Boosting visible-light hydrogen evolution of covalent-organic frameworks by introducing Ni-based noble metal-free co-catalyst

Covalent-organic frameworks (COFs) have been recognized as an emerging type of photocatalysts for H-2 evolution and some of them have shown really outstanding photocatalytic activity with the help of Pt co-catalyst. To avoid the utilization of noble metal in COF-based photocatalysts, for the first time, we designed and constructed a series of nickel hydroxide-modified COF (TpPa-2) composite materials Ni(OH)(2)-X%/TpPa-2 (X: molar fraction of Ni(OH)(2)), which show apparently improved photocatalytic H-2 evolution activity than that of the parent COF and the activity is comparable to that with Pt (0.3 wt%) co-catalyst. A series of Ni(OH)(2)-X%/TpPa-2 were prepared by in-situ adding TpPa-2 into the reaction system of Ni(OH)(2), and the resulting Ni(OH)(2)-X%/TpPa-2 exhibit a novel sandwich-like morphology. The results of photocatalytic hydrogen evolution under visible light irradiation show that the optimized photocatalytic H-2-evolution rate for Ni(OH)(2)-2.5%/TpPa-2 is up to 1895.99 mu mol.h(-1).g(-1), which is about 26.3 times higher than that of the parent TpPa-2 and is one of the best performing 2D COF-based photocatalyst for H-2 evolution. Further investigation confirm the improved activity should be attributed to the enhanced visible-light absorption of the composite materials contributed from Ni(OH)(2) and the synergetic effect of Ni(OH)(2) and metallic Ni derived from the in-situ reduction of Ni(OH)(2), which promoted the separation of photogenerated electron-holes of the resulting materials. This work not only presents a series of new photocatalysts for efficient H-2 evolution but also open an avenue for future design and synthesis of COF-based composite materials acting as a substitute of noble-metal-containing photocatalytic systems.