Imidazolium-Functionalized Chemically Robust Ionic Porous Organic Polymers (iPOPs) toward Toxic Oxo-Pollutants Capture from Water

Article abstract of DOI:10.1002/chem.202102399

Fabricating new and efficient materials aimed at containment of water contamination, in particular removing toxic heavy metal based oxo-anions (e. g. CrO₄^2?, TcO₄^?) holds paramount importance. In this work, we r

Full text of DOI:10.1002/chem.202102399

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Imidazolium-Functionalized Chemically Robust Ionic
Porous Organic Polymers (iPOPs) toward Toxic Oxo-
Pollutants Capture from Water
Arunabha Sen+,[a] Subhajit Dutta+,[a] Gourab K. Dam,[a] Partha Samanta,[a] Sumanta Let,[a]
Shivani Sharma,[a] Mandar M. Shirolkar,[b] and Sujit K. Ghosh*[a]
À
Abstract: Fabricating new and efficient materials aimed at
350.3 mggÀ 1 for iPOP-3 and iPOP-4 respectively), where ReO4
containment of water contamination, in particular removing
anions being the non-radioactive surrogative counterpart of
radioactive TcO4 ions. Noticeably, both iPOPs showed excep-
À
À
toxic heavy metal based oxo-anions (e.g. CrO42À , TcO4 ) holds
2À
À
paramount importance. In this work, we report two new
highly stable imidazolium based ionic porous organic poly-
mers (iPOPs) decorated with multiple interaction sites along
with electrostatics driven adsorptive removal of such oxo-
anions from water. Both the iPOPs (namely, iPOP-3 and iPOP-
4) exhibited rapid sieving kinetics and very high saturation
tional selectivity towards CrO4 and ReO4 even in presence
of several other concurrent anions such as BrÀ , ClÀ , SO4
NO3 etc. The theoretical binding energy calculations via DFT
method further confirmed the preferential interaction sites as
well as binding energies of both iPOPs towards CrO4 and
ReO4 over all other competing anions which corroborates
,
2À
À
2À
À
2À
uptake capacity for CrO4 anions (170 and 141 mggÀ 1 for
with the experimental high capacity and selectivity of iPOPs
toward such oxo-anions.
À
iPOP-3 and iPOP-4 respectively) and ReO4 (515.5 and
Introduction
carcinogenic and mutagenic impact on living beings.[5] Several
industrial sectors including leather tanning, steel manufactur-
ing, textile pigments & dyes, wood preservation etc. are involve
in chromium usage in huge amounts for diverse applications.
As is known, tanning industries generate ~35 L of chromium
contaminated wastewater solely for one kilogram of leather
production which subsequently pollute natural water bodies.[6]
Additionally, Cr (VI) based oxo-anions are found to weaken the
integrity of nuclear waste glass during its vitrification process
resulting in poor efficiency of the process.[6] Moreover, the
world has witnessed several incidents of ground water pollution
because of improper disposal of Cr (VI) containing wastewater.[7]
Hinkley groundwater contamination in California is one of the
famous example where ~1,400 million liters of chromium
containing wastewater was disposed into the natural
waterbodies.[8] In addition, other than Cr(VI)-based water
pollution issues, ground water contamination by nuclear power
plant generated radioactive wastes have become another major
concern.[9] In this regard, nuclear safety has become a genuine
concern as the last few decades have witnessed several nuclear
accidents, which lead to contamination of radioisotopes in large
scale along with their chemotoxicity and radiotoxicity to natural
Accessibility to fresh drinking water has become an imminent
threat in the 21st century that have direct impact on human
lives. The far-flung growth in industrialization and widespread
urbanization across the globe are the two prime reasons behind
such crisis and depletion of fresh water.[1] This situation might
become so dreadful that as many as one billion of global
population will experience utmost water crisis by 2025, as
predicted by United Nations.[2] Among various contamination
sources, water pollution by heavy metals (density>5 gcmÀ 3)
and their oxo-anionic complexes (CrO42À , MnO4 , SeO32À , AsO4
À
