Metal–Organic Frameworks as Fuels for Advanced Applications

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Article Cite This: Chem. Mater. 2019, 31, 4882−4888

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Metal−Organic Frameworks as Fuels for Advanced Applications: Evaluating and Modifying the Combustion Energy of Popular MOFs Hatem M. Titi,† Mihails Arhangelskis,† Athanassios D. Katsenis,† Cristina Mottillo,†,‡ Ghada Ayoub,† Jean-Louis Do,†,§ Athena M. Fidelli,† Robin D. Rogers,*,∥,⊥ and Tomislav Frišcǐ c*́ ,† †

Department of Chemistry, McGill University, 801 Sherbrooke St. W, Montreal H3A 0B8, Canada ACSYNAM, Incorporated, Montreal H1P 1W1, Canada § Department of Chemistry & Biochemistry, Concordia University, 7141 Sherbrooke Street West, Montreal, Quebec H4B 1R6, Canada ∥ 525 Solutions, Incorporated, P.O. Box 2206, Tuscaloosa, Alabama 35403, United States ⊥ College of Arts & Sciences, The University of Alabama, Tuscaloosa, Alabama 35487, United States

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‡

S Supporting Information *

ABSTRACT: Systematic investigation of combustion energies for popular metal−organic framework materials reveals energy content comparable to conventional energetic materials, which can be further modified and fine-tuned through the control of framework topology or isostructural ligand replacement to yield energy densities comparable to conventional energetic materials such as trinitrotoluene and hydrazine-, diesel-, or kerosene-based fuels.

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thermochemical properties of conventional MOFs,27−29 notably energy density (Ev, in MJ/dm3 or kJ/cm3) and specific energy (Eg, in MJ/kg or kJ/g). In order to evaluate the potential of conventional MOF designs for use in advanced fuel systems, we have now used combustion calorimetry to measure experimental specific energies and determine energy densities and combustion enthalpies (ΔHc) for representative examples of the most popular classes of MOFs (Figure 1). The herein presented systematic study on conventional MOFs that are either commercially available or readily synthesized in the laboratory reveals that Eg for several carboxylate-based MOFs is close to that of the energetic compounds such as trinitrotoluene (TNT) and hydrazine,30 whereas the specific energies of ZIFs can be significantly higher.29 Importantly, we show how Eg and Ev of ZIFs can be readily modified through control of MOF topology and/or engineered by chemical functionalization of the linker, leading to materials with specific energies higher than hydrazine fuels and approaching at least 60−65% of hydrocarbon fuels (Table 1), as well as tunable energy densities comparable to or exceeding those of hydrazine- or gasoline-based fuels.31−33

INTRODUCTION Metal−organic frameworks (MOFs) have emerged over the past two decades as readily designable microporous materials that can be functionalized for a wide range of applications from catalysis and selective gas separation to different types of conduction or light harvesting.1−11 Recently, MOF formation was reported as a route to generate new energetic materials by using energetic molecules as ligands.12−19 Our group20 has demonstrated a MOF-based strategy for generating new hypergolic solid fuels, that is, fuels that ignite simultaneously upon contact with an external oxidizer.21 Such hypergolic MOFs, being developed as advanced, safer alternatives to toxic hydrazine fuels in aerospace industries (e.g., for in-orbit propulsion),22,23 are based on using suitably functionalized imidazolate ligands as linkers in the synthesis of zeolitic imidazolate frameworks (ZIFs).20,24,25 Importantly, while hypergolic MOFs exhibit ultrashort ignition delays, they do not involve explosive, heat- or impact-sensitive components. Instead, the energetic effect upon ignition results solely from aerobic combustion of the framework.18 Similarly, the Matzger group has shown how a conventional MOF can be rendered explosive via inclusion of explosive guests, also taking advantage of the framework material as a fuel for explosive combustion.26 While the described materials open new uses for MOFs as cleaner fuels or safer explosives, these advanced applications will depend on the still poorly explored © 2019 American Chemical Society

Received: April 15, 2019 Revised: May 31, 2019 Published: June 3, 2019 4882

DOI: 10.1021/acs.chemmater.9b01488 Chem. Mater. 2019, 31, 4882−4888

Article

Chemistry of Materials

Figure 1. (a) Organic ligands used in the herein explored MOFs and (b) structures of herein studied MOFs, with hydrogen atoms omitted for clarity. Atoms of Zn/CoII, CuII, Al, Zr, N, O, and C are shown in purple, green, pink, cyan, blue, red, and gray, respectively.

