Fabrication and ultraviolet-shielding properties of silica-coated titania-doped ceria nanoparticles

A series of well-dispersed titania-doped ceria nanoparticles Ce1-xTixO2 were rapidly prepared by a novel salt-assisted solution combustion process using correspondent metal nitrates as oxidizers and ethyl glycol as fuel, and then coated with amorphous silica by seeded polymerization using tetraethyl orthoslicate (TEOS). The as-prepared samples were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and ultraviolet-visible light (UV-Vis) diffuse reflectance spectroscopy. The results indicated that compared with the as-prepared pure ceria nanoparticles, the red-shift phenomenon occurred for Ti-doped ceria nanoparticles with Ti incorporation. Meanwhile, the absorption intensity in the UV light region slightly decreased and transmission rate in visible light region was somewhat enhanced. In comparison with the silica-coated CeO2 nanopowders, the silica-coated Ce0.95Ti0.05O2 nanopowders displayed the same absorption intensity in the UV light region, broader UV absorption band and higher transmission rate in visible light region.     

Synthesis and characterization of Sb-doped SnO2-(CeO2-TiO2) composite thin films deposited on glass substrates for antistatic electricity and UV-shielding

Sb-doped SnO₂ (ATO)-(CeO₂-TiO₂) thin Films were deposited on glass substrates using the mixed solution including CeO₂-TiO₂ precursor and ATO particles by sol-gel dip coating process. ATO particles were prepared using low-temperature hydrothermal process. The mixed molar ratio of ATO to (CeO₂-TiO₂) vs the properties of CeO₂-TiO₂ thin film was investigated. The optical properties of the films were characterized by UV-visible transmission and infrared reflection spectra, the sheet resistance of ATO particles and films were measured by rubber sheeter (MYI-50) and four-point probe (HisuperGroup Inc, SDY-5), the surface morphology and structure of the films were analyzed using 3D Digitale Mikroskop and X-ray diffraction (XRD), respectively. The results showed that the ATO precursor solution lost weight completely at about 500 °C, and the ATO particles was obtained, which indicated the same rutile lattice structure as SnO₂. The glass substrates coated with ATO-(CeO₂-TiO₂) thin films showed better properties in antistatic electricity (10⁴-10⁶ Ω/?), shielding UV (almost 100%), visible light transmission (70%) and infrared reflection (>30%).     

Thermal stability of CeO<Subscript>2</Subscript>/ZrO<Subscript>2</Subscript> multilayer thin films prepared by pulsed laser deposition

Multilayers of CeO₂/ZrO₂ thin films were deposited on Si (100) substrates using pulsed laser deposition at an optimized oxygen partial pressure of 3×10⁻² mbar and at room temperature. The CeO₂ layer thickness was 10 nm, while the ZrO₂ layer thickness was varied as 10, 20 and 30 nm. CeO₂ and ZrO₂ layers were deposited alternately to obtain 25 bilayers. High temperature x-ray diffraction (HTXRD) results showed that the multilayer films had cubic ceria and tetragonal ZrO₂. Thermal expansion coefficients were calculated for CeO₂ and t-ZrO₂ and found to increase with the decrease of ZrO₂ layer thickness. The cross sectional transmission electron microscopy (XTEM) of CeO₂/ZrO₂ multilayer also indicated that ceria was found to be in cubic phase while zirconia contained predominantly tetragonal phase along with cubic phase in thermally annealed specimen.     

One-step solution combustion synthesis of micro-nano-scale porous Cu/CeO2 with enhanced photocatalytic properties

The Cu/CeO₂ nanoporous composite material was prepared via a one-step and energy-saving method of solution combustion synthesis(SCS).The phase composition,surface morphology and optical characteristics of Cu/CeO₂ were studied.The results show that the SCS products are composed of cubic fluorite CeO₂ and Cu.Due to the generation and escape of gas during the synthetic reaction,the SCS CeO₂ shows porous structure,in which the mesopores(diameter 10-17 nm) ...     

The growth and structure of thin oxide films on cerium ion-implanted nickel

Cerium ions were implanted into a high purity polycrystalline Ni to a dose of 2 × 10¹⁶ Ce⁺/cm². The radiation damage and distribution of Ce in Ni substrate were modified by postimplantation vacuum annealing. The Ce implants significantly decreased the NiO growth rate at 973 K. Thin oxide films formed on implanted Ni were composed of three well-defined sublayers, each with an essentially different microstructure. Cerium was present in the near surface region of the oxide in the form of CeO₂ particles, randomly distributed in NiO matrix, and Ce ion segregants at NiO grain boundaries. The size of CeO₂ particles, formed during the initial stages of exposure to oxygen, affected the inhibition of oxide growth. Vacuum annealing following implantation decreased the beneficial effect of Ce implants by increasing the size of CeO₂ particles. The role of Ce implants in inhibiting grain boundary diffusion in NiO is analyzed. As a result of this study, the growth mechanism of thin NiO films on Ce-implanted Ni is proposed.     

