Exfoliation of covalent organic frameworks for photocatalysis

Two-dimensional materials represented by graphene and organic polymers are attracting attention because of their unique electrical and photochemical properties. One of our dream as a chemist is that we would be able to achieve the exfoliation of any kinds of two-dimensional materials, like “turning the page of books to read a new chapter”.

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Jun 14, 2019
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Covalent organic framework structures (COFs) were used as a source of exfoliation of layered compounds in the liquid phase. At present, there has been little knowledge about the exfoliation in COFs having conjugated molecules as a unit. If COFs having conjugated molecules as a unit can be exfoliated to synthesize a two-dimensional conjugated polymer, it may lead to the creation of a new two-dimensional functional material.

In the present study, we report a new method to exfoliate porphyrin COFs into the 1-nm thick disk-like polymer by using axial ligand and metal ions. Using pyridines as the axial ligand, we achieved the exfoliation of porphyrin COFs by inhibiting the stacking of COFs between layers. We succeeded in synthesizing a disk-like two-dimensional polymer with a thickness of about 1-nm. In addition, when a complex of reduced graphene and platinum nanoparticles, and exfoliated disks, is formed, it responds to light of a wide wavelength range from visible to near infrared regions. Next, we would like to tackle challenging projects toward understanding the exfoliation processes as well as photochemical processes in COFs deeply, to add “a new chapter” on the two-dimensional materials as well as novel photo-functional materials.

Using solar energy to produce H2 from water holds tremendous promise for clean energy. The optimal photocatalysts require the harvesting broad spectrum of solar light. The ultrathin 2D porphyrin COFs exhibit efficient photocatalytic H2 production with the illumination of visible and NIR light, contributing that these polymers with broad light harvesting have the potential for use in artificial photosynthesis.

Our paper “Synthesis and photocatalytic activity of ultrathin two-dimensional porphyrin nanodisks via covalent organic framework exfoliation” published in Communication Chemistry can be read from here.

Mingshan Zhu and Yasuko Osakada

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Yasuko Osakada

Associate professor, Osaka university

Photochemistry, radiation chemistry, materials science

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