| Inspired by the complex and diverse morphology of calcium carbonate in nature,amorphous calcium carbonate(ACC)is induced into crystalline calcium carbonate with special morphology by controlling the synthesis concentration and pH of the precursor amorphous calcium carbonate(ACC)to improve the current situation of uneven calcium carbonate morphology,which has important research significance in materials chemistry.Meanwhile,the high specific surface area of ACC makes it widely used in the field of adsorption,such as the adsorption of dyes and heavy metal ions in the aqueous environment.Therefore,the study of the phase transition of ACC and its adsorption properties is of great relevance and research value.Under highly alkaline conditions,ACC with good stability was prepared by lowtemperature rapid mixing method,and the physicochemical properties of ACC induced to crystalline calcium carbonate at different pH conditions,ethanol-water volume ratios,and oilwater interface of Pickering emulsion were explored.It was characterized that the prepared pristine ACC was spherical with a particle size of about 100 nm.Under strongly alkaline conditions,the ACC was induced to calcite with the shape of mushrooms.Under neutral and weak alkaline conditions,it was predominantly converted to aragonite in the form of whisker.Under weakly acidic conditions,it formed a mixed phase of spherical,whisker,and square.The higher ethanol-to-water volume ratio inhibits the dissolution-recrystallization process of ACC and preserves the spherical structure of the original ACC as much as possible.On the oil-water interface of Pickering emulsion,ACC is converted into fibrous and progressively aggregates into flower-like form.The ACC is induced to transform into various calcium carbonate with different crystalline phases under different conditions,which is widely used in many fields such as fillers,pharmaceuticals,paper,and daily necessities.In this thesis work,ACC was applied in the field of adsorption using gentian violet dye to evaluate its adsorption effect and explore the optimal adsorption conditions,in addition to kinetic,thermodynamic,and mechanistic analysis of the adsorption process of gentian violet.The results showed that the removal amount of 1214.56 mg/g could be achieved after adsorption of 1000 mg/L of gentian violet solution for 160 min at an adsorption temperature of 308 K with the addition of 0.0378 g of ACC,and the adsorption process followed pseudosecond-order kinetics model with spontaneous heat absorption.In the solution,the unstable ACC will gradually dissolve-re-crystallize,and when ACC dissolves,the dye molecules adsorb on the surface of ACC and form new nucleation sites,transforming into crystalline calcium carbonate with the dye attached.Moreover,the specific surface area of ACC is larger than that of crystalline calcium carbonate,so there are more active sites,and finally,a better adsorption effect is achieved.To improve the stability of the prepared ACC and further enhance its adsorption effect,a purer and more stable magnesium-containing amorphous calcium carbonate(Mg-ACC)was prepared by adding the additive MgCl2·6H2O in this experiment.When 0.03 g Mg-ACC was added to 50 mL of 1000 mg/L gentian violet solution,the equilibrium adsorption amount reached 1469.33 mg/g at the adsorption temperature of 308 K,254.77 mg/g higher than the original ACC.To further broaden the application of ACC,the prepared Mg-ACC was used for the heavy metal Cu2+removal,and the effects of addition amount,initial copper ion concentration,temperature,and time were explored.At a temperature of 308 K,the addition amount of Mg-ACC was 0.05 g,and the removal amount could reach 253.06 mg/g for 500 mg/L copper sulfate solution after 100 min.Combined with kinetic and thermodynamic analyses and various characterizations,the removal mechanism was analyzed:the removal of Cu2+ by adsorption,hydrolytic precipitation,and precipitation transformation was achieved by ACC. |
PDF Full Text Request