Cerium Oxide Surface Research Articles

In Situ X‐Ray Photoelectron Spectroscopy Study of Atomic Layer Deposited Cerium Oxide on SiO2: Substrate Influence on the Reaction Mechanism During the Early Stages of Growth

AbstractThermal atomic layer deposition (ALD) of cerium oxide using commercial Ce(thd)4 precursor and O3 on SiO2 substrates is studied employing in‐situ X‐ray photoelectron spectroscopy (XPS). The system presents a complex growth behavior determined by the change in the reaction mechanism when the precursor interacts with the substrate or the cerium oxide surface. During the first growth stage, non‐ALD side reactions promoted by the substrate affect the growth per cycle, the amount of carbon residue on the surface, and the oxidation degree of cerium oxide. On the contrary, the second growth stage is characterized by a constant growth per cycle in good agreement with the literature, low carbon residues, and almost fully oxidized cerium oxide films. This distinction between two growth regimes is not unique to the CeOx/SiO2 system but can be generalized to other metal oxide substrates. Furthermore, the film growth deviates from the ideal layer‐by‐layer mode, forming micrometric inhomogeneous and defective flakes that eventually coalesce for deposit thicknesses above 10 nm. The ALD‐cerium oxide films present less order and a higher density of defects than films grown by physical vapor deposition techniques, likely affecting their reactivity in oxidizing and reducing conditions.

Dual surface-modification by oleic acid and epoxy-based silane coupling agent providing cerium oxide nanoparticles as additive in pentaerythritol oleate with improved high-temperature adsorption performance and tribological properties

An epoxy-based silane coupling agent (KH560) was grafted onto the surface of oleic acid-modified cerium oxide (CeO2-OA) nanoparticles in order to improve the competitive adsorption ability of the anti-wear additives in ester oils and simultaneously hinder the additive desorption owing to thermal disturbance under high-temperature condition. The as-prepared oleic acid-epoxy silane co-modified cerium oxide (CeO2-OA/E) nanoparticles were characterized. The effect of temperature on the adsorption behavior of trityl phosphate (TCP, a commercial high-temperature antifriction agent), CeO2-OA and CeO2-OA/E in PETO was studied using a dissipative quartz microbalance. Their tribological properties as the additives in pentaerythritol oleate (PETO), a polar ester base oil, were evaluated with a four-ball machine and a ball-on-block friction and wear tester; and their tribomechanism was explored with respect to their adsorption behavior on rubbed steel surfaces at elevated temperatures. It was found that the secondary surface-capping of CeO2-OA by the KH560 silane coupling agent resulted in great increases in the surface potential (from 54 mV to 396 mV) and thermal stability as well (the thermal decomposition temperature rose from 185 °C to 254 °C). Among the tesetd lubricant additives, CeO2-OA/E exhibited the highest adsorption mass, because of the highest surface potential the chemisorption ascribed to the epoxy group of the silane coupling agent. Particularly, CeO2-OA/E added in PETO exhibited better friction reduction and anti-wear properties at 150 °C than CeO2-OA and TCP, because CeO2-OA/E added in PETO formed tribofilm composed of CeO2 and SiO2 with excellent thermal stability as well as friction-reduction and antiwear effects through stable chemical adsorption and tribochemical reaction at elevated temperatures.

Simultaneous tracking of ultrafast surface and gas-phase dynamics in solid-gas interfacial reactions.

Real-time detection of intermediate species and final products at the surface and near-surface in interfacial solid-gas reactions is critical for an accurate understanding of heterogeneous reaction mechanisms. In this article, an experimental method that can simultaneously monitor the ultrafast dynamics at the surface and above the surface in photoinduced heterogeneous reactions is presented. This method relies on a combination of mass spectrometry and femtosecond pump-probe spectroscopy. As a model system, the photoinduced reaction of methyl iodide on and above a cerium oxide surface is investigated. The species that are simultaneously detected from the surface and gas-phase present distinct features in the mass spectra, such as a sharp peak followed by an adjacent broad shoulder. The sharp peak is attributed to the species detected from the surface, while the broad shoulder is due to the detection of gas-phase species above the surface, as confirmed by multiple experiments. By monitoring the evolution of the sharp peak and broad shoulder as a function of the pump-probe time delay, transient signals are obtained that describe the ultrafast photoinduced reaction dynamics of methyl iodide on the surface and in the gas-phase. Finally, SimION simulations are performed to confirm the origin of the ions produced on the surface and in the gas-phase.

