Thin Layers of Cerium Oxynitride Deposited via RF Sputtering.

Thin films of transition metal oxides and oxynitrides have proven highly effective in protecting stainless steels against corrosion in both chemically aggressive environments and biological fluids. In the present work, cerium zirconium oxynitride thin films were deposited to enhance the corrosion resistance of surgical-grade stainless steel to be used in osteosynthesis processes. Two techniques were employed: co-sputtering and radiofrequency (RF) sputtering, and the morphology and corrosion efficiency of the coatings deposited by each technique were evaluated. X-ray diffraction, X-ray photoelectron spectroscopy and field emission transmission electron microscopy were used to characterize the morphological and chemical structure, respectively. Additionally, the corrosion resistance of the oxynitride-coated surgical grade stainless steel system (ZrCeOxNy-AISI 316L) was assessed using Hank's solution as the corrosive electrolyte, to determine its resistance to corrosion in biological media. The results show that ZrCeOxNy coatings increase the corrosion resistance of surgical grade stainless steel by two orders of magnitude and that the Ce(III)/Ce(IV) equilibrium decreases the corrosion rate, thereby increasing the durability of the steel in a biological environment. The results show that Ce coatings increase the corrosion resistance of surgical grade stainless steel by two orders of magnitude and that the Ce(III)/Ce(IV) equilibrium decreases the corrosion rate, thereby increasing the durability of the steel in a biological environment.

Novel Sol-Gel Synthesis Route for Ce- and V-Doped Ba0.85Ca0.15Ti0.9Zr0.1O3 Piezoceramics.

To meet the current demand for lead-free piezoelectric ceramics, a novel sol-gel synthesis route is presented for the preparation of Ba0.85Ca0.15Ti0.9Zr0.1O3 doped with cerium (Ce = 0, 0.01, and 0.02 mol%) and vanadium (V = 0, 0.3, and 0.4 mol%). X-ray diffraction patterns reveal the formation of a perovskite phase (space group P4mm) for all samples after calcination at 800 °C and sintering at 1250, 1350, and 1450 °C, where it is proposed that both dopants occupy the B site. Sintering studies show that V doping allows the sintering temperature to be reduced to at least 1250 °C. Undoped BCZT samples sintered at the same temperature show reduced functional properties compared to V-doped samples, i.e., d33 values increase by an order of magnitude with doping. The dissipation factor tan δ decreases with increasing sintering temperature for all doping concentrations, while the Curie temperature TC increases for all V-doped samples, reaching 120 °C for high-concentration co-doped samples. All results indicate that vanadium doping can facilitate the processing of BCZT at lower sintering temperatures without compromising performance while promoting thermal property stability.

Exploring the Thermal-Oxidative Stability of Azithromycin Using a Thermoactivated Sensor Based on Cerium Molybdate and Multi-Walled Carbon Nanotubes.

The chemical stability of azithromycin (AZM) may be compromised depending on the imposed thermo-oxidative conditions. This report addresses evidence of this process under varying conditions of temperature (20-80 °C), exposure time to UV radiation (1-3 h irradiation at 257 nm), and air saturation (1-3 h saturation with atmospheric air at 1.2 L min-1 and 15 kPa) through electrochemical measurements performed with a thermoactivated cerium molybdate (Ce2(MoO4)3)/multi-walled carbon nanotubes (MWCNT)-based composite electrode. Thermal treatment at 120 °C led to coordinated water elimination in Ce2(MoO4)3, improving its electrocatalytic effect on antibiotic oxidation, while MWCNT were essential to reduce the charge-transfer resistance and promote signal amplification. Theoretical-experimental data revealed remarkable reactivity for the irreversible oxidation of AZM on the working sensor using phosphate buffer (pH = 8) prepared in CH3OH/H2O (10:90%, v/v). Highly sensitive (230 nM detection limit) and precise (RSD < 4.0%) measurements were recorded under these conditions. The results also showed that AZM reduces its half-life as the temperature, exposure time to UV radiation, and air saturation increase. This fact reinforces the need for continuous quality control of AZM-based pharmaceuticals, using conditions closer to those observed during their transport and storage, reducing impacts on consumers' health.

Synthesis of ultrasmall cerium oxide nanoparticles in deep eutectic solvent and their application in an electrochemical sensor to detect dopamine in biological fluid.

