III) Metal–Organic Framework for Ammonia

Jul 18, 2018 - Mixed-Valence Cobalt(II/III) Metal–Organic Framework for Ammonia ... and shows outstanding stability and reversibility in the cyclic ...
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Cite This: ACS Appl. Mater. Interfaces 2018, 10, 27465−27471

Mixed-Valence Cobalt(II/III) Metal−Organic Framework for Ammonia Sensing with Naked-Eye Color Switching Jindan Zhang,†,§ Jun Ouyang,†,§ Yingxiang Ye,† Ziyin Li,† Quanjie Lin,† Ting Chen,† Zhangjing Zhang,*,†,‡ and Shengchang Xiang*,†,‡

ACS Appl. Mater. Interfaces 2018.10:27465-27471. Downloaded from pubs.acs.org by KAOHSIUNG MEDICAL UNIV on 08/25/18. For personal use only.

†

College of Chemistry and Materials Science, Fujian Provincial Key Laboratory of Polymer Materials, Fujian Normal University, 32 Shangsan Road, Fuzhou 350007, China ‡ State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian 350002, PR China S Supporting Information *

ABSTRACT: The construction of colorimetric sensing materials with high selectivity, low detection limits, and great stability provides a significant way for facile device implementation of an ammonia (NH3) sensor. Herein, with excellent alkaline stability and exposed N sites in molecule as well as with naked-eye color switching nature generated from changeable cobalt (Co) valence, a three-dimensional mixed-valence cobalt(II/III) metal−organic framework (FJU-56) with tris-(4-tetrazolyl-phenyl)amine (H3L) ligand was synthesized for colorimetric sensing toward ammonia. The activated FJU-56 demonstrates a limit of detection of 1.38 ppm for ammonia sensing, with high selectivity in ammonia and water competitive adsorption, and shows outstanding stability and reversibility in the cyclic test. The NH3 or water molecules binding to the exposed N sites with the hydrogen-bond are observed by single-crystal X-ray diffraction, determining that the attachment of guest molecules to the FJU-56 framework changes the valence of Co ions with a naked-eye color switching response, which provides an ocular demonstration for ammonia capture and a valuable insight into ammonia sensing. KEYWORDS: metal−organic framework, ammonia sensing, naked-eye color switching, mixed-valence cobalt, tetrazole-based ligand, single-crystal X-ray diffraction colored free radicals37 or color-changeable metal sites38,39 were introduced into the MOFs, demonstrating the potential for the application of NH3-sensing materials. Nevertheless, problems emerge in the development of the related MOF materials. The accuracy of the NH3 gas detective would be negatively influenced because of the competitive adsorption of water and NH3 that extensively exists and because of the common attribute of two molecules in polarity, coordination, and hydrogen-bonding ability.38−40 However, rarely NH3 gassensing reports focus on the selectivity toward water and ammonia competitive adsorption; thus, the sensitivity and selectivity of MOF towards NH3 sensing still remain to be improved. Meanwhile, MOFs for ammonia sensing are expected to possess excellent alkaline stability because of the alkaline nature of NH3, and the NH3 environment can also lead to the disintegration of MOF structures along with a reduction in NH3 adsorption.41 Hence, the major challenges to be solved for MOF-based ammonia sensing include issues

1. INTRODUCTION With an annual production of over 100 million tons, ammonia (NH3) is one of the most widely manufactured chemicals in the world. However, it is a colorless gas with a pungent odor, causing ocular irritation and upper respiratory tract infection. Once leaked out, it is easily absorbed across the skin, threatening human life even at very low concentrations.1−3 During the past years, many attempts have been made to capture and detect NH3.4−9 Most NH3 sensors depend on the electrochemical method currently, while electromagnetic interference caused by the electrical signal occurs,10−12 and the facile and rapid detection requirement stimulates the development of colorimetric sensing materials.13−15 Among many candidates, metal−organic frameworks (MOFs) have attracted attention for their extraordinarily high surface areas,16−18 tunable nature of pore sizes/ curvatures,19−23 and designable interaction sites (such as open metal sites,24−30 Lewis acidic sites, or Brønsted acidity sites31,32) for stronger interactions with specific guest molecules, thus offering good selectivity.33−36 In previous reports, to construct MOFs with guest-responsive naked-eye colorimetric properties after incorporating NH3, intensely © 2018 American Chemical Society

