Organic acid tailors anhydrous magnesium carbonate: DFT-guided dehydration mechanism and morphology engineering

Mineral carbonation into Anhydrous Magnesium Carbonate (AMC) is a promising pathway for permanent CO₂ storage, yet the strong hydration of Mg 2+ hinders its precipitation under mild conditions. To overcome this limitation, organic acids ( l -ascorbic acid (LA), citric acid (CA), malic acid (MA), and tartaric acid (TA)) are employed as dual-functional agents: carbon sources and hydration disruptors. Through combined density functional theory (DFT) calculations and experimental validation, it is revealed that organic acids weaken the hydration shell of [Mg(H₂O)₆] 2+ by forming stable coordination bonds with Mg 2+ , significantly reducing the dehydration energy barrier (e.g., ΔG ‡ ₆-₅ decreased from 180.53 kJ/mol in H₂O to 76.71 kJ/mol for LA). Systematic hydrothermal synthesis demonstrates that LA enables high-purity AMC formation at 450 K, the widest temperature window among the tested acids. At the same time, TA requires ≥525 K. Crucially, each acid directs distinct AMC morphologies, hydrangea-like (LA), cubic (CA), layered (MA), and block-like (TA), attributed to site-specific adsorption on crystal surfaces. This work provides a molecular-level blueprint for overcoming the dehydration barrier in AMC synthesis and advances strategies for accelerating sustainable CO₂ mineralization.