Table 1. Unit Formula, Relative Molecular Weight of Unit Formula (Mr), Decomposition Temperature (Td), Calculated Density (ρc), Surface Areas, Cambridge Structural Database (CSD) Codes, Specific Energy (Eg), Energy Density (Ev), and Combustion Enthalpy (ΔHc) of Herein Explored MOFs Compared to Those of Selected Fuels and Energetic Materials surface area (m2/g) MOF c,36

SOD-Zn(MeIm)2 (ZIF-8) SOD-Zn(MeIm)2 (ZIF-8)d,36 dia-Zn(MeIm)239 SOD-Co(MeIm)2 (ZIF-67)40 RHO-Zn(EtIm)236 ANA-Zn(EtIm)237 qtz-Zn(EtIm)241 ANA-Zn(PrIm)242 ANA-Zn(BuIm)2 HKUST-1c,34 MIL-53(Al)c,35 UiO-6637 UiO-66-NH238 TNT30 diesel29 gasoline29 gasohol E85,29e kerosene29 hydrazine33 MMH33 UDMH33 magnesium48 aluminum48 boron49,50

unit formula

Mr

Tda (°C)

ρc (g/cm3)

BET

Langmuir

CSD code

Egb (kJ/g)

Ev (kJ/cm3)

ΔHc (kJ/mol)

C8H10N4Zn C8H10N4Zn C8H10N4Zn C8H10N4Co C10H14N4Zn C10H14N4Zn C10H14N4Zn C12H18N4Zn C14H22N4Zn C6H2CuO4 C8H5AlO5 C8H4.67O5.33Zr C8H5.67NO5.33Zr C7H5N3O6

227.9 227.9 227.9 221.1 255.6 255.6 255.6 283.7 311.8 201.6 208.1 277.4 292.4 227.1

498 656 498 397 471 461 492 484 566 350 618 584 449 28345

0.925 0.925 1.579 0.903 0.814 1.091 1.590 1.221 1.295 0.879 1.019 1.246 1.295 1.655 0.83 0.71

1350 1350

1760 1780

1510 1210 610

1990 1620 700

440 70 1340 950 870 960

520 100 1780 1270 1149 1275

VELVOY VELVOY OFERUN01 GITTOT01 MECWOH MECWIB EHETER GUPFAZ this work FIQCEN SABVUN01 RUBTAK SURKAT ZZZMUC01

20.9(1) 21.6(8) 20.76(3) 22.9(5) 24.0(3) 24.3(1) 23.5(2) 25.8(3) 28.0(5) 11.5(1) 14.1(2) 13.3(1) 12.26(1) 15.0 45.4 46.4 33.1 43.8 19.4f 28.3f 32.9f 24.0 31.0 58.5

19.4(1) 20.0(7) 32.7(1) 20.7(5) 19.5(3) 26.5(1) 37.2(3) 31.4(3) 36.3(6) 10.1(1) 14.4(1) 16.6(2) 15.87(2) 24.8 38.6 34.2 25.6 35.1 19.5f 24.7f 25.9f 43.0 83.8 135.8

−4769(19) −4919(175) −4722(10) −5068(119) −6132(81) −6218(28) −5988(55) −7307(78) −8726(152) −2324(10) −2937(29) −3691(45) −3584(13) −3399

