Controllable synthesis of rod-like aragonite CaCO3 via a facile gas diffusion method

Aragonite CaCO3 with uniform rod-like morphology was successfully synthesized via a simple gas diffusion method without any additives. The results show that well-defined rod-like aragonite crystals with high aspect ratios can be obtained within a temperature range of 50–80 °C and a Ca²⁺ concentration range of 0.8–1.5 mol·L-1. Within this range, the relationship between the average crystal length and temperature as well as Ca²⁺ concentration can be quantitatively described. Mechanistic analysis indicates that although aragonite has a higher formation energy than calcite from a thermodynamic perspective, its lower surface energy combined with a supersaturation ratio approaching 1 grants it a kinetic advantage in nucleation. Moreover, under continuous CO₂ introduction, aragonite can remain stable for a certain period of time. This work provides a green and straightforward pathway for the controllable synthesis of aragonite, highlighting that kinetic control, rather than thermodynamic factors, plays a critical role in polymorph selection.