Accepted Manuscript Fabrication of a capillary column coated with the four-foldinterpenetrated MOF Cd(D-Cam)(tmdpy) for gas chromatographic separation
Yan Zhang, Li Wang, Minghua Zeng PII: DOI: Reference:
S1387-7003(17)30332-5 doi: 10.1016/j.inoche.2017.04.029 INOCHE 6635
To appear in:
Inorganic Chemistry Communications
Received date: Revised date: Accepted date:
24 April 2017 28 April 2017 29 April 2017
Please cite this article as: Yan Zhang, Li Wang, Minghua Zeng , Fabrication of a capillary column coated with the four-fold-interpenetrated MOF Cd(D-Cam)(tmdpy) for gas chromatographic separation, Inorganic Chemistry Communications (2017), doi: 10.1016/ j.inoche.2017.04.029
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ACCEPTED MANUSCRIPT Fabrication
of
a
Capillary
Four-Fold-Interpenetrated MOF
Column
Coated
with
the
Cd(D-Cam)(tmdpy) for
Gas
Chromatographic Separation
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College of Chemistry and Chemical Engineering, Xinjiang Normal University, Urumqi 830054,
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Yan Zhanga, Li Wanga,*, Minghua Zengb,*
China
Hubei Collaborative Innovation Center for Advanced Organic Chemical Materials,
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b
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Ministry-of-Education Key Laboratory for the Synthesis and Application of Organic Functional Molecules, College of Chemistry and Chemical Engineering, Hubei University, Wuhan 430062,
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China
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To whom correspondence should be addressed. E-mail:
[email protected] (L. Wang).
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[email protected] (M. H. Zeng)
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ACCEPTED MANUSCRIPT
ABSTRACT: The diverse structures and unique properties of metal organic frameworks (MOFs) are attractive attributes for analytical application. In this work we apply the four-fold-interpenetrated
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MOF Cd(D-cam)(tmdpy) as the coating material in capillary columns for gas chromatographic
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separation of aromatic hydrocarbons (ether, acid and alcohol), linear alkane hydrocarbons (aldehyde, acid and ether). The good thermal and chemical stabilities as well as the provision of
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chromatographic stationary phase for gas separation.
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suitable host-guest interaction sites within the interpenetrating frameworks make it an excellent
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Keywords: MOFs, four-fold-interpenetrated, linear alkane hydrocarbons, gas chromatography
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ACCEPTED MANUSCRIPT Microporous metal-organic frameworks (MMOFs) have been paid extensive attention because of their potential applications in gas storage, separation, catalysis and other areas [1–9]. While most researchers have focused on the synthesis of MOFs with intricate and beautiful topologies with porous networks, increasing efforts have been made to explore their potential in real applications [10]. Depending on their high surface areas and adsorption affinities, one of the most promising applications for MOFs seems to be as the stationary phases for chromatography.
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Recently, MOF-508[11], MIL-101[12], and ZIF-8[13] have been revealed to be prospective
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stationary phases for packed columns and coated capillary columns in Gas Chromatography (GC)
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separation of xylene isomers and alkanes. Compare to the application of MOFs as stationary phase in Liquid Chromatographic column, the Gas Chromatographic stationary phase needs to be
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more stable thermally because the separation should be performed at relatively high temperature. Because “nature abhors a vacuum and interpenetration reduces voids” [14], thus this
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interpenetration greatly reduces the pore size and thus the available space within the MOFs structure. However, owing to the extreme stability from interpenetration and more host-guest
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interaction sites from small pore apertures, MOFs should have great potential to selectively adsorb and separate targets in Gas Chromatographic separation.
