Abstract:

Covalent organic frameworks (COFs) have lately emerged as a blooming class of potential materials for photocatalytic water splitting because of their high crystallinity, huge surface areas, and structural versatility. However, the photocatalytic performance for most pure COFs face some limitations factors, such as the significant recombination of photogenerated carriers and slow charge transfer. Herein, a novel thioether-functionalized pyrene-based COF (S₄-COF) was effectively produced and chosen as a support for the immobilization of ultrafine gold nanoparticles (Au NPs). S₄-COF photocatalyst with Au as cocatalyst demonstrates remarkable photocatalytic activity with a H₂ generation rate of 1377 μmol g^-1 h^-1 under visible light (>420 nm), which is ca. 4.5-fold increase comparing to that of pure S₄-COF (302 μmol g^-1 h^-1). Au NPs anchored on S₄-COF possess an ultrafine size distribution ranging from 1.75 to 6.25 nm with an average size centered at 3.8 nm, which benefits from the coordination interaction between thioether groups and Au. Meanwhile, the produced Au@S₄-COF can generate a stable photocatalytic H₂ generation during the four recycles and preserve its crystallinity structure after the stability testing. The Au NPs anchored on the S₄-COF photocatalyst can greatly accelerate the separation of photogenerated carriers and increase charge transfer because of the combined function of Au NPs and thioether groups. Such a method can not only prevent the aggregation of Au NPs onto thioether-containing COFs to achieve long-term photostability but also allow uniform dispersion for an ordered structure of photocatalysts. This work provides a rational strategy for designing and preparing COF-based photocatalysts for solar-driven H₂ production.

Key words: Photocatalysis, Covalent organic framework, Thioether functionalization, Gold nanoparticle, Coordination interaction, Photogenerated carrier separation