Lignin-coordination-guided fabrication of well-dispersed metallic-nitrogen-carbon catalysts to enable efficient Fenton-like chemistry

The spread of sustainable lignin-first biomass valorization has widely emphasized to bridge structure-activity relationships of highly-dispersed metallic-nitrogen-carbons in heterogeneous catalytic reaction, yet still challenging due to poor control of the local coordination environment. In the present work, we prepared the mass production of reactive M-N-C catalysts (M=Co, Fe, Mo, Ni and Mn) from well-defined lignin as a renewable bio-ligand via strong metal-coordination sites. A systematic investigation of decomposing tetracycline (TC) was carried out to evaluate the versatile paths of peroxymonosulfate (PMS) activation by mediating metallic redox sites, working pH adaptability, and cycling lifespan. The Co-N-C activated PMS system delivers an ultrahigh catalytic TC oxidation (98.82 %), followed by the Fe-N-C (96.79 %), Mn-N-C (94.8 %), Ni-N-C (90.17 %) and Mo-N-C (66.12 %). Benefitting from the unique electronic structures, zeta potentials, and multi-valent metallic species, the Co-N-C and Mn-N-C enable the efficient TC removal with stable reaction kinetics over the full pH range of 3-11, in which the Co-N-C also delivers a robust retention of similar to 92.7 % even after consecutive five cycles. Through the in-situ trapping, the superoxide radicals (O-2(center dot-)) dominate the TC oxidation by the low-valent Co species, whereas the main reactive oxygen species (ROS) of singlet oxygen (O-1(2)) is triggered by the Fe-N-C-aided PMS system. Accompanied by the theoretical simulation and charge transfer, a coupled behavior from tunable ROS and direct electron shuttling is exerted to adsorbing PMS on specific spin-state of the metallic spots and subsequent cleaving O-O in PMS within the multiple intermediates. We believe that this work not only dedicates to draw a blueprint of customizing lignin-coordinated metallic catalytic activity in the Fenton-like chemistry, but also affords the in-depth potentials of multifunctional water remediation within a waste-treats-pollutant scenario.