Removal of organic dyes and metal ions by cross-linked graft copolymers of cellulose obtained from the agricultural residue

Abstract

Cellulose extracted from agricultural residue, rice husk was functionalized through free radical grafting with a binary vinyl monomer mixture of 2-acrylamido-2-methylpropane sulfonic acid and acrylic acid in the presence of N,N'-methylene bisacrylamide cross-linker. To ascertain the grafting, the synthesized copolymer, Cell-g-AASO3H-co-AAc was characterized by FESEM, FTIR, XRD and thermal analytical techniques. The swelling behavior of the grafted copolymer, analyzed as a function of pH followed the order 7.0 > 9.4 > 2.2. The as-synthesized graft copolymer was used as an adsorbent for the removal of model malachite green, crystal violet, congo red dyes and Ni(II) and Cu(II) metal ions from aqueous solutions. The adsorption characteristics of the grafted copolymer were studied as a function of contact time, temperature, pH, and concentration. Cationic dyes were adsorbed maximum at pH 7.0 in 90 min contact time, whereas anionic dye was removed under acidic pH of 2.2 in 8 h. Maximum adsorption of Ni(II) and Cu(II) ions was observed at pH 6.0 and temperature of 30 °C after a contact time of 120 min. Among the various kinetic and adsorption isotherm models, the experimental adsorption data were best fitted in pseudo-second-order kinetic model and Langmuir isotherm model for organic dyes and metal ions. From Langmuir adsorption isotherm, maximum sorption capacities of 112.74 and 109.77 mg/g was reported for Ni(II) and Cu(II) ions, respectively. The current study thus proves that the Cell-g-AASO3H-co-AAc copolymer can efficiently be used as an adsorbent for uptake of harmful cationic as well as anionic dyes and toxic metal ions from industrial wastewater.