3À
etc.) have come forth as pressing concern, owing to their severe
toxic effect on living organisms upon bioaccumulation.[3] In
addition, such toxic oxo-anions are considered as the “priority
pollutants”, listed by Environment Protection Agency (EPA,
United States).[4] In this context, special attention has been
directed toward Cr(VI) based oxo-anions because of their
[a] A. Sen,+ S. Dutta,+ G. K. Dam, Dr. P. Samanta, S. Let, Dr. S. Sharma,
Prof. S. K. Ghosh
Department of Chemistry
À
water bodies. Among them, pertechnetate (TcO4 ) anion has
Indian Institute of Science Education and Research (IISER), Pune
Dr. HomiBhabha Road, Pashan, Pune 411008 (India)
E-mail: sghosh@iiserpune.ac.in
attracted much research attention mainly as one of its β-
emitting radioactive isotope technetium (99Tc), which possess a
very prolonged half-life period of 2.1×105 years. Moreover,
nuclear fission of 239Pu and 235U result into a very large fission
yield of radioactive 99Tc and approximately 305 metric tons
nuclear waste containing 99Tc have been discharged from
several nuclear power plants and weapons testing activities.[10]
[b] Dr. M. M. Shirolkar
Symbiosis Center for Nanoscience and Nanotechnology (SCNN)
Symbiosis International (Deemed University) (SIU)
Lavale, Pune 412115, Maharashtra (India)
[+] These authors contributed equally to this work.
Supporting information for this article is available on the WWW under
https://doi.org/10.1002/chem.202102399
À
The non-complexing characteristic of TcO4 along with its high
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mobility and solubility in water allows it to remain as low-level
nuclear-waste material.[11] Several techniques, for example,
adsorption, photocatalytic reduction, chemical precipitation, ion
exchange etc. have been utilized to combat this concern, but
among them, ion exchange based methods are preferred over
other methods owing to its comparatively simple and safe
processing, high affinity and selectivity, good performance in
low-concentration waste solution etc.[12] In addition, the state of
the art ion-exchangers present pitfalls such as lower uptake
efficiency, poor selectivity and slow kinetics which endows
possibilities to develop new alternative and more efficient ion
exchange materials.[13]
To address this demand, tremendous efforts have been
employed toward the development of new sorbent materials
featuring higher binding affinity and uptake efficiency.[14] To
this end, metal-organic frameworks (MOFs) and porous-organic
Polymers (POPs) have strongly established themselves as the
new generation ion exchangers owing to features such as tailor
made tunable pore surface, charge controllability, amenability
of design etc.[15] Although MOFs are known to offer good
kinetics and selectivity towards such oxo-anion extraction, but
poor physiochemical stability especially under highly acidic as
well as basic conditions limits the utility of these materials as
sorbents towards real-time environmental remediation and
nuclear fuel processing.[16] On the contrary, porous organic
polymers fabricated from stable covalent bonds not only exhibit
superior physiochemical stabilities even under extreme chem-
ical conditions but their additional beneficial features for
example high surface area, radiation resistibility etc. make them
front runner in comparison with other contemporary porous
materials.[17] Moreover, strategic utilization of neutral N-donor
based moieties such as imidazole and benzimidazole as differ-
ent crosslinking terminals with multiple halogen sites (À CH2X;
X-halogen) yield cationic porous organic polymers with positive
Scheme 1. Schematic representation of toxic oxo-anion capture in iPOPs.
moieties, π electron rich surface etc. contribute to superior
selectivity of these materials toward such oxo-anions[5c–d,11] On
account of such structural diversity and physiochemical stabil-
ity, cationic porous organic frameworks certainly can be an
appropriate candidate for sequestration of such hazardous oxo-
anionic pollutants from water.
