Enhanced electro-reduction of Fe3+ to Fe2+ by acidified carbon nanotube-modified graphite cathode and its application in a novel Fenton process for p-nitrophenol degradation

Abstract

The compared electro-reduction of Fe3+ to Fe2+ was investigated using graphite cathode (GC), carbon nanotube-modified graphite cathode (CNT/GC) and acidified carbon nanotube-modified cathode (ACNT/GC). ACNT/GC exhibited the best performance of Fe3+ reduction and the reduction rate of 94.7 % was achieved by the electrolysis of 120 min at a cathode potential of 0.3 V (vs. SCE), which indicated the high activity of ACNT towards the electro-reduction of Fe3+ to Fe2+. Based on the above findings, two Fenton processes were developed for p-nitrophenol (PNP) degradation. One Fenton process was characterized by the simultaneous electro-reduction of Fe3+ (ER-Fenton). Under the condition of low Fe2+ dosage, ER-Fenton process provided the faster PNP degradation than conventional Fenton process. But in ER-Fenton process, the invalid decomposition of H2O2 by anodic oxidation decreased the utilization efficiency of H2O2. For the purposes of decreasing ferrous salt dosage, reducing iron sludge and enhancing the effectiveness of H2O2, another novel Fenton process was developed by employing the sequencing batch electro-reduction of Fe3+ (SBER-Fenton). It was found SBER-Fenton process presented not only the effective regeneration of Fe2+, but the effective H2O2 utilization due to the batch addition of H2O2, and as a result, under the lower Fe2+ dosage condition, this recommended process provided the better PNP degradation than conventional Fenton process according to the concentration decays of PNP and TOC. The presented results confirmed that SBER-Fenton process was able to decrease Fe2+ dosage for the effective Fenton oxidation, thus reducing the generation of iron sludge in the subsequent treatment.