Facet-Dependent Pre-Dissociation of Typical Metal Oxide Nanoparticles: Atomic-Scale Mechanisms and Environmental Interfacial Regulation

Abstract

Dissolution of crystal-based nanoparticles (MNPs) is crucial for determining their environmental fate and toxicity. However, the regulatory roles of intrinsic crystal facets and aqueous conditions in the initial dissolution remain unresolved. Using ZnO as a typical model, this study employed density functional theory (DFT) to reveal facet-dependent pre-dissociation mechanisms under different aqueous conditions. In pure water, the polar (0001) facet was actively dissolving via adsorption of $H_2O$, triggering synergistic bond weakening and placing it in a facile pre-dissociation state. In contrast, the nonpolar (10-10) and (11-20) facets exert a structural buffering effect through their inherent coordination heterogeneity, thereby maintaining lattice integrity. For the effects of environmental conditions, typical small molecular organic acids (such as oxalic acid) can extract electrons from surfaces to show strong complexation, leading to deep surface cationization and exacerbating lattice distortion. Under acidic conditions, $H^+$ preferentially attacks surface lattice oxygen, significantly weakening the local ZnO bonds and promoting dissolution. This study established an atomic-scale relationship between facet structure, interfacial charge speciation and lattice ion release, confirming the key role of intrinsic facets in determining the environmental fate of MNPs. It provides theoretical support for designing novel, safe nanomaterials through facet engineering.