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Research Article Cite This: ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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Binding CO2 from Air by a Bulky Organometallic Cation Containing Primary Amines Yang-Hui Luo,* Chen Chen, Dan-Li Hong, Xiao-Tong He, Jing-Wen Wang, Ting Ding, Bo-Jun Wang, and Bai-Wang Sun* School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211189, PR China S Supporting Information *

ABSTRACT: The organometallic cation 1 (Fe(bipy-NH2)32+, bipy-NH2 = 4,4′-diamino-2,2′-bipyridine), which was constructed in situ in solution, can bind CO2 from air effectively with a stoichiometric ratio of 1:4 (1/CO2), through the formation of “H-bonded CO2” species: [CO2−OH−CO2]− and [CO2−CO2−OH]−. These two species, along with the captured individual CO2 molecules, connected 1 into a novel 3D (three-dimensional) architecture, that was crystal 1· 2(OH−)·4(CO2). The adsorption isotherms, recycling investigations, and the heat capacity of 1 have been investigated; the results revealed that the organometallic cation 1 can be recycled at least 10 times for the real-world CO2 capture applications. The strategies presented here may provide new hints for the development of new alkanolamine-related absorbents or technologies for CO2 capture and sequestration. KEYWORDS: organometallic cation, amine-functionalized, CO2 capture, “H-bonded CO2”, recycling potential

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INTRODUCTION As one of the greatest environmental concerns facing our civilization, the storage, separation, and purification of carbon dioxide (CO2) have attracted much attention today,1−3 not only in the environmental science and industry field but also in the energy and life science field.4−6 To solve this problem, the key aspect is the development of materials or establishment of technologies that can bind CO2 effectively and are environmentally friendly and energy efficient. To date, the use of the aqueous alkanolamine absorbents (monoethanolamine (MEA) and triethanolamine (TEA)),7−10 the solid porous adsorbent materials,11−14 and the metal−organic frameworks/materials (MOFs/MOMs) with a large surface area and high porosity15−22 are the three main strategies that have been intensively investigated for CO2 capture and sequestration. Note that these strategies were run by using the high affinity of organic amines23 or unsaturated metal centers,24 which chemically interact with CO2. However, these strategies suffered several limitations for real-world applications in CO2 capture; the main drawbacks are the high energy costs associated with activation, regeneration, and recycling of these sorbent materials, especially for the conventionally employed aqueous alkanolamine absorbents.1 More recently, Cadiau,25 Zaworotko26 and co-workers, and Winpenny et al.27 have demonstrated that the terminal fluorides in the coordinately saturated MOMs AlFFIVE-1-Ni ([Ni(pyrazine)2(MF5(H2O))n, M = Al, Fe]), SIFSIX-3-Zn ([Zn(pyrazine)2(SiF6)]n), and a Cr8 metallacrown ([CrF(O2CtBu)2]8), respectively, are able to selectivity separate CO2 from N2 through favorable C···F interactions. These tempting results have greatly expanded the © XXXX American Chemical Society

material species for CO2 capture. In general, the aminefunctionalized materials, which show robust affinity to CO2 molecules, have occupied a special position because the most prevalent industrial process for CO2 capture and sequestration is the absorption in aqueous alkanolamine (Scheme 1). Note that one drawback of alkanolamine is the formation of strong covalent bonds between absorbents and CO2 molecules. Consequently, the seeking for alkanolamine alternatives that are in contact with CO2 molecules through moderate van der Waals forces for solution absorption is inevitable. There were indeed several examples of amine-functionalized MOFstructures that have shown the potential for reversible CO2 capture with excellent selectivity;28−30 the amine-containing materials as solution absorbents that bind CO2 molecules through the formation of moderate intermolecular interactions remain unreported. Herein, we report a new organometallic cation Fe(bipyNH2)32+ (1) (bipy-NH2 = 4,4′-diamino-2,2′-bipyridine), which acts as an effective CO2 capturer, through the formation of N− H···O hydrogen bonding contacts involving NH2 groups and CO2 molecules in solution. Cation 1 was formed in situ in solution; it bound CO2 from air with a stoichiometric ratio of 1:4 (1/CO2) and co-crystallized in the form of 1·2(OH−)· 4(CO2). It is interesting that the organometallic cation 1 induced a part of CO2 and H2O molecules to form two different “H-bonded CO2” species (H = hydrogen): [CO2− Received: January 19, 2018 Accepted: February 27, 2018

