Papers by Keyword: Ceria

Abstract: The Chemical Mechanical Planarization (CMP) process (polishing and substrate cleaning) results in defects that can be classified as mechanical (i.e., scratching), chemical (i.e., corrosion), or physiochemical (i.e., adsorbed contaminants) according to the mechanism of formation. This work will focus on the rationale design of p-CMP cleaning systems for emerging materials (silicon carbide (SiC)) that activate the cleaning chemistry via external stimuli such as megasonic energy. More specifically, using megasonic energy in the presence of supramolecular assemblies such as micelles and vesicles was employed for a “soft” (low shear force) defect removal process. Results indicate a correlation between the structure of the “soft” cleaning additives and induced megasonic energy on overall simulated defect removal. It was determined that effective particle removal was a second-order kinetic process with a concentration dependency (i.e. above and below the critical micelle concentration (CMC)) emerging as a key driver for the defect removal rate. Although, one apparent drawback is the generation of post-cleaning carbon residue due to the adsorption of the supramolecular structures to the SiC substrate.

Abstract: In this paper, we have studied the EPR spectra, X-ray diffraction and Raman Analysis, Microstructures-morphology of the Ceria NPs calcined at different temperatures of 700 °C, 850 °C ,these materials have been synthesized by Co precipitation (CPT) method by using Cerium tri-nitrate hexahydrate and potassium carbonate solutions. Then synthesized precipitate was heated at 70 °C for 20 hour. Slow grinding of the precipitate and calcined for 3 hours at different temperatures viz. 700 °C and 850 °C to form fine Cerium oxide powder-Ceria NPs. The EPR measurements were made using continuous wave spectrometer (X-band, Bruker Biospin EMX Plus). The g values were obtained by using diphynelpirichylhydrageyl (DPPH-C₁₈H₁₂N₅O₆) sample and got g value is around 1.97. This g tensor is decreased when the calcined temperature are increased, EPR parameters are also changed as the calcined temperature increases. When the calcined temperature is increased from 700 °C to 850 °C, a doublet separated, intensity increased. The X-Ray diffraction pattern shows the nature of the Ceria NPs crystal, with a cubic structure and got the lattice parameters 5.392 Å for samples calcined at temperature of 700 °C and 5.357 Å at 850 °C which shows decreasing trend in lattice parameter with calcination temperature. The intensity of Raman peaks is also shifted upwards with a rise in temperature. This intensity difference could be because of the rise in vibrational amplitudes of the closest neighboring bonds because of the increase in particle size 11.3± 1.0 to 15.6± 1.0 nm at calcination temperatures of 700 °C and 850 °C and the Raman peak of peak I, 461 cm^-1 and peak II, 463 cm^-1 respectively. Other peaks were not observed in this Raman pattern. The EDS analysis confirms the presence of the Ce and O atoms in the synthesized samples. Spherical shapes and homogeneously distributed Ceria NPs and a rather tendency for agglomeration were confirmed.

Abstract: This study explored adsorptive property of ceria nanocrystal as an adsorbent for amoxicillin removal from water. Ceria nanocrystal was synthesized by employing precipitation method and characterized by using XRD and N₂ adsorption-desorption analysis. The adsorption experiment was performed by managing amoxicillin in natural condition. Then, parameters in the adsorption experiment, such as adsorbent dosage, contact time, temperature and initial concentration of amoxicillin are varied. The XRD pattern illustrated that the average crystallite size of ceria nanocrystal formation was 13.08 nm. N₂ adsorption-desorption analysis showed that ceria nanocrystal was mesoporous with specific surface area of ​​65.26 m²/g. The amoxicillin adsorption of ceria nanocrystal adsorbent was described by Langmuir isotherm model with maximum adsorption capacity of 37.17 mg/g. The adsorption kinetic of ceria nanocrystal corresponded to the pseudo-second order model. Removal efficiency of amoxicillin by ceria nanocrystal was approximately 80% within 60 minutes over temperature range 303-323K. Those parameter results are described that ceria nanocrystal adsorbent is feasible as a rapid amoxicillin removal from water.

Abstract: A Cerium (IV) oxide nanoparticle (nanoceria) is widely used in different applications such as biomedicine and catalysis due to its unique structural, morphological and catalytic properties. In this report, the dispersion of nanoceria in both aqueous and non-aqueous (methanol and ethanol) media were studied. Adsorption-desorption processes were observed upon addition of different classes of surfactants such as citric acid (CA), cetrimonium bromide (CTAB) and diethanolamine (DEA). Stable dispersions were obtained in both aqueous, non-aqueous and electrolyte assisted media with the overall mechanism being hydrolysis, dissolution and adsorption. XRD, FE-SEM, FTIR and DLS have been used in the present study to characterize the nanoceria and to quantitatively analyze their average particle size distributions in a unique electrolyte mixture of (0.1 M NaOH/ 65% HNO₃:H₂O, 1:1 v/v) which has not been reported previously. The surface charge study was carried out across a wide pH range between 1.4 – 9.6 and the isoelectric points (IEP) with respect to 15 ml H₂O and 50 ml H₂O dispersed phases occurred at a pH of about 6.5 and 6.7 respectively. The present study could be useful in a wide range of applications including nanoparticle synthesis, stabilization, and adsorption of toxic materials, biomedical and pharmaceutical.

