Porphyrin based porous organic polymers: Novel synthetic strategy and exceptionally high CO2 adsorption capacity

Article abstract of DOI:10.1039/c1cc14275e

Iron containing porous organic polymers (Fe-POPs) have been synthesized by a facile one-pot bottom-up approach to porphyrin chemistry by an extended aromatic substitution reaction between pyrrole and aromatic dialdehydes in the presence of small amount of Fe(iii). The Fe-POPs possess very high BET surface area, large micropores and showed excellent CO₂ capture (～19 wt%) at 273 K/1 bar.

Full text of DOI:10.1039/c1cc14275e

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COMMUNICATION
Porphyrin based porous organic polymers: novel synthetic strategy and
exceptionally high CO adsorption capacityw
2
Arindam Modak, Mahasweta Nandi, John Mondal and Asim Bhaumik*
Received 15th July 2011, Accepted 24th October 2011
DOI: 10.1039/c1cc14275e
Iron containing porous organic polymers (Fe-POPs) have been
synthesized by a facile one-pot bottom-up approach to porphyrin
chemistry by an extended aromatic substitution reaction between
pyrrole and aromatic dialdehydes in the presence of small
amount of Fe(III). The Fe-POPs possess very high BET surface
their potential application in CO capture from the atmosphere is
2
a big challenge today.
Porphyrin based organic polymers are very exciting in this
context due to the presence of basic pyrrole containing macro-
cyclic cavity, which facilitates strong interaction with Lewis
area, large micropores and showed excellent CO
at 273 K/1 bar.
2
capture (B19 wt%)
2
acid CO . Pre-synthesized metallo-porphyrin monomers have
been used for designing porous organic polymers (POPs) either
via a C–C cross coupling reaction using expensive Pd-catalyst or
1
1
condensation with tetra(4-aminophenyl) methane. But none of
the process is simple and the synthesized materials capture high
Advancement of society largely depends on usage of petroleum
products and burning of fossil fuels, which emit CO , one of the
2
amount of CO . Our design and synthesis strategy for POPs
2
major greenhouse gases responsible for global warming. With the
advancement of the society, the carbon level in the atmosphere is
increasing and the situation is turning worse day by day. Hence,
novel strategies for developing highly efficient materials for CO2
sequestration or separation from flue gases are very demanding
and have a direct environmental impact via greenhouse gas
remediation. Geologic sequestration, i.e. injecting the captured
involved a bottom up approach that produces the building block
porphyrinic molecules as the basic component in situ. This
unique methodology using an extended aromatic substitution
reaction of pyrrole with several di-aldehydes (Scheme 1, n = 1,2,3)
to construct a porous porphyrinic network is very simple and
produces a highly porous network.
The synthesis involved simple one-pot aromatic electrophilic
substitution on pyrrole with several aromatic di-aldehydes
containing para –CHO groups for extended cross-linking from
the macrocyclic porphyrin repeating units (Scheme 1) through a
2
CO stream into a targeted underground geologic component,
has been proposed as a feasible way to control the carbon level in
1
the atmosphere. However, due to several drawbacks of this
system, alternative methods i.e. chemisorption on solid oxide
surfaces or physical adsorption on porous solids like silicates,
2
activated carbons, etc. have attracted increasing attention
3
recently. However, only very high surface area MOFs, ZIFs,
4
5
COFs, porous BCN, amorphous supramolecules like
6
7
2
cucurbit[7]uril have shown significant CO adsorption at atmo-
spheric pressure. Unlike framework materials, organic polymers
belong to such group of materials where wide scope of utility
could be manifested by varying the functionality through judicial
choice of organic functional monomers. Pure organic polymers
like hypercrosslinked polymers or polymers with intrinsic micro-
8
9
porosity (HCPs/PIMs), porous aromatic frameworks (PAFs),
10
and related porous polymeric frameworks have been designed
starting from a variety of building blocks. But only few of them
showed outstanding CO adsorption capacity. Thus, designing a
2
new class of high surface area organic polymers and exploring
Department of Materials Science, Indian Association for the
Cultivation of Science, Jadavpur, Kolkata–700 032, India.
E-mail: msab@iacs.res.in; Fax: +91-33-2473-2805;
Tel: +91-33-2473-4971
w Electronic supplementary information (ESI) available: FTIR, TGA,
1
3
FE SEM, C CP-MAS NMR, DRS, PL and N
Fe-POPs. See DOI: 10.1039/c1cc14275e
2
-sorption data of
Scheme 1 Formation of molecular building blocks of Fe-POPs.
This journal is c The Royal Society of Chemistry 2012
2
48 Chem. Commun., 2012, 48, 248–250