N2H4 CH6N2 C2H8N2 Mg Al B

32.0 46.1 60.1 24.3 27.0 10.8

0.81 1.00 0.87 0.79 1.74 2.70 2.37

−622 −1304 −1979

Measured by DSC in air at a heating rate of 10 °C/min. bMeasured by combustion calorimetry. cObtained from Sigma-Aldrich. dObtained from ACSYNAM, Inc. e85:15 mixture of ethanol and petrol. fCalculated from ΔHc values from ref 33. a

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RESULTS AND DISCUSSION 34

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and purity of all explored MOFs were validated by powder Xray diffraction (PXRD) and thermogravimetric analysis (TGA) in air. Brunauer−Emmet−Teller (BET) and Langmuir surface areas for all materials were established by nitrogen sorption measurements, yielding values consistent with literature reports (see Supporting Information, Sections S3−S6, also Table 1). All combustion experiments were carried on a 6200 Isoperibol Calorimeter using ca. 0.5 g of the MOF. The herein reported Eg value for each MOF is an average of three measurements, and the corresponding Ev was calculated from it

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The HKUST-1, MIL-53(Al), and ZIF-8 MOFs were purchased from Sigma-Aldrich, with a sample of ZIF-8 also obtained from ACSYNAM. The UiO-6637 and UiO-66-NH238 frameworks, as well as a series of ZIFs39−42 based on twosubstituted imidazolate ligands, were synthesized via reported procedures (Figure 1, also see Supporting Information, Sections S1 and S2).43,44 All materials were washed with methanol, evacuated, and stored in argon before use. Identity 4883

DOI: 10.1021/acs.chemmater.9b01488 Chem. Mater. 2019, 31, 4882−4888

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Chemistry of Materials

Significantly, larger Eg, Ev, and ΔHc are observed for ZIFs. Using an in-house synthesized sample, we have reported20 that the popular sodalite (SOD) topology framework ZIF-8, based on zinc nodes and 2-methylimidazolate (MeIm−, Figure 1) linkers, exhibits ΔHc of ca. 4800 kJ/mol. This ΔHc value translates to Eg and Ev of ca. 21 kJ/g and 20 kJ/cm3, respectively, which exceeds the values for TNT and hydrazine.20 These observations are here confirmed using ZIF-8 samples obtained from two commercial sources, SigmaAldrich and ACSYNAM (Table 1). Eg, Ev, and ΔHc are further slightly increased (by ca. 5%) in ZIF-67, a SOD framework isostructural to ZIF-8, but based on cobalt(II) nodes. This small increase in ΔHc might be associated with additional oxidation of metal nodes to form Co3O4,46 which does not take place in the case of zinc frameworks. Although small, this difference in ΔHc between ZIF-8 and ZIF-67 illustrates change in choice of the metal node as a potential means to control the combustion energy content of a MOF. A different route to modify the fuel properties of a ZIF is revealed by comparing ZIF-8 to its nonporous diamondoid (dia) topology polymorph. Whereas the ΔHc values for the two polymorphs are expected to be very similar because of their identical chemical composition, the higher density of close-packed dia-Zn(MeIm)2 leads to a significant increase in Ev to ca. 33 kJ/cm3. This energy density is close to values for conventional hydrocarbon fuels such as gasoline or kerosene and exceeds values for hypergolic hydrazine-based fuels monomethylhydrazine (MMH) and unsymmetrical dimethylhydrazine (UDMH) (Table 1).31−33 The significant effect of polymorphism on energy density is also evident from comparing the three topologically distinct varieties of the zinc 2-ethylimidazolate Zn(EtIm)2 framework, with zeolite rho (RHO), analcime (ANA), and quartz (qtz) topologies. The ΔHc values for all three polymorphs are comparable, as expected, and are around 6−6.2 kJ/mol. Similarly, the corresponding Eg values are mutually similar and are around 24 kJ/g. However, because of the increasing density in the order RHO < ANA < qtz, the corresponding Ev differs greatly between the materials and ranges from 19.5 kJ/cm3 for the low-density RHO-Zn(EtIm) 2 to a high value of 37.5 kJ/cm3 for nonporous qtz-Zn(EtIm)2. The Ev for qtzZn(EtIm)2 exceeds the values for gasoline (34.2 kJ/cm3) and kerosene-based jet fuel (35.1 kJ/cm3) and is on par with diesel (38.6 kJ/cm3, Table 1).31 Comparison of combustion energy for polymorphs of Zn(MeIm)2 and Zn(EtIm)2 clearly demonstrates control over framework topology and polymorphism47 as potential tools to increase or decrease the energy density of a ZIF. Comparison of ΔHc reveals a higher value for Zn(EtIm)2 compared to that for Zn(MeIm)2 systems. This difference, readily explained by the presence of an additional CH2 fuel group in the Zn(EtIm) 2 framework (see Supporting Information, Section S7 for the analysis of combustion energy with respect to the content of C, H, N, O, and metal), illustrates a potential strategy to manipulate the combustion energy properties of ZIFs by introducing additional hydrocarbon groups. Switching from a 2-ethyl-substituted linker in RHO-, ANA-, or qtz-Zn(EtIm)2 frameworks to an analogous but more fuel-rich 2-propylimidazolate linker yields the previously reported ANA-topology Zn(PrIm)2 framework, which is isostructural to ANA-Zn(EtIm)2. The measured ΔH c for ANA-Zn(PrIm) 2 was found to be around −7300 kJ/mol, which is ca. 1100 kJ/mol more exothermic

