Removal of diclofenac from aqueous solution with multi-walled carbon nanotubes modified by nitric acid

Modified multi-walled carbon nanotubes (MWCNTs) were used as adsorbents for removal of diclofenac. The reaction conditions were examined. Langmuir, Freundlich, Temkin, and Dubinin–Radushkevich isotherm models were applied to determine appropriate equilibrium expression. The results show that the experimental data fit the Freundlich equation well. Thermodynamic parameters show that the adsorption process is spontaneous and exothermic. The kinetic study indicates that the adsorption of diclofenac can be well described with the pseudo-second-order kinetic model and the process is controlled by multiple steps.

Graphical abstractPurified multi-walled carbon nanotubes (MWCNTs) are used to adsorb diclofenac from aqueous water. The structures of modified MWCNTs and diclofenac are shown. After modification, hydroxyl group (–OH) is introduced and carbonyl (–CO) functional groups are formed on MWCNTs surface. Diclofenac can be effectively adsorbed under optimal conditions, with a best adsorption efficiency of 94.6%. The different atoms and functional groups are highlighted in different colors.Figure optionsDownload full-size imageDownload as PowerPoint slide