Cerium Hydroxide Research Articles

Inhibition of pH fronts in corrosion cells due to the formation of cerium hydroxide

The effect of cerium-based corrosion inhibitors on the pH front between the alkaline cathode and acidic anode in corrosion cells has been studied. The cerium component of these inhibitors can affect the pH front since it precipitates in an alkaline environment as cerium hydroxide, which is important since the corrosion inhibition mechanism of the cerium component is a result of its deposition as a highly electrical resistive (passivation) layer on the cathode. It is studied whether the cerium can reach the cathode when fed into the corrosion cell from an external source after the onset of corrosion. To this end a simulation model was set up that includes the Poisson–Nernst–Planck theory to describe ion transport and the Frumkin–Butler–Volmer equation to describe charge transfer at the electrodes. In this model both the self-dissociation of water and the formation of cerium hydroxide are taken into account. To support our findings experimentally a corrosion cell consisting of an aluminum and copper electrode was used, in which the pH fronts were visualized using a pH-indicator. Two types of inhibitors were used; namely, highly soluble CeCl3 and sparsely soluble cerium dibutylphosphate, Ce(dbp)3. The results show that CeCl3 can reduce the size of the alkaline region and reach the cathode to form a passivation layer, whereas the solubility in case of Ce(dbp)3 is too low to supply sufficient amounts of trivalent cerium cations to penetrate the alkaline region. This behavior can be explained by the simulation results, which reveal a threshold for the corrosion inhibitor solubility below which no passivation of the cathode occurs.

Fluoride adsorption on an Fe–Al–Ce trimetal hydrous oxide: Characterization of adsorption sites and adsorbed fluorine complex species

To better understand fluoride (F) adsorption mechanisms of metal oxide-based adsorbent, a previously developed iron–aluminum–cerium hydroxide (Fe–Al–Ce) adsorbent with a high adsorption capacity for F was investigated using various spectroscopic methods including X-ray photoelectron spectroscopy (XPS) and 19F magic-angle spinning nuclear resonance (19F MAS NMR). XRD and BET results showed that the Fe–Al–Ce adsorbent maintained an amorphous structure with high specific surface areas and large pore volumes. Deconvolution of XPS O1s peaks showed a quantitative ligand exchange relationship between the metal–hydroxyl (−OH) groups and F ions. Deconvolution of XPS F1s peaks showed that the F ions were able to substitute for all three metal–OH groups. Ce–OH was the preferential adsorption site at low F load (10mgg−1), while Al–F became the most abundant complex species with increasing F loads (80 and 138mgg−1). Three types of complex species (Al3–F, Cex–Fy and Fex–Fy) were identified by 19F MAS NMR analysis under 20 and 80mgg−1 F loads. AlF3 was suggested as the dominant specie at a high F load (138mgg−1) by both of 19F MAS NMR and XRD analysis.

Electrophoretic mobility and computations of solid-aqueous solution equilibria for the bastnaesite-H2O system

Measurements of the electrophoretic mobility of bastnaesite in aqueous solutions of sodium nitrate reveal that the isoelectric point (iep) of this cerium fluocarbonate occurs at about pH 9.3. These results also indicate that the pH affects significantly the electrophoretic mobility of bastnaesite, which becomes more positive as the pH decreases and more negative as the pH increases from the iep. Computations of solid-solution equilibria for the bastnaesite-H2O system closed to the atmosphere as a function of pH indicate that cerium fluoride precipitates in acidic solutions, whereas cerium hydroxide precipitates in alkaline solutions. When the initial amount of bastnaesite is fixed at 0.05 wt.% (the solids concentration used for electrokinetic experiments), these computations reveal that bastnaesite is the only solid phase in the pH range from 5.75 to 8.55, it coexists with CeF3(s) between pH 5.22 and pH 5.74, and with Ce(OH)3(s) between pH 8.56 and pH 10.12. Cerium fluoride and cerium hydroxide are the only solid phase below pH 5.2 and above pH 10.2, respectively. According to these computations, the dissolution-precipitation processes that occur when bastnaesite is equilibrated in aqueous solutions at different pH values determine the solid phases present in the system. In turn, these processes must affect the electrokinetic potential at the solid-solution interface, and they must be considered for explaining electrokinetic measurements as a function of pH when bastnaesite is the original solid phase in aqueous suspensions.

