Efficient Photocatalytic Hydrogen Evolution on Band Structure Tuned Polytriazine/Heptazine Based Carbon Nitride Heterojunctions with Ordered Needle-like Morphology Achieved by an In Situ Molten Salt Method

Abstract

Polymeric carbon nitride (CN) is a fascinating metal-free photocatalyst for active solar energy conversion via water splitting. However, the photocatalytic activity of CN is significantly restricted by the intrinsic drawbacks of fast charge recombination because of incomplete polymerization. Herein, an in situ ionothermal molten salt strategy has been developed to construct polytriazine/heptazine based CN isotype heterojunctions from low cost and earth-abundant urea as the single-source precursor, with the purpose of great promoting the charge transfer and separation. The engineering of crystallinity and phase structure of CN has been attempted through facile tailoring of the condensation conditions in a molten salts medium. Increasing the synthetic temperature and eutectic salts/urea molar ratio lead to the formation of CN from bulk heptazine phase to crystalline polytriazine imide (PTI) phase, while CN isotype heterojunctions are in situ created at moderate synthetic temperature and salts amount. As evi...