Ab Initio Molecular Dynamics Study of the Proton Transfer in Hydroxyl Ion-Induced Hydrolysis of Aluminum Monomers

Abstract

The hydrolysis process of Al(H 2 O) 6 3+ induced by hydroxyl ions (OH − ) is significant to aluminum solution chemistry. Previous investigations of hydrolysis reactions have primarily relied on static calculations in an implicit solvent environment. Herein, we employ ab initio molecular dynamics (AIMD) to investigate the evolution process of Al(H 2 O) 6 3+ under various local alkaline conditions in an explicit solvent environment. Our work demonstrates the effect of solvent water in hydrolysis reactions. Specifically, the stepwise hydrolysis reaction induced by hydroxyl ions involves water wire compression and concerted proton transfers. Dehydration reactions occur when the number of hydroxyl ligands attached to the aluminum ion (Al 3+ ) equals or exceeds three. Moreover, the Al(H 2 O) n (OH) 3 species exhibit unique hydrolysis and dehydration reaction characteristics compared to other species. The geometrically stable aluminum monomers determined by AIMD are Al(H 2 O) 5 (OH) 1 2+ , Al(H 2 O) 4 (OH) 2 + , Al(H 2 O) 1 (OH) 3 , and Al(OH) 4 − . In addition, the topological analysis analyzes the interaction between Al 3+ and coordinated H 2 O in different configurations, indicating the weakest interaction appearing in Al(H 2 O) n (OH) 3 species.