Adsorption of Congo Red from Aqueous Solutions by Alginate-Nanocellulose-Polyethyleneimine Hydrogel Beads.

Biobased adsorbents have been developed for the removal of dye contaminants in aqueous solution. Hydrogel beads from alginate containing TEMPO-oxidized cellulose nanofibers (TOCNF) grafted with polyethyleneimine (PEI), namely Al/TOCNF-PEI, were prepared and evaluated as a new adsorbent for Congo Red (CR). The Al/TOCNF-PEI hydrogel beads were made with various concentrations of TOCNF/PEI, the optimum concentration is 45 wt% or Al/TOCNF-PEI45. The hydrogel was characterized by using Fourier-Transform Infrared spectroscopy and Scanning Electron Microscopy. The adsorption performance of the Al/TOCNF-PEI hydrogel beads towards CR was investigated in terms of changing of TOCNF-PEI content, initial concentration, pH, contact time, and adsorbent dosage. The maximum capacity of the adsorbent for CR was found to be 9.437 mg/g at the optimal conditions (pH = 3; T = RT) with the removal efficiency reaching 95 %. This result was ascribed to occur due to the electrostatic attraction between the protonated hydroxyl group and ammonium moiety of the hydrogel beads and the anionic sulfonate group of the CR. Upon fitting the adsorption data, the adsorption mechanism was consistent with the Freundlich isotherm and pseudo-second-order kinetic models. Based on this finding, the low-cost Al/TOCNF-PEI45 hydrogel beads demonstrated a great potential for the removal of hazardous dyes in wastewater. [ABSTRACT FROM AUTHOR]