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Ligands that accelerate nanoceria dissolution may greatly affect its fate and effects. This project assessed the carboxylic acid contribution to nanoceria dissolution in aqueous, acidic environments. Nanoceria has commercial and potential therapeutic and energy storage applications. It biotransforms in vivo. Citric acid stabilizes nanoceria during synthesis and in aqueous dispersions. In this study, citrate-stabilized nanoceria dispersions (∼4 nm average primary particle size) were loaded into dialysis cassettes whose membranes passed cerium salts but not nanoceria particles. The cassettes were immersed in iso-osmotic baths containing carboxylic acids at pH 4.5 and 37 °C, or other select agents. Cerium atom material balances were conducted for the cassette and bath by sampling of each chamber and cerium quantitation by ICP-MS. Samples were collected from the cassette for high-resolution transmission electron microscopy observation of nanoceria size. In carboxylic acid solutions, nanoceria dissolution increased bath cerium concentration to >96% of the cerium introduced as nanoceria into the cassette and decreased nanoceria primary particle size in the cassette. In solutions of citric, malic, and lactic acids and the ammonium ion ∼15 nm, ceria agglomerates persisted. In solutions of other carboxylic acids, some select nanoceria agglomerates grew to ∼1 micron. In carboxylic acid solutions, dissolution half-lives were 800–4000 h; in water and horseradish peroxidase they were ≥55,000 h. Extending these findings to in vivo and environmental systems, one expects acidic environments containing carboxylic acids to degrade nanoceria by dissolution; two examples would be phagolysosomes and in the plant rhizosphere. [ABSTRACT FROM AUTHOR]

• Cerium ions, known to produce adverse biological effects, are removed by dialysis. • Characterization of citrate-coated nanoceria prepared via hydrothermal synthesis. • Results include size and morphology, surface composition, and crystallinity. • Investigation of the ceria-citrate complexation bonding structures. 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. 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. 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. [ABSTRACT FROM AUTHOR]