Ceria Nanoparticles Research Articles

High-throughput synthesis of CeO2 nanoparticles for transparent nanocomposites repelling Pseudomonas aeruginosa biofilms

Preventing bacteria from adhering to material surfaces is an important technical problem and a major cause of infection. One of nature’s defense strategies against bacterial colonization is based on the biohalogenation of signal substances that interfere with bacterial communication. Biohalogenation is catalyzed by haloperoxidases, a class of metal-dependent enzymes whose activity can be mimicked by ceria nanoparticles. Transparent CeO2/polycarbonate surfaces that prevent adhesion, proliferation, and spread of Pseudomonas aeruginosa PA14 were manufactured. Large amounts of monodisperse CeO2 nanoparticles were synthesized in segmented flow using a high-throughput microfluidic benchtop system using water/benzyl alcohol mixtures and oleylamine as capping agent. This reduced the reaction time for nanoceria by more than one order of magnitude compared to conventional batch methods. Ceria nanoparticles prepared by segmented flow showed high catalytic activity in halogenation reactions, which makes them highly efficient functional mimics of haloperoxidase enzymes. Haloperoxidases are used in nature by macroalgae to prevent formation of biofilms via halogenation of signaling compounds that interfere with bacterial cell–cell communication (“quorum sensing”). CeO2/polycarbonate nanocomposites were prepared by dip-coating plasma-treated polycarbonate panels in CeO2 dispersions. These showed a reduction in bacterial biofilm formation of up to 85% using P. aeruginosa PA14 as model organism. Besides biofilm formation, also the production of the virulence factor pyocyanin in is under control of the entire quorum sensing systems P. aeruginosa. CeO2/PC showed a decrease of up to 55% in pyocyanin production, whereas no effect on bacterial growth in liquid culture was observed. This indicates that CeO2 nanoparticles affect quorum sensing and inhibit biofilm formation in a non-biocidal manner.

Oxygen vacancy concentration in nanoobjects of CeO2−δ: Effects of characteristic size, morphology, and temperature

A theoretical model has been developed that adequately describes the formation of oxygen vacancies in ceria at the nanoscale. The intrinsic regime of vacancy formation under equilibrium conditions is considered. An analytical relation describing the dependence of the enthalpy of oxygen vacancy formation on the characteristic size and morphology of nanoobjects is derived. This made it possible to perform quantitative calculations of the concentration of oxygen vacancies in cerium oxide nanoobjects for a wide range of their characteristic sizes, morphology and temperature. It is shown that the size effect becomes noticeable for the concentration of surface and bulk oxygen vacancies, approximately, at the characteristic sizes of nanoobjects less than 20 nm and 30 nm, respectively. The effect of morphology on the concentration of oxygen vacancies increases with a decrease in the characteristic size of nanoobjects. This effect is more significant for the concentration of bulk oxygen vacancies than for the concentration of surface oxygen vacancies. In addition, the morphological effect and the size-effect decrease with increasing temperature. In thin films of ceria, the concentration of bulk oxygen vacancies at 300 K is 1011 and 103 times lower than that of spherical ceria nanoparticles, with their characteristic size of 4 nm and 40 nm, respectively. At 1000 K, this ratio is 3∙103 and 7, respectively. Thus, the oxygen storage capacity is higher for spherical nanoparticles and increases with a decrease in their characteristic size.

A Label-Free Colorimetric Assay Based on Gold Nanoparticles for the Detection of H2O2 and Glucose

The significance of sensing hydrogen peroxide (H2O2) is due to its ubiquity, being a potential biomarker as well as an end-product of several oxidation reactions. Herein, based on gold nanoparticles (AuNPs) and coupled with single-stranded DNA (ssDNA) and ceria nanoparticles (CeO2), we developed a novel colorimetric method to detect H2O2 and glucose in NaCl solutions. In the presence of H2O2, ssDNA adsorbed on the surface of CeO2 could be released and subsequently decorated AuNPs, resulting in a distinct color change of the aqueous solution from purple to red, which could be observed by the naked eye. Since H2O2 can be produced in the process of glucose oxidation by glucose oxidase (GOx), this approach can also be employed to detect glucose. By employing this sensing system, the detection limits for H2O2 and glucose are about 0.21 μM and 3.01 µM, respectively. Additionally, monitoring the content of glucose in blood serum samples was successfully achieved by the proposed strategy. This work opens a potential avenue for the quantitative detection of H2O2 and glucose in clinical diagnostics.

