Wood-based biochar as an excellent activator of peroxydisulfate for Acid Orange 7 decolorization

Wood-based biochar, as a metal-free heterogeneous activator of peroxydisulfate (PDS), was successfully prepared by pyrolysis of polar sawdust for efficient removal of Acid Orange 7 (AO7). The results demonstrate PDS could be effectively activated by wood-based biochar, and AO7 was rapidly eliminated in a wide range of pH value (3.0–10.0) with AO7 removal achieved ≥ 99.3% after 14 min reaction. The dominant reactive species in the biochar/PDS system were verified via radical quenching tests and electron paramagnetic resonance (EPR) technique. It is speculated that sulfate radicals (SO4•−) and hydroxyl radicals (•OH) were formed on the surface of biochar. Based on the results of X-ray photoelectron spectroscopy (XPS), π-electron density and oxygen-containing functional groups (especially C–OH) on biochar surface were active centers for the catalytic reaction. Recycle experiments of biochar for 4 runs were carried out and the regeneration method of the catalyst was also studied. [Display omitted] •Wood-based biochar was an excellent activator of peroxydisulfate.•C–OH and π-electron density were accounted for the generation of reactive radicals.•Surface reaction was the controlling step of the biochar/PDS process.•Surface-bound radicals were responsible for dye removal.•The reusability of biochar can be improved by thermal treatment method.