The Study On Stability Of Nanobubble And Its Influence On Crystal Form And Morphology Of Calcium Carbonate

Nanobubble has the characteristics of extraordinary stability,charged surface,high mass transfer efficiency,high specific surface area and free radical generation upon rupture,which has been widely used in medicine,agriculture,environment and mineral flotation,however,the mechanism about stability remains unclear and its application in the synthesis of inorganic materials is still limited.In this study,the stability of air nanobubbles in water was explored,besides the effect of ethanol and strong electrolyte on the stability of nanobubbles was studied;meanwhile,based on the compound decomposition method,in water and ethanol-aqueous solution,the regulation and mechanism of air nanobubbles on crystal form and morphology of calcium carbonate was investigated,the calcium carbonate obtained was applied to the removal of cadmium（Cd）in wastewater.The main conclusions are as follows:（1）Based on surface enrichment of ions and the extended DLVO（Derjaguin-Landau-Vervey-Overbeek）theory,the stability of air nanobubbles in water,strong electrolyte solution and ethanol-aqueous solution was studied.The results indicated that nanobubble could remain stable in deionized water,the high concentration of strong electrolyte could ruin the double layer of the nanobubbles,and the total potential energy between the nanobubbles is always negative,so it was difficult for the nanobubbles to exist stably for a long time.Low concentration of ethanol could improve the stability of the nanobubbles,while high concentration of ethanol would decrease the surface charge density and increased the size of the nanobubbles,leading to a decrease in stability.（2）The influence of air nanobubbles on the crystal form of calcium carbonate in water was revealed.The results showed that after 4 hours,there was still a mixture of vaterite（33.6%）and calcite（66.3%）in the deionized water,with the concentration of nanobubbles increasing,the mass fraction of calcite increased linearly and reached 100%when the concentration of nanobubbles was 2.96×10⁸ particles/ml,indicating that nanobubbles acted as the binder in strengthening the coagulation between calcite and vaterite,enhancing the transformation from vaterite to calcite.（3）The influence of air nanobubbles on the crystal form and morphology of calcium carbonate in ethanol and water mixed solution was explored,the prepared calcium carbonate was applied to the removal of Cd²⁺in wastewater.The results showed that due to the interaction of nanobubbles and ethanol concentration in this system,vaterite with different morphologies（spherical,flower-like and root-like）could be obtained,simultaneously,to some extent,which could increase the content of vaterite.Among them,the flower-like vaterite has excellent removal capacity under acidic conditions,the Cd²⁺absorption capacity was 1099.84 mg/g.