Reconstructing delocalized π electron structure of C3N4 nanosheets for enhanced visible light photocatalytic hydrogen evolution

Abstract

For improving the essential photocatalytic H2 evolution activity of C3N4, strategies via simultaneously modulating the delocalized π electron structure and defects are feasible but challenging. Herein, a C3N4 nanosheets material defined as C3N4-NS-RN with expansive delocalized π electron structure and enriched N vacancies was synthesized successfully via a facile post heat treatment. Firstly, a precursor of C3N4 nanosheets defined as C3N4-NS-PN with corrugate tri-s-triazine basal plane and abundant NHx groups in aromatic conjugate system was prepared. Fourier transform infrared spectra, X-ray photoelectron spectroscopy and nuclear magnetic resonance demonstrated C3N4-NS-PN had an enhanced delocalized π electron configuration via van der Waals coupling effect. However, the delocalization of π electrons across the basal plane was disturbed due to the corrugate conjugate plane. For further reconstructing delocalized π electron structure of C3N4-NS-PN, C3N4-NS-RN was synthesized via eliminating NHx groups and introducing enriched N vacancies in the conjugate system. Photoluminescence spectroscopy and electron paramagnetic resonance verified C3N4-NS-RN had an enhanced delocalized π electrons structure than C3N4-NS-PN. The photocatalytic H2 evolution activity of C3N4-NS-RN was steady and was about 1.8 and 6.1 times of C3N4-NS-PN and the bulk C3N4, respectively.