Facile synthesis of calcium carbonate with an absolutely pure crystal form using 1-butyl-3-methylimidazolium dodecyl sulfate as the modifier

Calcium carbonate (CaCO₃) nanocrystals with controllable polymorph and morphology have been successfully synthesized with the aid of an effective control agent, a halogen-free, low-cost ionic liquid surfactant, 1-butyl-3-methylimidazolium dodecylsulfate ([C₄mim][C₁₂SO₄]) in a supersaturated aqueous solution. For the first time, facile preparation of pure lens-like vaterite, sheet-like calcite, and peanut-like aragonite was all achieved in the [C₄mim][C₁₂SO₄] aqueous solution through changing the concentration, temperature, and initial pH value and adding magnesium ions. Washed by water and ethanol, all the aggregates were free of [C₄mim][C₁₂SO₄] and can be stable at least 1 month in air. The crystal form of the aggregates changed from pure calcite to pure vaterite at room temperature only through increasing [C₄mim][C₁₂SO₄] concentration. Formation of the ordered CaCO₃ structures is mainly ascribed to the aggregation of the primary nanoparticles whose formation mechanism is related to the change of supersaturation. This study can provide a facile and environment-friendly method to fabricate CaCO₃ crystal aggregates with various morphologies and polymorphs and can be used for large-scale industrial production and biomimetic synthesis.