Promotional effects of Nb2O5 on ceria doped Ni catalysts for selective hydrogenation of 1,3-butadiene to butenes: Combined experimental and DFT approach

Developing low cost, active and selective catalysts that would replace the more deployed noble metals is desirable for hydrogenation of 1,3-butadiene. Herein, we prepared Ni catalysts supported on niobium-cerium oxides and characterization was carried out with TGA, XRD, H2-TPR, H2-TPD, HR-TEM, XPS, FTIR, N2 adsorption–desorption, and EDS mapping. Density functional theory (DFT) computes the reaction energies controlling the 1,3-butadiene hydrogenation. H2-TPR revealed that the inclusion of niobium oxide in the catalysts confer stronger metal support interaction that promotes the surface and bulk reduction of cerium oxide and leads to the improvement in the formation of surface Ce3+ as confirmed from the XPS analysis. 1,3-butadiene conversion was tested between 100 °C-350 °C and the catalysts exhibit high conversion at lower Ni loading. We found that the niobium inclusion directed the selectivity towards near complete butene formation even at higher temperature. The onset of decline in activity was observed at temperatures above 250 °C with the simultaneous formation of propene and propane and the disappearance of butane. Guided by the reaction results and the temperature programmed oxidation analysis (TPO), we proposed the reaction mechanism leading to the deactivation, and this entails butane decomposition to propene and surface carbene, while propane is formed from propene, the surface carbene occasioned in the formation of harmful carbon as evident from TPO results. Carbonaceous species formed on the catalysts were minimized on the niobium containing catalysts.

Impact of Atomic Defects on Ceria Surfaces on Chemical Mechanical Polishing of Silica Glass Surfaces.

This study investigates the impact of atomic defects, such as oxygen vacancies and Ce3+ ions, on cerium oxide (ceria) surfaces during chemical mechanical polishing (CMP) for silica glass finishing. Using density functional theory (DFT) and reactive molecular dynamics simulations, the interaction of orthosilicic molecules and silica glass with dry and wet ceria surfaces is explored. Defects alter the surface reactivity, leading to the dissociation of orthosilicic acid on oxygen vacancies, forming a strong Si-O-Ce bond. Hydroxylated surfaces exhibit easier oxygen vacancy formation and thermodynamically favored substitution of hydroxyl groups with orthosilicic acid. A new ReaxFF library for silica/ceria interfaces with defects is validated using DFT outcomes. Reactive MD simulations demonstrate that ceria surfaces with 30% Ce3+ ions on (111) planes exhibit higher polishing efficiency, attributed to increased Si-O-Ce bond formation. The simultaneous presence of oxygen vacancies and various acidic and basic sites on ceria surfaces enhances the polishing efficiency, involving acid-base reactions with silica. Defective surfaces show superior efficiency by removing silicate chains, contrasting with nondefective surfaces removing isolated orthosilicate units. This study provides insights into optimizing CMP processes for high-precision glass industry surface finishing.

Effect of Surface Treatment of Nanocrystalline CeO2 on Its Dephosphorylation Activity and Adsorption of Inorganic Phosphates.

The surface of nanocrystalline cerium oxide (CeO2) was treated with various chemical agents by a simple postmodification method at 25 °C and atmospheric pressure. Hydrogen peroxide, ammonium persulfate, deionized water, ascorbic acid, and ortho-phosphoric acid were used in order to study and evaluate their effect on surface materials, such as surface area, crystallite size, number of surface hydroxyl groups, particle morphology, and Ce3+/Ce4+ ratio. Paraoxon-methyl (PO) decomposition and inorganic phosphate adsorption were used to evaluate the effect of surface treatment on catalytic and adsorption properties. CeO2 surface was studied by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and acid-base titration. While the treatment procedure affected the number of surface hydroxyl groups and the amount of bulk surface oxygen vacancies, only negligible changes were observed in the Ce3+/Ce4+ ratio. Interestingly, surface treatment affected the ability to decompose PO, but only a small effect on inorganic phosphate adsorption was observed, indicating the robustness of CeO2 for the latter. A mechanism for possible interaction of the used chemicals with the CeO2 surface was proposed.

