Effective inter-chain charge transfer and high charge mobility in polymeric carbon nitride arising from controllable molecular structures for enhanced photocatalytic H2O2 and H2 production

Abstract

For the efficient photocatalytic activity of polymeric photocatalysts, it is necessary to construct effective charge-transfer channels as well as to promote charge mobility. Here, KCl/LiCl salt assisted polycondensation is proposed to synthesize polymeric carbon nitride with a controllable molecular structure. It is notable that the cross-linking degree and the building blocks can be controlled by the ratio of KCl/LiCl. Specifically, with an increasing KCl content in the KCl/LiCl salt system, the product gradually changes from a highly cross-linked two-dimensional carbon nitride to an almost non-crosslinked one. This decreasing cross-linking degree is accompanied by a continuous change of the molecular units from triazine to heptazine. The cross-linking can serve as the inter-chain charge-transfer channel whereas more conjugated subunits will improve the charge mobility. By optimizing the KCl content, effective inter-chain charge transfer and high charge mobility can be realized simultaneously. The optimized polymeric carbon nitride exhibits excellent photocatalytic performance for both H₂O₂ and H₂ production. Significantly, the apparent quantum efficiency (AQE) for H₂O₂ production reaches 56.6% at 420 nm, which is much higher than that of most of the reported carbon nitride-based photocatalysts.