Synthesis, characterization and adsorption of cationic dyes by CS/P(AMPS-co-AM) hydrogel initiated by glow-discharge-electrolysis plasma

In this work, a novel chitosan/P(2-acrylamido-2-methyl-1-propanesulfonic acid-co-acrylic amide) (CS/P(AMPS-co-AM)) hydrogel was successfully prepared by a simple one-step method using glow-discharge-electrolysis plasma (GDEP) initiated copolymerization, in which N,N'-methylenebisacrylamide was used as a cross-linking agent. A copolymerization mechanism of AMPS and AM onto CS initiated by GDEP was proposed. The structure, thermal stability and morphology of CS/P(AMPS-co-AM) hydrogel were characterized by Fourier transform infrared (FTIR), X-ray diffraction (XRD), TG/DTG, and scanning electron microscope (SEM). This hydrogel was employed as an absorbent for the removal of methylene blue (MB) and malachite green (MG) from aqueous solutions. The effects of pH, contact time and equilibrium concentration on the dye adsorption were investigated batchwise. FTIR and XRD indicated that AM and AMPS were grafted onto the CS backbone successfully, forming copolymer. TG/DTG suggested that grafted AMPS and AM onto CS could change the thermal stability of the CS. SEM showed a unique three-dimensional porous structure for the CS/P(AMPS-co-AM) hydrogel. The optimum pH for the removal of cationic dyes was 5.8, and time of adsorption equilibrium was achieved in 90 min. The CS/P(AMPS-co-AM) hydrogel exhibited a very high adsorption potential, and its adsorption capacities calculated based on the Langmuir isotherm for MB and MG were 1,538.5 and 917.4 mg g(-1), respectively. The dye adsorption data fitted well to the pseudo-second-order model and Langmuir model at 25 degrees C with pH 5.8.