Goethite/biochar-activated peroxymonosulfate enhances tetracycline degradation: Inherent roles of radical and non-radical processes.

While biochar supported iron materials have been widely studied in advanced oxidation processes (AOPs), little is known about the effect and mechanism of goethite/biochar in sulfate radical (SO4-) based AOPs. Herein, a novel goethite/biochar composite was applied as peroxymonosulfate (PMS) activator for tetracycline (TC) degradation in the water. The superior catalytic efficiency of goethite/biochar was achieved through radical (OH and SO4-) and non-radical (1O2) processes according to the radicals quenching experiments and electron paramagnetic resonance analysis. Carbonyl group and Fe species were the main active sites on the surface of goethite/biochar, which was demonstrated by combining Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy and reaction kinetic experiments. Furthermore, nine main by-products of TC degradation were detected by liquid chromatography-mass spectrometry and the reasonable degradation pathway was proposed according to the molecular structure analysis. Overall, the goethite/biochar materials could be applied to activate PMS for TC degradation, and this study will benefit the application of iron/biochar materials in practical water treatment.