| Undivided electro-Fenton cells are widely applied inwastewater treatment due to their high efficienciesin degrading hazardous pollutants. Anodic oxidation may play a role in the pollution removal inundivided electro-Fenton cells, which is usually ignored by researchers. In this work, the anodicoxidation possibly involved in undivided electro-Fenton cells was investigated with a graphite paper as the anode electrode and Rhodamine B (RhB) as the probe pollutant. Partial degradation of RhB was observed when an external voltage of+2.0 V was applied to the graphite anode with continuous O2supply. The degradation efficiency of RhB was enhanced by decreasing the pH of electrolyte. Total decolorization of RhB was achieved after 2 and 12 hrs of electrolysis at pH 3.0 and 6.8, respectively, the RhB removal efficiencies were significantly improved to 36.6±3.0% and 30.2±9.5%.Neither the direct oxidation nor the oxidation by reactive oxygen species mechanism was responsible for the degradation of RhB at the graphite anode. Therefore we propose a new mechanism for anodic oxidation of graphite electrodes, in this reaction,the unsaturated groups in the carbon as catalyzer. The anodic current was necessary to initiate such a reaction by activating the catalytic centers in these unsaturated functional groups to oxidize pollutants.Acid mine drainage (AMD) contains a large amount of ferrous iron and the recovery of iron oxides from the AMD has been of extensive research interest. Previously our laboratory presents a novel air-cathode fuel cell strategy to in-situ utilize ferrous iron in the AMD for the fabrication of heterogeneous electro-Fenton catalysts.But if we want to simulate the real acid mine drainage in the environment, we should take the other heavy metal ions present in AMD into account. According to the related literature, we find ten times as much Fe2+ as Mn2+, Cu2+, Al2+, Zn2+, Ni2+, Co2+.So we respectively follow the 10:1 ratio to fabricate the air-cathode fuel cell. We also arrange another set of experiment for reference, the ratio of Fe2+and other heavy metal ions is 1:1. The metal compound/graphite felt (GF) composites were fabricated from a synthetic AMD and their catalytic activities towards the electro-Fenton reaction were evaluated at neutral pH with Rhodamine B (RhB) as a probe pollutant. The initial concentration of Rhodamine B is 25mg/L, after 5h degradation,the electrodes from the ratio of Fe2+ and other heavy metal ions is 10:1,iron oxide/GF doped with aluminum, zinc, manganese has a high electricalFenton catalytic activity.Iron oxide/GF doped with copper, nickel, cobalt has a lower catalytic activity.And another group, the electrodes from the ratio of Fe2+ and other heavy metal ions is 10:1, consistent with the front results... |
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