The key role of persistent free radicals on the surface of hydrochar and pyrocarbon in the removal of heavy metal-organic combined pollutants

We show that persistent free radicals (PFRs) on the surface of biochar can produce hydroxyl radicals (•OH) by catalyzing H 2 O 2 to facilitate the removal of the combined pollutant BPA-Cr(VI). Microstructure characterization showed that the structures of pyrocarbon and hydrochar were significantly different when prepared at different temperatures. As the preparation temperature and preparation time for biochar increased, the concentration of PFRs first increased and then decreased. When biochar, PFRs, and H 2 O 2 were present in the same solution, the single pollutants BPA and Cr(VI) as well as the combined pollutant BPA-Cr(VI) could be removed effectively, with removal rates greater than 90%. However, when PFRs, BPA, H 2 O 2 , and Cr(VI) were present in the same solution, Cr(VI) competed with H 2 O 2 for electrons and promoted the removal of BPA. The results of this study could be applied to sludge recycling and be used to develop approaches to catalytically degrade combined pollutants.