Phytotoxic effect of sub-3-nm crystalline ceria nanoparticles on the hydroponic growth of Daikon radish microgreens.

Cerium oxide nanoparticles (ceria NPs) have been widely used in many industrial applications. They have been proposed as a potential remedy for reducing oxidative stress in biological systems. General concerns over the toxicity of engineered ceria NPs have led to studies of their phytotoxicity in plants. Most of these plant growth studies were conducted in soil using grain crops and commercial ceria NPs of sizes from 6 nm to 100's nm. In this paper, we report our evaluation of the phytotoxicity and uptake of sub-3-nm crystalline ceria NPs by exposing Daikon radish (Raphanus sativus var. longipinnatus) microgreens to these NPs with environmentally relevant concentrations under hydroponic growth conditions. Aqueous suspensions of different concentrations of these ceria NPs (0.1 ppm, 1 ppm, and 10 ppm) were applied to these microgreens for the last 7 days of the 12-day growth period. Our results revealed the uptake of cerium by plant roots and the translocation of cerium to the stems and the cotyledons (seed leaves). The accumulation of cerium was found to be maximum at the roots, followed by the cotyledons and the stems of the plants. Even at the lowest concentration (0.1 ppm) of the sub-3-nm ceria NPs, the accumulation of cerium at the roots significantly stunted the root growth. However, these NP treatments did not show significant changes to the distributions of macro-minerals (Mg, K, and Ca) and micro-minerals (Zn and Cu) in the microgreens at the end of the 12-day growth period. The phytotoxic effect of sub-3-nm crystalline ceria nanoparticles on the hydroponic growth of Daikon radish microgreens was studied. The cerium uptake by the plant and its effect on the bioavailability of major macro-minerals and micro-minerals within the plant were examined.

A drug-free nanozyme for mitigating oxidative stress and inflammatory bowel disease

Inflammatory bowel disease (IBD) is an incurable disease of the gastrointestinal tract with a lack of effective therapeutic strategies. The proinflammatory microenvironment plays a significant role in both amplifying and sustaining inflammation during IBD progression. Herein, biocompatible drug-free ceria nanoparticles (CeNP-PEG) with regenerable scavenging activities against multiple reactive oxygen species (ROS) were developed. CeNP-PEG exerted therapeutic effect in dextran sulfate sodium (DSS)-induced colitis murine model, evidenced by corrected the disease activity index, restrained colon length shortening, improved intestinal permeability and restored the colonic epithelium disruption. CeNP-PEG ameliorated the proinflammatory microenvironment by persistently scavenging ROS, down-regulating the levels of multiple proinflammatory cytokines, restraining the proinflammatory profile of macrophages and Th1/Th17 response. The underlying mechanism may involve restraining the co-activation of NF-κB and JAK2/STAT3 pathways. In summary, this work demonstrates an effective strategy for IBD treatment by ameliorating the self-perpetuating proinflammatory microenvironment, which offers a new avenue in the treatment of inflammation-related diseases.Graphical

Preparation, Characterization of Green Synthesis CeO2 Nanoparticles and Their Photocatalytic Activity towards Malachite Green Dye

AbstractThe synthesis of green ceria nanoparticles using Aloe Vera leaf extract was conducted in this study and comparison with the chemical synthesis one. The prepared samples were characterized and the photoactivity of the prepared ceria was estimated towards the degradation of malachite green dye under UV irradiation. The photodegradation% reached maximum in the case of using 3 g/L of the ceria nanoparticles prepared chemically. This is related mainly to the superior properties of the prepared ceria. Like surface area, lattice parameter, particle size, the concentration of Ce3+ ions, oxygen vacancies, adsorbed .OH radicals, and optical properties. Finally; the scavenger experiments indicated that the .OH and h+ radicals play a main role in the photodegradation process in comparison to O2.− radical.

Therapeutic Hydrogel Patch to Treat Atopic Dermatitis by Regulating Oxidative Stress.

Atopic dermatitis (AD) is a chronic inflammatory disease associated with unbalanced immune responses in skin tissue. Although steroid drugs and antihistamines are generally used to treat AD, continuous administration causes multiple side effects. High oxidative stress derived from reactive oxygen species (ROS) has been implicated in the pathogenesis of AD. A high level of ROS promotes the release of pro-inflammatory cytokines and T-cell differentiation, resulting in the onset and deterioration of AD. Here, we report a therapeutic hydrogel patch suppressing the high oxidative stress generated in AD lesions. The hydrogel embedded with ROS-scavenging ceria nanoparticles leads to the decrease of both extracellular and intracellular ROS and exhibits cytoprotective effects in a highly oxidative condition. AD-induced mouse model studies show enhanced therapeutic outcomes, including a decrease in the epidermal thickness and levels of AD-associated immunological biomarkers. These findings indicate that a ROS-scavenging hydrogel could be a promising therapeutic hydrogel patch for treating and managing AD.

