UV-assisted sorption of efavirenz and levonorgestrel from aqueous solution using S-doped carbon nanotubes

The presence of pharmaceutical compounds such as efavirenz and levonorgestrel in water resources has become an issue of great social and scientific concern in recent years due to their considerable effects on aquatic ecosystems and human health. This study aims to address this concern by synthesizing sulphur-doped carbon nanotubes (S-CNT) from macadamia nutshells for use in the efavirenz (EFA) and levonorgestrel (LVG) from an aqueous solution. The synthesized S-CNT was characterized for its functional groups, surface morphology, and crystallinity using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X-ray diffractogram (XRD) techniques. SEM micrographs showed tubular features on the material’s surface. The efficiency of the synthesized S-CNT towards EFA and LVG removal was assessed using batch experiments in the presence of 250 nm UV. The maximum removal efficiencies for EFA and LVG were 99 and 98%, respectively, at optimum conditions of pH 2, dosage of 0.3 g/50 mL, and initial concentration of 2.5 ppm after 90 min agitation time. The removal of FEA and LVG involved both photodegradation and adsorption, wherein the EFA and LVG were degraded into C14H8ClF3NO± and C13H10ClF3N±; C15H21O3‾ and C21H29O3‾, respectively, by the UV light followed by their subsequent adsorption onto the surface of the S-CNT. The adsorption kinetics data yielded R2 ≥ 0.98 for both pseudo-first-order and pseudo-second-order reaction kinetics models for both EFA and LVG, indicating the possibility of physisorption and chemisorption processes. The isotherm data fitted better to the Freundlich isotherm model, indicating that the removal occurred on a heterogeneous surface. Based on these findings, S-CNT can potentially remove EFV and LVG from wastewater.