Cerium Salts Research Articles

Characteristics of high-performance anti-corrosion/anti-wear ceramic coatings on magnesium‑lithium alloy by plasma electrolytic oxidation surface engineering

High-performance anti-corrosion/anti-wear coatings on superlight magnesium‑lithium (MgLi) alloy with exceptional durability are of great interest for fundamental research and practical applications. In the present study, oxide coatings are produced on MgLi alloy by electrochemical surface engineering––plasma electrolytic oxidation in an alkaline silicate electrolyte with addition of cerium salt. To understand the nature of coatings, we investigate their surface and cross-sectional morphologies, wettability (35 ± 3° vs 78 ± 2°), phase and chemical compositions, corrosion and tribological behaviors. Our findings show that the oxide coating prepared with cerium salt has a more compact structure with fewer defects (18 μm in thickness). Importantly, it substantially enhances the corrosion resistance of MgLi alloy by three orders of magnitude and significantly retards the occurrence of localized corrosion (150 h), along with notably improved anti-wear performance (friction coefficient of 0.19).

H2 production over Pt-Ni/CeO2-SiO2 via ethanol reforming in a fluidized bed

The aim of the present work is to study the application of a fluidized bed reactor for oxidative steam reforming of ethanol (OESR) over a bimetallic 3wt% Pt-10wt% Ni/CeO2-SiO2 catalyst. In particular, the effect of cerium salt precursor (nitrate (N), ammonium nitrate (AN) and acetylacetonate (AC)) on catalyst activity and stability was investigated. Three catalysts were synthetized. In all cases, the support was composed of a CeO2-SiO2 mixed oxide and the ceria content for all the catalysts was fixed to 30 wt%. The tests were carried out at a steam to ethanol ratio (f.r.) of 4 and oxygen to ethanol ratio (o.r.) of 0.5; temperature was fixed to 500°C and the weigh hourly space velocity (WHSV) to 12.3 h-1. All the samples displayed a partial deactivation with time-on-stream and ethanol was completely converted only for few hours. The initial H2 yield was very close to the predicted thermodynamic value (41.5%) and a gradual yield lowering was observed over the three catalysts. However, after 80 h of test, all the samples reached a plateau condition, with no more variation in selectivity. It is worthwhile noting that, for the sample AC, the final conversion was attested to 75%, while the other two catalysts displayed a similar behaviour with plateau conversion of almost 60%. In addition, a higher H2 yield (20%) was recorded after 100 h of test for the sample AC and the carbon formation rate measured after the test on the latter catalyst was almost 1 half of the values found for the catalysts N and AN: in the case of acetylacetonate, the organic group of the salt probably assures a templanting effect, which protects ceria molecules, improving their dispersion and increasing catalyst activity towards both reforming and carbon gasification reactions.

Characteristics of the response of the microalga (Dunaliella viridis) to cerium compounds in culture

Recently, nanobiotechnology has been developing intensively; therefore, various properties of nanoparticles, which depend on their origin, concentration, and size, are of interest. It is known that CeO2 nanoparticles cause a positive biological effect. These particles are able to penetrate through biomembranes. At the same time, there are assumptions about a high degree of biological risks when using nanomaterials, and it is obvious that the biosafety of nanomaterials is decisive in the development of new products, including for medicine. The cytotoxicity of samples of cerium salts and cerium dioxide nanoparticles of different sizes was assessed at different concentrations using D. viridis. The cytotoxicity level by morphological and functional disorders of D. viridis was investigated, as determined by the change in cell shape, accumulation of inclusions, loss of flagellum, change in nature and movement, the formation of micro- and macroaggregates by D. viridis cells and exometabolite release. The cytotoxicity coefficient was calculated as a quotient of total detected changes divided by their number. It was shown that cerium salts (cerium (IV) ammonium nitrate and cerium (III) chloride) had pronounced cytotoxicity, which exceeded cytotoxicity values of the control by 7 and 6 times, respectively. Cerium dioxide nanoparticles with a size of 6 nm at a concentration of 0.01 M showed intermediate cytotoxicity, which exceeded control values by 3.5 times, and after the effect of nanoparticles with a size of 2 nm at a concentration of 0.1 M, the cytotoxicity coefficient corresponded to control values. The addition of inactivated blood serum to the incubation mixture resulted in a decreased cytotoxic effect of cerium dioxide. The use of D. viridis as a test system will supplement the arsenal of biotesting tools for nanomaterials and the study of the mechanisms of their effect.

