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based catalysts for organic transformations and electrocatalytic
oxygen evolution reaction.[34a,42,43] Several experimental and
theoretical inputs reveal that the COF not only provides sup-
port for the growth of small-sized nPs but also delivers a syner-
gistic structural and electronic influence on the catalytic proc-
ess.[37a] Here, we report a microporous resorcinol-phenylenedia-
mine COF with ability to capture CO2 selectively. Further, a
composite water/chemical-stable catalyst synthesized by grow-
ing small-sized silver nPs using this COF as support catalyzes
the conversion of propargyl alcohols into their corresponding
cyclic carbonates in the presence of CO2. The fact that the con-
version does not transpire in the absence of the COF confirms
that the COF plays a key role in trapping and activating the
CO2 molecules. There are few reports on CO2 conversion using
COF where epoxides and propargyl amines are being used as
the reagent for chemical fixation.[8d,13c] But, to the best of our
knowledge, this is the first report of COF based heterogeneous
catalyst to convert CO2 into a-alkylidene cyclic carbonates
using propargyl alcohols with high selectivity and yields.
gram which suggested P6 (FOM: >50) space group as the
best-fit highest symmetry. So, an initial model was constructed
in this hexagonal space group via atomic manipulation. How-
ever, the asymmetric dispositioning of the -OH groups of the
resorcinol unit lowers the symmetry to Monoclinic. This struc-
ture was further geometry-optimized using tight-binding den-
sity functional theory algorithm embedded in the Materials
Studio. The lowest energy structure adopts a P2/m space
group (a=22.12; b=22.12; c=3.52; b=1208, table S1). The
diffraction pattern of this model was refined against the exper-
imental PXRD using the Pawley routine; it yielded an excellent
fit (Figure 2A, refined cell: a=22.04; b=21.50; c=3.52; a=
89.758, g=89.858, b=119.918; Rp=4.5 and wRp=6.56). The
experimental PXRD pattern agreed better with the simulated
PXRD pattern of the eclipsed form (Figure S1). In this finalized
structure, the COF has a uniform one dimensional (1D) pores
of size ~14 ꢀ (factoring the van der Waal radii of the atoms),
which agrees well with the experimentally determined pore
size.
Solid-state magic-angle spinning NMR (SS-MAS NMR) spec-
trum reveals the characteristics of chemical shifts. Peaks in the
range of d=110 to 120 ppm have been assigned to the aro-
matic carbons. Notably, the presence of a peak at d=182 ppm
suggests that the -OH groups are tautomerised to keto form in
the COF (Figure S2).[34a,41a] Further, the peak at d=148 ppm is
seen due to the imine bond formation in the COF. While the
characteristic chemical shift due to C=C-N is obtained at d=
134 ppm signifying the existence of the COF in the keto form
under the ambient conditions. The Infra-Red (IR) stretching
band at 1607 cmÀ1 is assigned to the vibration of ÀC=O bonds.
Peaks at 1513 and 1457 cmÀ1 are observed due to the stretch-
ing of C=N and C=CÀN bonds, respectively (Figure S3).[34a]
Thermo gravimetric analysis (TGA) shows that the COF is stable
up to 3008C (Figure S4). An initial mass loss (29%) due to the
loss of occluded solvent molecules trapped within the COF
pores is observed. This substantial solvent loss reflects the po-
rosity. The observed thermal stability is corroborated by the
variable temperature PXRD (VTPXRD), where it is observed that
the COF retains its crystallinity even after heating at 2508C
(Figure S5).
Results and Discussion
IISERP-COF15 was synthesized via a simple Schiff base conden-
sation between triformyl-resorcinol and phenylenediamine
under solvothermal conditions. The aldehyde and amine were
dissolved in a mixture of dioxane and mesitylene (1:1 v/v). To
this mixture, 0.5 mL acetic acid (6n) was added as a catalyst.
The mixture was heated in a pyrex tube at 1208C for three
days (Scheme S1). The resulting solid product was cleaned by
soxhlet extraction using dimethylformamide (DMF) and tetra-
hydrofuran (THF). The crystalline nature of COF was confirmed
by powder X-ray diffraction.
A two-dimensional (2D) COF structure formed by p-stacking
of layers having hexagonal windows was modeled, in agree-
ment with the experimental powder X-Ray diffraction, using
the Material Studio Programme (Figure 1). For the structure so-
lution, we opted a similar routine as reported in our earlier
works.[34a,37a,42,43] To ascertain the best possible space group,
we have indexed the powder X-ray pattern in the XCELL pro-
The permanent porosity of the COF was determined using
N2 adsorption at 77 K. The COF exhibits a type-I adsorption iso-
therm with a saturation N2 uptake of 15 mmolgÀ1. The COF
has remarkably high Brunauer-Emmet-Teller (BET) and Lang-
muir surface areas 1230 and 1540 m2 gÀ1, respectively, calculat-
ed from the N2 at 77 K isotherm (Figures 2B and S6). The iso-
therm, when fitted with the non-local density functional
theory (NLDFT) yields a pore-size of 12 ꢀ and a pore volume of
0.6332 cm3 gÀ1 (inset of Figure 2B). The solidity of IISERP-
COF15 has been validated under various harsh chemical condi-
tions such as 6n HCl, 6n H2SO4, 6n NaOH and even in boiling
water for 24 hours (Figure 2C). Further, 77 K N2 adsorptions
carried out on the post-chemically-treated samples and the ex-
tracted pore size distributions; confirm the structural stability
which corroborates well with the retention of crystallinity ob-
served from the PXRD (inset of Figure 2C). Thus, IISERP-COF15
can be a suitable candidate for practical gas separation appli-
Figure 1. (A) Three dimensional structure of the COF viewed along the c-axis
showing the hexagonal pores. (B) Single channel view of the COF illustrating
the heteroatoms lining its pore-wall. (C) View of p-stacked layers with an
AAA…. arrangement. Color codes; Gray: Carbon; Blue: Nitrogen; Red:
Oxygen; White: Hydrogen.
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Chem. Asian J. 2019, 00, 0 – 0
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