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DOI: 10.1021/acsami.8b01044 ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

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ACS Applied Materials & Interfaces

Scheme 1. Synthesis of Organometallic Cation 1 in Situ and the Formation of “H-Bonded CO2” Species, [CO2−OH−CO2]− and [CO2−CO2−OH]− (Upper)a

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The reaction of CO2 with MEA and TEA to form carbamate and bicarbonate products, respectively (lower), has been presented for comparison.

Figure 1. Binding motif of CO2 molecules and hydroxyl anions to the complex cation 1 (a); Different environments of individual CO2 (b) and “Hbonded CO2” species CO2−OH−CO2 (c) and CO2−CO2−OH (d).

OH−CO2]− and [CO2−CO2−OH]− (Scheme 1). These two species, along with the other part of the captured individual CO2 molecules, connected 1 into a novel three-dimensional (3D) architecture. In addition, the adsorption isotherms, recycling investigations, and the heat capacity measurements of 1 have been performed, which have revealed that organometallic cation 1 has shown the potential to act as alkanolamine alternatives for the real-world CO2-capture

applications. To the best of our knowledge, this is the first example of a mononuclear organometallic cation for solutionstate CO2 capture.

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RESULTS AND DISCUSSION

The organometallic cation 1 was obtained by the reaction of a high-spin state compound [Fe(H2Bpz2)2(bipy-NH2)] (pz = B


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Figure 2. FT-IR spectra of crystal 1·2(OH−)·4(CO2) (a) and the enlargement of the asymmetric stretching bands for captured CO2 (b). TGA profiles of crystal 1·2(OH−)·4(CO2) in temperature range 50−500 °C (c) and FT-IR spectra of the heating residual species 1·2(OH−) (d).

pyrazolyl)31 with a bipy-NH2 ligand with a stoichiometric ratio of 1:2 (0.2 mmol) in a methanol−water solution (see the Experimental Section). Slow evaporation of the resulting solution under ambient conditions gives block red crystals. Single-crystal X-ray diffraction (XRD) at 100 K revealed that the block red crystal is complex 1·2(OH−)·4(CO2). It crystallizes in the monoclinic C2/c space group; its asymmetric unit (ASU) consists of an entire molecule of the Fe(bipyNH2)32+ cation, four CO2 molecules, and two hydroxyl anions (Figure S1). The formation of complex 1·2(OH−)·4(CO2) can be rationalized as follows (Scheme 1): the reaction of the ligand bipy-NH2 with the neutral compound [Fe(H2Bpz2)2(bipyNH2)] led to the formation of the organometallic cation 1 (Fe(bipy-NH2)32+), and for purpose of charge balance, the amino groups in cation 1 were expected to react with CO2 and/ or H2O to form some species that are similar to carbamate or bicarbonate. To our surprise, the organometallic cation 1 induced the formation of two different “H-bonded CO2” species, [CO2−OH−CO2]− and [CO2−CO2−OH]−, other than carbamate or bicarbonate.32,33 For the organometallic cation 1, the Fe(II) ion center has shown a distorted octahedral coordination geometry with six coordinating nitrogen atoms from the three bipy-NH2 ligands. The Fe−N coordination bond distances at 100 K are in the range of 1.966(7)−1.979(6) Å, and the distortion parameter ∑ was found to be 43.5(5)°; these values are characteristic of a low-spin state Fe(II) ion,34,35 as has been confirmed by the magnetic susceptibility measurements (Figure S2). Note that in the crystal, five out of the six amino groups on cation 1 interact

