Study On Mineralization Of Calcium Carbonate Induced By Amino Acid Carbon Quantum Dots (CDs)

Calcium carbonate（CaCO₃）is a kind of mineral widely existing in nature and widely used in plastics,papermaking,coatings and other industrial fields.Many scholars use biomimetic mineralization method to prepare CaCO₃ with different morphologies and crystal types to meet the needs of industry.In this paper,three kinds of amino acid carbon quantum dots were prepared and used to induce CaCO₃ mineralization respectively.The details are as follows:1.Using Serine and aspartic acid as carbon sources and ethylenediamine as nitrogen sources,Serine and aspartic acid carbon quantum dots（S-CDs）and aspartic acid carbon quantum dots（A-CDs）with uniform dispersion and good water solubility were prepared by microwave method,and S-CDs and A-CDs were used as additives,respectively.The mineralized growth of CaCO₃ was induced by the classical ammonium carbonate gas diffusion method.The results show that the CaCO₃ crystals mineralized by S-CDs are calcite with the size of 25μm.With the increase of additive concentration,the morphology of the CaCO₃ crystals is gradually changed from regular cube to layered polyhedron.The CaCO₃ crystals mineralized by A-CDs are the mixture of calcite and vaterite.The morphology of vaterite changes from spherical to double spherical shape with rough surface and finally to coarse rod-like structure.2.A series of carbon quantum dots of glutamic acid（G-CDs）were prepared by microwave method using glutamic acid and ethylenediamine as raw materials,and the mineralization of CaCO₃ was induced by ammonium carbonate gas diffusion method using G-CDs as additive.The effects of raw material ratio of G-CDs,concentration of G-CDs and concentration of calcium ions on the mineralization process were studied.The results show that the synthesized G-CDs has uniform size and good dispersion,and can be used as an additive in the mineralization process.The CaCO₃ crystals obtained by using G-CDs with lower carboxyl content on the surface as additives are of the same type as those obtained without additives,both of which are calcite.When G-CDs-1 with high carboxyl content on the surface is used as an additive,CaCO₃crystals obtained by mineralization are mixtures of calcite and vaterite phase.With the increase of G-CDs-1 concentration,the content of vaterite increases,and petal-shaped,spherical and erinaceus shaped CaCO₃ particles can be obtained.With the increase of calcium ion concentration,the content of vaterite increases,and the CaCO₃ particles in the shape of pumpkin,eritrinus erinaceus,gyroscope-like,hydrangea and pebble can be obtained.3.The growth process of CaCO₃ crystal with G-CDs-1 as additive was systematically studied by means of time evolution experiment,measurement of electrical conductivity and fluorescence test.The experimental results show that the carboxyl group（-COOH）on the surface of G-CDs-1 attracts Ca²⁺in the solution electrostatically.When CO₂ diffuses into the solution,it induces the formation of CaCO₃,which exists in the form of tiny ACC particles.With the accumulation of ACC particles,CaCO₃ with different morphologic morphology is gradually mineralized.The surface roughness of CaCO₃ crystal is related to supersaturation in solution.Fixing additive concentration and increasing Ca²⁺concentration will increase supersaturation of solution,resulting in crystal roughness.