According to the WHO, an estimated 1.28 billion people within the ages of 30 and 79 suffer from hypertension. Losartan is one of the most prescribed anti-hypertensives, with around 51 million prescriptions handed out in the US alone [1]. Such an excessive consumption has led to the accumulation of losartan and its metabolites in water bodies in concentrations of ng/L to mg/L [2]. Electrochemical advanced oxidation processes (e-AOPs) are relatively clean technologies used to achieve the degradation of such recalcitrant pollutants. Among different electrodes, Boron doped diamond (BDD) has an enhanced rate of generating reactive oxygen species (ROS) and a high potential window leading to the complete mineralization of recalcitrant pollutants. In this work, the role of the operating parameters on the electrochemical degradation of Losartan has been studied. The effect of (i) different cathodes, (ii)electrolytes (iii) current density, and (iv) pH on the process has been evaluated. A reaction pathway could be proposed by identifying transformation products in different electrolytes.
Experimental Procedure:
120mL of the solution containing 0.5mg/L of Losartan was degraded electrochemically in 0.1M electrolyte (Na2SO4 or NaCl) using 8 cm2 BDD anode in batch mode. Five different cathodes with an active area of 8 cm2 were used. The current density was 25mA/cm2, and experiments were performed at the inherent pH of the electrolyte. To identify TPs, the experiments were performed with an initial losartan concentration of 5mg/L. The losartan degradation was monitored by HPLC (HPLC: Alliance 2695, Waters) equipped with a photodiode array detector.
Results and Discussion:
The effect of different cathode materials in 0.1M Na2SO4 and 0.1M NaCl have been illustrated in Fig. 1 (a & b). Irrespective of the cathodes, the degradation of losartan was faster in the case 0.1M NaCl as compared to 0.1M Na2SO4. The presence of chlorides in the electrolytes leads to the formation of reactive species diffused in the bulk solution and enhances the losartan oxidation until a specific concentration. However, it has been reported that a massive increase in the chloride concentration can slow the degradation [3]. For the different cathode materials examined, the rate constant was the highest for carbon cloth (0.1399 min-1) in 0.1M and graphite (1.977 min-1) in 0.1M NaCl. The lowest rate constant values were obtained in both the electrolytes using BDD as cathode material.
Conclusion:
Electrochemical oxidation over a BDD anode showed high efficiency for the degradation of the pharmaceutical Losartan. The removal depends on the operation parameters and cathode materials, while the electrolyte significantly alters kinetics and possibly modifies the degradation pathway. The role of the cathode material is usually ignored in similar studies; therefore, further research is needed in this direction.
References:
[1] Losartan - Drug Usage Statistics, ClinCalc DrugStats Database, (n.d.). https://clincalc.com/DrugStats/Drugs/Losartan (accessed April 23, 2022).
[2] A. Ioannidi, O.S. Arvaniti, M.-C. Nika, R. Aalizadeh, N.S. Thomaidis, D. Mantzavinos, Z. Frontistis, Removal of drug losartan in environmental aquatic matrices by heat-activated persulfate: Kinetics, transformation products and synergistic effects, Chemosphere. 287 (2022) 131952. https://doi.org/10.1016/j.chemosphere.2021.131952.
[3] O.S. Arvaniti, I. Konstantinou, D. Mantzavinos, Z. Frontistis, Destruction of valsartan using electrochemical and electrochemical/persulfate process. Kinetics, identification of degradation pathway and application in aqueous matrices, Journal of Environmental Chemical Engineering. 9 (2021) 106265. https://doi.org/10.1016/j.jece.2021.106265.