Received: May 11, 2018 Accepted: July 18, 2018 Published: July 18, 2018 27465

DOI: 10.1021/acsami.8b07770 ACS Appl. Mater. Interfaces 2018, 10, 27465−27471

Research Article

ACS Applied Materials & Interfaces

hydrochloric acid (100 mL, 2 M) was added into the solution. The resulting mixture was extracted with CH2Cl2 (5 × 50 mL), washed with ethylenediaminetetraacetic acid-2Na aqueous solution (5 × 100 mL), evaporated under a rotary evaporator, and dried over anhydrous MgSO4. The crude product was purified by flash chromatography on silica gel using CH2Cl2 as an eluent to afford 0.90 g (67.8%) of tris-(4cyanophenyl)amine as a primrose yellow powder. 2.2.2. Synthesis of Tris-(4-tetrazolyl-phenyl)amine (H3L). A mixture of tris-(4-cyanophenyl)amine (1.00 g, 3.13 mmol), NaN3 (1.02 g, 15.65 mmol), and ammonium chloride (0.84 g, 15.65 mmol) in anhydrous DMF (10 mL) was heated at 100 °C in a 50 mL roundbottom flask for 28 h with nitrogen. Upon cooling to RT, the aqueous layer was treated with dilute HCl (50 mL, 2 M) until no further precipitate formed. The precipitate was then collected by filtration, washed with distilled water (3 × 250 mL), and dried in air for 12 h to afford 2.14 g (95.5%) of H3L as a yellow powder. 1H NMR (DMSOd6, 600 MHz): 8.01 (d, 6H, H3), 7.31 (d, 6H, H2) ppm. Elemental analysis: C, 56.23; H, 3.65; N, 40.12%; calcd result for C21H15N13: C, 56.12; H, 3.36; N, 40.52%. 2.2.3. Synthesis of [Co(H0.27L)]·4H2O·0.5DMF (FJU-56, CCDC No. 1838172) Crystal. CoCl2·6H2O (11.90 mg, 0.05 mmol), H3L (44.94 mg, 0.10 mmol), 4 mL of DMF, 3 mL of anhydrous methanol, and four drops of dilute HCl (2 M) were heated in a 21 mL vial at 80 °C for 3 days, and then a yellow hexagon FJU-56 flake was obtained. Elemental analysis for FJU-56 (C45H47Co2N17O9) (%) calcd: C, 42.35; H, 7.45; N, 29.65. Found: C, 42.82; H, 8.28; N, 29.86. The highest peak (1.44 e Å−3) in the FJU-56a structure is located 0.952 Å from the Co1 atom. The freshly prepared sample of FJU-56 was soaked in ∼10 mL of methanol for 1 h, and then the solvent was decanted. Following the procedure of methanol soaking and decanting 10 times, the solvent-exchanged samples were activated by vacuum at RT for ∼24 h till the pressure of 5 mmHg, to get the activated sample FJU-56 (FJU-56a, CCDC no. 1838173). 2.2.4. Synthesis of NH3-Loaded FJU-56a (FJU-56a-NH3, CCDC No. 1838175) and H2O-Loaded FJU-56a (FJU-56a-H2O, CCDC No. 1838276). FJU-56a was set in a small vial, and then the vial was placed in ammonia aqueous solution (NH3[aq]) vapor for 4 h, and FJU-56a-NH3 with a brown color was obtained. Similarly, FJU-56a was set in water vapor for 4 h, and FJU-56a-H2O with blue-violet color was obtained. In the circle test, FJU-56a-NH3 was placed in a drying oven at 70 °C overnight to get FJU-56a; the ammonia adsorption and desorption process was repeated five times. 2.3. SCXRD Studies. Data collection and structural analysis of the FJU-56 crystal were collected on an Agilent Technologies Super Nova single-crystal diffractometer equipped with graphite monochromatic Cu Kα radiation (λ = 1.54184 Å). The crystal was kept at 150 K during data collection. Using Olex2,46,47 the structure was solved with the Superflip structure solution program using charge flipping and refined with the ShelXL48 refinement package using least-squares minimization. All nonhydrogen atoms were refined with anisotropic displacement parameters. The hydrogen atoms on the ligands were placed in idealized positions and refined using a riding model. We employed PLATON49/SQUEEZE to calculate the diffraction contribution of the solvent molecules and thereby produce a set of solvent-free diffraction intensities. The detailed crystallographic data are shown in Tables S1 and S2. 2.3.1. SCXRD for FJU-56a-NH3 and FJU-56a-H2O. The solventexchanged single crystal of FJU-56 was epoxied onto a thin glass fiber and carefully inserted into a 1.0 mm borosilicate capillary and pretreated in the same way as for the gas adsorption measurements to get the guest-free FJU-56a. The capillaries were exposed to dry ammonia for 4 h and finally sealed by a torch. After that, the NH3loaded single crystal was immediately removed to a dry liquid nitrogen atmosphere (100 K) for structural analysis. SCXRD tests for FJU-56a-H2O were similar processes, except that capillaries with FJU-56a were exposed to water vapor.