Design and synthesis of Fe-Ce-O@C with efficient photocatalytic activity

Fe-Ce-OH@AR14 was obtained via the adsorption of acid red 14(AR14) on Fe-Ce-OH prepared by the codeposition of cerium nitrate hexahydrate,ferric nitrate nonahydrate,and ammonia,and then Fe-Ce-O@C with high photocatalyic efficiency was synthesized by the calcination of Fe-Ce-OH@AR14 in N₂.For comparison,Fe-Ce-O was also prepared by the calcination of Fe-Ce-OH in N₂.The obtained materials were characte rized by X-ray diffraction(XRD),Raman,X-ray photoelectron spectroscopy(XPS...     

Effect of interaction between different CeO2 plane and platinum nanoparticles on catalytic activity of Pt/CeO2 in toluene oxidation

The plane exposure of support vitally affects the catalytic performance of the catalyst. In this work, CeO₂ nanorods ((110) plane exposure), nano-octahedrons ((111) plane exposure) and nano-cubes ((100) plane exposure) were prepared as the supports of Pt/CeO₂ samples to investigate the effect of CeO₂ plane exposure on total toluene oxidation. Characterizations reveal that the (110) plane of CeO₂ is more helpful to the dispersion of Pt species, followed by (111) face. The improved dispersion of Pt species can enhance the metal-supports interaction, which promotes the electron transfer of CeO₂ carrier to Pt nanoparticles and the adsorption-activation of O₂, thereby facilitating the total oxidation of toluene via the Langmuir–Hinshelwood (L-H) mechanism. Therefore, Pt/CeO₂-r (nanorods) sample expresses excellent catalytic performance of toluene oxidation. Finally, the procedure of toluene total oxidation was studied by in-situ diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy. We expect that this work can contribute to the development of an effective sample for the decomposition of volatile organic compounds (VOCs).     

Synthesis of CeO_2/fly ash cenospheres composites as novel photocatalysts by modified pyrolysis process

A novel fly ash cenospheres(FACs)-supported CeO2 composite(CeO2/FACs) was successfully synthesized by the modified pyrolysis process.The prepared composites were characterized by X-ray diffraction(XRD), scanning electron microscopy(SEM), X-ray photoelectron spectroscopy(XPS), and diffuse reflection spectra(DRS) techniques.XRD results indicated that the CeO2 film coated on cenospheres was a face-centered cubic structure.SEM images confirmed that the CeO2 film was relatively compact.XPS results showed that Ce was present as both Ce4+ and Ce3+ oxidation states in CeO2 film coated on FACs substrate.The bandgap of the composite was narrower compared with the pure CeO2.The as-prepared material exhibited good photocatalytic activity for the decolorization of methylene blue(MB) under visible light irradiation, and the first-order reaction rate constant(k) of 0.0028 min–1 for CeO2/FACs composite was higher than 0.0015 min–1 of pure CeO2.The fact that they floated on water meant that CeO2/FACs composites were easily recovered from water by filtration after the reaction.The recycling test revealed that the composites were quite stable during the MB photocatalytic decolorization.The CeO2/ FACs catalyst was therefore promising for practical use in the degradation of pollutants or water cleanup.     

Structure and chemical states of highly eptiaxial CeO2（001） films grown on SrTiO_3 substrate by laser molecular beam epitaxy

Highly epitaxial and pure（001）-oriented CeO2 films were grown on SrTiO3（001） substrates by laser molecular beam epitaxy method without any gas ambient.Layer-by-layer epitaxial growth mode of CeO2 was confirmed by in situ reflection high-energy electron diffraction（RHEED） observations.High-resolution X-ray diffraction（HRXRD） and high-resolution transmission electron microscopy（HRTEM） results indicated the STO（100）//CeO2（100）,STO[100]//CeO2 [110] epitaxial relationship for out-of-plane and in-plane,respectively.The formation mechanism of the epitaxial film was also discussed in the light of a theoretical model.Chemical states of the LMBE ceria films were evaluated and evidences for the existence of Ce3＋and oxygen vacancies were presented.     

