Preparation of graphene oxide-supported hydrogel adsorbent for Zn ions removal

A composite hydrogel was prepared using in situ polymerisation of acrylic acid and acrylamide monomers. The prepared hydrogel was improved by addition of graphene oxide nanosheets in the range of 0.1–0.3 wt%. These modified samples were then employed for the adsorption of zinc ions. The batch adsorption experiments were carried out at ambient conditions and pH = 7.0. The adsorbents’ morphological features, structural characteristics and mechanical behaviours were assessed using techniques such as Fourier transform infrared spectroscopy, scanning electron microscopy, X-ray diffraction and dynamic mechanical thermal analysis. Incorporating graphene oxide into pure hydrogels markedly enhances their mechanical robustness and swelling behaviour. When graphene oxide is added at levels up to 0.2 wt%, there is a notable elevation in the glass-transition temperature and the mechanical modulus of the hydrogels. In contrast, further addition of graphene oxide decreases the mechanical properties due to nanoparticle agglomeration. The water diffusion and the swelling mechanism follow pseudo-Fickian and Schott kinetic models, respectively. The adsorption kinetics followed a pseudo-second-order model, reaching equilibrium within 75 min. The data from the adsorption isotherm conformed well to the Langmuir model.