Preparation and adsorption properties of a novel superabsorbent based on multiwalled carbon nanotubes-xylan composite and poly(methacrylic acid) for methylene blue from aqueous solution.

A novel superabsorbent was prepared by the copolymerization reaction between multiwalled carbon nanotubes (MWCNTs)-xylan composite and poly(methacrylic acid) (PMAA) in the presence of N,N′-methylenebisacrylamide as cross-linker and the redox initiation system (NH)4S2O8-anhydrous Na2SO3 as initiator for adsorbing methylene blue (MB) from aqueous solution. First, covalent modification of MWCNTs with a natural polymer xylan was achieved by the nucleophilic substitution reaction. The obtained xylan modified MWCNTs-xylan composite was characterized by transmission electron microscope, Fourier transform infrared spectroscopy, X-ray photoelectron spectrometer, and thermal gravimetric analysis. The results indicated that the hydroxyl groups of xylan participated in the formation of MWCNTs-xylan composite, and MWCNTs-xylan composite contained 32% xylan and about four molecule chains of xylan were grafted onto 5,000 carbon atoms of MWCNTs sidewalls. Subsequently, a novel superabsorbent based on MWCNTs-xylan composite and PMAA was prepared and characterized by Fourier transform infrared spectroscopy, scanning electron microscope, and swelling test. The results proved that superabsorbent was successfully prepared by copolymerization reaction and found that the superabsorbent evidently presented three-dimensional network structure. Swelling process of superabsorbent complied with the Fick's law. Adsorption property of superabsorbent for MB was also systematically studied by investigating these parameters, such as superabsorbent dosage, initial MB concentration, contact time, ion strength, and pH. The superabsorbent presented a higher adsorption capacity and removal rate for MB. The adsorption data were fitted by Langmuir, Freundlich isotherm models, and four adsorption kinetic models. Freundlich isotherm model better fitted the equilibrium data than Langmuir, and adsorption kinetics could be well described by pseudo-second-order kinetic and intraparticle diffusion. These results indicated that the superabsorbent can be used as an efficient absorbent for removal of MB from aqueous solution. POLYM. COMPOS., 35:1516-1528, 2014. © 2013 Society of Plastics Engineers [ABSTRACT FROM AUTHOR]