by taking into account the density and molecular weight calculated from the reported structural data and chemical composition, respectively. Combustion enthalpy (ΔHc) was calculated from Eg by considering the change in number of moles of gas in the combustion reaction (see the Supporting Information) to form metal oxides ZnO (for explored zincbased ZIFs), Co3O4 (for ZIF-67), CuO (for HKUST-1), Al2O3 (for MIL-53(Al)), and ZrO2 (for UiO-66 and UiO-66-NH2) (see the Supporting Information). Results of combustion calorimetry and selected structural information for all herein studied MOFs are shown in Table 1, and the corresponding plot of Eg and Ev is shown in Figure 2.

Figure 2. Comparison of energy density (Ev) and specific energy (Eg) for herein explored MOFs, calculated from experimentally measured ΔcH values.

For carboxylate MOFs, the data reveal high Eg values, approaching 15 kJ/g for zirconium-based UiO-frameworks and MIL-53(Al), while Ev values range from 14 to 17 kJ/cm3. Whereas these Eg values are close to that reported for the energetic compound TNT, the Ev values are significantly lower than for most popular fuels or energetic compounds, consistent with the microporous nature of the explored MOFs (Table 1). The measured Eg and Ev are the lowest for copper(II)-based HKUST-1, which can tentatively be related to a difference in the linker structure and the oxidation state of the metal, compared to other herein explored carboxylate MOFs. Specifically, HKUST-1 is based on 1,3,5-benzenetricarboxylate linkers (Figure 1), exhibiting three metal−ligand connection sites per molecule, unlike terephthalate linkers in aluminumbased MIL-53(Al) and zirconium-based UiO systems (Figure 1), which exhibit only two metal−ligand connection sites. At the same time, the oxidation state of the Cu2+ metal ion in HKUST-1 is lower compared to that of Al3+ and Zr4+ ions in MIL-53- and UiO-MOFs, respectively. These parameters dictate a 1:1.5 stoichiometric ratio of organic linkers to metal ions in the formula unit of HKUST-1, which is lower than the 1:1 ratio found in the formula units of MIL-53(Al) and UiO-MOFs (Table 1). As the linker represents a combustion fuel, the lower ligand-to-metal ratio in HKUST-1 is expected to lead to a lower ΔHc. Overall, ΔHc for carboxylate MOFs increases in the order HKUST-1 < MIL-53(Al) < UiO-66 ≈ UiO-66-NH2, a trend which might also be related to the stabilities of the resulting oxides. 4884

