Search

Direct contact membrane distillation (DCMD) process was applied for the treatment of textile dyes solutions using a flat-sheet polyvinylidene fluoride (PVDF) membrane. Both cationic (Maxilon Blue 5G, Drimarene Yellow K-2R) and anionic (Sodium Fluorescein) dyes have been considered. A model-type of a textile wastewater solution containing salts and the three cited dyes have also been tested to simulate real discharges of textile industries. The effects of DCMD operating parameters on the permeate flux and separation factor have been studied. Fouling phenomenon on both the membrane surface and in its pores was investigated by means of various characterization techniques and the permeate flux reduction factor together with the irreversible fouling index were determined. Different fouling mechanisms in DCMD could be established for each type of dye.

3 ABSTRACT: In this work, the decolorization of Methyl Orange was conducted using catalysts prepared by impregnation of copper on natural clay in the presence of H2O2. The catalysts Cu-clay, prepared from the concentrated metal precursor of (impregnation ratio, W(Cu(NO3)2)/W(clay) = 1,5%-7,5%) were characterized by several methods such as X-ray diffraction (XRD), electronic scan microscopy (SEM), x-ray fluorescence (FX), and Brunauer-Emmett- Teller (BET). Important factors affecting catalyst activity and methyl orange removal efficiencies were studied: the effects of temperature, oxidant concentration, and catalyst dosage. The results showed, a very significant activation of hydrogen peroxide by the catalyst, the Methyl Orange depletion percentage reaching 94 % after 2 h, and very stability of the catalyst. It was also observed that the best catalyst, at a reaction temperature of 25°C. 2,5ml of H2O2 and 4.0 g/L of 5% Cu-clay, 94% decolorization was achieved within 120 min treatment. Although the Cu show high activity, their stability and reusability still need improvement.

The properties of polarons and bipolarons are studied by the variational method taking into account the density of state for Van Hove singularity (V.H.S) in two-dimension (2D) in the presence of a perpendicular magnetic field. It should be noticed that the bipolaron stability region is relatively sensitive to the application of a magnetic field. In 2D, for ωc = 0.8 the value of αc = 1 is compared to αc = 1.6 for ωc = 0. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The impurity binding energy in the absence and in the presence of honfined LO-phonon interaction in a cubic quantum dot for several values of the mass ratio λ and for several heights of the barrier has been calculated using a variational approach. The quantum confinement is described by a finite potential well. The charge carrier (electron and ion)-phonon coupling is treated within the adiabatic approximation. The results show that this effect increases, reaches a peak value and then decreases as the dot size increases and depends strongly on the impurity position. The confined LO-phonon effect decreases by displacing the impurity from the center to the dot boundary.

The ion exchange of hydrogenophosphate ion in Zn–Al–chloride layered double hydroxides was investigated. The chloride precursors prepared by coprecipitation at pH 10 preserved their lamellar structure following ion exchange. It was found that the aging time is important in controlling the crystallization of the phosphate-exchanged compounds; long aging times of more than 8 h lead to poorly crystallized phases. The grafting of the anion onto hydroxylated sheets by moderate thermal treatment was confirmed by a combination of several techniques, including powder X-ray diffraction (XRD), infrared (IR) spectroscopy, and thermal analyses.

The ion exchange of chloride by hydrogenophosphate in the [Zn–Al–Cl] layered double hydroxide was investigated by using X-ray diffraction and infrared spectroscopy. The effects of [Zn2+/[AI3+] ratio in [Zn–Al–Cl], anion concentration in the solution, aging time and temperature of the solution on the ion exchange were studied. The best sample in terms of crystallinity and extent of ion exchange was obtained by carrying out the exchange reaction at 25°C in a 0.01 M HPO42− solution at pH 8 with at least 5 h of aging time. A sample prepared under these conditions was further characterized by X-ray microanalysis.

Summary The synthesis of zinc-chromium Lamellar Double Hydroxides (LDHs) intercalated by sulfate anions was carried out using three synthetic methods. The combination of coprecipitation and anionic exchange in one stage allows to prepare the well organised [Zn-Cr-SO 4 ] LDHs. Depending on pH conditions and washing process the sulfate intercalated LDH exhibits two 2H hexagonal varieties with different layer spacings d≈8.9A and d≈HA at room temperature; this latter with superstructure was related to the insertion of the alkaline interlamellar cations.

The synthesis of zinc–chromium lamellar double hydroxides (LDHs) intercalated by sulfate anions is carried out with a one-step method that combines coprecipitation and anionic exchange. The materials obtained in a reactor containing a sodium sulfate solution are compared with those prepared from lithium, potassium, and ammonium sulfate solutions. The compounds are characterized by chemical analysis, powder X-ray diffraction, and infra-red spectroscopy. Depending on pH conditions, the washing process, and the nature of the monovalent cation, the sulfate intercalated compounds exhibit two 2H hexagonal varieties with different layer spacings d ≈8.9 A and d ≈11 A at room temperature; this last phase is related to the insertion of alkaline interlamellar cations. Under dry air, the loss of intercalated water leads to a 3R rhombohedral variety with d ≈8.2 A. A second rhombohedral variety with d ≈10.9 A is reversibly obtained from the “8.9 A” phase under high relative humidity. These four [Zn–Cr–SO 4 ] LDHs differ by their stacking sequences and interlamellar distances and can be selectively obtained.

Thin films of lead titanate were prepared in-situ using radio-frequency magnetron sputter-deposition. The in-situ perovskite phase formation has been studied as a function of the substrate material, the substrate temperature (TS) and the sputtered lead flux. The incident lead flux is controlled by the lead content in the target (X). Perovskite phase can be obtained under a relatively wide range of sputtering conditions with control of the Pb content in the film. The formation temperature of the perovskite phase increased when the incident Pb flux increased. With an appropriate combination of TS and X, it is possible to grow, at relatively low temperature, stoichiometric thin films compatible with semi-conductor substrates. For example, PbTiO3 films have been deposited on silicon and gallium arsenide substrates at 440°C; these films present ferroelectric properties.