Interlayer-stacking mode modulation in an imine covalent organic framework for efficient photocatalytic hydrogen production†

Abstract

Two-dimensional conjugated covalent organic frameworks (COFs) have emerged as a new class of promising photocatalysts for solar-hydrogen energy conversion. The regulation of their interlayer stacking mode is one of the important strategies to modulate their properties and photocatalytic performance. Historically, the staggered AB mode has seldom demonstrated greater photoactivity than the corresponding eclipsed AA mode. Herein, a contrary example is presented, wherein the AB-stacked PyDBTSO-AB COF outperforms its AA-stacked isomer, PyDBTSO-AA COF. This pair of isostructured COFs were synthesized from the same tetraaniline-functionalized pyrene (Py) monomer and dibenzaldehyde-functionalized dibenzothiophene sulfone (DBTSO) monomer under conventional solvothermal conditions in an o-dichlorobenzene/butanol/acetic acid-mixed medium and under ionothermal conditions in 1-butyl-3-methylimidazolium tetrafluoroborate ionic liquid, respectively. Structural characterizations discovered that PyDBTSO-AA possesses a larger specific surface area and void pore volumes, whereas PyDBTSO-AB exhibits greater hydrophilicity and a shorter interlayer π-π stacking distance. Furthermore, electrochemical impedance spectroscopy and photocurrent responsive experiments revealed that PyDBTSO-AB has a smaller charge transport impedance and a larger photocurrent responsiveness compared to PyDBTSO-AA. Finally, in photocatalytic hydrogen production experiments conducted with Pt co-catalyst under full-arc Xe light irradiation, PyDBTSO-AB achieved a hydrogen evolution rate of 109 mmol g-1 h-1, more than twice as that displayed by PyDBTSO-AA. Consequently, this research emphasizes the equal importance of the AB-stacking mode in comparison to the AA-stacking mode within the realm of photocatalytic COF design, and provides new insights into the manner in which their interlayer-stacking modes influence the ultimate photocatalytic activities.