Supramolecular preorganization effect to access single cobalt sites for enhanced photocatalytic hydrogen evolution and nitrogen fixation

Ever-increased investigation has been focused on designing photocatalysts comprising intimately interfaced photo-absorbers and co-catalysts for promoting the separation of electron-hole pairs and surface redox reaction. Herein, we present a photocatalytic system in which the single-site-cobalt-atom is firmly trapped and stabilized into the frameworks of porous crimped graphitic carbon nitride (g-C3N4), proposing as advanced photocatalysts for solar-photon-driven hydrogen production and nitrogen fixation. A single molecular source of dicyandiamide was used to partly transformed and then in-situ preorganized into supermolecular precursor, which could coordinate with cobalt ions and manipulate the interactions under elevated temperature prior to the condensation to form atomically Co dispersed g-C3N4 materials. Theoretical evaluation and experimental validation identified that the chemical integration of single-site-cobalt-atom on g-C3N4 is critical in optimizing the electron and band structures and accelerating the interfacial charge transfer process. As a result, the as-obtained Co@g-C3N4 possesses an exceptional photocatalytic hydrogen production rate (2481 μmolh−1g−1, λ > 420 nm) and conspicuous nitrogen photofixation performances under visible-light irradiation. Such concerted catalysis attributes to the negative shift of the Fermi level in Co@g-C3N4 system deriving from the induced charge-transfer effect, which effectively gains the reducibility of electrons and creates more active sites for photocatalytic reactions. © 2020