Facet-selective anisotropic growth of 1D calcite nanowhiskers via Mg/Zn/SO₄ additive-assisted carbonation

Achieving highly anisotropic, whisker-like calcium carbonate (CaCO₃) architectures while retaining the thermodynamically stable calcite phase remains a significant challenge. Here, we present a staged additive-assisted carbonation strategy employing Mg, Zn, and SO₄ species to produce sub-micrometer calcite nanorods and whiskers. Powder X-ray diffraction identifies the product as calcite without detectable metastable polymorphs, and scanning electron microscopy reveals highly porous, cauliflower-like secondary agglomerates. Transmission electron microscopy directly visualizes the embedded one-dimensional primary nano-units (lengths 393-406 nm; aspect ratios 4-7), and indexed lattice fringes establish their identity as calcite. N₂ physisorption further indicates a mesopore-dominated architecture with a specific surface area of 9.58 m²/g. On the basis of these multiscale observations and the established crystal-chemical behavior of Mg²⁺, Zn²⁺, and SO₄²⁻ at carbonate surfaces, we propose a facet-selective growth model in which synergistic kinetic inhibition by Mg and SO₄ suppresses lateral thickening while Zn-mediated surface interactions are inferred to promote anisotropic elongation along the crystallographic c-axis. These findings provide mechanistic insights and a scalable pathway for engineering one-dimensional calcite morphologies for advanced structural and environmental applications.