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The synthesis and characterization of a hydrochar/CeO2 composite along with its evaluation in methylene blue degradation under visible light are presented. The methodology consisted of a single-pass hydrothermal method, having as synthesis conditions 9 h of reaction time, 210 °C, autogenous pressure, and a biomass/CeO2 ratio of 100:1. The composite characterization revealed good dispersion of CeO2 in the carbonaceous matrix and significant synergy in the composite activation using visible irradiation. The photodegradation experiments showed an efficiency of 98% for white LED light, 91% for UV light, 96% for solar irradiation, and 85% for blue LED light using as conditions pH 7.0, 50 mg of composite, 50 mL of solution, 10 mg/L of dye initial concentration, and 120 min of contact time. Meanwhile, the reusability experiments evidenced a reuse capacity of up to five times with a constant photodegradation efficiency (99%); moreover, it was determined that the presence of electrolytes at pH below 7.0 during degradation negatively affected methylene blue degradation. Finally, the results of this work demonstrate that the hydrochar/CeO2 composite can be synthesized by a green method and used for the efficient treatment of water contaminated with methylene blue.

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This work presents the effect of CeO2 nanoparticles (CeO2-NPs) on Cu-50Ni-5Al alloys on morphological, microstructural, degradation, and electrochemical behavior at high temperatures. The samples obtained by mechanical alloying and spark plasma sintering were exposed to a molten eutectic mixture of Li2CO3-K2CO3 for 504 h. The degradation of the materials was analyzed using gravimetry measurements and electrochemical impedance spectroscopy. Different characterization techniques, such as X-ray diffraction and scanning electron microscopy, were used to investigate the phase composition, parameter lattice, and microstructure of Cu-Ni-Al alloys reinforced with CeO2-NPs. The hardness of the composite was also examined using the Vickers hardness test. Gravimetry measurements revealed that the sample with 1 wt.% CeO2-NPs presented the best response to degradation with a less drastic mass variation. Impedance analysis also revealed that by adding 1 wt.% CeO2-NPs, the impedance modulus increased, which is related to a lower porosity of the oxide film or a thicker oxide layer. The microhardness also significantly increased, incorporating 1 wt.% CeO2-NPs, which reduced with higher CeO2-NPs content, which is possibly associated with a more uniform distribution using 1 wt.% CeO2-NPs in the Cu-Ni-Al matrix that avoided the aggregation phenomenon.

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The interaction between metal and metal oxides at the nanoscale is of uttermost importance in several fields, thus its enhancement is highly desirable. In catalysis, the performance of the nanoparticles is dependent on a wide range of properties, including its shape that is commonly considered stable during the catalytic reaction. In this study, highly reducible CeO2-x nanoparticles are synthesized aiming to provide Cu/CeO2-x nanoparticles, which are classically active catalysts for the CO oxidation reaction. It is observed that the Cu nanoparticles shape changes during reduction treatment (prior to the CO oxidation reaction) from a nearly spherical 3D to a planar 2D shape, then enhances the Cu-CeO2-x interaction. The spread of the Cu nanoparticles over the CeO2-x surface during the reduction treatment occurs due to the minimization of the total system energy. The shape change is accompanied by migration of O atoms from CeO2 surface to the border of the Cu nanoparticles and the change from the Cu0 to Cu+1 state. The spreading of the Cu nanoparticles influences on the reactivity results toward the CO oxidation reaction since it changes the local atomic order around Cu atoms. The results show a timely contribution for enhancing the interaction between metal and metal oxide.

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The photocatalytic hydrogen evolution reaction (HER) by water splitting has been studied, using catalysts based on crystalline TiO2 nanowires (TiO2NWs), which were synthesized by a hydrothermal procedure. This nanomaterial was subsequently modified by incorporating different loadings (1%, 3% and 5%) of gold nanoparticles (AuNPs) on the surface, previously exfoliated MoS2 nanosheets, and CeO2 nanoparticles (CeO2NPs). These nanomaterials, as well as the different synthesized catalysts, were characterized by electron microscopy (HR-SEM and HR-TEM), XPS, XRD, Raman, Reflectance and BET surface area. HER studies were performed in aqueous solution, under irradiation at different wavelengths (UV-visible), which were selected through the appropriate use of optical filters. The results obtained show that there is a synergistic effect between the different nanomaterials of the catalysts. The specific area of the catalyst, and especially the increased loading of MoS2 and CeO2NPs in the catalyst substantially improved the H2 production, with values of ca. 1114 µm/hg for the catalyst that had the best efficiency. Recyclability studies showed only a decrease in activity of approx. 7% after 15 cycles of use, possibly due to partial leaching of gold nanoparticles during catalyst use cycles. The results obtained in this research are certainly relevant and open many possibilities regarding the potential use and scaling of these heterostructures in the photocatalytic production of H2 from water.