associated with stability and reversibility as well as sensitivity and selectivity. Herein, tetrazole-based ligand [tris-(4-tetrazolyl-phenyl)amine, H3L] was used to coordinate a mixed valence Co ion to form a novel three-dimensional (3D) porous MOF (FJU56) for ammonia sensing based on three aspects: (1) incorporating tetrazole-based ligands with multiple nitrogen sites as Lewis base centers into MOFs were thought to enhance the gas uptake ability and selectivity on account of the dipole−quadrupole interactions.42−44 Because ammonia is a Lewis base and a reducing agent, the multiple nitrogen sites can significantly improve the capture selectivity toward ammonia molecules via acid−base interaction. (2) To build a MOF with excellent stability, the mixed valence Co(II/III) ion was used as connector for the N−Co bond.45 (3) Upon coordination environment change induced by ammonia adsorption, the valence of Co(II/III) would change with naked-eye color switching and hence can be utilized as colorimetric ammonia-sensing material for facile device implementation. As expected, the activated FJU-56 demonstrates great selectivity and sensitivity with naked-eye color switching for ammonia sensing in the competitive adsorption tests of water and ammonia with outstanding stability, reversibility, and durability in the cyclic test. Notably, this work bridges the theoretical gap of the working mechanism of colorimetric sensing materials, particularly focusing on the mixed valence Co(II/III) MOF for ammonia sensing. The ammonia molecule in the channels of MOF was identified by using single-crystal X-ray diffraction (SCXRD) technology, determining that the attachment of guest molecules to the MOF changes the coordination environment of metal ions with a naked-eye color-switching response, which provides an ocular demonstration for ammonia capture and valuable insight into ammonia sensing.

2. EXPERIMENTAL SECTION 2.1. Materials and Measurements. All reagents and solvents used in the synthesis are commercially available and used as supplied without further purification. Powder XRD (PXRD) was carried out with a PANalytical X’Pert3 powder diffractometer equipped with a Cu sealed tube (λ = 1.541874 Å) at 40 kV and 40 mA over the 2θ range of 5−30°. The Fourier transform infrared (KBr pellets) spectra were recorded in the range of 400−4000 cm−1 on a Thermo Nicolet 5700 FT-IR instrument. Thermal analysis was carried out on a Mettler TGA/SDTA 851 thermal analyzer from 30 to 600 °C at a heating rate of 10 °C min−1 under a nitrogen atmosphere. Elemental analyses (C, H, and N) were performed on a PerkinElmer 240C analyzer. X-ray photoelectron spectroscopy (XPS) measurements were conducted on a VG Scientific ESCA Lab Mark II spectrometer using Al Kα as the Xray source. All binding energies were referenced to the C 1s peak of the surface adventitious carbon at 284.6 eV. Ultraviolet−visible (UV− vis) diffuse reflectance spectra were measured using a PerkinElmer model Lambda 950 spectrometer, with a BaSO4 plate as the standard (absorbance). The N2 sorption isotherms were measured at 77 K with liquid nitrogen on a Micromeritics ASAP 2020 HD88 surface area analyzer. 2.2. Syntheses. The ligand H3L was prepared according to a published method.42−44 The synthetic process is provided in Scheme S1. 2.2.1. Synthesis of Tris-(4-cyanophenyl)amine. A mixture of tris(4-bromophenyl)amine (2.00 g, 4.15 mmol) and CuCN (1.70 g, 18.98 mmol) was heated at reflux in 25 mL of anhydrous dimethylformamide (DMF) for 6 h under a nitrogen atmosphere at 150 °C. Upon cooling to room temperature (RT), the FeCl3/H2O/ ethanol (8.00 g/10 mL/8 mL) mixture solvent was added to the reaction mixture and then heated to 125 °C. Then, dilute 27466

