Hydrothermal Synthesis of CeO2 and Ce0.9Fe0.1O2 Nanocrystals

Pure and 10 mol% Fe3+ doped CeO2 nanocrystals were synthesized by hydrothermal method using two different basic solutions (NH4OH and NaOH). All the samples were calcinated at 140 degrees C and 200 degrees C. The characterization of crystalline structure, vibrational and optical properties was performed using X-ray diffraction, Raman spectroscopy and spectroscopic ellipsometry. The obtained results showed that the Fe-doped samples are solid solutions with different size of nanocrystals, very dependent on the synthesis temperature and type of basic solution. The Raman measurements demonstrated electron molecular vibrational coupling and increase of oxygen vacancy concentration whereas doping provokes a small decrease of optical absorption edge in comparison with pure ceria.International School and Conference on Photonics (PHOTONICA09), Aug 24-28, 2009, Belgrade, Serbi

Effect of Fe2+ (Fe3+) Doping on Structural Properties of CeO2 Nanocrystals

We have measured the Raman scattering and magnetization of pure and Fe2+(Fe3+) doped CeO2 nanopowders at room temperature. The Raman scattering spectra revealed the existence of CeO2 fluorite cubic structure for all investigated samples. The Raman active mode at about 600 cm(-1), seen in all samples, can be ascribed to the CeO2 intrinsic oxygen vacancies. Additional Raman modes at 720 cm(-1), 1320 cm(-1) and 1600 cm(-1), which appear in the spectra of doped samples, can be assigned to maghemite (gamma-Fe2O3) cation deficient structure, to 2 omega(LO) IR-allowed overtone and two magnon structure, respectively. This implies that our powders are composed of mixed valence states and have defective structure. Presence of oxygen defect states and magnetic ions can be responsible for the observed ferromagnetism at room temperature in both pure and Fe doped samples.Symposium on Raman Scattering in Materials Science, Sep 15-19, 2008, Warsaw, Polan

Infrared study of laser synthesized anatase TiO2 nanopowders

Nanosized titanium dioxide (TiO2) is synthesized by laser-induced pyrolysis using titanium isopropoxide as a liquid precursor. The specific surface area of as-produced nanopowders measured by the Brunauer-Emmett-Teller method (BET) varies from 84 to 110 m(2)g(-1). X-ray diffraction (XRD) and Raman scattering, showed that the TiO2 nanocrystals had an anatase structure. The rain size of the nanoparticles was estimated from scanning electron microscopy, XRD and BET measurements. The reflection spectra of nanocrystalline TiO2 pressed pellets has been measured in the region between 80 and 1500 cm(-1) by Fourier transform infrared spectroscopy. To interpret the experimental results, a model based on a generalized Bruggeman effective medium approximation of a dielectric function has been proposed. It is based on the polycrystalline character of TIO2 nanoparticles including island-structure and porosity of the nanopowders, along with the anatase single crystal dielectric functions. Thus, by comparing the results of calculated and experimental infrared (IR) spectra, the values of microscopic parameters of nanocrystalline powders can be deduced

The size and strain effects on the Raman spectra of Ce1-xNdxO2-delta (0 LT = x LT = 0.25) nanopowders

Ultrafine Ce1-xNdxO2-delta (x = 0-0.25) powders were synthesized by self-propagating room temperature synthesis. Raman spectra were measured at room temperature in the 300-700 cm(-1) spectral range. The shift and asymmetric broadening of the Raman F-2g mode at about 454 cm(-1) in pure and doped ceria samples could be explained with combined size and inhomogenous strain effects. Increased concentration of O2- vacancies with doping is followed by an appearance of new Raman feature at about 545 cm(-1). (c) 2005 Elsevier Ltd. All rights reserved

Ce1-xY(Nd)(x)O2-delta nanopowders: potential materials for intermediate temperature solid oxide fuel cells

