Crystallization Of Calcium Carbonate In Mixed Solvents Of Ethanol And Water

In this paper, calcium carbonate crystals with different kinds of morphologies and formshave obtained in mixed solvents of alcohol and water due to diffrernt conditions. XRD, SEMand Micro-Raman were used as characterization methods to investigate the effect of agingtime, L-cysteine SAMs, ionic liquids concentration and volume ratio of alcohol to water incontrolling the polymorphs, morphology and orientation of calcium carbonate crystals.L-cysteine SAMs induced the crystals of calcium carbonate in ethanol-water mixtureswith volume ratio of ethanol to water is v:v=1:1. Only calcite crystals with (104) plans wereobtained on SAMs, but in solution the main products were vaterite. In solution, flower-likeand leaf-like vaterite were obtained depends on the aging time being3h and12h, respectively.However on the templates of SAMs, calcites with quite different morphologies (from porousto smooth surfaces) were obtained when the aging time changed. The possible mechanism ofthis experiment maybe that the exerted functional groups of L-cysteine SAMs inalcohol-water mixtures is different from that in water, which results in different orientation ofcalcite. The effect of solvent microscopic inhomogeneity in mixed solvents maybe relate tothe structure and morphology of crystals.Calcite-vaterite mixed crystals with different morphologies were obtained on L-cysteineSAMs using ionic liquids as additives in ethanol-water mixtures (v:v=1:1). The morphologyof the calcium carbonate crystals, especially vaterite, changed obviously with the increase ofionic liquids concentration. The appearance of vaterite changed from leaf-like to flower-likewhich mostly aggregated from spherical micelles, then finally to dumpling-like crystals.When the concentration of ionic liquids is2.5mmol/L, the morphology of vaterite is mostlythe same as that in ethanol/water mixtures without ionic liquids. When the concentration ofionic liquids is5mmol/L, the morphology of vaterite is spherical-like vaterite that gatheredinto flower-likel crysals. When the concentration of ionic liquids is7.5mmol/L, the shape ofvaterite is rarely seen, which is dumpling-like. With the concentration of the ionic liquidsincrease to10mmol/L, the morphology of vaterite is still dumpling-like.Calcium carbonate crystals with special morphology were obtained by changing thevolume ratio of ethanol to water (v:v=3:7and v:v=7:3) and the aging time(3h and12h). The morphology of vaterite changed with diferent volume ratio of ethanol to water and agingtime. When the aging time was3h, only vaterite were obtained; but when the aging time was12h vaterite with little calcite can be seen. Possible reason is that as the aging time prolonged,a small amount of metastable vaterite will change to thermodynamic stabled calcite. But whenwe use1-butyl-3-methylimidazolium bromide as modifier in ethanol-water mixtures (v:v=3:7and v:v=7:3, respectively), a completely different phenomenon appeared. when v:v=3:7,half-flower-ball-like vaterites with its petals arrange a layer by layer were obtained; it is moreobvious when v:v=7:3, which looks like aggregate layer upon layer.