Adsorption of sodium diclofenac in aqueous medium using graphene oxide nanosheets.

In this work, the adsorption of sodium diclofenac (DCF) on graphene oxide nanosheets (GON) was evaluated. GON was synthesized by the modified Hummers method and characterized regarding its composition, morphology, and surface load. It was applied in batch adsorption tests. The process was evaluated from the kinetic, isothermal and thermodynamic properties, and parameters such as adsorbent mass and solution pH were optimized. The best working condition was observed at the natural pH of the solution (6.2) and 0.25 g L-1 adsorbent dosage. The pseudo-first-order and pseudo-second-order models were applied to verify the behaviour of the adsorption kinetics, and the adsorption isotherms were also developed at temperatures ranging from 25°C to 45°C. The isotherm models of Langmuir, Freundlich, and Temkim were applied to the equilibrium data. The thermodynamic parameters of enthalpy, entropy, and Gibbs free energy were evaluated to describe the behaviour of the adsorptive process. The maximum adsorption capacity of DCF at 25°C was 128.74 mg g-1 with a removal rate of 74% in 300 min. The process was favourable and spontaneous with adsorptive capacity decreasing with increasing temperature. In addition, an adsorption mechanism was proposed to show the possible bonds that occur between adsorbate and adsorbent and the interactions formed through the influence of pH.