Measurement and correlation of PVT for organic-inorganic hybrid nanoparticles

PVT behaviors of decanoic acid-modified ceria (C10CeO2) nanoparticles was measured with a bellows type apparatus at temperatures from 312.3 K up to 471.7 K and pressures from 10 up to 200 MPa. As a comparison with organic molecules, PVT behaviors of decane was measured at temperatures from 298.5 K up to 472.6 K and pressures from 10 up to 200 MPa. The atmospheric density of samples at each temperature was measured and adopted as a reference density in analyzing the outputs of volume change from the measured data with the bellows type apparatus. The obtained PVT data were correlated by the Tait equation to calculate volumetric properties. The PVT data for the C10CeO2 nanoparticles were also used to determine the parameters of Sanchez-Lacombe equation of state (EoS). These parameters allowed us to apply Sanchez-Lacombe EoS for the C10CeO2 nanoparticle as a pseudomolecule.

MnII/III and CeIII/IV Units Supported on an Octahedral Molecular Nanoparticle of CeO2.

The preparation of three new heterometallic clusters [Ce6Mn12O17(O2CPh)26] (1), [Ce10Mn14O24(O2CPh)32] (2), and [Ce23Mn20O48(OH)2(tbb)46(H2O)4](NO3)2 (3; tbb- = 4-tBu-benzoate) is reported. They all possess unprecedented structures with a common feature being the presence of an octahedral CeIV-oxo core: a Ce6 in 1, two edge-fused Ce6 giving a Ce10 bioctahedron in 2, or a larger Ce19 octahedron in 3. Complex 1 is the first Ce6 cluster with a central μ6-O2-. 2 and the cation of 3 are molecular nanoparticles of CeO2 (ceria) because they possess the fluorite structure of bulk ceria and are thus ultrasmall ceria nanoparticles in molecular form. The {Ce19O32} octahedral subunit of the cation of 3 had been predicted from density functional theory studies to be one of the stable fragments of the CeO2 lattice, but has never been previously synthesized in molecular chemistry. Around the Ce/O core of 1-3 is an incomplete monolayer of Mnn ions disposed as four Mn3, two Mn7, and four Mn5 units, respectively. This represents a clear structural similarity with composite (phase-separated) CeO2/MnOx mixtures where at high Ce:Mn ratios the Mn atoms segregate on the surface of CeO2 phases. Variable-temperature dc and ac magnetic susceptibility studies have revealed S = 2, S = 1/2, and S = 3/2 ground states for 1-3, respectively. Fitting of the 5.0-300 K dc data for 1 to a two-J model for an asymmetrical V-shaped Mn3 unit with no interaction between the end MnIII ions gave an excellent fit with the following values: J1 = 5.2(3) cm-1, J2 = -7.4(3) cm-1, and g = 1.96(2).

Synthesis of CuO‐Loaded Ceria Hollow Spheres for Catalytic CO Oxidation

AbstractCopper‐ceria has been widely investigated as an active heterogeneous catalyst for CO oxidation reaction. Herein we report a reliable synthesis of CuO loaded ceria hollow spheres (CHS‐CuO) which show an outstanding performance of 6.1712 μmolCO⋅gcat−1⋅s−1 CO consumption rate at 120 °C over other reported ceria‐based catalysts for the CO oxidation reaction. The performance is superior to CuO loaded ceria nanoparticles (CNP‐CuO) and ceria hollow spheres (CHS), due to hollow structure, large surface area, more adsorptive oxygen and subsequent lower activation energy. TEM images reveal CuO nanoparticles are uniformly dispersed on the surface of ceria hollow spheres. XPS investigation shows that Cu2+ is the dominant copper species in CHS‐CuO. The synthesis reliability is demonstrated with the case of Ag loaded CHS fabrication. The reported strategy enables the fabrication of similar bimetal hollow spheres, holding good promise for various heterogeneous catalysis.