A solvothermal synthesis of ultrasmall cerium oxide nanoparticles (USCeOxNPs) with an average size of 0.73 ± 0.07 nm using deep eutectic solvent (DES) as a stabilizing medium at a temperature of 90 ºC is reported. Transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS) were used to morphologically characterize the USCeOxNPs. These revealed approximately spherical shapes with emission lines characteristic of cerium. Selected area electron diffraction (SAED) was used to determine the crystalline structure of the cerium oxide nanoparticles (CeO2NPs), revealing the presence of crystalline cubic structures. The USCeOxNPs-DES/CB film was characterized by scanning electron microscopy (SEM), which demonstrated the spherical characteristic of CB with layers slightly covered by DES residues. DES was characterized by Fourier transform infrared (FT-IR) and nuclear magnetic resonance (NMR), indicating its formation through hydrogen bonds between the precursors. An electrochemical sensor for dopamine (DA) determination in biological fluids was developed using the USCeOxNPs together with carbon black (CB). An enhanced current response was observed on DA voltammetric determination, and this can be attributed to the USCeOxNPs. This sensor displayed linear responses for DA in the range 5.0 × 10-7 mol L-1 to 3.2 × 10-4 mol L-1, with a limit of detection of 80 nmol L-1. Besides detectability, excellent performances were verified for repeatability and anti-interference. The sensor based on USCeOxNPs synthesized in DES in a simpler and environmentally friendly way was successfully applied to determine DA in biological matrix.

Cerium oxide nanoparticles: Chemical properties, biological effects and potential therapeutic opportunities (Review).

The chemistry of pure cerium oxide (CeO2-x) nanoparticles has been widely studied since the 1970s, especially for chemical catalysis. CeO2-x nanoparticles have been included in an important class of industrial metal oxide nanoparticles and have been attributed a range of wide applications, such as ultraviolet absorbers, gas sensors, polishing agents, cosmetics, consumer products, high-tech devices and fuel cell conductors. Despite these early applications in the field of chemistry, the biological effects of CeO2-x nanoparticles were only explored in the 2000s. Since then, CeO2-x nanoparticles have gained a spot in research related to various diseases, especially the ones in which oxidative stress plays a part. Due to an innate oxidation state variation on their surface, CeO2-x nanoparticles have exhibited redox activities in diseases, such as cancer, acting either as an oxidizing agent, or as an antioxidant. In biological models, CeO2-x nanoparticles have been shown to modulate cancer cell viability and, more recently, cell death pathways. However, a deeper understanding on how the chemical structure of CeO2-x nanoparticles (including nanoparticle size, shape, suspension, agglomeration in the medium used, pH of the medium, type of synthesis and crystallite size) influences the cellular effects observed remains to be elucidated. In the present review, the chemistry of CeO2-x nanoparticles and their impact on biological models and modulation of cell signalling, particularly focusing on oxidative and cell death pathways, were investigated. The deeper understanding of the chemical activity of CeO2-x nanoparticles may provide the rationale for further biomedical applications towards disease treatment and drug delivery purposes.

Brazilin-Ce nanoparticles attenuate inflammation by de/anti-phosphorylation of IKKß.

Inflammation is associated with a series of diseases like cancer, cardiovascular disease and infection, and phosphorylation/dephosphorylation modification of proteins are important in inflammation regulation. Here we designed and synthesized a novel Brazilin-Ce nanoparticle (BX-Ce NPs) using Brazilin, which has been used for anti-inflammation in cardiovascular diseases but with narrow therapeutic window, and Cerium (IV), a lanthanide which has the general activity in catalyzing the hydrolysis of phosphoester bonds, to conferring de/anti-phosphorylation of IKKß. We found that BX-Ce NPs specifically bound to Asn225 and Lys428 of IKKß and inhibited its phosphorylation at Ser181, contributing to appreciably anti-inflammatory effect in cellulo (IC50 = 2.5 µM). In vivo mouse models of myocardial infarction and sepsis also showed that the BX-Ce NPs significantly ameliorated myocardial injury and improved survival in mice with experimental sepsis through downregulating phosphorylation of IKKß. These findings provided insights for developing metal nanoparticles for guided ion interfere therapy, particularly synergistically target de/anti-phosphorylation as promising therapeutic agents for inflammation and related diseases.