DOI: 10.1021/acsami.8b07770 ACS Appl. Mater. Interfaces 2018, 10, 27465−27471

Research Article

ACS Applied Materials & Interfaces

3. RESULTS AND DISCUSSION 3.1. Crystal Structures. The FJU-56 crystals are flaky hexagon shaped and are synthesized by using the solvothermal method with solid CoCl2·6H2O and H3L reacting in DMF− CH3OH solution for 3 days. SCXRD reveals that FJU-56 crystallizes in the hexagonal space group P63/mmc and forms a 3D MOF. As shown in Figure 1a, the asymmetric unit contains

rhombic channels along the c axis with a 3D interconnecting structure (Figure 1c). In addition, the dimension of this channel is estimated to be around 16.725 × 10.138 Å. Topological analysis of the FJU-56 network reveals that it is a nia net (Figure 1d), and the Schläfli symbol is (412·63)(49·66) determined by TOPOS. After elimination of the guest solvent molecules, the calculated free volume in the fully desolvated structure FJU-56 (activated FJU-56, FJU-56a) is 46.7% by PLATON.50 The calculated Co valences from the band valence analysis for FJU-56 and FJU-56a are 2.7326 and 2.7848, respectively (Table S4), and are in agreement with the XPS results (Tables S3 and S4 and Figure S2). Removing the solution molecule from FJU-56 changes the coordination environment and then changes the valence of the Co ion, and the molecular formula switches from [Co(H0.27L)]·4H2O·0.5DMF for FJU-56 to [Co(H0.22L)] for FJU-56a with naked-eye color switching from yellow to red. 3.2. Stability and Porosity of FJU-56. The PXRD pattern of FJU-56 powder is coincident with the simulated one from the single-crystal data, indicating the high purity and homogeneity of the synthesized powder (Figure 2a). Furthermore, the robustness for FJU-56a was observed by PXRD after the as-synthesized samples were exchanged with CH3OH several times and activated at RT for 24 h under high vacuum. The results indicate that the FJU-56 MOF is stable after the activation (Figure 2a). To evaluate the porosity of FJU-56a, the adsorption isotherms for N2 at 77 K around 1 atm were measured (Figure 2b). The inset in Figure 2b shows the pore size distribution of FJU-56a calculated by the nonlocal density functional theory (NLDFT) method.51 FJU56a exhibits a type-I isotherm with micropores located in the range of 0.5−0.8 nm and 1.5−1.75 nm, and the Brunauer− Emmett−Teller surface area and Langmuir surface area are 789.4142 and 1059.0478 m2 g−1, respectively. From the highest adsorption value of 268.2850 cm3 g−1 (N2), the total pore

Figure 1. Crystal structure of FJU-56. (a) Coordination environment of Co atoms; (b) triply bridged Co-tetrazol 1D chainlike building block along the c axis; (c) 3D structure of FJU-56 formed by H3L ligands linking Co-tetrazol chains; (d) schematic representation of the 3D nia topology.

one ligand and one Co ion. Each Co is octahedrally coordinated by six nitrogen atoms (N1) from six different L ligands. The octahedral cobalt connectors link the tetrazolate ligands, forming one-dimensional Co-tetrazol chainlike building block along the c axis (Figure 1b). Then, the Co-tetrazol chain connects to six adjacent similar chains, thus generating

Figure 2. (a) PXRD patterns of FJU-56; (b) N2 sorption isotherm of FJU-56a at 77 K; the inset represents the pore size distribution of FJU-56a calculated by the NLDFT method; (c) variable-temperature PXRD patterns of FJU-56; the inset is the TG analysis; (d) PXRD profiles of FJU-56 samples soaked in aqueous solutions with pH = 1, 2, 4, 6, 9, 11, 13, and 14 for 24 h. 27467

DOI: 10.1021/acsami.8b07770 ACS Appl. Mater. Interfaces 2018, 10, 27465−27471

Research Article

ACS Applied Materials & Interfaces

Figure 3. (a) Time-dependent UV−vis diffuse reflectance spectra of FJU-56a after exposed to NH3[aq] for different times; (b) time-dependent UV−vis diffuse reflectance spectra of FJU-56a after exposed to NH3[aq] with different concentrations; (c) A0/A curve vs NH3[aq] concentration, where A0 is the FJU-56a absorbance at 575 nm before exposed to NH3[aq] and A is the FJU-56a absorbance at 575 nm after exposed to NH3[aq]; (d) response to NH3[aq] during five circles. BaSO4 is used as the background; the inset in (a) is the digital photograph of FJU-56a and FJU-56aNH3.

