₃）₃crystal was compared.It is found that CTAB has the strongest adsorption capacity on the（020）crystal plane,that is,the growth of the（020）crystal plane is most hindered,and the probability of the crystal plane appearing in the equilibrium state is the largest,indicating that the morphology of Ce₂（CO₃）₃crystal controlled by CTAB is one-dimensional rod-like along the（020）crystal plane.Then,the phase structure and morphology of Ce₂（CO₃）₃crystals were characterized by SEM and XRD.The experimental results are consistent with the simulation results.