Considering all these aspects, here we present two novel
chemically stable ionic porous organic polymers (iPOPs), iPOP-3
and iPOP-4 fabricated from nitrogen rich triazine core and
imidazole derivatives, bearing exchangeable bromide (BrÀ )
anions inside the porous networks (Figure 1). Both the com-
pounds are found to show highly selective and efficient capture
2À
À
of toxic and hazardous CrO4 and ReO4 anions from water,
À
while ReO4 anions were being utilized as a corresponding
surrogate for radioactive TcO4À ions (Scheme 1).
quaternized nitrogen site and exchangeable counter halide Results and Discussion
anions. The electrostatic interaction between the counter halide
anions and the host framework are known to be very weak due
to which the halide counter anions assist in dispersion of
cationic iPOP particles in water, resulting in rapid and efficient
trapping of the aimed anionic pollutants in water via ion-
exchange. Additionally, incorporation of different binding sites
inside the network such as triazine core, imidazole based
The compounds iPOP-3 and iPOP-4 were synthesized via one-
condensation reaction between imidazole for iPOP-3 and
benzimidazole for iPOP-4 with Tris-(4-bromomethyl-phenyl)-
[1,3,5]triazine for 24 h under inert atmosphere (Schemes S1–S3).
The as-made compounds were thoroughly washed with differ-
ent solvents (DMF, DMSO, THF, Toluene, MeOH, acetone and
Figure 1. Schematic representation of synthesis of iPOP-3 and iPOP-4.
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water) post synthesis to remove the trapped small chain
oligomers as well as unreacted starting materials. Further, both
compounds were dipped in DCM, THF and acetonitrile (1:1:1)
mixture for 72 h for solvent exchange with changing of solvents
frequently in repeated interval of 12 h and were kept under
desolvated iPOP-3 and iPOP-4 networks (Figure S13–S18). FTIR
spectroscopy revealed peaks ~1520 cmÀ 1 corresponding to
C=N stretching frequency of constituent triazine and imidazole
linkages. The peaks around ~1150 cmÀ 1 and 750 cmÀ 1 are
indicative of the presence of imidazolium based functional
groups. Moreover, the peaks around ~1420 cmÀ 1 represents the
stretching frequency of the methylene (-CH2-) functional groups
present while the peak at ~1370 cmÀ 1 represents the presence
of triazine rings present in iPOP-3 and iPOP-4 (Figures 2c,
S9).[18,20–21] To access the stability aspect of these iPOPs, they
were subjected to harsh condition treatment of acidic (1 N HCl)
as well basic (1 N NaOH) solutions for 24 h. The post treated
samples were thoroughly characterized with solid state NMR
(SS NMR), TGA and FTIR techniques. 13C SS NMR did not show
any deviation from original spectra with no emergence of any
new peaks accounting for unaltered structural features (Fig-
ure S10–S11). The TGA data revealed analogous profile to that
of the pristine phase of iPOP-3 and iPOP-4 (Figure S4–S5)
confirming the retention of thermal as well as chemical stability.
Moreover, FTIR measurements substantiated the presence of all
the characteristic peaks when compared with the pristine
compounds (Figure 2c, S9). Further, we have performed low-
temperature gas adsorption N2 (77 K) as well as CO2 (195 K)
data to substantiate the porosity of both iPOPs (Figure S8). We
observed very lower uptakes for N2 (77 K) for both iPOPs
whereas the CO2 (195 K) adsorption profiles substantiated the
inherent porosity with an uptake of 64 mLgÀ 1 for iPOP-3 and
49 mLgÀ 1 for iPOP-4. Additionally, the chemically robust nature
of these iPOPs were further substantiated from its outstanding
performance upon exposure to various chemical environments.
A minimal loss in residual weight % (Figure S12) was observed
when both of the compounds were immersed in a wide array of
solutions advocating for its highly stable nature.