Colourful Chemistry – from Hybrid Flow Batteries to a Powerful Redox Flow Battery with Impressive Colour Changes for a Phenomenological Approach

The energy transition towards a larger share of renewables requires energy storage devices with redox flow batteries playing a central role for stationary large-scale storage. The most promising and developed one is the vanadium redox flow battery. However, vanadium compounds are toxic, harmful to the environment and hardly suitable for use in schools – in addition, the worldwide occurrence of vanadium minerals is limited. In Freiburg, the aim of a research project was to make the topic of storage systems accessible to students both at university and in chemistry classes, because they will be the generation that will or must help shape this development. Therefore, hybrid flow batteries with harmless electrolytes, a common metal electrode and a simplified construction needed to be built for school application. Utensils from medical technology such as plastic syringes or extension lines are well suited for building cost-effective hybrid flow batteries for chemistry lessons. With such materials, electrolytes can be circulated with a pump that generates an efficient electrolyte flow. Freiburg’s design makes it possible to charge and discharge electrolytes in just a few minutes and the electrochemical reactions get visible through colour changes. In the field of redox flow batteries where the energy is stored in two electrolytes, a high-performance cell based on iron and cerium salts is also presented. With this battery, the anolyte and catholyte can be oxidised or reduced in a short time and electrolytes which change their colours during the electrochemical reaction are used as well. Thus, the operating principle of flow batteries can impressively be demonstrated by changing the properties of the electrolytes at the phenomenological level.

Effect of sol-gel sealing treatment loaded with different cerium salts on the corrosion resistance of Fe-based amorphous coating

Porosity defects inevitably formed in the preparation of high-velocity oxy-fuel (HVOF)-sprayed Fe-based amorphous coating, which greatly affected the corrosion resistance and service lives of Fe-based amorphous coating. Sealing treatment could be an effective candidate method to alleviate the problem above. In this paper, three sealed coatings including sol-gel (SG) coating, sol-gel with cerium nitrate (SCN) coating and sol-gel with cerium tartrate (SCT) coating were applied on Fe-based amorphous coating. The influence of sealing treatment on the structure and corrosion resistance of Fe-based amorphous coating was investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR) and electrochemical methods. The results revealed the corrosion resistance of Fe-based amorphous coating was enhanced after sealing treatments in comparison with that of unsealed coating. However, the density of SCN coating was reduced compared with that of SG coating, although it had corrosion inhibition effect. SCT coating exhibited the best in eliminating defects and enhancing the corrosion resistance among three sealed coatings. Moreover, the combined protection mechanism of SCT coating was proposed and discussed.

Hygienic coatings with bioactive nano-additives from Senna occidentalis-mediated green synthesis

Nowadays urban populations spend 90% of their time in buildings where microbial growth lead to hazardous environments which produce health problems characterized by irritation of the respiratory tract, infections, allergies and asthma. Some research lines seek to obtain antimicrobial materials to prevent such health problems. Green synthesis of different nanoparticles was carried out to explore their antimicrobial potential. Solutions of silver, copper, cerium, lanthanum and zinc salts were used as source of metal ions for the synthesis process. Aqueous plant extract from Senna occidentalis, a small shrub, was used, for the first time, as reducing and stabilizing agent to obtain additives to bioactive coatings. The stable synthesis products were evaluated by UV–vis spectroscopy and their antimicrobial properties were assessed. Other characterizations by transmission electron microscopy and Fourier transformed infrared spectroscopy were also performed. Silver and copper nanoparticles were stable over time. However, only silver nanoparticles showed antibacterial and antifungal activity and were used for obtaining antimicrobial waterborne acrylic paints. The formulation with 25 mg/100 g resulted in efficient inhibition of the fungal and bacterial biofilm.

