Polyoxometalate-based gelating networks for entrapment and catalytic decontamination

Article abstract of DOI:10.1039/c7cc05657e

We report the synthesis and characterization of a new class of organic/inorganic hybrid polymers composed of covalently-bound 1,3,5-benzenetricarboxamide linkers and anionic polyoxovanadate clusters with varying counter-cations. These materials form gels within seconds upon contact with polar aprotic organic liquids and catalyze the degradation of odorants and toxic molecules under mild conditions including aerobic oxidation of thiols, hydrogen peroxide-catalyzed oxidation of sulfides, and hydrolysis of organophosphate chemical warfare agent analogues.

Full text of DOI:10.1039/c7cc05657e

ChemComm
View Article Online
View Journal
COMMUNICATION
Polyoxometalate-based gelating networks for
entrapment and catalytic decontamination†
Cite this:DOI: 10.1039/c7cc05657e
Kevin P. Sullivan,a Wade A. Neiwert,‡a Huadong Zeng,§a Anil K. Mehta,a Qiushi Yin,a
Daniel A. Hillesheim,¶a Skanda Vivek,8b Panchao Yin, **c Daniel L. Collins-Wildman,a
Received 20th July 2017,
Accepted 30th September 2017
b
a
Eric R. Weeks,
Tianbo Liuc and Craig L. Hill
*
DOI: 10.1039/c7cc05657e
rsc.li/chemcomm
We report the synthesis and characterization of a new class of producing a significant change in volume between the swollen and
organic/inorganic hybrid polymers composed of covalently-bound unswollen states, making them attractive for materials designed to
1,3,5-benzenetricarboxamide linkers and anionic polyoxovanadate protect against toxic compounds.11,14,15 Development of materials
clusters with varying counter-cations. These materials form gels for the sequestration and decontamination of chemical warfare
within seconds upon contact with polar aprotic organic liquids and agents (CWAs), including organophosphorus (OP) nerve agents such
catalyze the degradation of odorants and toxic molecules under as Sarin and VX, and blister agents such as sulfur mustard (HD), has
mild conditions including aerobic oxidation of thiols, hydrogen been a priority for decades due to their high toxicity and potential
peroxide-catalyzed oxidation of sulfides, and hydrolysis of organo- for large-scale release.16 Several types of materials have been shown
phosphate chemical warfare agent analogues.
to catalyze hydrolysis of OP agents or oxidation of HD into nontoxic
products,17,18 and entrapment of CWAs through gelation has been
Inorganic/organic polymers are important in multiple disciplines reported,19 but a material that could both sequester and catalytic
as they allow for synergy between the physical properties of decontaminate toxic molecules would represent a significant
traditional polymers and versatility in function of inorganic advance in the field of protective materials.
compounds.1–3 Polyoxometalates (POMs), oligomeric aggregates
We report here a polymer composed of C3-symmetric
of metal cations bridged by oxide anions, have received significant 1,3,5-benzenetricarboxamide units covalently connected with
attention for their applications in many fields, including catalysis, POM clusters. The material forms gels upon simple addition of
energy conversion, memory storage, and medicine, among others.4,5 a liquid, including the chemical warfare agent analogue
Combining POMs with organic components to create organic/ dimethyl methylphosphonate (DMMP). This polymer and its
inorganic hybrid molecules or polymers allows for the rational derivatives are additionally capable of catalyzing both hydro-
design of multifunctional compounds with unique properties.6–10
lysis of nerve agent simulants and aerobic oxidation reactions
Materials that respond to external stimuli play an increasing under mild conditions. The physical and chemical properties of
role in a diverse range of applications, including protection the polymer can be readily altered through exchange of the
against chemical or biological threats.11–13 Three-dimensional POM counter cations, allowing for the creation of a wide variety
polymer systems can swell through adsorption of solvent molecules, of new responsive and reactive materials.