volume of 0.4145 cm3 g−1 can be obtained and is equivalent to the theoretical value. The stability of FJU-56 was measured by using the PXRD and thermogravimetric (TG) analysis technologies. As shown in Figure 2c, the variable-temperature PXRD and TG tests reveal that FJU-56a can stay stable until 300 °C, and a temperature-induced single-crystal-to-single-crystal phase transition occurred at 180 °C (Table S5). To further investigate the chemical stability of FJU-56, PXRD tests were recorded after the MOF powders were soaked in aqueous solutions with different pH values. The PXRD patterns demonstrate that the crystallinity and framework integrity of FJU-56 can be wellretained in pH = 2−14 aqueous solutions for 24 h (Figure 2d). These results show that FJU-56 is tolerable in wide pH ranges and shows excellent stability in alkaline solution, especially. 3.3. Response to Ammonia Exposure. With excellent alkaline stability and exposed N sites (N2 in Figure 1a) in molecule as well as in naked-eye color-switching nature generated from changeable Co valence, FJU-56a is expected to be an ideal material for ammonia sensing. To explore the performance of FJU-56a for ammonia sensing, FJU-56a was exposed to ammonia aqueous solution (NH3[aq]) vapor. As shown in the inset in Figures 3a and S6, the color of the activated compound changes from red to brown. The timedependent solid UV−vis diffuse reflectance spectra of FJU-56a laid in NH3[aq] circumstance were used to record the colorswitching process (Figure 3a). In this work, the main UV absorption band at 350 nm for FJU-56a can be attributed to ligand H3L.52−56 Compared with the band of ligand H3L (375 nm), the blue shift and higher absorbance in 500−750 nm region result from the coordination of ligands with Co ions (Figure S7). With the exposure time in NH3[aq] vapor increasing, the absorbance of FJU-56a decreases at 350 nm and in 500−750 nm region with a visual color change from red to brown.

In the NH3[aq] vapor, ammonia and water are concurrent, and to eliminate the influence of water and evaluate the selectivity, FJU-56a was exposed to water vapor without ammonia. As shown in the insets of Figure S11, FJU-56a quickly changes from red to dark blue-violet in the water steam atmosphere. The UV−vis diffuse reflectance spectra clearly shows that the absorbance increases significantly at 350 nm and in the range of 500−750 nm (Figure S11a). The different color responses of FJU-56a in NH3[aq] and water vapor demonstrate that FJU-56a tends to capture ammonia more than water and is immune to the negative influence of moisture. Figure 3b shows the UV−vis diffuse reflectance spectra of FJU-56a exposed to different concentrations of NH3[aq] (0− 10 ppm), and an obvious absorbance decrease in the range of 500−750 nm with an increase in the NH3[aq] concentration can be observed. The plot of absorbance shifts in 575 nm with changing NH3[aq] concentration is shown in Figure 3c. The limit of detection (LOD) of FJU-56a for ammonia capture is calculated by fitting the plot with the following equation.57−60 (A 0 /A) = KSV[M] + 1

where A0 is the FJU-56a absorbance exposed to 0 wt % NH3[aq] and A is the FJU-56a absorbance after exposed to NH3[aq]. The calculated KSV is 0.00503 ppm−1 and R2 is 0.978627. The calculated KSV is comparable to the values in the reported fluorescence and colorimetric ammonia sensor;61 and the obtained LOD value is 1.38 ppm. In control experiments, FJU-56a was exposed to H2O/ethanol solution with different water concentrations to further eliminate the influence of water (Figure S11b). The result agrees with timedependent UV−vis diffuse reflectance spectra that FJU-56a has different responses to water and NH3[aq], and it is facile to distinguish them. As a consequence, ammonia exposure tests 27468

DOI: 10.1021/acsami.8b07770 ACS Appl. Mater. Interfaces 2018, 10, 27465−27471

Research Article

ACS Applied Materials & Interfaces

2.7848, 2.6960, and 2.7401, respectively. Incorporating the UV−vis diffuse reflectance spectra results, it can be determined that the NH3 molecule adsorption occurs at the exposed N sites in the ligand, and the adsorption behavior changes the coordination environments of Co ions, which leads to nakedeye color switching. The identifying of the ammonia molecule in the channels of MOF provides an ocular demonstration for ammonia capture and sensing.

