Utilisation of eco-friendly and low cost 3D graphene-based composite for treatment of aqueous Reactive Black 5 dye: Characterisation, adsorption mechanism and recyclability studies

The current research aimed to develop an eco-friendly three-dimensional (3D) graphene oxide/high molecular weight chitosan (GO/HCS) composite for the removal of Reactive Black 5 (RB5) dye. The adsorption performance of the 3D GO/HCS adsorbent was elucidated by varying the adsorbent dosage (1–50 mg), agitation speed (50–250 rpm), initial RB5 concentration (100–600 mg/L), pH (2–11), temperature (30–70 °C) and contact time (1–90 min). The equilibrium behaviour of the 3D GO/HCS adsorbent was best described by the Langmuir isotherm (SNE: 2.27 to 3.92), demonstrating a maximum adsorption capacity of 638.93 mg/g. The kinetic study showed a relatively fast RB5 dye adsorption by the as-synthesised 3D GO/HCS composite. The dye uptake by the composite was thermodynamically spontaneous (∆G: -39.15 to -17.90 kJ/mol) and endothermic (∆H: 5.60 to 31.64 kJ/mol). The adsorption mechanisms were assayed by pH test, Fourier transform infrared and X-ray photoelectron spectroscopy. The results substantiated that electrostatic attraction and π − π stacking were the prevailing uptake mechanisms. The 3D GO/HCS composite exhibited high structural stability and RB5 dye removal efficiencies within pH of 2–10. Furthermore, the exhausted 3D GO/HCS adsorbent was easily recovered from the liquid phase. The adsorbent was successfully applied in 5 cycles of adsorption-regeneration, preserving 90% of its adsorption capacity. The excellent adsorption and regeneration efficiencies inferred that the 3D GO/HCS macrostructure was highly efficient and recyclable for aqueous RB5 dye sequestration.