Chemistry Reference
In-Depth Information
Fig. 2.14
The representative building blocks with different geometries to design 3D COFs
Compared with 2D COFs, 3D COFs are relatively rare owing to their limited
building units. The following strategies are employed to construct 3D COFs: (1) the
self-condensation of tetrahedral (3D-T4)
T
4
) nodes; (2) co-condensation of tetrahedral
nodes with linear (2D-
C
2
) or triangular (2D-
C
3
) building blocks. The pioneering work
of rational design for 3D COFs was achieved by Yaghi et al. [
11
]. In the synthesis,
tetra(4-dihydroxyborylphenyl)methane (TBPM), and tetra(4-dihydroxyborylphenyl)
silane (TBPS) are selected as the tetrahedral nodes (Fig.
2.15
). Dehydration reaction
of borate acid produces triangular B
3
O
3
ring. Via self-condensation of tetrahedral
blocks and co-condensation with the triangular units, two preferred nets are envi-
sioned, which are ctn and bor, respectively. The self-condensation of the tetrahedral
TBPM and TBPS give COF-102 and COF-103, respectively, both of which are ctn
topology. Additionally, hexahydroxytriphenylene (HHTP) could be used as triangular
units. In contrast, the co-condensation of HHTP with TBPS forms COF-108 with a
bor topology.
Another successful example of 3D COFs is illustrated by Yan et al. [
12
].
Combining a tetrahedral alkyl amine with planar triangular building units, 3D
base-functionalized COFs, BF-COF-1, and BF-COF-2 are obtained (Fig.
2.16
).
PXRD analysis indicates that they are ctn topology. N
2
sorption shows that they
are microprous. It is notable that they have excellent catalytic activities with high
conversion yield owing to their highly efficient size selectivity.
Besides the ctn and bor type COFs, another developed type is dia topology. It is
worth mentioning that COF-300 reported by Yaghi et al. is the first imine-linked 3D
COF (Fig.
2.17
) [
13
]. To form COF with dia topology, the basic building units are
tetrahedral nodes. The condensation of the tetrahedral building block tetra-(4-anilyl)
methane with the linear linking unit terephthaladehyde produces a material with