with two different CO2 molecules, whereas the last amino group comes in contact with a “H-bonded CO2” species (Figure 1a). Of all captured CO2 molecules in crystal 1· 2(OH−)·4(CO2), some were individual ones that were surrounded by six different organometallic cations of 1, through the formation of moderate N−H···O (average N···O distances of 2.95(3) Å) hydrogen bonding contacts, forming a “core− shell” motif (Figure 1b), whereas the other CO2 molecules participated in the formation of “H-bonded CO2” species [CO2−OH−CO2]− and [CO2−CO2−OH]−. Note that the species [CO2−OH−CO2]− was also binding to six different organometallic cations of 1 through moderate N−H···O (average N···O distances of 2.89(3) Å) hydrogen bonding contacts (Figure 1c), whereas the other species [CO2−CO2− OH]− was just binding to one molecule of 1, unexpectedly, also through N−H···O (N···O distances of 2.90(3) Å) hydrogen bonding contacts (Figure 1d). It’s worth noting that the distances of hydrogen bonding contacts involving “H-bonded CO2” species and organometallic cation 1 were closer than those of the individual CO2 molecules, demonstrating the presence of electrostatic interaction between the “H-bonded CO2” species and organometallic cation. The presence of the above-mentioned three different types (two kinds of “H-bonded CO2” species and individual CO2 molecules) of CO2 in crystal 1·2(OH−)·4(CO2) can also be demonstrated by the Fourier transform infrared (FT-IR) spectroscopy. Figure 2a,b shows three different asymmetric stretching bands that have been observed at around 2377, 2348, and 2315 cm−1, respectively, corresponding to the “H-bonded C


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ACS Applied Materials & Interfaces CO2” species [CO2−CO2−OH]−, individual CO2 molecules, and “H-bonded CO2” species [CO2−OH−CO2]−. In addition, the bending bands of CO2 were also observed at 670 cm−1.27,36 It should be noted that it was these moderate N−H···O hydrogen bonding contacts as well as the formation of “Hbonded CO2” species that are responsible for the small O CO angles of CO2 molecules, varying from 117.7(10) to 131.8(9)°. The above-mentioned versatile intermolecular N−H···O hydrogen bonding contacts, involving amino groups and CO2 molecules, connected the organometallic cation 1 into a novel 3D architecture. It is interesting that there are two different kinds of holes that can be viewed from the 3D architecture, one is round (in yellow) and the other is tabular (in brown, Figure 3a). What is more, these two different holes were evenly

heating residual species 1·2(OH−), which was confirmed by elemental analysis and FT-IR spectroscopy (Figure 2d)). Note that the removal of CO2 molecules has resulted in the collapse of this 3D architecture, as has been demonstrated by the powder XRD (PXRD) measurements (Figure 4). In other

Figure 4. PXRD patterns of crystal 1·2(OH−)·4(CO2), heating residual species 1·2(OH−), and the crystalline products of recycled batch.