°
vacuum around 90 C for 24 h to obtain the guest free
desolvated phase of iPOP-3 and iPOP-4. The guest free phases
of both polymers were thoroughly characterized with 13C-CP-
MAS NMR (cross polarization magic angle spinning nuclear
magnetic resonance), Fourier transform infra-red (FTIR) spectro-
scopy, field emission scanning electron microscopy (FESEM),
energy dispersive X-ray analysis (EDX) and thermogravimetric
analysis (TGA). The 13C-CP-MAS NMR studies exhibited peaks
around ~114 ppm to ~142 ppm (d, e, f), which corresponds to
presence of aromatic carbons of imidazole and benzene rings
respectively.The peak around ~51 ppm (a,b) corresponds to the
formation of the methylene linkages attached with both the
nitrogens of imidazole for iPOP-3 and benzimidazole for iPOP-4
for the expansion of the cationic polymeric networks. The peaks
around ~169 ppm (c) corresponds to the carbon atoms of the
triazine rings present at the core of iPOP-3 and iPOP-4
(Figure 2a, S1).[18,20] TGA analysis of iPOP-3 showed an initial
°
weight loss (~8%) around 75 C in the pristine phase which
might be attributed to the trapped solvent molecules which
were removed via desolvation. The TGA curve for the
desolvated phase of iPOP-3 showed negligible weight loss until
°
300 C while the profile for iPOP-4 shows negligible weight loss
°
until 350 C confirming guest free nature (Figures 2b, S3). FESEM
images revealed the presence of agglomerated particles while
EDX spectroscopy and elemental mapping showed the homo-
geneous presence of free BrÀ as the counter anions in the
Such physiochemical stability along with cationic nature of
both compounds propelled us to evaluate its potential towards
toxic oxo-anion trapping from water. Depending upon the pH
of the medium, hexavalent chromium oxo-anions, i.e. chromate
(CrO42À ) and dichromate (Cr2O72À ), primarily remain in intercon-
vertible equilibrium. Hence, we further performed the capture
experiments with chromate in this work. Initially, we dipped
5 mg of both iPOP-3 and iPOP-4 in a 5 mL 2 mM aqueous
CrO42À solution individually and monitored the trapping process
via both naked eye color change and UV-Vis spectroscopy. A
gradual color change from yellow to almost colorless for both
the solutions was observed within just 1 h illustrating rapid
2À
capture of CrO4 by both the compounds (Figures 3a–c).
Enthused from such fast kinetics, we have carried out in situ
2À
titration of CrO4
capture in water for both iPOPs and
monitored via UV-Vis spectroscopy where 2 mL 0.5 mM aque-
2À
ous solution of CrO4 was added to 1 mg of both compounds
individually and the absorption maxima (λmax) at 372 nm for
2À
CrO4 ion was monitored (Figures 4a and d). The diminishing
trend in UV-Vis spectra at 372 nm with increment of time
2À
affirmed trapping of CrO4 anions in case of both compounds.
As was observed, the anion trapping took place in a rapid
manner with almost ~60% and ~55% removal of CrO4 ions
were observed within just 2 min while almost ~90% and ~80%
Figure 2. (a) Solid state NMR for iPOP-3, the ‘*’ marked peaks correspond to
side bands; (b) TGA profiles for compound iPOP-3; (c) FTIR profiles for
compound iPOP-3.
2À
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intervals. Notably, both compounds exhibited similar rapid
À
kinetics as almost ~75% and ~55% of ReO4 anions were
found to be trapped within just 2 min by iPOP-3 and iPOP-4
respectively (Figures 4b and e). The percentage removal vs.
time studies further corroborated with the rapid kinetics of the
capture processes (Figure S41, S43). In addition, the saturation
À
uptake capacities of ReO4 ions evidenced from UV-Vis spectro-
scopy are 515.5 mggÀ 1 and 350.3 mggÀ 1 for iPOP-3 and iPOP-4
respectively (Figure S41, S42), among which iPOP-3 was found
to stand tall among the highest values reported in the regime
of porous materials (Table S2). 13C NMR data of post pollutant
capture phase corroborated well with the pristine compound
while FTIR spectra revealed the presence of characteristic peaks
for both the compounds with a new peak at ~918 cmÀ 1
À
corresponding to the ReO4 anions (Figure S19–S20, S23–S24).
