Microporous 3D Covalent Organic Frameworks for Liquid

Subscriber access provided by UNIV AUTONOMA DE COAHUILA UADEC

Article

Microporous 3D Covalent Organic Frameworks for Liquid Chromatographic Separation of Xylene Isomers and Ethylbenzene Jinjing Huang, Xing Han, Shi Yang, Yongyong Cao, Chen Yuan, Yan Liu, Jian-guo Wang, and Yong Cui J. Am. Chem. Soc., Just Accepted Manuscript • DOI: 10.1021/jacs.9b03075 • Publication Date (Web): 15 May 2019 Downloaded from http://pubs.acs.org on May 15, 2019

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Journal of the American Chemical Society

Microporous 3D Covalent Organic Frameworks for Liquid Chromatographic Separation of Xylene Isomers and Ethylbenzene Jinjing Huang,†,§ Xing Han,†,§ Shi Yang,† Yongyong Cao,‡ Chen Yuan,† Yan Liu,† Jianguo Wang,‡ and Yong Cui†,* †School

of Chemistry and Chemical Engineering and State Key Laboratory of Metal Matrix Composites, Shanghai Jiao Tong University, Shanghai 200240, China ‡Institute of Industrial Catalysis, College of Chemical Engineering, Zhejiang University of Technology, Hangzhou, 310032, China

Supporting Information ABSTRACT: Microporous covalent organic frameworks (COFs) hold great potential for small molecule separation, but are yet challenging to design and synthesize. Here we report a framework interpenetration strategy to make microporous COFs for efficient separations of C8 alkyl-aromatic isomers. Two pairs of microporous three-dimensional (3D) salen- and Zn(salen)-based COFs are prepared by Schiff-base condensation of ethanediamine with tetrahedral tetra(salicylaldehyde)-silane or -methane derivatives in the presence or absence of metal ions. The four 3D COFs are isostructural and have a 7-fold interpenetrated diamondoid open framework with less than 8.0 Å wide tubular channels. They exhibit permanent porosity, high thermal stability and good chemical resistance. The two COFs functionalized with uncoordinated salen groups can serve as stationary phases for high-performance liquid chromatography to provide baseline separation of xylene isomers and ethylbenzene with excellent column efficiency and precision, whereas the COFs with Zn(salen) motifs cannot achieve high-resolution separation. The salen-COFs showed high affinity to the o-xylene, allowing fast and selective separation of the o-isomer from the other isomers within seven min. This is the first report utilizing COFs to separate the practically important aromatic isomers. This work highlights new opportunities in designing microporous COFs and paves the way to expand the potential applications of COF materials.

INTRODUCTION

As

a burgeoning class of crystalline porous solids,1 covalent organic frameworks (COFs) constructed from organic building blocks via covalent bonds have shown promise in a variety of areas such as molecule storage and separation,2 catalysis,3 optoelectronics,4 sensing and detection,5 energy storage6 and drug delivery.7 One salient feature of COFs is that their network structures, pore surfaces and functionalities can, at least in principle, be precisely controlled and finely tuned by the judicious choice of organic building blocks.8 While high mesoporous volumes and surface areas are desirable for many applications,9,10 such wide pores often do not allow for size selective sieving and capturing substrates having small and similar sizes, limiting their uses, for example, in separation and purification of gases and light hydrocarbon mixtures.11 In contrast, microporous COFs may meet the demands for the growing applications emerging in processes involving small molecules owing to their small pore sizes and volumes.11,12 However, most of the reported COFs to date are restricted to mesoporous regime,3b,13 and only a small fraction of COFs with microporous structures are reported.2b,9a,14 This is presumably due to that 2D COFs tend to form mesoporous structures,8,10 whereas 3D COFs are hard to crystallize.10,15 In this work, we demonstrated interpenetration of 3D frameworks can be an efficient strategy to make microporous COFs for separating C8 alkyl-aromatic mixtures. Separation and purification of petrochemical feedstock are essential in laboratory and industrial scales.16 In particular, the three isomers of xylene, o-xylene, m-xylene, and p-xylene, together with ethylbenzene (EB) constitute the so-called C8 aromatic compounds, which are known as important raw materials

