The characterization of purified citrate-coated cerium oxide nanoparticles prepared via hydrothermal synthesis

Hypothesis: Cerium oxide nanoparticles were synthesized using a hydrothermal approach with citric acid as a stabilizing agent. Citric acid adsorption onto the nanoceria particle surface can cease particle formation and create a stable dispersion for an extended shelf life. The product was dialyzed immediately following the synthesis to remove unreacted cerium that could contribute to biological effects. Nanoparticle characterization results are expected to help identify the surface citrate bonding structure. Experiments: Many characterization techniques were utilized to determine size, morphology, surface properties, and citrate complexation on the nanoceria particle surface. These included transmission electron microscopy, electron energy loss spectroscopy, dynamic light scattering, x-ray diffraction, thermogravimetric analysis, Fourier-transform infrared spectroscopy, Raman spectroscopy, UV–Vis absorption spectroscopy, zeta potential, and ¹³C solid-state nuclear magnetic resonance spectroscopy. Findings: Primary particles were hexagonal, determined to be 4.2 nm in diameter. The hydrodynamic diameter of the dialyzed product was 10.8 nm. Each agglomerate was estimated to contain an average of 5.7 particles. The citrate coating contained 2.8 citrate molecules/nm², corresponding to an approximate citrate monolayer. Citrate complexation with the nanoceria surface includes the central carboxyl geminal to the hydroxyl and perhaps one of its terminal carboxyl groups.