In situ formation of a covalent organic framework on g-C3N4 encapsulated with nanocellulosic carbon for enhanced photocatalytic N2-to-NH3 conversion

Abstract

Photocatalytic nitrogen fixation has become a promising strategy to realize artificial ammonia synthesis. Graphitic carbon nitride (g-C3N4, GCN) exhibits significant possibilities for photocatalytic nitrogen fixation, but slow photo-generated electron transfer/separation still restricts its photocatalytic performance. Therefore, we fabricate a novel covalent organic framework (COF) hetero-bridging on g-C3N4 encapsulated with nanocellulose-derived carbon (CF) via a simple two-step thermal condensation method. With COF and CF acting as the co-catalysts, the optimum NH3 yield on GCNc/COF can reach up to 238.1 μmol·g−1·h−1, which is 8.92 times higher than that of the pristine GCN under visible light irradiation. The prominently photocatalytic enhancement of the resultant GCNc/COF is first ascribed to the incorporation of COF (463.6 m2·g−1) with net-like structure for N2 molecules conspicuous activation/adsorption. Moreover, the coupled cellulosic carbon fibers served as a co-catalyst can not only prolong the light-harvest, but also facilitate the migration/seperation of photogenerated carriers. Therefore, this work provides a probable mechanism for the significantly enhancement of photocatalytic nitrogen fixation and threads for the design of highly active catalysts for NH3 photo-generation.