and are usually obtained as a mixture of isomers.17 However, their similar boiling points make distillation separation of all four almost impossible,18 whereas their comparable sizes and polarizabilities limit the ability of adsorbents to distinguish between the different isomers.19 The isolation of all four isomers using a single process has yet to be realized, thereby stimulating great efforts to develop more efficient technologies.20 Metalorganic frameworks (MOFs) have been extensively explored for separation of hydrocarbon mixtures including xylene isomers and EB based on size and shape selectivity.21 In contrast, despite great efforts, there are no COFs that have been reported to be capable of separating xylene isomers and EB.2b,15g,22 Herein, we described the synthesis and characterization of two pairs of microporous 3D salen- and metallosalen-based COFs by Schiff-base condensation reactions of ethanediamine with tetrahedral tetra(salicylaldehydes)silane or tetra(salicylaldehydes) methane derivatives. The four isostructural COFs adopt a 7-fold interpenetrated diamondoid open framework with less than 8.0 Å wide tubular channels lined by salen- or metallosalen units. As a proof-of-concept application, the COFs are used as stationary phases for high performance liquid chromatography (HPLC) to separate xylene isomers and EB. The salen-COF-packed columns provide high resolution and selectivity for the mixture separation, whereas the Zn(salen)-COFs failed to offer such high-resolution separation.

RESULTS AND DISCUSSION Synthesis and Characterization. As shown in Scheme 1, COFs 1 and 2 were synthesized by solvothermal reactions of SiTHBA23 or C-THBA24 (0.038 mmol) and ethanediamine (0.076 mmol) in 1.7 mL of n-BuOH/o-DCB/3 M AcOH(5:10:2, v/v/v) at

ACS Paragon Plus Environment

Journal of the American Chemical Society 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

120 ˚C for 72 hours, which afforded yellow crystalline powders in ∼80% yields. COFs 1-Zn and 2-Zn were obtained by reacting Si-

Page 2 of 9

THBA or C-THBA (0.038 mmol) and ethanediamine

Scheme 1. Synthesis of two pairs of 3D salen- and metallosalne-based COFs.

(0.076 mmol) in 1.7 mL of n-BuOH/o-DCB/3 M AcOH(5:10:2, v/v/v) in the presence of Zn(OAc)2·2H2O (0.095 mmol), which produced yellow crystalline powders as well. Besides, COF 1-Zn and 2-Zn can also be obtained by postsynthetic metalation of 1 and 2 with Zn ions, as evidenced by spectroscopic and PXRD characterizations (Figures S1, S2 and S8). All four COFs are not soluble in water and common organic solvents such as MeOH, DMF, THF and DCM. The as-synthesized four COFs were characterized by spectroscopic techniques. In the FT-IR spectra of COFs 1 and 2, the characteristic C=O stretching bands (1654 cm−1) disappeared, indicative of the consumption of the aldehydes. The appearance of characteristic C=N stretching band (1637 cm-1), thus indicating the formation of imine linkages, the case of which were also found for COFs 1-Zn and 2-Zn (Figure S1). The 13C crosspolarization magic-angle spinning (CP/MAS) NMR signals of COFs can be explicitly assigned as the proposed structure. Specifically, the typical signal at 161 ppm indicates the successful formation of imine bonds via the condensation of ethanediamine (en) and Si-THBA or C-THBA (Figure S2). Thermal gravimetric analysis (TGA) reveals the COFs are all stable up to 350 °C under N2 atmosphere (Figure S3). Scanning electron microscopy (SEM) images showed the all COF powders possess a rod like morphology with an average particle size of 5-10 μm (Figure S4). Crystal Structure. The crystal structures of the four COFs were resolved by the powder X-ray diffraction (PXRD) measurements in conjunction with structural simulations. After considering these possible nets with different space groups, the detailed simulation (see section S8 in the SI for details) clearly suggested that the four COFs are proposed to adopt a 7-fold interpenetrated dia topology with Fdd2 space group (Figure 1). Full profile pattern matching (Pawley) refinements for these 3D

COFs were carried out and the refinement results yield unit cell parameters nearly equivalent to the predictions with good agreement factors (a = 29.80 Å, b = 57.97 Å, c = 9.31 Å, α = β = γ = 90.0°, Rwp= 4.07% and Rp= 3.16% for COF 1; a = 29.37 Å, b = 56.29 Å, c = 9.13 Å, α = β = γ = 90.0°, Rwp = 4.66% and Rp = 2.71% for COF 2). The main PXRD peaks at 6.09°, 6.66°, 10.95°, 11.88°, 13.35°, 14.61°, 16.87° and 18.24° can be assigned to the (040), (220), (131), (400), (440), (171), (371) and (531) facets for COF 1, respectively. Similarly, the diffraction peaks at 6.27°, 6.78°, 11.18°, 12.03°, 12.83°, 13.59°, 14.07°, 15.41°, 17.24° and 17.99°, corresponding to the (040), (220), (131), (400), (151), (440), (331), (351), (371) and (511) facets for COF 2. The unit cell parameters of COFs 1-Zn and 2-Zn showed a slight change compared with the COF 1 and 2. Both materials exhibit unit cells with a = 29.88 Å, b = 59.22 Å, c = 9.45 Å, α = β = γ = 90.0°, Rwp = 4.35% and Rp = 6.14% for 1-Zn; a = 29.88 Å, b = 56.86 Å, c = 9.16 Å, α = β = γ = 90.0°, Rwp = 4.52% and Rp = 2.49% for 2-Zn. The diffraction peaks at 5.97°, 6.62°, 10.78°, 11.84°, 13.26°, 14.35°, 16.63° and 18.11° for COF 1-Zn can be assigned to the (040), (220), (131), (400), (440), (151), (440), (331), (351), (371) and (511) facets of space group of Fdd2. Strong diffraction peaks at 6.21°, 6.71°, 11.13°, 11.92°, 12.75°, 13.45°, 13.97°, 15.30°, 17.11° and 17.86° for 2-Zn can be assigned to the (040), (220), (131), (400), (151), (440) and (331) facets of space group Fdd2, respectively. As shown in Figure 2, in all of the four COFs, seven sets of independent diamond networks are interwoven to give 1D tubular channels with an opening of 7.8  12.3 Å2 for 1 and 1-Zn and 7.6  11.9 Å2 for 2 and 2-Zn. Notably, several mesoporous 3D salphen-based COFs and their metal-containing counterparts constructed from similar building units have recently been prepared, in which framework interpenetration was suppressed by

