A Unified Gas-Liquid Carbonation Platform for Habit-Controlled Calcite Nanostructures

Calcite habit engineering offers a route to transform CO₂ mineralization from bulk sequestration into value-added nanomaterial production. Here, we demonstrate that additive chemistry and seeding strategy can serve as separable, recipe-level levers for directing calcite habit formation within a unified CaO/Ca(OH)₂ gas-liquid carbonation platform. This strategy highlights how solution-mediated habit control can bridge fundamental calcite crystallization mechanisms with scalable CO₂ utilization and value-added carbonate nanomaterial production. Sodium glutamate yielded ~100 nm rhombohedral nanoparticles, staged MgSO₄/ZnSO₄ dosing produced whisker-like crystalline nanorods with aspect ratios of 4-7, and two-step seeded carbonation with NH₄Cl generated fusiform spindle subunits that assembled into hierarchical rosette architectures. X-ray diffraction confirmed calcite as the only crystalline calcium carbonate phase detected under the present measurement conditions, with no detectable aragonite or vaterite reflections. SEM/TEM revealed distinct primary-subunit architectures, including internal striations in spindle particles indicative of oriented attachment. Thermogravimetry, N₂ physisorption, and EDS further distinguished the products and showed that Mg/Zn/S modifiers in the whisker route are retained predominantly at crystal surfaces rather than incorporated into the calcite lattice. These results define calcite habit control through two independent levers: additive-driven facet selectivity and kinetic decoupling of nucleation from growth/assembly. The platform links scalable synthesis, CO₂ utilization, and functional carbonate design.