Enhancement of Visible‐Light‐Driven Hydrogen Evolution Activity of 2D π‐Conjugated Bipyridine‐Based Covalent Organic Frameworks via Post‐Protonation

Abstract

Photocatalytic hydrogen (H2) evolution represents a promising and sustainable technology. Covalent organic frameworks (COFs)‐based photocatalysts have received growing attention. A 2D fully conjugated ethylene‐linked COF (BTT‐BPy‐COF) was fabricated with a dedicated designed active site. The introduced bipyridine sites enable a facile post‐protonation strategy to fine‐tune the actives sites, which results in a largely improved charge‐separation efficiency and increased hydrophilicity in the pore channels synergically. After modulating the degree of protonation, the optimal BTT‐BPy‐PCOF exhibits a remarkable H2 evolution rate of 15.8 mmol g−1 h−1 under visible light, which surpasses the biphenyl‐based COF 6 times. By using different types of acids, the post‐protonation is proved to be a potential universal strategy for promoting photocatalytic H2 evolution. This strategy would provide important guidance for the design of highly efficient organic semiconductor photocatalysts.

Thiadiazole-Derived Covalent Organic Framework Macroscopic Ultralight Aerogel

“…Sulfur atoms with a negative charge can attract the H with a positive charge in water molecules, and nitrogen atoms with a positive charge can attract the O atom with a negative charge in water molecules. COFs with hydrophilicity usually showed a potentially photocatalytic hydrogen evolution property according to previous research. − The electronic band structure from density functional theory (DFT) calculation also indicates that NNS-VCOF is a potential candidate to thermodynamically transfer photoexcited electrons to H + for hydrogen evolution because the energy of the conduction band minimum ( E CB ) value (−2.80 eV) is positioned higher than the standard potential of H + /H 2 (−4.44 eV) (Figure c). , So NNS-VCOF is an excellent thermal insulation and flame-retardant material as a macroscopic object, and also may be a potential photocatalytic hydrogen evolution material in the powder state.…”

Zwitterionic and Hydrophilic Vinylene-Linked Covalent Organic Frameworks for Efficient Photocatalytic Hydrogen Evolution

“…Furthermore, the water contact angle of Zi-VCOF-1 is also lower than that of most organic materials (60–100°) due to its unusual sulfonic-pyridinium zwitterionic pair . Water vapor adsorption and desorption isotherms at 293 K for Zi-VCOFs show that not only the external surface of the materials can interact with water, but the internal pore structure also is accessible to water, thus increasing number of potential sites for photocatalytic hydrogen evolution (Figure b). – The water isotherms for Zi-VCOFs also show that Zi-VCOF-1 (water vapor adsorption 386.8 cm 3 g –1 ) possessed a higher water sorption capacity and photocatalytic potential than Zi-VCOF-2 (water vapor adsorption 299.4 cm 3 g –1 ).…”

Postsynthetic Annulation of Three-Dimensional Covalent Organic Frameworks for Boosting CO2 Photoreduction

“…Different from layer-stacked 2D COFs, − 3D COFs possess high-accessible surface area and abundant active sites and are thus utilized as a promising platform to design photocatalysts for energy transformation, − especially in CO 2 photoreduction. For example, two types of 3D COFs were recently constructed from 4-connected porphyrin units and 6-connected linkers .…”