AVS 59th Annual International Symposium and Exhibition
    Surface Science Tuesday Sessions
       Session SS-TuP

Paper SS-TuP26
Ligand Functionalized Cerium Oxide Nanoparticles - Investigating the Mode and Energetics of Binding

Tuesday, October 30, 2012, 6:00 pm, Room Central Hall

Session: Surface Science Poster Session
Presenter: A.S. Karakoti, Pacific Northwest National Laboratory
Authors: A.S. Karakoti, Pacific Northwest National Laboratory
Z. Lu, Pacific Northwest National Laboratory
W. Wang, Pacific Northwest National Laboratory
P. Nachimuthu, Pacific Northwest National Laboratory
H. Wang, Pacific Northwest National Laboratory
P. Yang, Pacific Northwest National Laboratory
S. Thevuthasan, Pacific Northwest National Laboratory
Correspondent: Click to Email
Despite the significant amount of work done on functionalization of nanoparticles for various applications, studies on the determining the fundamental molecular level interaction between the various ligands and nanoparticle surfaces have been limited due to the inherent challenges associated with the characterization of highly reactive and dynamic nature of these particles. In order to obtain a fundamental understanding of nanoparticle-ligand interaction, cerium oxide nanoparticles (ceria) functionalized with simple ligands such as carboxylic acids were studied to characterize the nature of bonding, configuration of ligands and the energetics of the ligand-nanoparticle interactions. Mono-disperse ceria nanoparticles were synthesized by thermal hydrolysis process and functionalized with carboxylic acid groups from various organic ligands. The size distribution and morphology of the nanoparticles prior to and following functionalization were characterized by various imaging and spectroscopy tools to ascertain the integrity of nanoparticles. In-situ x-ray photoelectron spectroscopy (XPS) from aqueous solution of functionalized ceria nanoparticles frozen at liquid nitrogen temperature was performed to avoid any surface contamination and preserve the chemistry of the functionalized nanoparticles. XPS data suggests that the following functionalization the ceria nanoparticles predominantly exist in Ce4+ oxidation state. From XPS elemental quantification it was found that the oxygen from carboxylate molecules becomes a part of the ceria lattice to maintain the stoichiometry and bind to the ceria surface in bidentate orientation. Sum frequency generation vibration spectra (SFG-VS) showed the presence of OCO modes of vibration on the surface of cerium oxide confirming the bidentate mode of bonding between carboxylate and ceria nanoparticle surface. In addition isothermal titration calorimetry was used to determine energetics of ligand binding on the surface of nanoparticles. Results from these characterizations were combined with the periodic density functional theory (DFT) calculations to develop a complete visualization of the interaction of organic ligands with nanoparticle surfaces.