Methylene Blue Sorption Phenomena onto Pectin, Brea Gum, Montmorillonite Based Hydrogels: Kinetic and Thermodynamic Assessment

Abstract

The wastewater treatment, particularly the removal of organic contaminants, is often carried out by adsorption with solids. Hydrogels present a great swelling capacity that can be enhanced by the incorporation of nano-clays such as montmorillonita (Mt). Methylene blue is a common component of industrial effluents and its ecotoxicity in well-known. The aim of this work was to evaluate the adsorption capacity of hydrogels based on pectin and brea gum with Mt nanoparticles. The hydrogels were physically characterized, it was observed that Mt is exfoliated into the matrix, and affects the swelling and erosion of them. Incorporation of Mt caused an increment of swelling of approximately 150% at pH 6.5. The effects of various experimental parameters have been investigated. The temperature effect on the adsorption rate indicated an endothermic process with activation energy of 33.231 kJ mol−1. The removal % of MB at 45 °C, pH 2.5 and 75 mg L−1 of MB solution presented a value of 97%. The adsorption kinetic was analysed through different mathematical models (pseudo-first order, pseudo-second order, intra-particle, and Boyd models). Statistics and further analysis of the kinetics constants indicated that the pseudo-second order model better represents the behaviour of the samples. The application of intra particle model and Boyd model indicates that the adsorption phenomenon occurs in two stages. The first stage, of short duration, is related to the boundary layer. The second stage, which controls the process, is related to the chemical adsorption of the dye on the polymeric structure of the hydrogel.