Reaction of C6H3(CONHC(CH2OH)3)3 (trisBTA) and (TBA)3-
[H3V10O28] in N,N-dimethylacetamide (DMA) affords a gel material
that is isolated as a red insoluble powder with the formula
[(n-C4H9)4N]2n[(V6O13)n[((OCH2)3CNHCO)3C6H3]x[((OCH2)3-CNHCO)2-
((HOCH2)3CNHCO)C6H3]y[(OCH2)3CNHCO((HOCH2)3CNHCO)2-
C6H3]z] (TBA-polyV6, x = triply bound trisBTA, y = doubly-bound
trisBTA, z = singly-bound trisBTA) (Fig. 1a).
a Department of Chemistry, Emory University, Atlanta, GA 30322, USA.
E-mail: chill@emory.edu
b Department of Physics, Emory University, Atlanta, GA 30322, USA
c Department of Polymer Science, University of Akron, Akron, OH 44325, USA
† Electronic supplementary information (ESI) available. See DOI: 10.1039/
c7cc05657e
‡ Present address: Department of Chemistry, Bethel University, St. Paul, MN
55112, USA.
Solid-state cross-polarization magic angle spinning (CP-MAS)
§ Present address: McKnight Brain Institute, University of Florida, Gainesville, FL 13C NMR on TBA-polyV6 reveals POM-bound trisBTA linkers
32611, USA.
in the product and confirms the covalent attachment between
the linkers and POM units, indicated by a shift in the alcohol
¶ Present address: ABT Molecular Imaging, Inc., Louisville, TN 37777, USA.
8 Present address: School of Physics, Georgia Institute of Technology, Atlanta,
Georgia 30332, USA.
methylene peak upon binding to the hexavanadate units (Fig. 1b).
A single peak in both solid-state and solution 51V NMR spectra
** Present address: Chemical Engineering and Materials Division, Oak Ridge
National Laboratory, Oak Ridge, TN 37831, USA.
confirms the presence of hexavanadate (V6) units within the
This journal is ©The Royal Society of Chemistry 2017
Chem. Commun.

View Article Online
Communication
ChemComm
Fig. 2 (a) Swelling of TBA-polyV6 (left) in the presence of dimethyl methyl
phosphonate (DMMP) (right). (b) Swelling of TBA-polyV6 (left) in the
presence of DMF (right). (c) Analysis of swelling rate using particle tracking
after exposure to DMF. (d) Swelling behavior measured in mL of liquid per
gram of material after 24-hour exposure.
Fig. 1 (a) Representation of TBA-polyV6, indicating triply-bound (x) doubly-
bound (y) and singly-bound (z) linkers. (b) Solid-state 13C NMR of TBA-polyV6.
TBA+ (*) peaks are indicated. Orange and red spheres represent V(V) and O2À
respectively.
,
polymer (Fig. S1, ESI†).20 Comparisons between the V–O stretch- of the crosslinked polymer and hydrogen-bonding interactions,
ing frequencies in the infrared spectrum of the polymer to a as is observed in other 1,3,5-tricarboxamide-based polymers
known monomeric hexavanadate further supports the presence of (Fig. S6, ESI†).22 Comparing the swelling capability of TBA-polyV6
V6 units (Fig. S2, ESI†).21
Deconvolution of the solid-state 13C NMR spectrum as well liquid entrapment (Fig. S7, ESI†).
to other absorbent materials reveals its high capacity for organic
as XPS data indicate that the polymer is composed of highly
Significantly, we observed that TBA-polyV6 can form gels
branched strands (Fig. S3 and S4, ESI†). These extensively cross- when exposed to OP agent analogues. Addition of the G-series
linked fiber structures can be seen in electron microscopy nerve agent analogue DMMP results in a substantial index of
images of the material (Fig. S5, ESI†). The extensively cross- swellability (Q) value of 10 mL gÀ1 (Fig. 2a and d), also with
linked structure of the polymer results in the material possessing rapid swelling kinetics. Studies using highly-crosslinked polymers
a relatively high BET surface area of 430 m2 gÀ1
.
