Capture Of CO₂ By Switchable Solvents To Produce Valuable Materials Of CaCO₃

CO₂ mitigation strategies based on CO₂ capture and storage?CCS?and CO₂ capture and utilization?CCU?have been promising techniques for reducing greenhouse gas emissions.Mineral carbonation is one of the accounted technologies to store CO₂ permanently but also to produce value-added materials such as CaCO3 that has proven industrial interest with potential applications in improving existing material and advanced material design.Controlling of polymorphs,morphologies and sizes of CaCO3 particles has been an interest of many studies but also challenge in the crystallization process of CaCO3 particles.In this work,we discovered a novel and cyclic synthetic approach for controlling crystal polymorphs of CaCO3 by using green CO2-responsive switchable solvents which acted as both the CO₂ capturer for the carbonate source and the polymorphisms director.Two typical CO2-responsive switchable solvents,1,8-Diazabicyclo?5.4.0?undec-7-ene?DBU?and N-Butyldimethylamine?BDA?with CaCl2 as a calcium source were employed.The effect of temperature,calcium concentration,CO₂ pressure and reaction time was described.Results show that this developed framework permits producing any crystalline CaCO3 phases including metastable vaterite and aragonite in pure phases by selecting a suitable solvent and adjustment of the reaction conditions.Furtherly,the mechanism study demonstrates that the solvents attached on the surface of the primary nanoparticles to selectively control and direct the growth of any specific polymorph phases.For DBU system,when CO₂ was bubbled at lower pressure?0.12 MPa?,the formation of vaterite was obtained at lower temperature?30 ??and lower calcium concentration?0.09 mol/L?while aragonite was obtained at high temperature?70 ??and high calcium concentration?1.62 mol/L?;under supercritical CO₂ condition,vaterite was obtained at lower temperature?40 ??,lower calcium concentration?0.09 mol/L?and 8.0 MPa CO₂ pressure while aragonite was obtained at high temperature?70 ??,high calcium concentration?1.62 mol/L?and 12.0 MPa CO₂ pressure.For BDA system,when CO₂ was bubbled at lower pressure?0.12 MPa?,only vaterite was obtained at lower temperature?25 ??and lower calcium concentration?0.36 mol/L?;under supercritical CO₂ condition,only calcite was found.Therefore,it is of great industrial benefit to employ those solvents to control both unstable polymorphs without further addition of additives or surfactants.Additionally,this process attributed to solvent recovery and regeneration of the initial reactants,thus being an environmentally risk-free route.