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hydrothermal reaction in the presence of very small amount of
FeCl at 453 K for 3 days. Reactions were accomplished by
treatment of freshly distilled pyrrole with terephthaldehyde
POP-1), biphenyl-dicarboxaldehyde (POP-2) and p-terphenyl-
presence of 0.00267 mmol of Fe/g of Fe-POP-1, which is much
3
lower than one Fe atom/porphyrin unit. This result suggested that
many of the porphyrin units are Fe-free and can interact with
1
3
(
Lewis acid, CO . The solid state C CP-MAS NMR spectrum of
2
dicarboxaldehyde (POP-3) in glacial acetic acid medium in a high
pressure Teflon lined autoclave. Under acidic synthesis conditions,
aromatic aldehyde first gets activated through protonation, this is
followed by electrophilic aromatic substitution at the activated
carbon atoms of the pyrrole ring and then condensation to yield
macrocyclic porphyrin building blocks with free –CHO groups.
This undergoes further condensation with pyrrole and di-aldehydes
to form dark brownish extended porous organic polymeric
network structures. The product yields vary from 44%–21%
based on the starting pyrrole and aldehyde amounts. Fe-POPs
are stable on exposure to boiling water and conc. HCl, suggesting
highly cross-linked and robust structures.
Fe-POPs showed four resonances between 110.0 to 153.5 PPM
depending upon the aldehyde (Fig. S5a–b, ESIw). In Fe-POP-3,
peaks at 126.3 and 136.2 PPM correspond to phenyl carbon atoms
11b
and those at 119 and 153.5 PPM to porphyrin macrocycles.
1
3
These C MAS NMR spectra showed no signal corresponding to
free aldehyde or pyrrole, confirming the complete polymerization
of pyrrole and di-aldehydes. Moreover, UV-vis DRS (Fig. S6, ESIw)
and PL emission bands (Fig. S7, ESIw) also suggested the presence
of porphyrin moieties in these Fe-POPs.
Porous properties of these POPs have been established from
the N sorption analysis at 77 K. Prior to nitrogen adsorption
2
measurement, the polymers were rigorously washed by Soxhlet
extractions with water, ethanol, dry THF, acetone and dichloro-
methane, respectively, and then dried under vacuum at 393 K
Powder XRD analysis of these Fe-POPs revealed no strong
diffraction peaks, implying that the microporous polymers are
composed of an amorphous network (Fig. S1, ESIw). It is
pertinent to mention that using pre-synthesized metallo-
2
for 3 h. As evidenced from Fig. 1, N sorption isotherms for
Fe-POPs show type I isotherm, typical for microporous solids,
where a steep gas uptake at low relative pressure and their
1
1
porphyrin building blocks for POP formation also resulted
in materials without any definite XRD pattern (except prede-
signed metalloporphyrin building blocks used for the synthesis
mostly flat extrapolation in the intermediate sections of P/P
0
are observed. While changing from phenyl linker to biphenyl
1
2
of COFs ) suggesting the irreversibility of the reaction or
nearby completion of polymerization and formation of a
purely amorphous highly cross-linked polymer. In our synthetic
approach the cross-linking points of these POPs are the porphyrin
ring formation involving the reaction of four pyrroles and four
aldehyde molecules followed by an extended aromatic substitution
reaction. Under acidic pH in the presence of an Fe(III) oxidant, the
only other possibility is the polymerization of pyrrole to give
polypyrrole or oligopyrrole, terminal substituted dipyrromethane
or macrocycle containing 5 or more pyrrole moieties. However,
absence of any broad peak at ca. 24.0 degrees of 2y (characteristic
and then to p-terphenyl BET surface areas of POP-1, 2 and 3 varied
2
À1
from 875 to 855 and 750 m g respectively (Table S1, ESIw).
Pore size distributions (Fig. S8, ESIw) indicated peak pore
diameters of 1.1, 1.04 and 0.75/1.75/2.6 nm for Fe-POP-1,
2 and 3 materials, respectively. Existence of super micropores/
mesopores in Fe-POP-3 could be attributed to the large
p-terphenyl linker between the repeating porphyrin units. Thus
1
3
from C solid state NMR and surface area analysis we can
conclude that complete condensation of pyrrole with di-aldehydes
in the formation of porphyrin networks occurred instead
1
4
of formation of linear or branched polypyrroles. Again
FeCl has also played a pivotal role in the formation and
1
3
peak of amorphous polypyrrole polymer) rules out the possibility
of the polymerization of pyrrole in Fe-POPs under the synthesis
conditions. Further, the surface areas of the resulting Fe-POPs are
3
in situ build-up of the nucleus porphyrin cavity resulting in
highly porous extended network material with random
2
À1
750–875 m
g
(see below) whereas the maximum attainable
arrangement of pores. In the absence of FeCl a very dirty
3
surface area of polypyrrole or other oligopyrroles (under identical
2
synthesis conditions in the absence of the dialdehyde) is 60.0 m g
À1
only. This also rules out the possibility of impurity phases and
suggested that porphyrin building blocks are randomly oriented.
FE-SEM revealed that Fe-POP-1 is composed of uniform
nanospheres (Fig. S2a, ESIw) of dimension ca. 50–100 nm which
are self-assembled to form uniform large spherical particle of
ca. 350–700 nm. Such hierarchical morphological feature is quite
unique and interesting particularly for applications in adsorption
and catalysis. Fe-POP-2 and Fe-POP-3 also show similar
morphology (Fig. S2b–c, ESIw). TGA (Fig. S3a–c, ESIw) analysis
of all three samples revealed high thermal stability, up to 523 K.
The FT-IR spectra of all the materials (Fig. S4, ESIw) suggest the
-1
absence of C=O groups (1720–1740 cm ) of the aldehyde
confirming the formation of polymeric networks. Other bands
corresponding to phenyl and pyrrole moieties (Supporting infor-
mation) confirmed the direct incorporation of the pyrrole moiety
and formation of microporous porphyrin networks. Further, these
-
1
Fe-POPs exhibit a new vibration band at 1001 cm attributed to
the strong coordination of Fe(III) with porphyrin units. Existence
of Fe is also evident from AAS analysis, which suggests the
Fig. 1 Nitrogen sorption isotherms for different Fe-POPs: Fe-POP-1
(a), Fe-POP-2 (b) and Fe-POP-3 (c).
This journal is c The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 248–250 249