The free energy of formation of Ce2O2S and the nonstoichiometry of cerium oxides

The free energy of formation of Ce₂O₂S was determined by equilibrating CeO₂with COCO₂-SO₂ gas mixtures in the temperature range 900 to 1400°C. There was no significant sulfur solubility in cerium oxide and the free energy of formation of Ce₂O₂S was considerably less than previously estimated; it is 12 kcal (50 kJ) lower at 1300°C The oxygen dissociation pressures for the nonstoichiometric cerium oxide was also measured by equilibrating CeO₂ with CO-CO₂ gas mixtures in the temperature range 1000 to 1450°C and oxygen pressures from 10^-6 to 10^-18 atm. The results indicate a very large range of nonstoichiometry from CeO₂ to at least CeO_1.72. The new thermodynamic information was used to estimate the phase equilibria for the Fe-Ce-S-O system. The calculations indicate that for a steel with normal sulfur levels treated with aluminum and rare earth deoxidizers very little Ce₂O₃will form but rather Ce₂O₂S or cerium Sulfides. Also the stability range of Ce₂O₂S is smaller than previously believed.     

Performance of Pd/CeO2-ZrO2-Al2O3 catalyst for motorcycle

The Pd-only catalysts for motorcycle were prepared by impregnating CeO2-ZrO2-Al2O3 and CeO2-ZrO2+Al2O3 with PdCl2 aque-ous solution and characterized by X-ray diffraction (XRD), oxygen storage capacity (OSC) and H2-temperature-programmed reduction (H2-TPR) methods. The XRD result indicated that the CeO2-ZrO2-Al2O3 compound prepared by co-precipitation formed a single solid solu-tion and had good thermal stability, and Pd phase was not observed in all catalysts. The TPR results showed that the reduction temperature of Pd/CeO2-ZrO2-Al2O3 catalyst was lower than that of Pd/CeO2-ZrO2+Al2O3 catalyst whether they were fresh or aged catalysts. The Pd/CeO2-ZrO2-Al2O3 exhibited high three-way catalytic activity at low temperature, high thermal stability, and wide working window, sug-gesting a great potential for applications.     

Optical and electrical conductivity properties of rare earth elements (Sm,Y, La,Er) co-doped CeO2

In this research, un-doped CeO₂ and Ce_0.85La_0.10M_0.05O₂ (M: Sm, Er, Y) compounds were synthesized by hydrothermal method and the multi-functional properties are reported. Oxygen defects were created with the additives of rare earth ions. The electrical and luminescence behaviors of the synthesized compounds were investigated in accord with the types of additives. The synthesized products were characterized by X-ray diffraction (XRD) analysis, Brunauer–Emmett–Teller (BET) measurement, UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM), photoluminescence (PL) spectroscopy and electrochemical impedance spectroscopic (EIS). All synthesized compounds are found to be nano-structured and have cubic phase. The total conductivity of all samples was calculated. Hence, the total conductivity of un-doped CeO₂, Ce_0.85La_0.10Y_0.05O₂, Ce_0.85La_0.10Er_0.05O₂ and Ce_0.85La_0.10Sm_0.05O₂ is found to be 2.07 × 10^?10, 5.70 × 10^?4, 1.0 × 10^?3 and 0.0747 S/cm, respectively. Also, bandgap energy (E_g) of these samples calculated from UV visible absorption spectra is discussed, and the optical results show variation between 3.2 and 2.15 eV. Additionally, the luminescence properties of the compounds were investigated and different emissions occur depending on the additive type. Accordingly, photoluminescent emission spectra of Ce_0.85La_0.10Y_0.05O₂, Ce_0.85La_0.10Er_0.05O₂ and Ce_0.85La_0.10Sm_0.05O₂ phosphors indicate that these phosphors have red, green and orange-red colors, respectively.     

