Controlled synthesis of submicron calcite and vaterite nanoparticles via unbalanced stoichiometry and surfactant modulation

The controlled synthesis of calcium carbonate (CaCO₃) at the submicron and nanometric scales remains a central challenge due to the thermodynamic predominance of calcite and the metastability of vaterite. In this study, we demonstrate that considering the salts route of CaCl 2 and Na₂CO₃ and an unbalanced stoichiometric approach—based on calcium-rich conditions and limited water availability—leads to the formation of unconventional submicron calcite crystals (200–300 nm) without the use of organic additives. This size reduction is attributed to suppressed ion mobility, early-stage gelation, and growth inhibition caused by restricted solvent-mediated exchange. In a subsequent stage, the addition of sodium dodecyl sulfate (SDS) and fatty acid derivatives from soybean oil (FADS) act as a combined surfactant and coating system, promoting the selective nucleation and stabilization of spherical vaterite nanoparticles below 100 nm combined with almost all others submicron size. Through process control, two distinct paths were achieved: the first stabilized vaterite—a metastable CaCO3 polymorph prized for advanced uses because of its high solubility, low density, and spherical form—whereas the second produced calcite. Notably, this calcite route still managed to deliver submicron particles (near to 0.260 μm) with an elevated surface area (close to 8 m 2 /g) despite forming the thermodynamically stable phase. These findings highlight two complementary routes—physical constraint via stoichiometry and chemical modulation via additives—for tuning CaCO₃ phase and particle characteristics, offering scalable pathways for the production of mineral fillers and functional nanomaterials.