DOI: 10.1021/acs.chemmater.9b01488 Chem. Mater. 2019, 31, 4882−4888

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Chemistry of Materials

around 60−65% of the value reported for gasoline and related fuels and a high Ev of 36.3 kJ/cm3, which exceeds hypergolic rocket fuels MMH and UDMH, and is in the range of popular hydrocarbon fuels (Table 1).31 These values are below those of some actual (aluminum) or proposed (boron) high-energy solid fuels48−50 but already close to those of the magnesium fuel (Table 1, Figure 4, also see Supporting Information, Section S9).

than its 2-ethyl-substituted homologue, providing a MOF that combines a high energy density (31 kJ/g) close to that of gasoline (34.2 kJ/cm3) or kerosene-based jet fuel (35.1 kJ/ cm3),31,32 with a microporous surface area of 440 m2/g (Table 1). In order to effect a further increase in energy density, we used 2-butylimidazole (HBuIm) as the ligand. To the best of our knowledge, the Zn(BuIm)2 framework has so far not been reported. Mechanochemical synthesis provided a material that, based on PXRD analysis (see the Supporting Information), was isostructural to ANA-topology Zn(EtIm)2 and Zn(PrIm)2 frameworks (Table 1). The composition Zn(BuIm)2 for the new material was confirmed by TGA in air (see the Supporting Information), and the crystal structure was elucidated by structure solution from PXRD data. Rietveld refinement in the cubic space group Ia3̅d (Figure 3a) with the unit cell

Figure 4. Comparison of Eg and Ev for herein studied MOFs to those of typical gasoline, hydrazine (MMH and UDMH), and magnesium fuel.29,48,49 Values for carboxylate MOFs are in green and for ZIFs in red.

As ANA-Zn(EtIm)2, ANA-Zn(PrIm)2, and ANA-Zn(PrIm)2 frameworks are isostructural, increasing the length of the 2-hydrocarbon chain substituent on the linker effectively increases the energy released in the combustion with almost no impact on the overall structure or network density (i.e., the number of tetrahedral centers per unit volume, T/ nm3, Figure 5) of the material. Specifically, the Ev for isostructural, topologically identical ANA-Zn(EtIm)2, -Zn(PrIm)2, and -Zn(BuIm)2 consistently increases by 4.9 kJ/ cm3 per CH2 unit. To the best of our knowledge, such ability to engineer Ev without introducing any significant change in the structure of the material is unique to MOFs and has so far not been reported in the design of fuel materials. Furthermore, the network density of ANA-Zn(EtIm)2 (2.57 T/nm3) is very close to that of ZIF-8 (2.45 T/nm3). Consequently, the herein explored ANA-topology ZIFs and ZIF-8 reveal the ability to fine-tune the energy density of a MOF across almost 20 kJ/cm3, with little or no change in network density and with retention of microporosity even at relatively high Eg [440 m2/g for ANA-Zn(PrIm)2].

Figure 3. (a) Final Rietveld fit and an illustration of the crystal structure of ANA-Zn(BuIm)2 along the crystallographic (100) direction, with hydrogen atoms omitted for clarity. (b) Nitrogen sorption isotherms at 77 K for ANA-Zn(BuIm)2, corresponding to a BET surface area of 70 m2/g. Adsorption and desorption are shown by blue and red circles, respectively.

