Removal of a non-steroidal anti-inflammatory by adsorption on polypyrrole/multiwalled carbon nanotube composite-Study of kinetics and equilibrium in aqueous medium

The purpose of this study was to evaluate the effect of the adsorption of the potassium diclofenac (PD) on a pristine multiwalled carbon nanotube (pristine MWCNT) and on the composite formed by the addition of polypyrrole (PPy) to pristine MWCNT, named PPy/MWCNT. They were characterized by scanning electron microscopy, infrared spectroscopy, thermogravimetric analysis, Brunauer-Emmett-Teller, surface wettability and point of zero charge. The adsorption procedure of the PD in the adsorbent materials was analysed by varying some parameters. After optimization, the materials exhibited adsorption of 93.48% and 94.98%, for pristine MWCNT and PPy/MWCNT, respectively. The kinetic data were adequately adjusted to the pseudo-second-order model for the two materials. The results of the isotherm studies showed that the models that best fit the data were the dual-site Langmuir-Freundlich and Fritz-Schlunder models, presenting Q = 59.67 mg g(-1) for the pristine MWCNT and Q = 229.93 mg g(-1) for the PPy/MWCNT. The thermodynamic study showed that from the values of Delta H and Delta G it was possible to conclude that an endothermic and favourable adsorption process occurred during the study. It can be observed that the addition of PPy in MWCNT causes a significant improvement in the maximum adsorption capacity of pristine MWCNT.