An unexpected phase transformation of ceria nanoparticles in aqueous media
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An unexpected phase transformation of ceria nanoparticles in aqueous media Satyanarayana V.N.T. Kuchibhatla1,a)b) , Ajay S. Karakoti2, Andreas E. Vasdekis1,c), Charles F. Windisch, Jr.3,d), Sudipta Seal4, Suntharampillai Thevuthasan1, Donald R. Baer1 1
Environmental and Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, USA School of Engineering and Applied Science, Division of Biological and Life Sciences, School of Arts and Sciences, Ahmedabad University, Ahmedabad, Gujarat 380009, India 3 FCSD, Pacific Northwest National Laboratory, Richland, Washington 99354, USA 4 Nanoscience and Technology Center, Advanced Materials Processing and Analysis Center, Department of Materials Science and Engineering and College of Medicine, University of Central Florida, Orlando, Florida 32816, USA a) Address all correspondence to this author. e-mail: [email protected] b) Current address: Parisodhana Technologies Pvt., Ltd., Hyderabad, Telangana 500074, India. c) Current address: Department of Physics, University of Idaho, Moscow, ID 83844, USA. d) Current address: Columbia Basin College, Pasco, WA 99301, USA. 2
Received: 21 August 2018; accepted: 16 November 2018
Cerium oxide nanoparticles (CNPs) are of significant interest to the scientific community due to their widespread applications in a variety of fields. It is proposed that size-dependent variations in the extent of Ce31 and Ce41 oxidation states of cerium in CNPs determine the performance of CNPs in application environments. To obtain greater molecular and structural understanding of chemical state transformations previously reported for ceria of 3 nm nanoparticles (CNPs) in response to changing ambient conditions, microXRD and Raman measurements were carried out for various solution conditions. The particles were observed to undergo a reversible transformation from a defective ceria structure to a non-ceria amorphous oxyhydroxide/ peroxide phase in response to the addition of 30% hydrogen peroxide. For CNPs made up of ;8 nm crystallites, a partial transformation was observed, and no transformation was observed for CNPs made up of ;40 nm crystallites. This observation of differences in size-dependent transition behavior may help explain the benefits of using smaller CNPs in applications requiring regenerative property.
Introduction Cerium oxide nanoparticles (CNPs) are widely used in a variety of applications [1, 2], including those associated with catalysis [3, 4], fuel cells [5], solar energy [6, 7], and protecting human health [4, 8, 9]. However, there are also concerns about the fate and possible deleterious impacts of CNPs on the environment and their potentially toxic effects on human exposure [10, 11]. Relevant to many applications is the ability of CNPs to transform between Ce31 and Ce41 oxidation states, alter structure, and change shape [12, 13, 14]. Greater knowledge of the nature of the transformations of CNPs is important to understand the desirable and undesirable properties of CNPs and the observed in
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