Adsorption and Structural Effects of Formic Acid on Magnetite Surfaces

Magnetite (Fe₃O₄) nanoparticles have a high potential for diverse applications like waste-water treatment, catalysis, and hybrid materials. Formic acid is usually present in ambient conditions and can be viewed as the smallest representative of the carboxylic acids, which are used to functionalize magnetite nanoparticles. Here, we present results from density functional theory (DFT) calculations on the adsorption and structural effects of formic acid on magnetite (001) and (111), which represent the major facets of magnetite nanoparticles. The relevant aspects are compared to results from collaborating experimentalists employing a range of surface science techniques. Insights on the near-surface restructuring of magnetite (001) upon dissociative formic acid adsorption are presented. For the (111) surface, a heterogeneous adsorption mechanism in quasi-bidentate as well as chelating geometries, and ordering in a local (√3×√3)R30° superstructure stabilized by defects are observed. As an outlook, the inclusion of our results into a newly parametrized empirical force field is presented as a step towards multi-scale modelling.