Synthesis and characterization of a high capacity ionic modified hydrogel adsorbent and its application in the removal of Cr(VI) from aqueous solution.

Graphical abstract Highlights • Novel hydrogels were synthesized by anionic and cationic modification. • −COOH and NR 3 ⁺ groups on hydrogels increases Cr(VI) adsorption capacity. • The modified hydrogels had superior maximum adsorption capacity of Cr(VI). • Adsorbents can be easily regenerated for succeeding adsorption cycles. Abstract Two modified hydrogels, CL- g - p AA and CL- g - p DMC, are prepared from hydrogels graft copolymerization with acrylic acid and methacryloxyethyl trimethyl ammonium chloride, respectively. The as prepared samples were characterized by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, Scanning electron microscopy (SEM) and Thermogravimetric (TG). Batch experiments were performed to determine the ability of CL- g - p AA and CL- g - p DMC to remove Cr(VI) from solution. The effect of pH, dosage and co-existing anions on Cr(VI) removal were investigated along with regeneration activity. The adsorption of Cr(VI) decreases with the increase of pH and temperature. The introduction of −COOH and-[N⁺(CH 3) 3 ] (NR 3 ⁺) groups on hydrogels increases Cr(VI) adsorption capacity. Based on cost and actual water considerations the optimum adsorption occurs at pH 5, at a temperature of 298 k, with an adsorbent dose of 0.1 g L⁻¹ and with the contact time 500 min for the Cr (VI) removal. The usual metal ions of natural water would not inhibit the complexion reaction between hydrogels and Cr(VI). The modified hydrogels exhibited adsorption capacities of 85.47 mg g⁻¹ for CL- g - p AA and 105.26 mg g⁻¹ for CL- g - p DMC. The adsorption kinetic studies display adsorption to be the pseudo-second-order rate model. The adsorption isotherms of Cr(VI) on the CL- g - p AA and CL- g - p DMC were well fitted by the Langmuir isotherm equation. The Cr(VI) adsorption is endothermic and the CL- g - p DMC exhibits high regeneration efficiency. From the results, it was concluded that CL- g - p AA and CL- g - p DMC were underlying materials for the separation and preconcentration of Cr(VI) from wastewater. [ABSTRACT FROM AUTHOR]