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Here we report the fabrication of capillary columns coated with the four-fold-interpenetrated MOF Cd(D-cam)(tmdpy) for gas chromatographic separation. The same 4-fold interpenetration
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polar diamond networks may adopt parallel, orthogonal, and anti-parallel arrangements, and giving very similar voids but totally different pore shapes [15]. Each D-cam ligand bridges two framework,
this
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Cd2+ sites to form a “Z” chain, which connected to tmdpy ligands to build a four-connected 3D 3D
framework
adopt
anti-parallel
arrangements
to
construct
a
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four-fold-interpenetrated framework. Such interpenetrating mode that not all the directions of diamond nets are parallel is very critical to create the unique channel surface for separating gas molecules with slightly-different size and shape. For the present study we chose aromatic hydrocarbons (ether, acid and alcohol) and linear alkane hydrocarbons (aldehyde, acid and ether) as the targets because they are biochemically important compounds in food, medicine and flavor with their antimicrobial and antibacterial activity. The good thermal and chemical stabilities and host-guest interaction sites from interpenetration make it an excellent gas chromatographic solid phase for the separation.
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ACCEPTED MANUSCRIPT Cd(CH3COO)2·3H2O (0.133 g,0.5 mmol), D(+)-camphoric acid (D-cam) (0.1 g,0.5 mmol), 4,4’-trimethylenedipyridine (tmdpy) (0.10 g, 0.5 mmol), NaOH (0.04 g, 1 mmol) and deionized water (15 mL) were mixed in a 25 mL Teflon-lined stainless steel vessel. The vessel was then sealed and heated at 160 °C for 3 days. The autoclave was cooled to room temperature, and transparent colorless crystals were collected in 78% yield (based on Cd). The MOF crystal was
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synthesized according to the method of Zhang et al [16]. The powder X-ray diffraction (PXRD) pattern of Cd(D-cam)(tmdpy) was collected on a
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Bruker D8 ADVANCE X-ray diffractometer using Cu Kα radiation ( λ = 1.5418 Å) in the 2θ
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angular range of 15–60°. Infrared spectrum was measured at room temperature by transmission through a KBr pellet containing 1% of the compound by use of a Shimadzu IR Affinity-1 Fourier
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transform infrared spectrometer in the range from 400 to 4000 cm−1. Thermogravimetry (TG) was obtained on a NETZSCH STA 449F3 simultaneous thermal analyzer instrument under a
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flowing nitrogen atmosphere from 40 to 1000 °C at a heating rate of 10 °Cmin–1. The Scanning Electron Microscope (SEM) imaging was performed on a Hitachi SU8010 cold Field Emission
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Scanning Electron Microscope. Capillary columns were carefully cut with a ceramic cutter to ensure a relatively clean break and stick on the sample stage, and coated with approximately 2
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nm layer of gold using an Emitech K550X automated sputter coater. Gas chromatographic separations were performed on an Agilent 6890N gas chromatography
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system with a flame ionization detector (FID), and high purity nitrogen (99.999%) employed as the carrier gas. All injections had the following common conditions: injection temperature mLmin–1.
