Regeneration and reuse of the carbon nanotubes for the adsorption of selected anticancer drugs from water matrices

Abstract Effective methods of water and wastewater purification are still being investigated. Among several methods, sorption onto carbon nanotubes (CNTs) is very promising solution. CNTs possess high potential to remove a wide range of chemicals from water, including pharmaceuticals, which are frequently found in various aqueous samples. Crucial aspect of the application of CNTs as adsorbents is the possibility to use the material multiple times with the material maintaining its sorption potential and capacity. For this reason, thermal and chemical regeneration of Multi-Walled Carbon Nanotubes (MWCNTs) was investigated in our study. The conditions of thermal regeneration were set at 300 °C for 2 h. Higher temperatures caused large losses of MWCNTs. Next, the adsorbent was put in a cycle of contamination – regeneration, where it was mixed with wastewater treatment plant influent for 16 h, then dried and thermally regenerated. After thermal treatment, the sorption level (%) of three anticancer drugs — cyclophosphamide, ifosfamide and 5-fluorouracil — was determined. The obtained results proved that there was no negative influence on the sorption level of any investigated pharmaceuticals after 5 cycles of contamination – thermal regeneration. An additional regeneration method of MWCNTs with 3 M HNO3 was proposed, but the sorption level of cyclophosphamide after such treatment decreased from around 50 % (for untreated and thermally regenerated MWCNTs) to around 30 %. It suggests that contact with acid changed MWCNTs, probably by introducing additional functional groups onto their surface. The performed elemental analysis, Raman spectroscopy and both SEM and TEM images, confirm these predictions.