Preparation and characterization of xanthan gum-cl-poly(acrylic acid)/o-MWCNTs hydrogel nanocomposite as highly effective re-usable adsorbent for removal of methylene blue from aqueous solutions

In this work, xanthan gum-cl-poly acrylic acid (XG-cl-pAA) hydrogel and xanthan gum-cl-poly acrylic acid/oxidized MWCNTs (XG-cl-pAA/o-MWCNTs) hydrogel nanocomposite was successfully surface modify by microwave assisted copolymerization, in which N, N'-methylenebisacrylamide (MBA) was used as a cross-linking agent. A copolymerization of acrylic acid (AA) onto xanthan gum (XG) initiated by microwave radiation method. Different weight percentages of oxidized MWCNTs were incorporated into the hydrogel matrix during the grafting reaction. An optimum hydrogel based on maximum swelling capacity further incorporated with oxidized MWCNTs to form XG-cl-pAA/o-MWCNTs. The structure, thermal stability, wettability and morphology of XG-cl-PAA and XG-cl-PAA/o-MWCNTs were characterized by fourier transform infrared (FTIR), Raman, X-ray diffraction (XRD), Thermogravimetric analysis (TGA), Contact angle, and scanning electron microscope (SEM). The effects of pH, contact time and equilibrium concentration on the MB dye adsorption were investigated batch wise. Optimal conditions were obtained at pH⩾6 due to the generation of negatively charged groups (COO-) in the adsorbent, which can strongly interact with the positive charges from MB and time of adsorption equilibrium was achieved in 30 min. The XG-cl-PAA/o-MWCNTs hydrogel nanocomposite exhibited a very high adsorption potential, and its adsorption capacities calculated based on the Langmuir isotherm for MB was 521.0 mg/g at 30 °C. The dye adsorption data fitted well to the pseudo-first-order model and Langmuir model. The adsorption-desorption cycle of hydrogel nanocomposite was repeated several times without significant loss of adsorption capacity.