Inorganic acid-derived hydrogen-bonded organic frameworks to form nitrogen-rich carbon nitrides for photocatalytic hydrogen evolution

Abstract

Hydrogen-bonded organic framework (HOF) materials, which feature unique structures, are generally used for gas separation. To fabricate HOF-like precursors with diverse morphologies and further extend their application to hydrogen evolution, melamine has been reacted with inorganic acids (H₂SO₄, HNO₃ and HCl) in this work. After calcining, the framework structure can maintain its major features while being converted into porous nitrogen–rich carbon nitrides. Moreover, the influence of different acid radicals on the “N-rich effect” was also investigated. The results show that the reaction procedure enriches the nitrogen content in all the newly synthesized carbon nitride products compared with bulk carbon nitride. This enrichment is attributed to the preferential formation of high-N-ratio triazine over heptazine. The carbon nitrides prepared from the HOF precursors contain more active sites [N-(C)3] and tune the bandgap by stabilizing the energy level of the conduction band. Moreover, heterogeneous sulfur doping using H₂SO₄ is another key factor in changing the energy-level structure. Thus, our method provides a feasible way to prepare graphite carbon nitride materials with preeminent photocatalytic activity.