Nanopowdered solid solution Ce1-xY(Nd)(x)O2-delta samples ( 0.1 LT = x LT = 0.25) were made by self-propagating room temperature (SPRT) synthesis. The first-order Raman spectra of Ce1-xY(Nd)(x)O2-delta samples measured at room temperature exhibit three broad features: the main Raman active F-2g mode at about 450 cm(-1) and two broad features at about 550 (545) and 600 cm-1. The mode at similar to 600 cm(-1) was assigned to the intrinsic oxygen vacancies due to the nonstoichiometry of ceria nanopowders. The mode at about 550 (545) cm(-1) was attributed to the oxygen vacancies introduced into the ceria lattice whenever Ce4+ ions are replaced with trivalent cations (Y3+, Nd3+). The intensity of this mode increases with doping in both series of samples, indicating a change of O2- vacancy concentration. The mode frequency shifts in opposite direction in Y- and Nd-doped samples with doping level, suggesting that different types of defect space can occur in Y- and Nd-doped ceria nanopowders.International School and Workshop on Nanoscience and Nanotechnology, Nov 14-16, 2005, Monte Porzio Catone, Ital

Photocatalytic degradation of metoprolol in water suspension of TiO2 nanopowders prepared using sol-gel route

Nanocrystalline titanium dioxide (TiO2) powders have been synthesized by sol-gel method using titanium tetrachloride (TiCl4) or tetrabutyl titanate (Ti(OC4H9)(4) as precursors, different alcohols and calcination temperatures in the range from 400 to 650 A degrees C. The photocatalytic activity of as-prepared powders has been tested for the degradation of metoprolol tartrate salt, a selective beta-blocker used to treat a variety of cardiovascular diseases, and compared to photocatalytic activity obtained from Degussa P25. Nanosized TiO2 powders prepared from TiCl4 and amyl-alcohol, calcined at 550 A degrees C, displayed an activity comparable to Degussa P25, whereas the sample from the same series, calcined at 650 A degrees C, showed higher photocatalytic activity in the whole range of the catalyst loading. Structural, morphological and surface properties of synthesized TiO2 nanopowders have been investigated by XRD, SEM, EDS and BET measurements, as well as FTIR and Raman spectroscopy, in order to find out the material properties which enable rapid an efficient decomposition of metoprolol under UV radiation

Improved efficiency of sol-gel synthesized mesoporous anatase nanopowders in photocatalytic degradation of metoprolol

The structural and morphological properties of mesoporous anatase nanopowders, synthesized by sol-gel method, have been modified by varying the duration of calcination, in order to obtain more efficient photocatalyst than Degussa P25 in the degradation of relatively large pollutant molecules ( GT 1 nm in size). According to X-ray diffraction analysis, the crystallite size was increased from 13 to 17.5 nm with the increase of calcination time from 1 to 7 h. The analysis of nitrogen sorption experimental data revealed that all samples were mesoporous, with a mean pore diameters in the range of similar to 5-9 nm. The corrugated pore structure model was employed to evaluate pore structure tortuosity. Nanopowder properties have been related to the photocatalytic activity, tested in the degradation of metoprolol tartrate salt, selective beta(1)-blocker used in a variety of cardiovascular diseases, with molecular size of 0.610 nm x 1.347 nm. The study has demonstrated that samples calcined for 4 and 5 h have displayed higher photocatalytic performance than Degussa P25, whereas the sample calcined for 3 h has shown comparable activity. (C) 2013 Published by Elsevier Ltd

Passivity breakdown of carbon steel in hot potassium carbonate solutions

The original publication can be found at www.springerlink.comThis research studied passivity breakdown of carbon steel in conditions typical of hot potassium carbonate (HPC) acid gas processing plants. The pitting potential, evaluated from polarisation curves, indicated resistance to pitting increased with increasing equivalent carbonate concentration. The pitting potential was much more positive than the free corrosion potential for uninhibited concentrated carbonate solutions with pH values of 8.5 to 9.5. Therefore pitting is not an issue in these solutions. However, the carbon steel was susceptible to pitting corrosion in the dilute 1.0% bicarbonate solution of pH 8.0 for chloride concentrations in excess of 0.5 wt%. The critical chloride concentration was considerably above the maximum concentration of 0.1 wt% recorded in a typical HPC plant. Consequently chlorides should not usually be of concern to plant integrity.S. J. Harjac, A. Atrens, C. J. Moss and V. Linto