Carboxylic acids accelerate acidic environment-mediated nanoceria dissolution

Ligands that accelerate nanoceria dissolution may greatly affect its fate and effects. This project assessed the carboxylic acid contribution to nanoceria dissolution in aqueous, acidic environments. Nanoceria has commercial and potential therapeutic and energy storage applications. It biotransforms in vivo. Citric acid stabilizes nanoceria during synthesis and in aqueous dispersions. In this study, citrate-stabilized nanoceria dispersions (∼4 nm average primary particle size) were loaded into dialysis cassettes whose membranes passed cerium salts but not nanoceria particles. The cassettes were immersed in iso-osmotic baths containing carboxylic acids at pH 4.5 and 37 °C, or other select agents. Cerium atom material balances were conducted for the cassette and bath by sampling of each chamber and cerium quantitation by ICP-MS. Samples were collected from the cassette for high-resolution transmission electron microscopy observation of nanoceria size. In carboxylic acid solutions, nanoceria dissolution increased bath cerium concentration to >96% of the cerium introduced as nanoceria into the cassette and decreased nanoceria primary particle size in the cassette. In solutions of citric, malic, and lactic acids and the ammonium ion ∼15 nm, ceria agglomerates persisted. In solutions of other carboxylic acids, some select nanoceria agglomerates grew to ∼1 micron. In carboxylic acid solutions, dissolution half-lives were 800–4000 h; in water and horseradish peroxidase they were ≥55,000 h. Extending these findings to in vivo and environmental systems, one expects acidic environments containing carboxylic acids to degrade nanoceria by dissolution; two examples would be phagolysosomes and in the plant rhizosphere.

Hydrogen production by oxidative reforming of ethanol in a fluidized bed reactor using a Pt Ni/CeO2SiO2 catalyst

Abstract Oxidative steam reforming of ethanol (OESR) was investigated over Pt Ni/CeO2 SiO2 catalysts prepared from different cerium salt precursors. During stability tests performed at 500 °C, steam/ethanol ratio (S/E) of 4 and oxygen/ethanol ratio of 0.5 (O/E), the highest performance was recorded over the catalyst prepared form organic precursors. The most promising formulation was tested at different temperatures, S/E and O/E. Complete conversion was recorded during 100 h of the test at 600 °C, with a very low carbon formation rate (6.9·10−7 gcoke, oxidized·gcatalyst−1·gcarbon,fed−1·h−1). The increase of oxygen content in the reacting mixture from 5 to 7.5% had a beneficial effect on H2 yield, which rose of more than 20% after 100 h of test, and on the conversion of by-products. When steam/ethanol ratio grew from 4 to 6, a slightly lower performance improvement was observed. Therefore, the highest activity and stability during OESR over the Pt Ni/CeO2 SiO2 catalyst prepared from organic salts was achieved at 600 °C, O/E = 0.75 and S/E = 6.

Chiroptical sensing of unprotected amino acids, hydroxy acids, amino alcohols, amines and carboxylic acids with metal salts.

Optical chirality sensing of unprotected amino acids, hydroxy acids, amino alcohols, amines and carboxylic acids based on a practical mix-and-measure protocol with readily available copper, iron, palladium, manganese, cerium or rhodium salts is demonstrated. The generation of strong cotton effects allows quantitative ee analysis of small sample amounts with high speed. In contrast to previously reported assays the use of chromophoric reporter ligands and the control of metal coordination kinetics and redox chemistry are not necessary which greatly simplifies the sensing procedure with the benefit of reduced waste production and cost.

