Stepwise dissolution of silica surface in alkaline solution revealed by molecular modeling

Abstract

The atomic scale solid–liquid interfacial process dominates the macro-dissolution of silica, yet its direct experimental observation is challenging. Here we employed the reactive molecular dynamics to model this process in alkaline condition. An elevated temperature strategy under canonical ensemble (NVT) was applied to accelerate the process for sufficient sampling at temporal domain. A stepwise transformation from fully linked SiO4 network (Q3 and Q4) to reduced linkage and eventually aqueous species (Q0) was revealed. The simulated dissolution rate agrees well with the value predicted by empirical model. By tracing hydrogen atoms, we found that the dehydroxylated silica surfaces in alkaline electrolyte solutions underwent a transition from Si–O–Si bond cleavage-dominated (mainly reacted with OH−) to hydroxylation-dominated surface reactions. The free-energy reconstruction of well-tempered metadynamics reveals that 1500 K accelerates dissolution without altering the reaction pathways. These findings offer novel insights into the evolution of atomic-scale surface configurations during the dissolution kinetics of silica.