A facile synthesis of covalent carbon nitride photocatalysts by Co-polymerization of urea and phenylurea for hydrogen evolution

Phenylurea has been integrated into the traditional polymerization route of carbon nitride (CN) precursors (e.g., urea, thiourea, dicyandiamide, and ammonium thiocyanide) in a facile one-pot approach, to modify the chemical composition, electronic structure, and catalytic performance of graphitic CN (g-CN). Results revealed that the co-polymerization of phenylurea with urea dramatically modifies the optical and electronic properties of g-CN, leading to a remarkable improvement by a factor of 9 in the photocatalytic activity of g-CN (when coupled with Pt as a co-catalyst) in an assay of hydrogen evolution reaction, while still keeping a high catalytic stability during pre-longed operations. The active catalyst is eventually a hybrid organocatalyst that is a heterogeneous Pt catalyst supported on a urea-based polymer. The promotional effect of phenylurea as the co-monomer for urea on the activity and stability of Pt/g-CN could be related to the extension of delocalized π-conjugated system of CN heterocycles, as a result of the fusion of phenyl motifs in the CN framework. The thus created surface dyadic structure favors the separation and migration of charge-carriers photoexcited upon light illumination. This work highlights a wide accessibility of chemical protocols for the design and synthesis of functional CN photocatalysts at molecular levels by applying suitable CN precursors and co-monomers.