Surfactant-assisted synthesis of mesoporous silica/ceria–silica composites with high cerium content under basic conditions

Ordered mesoporous silica/ceria–silica composites were synthesized using cerium(IV) hydroxide and tetraethyl orthosilicate (TEOS) as co-precursors in the presence of hexadecyltrimethylammonium bromide (CTAB) under basic conditions. These composites consisted of Ce-doped mesoporous silica particles (about 500 nm) with highly ordered 2D hexagonal (p6mm) and 3D bicontinuous cubic (Ia3d) structures and irregular ceria-rich silica–ceria particles. Wide angle XRD, diffuse reflectance UV-vis, and XPS analyses showed that 10–24% of cerium was at the Ce3+ oxidation level and the remaining predominant fraction of Ce was at the Ce4+ oxidation level. The cerium loading was varied in these composite materials up to 43 wt% (∼3.1 mmol g−1). The specific surface areas of the mesoporous silica/ceria–silica composite samples obtained on the basis of nitrogen adsorption isotherms were higher than 350 m2 g−1 and their pore widths were between 3.3 and 3.5 nm. The mesoporous silica/ceria–silica samples were reduced at 850 °C under flowing H2 in a N2 environment. The crystal structure of the reduced samples changed to a hexagonally structured phase with the oxidation state of Ce3+, while the ordered mesostructure of silica was preserved.

Screening of Inorganic Adsorbents for Selective Adsorption of Thiophene from Model Gasoline

Hydrodesulfurization-treated (HDS-treated) gasoline with low sulfur content is an important source of primary fuel for fuel cells, although it contains sulfur compounds, thiophene (TP), benzothiophene (BTP), and thiophene alkylated derivatives, known as a poison for the reformer catalysts and the electrode catalysts of fuel cells. Adsorptive removal of TP from model organic liquid of HDS-treated gasoline was screened on different kinds of inorganic adsorbents: hydrous metal oxides, mixed metal oxides, aluminosilicates, acidic salts of multivalent metal, hetero polyacidic salt, and metal salts of iron hexacyanate. All the adsorbents showed very low TP uptake, less than 5% of the total TP amount when metal ions were not loaded on the adsorbent. On the other hand, some metal ion (Ag, Cu, and Ce) loaded adsorbents had good TP adsorptive properties. On simple metal oxides, Ag ion was better for the formation of adsorption center than Ce or Ni ions. In zeolite group, Ce-loaded Y-zeolite showed the largest TP uptake (99% of the total TP amount). Hydrous cerium oxide and the Ce-loaded adsorbents prepared from K4[Fe(CN)6], Silicagel, TiO2, and ZrO2 did not show TP selectivity. The effect of coexisting toluene on TP adsorption was studied from the TP solutions with and without toluene.

Granulation of Fe–Al–Ce trimetal hydroxide as a fluoride adsorbent using the extrusion method

Iron–aluminum–cerium hydroxide (Fe–Al–Ce), which has high fluoride (F) adsorption capacity, was granulated via extrusion with cross-linked poly (vinyl alcohol) (PVA) as the binder. The optimum granulation conditions for acquiring an adsorbent with a high F adsorption capacity and compression strength were: binder/Fe–Al–Ce powder ratio, 1.4; average cylinder diameter of granules, 1.6mm; and drying temperature, 65°C. The granulated Fe–Al–Ce (GFAC) exhibited a Langmuir maximum adsorption capacity of 51.3mgg−1 at pH 7.0±0.2. The GFAC in columns exhibited an accumulated F adsorption capacity of 5.7mgg−1 and 3.2mgg−1 at the breakthrough point (1.0mgFl−1) for treatment of F-spiked tap water (pH 7.8±0.2) and F-bearing groundwater (pH 8.2±0.2), respectively, which is several times higher than most reported F adsorbents under the same conditions. Energy dispersive X-ray micro analysis (EDX) showed that F was distributed evenly in the cross-section of the used GAFC, suggesting that most active sites inside the GFAC were available for F removal. A regeneration method using NaAlO2 solution to desorb F from the used GFAC was developed, permitting the GFAC to keep over 60% of its F adsorption capacity even after four adsorption–regeneration cycles. The results demonstrated that GFAC was superior in F adsorption performance to conventional adsorbents such as activated alumina.

