Methylene Blue Removal by Graphene Oxide/Alginate Gel Beads

Abstract

Methylene blue (MB) adsorption capacity in water matrices depends highly on the properties of each component of the adsorption systems. The most important one of these is the physicochemical properties of the adsorbent. A composite gel bead was prepared from graphene oxide (GO) and sodium alginate (SA) through a combination of freeze-drying and cross-linking with calcium chloride. Fundamental adsorption behavior of the gel beads for removal of MB from aqueous solutions has been investigated. The pH had mild influence on the adsorption, while adsorption increased as the adsorbent dosage, initial concentration, and contact time increased. The kinetic adsorption fitted the pseudo second-order and intraparticle diffusion models. The isotherm data followed the Langmuir and Freundlich models. The maximum adsorption capacity from the Langmuir isotherm equation reached 357.14 mg/g. The results of the thermodynamic investigations indicated that the adsorption reactions were spontaneous (ΔG<0, −13.79 kJ/mol), exothermic (ΔH<0, −46.7 kJ/mol). In addition, the adsorption capacity of the regenerated gel beads has little loss until four cycles.