Journal of the American Chemical Society
Communication
submicrometer throughout the dissected area of a 3D-printed
lattice.
two-stage postprinting network reorganization. At the nano-
scale, the fabricated COF monoliths exhibit high crystallinity
similar to their solution-phase-synthesized COFs yet impart
good mechanical robustness at the macroscale. Compared to
the solution-phase-synthesized counterparts, these 3D-printed
monoliths possess comparable measured surface areas and
hierarchical porous features, which can potentially increase the
mass transport rate for molecular storage, separation, and
catalysis. Furthermore, dual-COF monoliths with molecular-
level structural integration at the COF−COF interfaces have
been successfully fabricated using two COF precursor inks.
Our approach provides a facile method to fabricate
homogeneous and heterogeneous COF monoliths with high
crystallinity and designed macroscale 3D architectures, which
will pave the way for future applications that require
sophisticated 3D architectures.
11b
Following this method, another β-ketoenamine COF,
13
TpBD-Me , and an imine COF, TPE-COF, were success-
2
fully integrated into DIW-compatible materials (Figure 3).
3
D-printed to obtain a lattice pyramid (Figure S26). Although
the hexagonal framework had not been extensively formed
after heating at 90 °C for 24 h (Figure 3c, green), a crystalline
3
D-TpBD-Me monolith was obtained after solvent annealing
2
(Figure 3c, red), suggesting that the β-ketoenamine polymer
still reorganizes its network after removal of the F127 matrix.
2
2
crystalline fibrous structures were observed with hierarchical
porous features generated after F127 removal. In contrast,
mixing tetrakis(4-aminophenyl)ethene, terephthalaldehyde,
and F127 in the absence or presence of TsOH did not afford
a homogeneous hydrogel but instead yielded a nonprintable
yellow precipitate that gave rise to the rapid formation of large
imine polymer particles. To decrease the DP of the imine
polymer, aniline was introduced to form an imine intermediate
ASSOCIATED CONTENT
Supporting Information
■
*
S
Synthesis and characterizations (PDF)
(
Figure 3b), which subsequently reacted with tetrakis(4-
AUTHOR INFORMATION
*
10
aminophenyl)ethene through transimination polymerization
in the presence of F127. The 3D-printable hydrogel G3 was
obtained and printed into a lattice pyramid. Upon heating and
subsequent annealing under a N atmosphere, the crystalline
ORCID
2
2
(
3
Figure 3d) and SEM analyses (Figure S33) suggested that
D-TPE-COF possesses a periodically stacked 2D hexagonal
Author Contributions
M.Z. and L.L. contributed equally.
§
framework at the nanoscale with hierarchical porous features.
The polymer network reorganization in these 3D-printed
COF monoliths enables heterogeneous integration of different
imine and β-ketoenamine COFs in a spatially defined 3D
architecture. Cross-imination at the COF−COF interface
would allow two COF materials to covalently connect to
each other, therefore eliminating the binding issue in
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We acknowledge funding support from the American Chemical
Society Petroleum Research Fund (58377-DNI10), the
National Science Foundation EPSCoR New Hampshire
BioMade Center (1757371), and the startup fund of
Dartmouth College.
14
conventional fabrication methods. Two heterogeneous lattice
structures (Figure 3e) were 3D-printed using inks of G1 and
G2 and inks of G1 and G3. After the two-stage amorphous-to-
crystalline transformation, the mechanically robust dual-COF
monolith 3D-TpPa-1/TpBD-Me2 (Figure 3e) with high
crystallinity (Figure 3g) was obtained. SEM studies revealed
that the two COFs are seamlessly bound at the COF−COF
interface (Figure 3f), suggesting a molecular-level connection
between the two COFs. To further demonstrate the strong
interfacial binding between the two COFs, the concentration
of the TPE-COF precursors in G3 was intentionally kept
significantly lower than the precursor concentration in G1.
After annealing, the top layer composed of TPE-COF shrank
more than the bottom layer composed of TpPa-1, forcing the
heterogeneously 3D-printed monolith 3D-TpPa-1/TPE-COF
to bend into a half-round tubular structure (Figure 3e) at the
macroscale, demonstrating the strong interfacial interaction
between the two COFs.
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In summary, we have demonstrated a general method to
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