Composition control of electrodeposited nickel–cerium hydroxides by tuning the pH at the electrode/solution interface

A series of nickel–cerium hydroxides was prepared via electrodeposition with a designed pH testing system to measure the pH change at the electrode/solution interface in situ. The nickel and cerium contents of these hydroxides were determined by inductively coupled plasma-atomic emission spectrometry. The results indicate that the ratios of Ce/Ni in the obtained nickel–cerium hydroxides have a functional relationship with the pH values of the electrode/solution interface. A thermodynamic study of the Ni–H2O and Ce–H2O systems also confirmed the functional relationship between these systems. Therefore, by adjusting the pH value of the electrode/solution interface using simply designed equipment, the speciation distribution of the two kinds of metal ions in electrodeposition compounds can be controlled approximately.

Exceptional arsenic adsorption performance of hydrous cerium oxide nanoparticles: Part A. Adsorption capacity and mechanism

Hydrous cerium oxide (HCO) nanoparticles were synthesized by a simple precipitation process, and their arsenic adsorption performances were investigated. Due to their high specific surface area (198m2/g) and the presence of high affinity surface hydroxyl groups, HCO nanoparticles demonstrated exceptional adsorption properties in terms of adsorption capacity and kinetics on both As(III) and As(V). At neutral pH, the arsenic adsorption capacity of HCO reached over 170mg/g for As(III) and 107mg/g for As(V). Even at very low equilibrium arsenic concentrations, the amount of As(III) and As(V) adsorbed by HCO nanoparticles was still over 13mg/g at 10μg/L and over 40mg/g at 50μg/L, which are higher than the arsenic adsorption capacity for most commercial adsorbents. Over a wide pH range from 3 to 11, HCO nanoparticles could readily remove As(III) by adsorption, which was not observed previously on other arsenic adsorbents. Such exceptional arsenic adsorption properties by HCO nanoparticles were shown to derive from the strong inner-sphere complexion.

Exceptional arsenic adsorption performance of hydrous cerium oxide nanoparticles: Part B. Integration with silica monoliths and dynamic treatment

A novel composite adsorbent (SCO) was synthesized by integrating CeO2 nanoparticles into silica monoliths for the removal of arsenic from water in a dynamic flow through reactor. The silica monoliths provided 3-dimensional interconnected macropores for the effective transportation of water while a large amount of mesopores on the silica skeleton served as the sites for attachment of CeO2 nanoparticles. After impregnation and calcinations, CeO2 nanoparticles were firmly fixed on the walls of silica monoliths. The SCO composite demonstrated a superior arsenic removal performance on both lab-prepared and natural water samples. At a fast empty bed contact time of 4min, a high breakthrough bed volume of 20,000bv was achieved for the treatment of arsenic-contaminated natural water of ∼80μg/L to meet the maximum contaminant level of arsenic at 10μg/L for drinking water. Even after desorption/regeneration, the composite still maintained a strong arsenic adsorption performance, which is beneficial for their potential industrial applications.