have demonstrated correlations between swelling capability
TBA-polyV6 exhibits remarkable physical properties in the in polar organic liquids such as DMF and CWAs such as HD
presence of polar aprotic liquids, entrapping them upon con- and OPs.19
tact and forming gels within seconds (Video S1, ESI†). This
The physical and chemical properties of TBA-polyV6 can be
rapid gelation behavior was visualized under a microscope, and readily altered by exchange of the TBA+ counter cations. We
image analysis was used to obtain a qualitative measure of the employed this strategy to exchange the TBA+ cations for a
swelling kinetics (Fig. 2c and Video S2, ESI†). These gels remain variety of cations, but focus here on the lithium (Li-polyV6)
stable to inversion indefinitely after swelling, and can be and zirconium (Zr-polyV6) substituted analogues. Exchange
returned to the contracted solid form though addition of a occurs without changing the structure of the polymer (Fig. S8
nonpolar solvent such as toluene or diethyl ether, demonstrat- and S9, ESI†), but alters the gelation capability of the material
ing both rapid and reversible organogel-forming activity. The as demonstrated by the increased Li-polyV6 index of swellability
swelling parameters for several organic solvents are shown in in DMF and DMSO relative to TBA-polyV6 (Fig. 2d). Thus, we
Fig. 2d. This gelation behavior is attributed to both pore-filling establish the ability to tailor this new class of materials to
Chem. Commun.
This journal is ©The Royal Society of Chemistry 2017

View Article Online
ChemComm
Communication
exhibit desired swelling based on judicious counter cation polymers towards hydrolysis of OP analogues. TBA-polyV6
choice. catalyzes the hydrolytic breakdown of the OP nerve agent
Hexavanadate POMs are known to be active towards the analogue diethyl cyanophosphonate (DECP) to the nontoxic
oxidation of sulfides.23,24 To demonstrate the applicability diethyl phosphate (Fig. S15, ESI†), likely through the formation
of TBA-polyV6 for air-based oxidative removal reactions, we of multiple hydrogen-bonding interactions between the polymer
conducted studies on the catalytic oxidation of propane thiol and DECP.28 However, it is less effective against more realistic
(PrSH) to dipropyl disulfide (PrSSPr). This representative and challenging OP agent analogues. Zr-Based materials have
odorant is fully oxidized to the non-odorous disulfide, using received a great deal of attention for their high activities towards
oxygen to reoxidize the reduced POM units (130 turnovers in hydrolysis of OP nerve agents, particularly in recent work using
B6 days) (Fig. S10 and S11, ESI†). TBA-polyV6 is red in its powder Zr-based metal–organic frameworks (MOFs).17,30 Accordingly,
state and yellow when dispersed in solvent. Upon reduction of the Zr-substituted Zr-polyV6 shows significant activity for catalyz-
the POM, the material becomes dark green, providing a colori- ing the hydrolysis of dimethyl p-nitrophenylphosphate (DMNP)
metric detection capability (Fig. S10 and S12, ESI†).
and achieves full conversion to the hydrolysis products with a t1/2
More significantly, TBA-polyV6 catalyzes oxidation of the HD of 25 min (Fig. 4), which is comparable to the activity of several
simulant 2-chloroethyl ethyl sulfide (CEES) by the mild and zirconium-based MOF catalysts.30 We show, therefore, that this
environmentally-friendly oxidant hydrogen peroxide. CEES is polymer material can easily be tuned to significantly enhance its
completely and rapidly oxidized in the presence of TBA-polyV6 catalytic hydrolysis activity.