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A new highly sensitive, selective, and inexpensive electrochemical method has been developed for simultaneously detecting diethylstilbestrol (DES) and 17ß-estradiol (E2) in environmental samples (groundwater and lake water) using a graphite sensor modified by cerium oxide nanoparticles (CPE-CeO2 NPs). The developed sensor and the materials used in its preparation were characterized using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD). The ab initio simulation was used to evaluate the adsorption energies between both DES and E2 with the surface of the sensor. The peak current of oxidation of both hormones showed two regions of linearity. The region of greatest sensitivity was observed for the linear range of 10 nM-100 nM. The detection and quantification limits for this concentration range were 0.8/2.6 nM and 1.3/4.3 nM for DES and E2, respectively. The analytical performance of the developed method showed high sensitivity, precision, repeatability, reproducibility, and selectivity. The CPE-CeO2 NPs sensor was successfully applied to simultaneously detect DES and E2 in real samples with recovery levels above 98%.

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Various crystallite size estimation methods were used to analyze X-ray diffractograms of spherical cerium dioxide and titanium dioxide anatase nanoparticles aiming to evaluate their reliability and limitations. The microstructural parameters were estimated from several integral breadth methods such as Scherrer, Monshi, Williamson-Hall, and their variants: (i) uniform deformation model, (ii) uniform strain deformation model, and (iii) uniform deformation energy density model. We also employed the size-strain plot and Halder-Wagner method. For this purpose, an instrumental resolution function of an Al2O3 standard was used to subtract the instrumental broadening to estimate the crystallite sizes and strain, and the linear regression analysis was used to compare all the models based on the coefficient of determination. The Rietveld whole powder pattern decomposition method was introduced for comparison purposes, being the best candidate to fit the X-ray diffraction data of metal-oxide nanoparticles. Refined microstructural parameters were obtained using the anisotropic spherical harmonic size approach and correlated with the above estimation methods and transmission electron microscopy images. In addition, µ-Raman spectra were recorded for each material, estimating the mean crystallite size for comparison by means of a phonon confinement model.

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This study reports the preparation of TiO2 and CeO2 doped with different quantities of terbium and discusses the influence of this dopant on the photocatalytic activity of the semiconductors, with respect to the degradation of methylene blue, under ultraviolet and solar radiations. The oxides obtained were characterized by X-ray diffraction, infrared vibrational spectroscopy, diffuse reflectance spectroscopy, scanning electron microscopy, and dispersive energy spectroscopy. The results indicate that the presence of the dopant in TiO2 favored the formation of the anatase crystalline phase to the detriment of rutile, increased the band gap energy, and decreased the size of the nanoparticles. Doping CeO2 with Tb resulted in a fluorite-type crystalline structure, reduced band gap, and smaller particle size. The photocatalytic activity decreases as the concentration of terbium increases regardless of the radiation source and nature of the oxide. Furthermore, a better performance was observed for all semiconductors excited by solar radiation in comparison to ultraviolet light. The samples of pure TiO2 and TiO2 doped with 0.5 and 1% terbium showed total removal of the dye after less than 120 min of reaction, while the samples of pure CeO2 and CeO2 doped with 0.5% terbium showed approximately 80% and 57% of dye removal after 120 min, suggesting that these materials can be promising for the treatment of industrial effluents.

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Using catalytic converters is one of the most effective methods to control vehicle emissions. A washcoat of cerium oxide-zirconia (CeO2-ZrO2) has been used to enhance the performance of the catalytic converter device. To date, the prevalence of this material in the environment has not been assessed. In this study, we present evidence of the existence of inhalable zirconia in urban dust. Samples of the washcoat, exhaust pipe, topsoil, and road dust were analyzed by X-ray fluorescence, X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, photoluminescence (PL) spectroscopy, and thermally stimulated luminescence (TSL). The results showed a CeO2-ZrO2 phase separation after sintering. This causes the emission of ZrO2, CeO2, and CeZrOx particles smaller than 1 µm, which can likely reach the alveolar macrophages in the lungs. The Ce-Zr content in road dust exceeds geogenic levels, and a significant correlation of 0.87 (p < 0.05) reflects a common anthropic source. Chronic exposure to such refractory particles may result in the development of non-occupational respiratory diseases. The inhalable crystalline compounds emitted by vehicles are a significant environmental health hazard, revealing the need for further investigation and assessment of zirconia levels generated by automobiles in urban areas worldwide.

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Solar-to-chemical conversion via photocatalysis is of paramount importance for a sustainable future. Thus, investigating the synergistic effects promoted by light in photocatalytic reactions is crucial. The tandem oxidative coupling of alcohols and amines is an attractive route to synthesize imines. Here, we unravel the performance and underlying reaction pathway in the visible-light-driven tandem oxidative coupling of benzyl alcohol and aniline employing Au/CeO2 nanorods as catalysts. We propose an alternative reaction pathway for this transformation that leads to improved efficiencies relative to individual CeO2 nanorods, in which the localized surface plasmon resonance (LSPR) excitation in Au nanoparticles (NPs) plays an important role. Our data suggests a synergism between the hot electrons and holes generated from the LSPR excitation in Au NPs. While the oxygen vacancies in CeO2 nanorods trap the hot electrons and facilitate their transfer to adsorbed O2 at surface vacancy sites, the hot holes in the Au NPs facilitate the α-H abstraction from the adsorbed benzyl alcohol, evolving into benzaldehyde, which then couples with aniline in the next step to yield the corresponding imine. Finally, cerium-coordinated superoxide species abstract hydrogen from the Au surface, regenerating the catalyst surface.