Structural analysis and superconductivity of CeFeAsO1−xHx

We performed the neutron powder diffraction (NPD) and synchrotron x-ray diffraction measurements on CeFeAsO${}_{1\ensuremath{-}x}$(D,H)${}_{x}$ ($x$ $=$ 0.0 \ensuremath{-} 0.48) as a representative of 1111-type family of iron-based superconductors $Ln$FeAsO${}_{1\ensuremath{-}x}$H${}_{x}$ ($Ln$ $=$ lanthanoid). Deuterated and hydrogenated samples (CeFeAsO${}_{1\ensuremath{-}x}$D${}_{x}$ and CeFeAsO${}_{1\ensuremath{-}x}$H${}_{x}$) were synthesized by the solid-state reaction of a metal oxide, arsenides, and a hydride and a deuteride source under an applied pressure of 2 GPa. No distinct differences were found between the structural and superconducting properties of the hydride and deuteride samples. Rietveld analyses of the NPD patterns demonstrated that deuterium exclusively substitutes on the oxygen sites in the 1111-type structures according to the nominal composition. Bulk superconductivity was observed over a wide $x$ region (0.1 $x$ 0.4) and the superconducting dome had a rather flat shape with a maximum ${T}_{\mathrm{c}}$ $=$ 47 K at around $x$ $=$ 0.25. It was concluded from density functional theory calculations and comparison with the superconducting dome of the fluorine-substituted system that the charge state of the hydrogen substituting the oxygen sites was \ensuremath{-}1. The relationship between the lattice parameter $a$ and ${T}_{\mathrm{c}}$ in our samples prepared from metal hydrides is almost the same as that reported previously for samples prepared from cerium hydroxide. These results strongly suggest that H${}^{\ensuremath{-}}$ ions exclusively occupy the oxygen sites in both samples, regardless of the hydrogen species in the starting material.

Surface and structural characterisation of coprecipitated Ce x Zr1−x O2 (0 ≤ x ≤ 1) mixed oxides

CexZr1−xO2-mixed oxides with three different Ce/Zr ratios (Ce0.8Zr0.2O2, Ce0.5Zr0.5O2 and Ce0.2Zr0.8O2) along with pure cerium and zirconium oxides were prepared by coprecipitation of the metal hydroxides in alkali media and subsequent calcinations at 500 °C, using two different cerium precursors (Ce(NO3)3·6H2O or (NH4)2Ce(NO3)6). These samples were characterised by N2 adsorption at −196 °C, XRD, Raman spectroscopy, XPS and H2-temperature programmed reduction. Besides, the two mixed oxides with higher cerium content were calcined at higher temperature (1000 °C) with the additional purpose of studying their thermal stability and phase homogeneity. XRD and Raman spectroscopy confirm a significant improvement in the insertion of zirconium cations into the ceria lattice when the samples Ce0.8Zr0.2O2 and Ce0.5Zr0.5O2 are synthesised with (NH4)2Ce(NO3)6 instead of Ce(NO3)3·6H2O. This is attributed to a more homogeneous coprecipitation of cerium and zirconium hydroxides, leading to mixed oxides with better bulk oxygen mobility and smaller lattice parameter. Moreover, the mixed oxides prepared with the (NH4)2Ce(NO3)6 precursor and calcined at 1000 °C exhibit a single phase whereas phase segregation occurs in the counterpart mixed oxides prepared with the Ce(NO3)3·6H2O precursor. XPS analysis reveal correlations among O/(Ce + Zr) surface atomic ratio and total cerium content for both cerium precursors. Among the samples calcined at 1000 °C, Ce0.8Zr0.2O2 synthesised with Ce(NO3)3·6H2O is the only one that preserves the low-temperature surface reduction peak, and also shows a BET surface area slightly higher than those of the rest of samples calcined at high temperature.

Comparative study of different environmentally friendly (Chromium-free) methods for surface modification of pure magnesium

In this work, three different chromium-free methods of surface modification of pure magnesium were studied; namely, a cerium conversion coating, a carbonated coating and an anodic film. Scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS), micro Raman spectroscopy (MRS) and X-ray diffraction (XRD) were employed to study the morphology and composition of the surface after treatments. The corrosion resistance of the treated surfaces was evaluated by means of electrochemical impedance spectroscopy (EIS). XRD and MRS showed that conversion coatings obtained from cerium salts consisted of cerium oxides and hydroxides and the major component of the layer was CeO 2. The morphology of the cerium conversion coating consisted of a fiber-like structure that exhibited several network-like cracks. The carbonated coating was mainly composed of aragonitic CaCO 3, whereas the oxide layer formed in the anodizing process was a porous film made of MgO and some phosphate species compounds. The results of EIS tests indicated that calcium carbonated coating provided higher corrosion protection.

