Realizing a strong visible-light absorption band in piezoelectric 2D carbon nitride sheets for enhanced piezocatalysis

Piezoelectric photocatalytic water splitting is a viable approach to generate renewable energy and carbon nitride sheets (CNs) has emerged as a promising material. However, the narrow solar absorption range of CNs due to its wide-band-gap hinders its further development and practical applications. In this study, CNs with a strong visible-light absorption band and a sharp absorption edge beyond 574 nm are successfully prepared by developing a fluorination and defluorination strategy. Experimental results show that introducing cyano groups into the framework of CNs as well as the accompanied nitrogen vacancies at the edges maintains high piezoelectricity and that the separation of photo-generated electron-hole pairs by the piezo-polarization charges is enhanced in the modulated CNs. Under simultaneous visible-light exposure and the ultrasonic irradiation, the modulated CNs loaded with Pt cocatalyst as a photocatalyst show a superior photocatalytic hydrogen evolution rate of 13.53 mmol g−1 h−1, which is one of the highest record reported so far for carbon nitride-based materials. Theoretical calculations reveal that the introduction of cyano into CNs leads to a suitable band gap for visible light, which dramatically improves the photocatalytic ability. This study advances the investigation of piezoelectric photocatalytic water splitting, and is also an enabling technology for piezoelectric semiconductors for their practical applications.