Physical analysis of an acrylic resin modified by metal and ceramic nanoparticles.

BACKGROUND: Nanoparticles (NPs) have gained significant attention in various fields due to their unique properties and potential applications. Polymethyl methacrylate (PMMA) is an acrylic resin widely used in dentistry and medicine. However, the effect of different types of NP fillers on the physical properties of PMMA-based resins has not been thoroughly explored in the literature. OBJECTIVES: The present study aimed to evaluate the effects of 3 different types of NP fillers on the physical properties of an experimental PMMA-based resin as a function of the NP content and concentration. MATERIAL AND METHODS: Ten groups (n = 10) were designed. The specimens were composed of an acrylic resin, silicon dioxide (SiO2), cerium dioxide (CeO2), and titanium dioxide (TiO2) at the following ratios (wt%): group 1 (G1) - control; group 2 (G2) - 0.5% SiO2; group 3 (G3) - 1% SiO2; group 4 (G4) - 3% SiO2; group 5 (G5) - 0.5% CeO2; group 6 (G6) - 1% CeO2; group 7 (G7) - 3% CeO2; group 8 (G8) - 0.5% TiO2; group 9 (G9) - 1% TiO2; and group 10 (G10) - 3% TiO2. Transmission electron microscopy (TEM) was used to assess the quality of NP dispersion. Thermal stability was assessed with thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The effects of the abovementioned NPs on the properties of the resin were evaluated using the Archimedes principle for density, the Vickers hardness (VH) test and the impact strength (IS) test. Data analysis employed the oneand two-way analysis of variance (ANOVA), followed by Duncan's post hoc test at a significance level of 0.05. RESULTS: Transmission electron microscopy showed partial NP dispersion. All types of NPs enhanced the mechanical properties of the acrylic resin except for IS, which was similar to that of the control group. Among the types of NPs, irrespective of the weight percentage, CeO2 showed higher thermal stability and higher IS for 0.5 wt% and 1 wt% as compared to other groups, as well as the highest values of density at 0.5 wt%, 1 wt% and 3 wt%. Titanium oxide at 1 wt% presented a higher VH as compared to other groups. The fracture pattern was the same for all groups. CONCLUSIONS: Incorporating the tested NPs into the acrylic resin resulted in enhanced physical properties, primarily attributed to a lower NP content.

Degradation of carbamazepine in surface water: performance of Pd-modified TiO2 and Ce-modified ZnO as photocatalysts.

Carbamazepine is a widely used antiepileptic drug to control and treat a variety of disorders that is frequently detected in surface water, and in municipal and urban wastewater. This recalcitrant pollutant could be removed by alternative advanced oxidation technology such as heterogeneous photocatalysis. Ce-modified ZnO and Pd-modified TiO2 were synthesized by a microwave-assisted sol-gel method. According to the characterizations (Raman spectroscopy, UV-Vis diffuse reflectance spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy), a mixture of oxides was determined in both materials: CeO2/ZnO and PdO/TiO2. Photocatalytic degradation of carbamazepine in pure water under visible light (3 h) was assayed. The degradation percentage obtained with each catalyst was 80%, 53%, 20%, and 9% for ZnO, Ce-modified ZnO, TiO2, and Pd-modified TiO2, respectively. The leaching of Zn as a possible source of water contamination was tested, finding the lowest value for Ce-modified ZnO by adjusting the initial pH up to neutrality. Later, an environmentally relevant concentration of carbamazepine (228 µg L-1) was assayed, using local surface water (pH = 8.3). Despite the presence of other compounds in the real water matrix, after 5 h of photocatalysis, a 56% of degradation of the pharmaceutical and low leaching of Zn were achieved. The use of Ce-modified ZnO activated by visible light is a promising strategy for the abatement of pharmaceutical active compounds.

Cerium biosorption onto alginate/vermiculite-based particles functionalized with ionic imprinting: Kinetics, equilibrium, thermodynamic, and reuse studies.

