Covalent organic framework spherical nanofibers bearing carbon quantum dots for boosting photocatalytic hydrogen production

Covalent organic frameworks (COFs) are promising photocatalysts for water splitting, but their photocatalytic activity is limited by low utilization of visible light, and the high rate of photogenerated electron-hole pair complexation. In this work, a series of carbon quantum dot (CQD)-functionalized covalent organic frameworks, TAPT-COF-CQDs-X (X = 1, 2, 3, 4, 5 mg), were prepared by reaction of 2,4,6-tris(4-aminophenyl)-1,3,5-triazine (TAPT) and 2,4,6-trihydroxybenzene-1,3,5-tricarbaldehyde (TFP) using CQDs as the modulating agent. The hydrogen evolution rate of TAPT-COF-CQDs-3 was 69.57 mmol h-1 g-1 under visible light (lambda > 420 nm) and 6.21 mmol h-1 g-1 at longer wavelengths lambda > 520 nm, which were enhancements of 4.35 and 10.9 times that of TAPT-COF. The improved performance of TAPT-COF is attributed to the construction of Z-scheme heterojunctions, the formation of spherical nanofiber structures, enhanced absorption of visible light and a higher charge separation efficiency. DFT calculations indicated a lower energy barrier for H+ to H* reduction for reactions catalyzed by TAPT-COF-CQDs.