CNTs/ferrihydrite as a highly efficient heterogeneous Fenton catalyst for the degradation of bisphenol A: The important role of CNTs in accelerating Fe(III)/Fe(II) cycling

The generation of Fe(II) from Fe(III) is the rate-limiting step in the heterogeneous Fenton reaction, and accelerating this step is critical for enhancing the reaction efficiency and also the subject of extensive studies. In this work, the oxidized multi-walled carbon nanotubes (CNTs) were coupled with ferrihydrite (Fh) to synthesize novel and highly efficient heterogeneous Fenton catalysts (CNTs/Fh). Interestingly, the calculated apparent rate constants by 3%CNTs/Fh could reach ∼7.1 times as high as that by Fh, well in agreement with the accelerated decomposition rate of H2O2, as well as the enhanced generation rate of Fe(II) and hydroxyl radicals in the CNTs/Fh system. The density functional theory calculations and the cyclic voltammograms curves both well indicated that the Fe(III)/Fe(II) redox cycling on CNTs/Fh could be significantly enhanced during the Fenton reaction, from both dynamic (accelerating the electron transfer from H2O2 to Fh) and thermodynamic (lowering Fe(III)/Fe(II) redox potential) aspects.