Electrooxidation of amoxicillin in aqueous solution with graphite electrodes: Optimization of degradation and deciphering of byproducts using HRMS

Abstract

Contaminants of emerging concern (CECs) such as antibiotics have become a matter of worry in aquatic environments worldwide. Their presence in the environment has been increasing due to the inability of conventional wastewater and water treatments to annihilate them. Hence, attempts have been made to remove CECs using electrochemical oxidation (EO). Present study employed the low cost, active carbon based graphite sheet electrodes as anode and cathode to oxidize and degrade Amoxicillin (AMOX)- a β-lactum thiazolidine antibiotic. Optimization studies found pH 9, 45 mA cm−2, 81 cm2 electrode surface area, 6 mM electrolyte concentration and 60 min treatment time to be optimal for AMOX removal. Studies with varying concentrations of AMOX (20 mg L−1, 30 mg L−1 and 40 mg L−1) found that increase in concentrations of AMOX require higher current densities and treatment time for better TOC removal. High performance liquid chromatography photo diode array (HPLC-PDA) studies found 94% removal for 40 mg L−1 of AMOX at optimal conditions with 90% COD and 46% TOC removal. High resolution mass spectrometry (HRMS) studies using Ultra performance liquid chromatography-quadrupole time of flight-mass spectrometry (UPLC-Q-ToF-MS) identified major degradation mechanisms to be hydroxylation, β-lactum ring cleavage, breakage of thiazolidine ring chain from the aromatic ring and piperazinyl ring formation. The final byproducts of AMOX oxidation were carboxylic acids.