Electrochemical oxidation of amoxicillin in its pharmaceutical formulation at boron doped diamond (Bdd) electrode

Abstract

In this work, voltammetric and electrolysis experiments have been carried out on a conductive boron doped diamond (BDD) electrode in a solution containing amoxicillin in its pharmaceutical formulation. The physical characterization of the BDD surface by scanning electron microscopy (SEM) reveals a polycrystalline structure with grain sizes ranging between 0.3 and 0.6 µm. With Raman spectroscopy, BDD surface is composed of diamond type carbon (Csp3) and graphitic type carbon (Csp2). The XPS survey of the BDD surface has revealed the presence of C 1s and O 1s. The deconvolution of the C1s spectrum showed that the BDD surface chemical bonds were composed by C-C and C-H. The ferri/ferrocyanide redox couple showed a quasi reversible behavior on BDD and BDD showed a quasi metallic properties with a good electrical contact between the diamond coating and the silicono substrate. The electrochemical characterization of the BDD electrode in sulfuric acid electrolyte showed a wide potential window of 2.74 V. The oxidation of amoxicillin showed an irreversible anodic wave on the voltammogram in the domain of water stability indicating a direct oxidation of amoxicillin at BDD surface. The treatment of amoxicillin in the synthetic wastewaters under various constant current densities 20, 50, 100, 135 mA cm-2 on BDD showed that amoxicillin is highly reduced under 100 mA cm-2 reaching 92 % of the chemical Oxygen demand (COD) removal after 5 h of electrolysis. Investigation performed in perchloric acid as supporting electrolyte led to 87 % of COD removal after 5 h of electrolysis. Mineralization of amoxicillin occurs on BDD and the COD removal was higher in sulfuric acid than in perchloric acid owing to the involvement of the in-situ formed persulfate and perchlorate to the degradation process mainly in the bulk of the solution. The instantaneous current efficiency (ICE) presents an exponential decay indicating that the process was limited by diffusion. The specific energy consumed after 5 h of the amoxicillin electrolysis was 0.096 kWh COD-1 and 0.035 kWh COD-1 in sulfuric acid and in perchloric acid respectively.