Adsorption of pharmaceutical and heavy metal contaminants onto three-dimensional graphene based structures

Water contamination by pharmaceutical and heavy metal discharge is a serious environmental issue causing adverse effects on aquatic biota and human health. Despite showing promising pollutants decontamination efficiency, graphene oxide (GO) nanosheets are not feasible adsorbents for application in wastewater treatment. Therefore, three-dimensional (3D) graphene structures were synthesised and demonstrated to be practical adsorbents for pharmaceutical and heavy metal pollutants removal. This thesis describes the successful conversion of GO nanosheets into graphene macrostructures for the adsorption of pharmaceuticals and heavy metals from aqueous environment. In this research, several new 3D graphene-based structures were synthesised, namely reduced graphene oxide aerogel (rGOA), reduced graphene oxide aerogel decorated with δ-MnO2 (RGM) and zirconium functionalised graphene oxide aerogel (ZrGA). The rGOA was prepared by self-assembly of GO via chemical reduction with L-ascorbic acid while the RGM and ZrGA were assembled through ice-templating method fortified by carboxymethyl cellulose and incorporated with metal-based functionalising agents. Characterisation study revealed that the rGOA, RGM and ZrGA were amorphous and porous with hollow channels formed by interconnected graphene/binder layers. Chemical functional groups such as hydroxyl, carboxyl and epoxy groups were found in the adsorbents while Mn and Zr-based functional groups were detected in RGM and ZrGA, respectively. The simultaneous interaction of process parameters and optimisation of batch adsorption were investigated using response surface methodology. It was determined that rGOA and RGM exhibited highest adsorption capacities of 646.5 mg/g for diclofenac and 129.4 mg/g for acetaminophen, respectively. Furthermore, ZrGA showed highest adsorption capacities of 53.1 mg/g for Cu2+ and 41.6 mg/g for Ni2+. The adsorption equilibrium for diclofenac-rGOA system was best described by the Freundlich model while acetaminophen-RGM, Cu2+-ZrGA and Ni2+-ZrGA adsorption equilibria were best described by the Langmuir model. The adsorption of diclofenac onto rGOA and Ni2+ onto ZrGA involved physisorption as the systems adsorption kinetics were best modelled by the pseudo-first-order kinetic model. Meanwhile, acetaminophen and Cu2+ uptake by RGM and ZrGA, respectively, was by chemisorption as the systems adsorption kinetics were well represented by the pseudo-second-order kinetic model. Hydrogen bonding and electrostatic interactions were the predominant mechanisms of adsorption of the pharmaceuticals and heavy metals onto the 3D graphene-based structures. Fixed bed adsorption study demonstrated that rGOA and ZrGA could be used to remove the contaminants under continuous flow mode, however RGM was not suitable as its structure became unstable during the column operation. The study revealed that the breakthrough time was increased as the bed heights of rGOA and ZrGA increased, but decreased as the influent concentration and flowrate increased. The breakthrough curves obtained were well correlated to the Thomas and Yoon-Nelson models. The BDST model was used successfully to depict a linear relationship between column service time and bed height. Furthermore, the mass transfer analysis indicated the involvement of film mass transfer and pore diffusion