Cerium is an essential element for several applications in industry, therefore, recovering it from secondary sources is a promising strategy from an economic and environmental perspective. For this purpose, biosorption is a low-cost and effective alternative. The present work evaluated the recovery of Ce3+ from aqueous solutions using alginate/vermiculite-based particles (ALEV) functionalized by ionic imprinting. From the kinetic assays, it was verified that the uptake of Ce3+ followed the pseudo-second-order model and was mainly controlled by external diffusion. The Langmuir model better described the equilibrium data, and a maximum biosorption capacity of 0.671 mmol/g at 45 °C was attained. The evaluation of the thermodynamic quantities revealed that the process occurs spontaneously and endothermically. The particles reuse and Ce3+ recovery were achieved using 0.1 mol/L HCl or 1.0 mol/L CaCl2 solutions for up to four cycles of biosorption/desorption. The biosorbent was characterized before and posted Ce3+ biosorption to investigate the morphology, textural properties, crystallinity, thermal resistance, composition, and functional groups of the biosorbent.

Cerium oxide-doped PEDOT nanocomposite for label-free electrochemical immunosensing of anti-p53 autoantibodies.

A label-free nanoimmunosensor is reported based on p53/CeO2/PEDOT nanobiocomposite-decorated screen-printed gold electrodes (SPAuE) for the electrochemical detection of anti-p53 autoantibodies. CeO2 nanoparticles (NPs) were synthesized and stabilized with cyanopropyltriethoxysilane by a soft chemistry method. The nanoimmunosensing architecture was prepared by in situ electropolymerization of 3,4-ethylenedioxythiophene (EDOT) on SPAuE in the presence of CeO2 NPs. The CeO2 NPs and Ce/PEDOT/SPAuE were characterized by scanning and transmission electron microscopy, dynamic and electrophoretic light scattering, ultraviolet-visible spectrophotometry, X-ray diffraction, Fourier-transform infrared spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Ce/PEDOT/SPAuE was biofunctionalized with p53 antigen by covalent bonding for the label-free determination of anti-p53 autoantibodies by differential pulse voltammetry. The nanobiocomposite-based nanoimmunosensor detected anti-p53 autoantibodies in a linear range from 10 to 1000 pg mL-1, with a limit of detection (LOD) of 3.2 pg mL-1. The nanoimmunosensor offered high specificity, selectivity, and long-term storage stability with great potential to detect anti-p53 autoantibodies in serum samples. Overall, incorporating organo-functional nanoparticles into polymeric matrices can provide a simple-to-assemble, rapid, and ultrasensitive approach for on-site screening of anti-p53 autoantibodies and other disease-related biomarkers with low sample volumes.

New bimetallic adsorbent material based on cerium-iron nanoparticles highly selective and affine for arsenic(V).

Bimetallic oxy(hydroxides) have gain great interest in water treatment systems based on adsorption processes. Their high OH groups density, in addition to inheriting the oxides properties make them highly promising adsorbents of anions. In this work, highly affine and selective bimetallic oxyhydroxides of cerium and iron (Ce:Fe-P's) for arsenic(V) were synthesized by implementing an assisted microwave methodology. The Ce:Fe-P's were characterized by various techniques (SEM, FTIR, XRD and XPS) and the As(V) adsorption capacity and kinetics as well as the effect of pH and the presence of coexisting anions were determined. The results showed that Ce:Fe-P's have an outstanding As(V) adsorption capacity (179.8 mg g-1 at Ce = 3 mg L-1) even at low concentrations (120 mg g-1 at Ce = 37 µg L-1). Moreover, the adsorption equilibrium was reached very fast, just in 3 min, with an adsorption rate of 0.123 mg min-1, that is, 80% of the initial As(V) concentration of 5 mg L-1 was removed in the first 3 min. The arsenic adsorption capacity decreased only up to 20% at pH above 7, attributed to electrostatic repulsions due to the adsorbent's pHPZC, which was 6.8. On the other hand, the arsenic adsorption capacity of Ce:Fe-P's decreased just 21% in the presence of 10 mg L-1 of each of the following competing anions: F-, Cl-, SO42-, NO3-, PO43- and CO32-, which usually coincide in contaminated water with As(V). Ce:Fe-P's has proven to be one of the most promising As(V) adsorbent materials reported so far in the literature, because it presented an outstanding adsorption capacity and at the same time a very fast adsorption speed. Furthermore, the pH and the concentration of coexisting anions caused little interference in the adsorption processes. Due to the above, the Ce:Fe-P's is already in the process of intellectual protection.

Obtention of biochar-Fe/Ce using Punica granatum with high adsorption of ampicillin capacity.