words, the 3D architecture of organometallic cation 1 was just constructed in situ in solution state, on condition that there is the presence of water and CO2 molecules. In addition, the magnetic susceptibility measurements of the heating residual species 1·2(OH−) also have suggested a typical low-spin state Fe(II) ion (Figure S2). The collapse of the 3D architecture for crystal 1·2(OH−)· 4(CO2) upon the removal of CO2 molecules was further confirmed by field emission scanning electron microscopy (FESEM) measurements. Figure 5a shows that 1·2(OH−)· 4(CO2) displays a uniformly distributed nanocubical morphology. After heating under 140 °C for 1 h, the cubical morphology collapsed into “loose sand” (Figure 5b), and the latter corresponds to the heating residual species 1·2(OH−) (confirmed by elemental analysis). We further investigated the porosity of crystalline samples 1·2(OH−)·4(CO2) and the heating residual species 1·2(OH−) by running a N2 adsorption isotherm at 77 K. As we have expected, both of them were essentially nonporous, with a saturation capacity of around 16 and 7 cm3 g−1 at a partial pressure (P/P0) of 0.9 (Figure S3a). These results indicate that the organometallic cation 1 can be used only as a solution absorbent on considering CO2 capture. Adsorption isotherms for CO2 and N2 in crystalline samples 1·2(OH−)·4(CO2) were also measured at ambient temperatures (298 K) to a pressure of 5 bar; both display almost identical type-I behavior (Figure S3b). The adsorptions of CO2 and N2 over the present pressure range were all very low, reaching 0.036 and 0.025 mmol g−1 at 1 bar, respectively, and increasing gradually to 0.093 and 0.085 mmol g−1 at 5 bar, demonstrating again the nonporous characteristics of crystalline samples 1·2(OH−)·4(CO2). It should be noted that the nonporous characteristics of 1·2(OH−)·4(CO2) were attributed to the occupation of the holes on the 3D architecture by “Hbonded CO2” species and individual CO2 molecules; however, the nonporous characteristics of 1·2(OH−) were owing to the collapse of the 3D architecture. These results suggest that on the one hand, the organometallic cation 1 can bind only CO2 in solution by taking a manner different from the aqueous alkanolamine absorbents; on the other hand, the premise for

Figure 3. 3D architecture of the organometallic cation 1 viewed from the crystallographic c axis with two different kinds of holes, round (in yellow) and tabular (in brown), that are evenly distributed (a); padding style of the “H-bonded CO2” species and the individual CO2 molecules for the different holes (b).

distributed, where each round hole was surrounded by four tabular holes and vice-versa for each tabular hole (Figure 3a). As have been expected, the tabular holes were occupied by five different CO2 molecules at the center and the four opposite angles positions. However, for the round holes, four different CO2 molecules were symmetrically distributed as linings of the holes, with the central area unoccupied (Figure 3b). Thermogravimetric analysis (TGA, Figure 2c) of freshly prepared crystalline samples 1·2(OH−)·4(CO2) has shown gradual mass losses of 20.9% in the temperature range of 50− 150 °C, consistent with the loss of four molecules of CO2 per 1 (calculated 21.6%). Further decomposition of the residual 1· 2(OH−) species has been found between 150 and 500 °C (the D


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Figure 5. SEM images of crystalline samples 1·2(OH−)·4(CO2) (a) and its heating residual species 1·2(OH−) (heated under 140 °C for 1 h) (b); recycling yield of the different batches with samples heated under 140 °C (c); and comparison between the heat capacity of 4 mol % 1 (methanol− water solution) with MOF-177 and 20 mol % MEA aqueous solution (d).

were obtained when the crystalline 1·2(OH−)·4(CO2) samples were heated under 150 °C (please see the Supporting Information Table S2 for details). We then further repeated the above “crystallization− heating−re-dissolving” procedures in an infinite loop and found that for the 10th batch, the yield of products 1·2(OH−)· 4(CO2) decreased to about 89.9% (Figure 5c and Table S2). That is to say, the organometallic cation 1 can be recycled at least 10 times for the real-world CO2 capture applications. It should be noted that this number of recycling times was almost double that of the procedures of heating under 150 °C, where the yield of products 1·2(OH−)·4(CO2) decreased to about only 78% for the 5th batch (Figure 5c and Table S2), demonstrating again the significant influence of the heating temperature on the recycling ability the organometallic cation 1. The partial decomposition of the organometallic cation 1 upon heating was also verified by FESEM measurements. For the 5th batch products, the morphology changed from cubical to massive (Figure S4a), whereas for the 10th batch products the morphology was further lumpy (Figure S4b). Upon heating under 140 °C, both products collapsed into “loose sand” as expected (Figure S4c,d) but not thoroughly as the 1st batch products (Figure 5b). However, despite the different morphologies, the chemical nature of the different batch products was almost identical, as have been verified by the infrared (IR) spectra and PXRD patterns (Figure S5). Thus, the mechanistic thought on the recycling potential of the cation