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CONCLUSIONS In summary, we presented the first systematic investigation of combustion energies, including energy density, specific energy, and combustion enthalpy for a range of conventional and mostly commercially available MOFs. In contrast to traditional microporous materials such as zeolites, MOFs can be considered as potential fuels, which, upon combustion, are able to generate energy comparable to popular hydrocarbon fuels. This is particularly true for ZIFs based on nitrogencontaining heterocycles, exhibiting a high specific energy, approaching >60−65% that of gasoline. Importantly, we show

parameter a = 26.765(2) Å revealed a structure analogous to ANA-Zn(EtIm)2. The neighboring hydrocarbon chains in ANA-Zn(BuIm)2 form voids along the (111) direction that are accessible to a spherical probe of 3.0 Å diameter and amount to ca. 4% (ca. 800 Å3) of unit cell volume (see Supporting Information, Section S8), indicating that the MOF should not exhibit a high surface area. This was confirmed by nitrogen sorption analysis at 77 K, which revealed a BET surface area of only 70 m2/g (Figure 3b). Combustion measurement for ANA-Zn(BuIm)2 revealed an Eg of 28.0 kJ/g (ΔHc value of ca. −8700 kJ/mol) that is 4885

DOI: 10.1021/acs.chemmater.9b01488 Chem. Mater. 2019, 31, 4882−4888

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Chemistry of Materials

controlled, isoperibol oxygen bomb calorimeter. The combustion calorimeter was calibrated by benzoic acid. All measurements were carried out on a scale of 0.5 g of the sample and repeated three times. Thermal Analysis. Simultaneous TGA and differential scanning calorimetry (DSC) were conducted on a TGA/DSC 1 (MettlerToledo, Columbus, Ohio, USA), with samples (2 to 10 mg) placed in open 70 μL volume alumina crucibles. All measurements were done in a dynamic atmosphere of air (25 mL/min) in the range heated up to 800 °C at a constant rate of 10 °C/min. The experimental results are shown in Supporting Information, Section S4. Sample Activation. All samples were washed with methanol (30 mL) and centrifuged for 20 min at 4500 rpm, and the supernatant was separated. This process was repeated two times to assure the absence of any residual starting materials in the samples. The MOF samples were placed in a vacuum oven at 80−120 °C overnight and kept under argon. The nitrogen isotherms of the activated MOFs were measured on TriStar 3000, and the experiments were conducted at 77 K of a liquid nitrogen container. The experimental results are shown in Supporting Information, Section S3. Powder X-ray Diffraction. PXRD data were collected on a Bruker D2 Phaser diffractometer equipped with a LYNXEYE linear position-sensitive detector (Bruker AXS, Madison, WI, USA) using Ni-filtered Cu Kα radiation. The structures of MOF materials were verified by Pawley fitting of the experimental data to the previously published structure, and the results are shown in Supporting Information, Section S5. The PXRD pattern of ANA-Zn(BuIm)2 was collected on a Bruker D8 ADVANCE diffractometer equipped with a LYNXEYE-XE linear position-sensitive detector using Nifiltered Cu Kα radiation. Rietveld refinement of the structure ANA-Zn(BuIm)2 (Table S1) was performed using the software TOPAS Academic v. 6 (Coelho Software). The ANA-Zn(BuIm)2 structure was refined in the cubic Ia3̅d space group. Diffraction peak shapes were described by a pseudo-Voigt function, while the background was modeled with a Chebyshev polynomial function. The linker geometry was defined by a rigid body, which was given rotational and translational degrees of freedom, subject to the space group symmetry constraints. In addition, flexible torsion angles were used to refine the conformation of the butyl substituent. Fourier-Transform Infrared Attenuated Total Reflectance Spectroscopy. Spectra were recorded using a Bruker Alpha FT-IR (Bruker Optics Ltd., Milton, ON, Canada) decorated by a diamond crystal in the range of 4000−450 cm−1 and with a resolution of 4 cm−1. The experimental results are shown in Supporting Information, Section S6.

