Removal of pharmaceuticals from aqueous samples by adsorption using pristine polypyrrole as adsorbent: kinetic, isothermal and thermodynamic studies

Abstract

ABSTRACT Conductive polymers have been used as adsorbents to remove organic pollutants from aqueous samples. In this study, pristine polypyrrole (PPy) was used for the first time in the removal of potassium diclofenac (PD) and moxidectin (MOX) from aqueous solutions.PPy was properly characterised by scanning electron microscopy, thermogravimetric analysis, infrared spectroscopy, textural properties, wettability, and point zero charge. Through the characterisation results, it was observed that the adsorbent showed be favourable to adsorption, high temperature of thermal degradation, bands characteristic of the PPy,mesopore structures, and hydrophilicity. The results pointed that pH 6 favoured the removal, reaching percentages of 95.26% for PD and 99.75% for MOX.The kinetic data followed the model of pseudo second-order (PD: R2 = 0.872 and MOX: R2 = 0.887) with equilibrium reached in 20 min for PD and MOX. OThe best fit isotherm model was the dual-site Langmuir-Freundlich (R2 > 0.99), with maximum capacity adsorption of 221.23 mg g−1 for PD and 87.46 mg g−1 for MOX. Finally, the thermodynamic study showed that the adsorption process was spontaneous and endothermic. Through the reuse study, it was possible to show a good cost-benefit ratio when using the developed adsorbent material, since it can be used several times without losing its adsorption capacity. Finally, PPy showed great potential to be used in the adsorption of compounds with different physicochemical properties.