Kaolinite dehydroxylation at the atomistic scale: Water formation, release, and structural effects

Abstract

The early stages of kaolinite dehydroxylation were investigated using density functional theory combined with the climbing-image nudged elastic band method. Five distinct proton migration mechanisms leading to water formation and removal were examined in idealized bulk and surface slab models. Structural analysis revealed that the octahedral sheet is more flexible than the tetrahedral sheet, and that removal of OH groups mainly triggers Al–O bond rearrangements. Activation energies decrease from ~350 kJ/mol in bulk to ~150 kJ/mol in dehydroxylated slab systems, consistent with experimental values from the literature. Reaction energies are also lower in slab models, indicating enhanced thermodynamic stabilization by structural relaxation. Comparison with literature shows that slab models capture both the kinetic barriers and thermodynamic driving forces associated with the kaolinite-metakaolinite transformation. These findings highlight the importance of structural relaxation and OH spacing in determining the energetics of dehydroxylation, and provide atomistic insight in the first steps of the dehydroxylation process.