Sludge-derived biochar as efficient persulfate activators: Sulfurization-induced electronic structure modulation and disparate nonradical mechanisms

Sulfurized biochar derived from sewage sludge (SSB) was facilely synthesized and manifested upgraded performance in activation of peroxymonosulfate (PMS) and peroxydisulfate (PDS) for bisphenol A (BPA) elimination. The incorporated zigzag-edge sulfur effectively activated the sp2-hybridized graphene lattice, leading to the creation of more Lewis acid and basic sites in SSB. Singlet oxygen (1O2) generated from PMS oxidation at the Lewis acid sites was confirmed to be the dominated reactive species for BPA removal in the SSB/PMS system, whereas electron-transfer reactions comprising surface-confined complexes originated from the intimate contact between PDS and Lewis basic sites played the decisive role in the SSB/PDS system. Nineteen intermediates were identified in the two systems and degradation pathways of BPA were deduced accurately as well. This work not only provides a novel modification strategy for the cost-effective and environment friendly biochar-based catalysts but also deepen the insight into mechanisms of persulfate activation with carbonaceous materials.