Barrier effect of SiO_2 shell over hollow CeO_2/CuO@SiO_2 catalysts for broadening temperature window of total CO conversion

The hollow inverse CeO_2/CuO@SiO_2 catalysts with different Ce/Cu mass ratios were synthesized by the two-step hydrothermal and incipient wetness impregnation methods,and characterized by multitechnique characterizations,such as SEM,TEM,XRD,H_2-TPR,XPS and N_2 adsorption-desorption techniques.It is found that the hollow shell is composed of CuO and SiO_2,and CeO_2 nanoparticles are coated on the surface of CuO@SiO_2 support.And the CeO_2/CuO@SiO_2 catalyst with the Ce/Cu mass ratios of 1:1 denoted as 1 CeO_2/CuO@SiO_2,which possesses a maximum amount of highly dispersed copper species and medium-sized CuO as well as the highest concentration of oxygen vacancies,exhibits the highest catalytic activity and widest full CO conversion window.The barrier effect of the SiO_2 shell effectively prevents the reduction of CuO species,which broadens temperature window of CO total conversion and enhances CO_2 selectivity above 155℃over the 1 CeO_2/CuO@SiO_2 catalyst in comparison with the CuO-CeO_2 and CeO_2-CuO catalysts.     

Dissolution of alumina particles in CaO-Al2O3-SiO2-MgO slags

Abstract

The dissolution behaviour of alumina particles in CaO-Al₂O₃-SiO₂-MgO slags was studied by confocal scanning laser microscopy. Three different slag systems were investigated to evaluate the effect of changing the MgO content in a high silica tundish slag, and the effect of decreasing the silica content when dissolving the particles in a ladle slag. A particle of 80 mum diameter dissolved in 50 s in a simulated ladle slag but needed 100 s to dissolve in a high silica slag at the same temperature. When the silica content was decreased, a decrease in the alumina particle dissolution time was noted. During dissolution of alumina particles in a slag containing MgO, the alumina particle reacts with the slag to form an MgAlO₄ layer. No reaction layer was observed during the dissolution of alumina particles in slags that did not contain MgO. This work suggests that the dissolution time of large alumina particles is significant, increasing with particle size and with decreased temperature.     

Regulating local coordination environment of rhodium single atoms in Rh/CeO2 catalysts for N2O decomposition

Rh single atom catalysts(SACs) have been insensitively investigated recently due to the maximum utilization efficiency of Rh,one of the most expensive precious metals.Although great efforts have been made in the development and application of Rh SACs,there are few reports on the precise control of the local coordination environment of Rh single sites on CeO₂ and their catalytic performance for N₂O decomposition.Herein,Rh/CeO₂ catalysts with different Rh-O coordin...     

Low-temperature thermocatalytic particulate carbon decomposition via urea solution-combustion derived CeO_2 nanostructures

A facile,one-pot,urea solution combustion route was utilized to synthesize highly catalytic CeO_2 nanostructures.CeO_2 prepared under varying thermal conditions was characterized by electron microscopy,energy dispersive X-ray spectroscopy,X-ray diffraction,X-ray photoelectron spectroscopy,infrared and Raman techniques.As the synthesis temperature is raised from 400 to 1000℃,the crystallite size and dspacing of nanoparticles are observed to reduce while cell parameters remain in the same range.Particle size exhibits an accession from ～20 to ～50 nm along the process.Initial CeO_2 nanoparticles are detected as a composite structure of CeO_2 and graphitic carbon nitride(g-C_3 N_4) produced by the pyrolysis of urea.Concerning the solid carbon particulate oxidation capacity,an outstanding performance is exhibited by CeO_2 synthesized at 800℃ where the oxidation onset temperature is reduced by 27% compared with the others.The superior performance is attributed to the carbon nitride-generated unique CeO_2 nanomorphology consolidating ample reactive sites and facilitated oxygen delivery for a highly efficient thermocatalytic process.Concerning atmospheric pollution mitigation,synthesis of these CeO_2 nanostructures represents a cost effective and convenient abatement technique for carbon particulates in comparison to cost-intensive,environmentally detrimental and noble-metal based techniques.     

Characterization and electrochemical performance of CeO2 and Eu-doped CeO2 films as a manganese redox flow battery component

Hexagonal CeO_2 and Eu-doped CeO_2 nanoparticles were obtained using a facile microwave-hydro thermal method under mild conditions and their application towards manganese redox flow battery component were studied. The structural properties were studied by X-ray diffraction and indicate that samples present a fluorite structure. Raman spectroscopy shows Eu3+ ions substitute Ce~(4+) and generate oxygen vacancies. Electrochemical properties of pure and Eu-doped CeO_2 films deposited at graphite substrates investigated by cyclic voltammetry and galvanostatic charge—discharge indicate that dopant concentration affects the electrochemical properties of CeO_2. The increase in the reversibility redox of electrochemical systems observed is attributed to coexistence of Ce~(4+)/Ce~(3+) redox couple confirmed by XPS.Charge—discharge tests display coulombic and voltage efficiency values of above 80% and 90%, respectively. The obtained specific capacity for Ce_(0.99)Eu_(0.01)O_2(372.49 mAh/g) and pure oxide(334.84 mAh/g)indicates that both samples are promising for application in Mn-batteries.     