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250 °C and detection temperature 250 °C, the injection volume was 0.1 μL and flow-rate was 1
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Untreated fused-silica open tubular column (Yongnian Optic Fiber Factory, Hebei province, China) was filled with 1 M NaOH, sealed at both ends and maintained for 2 h. Thereafter, the capillary was washed successively with ultrapure water for 1 h, 0.1 M HCl for 2 h and ultrapure water until the outflow reached neutrality, and then dried by vacuum pumping. The columns were prepared by a dynamic coating method in accordance with previous method [17–18]. Briefly, one end of the column is immersed into a 10 mL ethanol suspension of 10 mg Cd(D-cam)(tmdpy) (1 mgmL–1) while the other end is exposed to a vacuum to begin the removal of ethanol solvent under vacuum pump, and then leave a wet coating layer on the inner wall of the capillary column. Finished columns are conditioned on the gas chromatograph by
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ACCEPTED MANUSCRIPT heating to 30 °C for 20 min, raising the temperature to 200 °C at 2 °Cmin–1 and maintaining for 120 min. This compound Cd(D-cam)(tmdpy) crystallizes in the chiral space group P21. In this structure, each Cd2+ adopts octahedral coordination of two nitrogen atoms from tmdpy and two chelating carboxylate from the camphorate; thus it has only divergent propagations (Fig. 1a). Each D-cam ligand bridges two Cd2+ sites. This structure is similar to dicoordinate oxygen sites in zeolites
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which are characteristic of the zeolite-type net with the AX2 formula. Therefore, this material
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possesses the four-connected 3D framework (Fig. 1b and 1c). Each sublattice can be represented
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topologically as four-fold interpenetrating frameworks with chiral diamond nets (Fig. 1d). Cd(D-cam)(tmdpy) undergoes no weight loss below 215 °C. Then the first weight loss of
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39.6% may be due to the loss of the tmdpy ligands (calc. 39.1%) between 215 and 355 °C (Fig. S1). The powder X-ray diffraction pattern agrees well with that simulated from the single crystal
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data, indicating the single phase and purity of the sample. PXRD after heating at 200 °C is also in good agreement with that of the as-synthesized compound, indicating the crystal structure and
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frameworks stability of this compound are not destroyed (Fig. S2). The photo of the single crystals of the compound and Cd(D.Cam)(tmdpy)-coated capillary
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column together with the scanning electron microscopy (SEM) images of the cross section of capillary column shows that the fabricated capillary column had 9.96 μm thick on the inner wall
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(Fig. 2).
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Fig. 1. (a) The coordination environment of Cd(II); (b) The 3D framework of Cd(D-cam)(tmdpy); (c) The
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simplified topological representation of a diamond net, D-Cam (blue), tmdpy (purple); (d) Topological
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representation of the four-fold interpenetrating diamond net.
Fig. 2. (a) The colorless block single crystal of Cd(D-Cam)(tmdpy); (b) The capillary column coated with this compound; (c) The part of the cross section of MOF-coated open tubular column and an approximately 9.96 μm thick Cd(D-Cam)(tmdpy) coating on the inner wall; (d) MOFs deposited on the inner wall of coated open tubular column.
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ACCEPTED MANUSCRIPT First, we used the aromatic hydrocarbons with different functional groups (HO–(R)C=O, R–OH,
RO–C(R')=O)
with
A1
((2E)-3-phenylprop-2-enoic
acid),
A2
((2E)
-3-phenylprop-2-en-1-ol) and A3 (methyl 3-phenylprop-2-enoate) chosen as test solutes (Fig. 3a). The mixtures were eluted in the order of A3, A2 and A1. Here three adsorbates have the same aromatic and C=C structure (Ar–C=C–R) but different functional groups of R–OH, RO–C(R')=O and HO–(R)C=O. Here dipole-dipole interactions [19] between
δ+
C=Oδ- from adsorbate and the
O–Cδ+ of D-cam carboxylate groups of adsorbent MOF and C–H···π attractive interaction
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δ-
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[20–21] between the positively charged hydrogen atoms and the π electrons of aromatic ring both
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from adsorbates and MOF are the dominant forces. Gas chromatography separation results show that the gas-solid interaction is in the order of HO–(R)C=O > R–OH > RO–C(R')=O.
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The statement about the molecular interaction between adsorbates and MOF is supported by FT-IR. Taking (2E)-3-phenylprop-2-enoic acid and MOF for example, the bands at 1680 cm–1 are assigned to the C=O stretching vibration mode of the carboxyl group [22–23]. In addition,
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the bands at 1451 cm–1 are assigned to the in-plane bending band of O–H [23–24]. Compared with the pure A1, the carboxyl stretching vibration band at 1680 cm–1 is weakened, whereas the
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band of the O–H of stretching vibration at 1451 cm–1 almost disappears (Fig. S3). These changes
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demonstrate that there are significant interactions between the A1 and Cd(D-cam)(tmdpy),
(a)
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involving mainly the polarized carboxyl C=O and O–H of A1 and MOF.
