Synthesis of Iron(III)-Doped Titania Nanoparticles and its Application for Photodegradation of Sulforhodamine-B Pollutant

Iron(III)-doped titania nanoparticles were prepared by modified sol-gel method using titanium (IV) butoxide and inorganic precursor iron(III) nitrate nonahydrate. Spectroscopic measurements show the onset of the band-gap transition to be red-shifted (~λ = 475 nm) to the visible region with increasing iron(III) ion content. Characterizations were preformed by X-ray diffractometry, electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. Photocatalysis experiments were performed with dye pollutant sulforhodamine-B in aqueous environment. Direct photocatalytic effect was observed in the dye degradation experiments when irradiated with visible light into the band gap of the iron(III)-doped titania.     

Colour centers and X ray spectra of potassium halide crystals

Possible correlations of the energy levels arising due to colour centers in a potassium halide crystal with the X-ray absorptions fine structure of potassium ion are discussed. Influence of the inner ionisation on the activation energy of the ions and on the potential surrounding them has been estimated using approximate equations.     

Thickness effect in the X-ray K absorption edge of nickel

Effect of absorber thickness on the X-ray K absorption edge of nickel has been recorded photographically. The extended structures show a variation in their relative intensities. In agreement with the earlier observations of Parratt and Sawada the structures in the immediate neighbourhood of the edge show a decrease in their absorption intensities and the fluctuations following them up to 140 eV. remain unaltered. In addition, it is found that the structures lying beyond 150 eV. from the edge become more pronounced on the increase of absorber thickness.     

Enhanced conductivity and electrical relaxation studies of carbon-coated LiMnPO4 nanorods

Lithium manganese phosphate (LiMnPO₄) nanorods were synthesized using the modified polyol method. Polyvinylpyrrolidone was used as a stabilizer to control the shape and size of LiMnPO₄ nanorods. Resin coating process was used to coat the carbon over the LiMnPO₄ nanorods. X-ray diffraction and Fourier transform infrared spectroscopy results showed the formation of LiMnPO₄ crystalline phase. The TEM image shows a uniform coating of the nano size (2.3 nm) carbon over the surface of LiMnPO₄ nanorods and the EDS spectrum of the carbon-coated LiMnPO₄ nanorods confirming the presence of carbon element along with the other Mn, P, and O elements. Impedance measurements were made on pure and carbon-coated LiMnPO₄ nanorods, and their conductivities were evaluated by analyzing the measured impedance data using the WinFIT software. More than two orders of magnitude of conductivity enhancement was observed in the carbon-coated LiMnPO₄ nanorods compared to pure ones, and the conductivity enhancement may be attributed to the presence of carbon over LiMnPO₄ nanorods. Temperature dependence of conductivity and ac conductivity were calculated using impedance data of pure and carbon-coated LiMnPO₄ nanorods. CR2032 type lithium ion coin cells were fabricated using pure and carbon-coated LiMnPO₄ nanorods and characterized by measuring charge–discharge cycles between 2.9 and 4.5 V at room temperature. More than 25 % of improved capacity was achieved in the carbon-coated LiMnPO₄ nanorods when compared to pure ones synthesized using modified polyol and resin coating processes.     

LIMIT CYCLES OF A GENERALIZED LINARD DIFFERENTIAL EQUATION VIA AVERAGING THEORY

We apply the averaging theory of first and second orders to a generalized Liénard differential equation to study the maximum number of limit cycles of the system.     

Solid-state electrochemical synthesis of ammonia: a review

Ammonia is one of the most produced chemicals worldwide, and it is not only a major end product but also an important energy storage intermediate. The solid-state electrochemical synthesis of ammonia has the promise to overcome the limitations of the conventional catalytic reactors such as the limited conversion, severe environmental pollution and high energy consumption. Solid-state electrolytes either protonic or oxide ion conductors have been reviewed and particular emphasis is placed on their application to synthesise ammonia. The highest rate of ammonia formation according to the type of electrolyte utilised were in the following order; solid polymers > Ce_0.8Gd_0.2O_2−δ-(Ca₃(PO₄)₂-K₃PO₄) composites > fluorites > perovskites > pyrochlores although the catalysts in electrodes also play an important role. The highest rate reported so far is found to be 1.13 × 10⁻⁸ mol s⁻¹ cm⁻² at 80 °C with a potential of 2 V using Nafion membrane, SmFe_0.7Cu_0.1Ni_0.2O₃ (SFCN), and Ni-Ce_0.8Sm_0.2O_2−δ as solid electrolyte, cathode and anode, respectively. Synthesising ammonia from steam and N₂, by-passing H₂ stage offers many advantages such as reduction of device numbers and then the overall costs. The factors affecting the rate of ammonia formation have been discussed as well.     

Cristallisation par onde acoustique : le cas de l'héliumCrystallization by acoustic waves: the case of helium

We establish a theoretical model to explain the nucleation of a crystal of helium by an acoustic over-pressure. We explain the interfacial laws for this ultra-fast cristallization, close to the sound speed. Assuming spherical symmetry and taking into account the experimental data, we recover the dynamics of the growth and melting during an over-pressure impulse. To cite this article: M. Ben Amar et al., C. R. Mecanique 331 (2003).