Benzoyl isothiocyanate as a precursor to design of ultrathin and high-crystalline g-C3N4-based donor-acceptor conjugated copolymers for superior photocatalytic H2 production

Graphitic carbon nitride (g-C3N4) has been demonstrated as ideal photocatalyst for photocatalytic H-2 evolution, but simultaneously improves the photocatalytic activity and the apparent quantum efficiency (AQE) remains a big challenge. Recently, ultrathin and donor-acceptor (D-A) conjugated structure have attracted considerable attention in photocatalytic H-2 evolution, which are capable to favorable provide more reactive sites and forward intramolecular charge separation. Inspired by these advantages, benzoyl isothiocyanate (BI) as a precursor is used to design the ultrathin g-C3N4 (UCN)-BIx D-A conjugated copolymers by copolymerization with urea, which can favor forward intramolecular charge separation so as to achieve ultrahigh photocatalytic activity and AQE in photocatalytic H-2 evolution. The experimental results and density functional theory (DFT) calculations reveal that the obtained UCN-BIx D-A conjugated copolymers not only represent effective suppression of charge reverses recombination and but also broaden the range of light absorption. Additionally, UCN-BIx D-A conjugated copolymers has higher crystallinity and more negative conduction band (CB) position relative to the pure g-C3N4. And femtosecond transient absorption (fs-TA) spectroscopy also indicates that UCN-BI400 D-A conjugated copolymer shows the forward transfer ability of charge carriers is enhanced effectively. Marvelously, the best photocatalytic H-2 evolution activity over UCN-BI400 D-A conjugated copolymer (5442.74 mu mol g(-1)h(-1)) has driven by visible light exhibits an 11.96-fold enhancement relative to pure g-C3N4. Most noteworthy, the AQE of 23.7% and 7.0% is achieved at 420 nm and 450 nm that far exceeds majority of the previously reported g-C3N4-based D-A conjugated structures and UCN nanosheets. This contribution extends a novel design concept of effectively combining the ultrathin and D-A conjugated structures to simultaneously improving the activity and AQE of photocatalytic H-2 production.