Eco-friendly biopolymer integrated three-dimensional hierachichal graphene materials for adsorptive removal of dyes and heavy metals

The discharge of effluent containing heavy metals and dyes from various industries has led to severe water pollution threatening all forms of life and the environment. Adsorption of these pollutants onto graphene oxide (GO) nanosorbent has potrayed promising results, however, its application in industrial wastewater remediation is restricted by its nano-sized dimension, making the recovery steps costly. Lately, three-dimensional (3D) graphene materials have attracted great attention as an effective adsorbent for wastewater treatment. The intrinsic properties of 3D graphene structure such as ultra large surface area and interconnected porous structure, can facilitate the transport of pollutants into the 3D network and provide abundant active sites for binding the pollutants. Ice-templating was selected as the synthesis route for 3D graphene structures in this research due to its facile steps, cost effectiveness, high scalability potential and tuneable material porosity. A new 3D graphene structure, GO/chitosan aerogel (GOCA), was fabricated via this technique and employed for Metanil Yellow (MY) and Reactive Black 5 (RB5) dyes removal. The GOCA adsorption performance was evaluated by varying prominent adsorption factors. The combined effects of multiple parameters and optimum conditions for the dyes removal were determined by response surface methodology (RSM). GOCA exhibited adsorption capacities of 418.35 and 656.96 mg/g for MY and RB5 dyes, respectively. For both dyes, the adsorption kinetic obeyed the pseudo-first-order and pseudo-second-order models at low and high concentration regions, respectively. The adsorption equilibria for the dyes were best fitted to the Langmuir isotherm. The GOCA adsorbent was easily separated after adsorption and regenerated for re-use in five adsorption-desorption cycles. The GOCA was further assessed for continuous adsorption of MY and RB5 dyes using fixed-bed columns. The breakthrough characteristics were investigated as a function of bed height, inlet dye concentration and feed flowrate. The greatest bed adsorption capacities attained were 157.06 and 247.96 mg/g for MY and RB5 dyes, respectively. FTIR spectroscopy confirmed that electrostatic attraction an