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significantly in wide-scale applications in environmental
research.
This work is partly funded by Nano Mission Initiative of
DST, New Delhi. AM and JM thank CSIR, New Delhi, for
their respective senior research fellowships.
Notes and references
1
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Fig. 2 Gravimetric CO uptake for Fe-POPs at 273 K.
4
1
31, 8875.
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In Fig. 2 we have plotted the CO adsorption isotherms at
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gravimetric uptake of POP-1 was 19.0 wt% and that for POP-2
and POP-3 were 18.6 and 9.0 wt%, respectively, at only 1 atm.
pressure. These curves are gradually increasing, suggesting
7
J. Tian, S. Q. Ma, P. K. Thallapally, D. Fowler, B. P. McGrail and
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2
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(
2
4
15
16
6
Rosi et al., and Zhou et al. and BCN graphene by Rao et al.
are quite interesting due to their very high absorption capacity and
crystallinity in their framework structure. Although our Fe-POPs
possess relatively low surface areas and amorphous framework
structures compared to the above-mentioned materials, they
9
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showed exceptionally high uptake for CO
organic network materials known till date the highest CO
observed was for porous benzimidazole-linked polymer (BILP-1).
2
. Among the porous
2
uptake
2
17
1
0 (a) A. P. Katsoulidis and M. G. Kanatzidis, Chem. Mater., 2011,
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À1
The CO
19 wt%). To the best of our knowledge this is the highest CO
uptake under these conditions (273 K, 1 bar pressure) for any
2
uptake observed in our Fe-POP-1 is 4.30 mmol g
(
2
porous organic network material. This higher CO adsorption
2
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2
the existence of basic porphyrin subunits in the polymeric
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1
5
network. It is interesting to note that for all the Fe-POP samples
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1
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´
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absorb large amount of CO
release the equivalent amount of CO
the pressure.
2
on exposure to atmosphere and can
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2
from its cavity while releasing
1
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In conclusion, we have designed a series of novel porphyrin
based porous organic polymers through a simple one-pot
bottom up approach involving extended aromatic substitution
on pyrrole with aromatic di-aldehydes. These materials possess
high surface areas and exhibited outstanding adsorption
1
4 A. Mihranyan, L. Nyholm, A. E. G. Bennett and M. Strømme,
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capacity for CO
2
. A simple and affordable synthetic approach
1
described herein for designing Fe-POPs may thus contribute
2
50 Chem. Commun., 2012, 48, 248–250
This journal is c The Royal Society of Chemistry 2012