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This work provides a comparative study on the corrosion protection efficiency of Ce, La films as well as Ce/La and La/Ce oxide bilayered coatings deposited onto AA7075 and AA6061 substrates by the radio frequency (RF) magnetron sputtering technique. The coating thickness ranged approximately from 12 to 835 nm, which changed with the deposition parameters and substrate composition. The relationship between microstructure, roughness and electrochemical performance is examined. The reactivity and crystallinity of rare earth (RE) films can be tailored by adjusting the sputtering parameters. Sputtered La films with thickness ca. 390 nm and average roughness of 66 nm showed the best corrosion protection properties in chloride medium as determined by potentiodynamic curves and electrochemical impedance spectroscopy (EIS). The method to obtain RE bilayered coatings, i.e., La/Ce or Ce/La as well as the substrate composition and applied power conditioned their inhibition properties. The RE bilayered coatings displayed better barrier properties than Ce films, which were poorer than those featured by La films.

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This work reports the effect of different amounts of ceria nanoparticles on UV resistance and barrier properties of water-based polyurethane (WPU) on glass and AA7075 aluminum alloy substrates. Hybrid coatings were synthesized from an aliphatic WPU⁻HDI (1,6-hexamethylene di-isocyanate) and cerium oxide nanoparticles (CeO2) with an average particle size distribution of about 25 nm. Different nanoceria amounts (1, 3 and 5 wt %), mixing times (30, 60 and 120 min) and methods to disperse the nanostructures into the polymer matrix (magnetic stirring and sonication) were evaluated. Initially, the dispersion of CeO2 nanoparticles embedded in the polymer matrix and displacement in the corrosion potential (Ecorr) were analyzed by confocal scanning laser microscopy (CLSM) and open circuit potential (Eocp) measurements. According to this behavior, the dispersion and water ratio required during the polymerization process were established. Coated samples obtained after the second stage were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and optical light microscopy. In addition, optical measurements on glass substrates were evaluated with UV-vis spectroscopy. The effect of the synthesis parameters on the corrosion behavior of WPU⁻CeO2/AA7075 systems was investigated with Eocp and electrochemical impedance spectroscopy (EIS) in a 3 wt % NaCl solution. In addition, the films were subjected to 180 h of accelerated weathering. The results show that the combination of specific nanoceria addition with the optimal synthesis parameters enhances optical transparence of WPU as well as barrier properties. From these, the coated specimens prepared with 3 wt % of ceria content and sonicated for 30 min showed a highly dispersed system, which results in a high charge transfer resistance. The observed properties in clear coats deposited on metallic substrates suggested an improvement in the appearance and less deterioration in UV exposure in comparison with pure WPU, enhancing the protective properties of the AA7075 aluminum alloy when exposed to a corrosive medium.

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We investigate the water-repellent ability of graphene-based surfaces stabilized on silicon carbide (SiC) and the nanocrystalline cerium oxide (CeO2) films electrodeposited on them. Water contact angle is revealed strongly dependent on the number of graphene monolayers on SiC, indicating partial permeability of graphene on SiC. Fluctuations in the roughness of textured surfaces as well as variations of oxygen vacancy content in CeO2 electrodeposits are determinant for the hydrophobicity of the interaction between water droplets and nanocrystalline CeO2 electrodeposits on monolayers graphene on SiC.

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The effects of nCeO2 on food quality are not well known yet. This research was performed to determine the impact of nCeO2 on radish (Raphanus sativus L.). Plants were cultivated to full maturity in potting soil treated with nCeO2 at concentrations of 0, 62.5, 125, 250, and 500 mg/kg. Germination, growth, photosynthesis, ionome, and antioxidants were evaluated at different growth stages. Results showed that at 500 mg/kg, nCeO2 significantly retarded seed germination but did not reduce the number of germinated seeds. None of the treatments affected gas exchange, photosynthesis, growth, phenols, flavonoids, and nutrients' accumulation in tubers and leaves of adult plants. However, tubers' antioxidant capacity, expressed as FRAP, ABTS(•-) and DPPH, increased by 30%, 32%, and 85%, respectively, in plants treated with 250 mg nCeO2kg(-1) soil. In addition, cerium accumulation in tubers of plants treated with 250 and 500 mg/kg reached 72 and 142 mg/kg d wt, respectively. This suggests that nCeO2 could improve the radical scavenging potency of radish but it might introduce nCeO2 into the food chain with unknown consequences.

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