the successful binding of CO2 from air with 1 was the presence of water. Thus, the organometallic cation 1 may act as both desiccant and CO2 absorbent for natural gas.25 To investigate the recycling ability of the organometallic cation 1 for the real-world CO2 capture applications, the reaction of 2 mmol (1.075 g) compound [Fe(H2Bpz2)2(bipyNH2)] with 4 mmol (0.745 g) bipy-NH2 ligand in a 50 mL methanol−water 4:1 (v/v) solution, under air conditions, has been performed (Experimental Section). Slow evaporation of the obtained solution under ambient conditions has resulted in 1.580 g products of 1·2(OH−)·4(CO2) (yield 96%, based on Fe(II) ion) in the residual 35 mL solution within 3 days (batch 1). The composition and phase purity of the products were verified by PXRD measurements (Figure 4). After heating the 1.580 g products at 140 °C for 1 h (the optimal heating temperature was screened to be 140 °C, please see the Table S2 in Supporting Information for screening details), the residual 1.24 g species were redissolved in another 50 mL methanol− water 4:1 (v/v) solution, and 1.56 g products of 1·2(OH−)· 4(CO2) (batch 2, recycling yield 98.7%, based on the crystalline products 1·2(OH−)·4(CO2) obtained from batch 1) can be obtained upon repeating the above-mentioned evaporation procedures, demonstrating almost no discount for the recycling ability of the organometallic cation 1. Note that this 1.3% discount of the recycling ability can be attributed to the partial decomposition of the organometallic cation 1 upon heating of the crystalline samples 1·2(OH−)·4(CO2), as have been demonstrated by the results of 97.5% recycling yield, which E