Probe into deposition mechanism of double pulse electrodepositing Ni-W-P matrix composite coatings containing CeO2 and SiO2 nano-particles

Ni-W-P matrix composite coatings reinforced by CeO₂ and SiO₂ nano-particles were prepared on common carbon steel surface by double pulse electrodeposition and the deposition mechanism was discussed. The results showed that the composite coatings with amorphous structure were obtained as-deposited. The initial growth behavior had alternatives and the nucleation was inhomogeneous because of obvious composition fluctuation. With the pulse deposition time increasing, some pearlite microstructures of the substrate were covered by some deposits and the composition fluctuation disappeared. Forward pulse currents promoted to form a great number of atomic beams composed of Ni, W and P atoms or CeO₂ and SiO₂ nano-particles as the core, which inhabited the growth of atomic beams. Reverse pulse currents eliminated concentration polarization and dissolved some surface boss of atomic beams. The solution of W and P atoms within Ni grains and embedding of CeO₂ and SiO₂ nano-particles within Ni-W-P matrix metal made atomic arrangement disordered. Finally, the atomic beams grew to amorphous small particles.     

CeO2 nanoscale particles: Synthesis,characterization and photocatalytic activity under UVA light irradiation

CeO_2 nanoparticles(NPs) were synthesized in alkaline medium via the homogeneous precipitation method and were subsequently calcined at 80 ℃/24 h(assigned as CeO_2-80) and 500 ℃/2 h(assigned as CeO_2-500). The as-prepared materials and the commercial ceria(assigned as CeO_2-com) were characterized using TGA-MS, XRD, SEM-EDX, UV-vis DRS and IEP techniques. The photocatalytic performances of all obtained photocatalysts were assessed by the degradation of Congo red azo-dye(CR) under UVAlight irradiation at various environmental key factors(e.g., reaction time and calcination temperature).Results reveal that CeO_2 compounds crystalize with cubic phase, CeO_2-500 exhibits smaller crystallite size(9 nm vs 117 nm) than that of bare CeO_2-com. SEM analysis shows that the materials are sphericallike in shape NPs with strong assembly of CeO_2 NPs observed in the CeO_2-500 NPs. EDX analysis confirms the stoichiometry of CeO_2 NPs. UV-vis DRS measurement reveals that, CeO_2-500 NPs exhibits a red-shift of absorption band and a more narrow bandgap(2.6 eV vs 3.20 eV) than that of bare CeO_2-com. On the contrary, Urbach energy of Eu is found to be increased from 0.12 eV(CeO_2-com) to 0.17 eV(CeO_2-500),highlighting an increase of crystalline size and internal microstrain in the CeO_2-500 NPs sample. Zeta potential(IEP) of CeO_2-500 NPs is found to be 7.2. UVA-light-responsive photocatalytic activity is observed with CeO_2-500 NPs at a rate constant of 10×10~(-3) min~(-1), which is four times higher than that of CeO_2-com(K_(app)=2.4×10~(-3) min~(-1)) for the degradation of CR. Pseudo-first-order kinetic model gives the best fit. On the basis of the energy band diagram positions, the enhanced photocatalytic performance of CeO_2-500 nano-catalyst can be ascribed to O_2~-, 'OH and R'~+ as the primary oxidative species involved in the degradation of RC under UVA-light irradiation.     

Preparation of Ce-TiO2/carbon aerogel electrode and its performance in degradation of 4-chlorophenol

Ce-TiO₂/CA (carbon aerogel) electrode was prepared by sol impregnation approach. The XRD (X-ray diffraction) and Raman spectra reveal that the TiO₂ is anatase. The UV–vis diffuse reflectance spectra show that the optical absorption edge for Ce-TiO₂/CA is red-shifted to 535 nm compared with TiO₂/CA. Under visible light irradiation, the photocurrent density increment on Ce-TiO₂/CA is 75 times that on Ce-TiO₂/FTO (fluorine-doped tin oxide). The electrochemical impedance spectroscopy reveals that the conductivity of Ce-TiO₂/CA is much better than the Ce-TiO₂/FTO. Furthermore, the Ce-TiO₂/CA can be used to the highest electrosorptive photodegradation for 4-chlorophenol wastewater degradation, which is ascribed predominantly to the efficient reduction of electron–hole pair recombination in the photocatalysts.