Ionic liquid anion-dependent growth mechanisms of nano-magnesium hydroxide: Crystallization kinetics, and DFT-guided precursor complexation studies

Nano‑magnesium hydroxide (MH), an environmentally friendly inorganic material, is widely used in flame retardancy, adsorption, and nanocomposites. However, precise control of its nanostructure and crystallization kinetics during synthesis remains a key challenge. This study aims to unveil the ionic liquid-mediated MH crystallization mechanism. MH was prepared via homogeneous precipitation using NaOH and MgSO₄·7H₂O as raw materials, with two 1-butyl-3-methylimidazolium-based ILs (ILA, ILB) as regulators. Via a synergistic approach of crystallization kinetics analysis and density functional theory (DFT) simulation, this study elucidated how ionic liquids (ILs) regulate MH nucleation and growth. Real-time conductivity monitoring tracked Mg 2+ dynamics, and the effects of temperature, reactant concentration, and IL type on MH crystallization kinetics were studied. DFT calculations optimized the precursor complexes (MgSO₄-ILA/ILB), while electrostatic potential (ESP) and atom-in-molecule (AIM) analyses resolved the coordination between anions and Mg 2+ as well as the regulatory mechanism of nucleophilic attack. Experiments show that under appropriate temperatures, ILs inhibit nucleation and induce smaller particles, with ILB more effective in growth control. ESP and frontier orbital analyses reveal IL cations affect growth kinetics and particle size through hydrogen bond-mediated nucleophilic attack direction and steric effects. This work reveals IL anions control MH crystallization via synergistic electrostatic, coordination, and steric effects, offering a framework for IL-based MH nanostructure customization.