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A3 A2
0
(b)
A1
solvent
A2
B1
solvent
B2
B1 B3 B2
A3
2 4 6 Retention Time (min)
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0
2
4
B3
6
Retention time (min)
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Fig. 3. Representative GC chromatograms on the Cd(D-am)(tmdpy)-coated open tubular column (10 m long × 0.25 mm i.d.) for the separation of: (a) A1: trans-cinnamic acid [(2E)-3-phenylprop-2-enoic acid); A2: cinnamyl alcohol [(2E)-3-phenylprop-2-en-1-ol]; A3: methyl cinnamate [methyl 3-phenylprop-2-enoate]; The temperature programming is from 60 °C to 120 °C at 30 °Cmin–1, then raising to 180 °C at 60 °Cmin–1, and maintain
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min.
(b)
B1:
decyl
aldehyde;
B2:
decanoic
acid;
B3:
butyl
butyryllactate
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ACCEPTED MANUSCRIPT [1-butoxy-1-oxopropan-2-yl butyrate]. Injection volume is 0.1 µL and flow rate is 1 mLmin–1. The temperature programming is from 40 °C to 120 °C at 20 °Cmin–1, then raising to 180 °C at 60 °Cmin–1, and maintain 5 min. Adsorbates used in separation via gas chromatography shown in Table S1.
We also examined the weak interaction between MOF and linear alkane hydrocarbons (aldehyde,
acid
and
ether),
B1
(decyl
aldehyde),
B2
(decanoic
acid)
and
B3
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(1-butoxy-1-oxopropan-2-yl butyrate) were chosen as test solutes, with the mixtures eluted in the
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order of B1, B3 and B2 (Fig. 3b). This three adsorbates have similar linear backbone structure
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but with different functional groups of H–(R)C=O, HO–(R)C=O, and RO–C(R')=O, but one more O–C=O group was added to B3. Among the three compounds, B2 (carboxyl) has most sites
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(both C=O and HO–C) for dipole-dipole interactions with the MOF, while B3 (ether) has more polarized groups (two C=O, two C–O) than C1 (one H–C=O). GC separation sequence indicates that the dipole-dipole interaction order is HO–(R)C=O > RO–C(R')=O > H–(R)C=O.
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In summary, we have successfully developed a stationary phase of Cd(D-cam)(tmdpy) having a 4-fold-interpenetrated diamond net which exhibited specific recognition and selectivity to
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separation of a series compounds with different functional groups (R–OH, H–C(R)=O,
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HO–(R)C=O, R–O–(R')C=O). This 4-fold-interpenetrated diamond metal-organic framework material as a new type of gas chromatographic stationary phase shows promising application in
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GC separation.
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Appendix A. Supplementary data
Include PXRD, TG, FT-IR and table of adsorbates separated on gas chromatography.
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Acknowledgment
This work is supported by the National Natural Science Foundation of China (NSFC, Grant No. 21365021 & 21371147) and Xinjiang Natural Science Foundation (XJNSF, Grant No. 2013711009). References [1] Z.Y. Gu, C.X. Yang, N. Chang, X.P Yan, Metal-organic frameworks for analytical chemistry: from sample collection to chromatographic separation, Acc. Chem. Res. 45 (2012) 734–745.
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Graphical abstract
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We have successfully developed a stationary phase of Cd(D-cam)(tmdpy) having a 4-fold-interpenetrated diamond net which exhibited specific recognition and selectivity to separation of a series compounds with different functional groups.
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ACCEPTED MANUSCRIPT Highlights
(1) A four-fold-interpenetrated MOF Cd(D-cam)(tmdpy) has been successfully synthesized by hydrothermal method. (2) The interpenetrating mode of Cd(D-cam)(tmdpy) is very critical to create the unique channel surface for separating gas molecules with slightly-different size and shape.
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(3) MOF-coated capillary column exhibited specific recognition and selectivity to separation of aromatic hydrocarbons and linear alkane hydrocarbons.
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