Engineering β-ketoamine covalent organic frameworks for photocatalytic overall water splitting

Abstract

Covalent organic frameworks (COFs) are an emerging type of crystalline and porous photocatalysts for hydrogen evolution, however, the overall water splitting activity of COFs is rarely known. In this work, we firstly realized overall water splitting activity of β-ketoamine COFs by systematically engineering N-sites, architecture, and morphology. By in situ incorporating sub-nanometer platinum (Pt) nanoparticles co-catalyst into the pores of COFs nanosheets, both Pt@TpBpy-NS and Pt@TpBpy-2-NS show visible-light-driven overall water splitting activity, with the optimal H2 and O2 evolution activities of 9.9 and 4.8 μmol in 5 h for Pt@TpBpy-NS, respectively, and a maximum solar-to-hydrogen efficiency of 0.23%. The crucial factors affecting the activity including N-sites position, nano morphology, and co-catalyst distribution were systematically explored. Further mechanism investigation reveals the tiny diversity of N sites in COFs that induces great differences in electron transfer as well as reaction potential barriers.

Construction of Crystalline Nitrone-Linked Covalent Organic Frameworks Via Kröhnke Oxidation

“…The Brunauer–Emmett–Teller (BET) surface areas were calculated to be 497.9 m 2 g –1 for CityU-1 and 190.7 m 2 g –1 for CityU-2 (Figure a). The good crystallinity, permanent porosity, good stability, and uniform one-dimensional channel endow COFs to be excellent platforms in many applications. ,,− …”

Advances in organic semiconductors for photocatalytic hydrogen evolution reaction

“…16 Currently, organic photocatalysts for the OWS without sacrificial donors are attractive but difficult to design. 17,18 One approach being the deposition of HER and OER co-catalysts, where the distribution of the two co-catalysts is critical. Another approach is to construct a Z schemes, whose complex device design and higher cost make it less attractive than a singlestep system, and where charge transfer requires overcoming additional processes related to the interface between the two materials.…”

Engineering the Electronic and Thermal Properties of Two-Dimensional Covalent Organic Frameworks

“…Interestingly, systematically increasing the linker lengths in 2D COFs have been shown to decrease the band gaps. , This has been ascribed to the systematic variations in the valence band maximum (VBM) that are primarily delocalized on the linkers, while the conduction band minimum (CBM) is preferentially localized at the nodes, which are not affected by the linker length variations . Furthermore, the distribution of charge densities and their spatial separation in COFs have also been shown to be critically important for their photocatalytic applications. − In this regard, Jin et al have shown that various combinations of nodes and linkers in sp 2 -carbon COFs can be used to tune the level of VBM and CBM, respectively, thus providing synthetic means to independently modulate the VBM and CBM through manipulating the structures of the nodes and linkers. Likewise, through an end-capping strategy, Yang et al synthesized vinylene-linked COFs end-capped with hydroxyl groups that showed modular band gaps and improved photocatalytic hydrogen evolution activity.…”

“…Furthermore, the distribution of charge densities and their spatial separation in COFs have also been shown to be critically important for their photocatalytic applications. − In this regard, Jin et al have shown that various combinations of nodes and linkers in sp 2 -carbon COFs can be used to tune the level of VBM and CBM, respectively, thus providing synthetic means to independently modulate the VBM and CBM through manipulating the structures of the nodes and linkers. Likewise, through an end-capping strategy, Yang et al synthesized vinylene-linked COFs end-capped with hydroxyl groups that showed modular band gaps and improved photocatalytic hydrogen evolution activity. For a thorough review of the optoelectronic properties of COFs, the readers are referred to a recent review conducted by Keller and Bein …”