Additionally, a homogeneous distribution of rhenium along
with the other elements in EDX and elemental spectra analysis
confirmed the incorporation of perrhenate anions inside the
pores of both the compounds (Figure S37–S40). Keeping in
mind the real time applicability of our materials, we were
prompted to test the competency of these compounds when
subject to harsh chemical environments. To validate this, we
have performed the oxo-anion capture experiments with both
iPOP-3 and iPOP-4 after they were exposed to 1(N) HCl and 1(N)
NaOH respectively. To our delight, both iPOPs exhibited almost
intact efficiency with the acid treated phases: 99% (iPOP-3),
Figure 3. Visual color change of aqueous solution of CrO42À and correspond-
ing iPOPs (a) upon addition of iPOP-3, (b) upon addition of iPOP-4, (c)
decrease in concentration of CrO42À with increment of time upon addition of
iPOP-3.
removal was achieved within 60 min using 1 mg of iPOP-3 and
iPOP-4 respectively (Figures 4a and d). The percentage removal
vs. time study corroborated with the fast kinetics of the capture
process by both iPOP-3 and iPOP-4 (Figure S31, S33). In
2À
95% (iPOP-4) for CrO4 and 98% (iPOP-3), 96% (iPOP-4) for
À
ReO4 whereas with base treated phases: 100% (iPOP-3), 94%
2À
(iPOP-4) towards CrO4 capture and 99% (iPOP-3), 95% (iPOP-
2À
À
addition, the saturation uptake capacity of CrO4 evidenced
4) towards ReO4 anions (Figure 4i). Such results indeed under-
from UV-vis spectroscopy are 170 mggÀ 1 and 141 mggÀ 1 for
iPOP-3 and iPOP-4 respectively (Figure S35–S36). It is note-
worthy to mention that these saturation uptake capacities are
accounted among the highest values reported in the literature
of porous materials (Table S1). The differential efficiency toward
pollutant capture performance of iPOP-4 in comparison with
iPOP-3 may be attributed to a combination of reduced porosity
as well as enhanced hydrophobicity (Figure S8, S65). Further-
more, the post-capture phases were characterized by SS NMR,
solid state UV-vis analysis, FTIR analysis, EDX and elemental
analysis studies. The SS NMR confirmed retention of the
characteristic peaks for both iPOPs in post-capture phases
(Figure S19–S20). FTIR analysis confirmed presence of all
characteristic peaks along with emergence of a new peak at
score the utility of these iPOPs in treatment of real-world
wastewater. Moreover, anion trapping by both the iPOPs
followed pseudo-second-order kinetics as the time dependent
uptake capacity fitting profile revealed that all the capture
processes were exclusively dependent upon the quantity of
adsorbent and the adsorbate used (Figure 4c, 4f, S47, S48). The
correlation coefficient (R2) values for iPOP-3 were found to be
2À
–
0.999 and 0.997 for CrO4 and ReO4 ions respectively. On the
other hand, R2 values of iPOP-4 were found to be 0.995 and
2À
–
0.999 for CrO4
and ReO4 anions respectively. The rate
constant (k2) values were found to be 0.00728 mg/g min
–
(CrO42À ) and 0.00621 mg/g min (ReO4 ) in case of iPOP-3 and
–
0.00938 mg/g min (CrO42À ) and 0.00735 mg/g min (ReO4 ) in
case of iPOP-4. Further, to substantiate the potential of these
iPOPs towards removal of such oxo-anions in very low
2À
~894 cmÀ 1 correlated with the CrO4 anions validating the
2À
retention of the network integrity (Figure S23–S24). In addition,
homogeneous distribution of chromium in EDX and elemental
spectra analysis confirmed the incorporation of chromate
anions inside the pores of both the compounds (Figure S25–
S30).
concentration, we have performed CrO4 removal experiments
with both iPOPs in a very low concentration range (10–
100 ppm). To our delight, both iPOPs have recorded almost
2À
100% removal efficiency toward CrO4 anions even in lower
concentration of 10 ppm (Figure S49–S50).
