Nitrogen coordination modulation of single-atom CoN4 enables dual-active-sites catalyst featuring synergistic organics adsorption and peroxymonosulfate activation

Minimizing the migration distance of short-lived radicals to targets is highly desirable for maximizing the heterogeneous Fenton-like catalytic performance. Herein, we design and fabricate a difunctional CoN4 single-atom catalyst, CoN4(29% pyrrolic N), composed of 29% pyrrole-type Co–N4 and 71% pyridine-type Co–N4 centers via atomic-level nitrogen coordination modulation, which enables dual-active-sites featuring synergistic peroxymonosulfate (PMS) activation and organic pollutant adsorption. Theoretical prediction and experiments demonstrate that the isolated Co site in pyridine-type Co–N4 has a relatively strong interaction with PMS than that in pyrrole-type Co–N4 because that the pyridinic N is more able to alter and optimize the electron distribution of the Co 3d orbital, namely an increased d-band center closer to the Fermi level and induced low spin-state Co formation, and thus facilitate electron transfer, enhance PMS adsorption, and reduce energy barriers of PMS activation. Meanwhile, the targets, including bisphenol A and other emerging pollutants, can be effectively adsorbed onto the pyrrolic N site in pyrrole-type Co–N4 via a "hard-soft interaction" principle and "donor–acceptor complex" process. This strategy minimizes essentially the mass transport limitation of the reaction by greatly reducing the transport distance of radicals towards pollutants. That is, the CoN4(29% pyrrolic N) can effectively induce the spatial confinement to restrict the space where the Fenton-like catalytic oxidaiton occurs in the vicinity of pollutants adsorbed, achieving rapid and effcient degradation and removal of emergying pollutants from water and wastewater.