Enhanced Photocatalytic Activity of Calix[4]arene-Based Donor–Acceptor Covalent Organic Frameworks by Dual Cocatalysts

The distinctive characteristics of covalent organic frameworks (COFs), including their high surface area, adjustable porosity, and sturdy chemical structure, render them appealing for potential use in photocatalytic applications. Nonetheless, the full utilization of their photocatalytic activity has been hindered by the limited charge separation and migration efficiencies of COFs, along with high exciton binding energies. In this research, calix[4]arene (C4A) and thiazolo[5,4- d ]thiazole (TzTz) were selected as electron donor and acceptor units, respectively, to produce C4A-TzTz-COF with donor–acceptor (D–A) properties, which represents one of the most effective approaches for promoting charge separation and transport in organic semiconductors. As a control, C4A-PA-COF was synthesized, and it was observed that the photocatalytic hydrogen evolution rate of C4A-TzTz-COF with donor–acceptor (D–A) features was 7.3 times greater than that of the former. Additionally, Ag nanoparticles (NPs) and Pt NPs were sequentially deposited on the surface of C4A-TzTz-COF. Ag NPs serve as providers of hot electrons under the localized surface plasmon resonance (LSPR) effect, with the hot electrons being injected at the conduction band of C4A-TzTz-COF. Pt NPs, acting as catalytically active sites, effectively capture hot electrons for cocatalysis. Ultimately, the donor–acceptor structure of Pt–Ag 3.0 /C4A-TzTz-COF, featuring a bimetallic system, significantly enhances the photocatalytic activity in the visible light range, leading to a 2.2-fold increase in the photocatalytic hydrogen evolution rate over C4A-TzTz-COF. The synergistic effects of the dual cocatalysts not only facilitate charge separation and transfer but also enable the efficient utilization of solar energy for sustainable energy conversion. This study provides valuable insights into the design and development of advanced COF-based photocatalytic materials with enhanced performance, paving the way for their widespread application in renewable energy and environmental remediation technologies.