Covalent Amide Bonding Interaction and π-π Stacking Constructed Carboxyl-Functionalized Diketopyrrolopyrrole Heterojunctions with Promoted Photocatalysis Performance

As semiconductor photocatalysts, heterojunctions have emerged as an attractive and promising research subject in the area of photocatalysis recently. However, inefficient carrier separation and charge recombination are the pivotal problems that restrict the photocatalytic performance. In this work, a new strategy based on both covalent and noncovalent interactions to construct type II heterojunctions by the introduction of carboxyl-functionalized diketopyrrolopyrrole (DPP) coupled with fluorene/phenyl polymers into g-C3N4 was developed, affording efficient photocatalytic water-splitting hydrogen production. The cooperation of covalent bonding interaction for heterojunctions efficiently improves the separation of photogenerated charges and then accelerates hydrogen production performance, compared to a single pi-pi interaction. Assembling by these two interactions, the effective internal embedded electric field (IEF) was successfully erected between DPP polymers and g-C3N4. Additionally, in situ XPS spectroscopy confirmed the orientation of electron flow from the polymers to g-C3N4 within the IEF under light illumination. Therefore, the HER up to 35.7 mmol<middle dot>h(-1)<middle dot>g(-1) (0.89 mmol<middle dot>h(-1), 25 mg of the photocatalyst) for the PDWCOOH/g-C3N4 heterojunction was achieved with an apparent quantum yield (AQY) of 28.2% under 550 nm. The HER of resultant heterojunctions is almost 40 times higher than that of pristine g-C3N4, directing the design and construction of efficient and well-performed heterojunctions for photocatalysis.