Cerium ion promotes the osteoclastogenesis through the induction of reactive oxygen species

Cerium and cerium containing materials have been drawing increasing attentions in industrial and biomedical applications in recent decades. The increased applications of cerium have also increased the risk of human body exposed to cerium ions. Due to its similar ionic radius to calcium(II), cerium(III) have found mainly deposited in the skeletal system. However, the effects of cerium(III) on the bone metabolism homeostasis remain poorly understood. In the present study, the effect of cerium(III) on the osteoclastogenesis which plays a pivotal role in bone metabolism homeostasis was investigated. Cerium(III) could enhance the expression and activity of NADPH oxidase1 (Nox1) leading to the elevation of intracellular reactive oxygen species (ROS) level. The augmentation of ROS level activated the RANKL dependent osteoclasts differentiation pathways resulted in the promotion of osteoclastogenesis, while anions associated with cerium(III) cation have no effects on the differentiation of osteoclasts. The cerium(III) activated osteoclasts exhibited enhanced bone resorption capability. These results provided fundamental information for understanding the potential effects of cerium(III) on the metabolism homeostasis of skeletal system which is of great reference value for future biomedical applications of cerium salts.

Cerium-based catalysts for N-oxidation of pyridine-based derivatives: homogeneous and heterogeneous systems

Herein, the catalytic properties of the cerium (IV) salt, cerium (IV)-sandwiched polyoxometalate (POM) and cerium (IV)-sandwiched polyoxometalate intercalated in layered double hydroxides (LDHs) in the H2O2-based green oxidation reactions have been evaluated. These cerium (IV)-based systems were applied as homogeneous and heterogeneous catalysts for the oxidation of pyridines. Despite the fact that the cerium (IV)-sandwiched polyoxometalate as a homogeneous reaction system gives good results, there are some disadvantages in recovery and reusability process. To overcome these problems, new nano catalyst was synthesized by intercalation of the Cerium (IV)-sandwiched polyoxometalate into tris(hydroxymethyl) aminomethane-modified layered double hydroxides (Tris-LDH-CO3). The as-prepared nanocomposite was characterized and used as an effective heterogeneous catalyst for the oxidation of pyridines under mild conditions in the presence of H2O2 as an oxidant. The new heterogeneous nanocomposite can be recovered and reused easily from the reaction media at least ten times without significant decrease in catalytic activity.

Cu-Ce-O catalyst revisited for exceptional activity at low temperature CO oxidation reaction

In the present study, CexCu1−xO2−δ (x = 0, 0.3, 0.5, 0.8, 0.9, and 1) catalysts were synthesized using a facile and reproducible combustion method and were evaluated towards the CO oxidation (CO-OX) and CO preferential oxidation (CO-PROX) reactions as inexpensive and active catalytic materials. Pure ceria and copper oxide were compared to CexCu1−xO2−δ mixed metal oxides for benchmarking purposes. The catalysts were prepared using citric acid (C6H8O7) as fuel and nitrate salts of cerium and copper as oxidizers under fuel rich conditions. A variety of techniques including XRD, EDX, BET, SEM, Raman, XPS, H2-TPR and CO2-TPD, were used to analyze the microstructural, thermal and redox properties that may influence CO oxidation performance. A profound effect of Cu content was revealed that not only impacts the structural and redox properties of the catalysts but also affects the catalytic activity. The Ce0.8Cu0.2O2−δ catalyst presented the most promising performance among many similar (Cu-Ce-based catalysts) as well as noble supported catalysts published in the literature with T50 = 62 °C and T100 = 78 °C, an activity that coincides with the availability of labile oxygen species at low temperature (T < 100 °C) and the enhanced CO2 desorption at low temperature (low CO2-philicity) of this catalyst.