Study of electronic, thermoelectric and optical properties of environment friendly Mg doped CeO2 for energy harvesting devices

According to the recent investigations on transition metal oxides it is shown that they have exceptional thermoelectric and optical properties. In this context, present study reports the effect of Mg doping on the electronic, thermoelectric, and optical properties of CeO2, through experimental and DFT calculations. These results are obtained, supposedly due to the ability of ceria nanoparticles to rapidly store and release oxygen, as it acts as an oxygen buffer. Further optimization can be expected by doping Mg which can increase the electrical conductivity of the ceria nanoparticles, thereby increasing the figure of merit. Effect of Mg can also be seen in the electronic and optical behavior of ceria nanoparticles as the band-structure of the system changes. All these changes result in thermoelectric figure of merit approaching to 2 ± 0.2 at room temperature and above.

Highly protective polyolefin coating modified with ceria nano particles treated with N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine for corrosion protection of carbon steel

A polyolefin coating was modified with cerium oxide nanoparticles treated with N,N,N',N'-Tetrakis(2-hydroxyethyl)ethylenediamine (THEEDA) as corrosion inhibitor for corrosion protection of carbon steel. Electrochemical Impedance Spectroscopy tests carried out in 0.05 M NaCl revealed low-frequency impedance modulus around 1012 Ω cm2 for the modified coating without significant changes after three months of immersion. The self-healing ability of modified coating was studied by combining different localized electrochemical techniques, namely localized impedance spectroscopy (LEIS), the scanning vibrating electrode technique (SVET), and scanning fiber-optic dissolved oxygen microsensor. This comprehensive study confirmed the ability of ceria nanoparticles treated with THEEDA to mitigate corrosion thanks to the synergistic protective role of ceria nanoparticles and THEEDA that inhibit both cathodic and anodic activities, respectively.

The Therapeutic Role of Nanoparticle Shape in Traumatic Brain Injury : An in vitro Comparative Study.

ObjectiveTo perform a comparative analysis of therapeutic effects associated with two different shapes of ceria nanoparticles, ceria nanorods (Ceria NRs) and ceria nanospheres (Ceria NSs), in an in vitro model of traumatic brain injury (TBI). MethodsIn vitro TBI was induced using six-well confluent plates by manually scratching with a sterile pipette tip in a 6×6-square grid. The cells were then incubated and classified into cells with scratch injury without nanoparticles and cells with scratch injury, which were treated separately with 1.16 mM of Ceria NSs and Ceria NRs. Antioxidant activities and anti-inflammatory effects were analyzed. ResultsCeria NRs and Ceria NSs significantly reduced the level of reactive oxygen species compared with the control group of SH-SY5Y cells treated with Dulbecco’s phosphate-buffered saline. The mRNA expression of superoxide dismutases was also reduced in nanoparticle-treated SH-SY5Y cells, but apparently the degree of mRNA expression decrease was not dependent on the nanoparticle shape. Exposure to ceria nanoparticles also decreased the cyclooxygenase-2 expression, especially prominent in Ceria NR-treated group than that in Ceria NS-treated group. ConclusionCeria nanoparticles exhibit antioxidant and anti-inflammatory effects in TBI models in vitro. Ceria NRs had better antiinflammatory effect than Ceria NSs, but showed similar antioxidant activity.

Humidity Sensing Ceria Thin-Films.

Lowering the constitutive domains of semiconducting oxides to the nano-range has recently opened up the possibility of added benefit in the research area of sensing materials, in terms both of greater specific surface area and pore volume. Among such nanomaterials, ceria has attracted much attention; therefore, we chemically derived homogeneous ceria nanoparticle slurries. One set of samples was tape-casted onto a conducting glass substrate to form thin-films of various thicknesses, thereby avoiding demanding reaction conditions typical of physical depositions, while the other was pressed into pellets. Structural and microstructural features, along with electrical properties and derivative humidity-sensing performance of ceria thin-films and powders pressed into pellets, were studied in detail. Particular attention was given to solid-state impedance spectroscopy (SS-IS), under controlled relative humidity (RH) from 30%–85%, in a wide temperature and frequency range. Moreover, for the thin-film setup, measurements were performed in surface-mode and cross-section-mode. From the results, we extrapolated the influence of composition on relative humidity, the role of configuration and thin-film thickness on electrical properties, and derivative humidity-sensing performance. The structural analysis and depth profiling both point to monophasic crystalline ceria. Microstructure analysis reveals slightly agglomerated spherical particles and thin-films with low surface roughness. Under controlled humidity, the shape of the conductivity spectrum stays the same along with an increase in RH, and a notable shift to higher conductivity values. The relaxation is slow, as the thickness of the pellet slows the return of conductivity values. The increase in humidity has a positive effect on the overall DC conductivity, similar to the temperature effect for semiconducting behavior. As for the surface measurement setup, the thin-film thickness impacts the shape of the spectra and electrical processes. The surface measurement setup turns out to be more sensitive to relative humidity changes, emphasized with higher RH, along with an increase in thin-film thickness. The moisture directly affects the conductivity spectra in the dispersion part, i.e., on the localized short-range charge carriers. Moisture sensitivity is a reversible process for thin-film samples, in contrast to pellet form samples.

