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Title: Acidities of Boehmite Low Miller Index Faces From First-Principles Molecular Dynamics
Abstract: The surface chemistry for minerals, particularly the protonation/deprotonation has broad impacts in chemistry, from catalysis, interfacial behavior of minerals, and absorbent materials. Due to the complexity of the surface and differing exposed planes of the nanoparticles, the individual site acidity is difficult to assess using experimental methods, unlike typical aqueous species. In this work, the acidity of surface sites found on the four primarily exposed boehmite faces was determined using thermal integration via ab initio molecular dynamics and compared against the semi-empirical multi-site complexation (MUSIC) model. The calculated pKa values were used to estimate the point of zero charge (PZC) for the basal plane, 9.36, in good agreement with experimental results 9.5 ± 0.5. Recent work from the Pacific Northwest National Lab (PNNL) has demonstrated the capability of producing boehmite nanoparticles with selective morphologies, i.e. determining which faces are present and at which surface area coverage by altering the synthesis process. Combining the knowledge of surface site acidity constants and morphology-controlled synthesis can be applied to current environmental remediation applications of boehmite that are hindered by environmental pH conditions.