Study On Preparation Of Hollow Calcium Carbonate With Different Morphology By High Pressure Carbonization And The Florecence Properties Of Eu³⁺

As an environment-friendly inorganic chemical material,hollow calcium carbonate is widely used in the field of drug molding agents due to its unique internal cavity porosity,shell surface properties and other excellent properties.At present,hollow calcium carbonate is mainly prepared by the method of double decomposition,but this method has the defect of complicated process and high cost.In order to break through the difficult problem of industrial preparation of hollow calcium carbonate,the paper adopts high-pressure carbonization method to prepare micro-nano graded hollow club-shaped hollow microspheres of calcium carbonate,and realizes in situ doping of Eu³⁺.The obtained product were characterized by transmission electron microscopy（TEM）,electron microscope（SEM）,X-ray double crystal powder diffraction（XRD）,Fourier transform infrared spectrometer（FTIR）specific surface area analyzer（BET）,thermogravimetric analyzer（TG）fluorescence spectrometer（PL）,the main results are as follows:（1）Basis on the uniformity and dispersiveness of the obtained hollow calcium carbonate sample through the single factor experiment,the optimal prepare conditions of hollow microspheres and hollow rod were determined as bellowed,respectively.（1）For micro-nano hierarchical structure of the hollow rod calcium carbonate:the carbonization temperature is 120℃,the amount of crystal control agent is 2 wt%,the initial Ca（OH）₂ concentration is 2%（wt）,the reaction last for 4 h stirring with a speed of 500 r·min^-1;（2）For micro-nano hierarchical structure hollow microsphere calcium carbonate:the carbonization temperature is 120℃,the crystal control agent added is 8 wt%,the initial Ca（OH）₂ concentration is 2%（wt）,the reaction last for 2 h with pressure of 2MPa and stirring with a speed of 500 r·min^-1.（2）The surface morphology and structure of the obtained samples were characterized by using TEM,SEM,XRD,TG,FTIR and BET,and the mechanism of preparation of hollow microspheres calcium carbonate was preliminary studied.The results showed that the prepared hollow rod calcium carbonate was assembled by small particles size of about 50～100 nm cubic particles,and the average length of the aggregates is about 1～2μm,the ratio of length to diameter is about 5:1;the thickness of the shell wall of hollow microsphere calcium carbonate is about 100 nm,and the size of Ca CO₃ particle assembled the shell wall is about 53 nm,with a diameter of 0.8～1.5μm.Both of the hollow structure Ca CO₃ are calcite type.High temperature and pressure environment can increase the neucleation rate and generate a number of small grains,ethylenediamine tetraacetic acid disodium chelate calcium ion can induce the primary particle to assemble into hollow microsphere calcium carbonate.（3）According to the optimal condition of the preparation of micro/nano calcium carbonate hierarchical structure of the hollow rod hollow microspheres,Eu³⁺was successfully doped into calcium carbonate in situ to make Ca CO₃:Eu³⁺phosphors by adding a certain amount of europium nitrate into the reaction at the beginning,and the fluorescence properties of the Ca CO₃:Eu³⁺phosphor was investigated.The results show that all the prepared different morphology Ca CO₃:Eu³⁺phosphor appear strong red luminescence.However,Under the excitation of 394 nm,the luminescence intensity was as follows:Ca CO₃:Eu³⁺phosphor is hollow microsphere>Hollow rod>>cubic;at the same time,with the increase of the molar ratio of Eu³⁺ion doping,the best doped molar ratio of cubic Ca CO₃:Eu³⁺phosphor in the hollow microsphere of micro-nano fractional structure was 4%Eu³⁺phosphor with the strongest fluorescence intensity.