Degradation of solid pharmaceutical waste using superoxide radical ion generated in ionic liquid/aprotic solvent mixture systems / Saba Humayun

Saba , Humayun (2024) Degradation of solid pharmaceutical waste using superoxide radical ion generated in ionic liquid/aprotic solvent mixture systems / Saba Humayun. PhD thesis, Universiti Malaya.

	PDF (The Candidate's Agreement) Restricted to Repository staff only Download (287Kb)
	PDF (Thesis PhD) Download (3592Kb)

Abstract

Environmental contamination by pharmaceuticals is on the rise, ensuing levels which are imminent globally. While the alleged harmful effects of drug waste are being rapidly substantiated at present, the development of effective and ‘greener’ techniques to degrade pharmaceuticals is a new challenge. This study explores a method using superoxide ion (O2●−) as the reactive oxygen species (ROS) for the degradation of APIs. Owing to the simplicity of its chemical structure and extensive research on the degradation of acetaminophen via various ROS, it was chosen for investigation as a model drug pollutant to thoroughly explore the advanced oxidation method. With an aim to further explore the universality of the oxidation process under investigation, the degradation of some other representative drug compounds was also examined; carbamazepine (CBM) and riluzole (RLZ) were additionally selected as target contaminants. The applicability of this oxidative degradation method on various pharmaceutical substances was validated using binary mixture systems consisting of butyltriethylammonium [BTEAmm+], triethylpentylammonium [PTEAmm+] and octyltriethylammonium [OTEAmm+] cations with bis(trifluoromethylsulfonyl)imide [TFSI−] anion-based hydrophobic ionic liquids (ILs) and acetonitrile (AcN) as an aprotic solvent (ApS). The ILs and AcN were used in varied combinations to generate O2 ●− for subsequent in-situ degradation of APIs. The O2 ●− was chemically generated by the dissolution of potassium superoxide (KO2) in [BTEAmm+][TFSI−]/AcN, [PTEAmm+][TFSI−]/AcN, [OTEAmm+] [TFSI−]/AcN and [EMIm+][TFSI−]/AcN systems to achieve complete degradation of the drugs. The novelty ofthis work lies in the demonstration of using IL/ApS binary mixtures which allow API removal of up to 98.9% within 210 mins of reaction. The extent of degradation of APIs was analyzed via the HPLC (high-performance liquid chromatography) technique by investigating the influence of different parameters and operating conditions, such as the amount of oxidant, nature of cations in ILs, length of cationic alkyl chain, ratio of IL:can (constituency of binary mixture), reaction time and reaction temperature. The most efficient degradation of ACTM was observed to occur utilizing 10% [OTEAmm+]/AcN as the reaction medium with a KO2/ACTM molar ratio of 50 at RT. A characteristic peak at the wavelength of 258 nm in UV-visible spectrophotometry was indicative of the stable generation of O2 ●− species, which confirms its presence in certain reaction media used. Cyclic voltammetry (CV) was used in order to further validate O2 ●− as a major reactive oxygen species generated in selected aprotic media, as evidently indicated by the oxygen reduction peak in the cyclic voltammograms. The ILs were recycled and found to be reusable for up to five replica cycles without significant changes in the degradation efficiencies, depicting the high efficacy of the environmentally benign regenerated media. Moreover, the evaluation of TOC decay determined that complete mineralization of APIs was achieved under optimum conditions. Degradation mechanism pathways for the pharmaceutical compounds were proposed based on LCMS analysis for the identification of intermediate transformation products resulting from drug oxidation. This work will serve to instigate further progression in the direct use of O2 ●− as a suitable alternative approach for environmental remediation pertaining to pharmaceutical contaminants.

Actions (For repository staff only : Login required)