This research presents the obtaining of a biochar (CB) from the use of pomegranate peel (Punica granatum) conditioned with iron and cerium nanoparticles (C-Fe/Ce), as well as its characterization by SEM (Scanning Electronic Microscopy), FTIR (Fourier Transform Infrared Spectrometry), TGA (Thermogravimetric analysis), EDS (Energy Dispersive Spectroscopy), XPS (X-Ray Photoelectron Spectroscopy) and evaluation of the adsorption capacity of ampicillin (AMP) in aqueous phase at 20, 30 and 40 °C. The maximum adsorption capacity for CB was 18.97 mg g-1 and for C-Fe/Ce, 27.61 mg g-1 at pH of 7, observing that with increasing temperature, the sorption capacity decreases in both materials, the experimental data was fitted to various mathematical models and the best fit was the pseudo-second order model for the kinetics, whilst for the adsorption isotherms the best fit was with the Langmuir model, indicating that the adsorption process is carried out in a monolayer on a homogeneous surface, through a chemisorption process. According to the thermodynamic parameters this process is carried out through an exothermic reaction. The results obtained indicate that both materials are suitable for the removal of AMP in the aqueous phase and that they can be reused up to 5 times.

Cerium oxide nanoparticle conjugation to microRNA-146a mechanism of correction for impaired diabetic wound healing.

Diabetic wounds represent a significant healthcare burden and are characterized by impaired wound healing due to increased oxidative stress and persistent inflammation. We have shown that CNP-miR146a synthesized by the conjugation of cerium oxide nanoparticles (CNP) to microRNA (miR)-146a improves diabetic wound healing. CNP are divalent metal oxides that act as free radical scavenger, while miR146a inhibits the pro-inflammatory NFκB pathway, so CNP-miR146a has a synergistic role in modulating both oxidative stress and inflammation. In this study, we define the mechanism(s) by which CNP-miR146a improves diabetic wound healing by examining immunohistochemical and gene expression analysis of markers of inflammation, oxidative stress, fibrosis, and angiogenesis. We have found that intradermal injection of CNP-miR146a increases wound collagen, enhances angiogenesis, and lowers inflammation and oxidative stress, ultimately promoting faster closure of diabetic wounds.

Engineered nanoceria modulate neutrophil oxidative response to low doses of UV-B radiation through the inhibition of reactive oxygen species production.

To avoid aging and ultraviolet mediated skin disease the cell repair machinery must work properly. Neutrophils, also known as polymorphonuclear leukocytes, are the first and most abundant cell types which infiltrate sites of irradiation and play an important role in restoring the microenvironment homeostasis. However, the infiltration of neutrophils in ultraviolet-B (UV-B) irradiated skin might also contribute to the pathophysiology of skin disease. The polymorphonuclear leukocytes activation induced by UV-B exposure may lead to prolonged, sustained NADPH oxidase activation followed by an increase in reactive oxygen species (ROS) production. Our previous work showed that cerium oxide nanoparticles can protect L929 fibroblasts from ultraviolet-B induced damage. Herein, we further our investigation of engineered cerium oxide nanoparticles (CNP) in conferring radiation protection specifically in modulation of neutrophils' oxidative response under low dose of UV-B radiation. Our data showed that even low doses of UV-B radiation activate neutrophils' oxidative response and that the antioxidant, ROS-sensitive redox activities of engineered CNPs are able to inhibit the effects of NADPH oxidase activation while conferring catalase and superoxide dismutase mimetic activity. Further, our investigations revealed similar levels of total ROS scavenging for both CNP formulations, despite substantial differences in cerium redox states and specific enzyme-mimetic reaction activity. We therefore determine that CNP activity in mitigating the effects of neutrophils' oxidative response, through the decrease of ROS and of cell damage such as chromatin condensation, suggests potential utility as a radio-protectant/therapeutic against UV-B damage.

Tuning the photoactivity of TiO2 nanoarchitectures doped with cerium or neodymium and application to colour removal from wastewaters.

