Enhancement of photo-Fenton catalytic activity with the assistance of oxalic acid on the kaolin-FeOOH system for the degradation of organic dyes

The Fenton reaction, as an important member of the advanced oxidation processes (AOPs), has gained extensive attention in recent years. However, the practical applications of the traditional Fenton process have been restricted by the poor degradation efficiency and the rigid pH range. In this study, we report a new strategy regarding the photo-Fenton oxidation of Rhodamine B (RhB) by kaolin-FeOOH (K-Fe) catalysts with the assistance of oxalic acid. It was found that the iron-oxalate complex was formed as oxalic acid was introduced into the K-Fe catalyst system by the chelation ability of oxalate. Benefiting from the high photosensitivity of the iron-oxalate complexes, the K-Fe/oxalic acid/H2O2/visible light system exhibited excellent catalytic activity towards the degradation of RhB under the optimized reaction conditions [(K-Fe) dosage = 1.0 g L-1, initial pH = 7.2, (oxalic acid) = 1.0 mM, (H2O2) = 0.5 mM], and its reaction rate constant for the degradation of RhB was 27.7 times greater than that of the K-Fe/H2O2/visible light system. More importantly, the K-Fe/oxalic acid/H2O2/visible system showed remarkable degradation efficiency over a wide pH range (3.3-10.8), which was superior to that of the traditional Fenton system. In addition, the degradation efficiency of RhB was found to remain at 94.7% after five cycles. This work is expected to provide an important approach for the application of the Fenton system.