The Synthesis Of Vaterite Calcium Carbonate Microspheres By Using CO₂Bubble As Template And Its Drug Release Properties

The vaterite calcium carbonate microspheres by using CO2bubbles template was synthesized and Some factors which effected on its morphology, crystal structure, yield, particle size were studied in this work. The release properties of sodium benzoate loaded in different morphology and crystal structure of CaCO3products were also investigated. The scanning electron microscope (SEM), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), differential thermal/thermo-gravimetric (DSC/TG) and laser particle size instrument were applied to characterize the products respectively. The main experimental content and experimental results are as follows:1. With calcium chloride as raw materials, adjusting the pH of the calcium chloride solution with ammonia. The sizes of hollow microspheres are about3.8u m, and about200nm in wall thicknesses. The microsphere surface is formed by the accumulation of particles scales flake calcium carbonate, the size of which are about200～300nm. Vaterite calcium carbonate starts to decompose at700℃, and ended up at820℃.Of all the three kinds of calcium carbonate samples, i.e. vaterite hollow vaterite calcium carbonate, flower-like vaterite calcium carbonate and calcite calcium carbonate, the hollow vaterite calcium carbonate showed the slowest release rate for sodium benzoate, the second was flower-like vaterite calcium carbonate, the calcite calcium carbonate showed the fastest release rate.2. Vaterite calcium carbonate product contained hollow microspheres was prepared successfully by adjusting the pH of the calcium chloride solution with ammonia, but when the pH value of calcium chloride solution was adjusted with NaOH, the calcite calcium carbonate was obtained. With the increase of the dosage of ammonia, the particle diameter and the yield of vaterite calcium carbonate increased. When the initial and terminate pH values were controlled in the range of9.5to10.5and7.0to8.5, respectively, the particles of vaterite calcium carbonate microspheres had a better morphology and dispersibility. Where the initial pH value was9.5, the prepared CaCO3particles had the best morphology and dispersibility with about4μ m in size. When theterminate pH value dropped to6.5～6.0, very small amounts of calcite generated.3. When calcium nitrate and calcium hydroxide were used as raw material, it’s easy to produce calcite calcium carbonate. however, when calcium nitrate and calcium hydroxide were used as raw material, it’s easy to form vaterite calcium carbonate. Off all four kinds of ammonium salt, i.e. NH4NO3,(NH4)2SO4, NH4Cl and NH4Ac, calcite calcium carbonate could be produced by adding NH4NO3, and vaterite calcium carbonate were obtained by using the other ammonium salts.4. When CO2gas was scattered into small bubbles with an air stone, the vaterite calcium carbonates with uniform particle size were synthesized, while gas flow rate was0.6L/min to1.0L/min, the best spheres of CaCO3particles were obtained, and while the gas flow rate was0.2L/min, flower-like spheres were produced.5. Of all the three kinds of surfactant CTAB, SDS, OP-10, the use of ionic surfactant CTAB and SDS made the vateritecalcium carbonate tent to convert into calcite calcium carbonate, however, non-ionic surfactanthad not effect on the morphology, crystal structure of vaterite calcium carbonate. 6.The prepared vaterite calcium carbonate had a better release performance for sodium benzoate than that of calcite type.