Comparison of chemical, ultrasonic and thermal regeneration of carbon nanotubes for acetaminophen, ibuprofen, and triclosan adsorption

Recovering the adsorption capacity of multi-walled carbon nanotubes (MWCNT) is of importance to the sustainable use of MWCNT for the adsorption of pharmaceuticals and personal care products (PPCP). In this study, different regeneration approaches, including chemical desorption, sonication, and thermal treatment were compared for their efficiencies in regenerating the adsorption capacities of a MWCNT for acetaminophen (AAP), ibuprofen (IBU), and triclosan (TCS). Among chemical solutions possessing different levels of hydrophobicity, pH and salt concentrations, a NaCl solution at a concentration of 0.1 M outperformed others due to the replacement of the adsorbed PPCP by Na + , and hence regenerated the used MWCNT. However, the higher desorption ratio of TCS and IBU (mainly governed by π–π interactions) than that of AAP (dominated by hydrogen-bonding interactions) was due to the smaller bond interactions of π–π interactions than hydrogen-bonding interactions. Furthermore, sonication of the MWCNT immersed in the NaCl solution increased the adsorption capacities of MWCNT by 4.9–33.7%, 36.8–46.9% and 1.1–6.8% for AAP, IBU, and TCS, respectively, possibly because the high-energy pulsation induced by sonication weakened the adhesive interaction between MWCNT and PPCP. Furthermore, thermal regeneration of the MWCNT at 380 °C led to the vaporization and/or oxidation of the adsorbed PPCP, while it maintained the characteristics of the MWCNT. Overall, these results imply that thermal regeneration is potentially the most effective approach for regenerating MWCNT.