Defects Engineering Leads to Enhanced Photocatalytic H₂ Evolution on Graphitic Carbon Nitride–Covalent Organic Framework Nanosheet Composite

Abstract

Graphitic carbon nitride nanosheet (CNS) represents an attractive candidate for solar fuel production. However, the abundant defects in CNS lead to serious charge recombination and limit the photocatalytic performance. Herein, the synthesis of a CNS–covalent organic framework (CNS–COF) nanosheet composite is presented for the first time. CNS with significantly reduced defects is first obtained by rationally tuning the thermal exfoliation conditions of bulk carbon nitride. Subsequent modification of the CNS with trace COF nanosheet through chemical imine bonding can not only passivate the surface termination of carbon nitride in the boundary region, but also establish strong electronic coupling between these two components. As a consequence, enhanced charge separation and photocatalytic activity are realized on the resulting CNS–COF nanosheet composite. Under optimum conditions, hydrogen is evolved at a rate of 46.4 mmol g−1 h−1. This corresponds to an apparent quantum efficiency of 31.8% at 425 nm, which is among the best values ever reported for carbon nitride‐based materials.

Unraveling the effect of defects, domain size, and chemical doping on photophysics and charge transport in covalent organic frameworks

“…This low mobility in thicker lms can be attributed to the presence of electronic defects, as well as to disorder at grain boundaries or in the interlayer stacking arrangement. [52][53][54][55][56] The size of the COF crystalline domains can also impact charge transport. In particular, defects arising from non-crystalline regions can trap the polarons, resulting in localization and subsequently yielding lower values of hole mobility and conductivity.…”

Progress and Perspectives on Covalent‐Organic Frameworks (COFs) and Composites for Various Energy Applications

“…Luo et al. synthesized carbon nitride nanosheet (CNS)‐COF by solvothermally treating TP (1,3,5‐triformylphloroglucinol) and TTA [4,4’,4’’‐(1,3,5‐triazine‐2,4,6‐triyl) trianiline] with CNS [115a] . Furthermore, the in situ construction of the CNS‐COF nanosheets complex with improved crystallinity was achieved by reacting the ‐CHO groups in TTA‐TP‐COF with the terminal −NH 2 groups of CNS.…”

Light-Driven Hydrogen Evolution Assisted by Covalent Organic Frameworks

“…Other strategies used have consisted in (1) the encapsulation of [Mo 3 S 13 ] 2− anionic clusters into the channels of the positively charged honeycomb-like β-ketoenamine linked COF generated from reaction of TP (Figure 3) with ethidium bromide, generating a remarkable HER photocatalyst able to produce 13.2 mmol H 2 •g −1 •h −1 over 18 h in the absence of Pt [49]; (2) the covalent modification of graphitic carbon nitride nanosheets (GCNS) by imine covalent bonding to the imine-linked COF formed from 4,4 ,4"-(1,3,5triazine-2,4,6-triyl)trianiline (TTA) and TP (Figure 3), yielding the extraordinary value of 46.4 mmol H 2 •g −1 •h −1 and an AQE of 31.8% at 425 nm in the presence of Pt [50]; and (3) the covalent anchoring of TpPa-1-COF onto reduced graphene oxide (rGO), achieving 12.0 mmol H 2 •g −1 •h −1 in the presence of Pt [51].…”