Polyacrylamide hydrogel-based nanocomposites containing graphene, kaolin or laponite: Physico-mechanical characterization and adsorption properties

Polyacrylamide (PAAm) hydrogel-based nanocomposites containing graphene, kaolin or laponite were prepared and tested as possible adsorbents for organic dyes. The morphology of basic hydrogels was controlled by varying the content of water in the reaction mixture and the composition of final adsorbents was modified by changing the type and amount of the additive. The impact of hydrogel morphology and applied additives on the physico-mechanical properties of prepared nanocomposites was investigated. Concerning morphology, the higher water content (i.e. larger pores) brings about the less rigid hydrogel or nanocomposite. Concerning additives, the addition of graphene or kaolin makes the nanocomposites less rigid, whereas the addition of laponite more rigid than the original PAAm hydrogels. The prepared kaolin and laponite nanocomposites swell in water less than the original hydrogels, the graphene nanocomposites do not exhibit an obvious trend. Both, the hydrogels and all their nanocomposites, swell more in aqueous NaCl solutions than in water. The adsorption properties of prepared nanocomposites toward six organic dyes was then systematically studied. Comparing to the original hydrogels, the adsorption capacity of nanocomposites varies with the type of additive: notably increases for laponite, slightly increases for graphene, and surprisingly decreases for kaolin nanocomposites. Concerning hydrogel morphology, the medium size of pores seems to be the most advantageous. The laponite nanocomposites are found to be efficient adsorbents for cationic dyes, especially those containing phenyl groups. In this case, the desorption of cationic dyes from the adsorbents can be efficiently done by using acid media.