Core@shell structured ceria@mesoporous silica nanoantibiotics restrain bacterial growth in vitro and in vivo

Due to its modular and flexible design options, mesoporous silica provides ample opportunities when developing new strategies for combinatory antibacterial treatments. In this study, antibacterial ceria (CeO2) nanoparticles (NP) were used as core material, and were further coated with a mesoporous silica shell (mSiO2) to obtain a core@shell structured nanocomposite (CeO2@mSiO2). The porous silica shell was utilized as drug reservoir, whereby CeO2@mSiO2 was loaded with the antimicrobial agent capsaicin (CeO2@mSiO2/Cap). CeO2@mSiO2/Cap was further surface-coated with the natural antimicrobial polymer chitosan by employing physical adsorption. The obtained nanocomposite, CeO2@mSiO2/Cap@Chit, denoted NAB, which stands for “nanoantibiotic”, provided a combinatory antibacterial mode of action. The antibacterial effect of NAB on the Gram-negative bacteria Escherichia coli (E.coli) was proven to be significant in vitro. In addition, in vivo evaluations revealed NAB to inhibit the bacterial growth in the intestine of bacteria-fed Drosophila melanogaster larvae, and decreased the required dose of capsaicin needed to eliminate bacteria. As our constructed CeO2@mSiO2 did not show toxicity to mammalian cells, it holds promise for the development of next-generation nanoantibiotics of non-toxic nature with flexible design options.

Nano-ceria and nano-zirconia reinforced polyurethane nanocomposite-based coated textiles with enhanced weather resistance

This work reports the effect of nano-ceria or cerium oxide (CeO2) nanoparticles and nano-zirconia or zirconium oxide (ZrO2) nanoparticles on the weather resistance property of polyurethane (PU) based coatings. The concentrations of ceria and zirconia nanoparticles (NPs) were varied in the PU coating formulation to obtain optimum weather resistance property. The prepared PU/ceria and PU/zirconia nanocomposite-based formulations were coated on a high strength polyester fabric by a knife coater. Coated fabrics were exposed in a weather-o-meter up to 300 h, in accelerated weathering conditions by controlling UV irradiance, humidity, temperature and dry/wet state. The weather resistance performance was analyzed by studying the UV protection factor (UPF) and the change in tensile properties (tensile strength and breaking extension). The chemical change after UV exposure was analyzed by Fourier Transform Infrared Spectroscopy (FTIR). The surface morphology was investigated before and after exposure by observing the tropology of the coated surface under SEM. Both the nanoparticles (ceria and zirconia) showed a great potential in enhancing the weather resistance property of PU-coated fabrics, while the weather resistance improved gradually with increasing the concentration of nanoparticles up to a certain percentage (5 wt%). After 300 h UV exposure, the change in carbonyl index (CI) was 25%, 8.6% and 12.8% for the fabrics coated with neat PU, PU/ceria (5 wt%) nanocomposite and PU/zirconia (5 wt%) nanocomposite, respectively. The photooxidative index (PI) of PU/ceria nanocomposite was also much lower than the PU/zirconia nanocomposites, especially at higher concentration of nanoparticles (5 wt% and 10 wt%). In case of PU/ceria nanocomposites, this significantly low CI and PI values indicated their better weather resistance potential compared to the PU/zirconia nanocomposites. As a consequence, after 300 h UV exposure, the percentage retention in tensile strength was significantly high for the fabric coated with PU/ceria nanocomposite (72%) in comparison to the neat PU (only 30%) and PU/zirconia nanocomposite (48%) coated fabric.

Controlling luminescent and redox properties of nanoceria

The unique antioxidant and radioprotective properties of cerium oxide nanocrystals (СеО2–х) in the biological environment has led to considerable attention to these nanocrystals of scientists from various fields. The influence of the defect structure on the mechanisms of antioxidant activity of nanocrystals is revealed, and possible ways to control both the defect structure and antioxidant properties of nanoparticles are shown. The luminescence properties and antioxidant activity of nanoceria and ceria-based mixed (CeO2—Re2O3 (Re = Y, Eu, Tb), CeO2—ZrO2) colloidal nanoparticles depends strongly on the type and concentration of doped ions and laser irradiation. The continuous UV irradiation with specific wavelengths leads to formation of additional Ce3+—Vo—Ce3+ complexes providing better antioxidant activity of pre-irradiated ceria nanoparticles.

