Polymorph discrimination of CaCO3 mineral in an ethanol/water solution:: Formation of complex vaterite superstructures and aragonite rods

Polymorph discrimination of CaCO3 mineral has been easily realized in an ethanol/water mixed solution system under mild conditions without using any organic additives. The phase transition from a mixture of calcite and aragonite to pure aragonite, and then to almost pure vaterite, can be nicely captured by the choice of a suitable ratio of ethanol to distilled water in the present reaction system. In addition, a complex self-assembly process for the formation of multilayered vaterite cakes in this binary solution system has been proposed. The cakelike vaterite crystals with multilayered structures are porous with an average pore size of 24.9 nm. The results demonstrated that such a binary reaction media could provide an alternative and versatile tool for controlling the polymorph and nanostructures of inorganic minerals through manipulating the thermodynamics and kinetics. This study provides an alternative polymorph switching route for CaCO3 mineral without using any additives and can even be scaled up as a green chemistry method for the industrial production of CaCO3 with different polymorphs.