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International audienceA native layered double hydroxide Mg–Al–CO3, denominated LDH, containing Mg(II) and Al(III) in the layers, was prepared by a co-precipitation method. Its calcined form Mg–Al, (CLDH), was obtained by calcination at 500°C. Both materials were characterized by powder X-ray diffraction (PXRD), Fourier transformation infrared spectroscopy, thermogravimetric analysis, and the determination of the point of zero charge. The porous structure of the solids was investigated by nitrogen adsorption at 77 K. The adsorptive affinity of these materials for Biebrich Scarlet was studied as a function of dye–adsorbent contact time, initial pH of the solution, initial dye concentration, and temperature. Sorption kinetics data fitted best to a pseudo-second-order model suggesting that the process of BS adsorption is controlled by reaction rate for interaction of dye molecules rather than by diffusion. Equilibrium data for both adsorbents were in accordance with both Sips and Langmuir isotherm models. The sorption capacity of CLDH was found to be almost independent on the initial pH, while sorption capacity of LDH was lower in neutral and alkaline conditions than at acidic pH. The adsorption process was also found to be spontaneous and endothermic in nature. © 2016 Balaban Desalination Publications. All rights reserved

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International audienceThe adsorption of basic dye (i.e. ethyl violet (EV) or basic violet 4) from aq. solns. onto the forest waste non-modified wild carob (NMWC) was carried out by varying some process parameters, such as initial concn., pH, and temp. The exptl. results showed that an increase in the pH from 2 to 7 led to a strong decrease in the adsorption capacity of the dye (EV) on NMWC, showing the predominance of the dispersion forces compared to the electrostatic interactions, owing to the cationic character of the dye and the pHpzc of the biosorbent (∼6). The adsorption process can be well described by means of a pseudo-second-order reaction model showing that boundary layer resistance was not the rate-limiting step, as confirmed by intraparticle diffusion. In addn., exptl. data were accurately expressed by the Sips equation if compared with the Langmuir and Freundlich isotherms. The high "m" values of the Sips model characterized a multilayer adsorption and the max. amt. adsorbed given by the Sips model was 100.4 mg/g at 20°C, namely close to the exptl. value and increased only weakly with the temp. The values of ΔG0 and ΔH0 confirmed that the adsorption of EV on NMWC was spontaneous and endothermic in nature. The pos. values of ΔS0 suggested an irregular increase in the randomness at the NMWC-soln. interface during the adsorption process

The removal of Methylene blue (MB) from aqueous medium using alkaline modified Maclura pomifera (NaOH-MMP) has been studied in this work. Results showed that a pH value of 6 was favorable for the adsorption of MB. Rate constants of pseudo-first-order, pseudo-second-order and nth kinetic model were determined to analyze the dynamic of the adsorption process; they showed that adsorption kinetics followed a pseudo-second-order and nth kinetic models. The Sips isotherm model was found to be the most relevant to describe MB sorption onto NaOH-MMP with a correlation factor R2 > 0.999. The adsorption capacity of NaOH-MMP was found to be 160 mg g−1 at 25 °C, confirming its biosorbent efficiency for the removal of MB dye from aqueous solutions. Thermodynamic parameters indicated that the MB adsorption onto adsorbent was feasible in nature, spontaneous, and exothermique.