A study of phosphate adsorption by different temperature treated hydrous cerium oxides

An alkaline precipitation method was introduced to produce hydrous cerium oxides. The prepared powder was characterized by Brunauer-Emmett-Teller (BET) nitrogen adsorption-desorption, X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectrometry, and thermal gravimetry (TG) approaches. The adsorbent has a chemical formula of CeO2·nH2O (n < 2) and a cubic fluorite-type structure after high temperature treatment. Adsorption capacity of different temperature treated hydrous cerium oxides does not directly correlate with BET specific surface area. Phosphate adsorption isotherms follow the Langmuir equation below the treatment temperature of 800°C. Phosphate adsorption causes no change on the structure of a hydrous cerium oxides, and no signs of CePO4 precipitates are found. The ion-exchanging structure of hydrous cerium oxide plays a fundamental role in phosphate adsorption. The structure is highly temperature resistant and forms adsorption sites which adsorb both water and some anions. Complete loss of adsorption ability cannot be achieved unless the treatment temperature is higher than 1200°C. Mechanism study shows that the adsorption of phosphates is mainly an anion-exchange process.

Phosphate Adsorption Ability of Granular Gibbsite and Cerium Hydroxide

In the present study, the phosphate adsorption abilities of granular materials, gibbsite (GB) and cerium hydroxide (CE), granulated with ethyl cellulose and ethanol, were investigated. For suitable granular conditions using GB or CE, the percentage of binder and amount of solvent were 10% and 3.25 mL/5 g for GB and 7.5% and 2.50 mL/5 g for CE. The amount of phosphate adsorbed by granular GB or CE was similar to that adsorbed by powdered GB or CE. The adsorption isotherms of phosphate were also similar for the granular and powdered materials. The results of a column experiment showed that when GB was used, the suitable concentration of sodium hydroxide as the desorption solution was 2 mmol/L. In these experiments, the amount of phosphate adsorbed was 31.4 mg/g, the amount of phosphate desorbed was 25.3 mg/g, and the recovery percentage was 80.5%. In contrast, when CE was used, the suitable concentration of sodium hydroxide was 500 mmol/L; the amount of phosphate adsorbed was 77.7 mg/g, the amount of phosphate desorbed was 57.8 mg/g, and the recovery percentage was 74.4%. Results also indicate that granular GB and CE could be used at least five times in a column without loss of absorption or desorption abilities. Moreover, granulation of GB and CE is possible using ethyl cellulose and ethanol.

ビタミンB12を用いたバイオインスパイアード触媒によるヒ素の無毒化処理とGaリサイクル

A simple technique for the detoxification of inorganic arsenic was successfully developed. It is believed that the proposed arsenic detoxification would be effective for rare-metal recovery. The objectives of the present study are as follows: (1) Development of the safe and efficient arsenic detoxification treatment technique, streamlining of processes, and cost reduction; (2) Establishment of a safe technique for recovering gallium from III-V compound semiconductors. The results are as follows. A bio-inspired catalyst system with vitamin B12 was developed for the detoxification reaction (turnover number for methyl transfer: >150). Inorganic arsenic was selectively removed from the acid solution of GaAs semiconductors by using a suitable adsorbent with cerium hydroxide. The removed inorganic arsenic was detoxified by using vitamin B12 and an amino acid. Without using the adsorbent with cerium hydroxide, the detoxified arsenic, arsenobetaine, was isolated from the mixture with gallium ion and arsenobetaine by column chromatography on silica gel after detoxification. As stated above, the proposed arsenic detoxification was used for the safe recovery of gallium from GaAs semiconductors, thus confirming that the technique was effective for the recovery of rare metals.

Synthesis of Amino Methylene Phosphonic Acid Resin-Supported Hydrated Cerium Oxide Hybrid Sorbent and its Application in Drinking Water

The hydrated cerium oxide (CeH) was synthesized and it was loaded on amino methylene phosphonic acid resin (APAR) to form the hybrid adsorbent CeH-APAR. The structure and thermal properties of CeH-APAR were tested by FTIR and TGA. And then, it was investigated that pH values and temperatures affected the adsorption property of CeH and CeH-APAR for fluoride ion. The results showed that CeH-APAR hybrid sorbent formed by Ce4+ and APAR with coordination bond is relatively stable below 270°C. Its adsorption property is similar to that of CeH, i.e. it is less affected by pH value, so it can be used in a wide pH range. Besides, under a stable pH, adsorption capacity of CeH-APAR also increases along with increasing temperature. As a result, it is a temperature-controlled sorbent and belongs to chemical adsorption.

