The use of modified multi-walled carbon nanotubes for the removal of selected pharmaceuticals from the aqueous environment

Adsorptive removal of two popular painkillers such as ibuprofen and paracetamol from aqueous solutions on carbon nanotubes (CNT) as well as carbon nanotubes functionalized with hydroxyl (CNT-OH) and carboxyl (CNT-COOH) groups was investigated. The effects of solution pH and ionic strength were studied. Adsorption kinetics and equilibrium study were also carried out. It was observed that the adsorption of both the drugs on all three adsorbents was strongly pH-dependent while the ionic strength of the solution did not affect the adsorption efficiency. Adsorption kinetic data were analyzed using pseudo-first-order and pseudo-second-order equa-tions and the results showed that adsorption kinetics followed the pseudo-second-order model. The Langmuir, Freundlich and Sips models were applied to describe the adsorption isotherm of the ibuprofen and paracetamol on the CNTs. The Langmuir isotherm provided the best correlation for the adsorption of drugs on all of the adsorbents, and the adsorption efficiency of ibuprofen and paracetamol increased in the order: CNT-OH < CNT < CNT-COOH. The adsorption capacities for CNT, CNT-OH, and CNT-COOH were found to be 50.76, 43.67 and 61.35 mg/g for ibuprofen, and 29.85, 17.95 and 38.76 mg/g for paracetamol, respectively.