π-Conjugated In-Plane Heterostructure Enables Long-Lived Shallow Trapping in Graphitic Carbon Nitride for Increased Photocatalytic Hydrogen Generation.

Abstract

The relatively short-lived excited states, such as the nascent electron-hole pairs (excitons) and the shallow trapping states, in semiconductor-based photocatalysts produce an exceptionally high charge carrier recombination rate, dominating a low solar-to-fuel performance. Here, a π-conjugated in-plane heterostructure between graphitic carbon nitride (g-CN) and carbon rings (Crings ) (labeling g-CN/Crings ) is effectively synthesized from the thermolysis of melamine-citric acid aggregates via a microwave-assisted heating process. The g-CN/Crings in-plane heterostructure shows remarkably suppressed excited-state decay and increased charge carrier population in photocatalysis. Kinetics analysis from the femtosecond time-resolved transient absorption spectroscopy illustrates that the g-CN/Crings π-conjugated heterostructure produces slower exciton annihilation (τ1 = 7.9ps) and longer shallow electron trapping (τ2 = 407.1ps) than pristine g-CN (τ1 = 3.6ps, τ2 = 264.1ps) owing to Crings incorporation, both of which enable more photoinduced electrons to participate in the photocatalytic reactions, thereby realizing photoactivity enhancement. As a result, the photocatalytic activity exhibits an eightfold enhancement in visible-light-driven H2 generation. This work provides a viable route of constructing π-conjugated in-plane heterostructures to suppress the excited-state decay and improve the photocatalytic performance.