and H2O2 (Fig. 3), showing its promise as an effective catalyst
The multifunctional polymer TBA-polyV6, composed of alter-
for the removal of HD under mild conditions. Additionally, this nating hexavanadate POM and trisBTA units has been synthe-
reaction selectively forms the less toxic 2-chloroethyl ethyl sized and characterized and is, to our knowledge, the first
sulfoxide (CEESO) without overoxidation to the harmful example of a material which forms gels upon contact with CWA
2-chloroethyl ethyl sulfone (CEESO2) product (Fig. S13, ESI†). analogues while simultaneously possessing catalytic oxidation
Both Zr-polyV6 and Li-polyV6 also exhibit catalytic sulfoxidation and hydrolysis functions. The catalytic redox processes proceed
activity (Fig. S14, ESI†) compared to related heterogeneous under mild conditions for the representative odorant propane
sulfoxidation catalysts.25,26 Through these two exemplary thiol and the HD analogue CEES. The chemical and physical
oxidation reactions, we demonstrate the applicability of the properties of TBA-polyV6 can be readily tuned by judicious
TBA-polyV6 polymer for catalytic oxidation of toxic or odorant choice of counter cation, producing the two exemplary com-
molecules under mild conditions.
pounds Zr-polyV6 and Li-polyV6. Li-polyV6 exhibits altered
Both polyoxometalate-catalyzed hydrolysis of phosphoester gelation properties, while Zr-polyV6 has increased ability to
bonds and hydrogen-bond-donor-catalyzed hydrolysis of OP hydrolyze OP analogues. This class of POM-based polymers
agents have been demonstrated in recent studies.27–29 We were represent the first examples of a new type of multifunctional
therefore encouraged to examine the effectiveness of these soft material with several potential applications, including
responsive catalytic materials for sequestration and deconta-
mination of deleterious compounds.
Fig. 4 Hydrolysis of DMNP catalyzed by Zr-polyV6
( ) in aqueous 0.45 M
Fig. 3 Oxidation of CEES by H2O2 catalyzed by TBA-polyV6. The mole
ratio of the catalyzed reaction ( ) was 1 V6: 120 CEES: 120 H2O2. The
uncatalyzed control reaction (K) was run with the omission of TBA-
polyV6. Reactions were repeated in triplicate and error bars are reported.
N-ethylmorpholine at pH 10.00, measured through formation of
4-nitrophenolate anion. The DMNP : Zr-polyV6 ratio was 10 : 1 based on
Zr4 units. Reactions run without catalyst (K) and TBA-polyV6
( ) are
shown. Reactions were run in triplicate and error bars are reported.
This journal is ©The Royal Society of Chemistry 2017
Chem. Commun.

View Article Online
Communication
ChemComm
F. Winnik, S. Zauscher, I. Luzinov and S. Minko, Nat. Mater., 2010, 9,
101–113.
12 J. Zhuang, M. R. Gordon, J. Ventura, L. Li and S. Thayumanavan,
Chem. Soc. Rev., 2013, 42, 7421–7435.
We thank S. Wu and B. Wang for help with NMR, L. Saraf
and H. Qian for help with EM imaging, J. Bacsa for obtaining
PXRD spectra, and C. Lea and J. Lang for help obtaining the
diffuse reflectance UV/Vis spectra. This work was funded by the
Defense Threat Reduction Agency (grant # HDTRA1-16-1-0029);
initial work was funded by the Army Research Office (grant #
W911NF-12-1-0136).
13 L. Bromberg, W. R. Creasy, D. J. McGarvey, E. Wilusz and T. A.
Hatton, ACS Appl. Mater. Interfaces, 2015, 7, 22001–22011.
14 A. Doring, W. Birnbaum and D. Kuckling, Chem. Soc. Rev., 2013, 42,
7391–7420.
15 B. O. Okesola and D. K. Smith, Chem. Soc. Rev., 2016, 45, 4226–4251.
16 B. M. Smith, Chem. Soc. Rev., 2008, 37, 470–478.
17 J. E. Mondloch, M. J. Katz, W. C. Isley Iii, P. Ghosh, P. Liao, W. Bury,
G. W. Wagner, M. G. Hall, J. B. DeCoste, G. W. Peterson, R. Q. Snurr, C. J.
Cramer, J. T. Hupp and O. K. Farha, Nat. Mater., 2015, 14, 512–516.
18 Y. J. Jang, K. Kim, O. G. Tsay, D. A. Atwood and D. G. Churchill,
Chem. Rev., 2015, 115, PR1–PR76.
