Comprehensive evaluation of the catalytic activity of alpha-ferric oxide in photocatalysis, Fenton-like and photo-Fenton systems for organics degradation: Performance and in-depth mechanism consideration

Abstract

Although alpha-ferric oxide (α-Fe2O3) has been widely used in photocatalysis, Fenton-like and photo-Fenton systems for organics degradation, its catalytic activity is still necessary to be evaluated scrupulously in full consideration of organics adsorption and homogeneous Fenton oxidation. In this work, nanoscale α-Fe2O3 was prepared by the direct calcination of FeCl3·6 H2O, and its true catalytic activity in photocatalysis, Fenton-like and photo-Fenton systems was evaluated by the degradation of rhodamine B (RhB) and tetracycline (TC). It was found that the activity of α-Fe2O3 in Fenton-like and photo-Fenton systems at pH 3.0 was higher than that at pH 7.0 and pH 9.0. Compared with photocatalysis and Fenton-like systems, photo-Fenton system exhibited greater organics degradation performance. In the photo-Fenton system, photocatalytic reactions can not only degrade organics directly and accelerate the redox cycle of Fe(II)/Fe(III), but also supply more active sites to promote H2O2 activation. Photocatalytic reactions caused more Fe leached, whereas dissolved Fe could enhance degradation performance significantly even at a very low concentration (0.15 mg L–1). An interesting result was that the increase of solution pH enhanced H2O2 decomposition in the photo-Fenton system, but the degradation performance decreased obviously. Overall, α-Fe2O3 does not have high activity in photocatalysis and Fenton-like systems, and its heterogenous Fenton-like activity may be overestimated in many references. α-Fe2O3 is more suitable to be applied in photo-Fenton system to remove organic pollutants from acidic wastewaters considering H2O2 utilization efficiency.