Fabrication of ultrafine cerium oxide nanoparticles as an aqueous colloidal solution with single-molecular dispersant via shear agitation reactor or one-pot hydrolysis

Herein, ultrafine CeO2 nanoparticles are synthesized using monomolecular amino acids as dispersants. Monomolecular amino acids are suitable dispersants for the dispersion of nanoparticles with a diameter of 1 nm. Batch-type room-temperature hydrolysis (RTH) synthetic method, which takes advantage of the low decomposition pH of Ce (IV) nitrate, and a shear agitation (SA) reactor, which is highly versatile for multicomponent systems of colloidal synthesis, are used. After adding glycine, ultrafine CeO2 colloids of sizes 1.1 and 1.2 nm are obtained via the batch-type RTH synthesis method and SA reactor, respectively. The smallest CeO2 colloid size is 0.7 nm, which earned at the close concentration of the saturation of glycine using the batch-type RTH method. Because RTH can slowly hydrolyze Ce (IV) nitrate over several hours, we were able to observe the initial stage of nucleation (0.7 nm), which passes instantaneously in the SA reactor. Furthermore, glycine was found to be particularly effective in stabilizing the surface of cerium oxide due to its high adsorption capacity. Therefore, cerium oxide, which is amorphous in the synthesis stage, remained amorphous up to 100 °C due to glycine adsorption, neutralized the colloidal dispersion to form precipitates, and crystallized at room temperature after glycine was removed by washing treatment, resulting in a fluorite structure with a crystallite diameter of 1.5 nm. This crystallite diameter is maintained after heat treatment at 200 °C for 30 min.

Surface modification of CeO2−x nanorods with Sn doping for enhanced nitrogen electroreduction

While the electrochemical nitrogen reduction reaction (NRR) represents a prospective blueprint for environmentally renewable ammonia generation, it has yet to overcome the limitations of weak activity and inferior selectivity. In this regard, surface modification tactic was constructed to markedly enhance the activity and selectivity via introducing Sn atoms into the surface of defective cerium oxide (denoted as Sn-CeO2−x) as the active and robust electrocatalyst for NRR under benign environment. The introduction of Sn atoms in CeO2−x can not only inhibit the HER activity of the catalyst but also modulate the electronic structure of ceria and optimize N-Ce interaction, thus enhancing NRR activity and selectivity. Outperforming all previous CeO2-based NRR catalysts, this catalyst has demonstrated an ammonia yield rate of 41.1 μg mgcat−1 h−1 and an exceptional Faradic efficiency of 35.3%. This work presents a viable approach for the development of advanced NRR electrocatalysts.

Vibrational frequencies of CO bound to all three low-index cerium oxide surfaces: A consistent theoretical description of vacancy-induced changes using density functional theory.

The facet-dependent adsorption of CO on oxidized and reduced CeO2 single crystal surfaces is reviewed, with emphasis on the effect of CO coverage and the ability of state-of-the-art quantum-mechanical methods to provide reliable energies and an accurate description of the IR vibrational frequency of CO. Comparison with detailed, high-resolution experimental infrared reflection absorption spectroscopy data obtained for single crystal samples allows the assignment of the different CO vibrational bands observed on all three low-index ceria surfaces. Good agreement is achieved with the hybrid density functional theory approach with the HSE06 functional and with saturation coverage. It is shown that CO is very sensitive to the structure of cerium oxide surfaces and to the presence of oxygen vacancies. The combined theoretical-experimental approach offers new opportunities for a better characterization of ceria nanoparticles and for unraveling changes occurring during reactions involving CO at higher pressures.

Polyphenol synergistic cerium oxide surface engineering constructed core-shell nanostructures as antioxidants for durable and high-performance proton exchange membrane fuel cells

