Thermodynamics and Kinetics of Adsorption of Diclofenac on Magnetic Multiwalled Carbon Nanotubes in an Aqueous Solution

We investigated the adsorption of diclofenac (an anti. inflammatory drug) in aqueous solutions by magnetic multiwalled carbon nanotubes (MWCNTs). The results showed that the amount of adsorbed diclofenac initially increased with magnetic MWCNT dosage and stabilized at a magnetic MWCNT dosage of 0.7 g.L-1. The amount of diclofenac adsorbed by the magnetic MWCNTs was 33.37 mg.g(-1) and the removal rate of diclofenac was 98.1%. The removal rate for the diclofenac increased and then decreased with the pH value of solution, but it decreased with the temperature of solution. Kinetic analysis was conducted using pseudo first and second order models. Regression results showed that the adsorption kinetics was more accurately represented by a pseudo second order model. The linear correlation coefficients and standard deviations of the Langmuir and Freundlich isotherms were determined and the results revealed that the Langmuir isotherm fit the experimental results well. The calculated thermodynamic parameters were: Delta G(0)<0 indicating that the adsorption of diclofenac on magnetic MWCNTs was spontaneous, Delta H-0<0 indicating that the absorption reaction was exothermic and that low temperatures are favorable for adsorption, and Delta S-0>0 indicating that the adsorption process was a entropy enhancing process.