Synthesis Of Nano - Vaterite By PASP Control In Reverse Microemulsion

Nanoscale calcium carbonate materials was widely used in modern industry because of its excellent properties. Vaterite calcium carbonate has better dispersion and larger specific surface area, therefore the synthesis of nanoscale vaterite will further improve the performance of the calcium carbonate materials.In this paper nanoscale vaterite calcium carbonate was synthesized by reverse microemulsion method with polyaspartic acid（PASP）. XRD, SEM was used to reseach calcium carbonate samples synthesized in different reverse microemulsion system prepared by cationic surfactant CTAB and anionic surfactants AES. TEM was used to studied different reaction time in the suitable reaction system to observe the precipitation process of nanoscale vaterite and to obtain structure analysis of the nanoscale vaterite samples. FTIR was used to study the surface composition and analyze the process mechanism of calcium carbonate precipitation in reverse microemulsion based on the basic principle of biomineralization.（1） In CTAB reverse microemulsion system, when the concentration of reactants was 0.1 0.5 mol/L, the percentage of vaterite of all samples were about 98%; The morphology of calcium carbonate samples was pie particle, particle size was 2 μm.The addition of PASP cause no significant impact on crystal forms of calcium carbonate samples and vaterite percentage.With the increase of the concentration of PASP, the morphology of calcium carbonate samples was changed, the center of the pie structure began to grow, when the concentration of PASP from 0.5 2.5 mg/ml,calcium carbonate samples from pie to spindle structure.（2） In AES reverse microemulsion system, when the concentration of reactants is0.1 0.5 mol/L, the percentage of vaterite is increased from 17% to 49.4%.At this point the morphology of calcium carbonate samples for nano particles, particles andlarge cube together.The percentage of vaterite increases with the increase of the concentration of PASP, when PASP concentration of 2.5 mg/ml, vaterite percentage was 95%, and the CLSM as the particle size distribution more uniform, better dispersion, particle size of 30 50 nm spherical particles.（3） The best reaction time is 2h. With the increasing of reaction time, the nanoscale crystals grew into larger spherical particles and the crystal size was ca 50 nm at the reaction time of 2 h. To further increase the reaction time to 12 h, the crystal size of ca. 100 nm was obtained and the nanoscale vaterite of CaCO₃ agglomerated into larger cluster.（4） Tthe crystal size of the nanoscale spherical particles with a diameter of 50 nm.The presence of mesoporous due to the accumulation of the nanocrystalline and mainly distributed was around 40-60 nm. The surface area and mesoporous volume of nanoscale vaterite Ca CO3 sample were improved significantly which achieved of27.012 m²/g and 0.15 cm₃/g.（5） With the adding of PASP in the W/O microemulsion,-COO-- ionized from PASP which was used as the template of vaterite would preferentially bond to Ca2+ via the electrostatic attraction and thus prevent the connection with AES and ensure the stability of the inverse microemulsion system, so eventually get spherical vaterite nanoparticles.