À
Along the same line, pertechnetate (TcO4 ) is another lethal
Enthused by their impressive uptake capacities, we were
motivated to investigate the selectivity of these iPOPs as real
wastewater effluents contain several interfering anions (such as
oxo-anion on account of being radioactive while 99Tc is β-
À
emitting in nature. Due to radioactivity of TcO4 , we have used
À
À
a non-radioactive surrogate viz. ReO4 , that have similar size-
SO42À , BrÀ , ClÀ , NO3 etc.) that coexists along with the targeted
charge distribution. Further, we have performed in situ titration
studies for ReO4À anions under UV-vis spectroscopy by monitor-
ing the intensity maxima (λmax) at 208 nm with increase in time
oxo-anions. The competing studies were carried out in presence
of various coexisting interfering anions in a 1:1 mixture of both
CrO4 and ReO4 oxo-anions individually. Both iPOPs exhibited
2À
À
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Figure 4. (a) UV-Vis spectra in presence of iPOP-3 for CrO42À , (b) UV-Vis spectra in presence of iPOP-3 for ReO4À , (c) Kinetic study of CrO42À ion capture with
iPOP-3, (d) UV-Vis spectra in presence of iPOP-4 for CrO42À , (e) UV-Vis spectra in presence of iPOP-4 for ReO4À , (f) Kinetic study of ReO4À ion capture with iPOP-
3, (g) Bar diagram for CrO42À removal efficiency of iPOP-3 in presence of BrÀ , ClÀ , NO3À and SO42À ions, (h) Bar diagram for ReO4À removal efficiency of iPOP-3
in presence of BrÀ , ClÀ , NO3À and SO42À ions, (i) Removal efficiency of acid and base treated phases of iPOP-3 and iPOP-4.
2À
À
excellent selectivity towards CrO4 and ReO4 as the removal
performance remained almost unaltered (�90%) in each case
confirming very high affinity of both the iPOPs toward such
oxo-anions (Figures 4g–h, S51, S52). Further, to strengthen and
verify our results regarding the selectivity of iPOPs, we have
performed Density Functional Theory (DFT studies) which
successfully validated our experimental findings (discussed in
details later).
compounds went back to their initial off-white color. Further,
the concentration of the released oxo-anions were verified via
UV-vis spectroscopy. The kinetics for release profile was noted
to be moderate but both the iPOPs were able to release almost
2À
all CrO4 anions within 24 h (Figure S53–S54, S63). The slow
kinetics indicate that both iPOP frameworks possess very high
affinity as well as favorable binding sites toward the oxo-anions
in comparison to BrÀ anion, which was further confirmed by the
theoretical DFT calculations. Similar results were obtained for
the release of perrhenate anions by the iPOPs. Notably, both
compounds exhibited almost same efficiency in first two cycles
of recyclability and it reduced to ~85% in 3rd cycle for both
iPOPs (Figure S53, S54). To get more insights about such
excellent selectivity and affinity of both iPOPs toward these
oxo-anions, we have executed DFT calculations using Discovery
Studio software package (Supporting Information contains
more simulation details). According to the experimental param-
Reusability of the sorbent material is one of the major
aspect in real-time water pollutant sequestration processes. In
this regard, we have carried out reversibility experiments with
2À
both iPOPs in which we dipped 5 mg of each oxo-anion (CrO4
and ReO4 ) occluded phase of iPOP-3 (iPOP-3@CrO42À , iPOP-
À
3@ReO4 ) and iPOP-4 (iPOP-4@CrO42À , iPOP-4@ReO4 ) in 2 M
À
À
aqueous solution of tetrabutylammonium bromide. A gradual
color change upon release of trapped CrO4 anions from
colorless to yellow was observed for both iPOPs while the
2À
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eters a monomeric unit of iPOP-3 and iPOP-4 was constructed,
consisting of triazine rings along with imidazole and benzimida-
zole respectively. The electrostatic potential (ESP) distribution
profile of monomers corroborated well with the uniform
delocalization of negative and positive charges surrounding
imidazole, benzene and triazine rings which further serve as the
preferential recognition sites for the incoming oxo-anions,
having lower charge density (Figure 5).
