Covalent organic frameworks with high quantum efficiency in sacrificial photocatalytic hydrogen evolution

Abstract

Organic semiconductors offer a tunable platform for photocatalysis, yet the more difficult exciton dissociation, compared to that in inorganic semiconductors, lowers their photocatalytic activities. In this work, we report that the charge carrier lifetime is dramatically prolonged by incorporating a suitable donor-acceptor (β-ketene-cyano) pair into a covalent organic framework nanosheet. These nanosheets show an apparent quantum efficiency up to 82.6% at 450 nm using platinum as co-catalyst for photocatalytic H2 evolution. Charge carrier kinetic analysis and femtosecond transient absorption spectroscopy characterizations verify that these modified covalent organic framework nanosheets have intrinsically lower exciton binding energies and longer-lived charge carriers than the corresponding nanosheets without the donor-acceptor unit. This work provides a model for gaining insight into the nature of short-lived active species in polymeric organic photocatalysts.

Unlocking Molecular Secrets in a Monomer-Assembly-Promoted Zn-Metalated Catalytic Porous Organic Polymer for Light-Responsive CO2 Insertion

“…To monitor the formation of the covalent acyl hydrazone linkage in our as-synthesized Zn@MA-POP , we have used the Fourier-transform infrared (FT-IR) spectroscopy technique (Figure S6 in the Supporting Information). The appearance of distinct characteristic peaks at 1263, 1620, and 1710 cm –1 , respectively, confirms the existence of −N–N, −CN–, and −CO bonds in our as-synthesized hydrazone-linked Zn@MA-POP material, clearly indicating the successful incorporation of monomeric units through the one-step polycondensation reaction. − Additionally, the stretching vibration peak appearing at 3240 cm –1 corresponds to the −NH bond of a secondary amine adjacent to a acyl group. As CO 2 adsorption on the catalyst surface is the pivotal parameter for CO 2 conversion into value-added chemicals and fuels, we have investigated the CO 2 uptake capacity of our as-synthesized Zn@MA-POP at two different temperatures (273 and 298 K).…”

Multi-Component Synthesis of a Buta-1,3-diene-Linked Covalent Organic Framework

“…The intensity of photoluminescence decreased monotonically when increasing the temperature. The excitons facilely go through radiative decay because the defects and traps are minimized by the freezing of structural configuration at low temperatures, whereas the excitons are easier to dissociate into charge carriers at high temperatures. − By fitting the integrated intensity of photoluminescence with the temperature using the Arrhenius equation, ,, the E b value of Py-Bde-COF was calculated to be 44.4 ± 1.5 meV (Figure b), which was a considerably low value in porous materials and even in D–A polymers and inorganic materials. ,,− These results clearly confirmed the efficient charge separation in the buta-1,3-diene linked COF.…”

Identifying the roles of imine and alkyne linkages in determining the photocatalytic hydrogen evolution over thiadiazole-based covalent organic frameworks

“…17 Both TeTz-COF1 and TeTz-COF2 display N 2 adsorption-desorption isotherms of type II with a type H3 hysteresis loop, indicating that they are materials with porous properties. The Brunauer-Emmett-Teller (BET) surface areas are 52.5 and 80.4 m 2 g −1 for TeTz-COF1 and TeTz-COF2 32 (Fig. 2a), respectively.…”