Enhanced electron density of the π-conjugated structure and in-plane charge transport to boost photocatalytic H2 evolution of g-C3N4

Abstract

Graphite carbon nitride (g-C3N4) has become an emerging metal-free photocatalyst and attracted the attention of researchers. However, pure g-C3N4 (PCN) prepared by traditional thermal condensation polymerization has a low polymerization of heptazine ring chains and a large number of charge recombination centers, which hinder in-plane charge transport, leading to undesirable photocatalytic performance. Herein, PCN fabrication by thermal treatment with ammonium oxalate monohydrate was performed to produce highly dispersed porous g-C3N4 nanosheets, and the integrity of their in-plane heptazine ring chains was successfully improved without introducing heteroatoms. Electron paramagnetic resonance and 13C nuclear magnetic resonance analyses revealed significantly increased electron density and delocalization of the π-conjugated structure. The obtained samples exhibited acceptable stability and photocatalytic activity, and the hydrogen reduction rates without and with the Pt co-catalyst were 11.2 and 5.3 times that of PCN.