Evaluation of the anticorrosion of waterborne epoxy coatings containing cerium salt-activated ceria nanoparticles deposited onto carbon steel substrates

The presence work investigates the corrosion protection of waterborne epoxy coatings containing CeO2 nanoparticles activated with cerium salt for the carbon steel substrates. First, the dispersion of activated nanoparticles in the epoxy matrix was observed by field emission scanning electron microscopy (FESEM). The electrochemical impedance spectroscopy (EIS) was carried out to evaluate the role of the activated-CeO2 nanoparticles in the organic coatings immersed in a 0.5 M NaCl solution. Thus, the effect of the cerium ion activated ceria nanoparticles on the coatings presented the artificial defect in the aggressive environment was examined via salt spray test. Complementary studies were performed using the cross-cut and pull-off test to assess the adherence properties of the samples. Results revealed that the presence of activated-CeO2 nanoparticles enhanced corrosion protection properties of waterborne epoxy coating without losing adherence properties.

Photocatalytic upgrading of natural gas.

Cerium salts catalyze formation of value-added molecules from methane and small alkanes

Radically transforming light hydrocarbons

Organic Chemistry The methane, ethane, and propane in natural gas are mostly inert under ambient conditions. Mainly they are burned to produce heat. Hu et al. show that a simple cerium salt paired with an alcohol can catalytically transform these and other simple hydrocarbons into reactive radicals at room temperature (see the Perspective by Kanai). The reactions rely on light to photolytically cleave cerium alkoxide bonds, producing alkoxy radicals that strip H atoms from the hydrocarbons and regenerate the alcohol. The resultant alkyl radicals readily add to azo compounds, olefins, and aromatics. Science , this issue p. [668][1]; see also p. [647][2] [1]: /lookup/doi/10.1126/science.aat9750 [2]: /lookup/doi/10.1126/science.aau5379

Thermodynamic properties of gaseous cerium molybdates and tungstates studied by Knudsen effusion mass spectrometry.

CeO2 -WO3 and CeO2 -MoO3 catalysts have shown excellent performance in the selective reduction of NOx by ammonia (NH3 -selective catalytic reduction) over a wide temperature range. Strong interaction between CeO2 and WO3 or MoO3 might be the dominant reason for the high activity of these mixed oxides. Studies of ceria-containing gaseous salts involve considerable experimental difficulties, since the transition of such salts to vapor requires high temperatures. To predict the possibility of the existence of gaseous associates formed by cerium and molybdenum (tungsten) oxides it is important to know their thermodynamic characteristics. Until the present investigation, gaseous cerium oxyacid salts were unknown. Knudsen effusion mass spectrometry was used to determine the partial pressures of vapor species and the equilibrium constants of gas-phase reactions, as well as the formation and atomization enthalpies of gaseous cerium molybdates and tungstates. CeO2 was evaporated from molybdenum and tungsten effusion cells containing gold metal as a pressure standard. A theoretical study of gaseous cerium gaseous molybdates and tungstates was performed by several quantum chemical methods. In the temperature range 2050-2400 K, CeO, CeO2 , XO2 , XO3 , CeWO3 , CeXO4 , CeXO5 (X = Mo, W) and CeMo2 O7 were found to be the main vapor species over the CeO2 - Mo (W) systems. On the basis of the equilibrium constants of the gaseous reactions, the standard formation enthalpies of gaseous CeWO3 , CeXO4 , CeXO5 (X = Mo, W) and CeMo2 O7 at 298 K were determined. Energetically favorable structures of gaseous cerium salts were found and vibrational frequencies were evaluated in the harmonic approximation. The thermal stability of gaseous cerium oxyacid salts was confirmed by high-temperature mass spectrometry. Reaction enthalpies of the gaseous cerium molybdates and tungstates from gaseous cerium, molybdenum and tungsten oxides were evaluated theoretically and the obtained values are in reasonable agreement with the experimental one.

Mechanoluminescence of Ce/Tb inorganic salts in methane-acetylene mixtures with inert gases.

