Graphene oxide (GO)/polyacrylamide (PAM) composite hydrogels as efficient cationic dye adsorbents

Composite hydrogels were prepared in the mixtures of graphene oxide (GO) and polyacrylamide (PAM) in water. The gelation behavior of the hydrogels was studied in detail. The formation of GO/PAM composite hydrogels were induced by various kinds of noncovalent interactions between GO sheets and PAM, including hydrogen bonding, electrostatic interaction, hydrophobic interaction, van der Waals force, the pi-pi stacking of GO sheets, and etc. Microstructures determined by TEM and SEM demonstrated that GO/PAM hydrogels displayed three-dimensional network structures, and the network of the gels gradually changed regular with the increasing concentration of GO at a fixed concentration of PAM (c(PAM)), conversely, with the increase in PAM concentration at a fixed concentration of GO (c(GO)), the hole-structures of gels become irregular. Similarly, at the fixed molar ratio of GO to PAM of 1:1, with the increasing total concentration, the hole-structures of gels also become irregular. The cationic dye molecules, i.e., Methylene Blue (MB) and Rhodamine 6G were efficiently entrapped to the xerogels within 20 and 60 min with the maximum adsorption value of 292.84 and 288 mg g(-1), respectively. The xerogels exhibited excellent adsorption efficiency and capability for the cationic dyes and were promising to act as toxic materials adsorbents. The adsorption kinetics of dye followed the pseudo-second order model and the dye adsorption isotherm follows both Langmuir and Freundlich adsorption isotherms model. (C) 2016 Elsevier B.V. All rights reserved.