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(PXRD) was recorded on a D8 ADVANCE XRD (Bruker, Germany) with Cu Kα radiation (λ = 1.54056 Å) at 40 mA and 45 kV. The sample was packed into a glass holder, and the diffraction patterns were collected over a 2θ range of 0−50 at a scan rate of 3° min−1. The single-crystal XRD data for 1·2(OH−)·4(CO2) was collected with a Bruker-AXS SMART APEXII diffractometer equipped with a charge coupled device type area detector and Mo Kα radiation (λ = 0.71073 Å) in ω − 2θ scan mode. The diffraction data were corrected for Lorentz and polarization effects and for absorption by using the SADABS program. The structures were solved by direct methods, and the structure solution and refinement based on |F|2 were performed with the SHELX software. All nonhydrogen atoms were refined with anisotropic displacement parameters, whereas all hydrogen atoms were positioned geometrically and refined with isotropic displacement parameters according to the riding model. All geometrical calculations were performed with the SHELXL-2014 software.39 The crystal data and structure refinement parameters for 1·2(OH−)·4(CO2) were summarized in Table S1, and the ASU is shown in Figure S1. Synthesis. 1·2(OH−)·4(CO2) was prepared as follows: a mixture of [Fe(H2Bpz2)2 (bipy-NH2)] (107.2 mg, 0.2 mmol) and bipy-NH2 (72.6 mg, 0.4 mmol) in a 24 mL methanol−water (v/v = 3:1) solution was stirred for 30 min under ambient condition, and the obtained brown solution was then kept undisturbed at ambient condition. Single crystals of 1·2(OH−)·4(CO2) suitable for XRD were formed within 3 days through slow evaporation technology. The block red crystals were collected by filtration (78.3 mg, Yield 96%). Elemental Anal. Calcd (%) for C34H32FeN12O10: C, 49.50; H, 3.91; N, 20.39. Found: C, 50.42; H, 3.82; N, 21.51. IR (KBr pellet, cm−1): 3411, 3201, 2376, 2348, 2042, 1637, 1620, 1556, 1468, 1366, 1339, 1299, 1264, 1235, 1015, 961, 868, 835, 578, 535. Thermogravimetric Analysis. TGA of the freshly prepared samples of 1·2(OH−)·4(CO2) shows gradual mass losses of 20.9% in the temperature range of 50−150 °C, consistent with the loss of four molecules of CO2 per 1 (calculated 21.6%). The heating residual species (heating under 150 °C) were found to be 1·2(OH−), as has been confirmed by elemental analysis (Calcd (%) for C30H32FeN12O2: C, 55.54; H, 4.97; N, 25.92. Found: C, 55.41; H, 5.02; N, 24.82) and FT-IR spectroscopy (Figure 2d). What is more, PXRD and FESEM measurements revealed the collapse of the 3D porous architecture of cation 1 after the removal of CO2. Recycling of 1 for the Real-World CO2 Capture Applications. Batch 1: 2 mmol (1.075 g) compound [Fe(H2Bpz2)2 (bipy-NH2)] and 4 mmol (0.745 g) bipy-NH2 ligand were mixed in a 50 mL methanol− water 4:1 (v/v) solution under ambient condition. After stirring for about 30 min, the resulting methanol−water solution was kept undisturbed under ambient conditions for slow evaporation. After 3 days, 1.580 g products of block red crystals 1·2(OH−)·4(CO2) was obtained (yield 96%, based on Fe(II) ion) in the residual 35 mL solution. The compositions and phase purity of these red crystal products were verified by PXRD measurements. The 1.580 g product of 1·2(OH−)·4(CO2) was then heated under 140 °C, giving 1.24 g heating residual species 1·2(OH−); the latter was used as the starting material for CO2 capture applications in batch 2. Batch 2: The residual 1.24 g species 1·2(OH−) from batch 1 were redissolved in another 50 mL methanol−water 4:1 (v/v) solution under ambient condition. After repeating the stirring and slow evaporation procedures as batch 1, 1.56 g products of crystalline 1· 2(OH−)·4(CO2) samples were obtained (recycling yield 98.7%, based on the crystalline products 1·2(OH−)·4(CO2) obtained from batch 1). Heating of the 1.56 g products under 140 °C gave 1.225 g residual species 1·2(OH−). Again, the 1.225 g residual species was further used as the starting material for CO2 capture applications in batch 3. After repeating the above “crystallization−heating−re-dissolving” procedures 10 times, the recycling yield of crystalline products 1· 2(OH−)·4(CO2) decreased to about 89.9% (based on the crystalline products 1·2(OH−)·4(CO2) obtained from batch 1). These data indicate that the organometallic cation 1 could be recycled at least 10 times for the real-world CO2 capturer applications.

1 can be proposed: the removal of CO2 from the crystalline samples 1·2(OH−)·4(CO2) has lead to partial decomposition of cation 1, which thus resulted in a massive morphology for the subsequent batch products; the latter became much harder to release CO2 for regeneration. To investigate the energy costs associated with recycling of the organometallic cation 1, the heat capacity measurements of 4 mol % methanol−water solution of heating residual species 1· 2(OH−) under a flow of nitrogen have been performed. Results revealed that 4 mol % 1 (methanol−water solution) exhibits an almost linear increase in the heat capacity with temperature, from 1.26 J g−1 K−1 at 20 °C to 2.14 J g−1 K−1 at 200 °C (Figure 5d). Note that the heat capacity of 4 mol % 1 was just slightly higher than that of MOF-17737 but still much lower than that of the 20 mol % MEA aqueous solution.38 Thus, the organometallic cation 1 has the potential to be developed as alkanolamine alternatives for the real-world CO2 capture applications. On considering the drawbacks of aqueous alkanolamine solutions for CO2 capture, the strategies present here may provide new hints into the development of more ideal solutionstate CO2 capture materials or technologies, based on the following reasons: (a) unlike the formation of a covalent bond between amine functionalities and CO2, which lead to the formation of carbamate or bicarbonate, the “H-bonded CO2” species are connected through intermolecular hydrogen bonding contacts, which requires relatively lower energy input for the release of CO2; (b) the relatively smaller heat capacity demonstrated lower regeneration energy costs; (c) the pH of the methanol−water solution was always maintained at around 8.0 during the reaction process, a value that almost has no corrosiveness toward any vessels. However, much effort should be taken to improve the recycling potential and operability of the organometallic cation 1 before it can be used as a practical real-world CO2 capturer.

