Heterocyclic spacer engineering in heteroporous covalent triazine frameworks for tunable hydrogen photocatalysis

The rational design of porous organic photocatalysts with high stability, visible-light absorption, and efficient charge separation is critical for advancing solar hydrogen production. In this work, we report the synthesis of a series of heteroporous covalent triazine frameworks (CTFs) incorporating nitrogen- and/or sulfur-rich heterocycles—thiazolothiazole (TZ), terthiophene (TT), benzo[c][1,2,5]thiadiazole (DPBT), and thiophene-substituted benzo[c][1,2,5]thiadiazole (DTBT)—through a mild polycondensation route using terephthalamidine and corresponding dialdehydes. These CTFs exhibit dual micro/mesoporosity, high thermal and chemical stability, and tunable electronic structures with band gaps ranging from 1.97 to 2.96 eV. Systematic evaluation revealed that TT-CTF delivered a high photocatalytic hydrogen evolution rate of 41,563 μmol g⁻¹ h⁻¹ under visible light (λ > 420 nm) with ascorbic acid as a sacrificial electron donor, far surpassing its analogues. This superior activity is attributed to its optimized electronic structure, high charge mobility, enhanced light harvesting, and reduced recombination, as supported by photoluminescence quenching, transient photocurrent response, impedance spectroscopy, and DFT calculations. This study highlights the pivotal role of heteroatom-rich linkers and heterojunction engineering in constructing next-generation organic photocatalysts for sustainable hydrogen production.