The mechanoluminescence of cerium (Ce) and terbium (Tb) lanthanide salts is studied in hydrocarbon [methane (CH4 ) and acetylene (C2 H2 )] and inert [helium (He), neon (Ne), argon (Ar), krypton (Kr), and xenon (Xe)] gaseous mixtures. The lines of *N2 , *Ln3+ , inert gases, *CH, and *C2 radicals resulted from the mechanochemical decomposition of CH4 and C2 H2 are observed in the emission spectrum. The luminescence intensity of the inert gases decreases with the hydrocarbon gas concentration in the mixture. The intensities of the *CH or *C2 bands remains almost unchanged within 15-100 vol% of CH4 or C2 H2 in the mixture. When the concentration of CH4 or C2 H2 is lower than 15%, the intensities of the CH or C2 bands increase achieving their maxima at 0.5-3% of the hydrocarbon. This is probably due to the optimal compositions of the mixtures with the most efficient generation of electrical discharges responsible for mechanoluminescence.

Adsorption of Cerium Salts and Cerium Oxide Nanoparticles on Microbubbles Can Be Induced by a Fluorocarbon Gas

Retrieving heavy metals from wastewaters has become an important environmental challenge. We report that exposing dilute aqueous solutions or dispersions of cerium compounds (CeO2, Ce(SO4)2, CeF4) to perfluorohexane-saturated air results in substantial adsorption of these salts at the air/water interface, as consistently reflected by a marked decrease in interfacial tension, as assessed by bubble-shape profile analysis tensiometry. No detectable adsorption is observed in the absence of the fluorocarbon. Adsorption to the interface is also achieved when, and only when, CeO2 nanoparticle dispersions are exposed to the fluorocarbon vapor. We also found that microbubbles could be generated in cerium salt solutions and CeO2 nanoparticle dispersions when they are formed in the presence of perfluorohexane-saturated air, without need for any surfactant or chelating agent. Optical microscopy, static light scattering, and ζ potential measurements were used to establish the ability for the fluorocarbon to induce the...

Selective functionalization of methane, ethane, and higher alkanes by cerium photocatalysis.

With the recent soaring production of natural gas, the use of methane and other light hydrocarbon feedstocks as starting materials in synthetic transformations is becoming increasingly economically attractive, although it remains chemically challenging. We report the development of photocatalytic C-H amination, alkylation, and arylation of methane, ethane, and higher alkanes under visible light irradiation at ambient temperature. High catalytic efficiency (turnover numbers up to 2900 for methane and 9700 for ethane) and selectivity were achieved using abundant, inexpensive cerium salts as photocatalysts. Ligand-to-metal charge transfer excitation generated alkoxy radicals from simple alcohols that in turn acted as hydrogen atom transfer catalysts. The mixed-phase gas/liquid reaction was adapted to continuous flow, enabling the efficient use of gaseous feedstocks in scalable photocatalytic transformations.

Passivation Process of Carbon Steel Cerium Salt and Silane Composite Membrane

In this paper, the acid quick passivation processwe adopted, put carbon steel after pretreatment, immerse in cerium salt solution and then form passivating film. Via orthogonal experiment, the optimum passivation process conditions are as follows: Ce(NO3)3.6H2O, 30 g/L; H2O2, 30 ml/L; pH value of 2; passivation time, 60s. Under the condition of the above, membrane resistance under the condition of 3% acidic copper sulfate intravenous drip experiment time can reach 1309s. Electrochemical impedance spectroseopy(EIS) measurements were assessed the corrosion resistane of passivation films; metallographic microscope and scanning electron microscopy(SEM) were used to characterize the composition structure and morphologies of sample surfaces; X-ray energy dispersive spectrometry (EDS) and X-ray photon spectro scopy (XPS) were used to identified the component of sample surfaces. The silane coupling agent was treated on the sample as two step passivation, in order to improve the anti-corrosion of cerium passivation film. Silane coupling agent secondary passivation process was that the sample was passivated for 1 minute in the KH-560 for 4% of silane coupling agent solution that the pH value is 2.5%, and cured for 1 hour under the condition of 120 °C . Neutral salt spray and EIS test results of cerium-silane composite passivation film show that theanti-corrosion performance of passivation film has been greatly improved. SEM and EDS analysis results showed that the silane coupling agent very well covered cracks and filled the pores on surface of the cerium salt passivation film.