Environmental Science Nano CRITICAL REVIEW Cite this: DOI: 10.1039/c4en00075g Received 30th April 2014, Accepted 5th July 2014 DOI: 10.1039/c4en00075g rsc.li/es-nano Applications and implications of nanoceria reactivity: measurement tools and environmental impact Daniel Andreescu, Gonca Bulbul, Rifat Emrah Özel, Akhtar Hayat, Naimish Sardesai and Silvana Andreescu * Cerium oxide nanoparticles or nanoceria have a unique structure and interesting and unusual redox and catalytic properties that vary with the size, shape, charge, surface coating and chemical reactivity. This paper highlights applications and environmental implications of nanoceria, and describes methodologies for the assessment of the reactivity and potential toxicological effects of these particles. The physical and chemical properties in the particle design that are responsible for their reactivity and transformation in environmental and biological conditions are described. Processes such as surface oxidation, formation of surface complexes and potential interaction with redox active components of the environment are discussed. An overview of analytical characterization methods for study of nanoceria properties, reactivity and impact, highlighting methodological challenges and limitations is presented. Examples discussed include strategies to determine physicochemical properties, cytotoxicity and antioxidant or pro-oxidant activity in various exposure environments. Development of new measurement tools to facilitate rapid assessment and accelerate screening of these particles for their reactivity and effects is discussed. Future research needs for environmental assessment of benefits and potential risks associated with the use of nanoceria are also provided. 1. Introduction Nanoceria particles (or cerium oxide nanoparticles, CeO 2 NPs) are used in a variety of applications including chemical mechanical polishing, catalysis, solid oxide fuel cells, environ- mental remediation, sensing and more recently biomedicine. 1 The popularity of these particles is a consequence of the many interesting mechanical, spectroscopic, catalytic and oxi- dant/antioxidant properties of these particles enabling them to be used as polishing agents for electronics, oxygen buffers, UV blockers, sorbets for environmental contaminants, colori- metric dyes for quantifying redox reactions and as synthetic antioxidants. 2–5 Ceria NPs are also used as diesel fuel addi- tives, resulting in release of these particles in the atmo- sphere. In spite of the many uses of these particles, little is known about their potential impact on the environment and human health. The useful properties of nanoceria are a consequence of the physical and chemical characteristics of these particles, and their reactivity, and can vary greatly with the size, shape, charge and surface coating. Many of the unique features are linked with the dual oxidation state of cerium at the NP sur- face enabling them to act as both oxidizing and reducing agents. The environmental and health effects are related with the aforementioned characteristics. Changes in both the oxi- dation state (switching between Ce 3+ and Ce 4+ ) and surface adsorption (e.g. through hydroxyl groups) have been identified as Environ. Sci.: Nano This journal is © The Royal Society of Chemistry 2014 Department of Chemistry and Biomolecular Science, Clarkson University, Potsdam, NY 13699-5810, USA. E-mail: eandrees@clarkson.edu Nano impact Nanoceria particles have great promise as active materials in biomedicine, microelectronics, environmental remediation, catalysis and sensing. The many useful properties of nanoceria are derived from the unique nanosize structure, surface reactivity and redox activity, which also pose significant environmental toxicological challenges. This paper provides a critical overview of the environmental implications of the reactivity of nanoceria. We survey research exploring the chemistry of nanoceria particles, their benefits and potential risks for the environment. We describe the role of the physicochemical and surface properties that are unique to their nanoparticulate form and discuss analytical methodologies for assessing and screening these particles. Finally, we provide an outlook of future research needs for study and environmental assessment of nanoceria. Published on 11 July 2014. Downloaded on 01/08/2014 19:17:16. View Article Online View Journal