The impact of cerium (Ce) and neodymium (Nd) rare-earth metal doping of TiO2 prepared by the hydrothermal method was investigated to tailor effective photocatalytic degradation of coloured wastewater under UV or visible illumination. The hydrothermal treatment of TiO2 decreased the pHpzc from 6.3 to 3.1-3.8 favouring the affinity for cationic water contaminants. Doping with Ce and Nd modified the crystallinity and the morphology of the photocatalysts and significantly increased the BET surface area and the adsorption capacity of cationic dyes. The photocatalytic activity under UV light irradiation decreased due to shielding of the catalyst active area by excessive amount of dye adsorbed. Conversely, the photocatalytic activity of the Ce and Nd doped TiO2 increased under visible light irradiation by 1.2 times as a result of the dye photosensitization effect. It was demonstrated that two-steps dark adsorption and photocatalytic reaction or one-step simultaneous adsorption and reaction can produce significantly different results for the photocatalytic degradation of dyes in coloured waters, the rate being controlled by the competitive adsorption of the reacting organics and the H2O/OH- species. The reaction is driven by the radical oxygen species (ROS) formed on the catalyst surface the nature of which, differs under UV or visible light irradiation. The Ce-doped TiO2 and Nd-doped TiO2 photocatalysts with 0.5% rare-earth content were found to be efficient in the degradation of MB in aqueous solution, removing the colour and reducing the toxicity of wastewaters.

Synthesis of silver-cerium titanate nanotubes and their surface properties and antibacterial applications.

Nano-heterostructures of titanate nanotubes were synthesized and they revealed a complex structure with the formation of TiO2 (anatase), CeO2, Ag2O and metallic silver nanoparticles on the outer walls and intercalation of Ce4+ and Ag+ into the interlayer spaces of the nanotubes by microwave-assisted hydrothermal process and subjected to ion exchange reactions. To the best of our knowledge, this is the first reported silver and cerium co-exchanged titanate nanotubes for bio-applications. The co-ion exchange processes preserved the original tubular structure of titanate nanotubes with significant changes of the superficial as well as interlamellar environment. This study opens up possibility of synthesizing complex, functional nano-heterostructure with the scope of modification of the final structure, especially the amount and oxidation state of the intercalated cation (Ce4+, Ce3+ and Ag+) as well as the quantity and variety of the decorating nanoparticles (CeO2, Ag2O or metallic Ag). The interplay of which, in turn, can lead to important biological properties and applications, owing to their ion-liberation capacity. The samples were tested in antibacterial activity with two different kind of bacteria (gram positive and negative), cell cytotoxicity and adhesion, and it was found that the nano-heterostructure formed shows high antibacterial activity with low cytotoxicity and high cell adhesion, which makes it a promising material for further health applications.

Antioxidative photochemoprotector effects of cerium oxide nanoparticles on UVB irradiated fibroblast cells.

The Ultraviolet-B radiation (UVB) might induce cellular redox imbalance which plays an important role in the development of skin disorders. Thus, the search for photochemoprotective alternatives with antioxidant efficacy would be a safe aspect towards prevention of skin diseases. Cerium oxide nanoparticles (CNPs) have antioxidant properties, that are mostly related to CNPs catalase and superoxide dismutase (SOD)-like antioxidative mimetic activity. Considering that, we investigated whether CNPs induce photochemoprotection against UVB-induced cellular damages on L929 fibroblasts. Our results showed that CNPs prevented UVB mediated L929 cell oxidative damage by reestablishing the oxidative balance through ameliorating the reactive oxygen species (ROS) level and enhancing the antioxidant enzyme activities.

Cerium Dioxide Particles to Tune Radiopacity of Dental Adhesives: Microstructural and Physico-Chemical Evaluation.

The insufficient radiopacity of dental adhesives applied under composite restorations makes the radiographic diagnosis of recurrent caries challenging. Consequently, the misdiagnosis may lead to unnecessary replacement of restorations. The aims of this study were to formulate experimental dental adhesives containing cerium dioxide (CeO2) and investigate the effects of different loadings of CeO2 on their radiopacity and degree of conversion for the first time. CeO2 was characterized by X-ray diffraction analysis, Fourier transforms infrared spectroscopy, and laser diffraction for particle size analysis. Experimental dental adhesives were formulated with CeO2 as the inorganic filler with loadings ranging from 0.36 to 5.76 vol.%. The unfilled adhesive was used as a control. The studied adhesives were evaluated for dispersion of CeO2 in the polymerized samples, degree of conversion, and radiopacity. CeO2 presented a monoclinic crystalline phase, peaks related to Ce-O bonding, and an average particle size of around 16 µm. CeO2 was dispersed in the adhesive, and the addition of these particles increased the adhesives' radiopacity (p < 0.05). There was a significant decrease in the degree of conversion with CeO2 loadings higher than 1.44 vol.%. However, all materials showed a similar degree of conversion in comparison to commercially available adhesives. CeO2 particles were investigated for the first time as a promising compound to improve the radiopacity of the dental adhesives.

