Two-Dimensional Porphyrin-Based Covalent Organic Framework with Enlarged Inter-layer Spacing for Tunable Photocatalytic CO₂ Reduction

Abstract

Two-dimensional (2D) porphyrin-based covalent organic frameworks (COFs) are one of the most promising candidates for photocatalytic carbon dioxide reduction reaction (CO2RR), which however still suffer from the hindered mass transfer during the catalysis procedure associated with the close packing of 2D COF layers due to the strong axial π–π stacking. Herein, condensation between the porphyrinic aldehydes p-MPor-CHO (M = H2, Co, and Ni) and 3,8-diamino-6-phenyl-phenanthridine (DPP) affords new porphyrin-based 2D COF architecture MPor-DPP-COFs (M = H2, Co, and Ni). The bulky phenyl substituent at the phenanthridine periphery of the linking unit reduces the axial π–π stacking, providing an enlarged inter-layer spacing of 6.0 Å according to high-resolution transmission electron microscopy. This, in combination with the large surface area (1021 m2 g–1) revealed by nitrogen sorption measurements at 77 K for CoPor-DPP-COF possessing electroactive Co ions, endows it with excellent photocatalytic activity for CO2RR with a CO generation rate of 10 200 μmol g–1 h–1 and a CO selectivity up to 82%. This work affords new ideas for achieving efficient photocatalytic CO2RR upon fine-tuning the inter-layer spacing of 2D COFs.

Three-Dimensional Covalent Organic Frameworks with Ultra-Large Pores for Highly Efficient Photocatalysis

“…In the four-step procedures for the photoreduction of CO 2 , including CO 2 adsorption, COOH* formation, CO* generation, and CO desorption, the formations of COOH* (CO 2 * + H + + e – → COOH*) were determined as the rate-determining step in both Co-Por and Ni-Por, with the highest free-energy barriers (1.23 eV for Co-Por and 1.67 eV for Ni-Por). As a result, the better CO 2 reduction performance on JUC-640-Co could be put down to the significantly lower free-energy barrier of Co-Por, compared with its nickelic counterparts, which were well compatible with the previously reported metalloporphyrin-based frameworks …”

Facet-Dependent Photocatalytic Behavior of Fe-soc-MOF for Carbon Dioxide Reduction

“…It is noteworthy that Fe-soc-O has the highest CO productivity of 1804 μmol g –1 h –1 , while Fe-soc-C has the best CO selectivity of 94.7%. Considering the CO production and selectivity, the Fe-soc-MOFs have comparable performance with some contemporary materials such as ZIF-67, HOF-25-Re, CoPor-DPP-COF, and HOF-25-Ni@GO-10 with a photosensitizer for photocatalytic CO 2 reduction, − and the details are summarized in Table S1. All the Fe-soc-MOFs are stable and unchanged during the photocatalytic reactions as evidenced by PXRD, FT-IR, N 2 and CO 2 adsorption isotherms, and SEM images (Figures S7–S9).…”

Macrocycle‐Based Covalent Organic Frameworks

“…In addition, the strong axial π-π stacking of 2D porphyrin COFs caused the close packing of layers, which hindered mass transfer during the catalysis procedure and further limited the catalytic performance. Wang et al [56] introduced bulky phenyl substituent to the monomer to reduce the axial π-π stacking. The authors synthesized COFs from the condensation of porphyrinic aldehyde p-Mpor-CHO (M = H 2 , Co, and Ni) and 3,8-diamino-6-phenylphenanthridine.…”