Adsorption characteristics of diclofenac sodium onto graphene nanoplatelets

Adsorption characteristics of diclofenac sodium (DCS) onto graphene nanoplatelets (GNP) were evaluated in this study. Batch adsorption experiments were carried out to study the efficiency of GNP to remove DCS. Optimum conditions such as contact time, adsorbent dosage, the initial concentration of DCS, pH, and temperature were investigated for the maximum removal of DCS. Maximum removal of 99% was observed at 25°C temperature, 3.5 g/L dosage of GNP, pH of 5, 5 mg/L concentration of DCS, and a contact time of 40 min. Moreover, three different isotherm models were applied to study the interactions between molecules of adsorbate and adsorbent. Langmuir isotherm was found to most suitable fit the data with an R2 value of 0.9967 and the Langmuir constant (KL) was found to be 1.0363 L/mg. Kinetic models were also examined, and it was observed that the adsorption process follows pseudo-second-order kinetics with a rate constant K2 = 1.8218 g/mg min. Finally, thermodynamic properties were calculated using Sip’s model which reflected the negative value of change in Gibbs free energy and the change in enthalpy was equal to –3.9089 KJ/mol confirming that the process is exothermic and spontaneous.