Conflicts of interest
There are no conflicts to declare.
19 C. Wilson, M. Main, N. Cooper, M. E. Briggs, A. I. Cooper and
D. Adams, Polym. Chem., 2017, 8, 1914–1922.
20 J. W. Han, K. I. Hardcastle and C. L. Hill, Eur. J. Inorg. Chem., 2006,
2598–2603.
21 Q. Chen, D. P. Goshorn, C. P. Scholes, X. L. Tan and J. Zubieta,
J. Am. Chem. Soc., 1992, 114, 4667–4681.
22 S. Cantekin, T. F. A. de Greef and A. R. A. Palmans, Chem. Soc. Rev.,
2012, 41, 6125–6137.
Notes and references
1 J. H. Jung, J. H. Lee, J. R. Silverman and G. John, Chem. Soc. Rev.,
2013, 42, 924–936.
2 L. Nicole, C. Laberty-Robert, L. Rozes and C. Sanchez, Nanoscale,
2014, 6, 6267–6292.
3 K. Y. Zhang, S. Liu, Q. Zhao and W. Huang, Coord. Chem. Rev., 2016,
319, 180–195.
23 J. W. Han and C. L. Hill, J. Am. Chem. Soc., 2007, 129, 15094–15095.
4 H. N. Miras, J. Yan, D.-L. Long and L. Cronin, Chem. Soc. Rev., 2012, 24 P. Yin, J. Wang, Z. Xiao, P. Wu, Y. Wei and T. Liu, Chem. – Eur. J.,
41, 7403–7430.
2012, 18, 9174–9178.
25 F. Carniato, C. Bisio, R. Psaro, L. Marchese and M. Guidotti,
Angew. Chem., Int. Ed., 2014, 53, 10095–10098.
5 S.-S. Wang and G.-Y. Yang, Chem. Rev., 2015, 115, 4893–4962.
6 Y.-F. Song and R. Tsunashima, Chem. Soc. Rev., 2012, 41, 7384–7402.
7 B. Zhang, P. Yin, F. Haso, L. Hu and T. Liu, J. Cluster Sci., 2014, 25, 26 J.-K. Li, J. Dong, C.-P. Wei, S. Yang, Y.-N. Chi, Y.-Q. Xu and C.-W. Hu,
695–710. Inorg. Chem., 2017, 56, 5748–5756.
8 A. Proust, B. Matt, R. Villanneau, G. Guillemot, P. Gouzerh and 27 A. Barba-Bon, A. M. Costero, M. Parra, S. Gil, R. Martınez-Manez,
´
´˜
´
G. Izzet, Chem. Soc. Rev., 2012, 41, 7605–7622.
9 W.-K. Miao, Y.-K. Yan, X.-L. Wang, Y. Xiao, L.-J. Ren, P. Zheng, C.-H.
Wang, L.-X. Ren and W. Wang, ACS Macro Lett., 2014, 3, 211–215.
F. Sancenon, P. A. Gale and J. R. Hiscock, Chem. – Eur. J., 2013, 19,
1586–1590.
28 M. R. Sambrook and S. Notman, Chem. Soc. Rev., 2013, 42, 9251–9267.
10 A. Dolbecq, E. Dumas, C. R. Mayer and P. Mialane, Chem. Rev., 2010, 29 M. K. Kinnan, W. R. Creasy, L. B. Fullmer, H. L. Schreuder-Gibson
110, 6009–6048. and M. Nyman, Eur. J. Inorg. Chem., 2014, 2361–2367.
11 M. A. C. Stuart, W. T. S. Huck, J. Genzer, M. Muller, C. Ober, 30 Y. Liu, A. J. Howarth, N. A. Vermeulen, S.-Y. Moon, J. T. Hupp and
M. Stamm, G. B. Sukhorukov, I. Szleifer, V. V. Tsukruk, M. Urban,
O. K. Farha, Coord. Chem. Rev., 2016, 346, 101–111.
Chem. Commun.
This journal is ©The Royal Society of Chemistry 2017