The chemical degradation of proton exchange membranes (PEMs) suffering from radical attack is a crucial issue in the development of proton exchange membrane fuel cells (PEMFCs), while incorporating cerium oxide (CeO2) nanoparticles (NPs) with regenerative redox properties to eliminate radicals could effectively alleviate degradation. However, the low stability and restricted activity of CeO2 in the PEMFC operating condition and the poor compatibility with PEM due to CeO2 agglomeration stimulate the urgency for structural modulation of CeO2. Achieving a balance of membrane performance and oxidation resistance through a rational surface modification strategy of CeO2 is important for expanding PEMFC applications. Herein, polyphenols surface functionalized CeO2 core-shell structure (CeO2@TP) were constructed via assembling oxidation-induced coupling tea polyphenols (TP) on CeO2 NPs. The TP oligomeric shell as a protective layer enhances the stability of CeO2, mitigating radical scavenging activity degradation and improving compatibility with PEMs. Physicochemical characterisation shows that the overall performance of the nanocomposite membrane is improved due to the interaction of CeO2@TP nanoparticles with the polymer matrix. Gratifyingly, the phenolic hydroxyl-rich reductive TP oligomeric shell accelerates the regeneration of Ce(IV) to Ce(III), increasing the proportion of Ce(III) and oxygen vacancies on the CeO2 surface, thus boosting antioxidation efficiency. As a result, the CeO2@TP-based PEMs exhibited an OCV decay rate of 0.22 mV h−1, a maximum power density of 1.06 W cm−2, an H2 crossover value of 2.18 mA cm−2, thickness retention (91.1%), and negligible Ce migration after 404 h of accelerated degradation testing. It is proven that the desired consequences of doping antioxidants in PFSA matrix can be intensified by surface modulation of the physicochemical properties of CeO2.

Influence of surface chemical properties of nanocrystalline CeO2 on phosphate adsorption and methyl-paraoxon decomposition

Nanocrystalline cerium oxide (CeO2) was used as an effective catalytic and adsorption material for the safe removal of selected phosphorus compounds. Several CeO2 samples were prepared by a simple coprecipitation method with subsequent annealing at temperatures between 400–600 °C, and their sorption ability for inorganic phosphates was studied together with their ability to decompose the organophosphorus compound - paraoxon methyl (PO) - with the goal to find the relations between the sorption and catalytic activity of the prepared materials. It was found that a complex set of physical and chemical characteristics (surface area, crystallite size, pore volume/size, the number of surface hydroxyl groups) plays a crucial role in the governing of adsorption ability and catalytic activity. From the dependence of some characteristics (i.e., the number of surface hydroxyl groups, BET surface area, crystallite size) on the annealing temperature and their mutual correlations, the model describing the degradation of organophosphate compounds on the surface of cerium oxide was deduced.

Synthesis, characterization and activity of CeO2 supported Cu-Mg bimetallic catalysts for CO2 to methanol

Cerium oxide was synthesized by thermal method using cerium carbonate hydrate and utilized as a catalysts support. Precipitation method was employed to deposit copper and magnesium oxides on the surface of cerium oxide. The synthesized Cu-Mg/CeO2 catalysts were characterized by different analytical techniques. FTIR studies confirmed the incorporation of copper and magnesium oxides on cerium oxide surface. Field Emission Scanning Electron Microscope (FESEM) revealed uniform distribution of both metal oxides on cerium oxide support. Nitrogen adsorption-desorption studies recorded surface profile of CeO2 loaded Cu-Mg bimetallic catalysts. The X-ray photoelectron spectroscopy (XPS) revealed existence of Cu and Mg metals in the form of Cu2+ and Mg2+ on CeO2 surface. Furthermore, the role of Ce was apprehended by XPS investigations in terms of methanol synthesis rate. Activities studied of the synthesized catalysts revealed the promoting role of Cu-Mg composition with highest activity of 71 g.meth/kg.cat.h was recorded for 4Cu-6Mg/CeO2 catalysts. The efficiency of CeO2 based Cu-Mg bimetallic catalysts was established by the comparative data from the literature in terms of methanol synthesis rate.

A molecularly imprinted sensing system for specific detection of monosaccharides based on CeO2 hollow nanosphere cascade enzyme system

Glucose oxidase (GOx) has unique catalytic properties and has been widely used in sensing and detection fields. However, the presence of isomers of target molecules greatly affects the catalytic ability and sensing accuracy. Therefore, it is particularly important to improve the specific detection of GOx for monosaccharides. Here, using β-D-glucose as a template molecule, molecularly imprinted polymers (MIPs) are prepared by self-initiated polymerization under mild conditions by continuously generating hydroxyl radicals on the surface of hollow metal cerium oxide (CeO2HNPs). A cascade catalytic system (CeO2HNPs@GOx-MIPs) with high specificity and selectivity for β-D-glucose detection was obtained. Impressively, the obtained cascade catalytic sensing system (CeO2HNPs@GOx-MIPs) showed a wide linear range of 1.2 μM–0.8 mM and a low detection limit of 1.0 μM. The isomer experiments show that the sensing system has satisfactory selectivity and excellent recycling stability and long-term shelf stability. Therefore, the synthesized β-D-glucose detection cascade catalytic system has broad application prospects in the precise sensing of monosaccharides and chemical food safety.

