The influence of pH and current density on an UV254 photo-assisted electrochemical process generating active chlorine and radicals for efficient and rapid ciprofloxacin mineralization compared to individual techniques

Abstract

A photo-assisted electrochemical process is herein evaluated with the aim of improving and accelerating the degradation and mineralization of Ciprofloxacin (CIP) in aqueous media, in comparison with single electrochemical or photochemical methods. Active chlorine species are initially electro-generated on a synthesized (Pechini method) Ti/TiO2-RuO2 DSA, and subsequently fragmented homolitically using UVC irradiation under very low fluency rate (3300 μW cm−2, λ = 254 nm) to produce radicals with higher oxidation potentials compared to the original active chlorine. A faster CIP degradation (5 min) and higher mineralization is obtained in the coupled system against the individual techniques. Variations of pH and current density in the UV-assisted electrochemical process reveal that a similar degradation rate is obtained during 60 min for pH 6 and 9 due to the co-existence of HOCl and OCl− species in this range of pH, leading to the possible production of highly reactive radicals (e.g. HOaq•, Claq•, Oaq-•) after chlorine species fragmentation. The highest total organic Carbon (TOC) removal was obtained at pH = 6 (70 % in 60 min), where the highest HOCl concentration is observed, thus, enhancing the HOaq• production. The contaminant degradation and mineralization strongly depend of the radicals formed from the irradiation of chlorine species, which on its turn rely on the redox couples formed as a function of pH: 3 (HOCl + Cl2), 6 and 9 (HOCl + OCl−). Mechanisms are proposed for these homolysis reactions, while the degradation pathway of CIP is rationalized using HPLC analyses during 60 min of electrolysis.