show that FJU-56a has high sensitivity with excellent selectivity for ammonia sensing. In reversibility and durability tests, FJU-56a undergoes five circles of ammonia adsorption and desorption (Figure S12). Figure 3d is the summarized peak values of absorbance for FJU-56a and FJU-56a-NH3 in each circle. When FJU-56a was exposed to NH3[aq] for 4 h, the absorbance of FJU-56a at 500 nm decreased 26.21% and can be recovered to 98.77% by heating at 60 °C for 6 h. In the second cycle, the absorbance of FJU-56a at 500 nm decreased 21.22% and then recovered to 96.97%. In the following cycles, the values show a negligible variation, demonstrating good stability and reproducibility toward the sensing of ammonia. To clarify the action principle of ammonia molecule on FJU56a, SCXRD was used to determine the crystal structure of FJU-56a-NH3 and FJU-56a-H2O. The results determine that the ammonia molecule is located between the two exposed nitrogen atoms (N2) of the two adjacent tetrazole rings with a hydrogen-bond length of 2.025 Å (Figure 4a). Compared with

4. CONCLUSIONS In summary, a novel 3D mixed-valence MOF (FJU-56) with Co(II/III) ions and tetrazolate ligands [tris-(4-tetrazolylphenyl)amine, H3L] was synthesized for ammonia sensing with naked-eye color response. The activated FJU-56 (FJU56a) shows excellent thermal and chemical stabilities and demonstrates great properties for NH3 sensing with high selectivity, a LOD of 1.38 ppm, and outstanding reversibility and durability in the cyclic test. SCXRD data determine that NH3 molecules bond to the exposed N sites in the H3L ligand through the hydrogen bond with a length of 2.025 Å, which is stronger and stable than the hydrogen bond between exposed N sites and the water molecule (2.069 Å). The NH 3 adsorption process is accompanied by change in the coordination environment of Co ions, leading to a visible color change from red to brown. This work provides a new way to design mixed-valence framework materials with guestresponsive and naked-eye colorimetric properties as practical high selectivity sensing materials for environmental pollutants.

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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/acsami.8b07770.

Figure 4. (a) Hydrogen bonds in FJU-56a-NH3; (b) view of FJU56a-NH3 along the c axis.

the hydrogen-bond length of 2.069 Å for FJU-56a-H2O (Figure S14), the formation of the hydrogen bond in FJU-56aNH3 is more possible, and that agrees with the UV−vis diffuse reflectance result that FJU-56a tends to capture ammonia more than water when the competition adsorption of ammonia and water exists. The band valence analysis declares that the adsorption of ammonia guest molecule impacts the coordination environment of Co ions, resulting in a molecular formula of [Co(H0.30L)·NH3] for FJU-56a-NH3 with a brown color. Further, to reveal the color-switching mechanism of FJU-56a, Table 1 summarizes the congruent relationship of color and the valence bond of Co ions in FJU-56, FJU-56a, FJU-56aNH3, and FJU-56a-H2O crystals. As shown in Table 1, the bond length of Co1−N1 changes from 2.124 to 2.136 Å after placing FJU-56a in NH3 gas, and H2O adsorption leads to a Co1−N1 length of 2.130 Å. The valence bond of Co ions in FJU-56, FJU-56a, FJU-56a-NH3, and FJU-56a-H2O is 2.7326,

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XPS spectra, infrared spectra, CO2 sorption isotherms, UV−vis diffuse reflectance spectra of FJU-56a/H3L/ FJU-56a-H2O, and circle tests (PDF) Crystallographic data for FJU-56, FJU-56a, FJU-56aNH3, and FJU-56a-H2O and selected bond lengths and angles for compounds (CIF)

AUTHOR INFORMATION

Corresponding Authors

*E-mail: [email protected] (Z.Z.). *E-mail: [email protected] (S.X.). ORCID

Yingxiang Ye: 0000-0003-3962-8463 Shengchang Xiang: 0000-0001-6016-2587 Author Contributions §

J.Z. and J.O. contributed equally to this work.

Table 1. Summary of the Color and Valence Bond on FJU56, FJU-56a, FJU-56a-NH3, and FJU-56a-H2O

Co−N1 dist/Å valence bond color N2−H hydrogen-bond dist/Å

FJU-56

FJU-56a

2.132(3) 2.7326 yellow

2.124(5) 2.7848 red

Notes

The authors declare no competing financial interest.

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FJU-56a-NH3 FJU-56a-H2O 2.136(5) 2.6960 brown 2.025

ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation of China (21273033, 21673039 and 21573042) and the Fujian Science and Technology Department (2014J06003). S.X. gratefully acknowledges the support of the Recruitment Program of Global Young Experts.

2.130(5) 2.7401 blue-violet 2.069

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DOI: 10.1021/acsami.8b07770 ACS Appl. Mater. Interfaces 2018, 10, 27465−27471

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