Abstract: CeO₂ nanoparticles were synthesized through the solvothermal process. It is observed that the water/ethanol mixed solvents were strongly influenced on the agglomeration. The average size of CeO2 nanoparticles was about in the range of 11-13nm and its distribution was narrow. With the increase of the ethanol composition, the surface area of CeO₂ was increased from 65.384m²/g to 84.649m²/g. The synthesized nanoparticles components, particle size, morphology and surface area were characterized by EDS, XRD, FE-SEM, FE-TEM and BET.

Abstract: In this study, α-Al₂O₃-CeO₂ core-shell nanoparticles were synthesized from the cerium acetate and the commercial α-Al₂O₃ nanoparticles as the starting materials via a wet chemical method. Poly (acrylic acid) (PAA) as an additive compound was used for the surface modification of alumina nanoparticles. Also, the effects of PAA content, pH value and calcination temperature on the synthesis behavior of α-Al₂O₃-CeO₂ nanoparticles were investigated. The formation of core-shell structure was investigated using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FE-SEM) equipped with energy dispersive X-ray spectroscopy (EDS). The results indicated that at the PAA=1.5 wt. %, pH=6 and calcination temperature=1150°C (as optimal conditions), the core-shell nanoparticles with alumina core and ceria shell and homogeneous size distribution were synthesized successfully.

Abstract: The high interest in the synthesis of mesoporous catalyst demands that novel materials are developed with simple methods capable of improving process yields. In this work, a novel heterogeneous mesoporous catalyst support has been synthesized using mesoporous SBA-15 loaded with mixed bimetal oxides of CeO₂ and MgO. Formation of the SBA-15 was actuated in air at room temperature (25°C) and in oven conditions at 100°C after which cerium nitrate and magnesium nitrate precursors were then impregnated into the SBA-15 framework and calcined at 550°C for each of the air and oven crystallization processes. XRD peak patterns confirmed SBA-15 formation and dispersion of nanocrystallites of CeO₂ and MgO within the porous framework of SBA-15. Both the air and oven dried processes produced mesoporous MgO-CeO₂/SBA-15 catalysts with isotherms that exhibit typical H1 type hysteresis confirming that they possess open-ended cylindrical mesopores. The structural data extracted gave average pore size, pore volume and surface area values in the ranges of 3-5.2 nm, 0.600-2.500 cc/g and 400-500 m²/g respectively which is ideal for several industrial applications.

Abstract: The reduction of pure WO₃ and Ce/WO₃ has been studied by using temperature programmed reduction (TPR), X-ray diffraction (XRD), and FESEM analysis. The reduction behavior were examined by non-isothermal reduction up to 900 oC then continued with isothermal reduction at 900 oC for 45 min under (40% v/v) carbon monoxide in nitrogen (CO in N₂) atmosphere. The TPR results shows that reduction peak of Ce/WO₃ were shifts to lower temperature as compared with to the pure WO₃. In addition, TPR results indicate that addition with ceria give better reducibility compared to pure WO₃. Based on the characterization of the reduction products after hold 45 min using XRD, pure WO₃ were completely converted to WO₂ and W metal phases. While, after addition of Ce to the WO₃, the reduction was enhanced to W phases and some suboxide W₅O₁₄ and W₃O₅ with no WO₂ phase remained and carbide observed. This is associated to the formation of alloy complex Ce₂WO₆ which gave remarkable effect to the reduction.

Abstract: A multi-scale method was developed, which utilized intrinsic relationships among zeta potential of particles, rheological properties of suspensions and particle size distribution (PSD), to analyze dispersion behavior of nanoparticles in concentrated suspensions. It was found that PSD of a kind of nanoceria particles by dynamic light scattering (DLS) method in solution A with concentration 5 wt% accorded well with that by direct TEM analysis, which meant the particles had been dispersed well. However, there had a significant difference when the concentration was increased to 20 wt%. When particles concentration increased from 5 wt% to 20 wt%, zeta potential in solution A changed from-150 mV to-100 mV, while zeta potential in solution B changed from-35mV to-45 mV. Variations of zeta potential of particles accorded well with rheological properties of suspensions too, from phenomenological models. When the suspensions composed by solution A and the nanoparticles with concentration about 20 wt% was diluted with its original solution to 5 wt%, the PSD of nanoceria could be measured indirectly, which accorded well with both that of a suspension prepared directly with near concentration and that from TEM images. Then a method to measure PSD of nanoparticles in concentrated suspension was brought forward.

Abstract: A novel process was developed to obtain high content of ceria powder directly from bastnasite mineral. The bastnasite was roasted with NaHCO₃ at 550 oC for 2 h, washed with water and dilute HCl respectively to remove impurities, and finally calcined in air. TG-DTA, XRD, XRF, SEM was used to characterize the decomposition process of bastnasite, crystalline phase, the chemical composition, and morphology of the product. The results showed that the concentration of HCl solution was the most important factor in the leaching process, and the calcining temperature of bastnasite mineral should be controlled below 600 oC. The optimal technological parameters were suggested as follows: leaching temperature at 45 oC, for 45min in 3 mol/L HCl, with the weight ratio of solid to liquid of 1:5, and the calcining of the leachate at 600 oC for 2 h. And the high content of ceria (T_REO > 80wt %, Ceria/T_REO > 85wt %) nanosized (20~100 nm) powder was obtained succeffully, which showed potential application in polishing materials.