2D/3D- C3N4/CeO2 S-scheme heterojunctions with enhanced photocatalytic performance

• Successfully developed a novel method to obtain g-C 3 N 4 /CeO 2 composite photo-catalysts via simple, ball milled thermal spreading technique. • Facile control of surface morphology of carbon nitride on ceria. The optical absorption is tuned by morphology control. • The optimum loading was found to be 7.5 wt. %. • Morphology with an intermediate thickness between very thin and bulk carbon nitride on ceria surface is important to achieve maximum efficiency. • High efficiency of methylene blue degradation and good recycling performance. A facile, green and easily scalable method has been developed to facilitate the construction of 2D-C 3 N 4 /3D-CeO 2 heterojunction materials. It uses only cheap urea and ceria in a thermal spreading technique that allows the controlled growth of carbon nitride layers on cerium oxide surface. The exfoliation of bulk carbon nitride and subsequent stabilization of layers on ceria takes place during thermal spreading technique in a single step. Simple variation of carbon nitride allowed to control the morphology of carbon nitride from highly dispersed thin layer up to bulk-like structures over ceria surface. The optical absorption was enhanced with 2D-C 3 N 4 /3D-CeO 2 materials. The variation of structure and consequent differences in the solar powered decomposition of methylene blue has been analyzed. Results reveal that, the optimum loading of 7.5 wt.% carbon nitride can lead to the formation of intermediate structure in between very thin layers and bulk-like structure, that achieves best contact between the two phases making effective heterojuctions. This best catalyst exhibits 98% conversion at a timing of 100 minutes. The radical scavenging studies showed that •O 2− and h+ performed an imperative role. In addition, a plausible mechanism of photo catalytic decomposition is also proposed for 2D-C 3 N 4 /3D-CeO 2 materials.

Interaction of Hydrogen with Cu-Modified Cerium Oxide Surfaces

We investigate the interaction between molecular hydrogen and ultrathin epitaxial CeO2 films modified with a 2% concentration of Cu atoms using X-ray photoemission spectroscopy (XPS) during thermal reduction cycles in H2. The XPS measurements are combined with density functional theory calculations to obtain further insight into the observed modifications of the film surface. Our results show that the presence of Cu atoms decreases the barrier for H2 dissociation in comparison to that on pure ceria surfaces, leading to the formation of surface OH groups after exposure to H2. Moreover, surface oxygen vacancies are generated already at mild temperatures (470 K), most likely via water formation and desorption. The presence of surface oxygen vacancies and hydroxyls contributes to the observed large increase in surface Ce3+ concentration with increasing reduction temperature. In spite of these atomic scale modifications, the surface morphology observed by scanning tunneling microscopy remains substantially unchanged on the length scale of tens of nm.

Degradation of parathion methyl by reactive sorption on the cerium oxide surface: The effect of solvent on the degradation efficiency

A simple and easily scalable “wet” procedure was used to prepare nanocrystalline cerium oxide capable of destroying the toxic organophosphate pesticide parathion methyl. The synthetic procedure consists of the direct precipitation of cerous salt with aqueous ammonia in the absence of CO 2 . The prepared cerium oxide was able to decompose the organophosphate compounds both in nonpolar (e.g., heptane) and polar aprotic (e.g., acetonitrile) solvents. However, in solvents with hydrogen-bond donating ability, the –OH groups on the cerium oxide surface were solvated and inactivated. The preferential solvation model was used to express the experimental dependencies of the cerium oxide degradation efficiency on the composition of the water-acetonitrile mixture. In certain solvent systems, some empirical polarity scales, such as the alpha-scale or the Dimrodth-Richardt parameter E T (30), may be correlated with the degradation efficiency of cerium oxide.