Theoretical DFT calculations provided valuable information
2À
À
regarding several favorable binding sites for CrO4 and ReO4
over other anions that is directly reflected in the binding energy
2À
values. The binding energies of CrO4 with the building units
of iPOP-3 and iPOP-4 were found to be À 304.45 kJ/mol and
À 544.45 kJ/mol respectively, which are much higher than the
binding energies of other anions (Figures 6a–f, S64). Similarly,
À
the binding energies of ReO4 anion with the building units of
iPOP-3 and iPOP-4 were found to be as high as À 413.12 kJ/mol
and À 603.12 kJ/mol respectively, which indicate strong inter-
À
actions as well as high affinity of both the iPOPs for ReO4
anions. The binding energies for BrÀ ion with the iPOPs building
units were found to be À 69.72 kJ/mol and À 74.82 kJ/mol,
which are much lower than the corresponding binding energies
of the target analytes aiding both these materials in kinetics,
capture efficiency and selectivity as observed in the experimen-
tal studies.
Conclusions
Figure 5. Monomer unit of iPOP-3 and iPOP-4 showing the electrostatic
potential isosurface (isodensity=0.001 a.u.) calculated using DFT-DMOL3-
B3LYP (a) and (c) represent top view of iPOP-3 and iPOP-4 respectively, (b)
and (d) represent top view ESP diagram of iPOP-3 and iPOP-4 respectively.
In conclusion, two new chemically stable cationic porous
organic polymers, namely iPOP-3 and iPOP-4, were synthesized
Figure 6. Optimized structures of monomeric unit of iPOP-3 with different binding anions and the corresponding binding energies calculated based on DFT-
DMOL3-B3LYP, (a) iPOP-3-(ReO4À ), (b) iPOP-3-(CrO42À ), (c) iPOP-3-(SO42À ), (d) iPOP-3-(NO3À ), (e) iPOP-3-(ClÀ ), (f) iPOP-3-(BrÀ ).
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and thereupon utilized for sequestration of toxic oxo-anions Conflict of Interest
2À
À
(CrO4 and ReO4 ) from water. Both compounds performed
remarkably well in terms of rapid kinetics, high uptake
efficiency and superior selectivity toward these oxo-anions. The
The authors declare no conflict of interest.
2À
À
uptake capacities of iPOP-3 for both CrO4 and ReO4 are
among the highest reported values in the arena of overall
porous materials. Furthermore, the theoretical calculations
along with DFT analysis brings forth insights regarding potential
recognition sites for oxo-anions as well as the emergence of the
exceptional selectivity and efficiency of both the iPOPs. In
addition, both compounds showed reusability up to three
cycles for the oxo-anions, advocating as potential candidates
for real-time utilization in such oxo-anion sequestration applica-
tions. The experimental findings of this work highlights that
iPOPs can serve as potent adsorbents toward wastewater
remediation with facile synthesis, exceptional removal efficiency
and high adsorption capacity.
Keywords: cationic frameworks · capture · oxo-anion · porous
organic polymers · water pollution
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a
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°
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desolvated phase of the compound (Scheme S2).
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Acknowledgements
A.S. and S.D. thank IISER-Pune for research fellowship. G.K.D.,
S.L. and S.S. thank CSIR for research fellowships. P.S. thank UGC
for research fellowship. M. M. S. thanks SIU Pune, India for
technical support. S.K.G. thanks SERB (Project No.CRG/2019/
000906) for funding.
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Manuscript received: July 2, 2021
Accepted manuscript online: July 14, 2021
Version of record online: ■■■, ■■■■
Chem. Eur. J. 2021, 27, 1–9
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These are not the final page numbers!

FULL PAPER
An example of utilization of
A. Sen, S. Dutta, G. K. Dam, Dr. P.
Samanta, S. Let, Dr. S. Sharma,
Dr. M. M. Shirolkar, Prof. S. K. Ghosh*
imidazole-functionalized chemically
robust cationic porous organic
polymers (POPs) for rapid and
efficient capture of hazardous dual
oxo-anionic pollutants from water.
The study will enrich the concept of
designing new efficient cationic
polymeric materials to tackle the
problems based on water pollution,
one of the most important threats
towards the initiative for a green and
clean environment.
1 – 9
Imidazolium-Functionalized Chemi-
cally Robust Ionic Porous Organic
Polymers (iPOPs) toward Toxic Oxo-
Pollutants Capture from Water