Chemical bonding of HF, HCl, and H2O onto YF3 surfaces: quantification by first principles

Abstract

The surfaces of waimirite β-YF3 have been studied for their fluorine and chlorine versus water affinity. Bonding patterns of HF, HCl, and H2O chemically adsorbed onto surfaces of (010), (100), (011), and (101) have been quantified by density functional theory applying energy decomposition analysis. We found that the adsorption of H2O is dominated by about 65% of electrostatics, which causes a low surface sensitivity and weak interactions. On the contrary, the adsorptions of HF and HCl are driven by strong hydrogen bonds resulting in a highly surface-dependent ratio of 30–60% electrostatic versus orbital contribution. Among the stoichiometric surfaces, the shortest and strongest hydrogen bonds and consequently most covalent bonding patterns are found within YF3 HCl. However, when including the preparation energy, each surface favors the adsorption of HF over HCl, which reproduces the higher affinity of yttrium towards fluoride over chloride, previously known for solutions, also for the solid state.