Functionalization of the polycrystalline cerium oxide with phenylphosphonic acid molecules

Abstract

This work reports a study of the functionalization of polycrystalline cerium oxide (pCeO₂) films by the phenylphosphonic acid (PPA) molecules deposited either in vacuum or from aqueous solution. The systems are characterized using synchrotron-based techniques, including core-level and valence-band photoelectron spectroscopy, resonant photoemission and near-edge X-ray absorption spectroscopy. PPA binds strongly to the pCeO₂ surface via the phosphonate group in a tridentate geometry, accompanied by deprotonation of the P–OH groups and the formation of surface hydroxyl groups. The binding configuration is independent of molecular deposition technique and oxide surface morphology. Thermal stability analysis reveals that low coverage PPA adlayers (0.07 ML) are prone to desorption and decomposition upon heating. In contrast, high coverage adlayers (0.17 ML), particularly those formed in the presence of water, exhibit higher thermal stability as no molecular decomposition was observed up to 400 °C. The deposition of PPA from aqueous solution is found to protect the surface of pCeO₂ films from reduction. The results contribute to the understanding of phosphonate–cerium oxide interactions by highlighting the influence of the deposition environment and surface morphology on molecular bonding and stability.