In situ NAP-XPS study of CO2 and H2O adsorption on cerium oxide thin films

Insights of CO2 and H2O activation on cerium oxide based catalysts are of great interest to many important catalytic processes, which are widely studied in model systems under ultrahigh vacuum conditions. Here, in situ near ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) was used to study CO2 and H2O adsorption on fully oxidized CeO2 and partially reduced CeO2−x surfaces. It is found that CO2 only weakly interacts with the stoichiometric CeO2 but strongly adsorbs on partially reduced CeO2−x surfaces with surface carbonate formation. H2O dissociatively adsorbs reversely on the CeO2 surface with H2O exposure pressure above 1 × 10−3 mbar, while H2O strongly dissociates on the partially reduced CeO2−x surfaces. The surface dissociated OH and H species are stable on the CeO2−x surface up to 600 K. Both CO2 and H2O adsorption cause clear reoxidation of partially reduced CeO2−x. This study provides new insights into CO2 and H2O interaction with cerium oxide surfaces at near ambient pressure conditions.

Enhanced catalytic performance of atomically dispersed Pd on Pr-doped CeO2 nanorod in CO oxidation

Single-atom noble metal catalysts have been widely studied for catalytic oxidation of CO. Regulating the coordination environment of single metal atom site is an effective strategy to improve the intrinsic catalytic activity of single atom catalyst. In this work, single atom Pd catalyst supported on Pr-doped CeO2 nanorods was prepared, and the performance and nature of Pr-coordinated atomic Pd site in CO catalytic oxidation are systematically investigated. The structure characterization using AC-HAADF-STEM, EXAFS, XRD and Raman spectroscopy demonstrate the formation of single atom Pd site and abundant surface oxygen vacancies on the surface of Pr-doped CeO2 nanorod. With the combination of the XPS characterization and DFT calculations, the oxidation state of Pd on Pr-doped CeO2 nanorod is determined lower than that on CeO2 nanorod. The turnover frequency of CO oxidation is markedly increased from 8.4 × 10−3 to 31.9 × 10−3 s with Pr-doping at 130 ºC and GHSV of 70,000 h−1. Combined with kinetic studies, DRIFT and DFT calculations, the doped-Pr atoms reduced the formation energy of oxygen vacancies and generate more oxygen vacancies around the atomically dispersed Pd sites on the surface of cerium oxide, which reduces the dissociation energy of oxygen, thereby accelerating the reaction rate of CO oxidation.

Insights into the Self-Optimized Hydrophobicity of Cerium Oxide Surface under Impact Abrasive Wear

Cerium oxide (CeO2) is one of potential candidates of hydrophobic coatings servicing in harsh environments. In this letter, abraded CeO2 surface was prepared using sandblasting treatment to investigate the wetting mechanism under the condition of impact abrasive wear. The water contact angle (WCA) of the abraded surface increased from 62.8° to 93.7° after aging in ambient air for about 700 h. The hydrophobic self-optimisation mechanism of the abraded CeO2 surface is due to the hierarchical structure formed during impact abrasive wear and the surface adsorption of airborne hydrocarbon, resulting the wetting state changed from “Wenzel state” to “Cassie-Baxter State”.

Investigation of dextran adsorption on polycrystalline cerium oxide surfaces

This study used non-reactive magnetron sputtered polycrystalline cerium oxide thin films as model substrates to mimic the surface morphology of cerium oxide nanoparticles. We investigated the interaction between dextran and polycrystalline cerium oxide surfaces by atomic force microscopy, X-ray photoelectron spectroscopy, and reflection-absorption infrared spectroscopy. A simplified sample preparation method probing solid-liquid interface was set up by conducting aqueous adsorption procedures in an argon-filled glove bag connected to an ultra-high vacuum chamber. We found that the adsorption of dextran from aqueous solution onto the polycrystalline cerium oxide surface leads to a mutual charge transfer between dextran and cerium ions, creating a surface accumulation of Ce3+. In the aqueous environment, dextran hydroxyl groups adsorbs on the polycrystalline cerium oxide surface competitively with the dissociated hydroxyl groups from water. By investigating glucose adsorbed onto polycrystalline ceria prepared by physical vapor deposition, we further confirmed the role of hydroxyl groups from polysaccharide during interaction with ceria. Thermal annealing of the dextran adsorbed polycrystalline cerium oxide surface results in desorption of weakly bonded dextran below 100 °C and decomposition of dextran above 100 °C.