Structure and reducibility of yttrium-doped cerium dioxide nanoparticles and (111) surface

Two decades of ceria nanoparticle research: structure, properties and emerging applications

Cerium oxide nanoparticles (CeNPs) are versatile materials with unique and unusual properties that vary depending on their surface chemistry, size, shape, coating, oxidation states, crystallinity, dopant, and structural and surface defects. This review encompasses advances made over the past twenty years in the development of CeNPs and ceria-based nanostructures, the structural determinants affecting their activity, and translation of these distinct features into applications. The two oxidation states of nanosized CeNPs (Ce3+/Ce4+) coexisting at the nanoscale level facilitate the formation of oxygen vacancies and defect states, which confer extremely high reactivity and oxygen buffering capacity and the ability to act as catalysts for oxidation and reduction reactions. However, the method of synthesis, surface functionalization, surface coating and defects are important factors in determining their properties. This review highlights key properties of CeNPs, their synthesis, interactions, and reaction pathways and provides examples of emerging applications. Due to their unique properties, CeNPs have become quintessential candidates for catalysis, chemical mechanical planarization (CMP), sensing, biomedical applications, and environmental remediation, with tremendous potential to create novel products and translational innovations in a wide range of industries. This review highlights the timely relevance and the transformative potential of these materials in addressing societal challenges and driving technological advancements across these fields.

Preferential location of zirconium dopants in cerium dioxide nanoparticles and the effects of doping on their reducibility: a DFT study

Structural properties and reducibility of zirconium-doped cerium dioxide systems were studied using periodic plane-wave calculations based on density functional theory. A systematic analysis of the results for nanoparticles of two sizes, Ce40-nZrnO80 ∼ 1.5 nm large and Ce140-nZrnO280 ∼ 2.4 nm large, in comparison with slab model data for Ce1-xZrxO2(111) surface has been performed focusing on specific nanoscale effects. Several loadings of Zr dopants ranging from 0.7 to 50 atomic metal percent have been considered. Subsurface cationic sites of ceria are calculated to be energetically most favourable for doping Zr4+ ions in all models. The system stability with several zirconium ions is defined by the relative stability of the occupied individual Zr4+ positions when only one zirconium ion is present. Data for the Ce70Zr70O280 nanoparticle with an equal number of Ce4+ and Zr4+ cations reveal that atomic orderings of neither separated oxide (Janus-type) particles nor randomly intermixed ones are more stable than the distribution of Zr atoms occupying all cationic positions inside the nanoparticle to minimize the presence of surface zirconium. The basicity of surface oxygen centers in nanoparticles is predicted to be decreased when Zr dopants are located in surface positions. The presence of Zr4+ dopants in CeO2 systems can notably lower the oxygen vacancy formation energy and shows interesting peculiarities at higher Zr loadings. Among them is the higher stability of inner oxygen vacancies in Zr-containing nanoparticles and enhanced oxygen mobility beneficial for application in catalysis and as a solid electrolyte with oxygen ions as charge carriers. Similar to pure ceria, Zr-doped ceria nanoparticles exhibit notably higher reducibility than the corresponding extended systems.

A Study of the Chemistries, Growth Mechanisms, and Antibacterial Properties of Cerium- and Yttrium-Containing Nanoparticles

Under the current climate, physicians prescribe antibiotics for treating bacterial infections, and such a limitation to a single class of drugs is disadvantageous since antibiotic-resistant bacteria have adapted to withstanding their stresses. Antibiotic alternatives are sought, and herein metal nanoparticles comprised of the rare earth elements cerium and yttrium were determined to invoke toxicity on methicillin-resistant Staphylococcus aureus (MRSA) and a multi-drug-resistant strain of Escherichia coli (MDR E. coli). Ceria nanoparticles, yttrium-doped ceria nanoparticles, and cerium-doped yttria nanoparticles were fabricated by a wet chemical route, homogeneous precipitation in hexamethylenetetramine (HMT). To demonstrate the drastic variations in nanoparticle structure and toxicity that occur when the synthesis method and solvent are substituted, two additional approaches involving solvothermal and hydrothermal reactions were pursued in the production of yttrium-containing nanoparticles. Intrinsic nanoparticle features of size, morphology, and composition were construed by physiochemical characterizations, which aided in the elaboration of chemical reaction and growth mechanisms. It was determined by in vitro plate count assays that ceria nanoparticles which had been doped using the yttrium metal precursor after 30 min of the HMT reaction, at 500 μg/mL, were the most effective at inhibiting MRSA growth without imposing significant cytotoxicity on human dermal fibroblast cells. A total of 500 μg/mL of cerium- and yttrium-containing nanoparticles, prepared in a 1:1 molar ratio, were similarly biocompatible and antimicrobial, in the case of MDR E. coli. Indeed, as this study showed, nanoalternatives to antibiotics are feasible, adaptable, and can be facilely produced. The possible clinical applications of the rare earth metal nanoparticles are variegated, and ceria and yttria nanoparticles are additionally credited in the literature as dynamic antioxidants, regulators of tissue regeneration, and anticancer agents.

Diffusion in gadolinium doped ceria thin films: a combined Monte Carlo and molecular dynamics study

The mobility of oxygen ions at surfaces and interfaces in solid oxide fuel materials is controversial. Experiments are complex and conflicting results for grain boundary and surface O2- diffusion have been obtained. Thus, it is not clear what the necessary conditions are to optimise O2- diffusion during the manufacturing process. To aid the interpretation of experimental results, combined Monte Carlo and molecular dynamics simulations were applied to model thin films of CeO2 on binary oxide substrates. The objective of this work is to determine the effects of both tensile lattice strain and segregation on the calculated diffusion coefficients. The distribution of Gd3+ and O2- ions has been interpreted as evidence for the formation of a space charge layer at both the interface and surface. The space charge layer impacts the calculated diffusion coefficients at the thin film surface. Moderate tensile strain in the CeO2 thin film has little influence on the segregation of Gd3+ ions.