Figure 5. Dependence of Ev on framework density (in tetrahedral nodes per unit volume, T/nm3) for selected ZIFs.

that the energy density of MOFs can be tuned to approach or even exceed those of kerosene, diesel, magnesium, or hydrazine rocket fuels. Whereas the specific energies and energy densities of herein investigated MOFs are smaller than for high combustion energy solids such as boron,49,50 the specific energy values are close to those of magnesium and aluminum fuels, with energy density in some cases exceeding that of magnesium. Our study shows that the modular design and the ability to direct the framework topology of ZIFs offer a means to control the energy content in a way that is not accessible to conventional fuels. Switching between different ZIF topologies enables tuning of energy density without changes to the chemical composition, as illustrated by qtz-, ANA-, and RHOtopology frameworks of zinc 2-ethylimidazolate. Conversely, modular design of ZIFs enables the introduction of increasingly fuel-rich substituents and tuning of combustion energy without changing the overall structure of the material, as illustrated by the isostructural series of ANA-topology zinc 2-ethyl-, 2-propyl-, and 2-n-butyl-substituted ZIFs. Overall, these results provide a so far missing overview of combustion energy properties of conventional MOFs and demonstrate that different classes of frameworks, particularly ZIFs, can exhibit high, as well as tunable energy density and specific energy. We believe that these results, in combination with intermediate-to-high microporosity and high thermal stability in general,23,46 indicate ZIFs as suitable, highly promising materials for the development of advanced tunable fuels and hypergols.

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.chemmater.9b01488.

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Further details of experimental procedures and calculations as well as PXRD, Fourier-transform infrared/ attenuated total reflectance and TGA/DSC data (PDF) Crystallographic data of ANA-Zn(BuIm)2 (CIF)

AUTHOR INFORMATION

Corresponding Authors

EXPERIMENTAL SECTION

*E-mail: [email protected] (R.D.R.). *E-mail: [email protected] (T.F.).

More details on experimental procedures and calculations are provided in the Supporting Information (Sections S1 and S2). Despite high energy contents, the herein explored materials are highly thermally stable and would not ignite even upon exposure to a blowtorch. Combustion Calorimetry. The combustion calorimetry measurements were carried out on a 6200 Isoperibol Calorimeter (Parr Instrument Company, Moline, IL), which is a microprocessor

ORCID

Hatem M. Titi: 0000-0002-0654-1292 Mihails Arhangelskis: 0000-0002-3075-1214 Athanassios D. Katsenis: 0000-0003-1150-3108 Tomislav Frišcǐ ć: 0000-0002-3921-7915 4886

DOI: 10.1021/acs.chemmater.9b01488 Chem. Mater. 2019, 31, 4882−4888

Article

Chemistry of Materials Author Contributions

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The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Funding

NSERC Discovery Grant (RGPIN-2017-06467), NSERC E. W. R. Steacie Fellowship (SMFSU 507347-17), NSERC Strategic Grant (STPGP 521582-18), Canada Research Excellence Chair program (grant 240634), AFOSR (FA955014-1-0306). Notes

The authors declare the following competing financial interest(s): CM and TF are co-founders, and RDR is a scientific advisory board member of ACSYNAM, Inc., which has provided one of the materials for the study.

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ACKNOWLEDGMENTS We thank Dr. A. Djuric, McGill University, for help in acquiring BET data. We acknowledge funding from the NSERC Discovery Grant (RGPIN-2017-06467), NSERC E. W. R. Steacie Fellowship (SMFSU 507347-17), NSERC Strategic grant (STPGP 521582-18), Canada Research Excellence Chair program (grant 240634), and AFOSR (FA9550-14-1-0306).

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ABBREVIATIONS HMeIm, 2-methylimidazole; MeIm−, 2-methylimidazolate; HEtIm, 2-ethylimidazole; EtIm−, 2-ethylimidazolate; HPrIm, 2-propylimidazole; PrIm−, 2-propylimidazolate; HBuIm, 2butylimidazole; H3BDC, 1,3,5-benzenetricarboxylic(trimesic) acid; H2BDC, 1,4-benzenedicarboxylic(terephthalic) acid; H2BDC-NH2, 2-amino-1,4-benzenedicarboxylic(2-aminoterephthalic) acid

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DOI: 10.1021/acs.chemmater.9b01488 Chem. Mater. 2019, 31, 4882−4888