Study of the adsorption of an organic pollutant onto a microporous metal organic framework.

In this study, the microporous metal organic framework-5 (MOF-5) has been synthesized to be used to remove methyl orange by adsorption. The adsorption experiments exhibit a good adsorption capacity at a catalyst dose of 0.1 g L-1 and for an initial concentration of 200 mg L-1, whereas the performance is stable over a wide pH range. The equilibrium adsorption data showed a sigmoidal course, which is well fitted by the Dubinin-Astakhov model applicable for physical adsorption processes (E = 0.055 kJ mol-1) onto heterogeneous surfaces and a more homogeneous pore structure (n = 9.9), with a maximum adsorption capacity of 1248.35 mg g-1. As can be observed from the evaluation of the kinetic data, the surface of the adsorbent is heterogeneous with different active sites for methyl orange (MO) adsorption. Moreover, based on the rate constant, it can be suggested that there is a specific interaction like electrostatic interaction between MO and the adsorbent for rapid and high uptake of the dye, whereas the adsorption phenomenon is reversible. According to the adsorption mechanisms, intra-particle and film diffusion models simultaneously controlled the rate sorption, which was confirmed by the calculated intra-particle diffusion and the film diffusion coefficients. The evaluation of the thermodynamic parameters revealed that the MO adsorption is spontaneous, endothermic and the randomness increases with the adsorption of MO.

Modeling biosorption of Cr(VI) onto Ulva compressa L. from aqueous solutions.

The marine biomass Ulva compressa L. (ECL) was used as a low-cost biosorbent for the removal of Cr(VI) from contaminated aqueous solutions. The operating variables were optimized: pH ∼ 2, initial concentration of 25 mg/L, solid/liquid ratio of 6 g/L and a temperature of 50 °C, leading to an uptake elimination of 96%. A full factorial experimental design technique enabled us to obtain a mathematical model describing the Cr(VI) biosorption and to study the main effects and interactions among operational parameters. The equilibrium isotherm was analyzed by the Langmuir, Freundlich and Dubinin-Radushkevich (D-R) models; it has been found that the adsorption process follows well the Langmuir model. Kinetic studies showed that the pseudo-second order model describes suitably the experimental data. The thermodynamic parameters indicated an endothermic heat and a spontaneity of the Cr(VI) biosorption onto ECL.