Removal of both anionic and cationic dyes from wastewater using pH-responsive adsorbents of L-lysine molecular-grafted cellulose porous foams

High adsorption efficiency, active to both anionic and cationic dyes and simple desorption are three main challenges of the existed adsorbents for decolorization of the dye-contained wastewaters. Porous foams based on L-lysine (Lys) molecular-grafted cellulose were firstly designed and fabricated to overcome those challenges. Cellulose were grafted with Lys in 1-butyl-3-methylimidazolium chloride (BMIMCl) via a chemical connection resulted from glycidyl methacrylate (GMA). The synthesized cellulose derivative (Cell-g-PGMA-Lys) was regenerated in the morphology of foam by non-solvent induced phase inversion from the BMIMCl-based solutions. The presence of Lys moieties and porous structure of Cell-g-PGMA-Lys were confirmed with a series of instrumental analysis. Both anionic reactive brilliant red X-3B (RBR X-3B) and cationic methylene blue (MB) were effectively adsorbed on and desorbed from Cell-g-PGMA-Lys by adjusting the solution pH value. Cell-g-PGMA-Lys had higher adsorption capacities than most of the reported adsorbents and was easy to separate from the decolorized water. It could be reused many times with little reduction of the adsorption capacity, which remained 86.9% and 92.5% for RBR X-3B and MB respectively after six adsorption-desorption cycles. The isothermal and kinetic adsorption proved that dyes were adsorbed single-layered on Cell-g-PGMA-Lys depending upon the electrostatic interaction between adsorbent and adsorbate.