Electrochemical treatment of Acid Red 1 by electro-Fenton and photoelectro-Fenton processes

Small volumes (100 mL) of acidic aqueous solutions with 30-200 mg L TOC of the toxic azo dye Acid Red 1 (AR1) have been comparatively treated by various electrochemical advanced oxidation processes (EAOPs). The electrolytic system consisted of a BDD anode able to produce OH and an air-diffusion cathode that generated H2O2, which subsequently reacted with added Fe to yield additional OH from Fenton’s reaction. Under optimized conditions (i.e., 1.0 mM Fe, 60 mA cm, pH 3.0, 35 oC), the analysis of the initial rates for decolourization and AR1 decay assuming a pseudo-first-order kinetics revealed a much higher rate constant for photoelectro-Fenton (PEF, ~ 2.7x10 s) compared to electro-Fenton (EF, ~ 0.6x10 s). Mineralization after 180 min was also greater in the former treatment (90 % vs 63 %). The use of UV radiation in PEF contributed to Fe(III) photoreduction as well as to photodecarboxylation of refractory intermediates, yielding a mineralization current efficiency as high as 85% during the treatment of solutions of 200 mg L TOC. Primary reaction intermediates included three aromatic derivatives with the initial naphthalenic structure and four molecules only featuring benzenic rings, which were totally mineralized in PEF.