A facile aqueous sol–gel method for high surface area nanocrystalline CeO2

Thermally stable high surface area nanocrystalline CeO2 was synthesized via an aqueous sol–gel method using cerium hydroxide and urea as precursors. The CeO2 sol is yellow colored and absorbs light over the range 200–500 nm. Nanocrystalline CeO2 particles derived from the sol are spherical in shape and range from 9 to 13 nm in diameter. The CeO2 powder has a high surface area of up to 85 m2 g−1 and a band gap of 3.1 eV. The method of preparation is facile, utilises low cost reagents and can be performed on a large scale.

Effect of cerium chloride on corrosion resistance and adhesion of chromate conversion coatings

The corrosion resistance, adhesion and morphology of the chromate conversion coating (CCCs) formed on AA6061 in a chromate conversion solution containing mainly potassium dichromate (K 2Cr 2O 7), chromic anhydride (CrO 3) and sodium fluoride (NaF), using cerium chloride (CeCl 3) as additive, were investigated by using potentiodynamic polarization curves, EIS, adhesion test and SEM. The corrosion resistance and adhesion of the CCCs are improved greatly by adding a small amount of CeCl 3 (from 20 to 40 mg/L), whereas the excessive CeCl 3 (60 mg/L) deteriorates these properties of the CCCs. The results of polarization curves are in good agreement with those of EIS. SEM photographs show that the precipitation of cerium hydroxide significantly affects the morphologies of CCCs.

Nanostructures and optical properties of hydrothermal synthesized CeOHCO 3 and calcined CeO 2 with PVP assistance

Submicronsized sphere- and disc-like cerium hydroxide carbonate structures were obtained by a hydrothermal method in the presence of polyvinyl pyrrolidone. Morphologies and sizes of the particles and their assembled structures are very sensitive to the concentration of polyvinyl pyrrolidone and the reaction time. As concentration of polyvinyl pyrrolidone increasing or hydrothermal reaction time elongating, the assembled structure experienced a morphology transition from sphere-like to disc-like and then to enlarged sphere-like again. The cerium hydroxide carbonate showed strong photoluminescence effect at room temperature. Ceria nanostructures can be obtained after a 500 °C calcining from cerium hydroxide carbonate precursors. The obtained products showed good ultraviolet absorption properties. Furthermore, the absorbance feature could be adjusted by changing the polyvinyl pyrrolidone concentration and reaction time during synthesis.

Removal of arsenic by a granular Fe–Ce oxide adsorbent: Fabrication conditions and performance

Iron–cerium hydroxide (Fe–Ce), which has shown a high arsenic (V) (As(V)) adsorption capacity in previous studies, was granulated using the vibration dropping method used to prepare small-sized fuel particles. Fabrication studies showed that the sintering process could not be used in the preparation of the granular Fe–Ce (GFC) adsorbent and that the optimum grain size was 1.0 mm for As(V) removal. The optimum sized GFC (GFC-1.0 mm) exhibited a Freundlich adsorption of 18.2 and 11.8 mg g −1 at an equilibrium concentration of 1.0 and 0.1 mg L −1, respectively. The GFC-1.0 mm also showed equivalent As removal performance to READ, a commercial adsorbent with CeO 2 as the sole metal oxide component (about 81%), under both space velocities of 240 and 24 h −1 in column tests. The cost for the manufacturing of GFC, however, is much lower since iron is the major metal component (about 80%). Energy dispersive X-ray microanalysis (EDX) results showed that As was distributed from the surface to the center of the GFC after the As(V) adsorption experiment, suggesting that nearly all active sites inside the GFC were available for the removal of As(V). The As(V) on the used GFC could be desorbed with an efficiency of 89% using 1.0 mol L −1 sodium hydroxide, and the GFC after desorption showed similar As adsorption performance with the fresh GFC. In conclusion, the GFC consisting of 80% Fe and 20% Ce exhibited As removal performance equivalent to the commercial adsorbent consisting only of Ce.