Influence of the Ce4+/Ce3+ Redox-Couple on the Cyclic Regeneration for Adsorptive and Catalytic Performance of NiO-PdO/CeO2±Î´ Nanoparticles for n-C7 Asphaltene Steam Gasification.

The main objective of this study is to evaluate the regenerative effect of functionalized CeO2±Î´ nanoparticles with a mass fraction of 0.89% of NiO and 1.1% of PdO in adsorption and subsequent decomposition of n-C7 asphaltenes in steam gasification processes. During each regeneration cycle, the adsorption capacity and the catalytic activity of the nanoparticles were evaluated. To estimate the adsorption capacity of the nanoparticles, adsorption kinetics were studied at a fixed concentration of n-C7 asphaltenes of 10 mg·L-1 as well as adsorption isotherms at three different temperatures at 25 °C, 55 °C, and 75 °C. To evaluate the catalytic activity, the loss of mass of the nanoparticles was evaluated by isothermal conversions with a thermogravimetric analyzer at 230 °C, 240 °C, and 250 °C, and at non-isothermal conditions involving a heating from 100 °C to 600 °C at a 20 °C·min-1 heating rate. The asphaltenes showed a high affinity for being adsorbed over the nanoparticles surface, due to the nanoparticles-asphaltene interactions are stronger than those that occur between asphaltene-asphaltene, and this was maintained during nine evaluated regeneration cycles as observed in the Henry's constant that increased slightly, with changes of 21%, 26% and 31% for 25 °C, 55 °C and 75 °C. Polanyi's adsorption potential decreases by 2.6% for the same amount adsorbed from the first cycle to the ninth. In addition, the catalytic activity of the nanoparticles did not change significantly, showing that they decompose 100% of the n-C7 asphaltenes in all cycles. However, the small decrease in the adsorption capacity and catalytic activity of the nanoparticles is mainly due to the presence and change in concentration and ratio of certain elements such as oxygen, iron or others at the surface of the nanoparticle as shown by X-ray photoelectron spectroscopy (XPS) analyses. Thermodynamic parameters of adsorption such as Δ H a d s o , Δ S a d s o , and Δ G a d s o and the effective activation energy (Ea) were calculated to compare adsorptive and catalytic performance during each cycle. There is an increase of 9.3% and 2.6% in the case of entropy and enthalpy, respectively, and a decrease of 0.5%, 3.1% and 6.5% for 25 °C, 55 °C and 75 °C respectively for the Gibss free energy from cycle 1 to cycle 9. It was found that these parameters are correlated with the Ce concentration and oxidation state ratios (Ce3+/Ce4+ couple) at the surface.

Ecological risk assessment of cerium for tropical agroecosystems.

Cerium (Ce) is present in high technology materials and in mineral P fertilizers and the use and discharge of such resources may change the natural status of Ce in the soil environment. Brazilian soils in farming areas are significantly exposed to increased levels of unintentionally-added Ce through intensive input of phosphate fertilizers. The aims of this study were to evaluate the ecotoxicological risk to plants growing in tropical soils contaminated with Ce, as well as to create a database to support future legislation regulating the limits of this element in Brazilian and conceivably other tropical soils. Eight crop species (corn, sorghum, rice, wheat, soybeans, sunflower, radish, and beans) were exposed to a Ce concentration gradient in two typical tropical soils (Oxisol and Inceptsol), and an artificial soil. Our findings showed that among the endpoints measured, Ce phytotoxicity was more pronounced on shoot dry matter than on percent germination and germination speed index. Sensitivity of plants is species specific and our data showed that sunflower and radish exposed to Ce were the most sensitive crop species. Soil properties such as pH, cation exchange capacity, and organic carbon may have influenced the severity of Ce phytotoxicity. Because of that, the Oxisol contaminated with this element caused higher phytotoxicity than the other soils tested. Our risk assessment results (hazardous concentration, HC5 = 281.6 mg Ce kg-1) support the idea that unintentional Ce input through P fertilizers does not pose a risk to soils of Brazilian agroecosystems.