Removal of amoxicillin and ketorolac combining an IrO₂-Ta₂O₅|Ti anode with a carbon paper cathode

Abstract

Contaminants in water resources are known to cause serious environmental and health issues. Despite using different methods to eliminate such chemicals, emerging contaminants are usually persistent, especially in conventional water treatment technologies. Electro-oxidation (EO) is a straightforward technique that has been proven effective for degrading pharmaceuticals in water. In this work, the performance of EO has been investigated using an IrO2-Ta2O5|Ti anode containing 18.79 % Ti, 58.09 % O, 7.06 % Ir, and 2.36 % Ta, with a roughness of 252.6 μm, a surface area of 0.0667 cm2, and a roughness factor of 0.07575, in different setups by combining it with either a titanium mesh or carbon paper (CP) as a cathode, with or without a constant air flow rate. The accumulation of hydrogen peroxide (H2O2), hydroxyl radical (•OH), and active chlorine was monitored to evaluate the performance of each setup in two different media (0.1 M NaCl and 0.1 M Na2SO4). The EO process was conducted at a cell potential of 2.5 V for 120 min, and the removal of amoxicillin (AMX) and ketorolac (KET) was assessed by Ultraperformance Liquid Chromatography coupled to UV–Vis Spectrometry (UPLC-UV/Vis). In this sense, using the IrO2-Ta2O5|Ti||CP system, 10 mg l-1 AMX showed a removal efficiency of 100 % after 6 min in 0.1 M NaCl and after 30 min in 0.1 M Na2SO4. In comparison, 10 mg l-1 KET showed a removal efficiency of 100 % after 5 min in 0.1 M NaCl and 82.5 % after 120 min in 0.1 M Na2SO4, with a corresponding decrease in toxicity within <10 min. The mineralization of AMX and KET solutions was determined using total organic carbon (TOC) analysis. Our results showed that higher H2O2 and •OH radicals were produced in a 0.1 M Na2SO4 medium. Moreover, in aerated systems, the 2e- oxygen reduction reaction (ORR) at CP contributed to the faster degradation of the drugs. The chlorine production accelerated the disappearance of both drugs in the NaCl medium. Finally, reaction routes for the AMX degradation in Na2SO4 and KET degradation in NaCl are proposed, considering the interfacial oxidants generated (H2O2, •OH, Cl2/HClO) and the corresponding by-products identified by High Performance Liquid Chromatography coupled to tandem Mass Spectrometry (HPLC-MS/MS). The decrease in toxicity was observed within <10 min.