Photo-oxidative degradation of polyacids derived ceria nanoparticle modulation for chemical mechanical polishing

The effects of photo-oxidative degradation of polyacids at various concentrations and with different durations of ultraviolet (UV) irradiation on the photo-reduction of ceria nanoparticles were investigated. The effect of UV-treated ceria on the performance of chemical mechanical polishing (CMP) for the dielectric layer was also evaluated. When the polyacids were exposed to UV light, they underwent photo-oxidation with consumption of the dissolved oxygen in slurry. UV-treated ceria particles formed oxygen vacancies by absorbing photon energy, resulting in increased Ce3+ ions concentration on the surface, and when the oxygen level of the solution was lowered by the photo-oxidation of polymers, the formation of Ce3+ ions was promoted from 14.2 to 36.5%. Furthermore, chain scissions of polymers occurred during the oxidation process, and polyacids with lower molecular weights were found to be effective in ceria particle dispersion in terms of the decrease in the mean diameter and size distribution maintaining under 0.1 of polydispersity index. With increasing polyacid concentration and UV irradiation time, the Ce3+ concentration and the dispersity of ceria both increased due to the photo-oxidative degradation of the polymer; this enhanced the CMP performance in terms of 87% improved material removal rate and 48% lowered wafer surface roughness.

Ceria nanoparticles anchored on graphitic oxide sheets (CeO2-GOS) as an efficient catalyst for degradation of dyes and textile effluents

Herein, we report a Ceria-graphitic oxide sheets (CeO2-GOS) nanocomposites photo catalyst synthesized by simple and green methods for the degradation of textile effluents and dyes. In the first step, green treated CeO2 NPs were synthesized through a simple organic reduction method. Further, green synthesized CeO2 NPs were anchored with GOS to produce CeO2-GOS nanocomposites by a sol-gel method. The phase morphology and structure of CeO2-GOS nanocomposites was systematically characterized through X-ray diffraction, Raman spectroscopy, zeta potential, Fourier transform infrared spectroscopy (FT-IR), High-Resolution Transmission Electron Microscope (HR-TEM), and X-ray photoelectron spectroscopy (XPS) analysis. Under visible light irradiation, the CeO2-GOS nanocomposites photo catalyst exhibited 83%, 78%, and 70% degradation efficiencies for rhodamine B, methylene blue, and textile effluent, respectively. Due to the synergistic impact of GO, it act as an elastic conductive channel permitting improved charge transport, the fabricated CeO2-GOS nanocomposites showed a significant retort to photo catalysis of rhodamine B, methylene blue, and textile effluent. CeO2-GOS nanocomposites may yield unique insight into the synthesis of green nanocomposites and their application in environmental remediation due to their better photo catalytic activity.

Ce3+ concentration control on the surface of ceria nanoparticles and the stability of surface Ce3+ in aqueous, silica, and PVA media

Nanoceria (CeO2-x) with controllable surface Ce3+/Ce4+ ratios were directly synthesized without the use of surfactant organic molecules or complexing agents. All processes were carried out in aqueous solutions at room temperature, which is very advantageous for cost effective and large-scale productions. Importantly, higher Ce3+ concentrations on the surface of nanoceria have been achieved by increasing the pH of the aqueous solution for the synthesis. When nanoceria prepared at higher pH values were dispersed in deionized water to form aqueous colloidal solutions, the oxidation of excess surface Ce3+ to Ce4+ proceeded within ~6 h. This behavior of nanoceria with high surface Ce3+ concentration in aqueous media should be recognized for practical applications in biomedical systems because therapeutic potentials are based on the surface Ce3+/Ce4+ redox switch. Fortunately, the excess surface Ce3+ stability could be enhanced by embedding ceria nanoparticles in the mesopores of silica. The resulting ceria@silica composite revealed significantly smaller extents of oxidation as well as much slower rates of oxidation in aqueous media so that the oxidation continued for ~5 days after dispersing in water. In contrast, excess Ce3+ ions on the surface of nanoceria were relatively stable in atmospheric condition or PVA media. Therefore, the nanoceria with excess surface Ce3+ concentrations prepared in this work could be exploited for outdoor antioxidant applications of transparent UV-screening films.