Sorption behavior of polyvinyl alcohol/bentonite hydrogels for dyes removal

Abstract

Hydrogels seem as possible materials to solve the dyes contamination in water. In this study, polyvinyl alcohol (PVA) based nanocomposite hydrogels having 3 wt.% bentonite were prepared by an innocuous physical crosslinking method. Although it is known the raw clay powder presents a good capability to uptake dyes, its removal after use and posterior reuses are very complicated to be performed. On the other hand, PVA matrix offers the possibility to support the clay, ensuring an easy removal and thus the possibility of conducting reuses. Thus, the aim of this work was to evaluate the performance of a composite hydrogel obtained by the employment of eco-friendly and economical both materials (PVA and bentonite) and method (freezing/thawing) as an efficient dye remover. Specifically, methylene blue (MB) was selected as model dye. The kinetics and the mechanisms involved in the adsorption process were analyzed, and also reuse assays were effectively conducted. The obtained results showed that the nanocomposite hydrogel exhibited improved adsorption capacities in a wide range of MB concentrations, compared with neat PVA hydrogel. The experimental values were correctly modeled by using Freundlich equation. Moreover, the negative values of ∆G indicate that the MB adsorption onto PVA-bent nanocomposite is a favorable process at the considered work temperatures, and the interactions that take place are physisorption ones, such as Van der Waals.