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EXPERIMENTAL SECTION

Materials and Methods. All syntheses were performed under ambient conditions. Compound [Fe(H2Bpz2)2(bipy-NH2)] was prepared in our previous work,31 and 4,4′-diamino-(2,2′-bipyridine) and solvents were all obtained commercially and used as received. Physical Measurements. Elemental analyses of crystals 1· 2(OH−)·4(CO2) and 1·2(OH−) species were performed by a VarioEL III elemental analyzer for carbon, hydrogen, and nitrogen. The IR spectra were recorded on a Shimadzu IR prestige-21 FTIR-8400S spectrometer in the spectral range 4000−500 cm−1, with the samples in the form of potassium bromide pellets. TGA profiles of 1·2(OH−)· 4(CO2) were performed using a Mettler-Toledo TGA/DSC STARe System at a heating rate of 10 K min−1 under an atmosphere of dry N2 flowing at 20 cm3 min−1 over a range from 50 to 500 °C. The heat capacity measurements were performed on a STD instruments Q600 differential scanning calorimeter (DSC) equipped with a refrigerated cooling system RSC90 under a nitrogen flow. Baseline data for the empty heating chamber were collected between temperatures of −90 and 300 °C, followed by a temperature calibration using the melting point of an indium sample. The heat flow data were collected using a temperature ramp rate of 5 °C/min in the temperature range of −50 to 200 °C, using a temperature modulation of ±1 °C every 60 s. Magnetic susceptibility data of crystals 1·2(OH−)·4(CO2) and 1· 2(OH−) species were collected using a quantum design vibrating sample magnetometer in a physical property measurement system with an applied magnetic field of 2000 Oe in the temperature range of 5− 305 K with a cooling rate of 2 K/min. Measurements were performed on freshly prepared crystal samples and the heating residual with about 10 mg. FESEM measurements were carried out on HITACHI S-4800 working at an accelerating voltage of 20 kV. X-ray powder diffraction F


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CONCLUSIONS In summary, the organometallic cation 1 (Fe(bipy-NH2)32+), which was formed in situ and carries abundant functional amino groups, acts as an effective CO2 capturer under air condition. 1 induced the formation of “H-bonded species” species, [CO2− OH−CO2]− and [CO2−CO2−OH]−, which connected 1 into a novel 3D architecture. The adsorption isotherms, recycling investigations, and the heat capacity measurements revealed that the CO2 capture ability of organometallic cation 1 in present work may provide new hints for the development of new amine-containing materials or technologies for CO2 capture and sequestration.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acsami.8b01044. Crystal data and asymmetric unit of crystal 1·2(OH−)· 4(CO2), magnetic properties, the optimal heating temperature screening procedures, adsorption isotherm, additional SEM images, IR spectra, and PXRD patterns (PDF)

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AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (Y.-H.L.). *E-mail: [email protected] (B.-W.S.). ORCID

Yang-Hui Luo: 0000-0002-5555-2510 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This research was supported by the Natural Science Foundation of China (grant no. 21701023), Natural Science Foundation of Jiangsu Province (grant no. BK20170660), Fundamental Research Funds for the Central Universities (no. 3207047407), and PAPD of Jiangsu Higher Education Institutions.

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