2 ACS Paragon Plus Environment

Page 3 of 9

introducing the bulky 4,5-dihalophenylene-1,2-diamines as linkers.15h

b)

15 20 2 Theta

200

3

dV (cm /g)

2.5

100

2.0 1.0 0.5

10

0.2

0.4

20 30 40 Pore width (Å)

0.6

0.8

50

1.0

25

30

131 400 151 440 331 351 371 511

Space group: Fdd2 Rwp = 4.52% Rp = 2.49%

15 20 2 Theta

25

30

COF 2-Zn

COF 1-Zn 2.5 2.0

100

0.0

0.0

10

150

7.8 Å

1.5

0

5

f)200

COF 2

COF 1

220 040

30

3

e)300

25

040

371 531

Rp = 6.14%

15 20 2 Theta

dV (cm /g)

10

10

d)

N2 Uptake (cm3/g)

5

5

30

Space group: Fdd2 Rwp = 4.35% 131 400 440 171

040

c)

25

400 151 440 331 351 371 511

15 20 2 Theta

Rp = 2.71%

131

10 220

5

Rp = 3.16%

Space group: Fdd2 Rwp = 4.66%

220

371 531

Space group: Fdd2 Rwp = 4.07% 131 400 440 171

040

220

a)

N2 Uptake (cm3/g)

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


50

7.8 Å

1.5 1.0 0.5 0.0

0

10

0.0

0.2

0.4

20 30 40 Pore width (Å)

0.6

0.8

50

1.0

P/P0

P/P0

Figure 1. PXRD patterns of (a) COF 1, (b) COF 2, (c) COF 1-Zn, and (d) COF 2-Zn with the experimental profiles in black, Pawley refined in red, calculated in blue and the difference between the experimental and refined PXRD patterns in green. N2 adsorption-desorption isotherms (77 K) and pore size distribution profiles (insert) of (e) COFs 1 and 2, and (f) COFs 1-Zn and 2-Zn.

Pore sizes are dependent on the framework interpenetration. The higher is the framework interpenetration, the smaller is the pore sizes.11c The present 7-fold interpenetrated frameworks have much smaller channels and pores than those interpenetrated networks, a feature of value in small molecule separation.11,12 Nitrogen (N2) adsorption-desorption isotherms were conducted at 77 K to evaluate the porosity of the COFs. They all displayed the type I isotherms (Figures 1e and 1f), indicative of their microporous nature. The Brunauer-Emmett-Teller (BET) surface areas were calculated to be 666 and 701 m2 g−1 for COFs 1 and 2, respectively, and the total pore volumes were 0.43 cm3 g-1 and 0.38 cm3 g-1 at P/P0 = 0.99. The pore size distribution analysis using the nonlocal density functional theory (NLDFT) gave rise to a mean pore width 7.8 Å for the two salen-based COFs (Figure 1e, inset). The isostructural COFs 1-Zn and 2-Zn also exhibited the

type I isotherm, and the surface areas were calculated as 460 m2 g−1 and 535 m2 g−1, and the total pore volumes were 0.31 cm3 g-1 and 0.22 cm3 g-1 at P/P0 = 0.99, respectively. Pore size distributions of them calculated by NLDFT showed pores with a size of 7.8 Å for both 1-Zn and 2-Zn (Figure 1f, inset), which is in good agreement with their simulated values. The pair of salenCOFs or Zn(salen)-COFs exhibited similar BET surface areas and pore volumes owing to their isostructural feature. The incorporation of Zn ions into the COFs led to a decrease in surface areas and pore volumes, presumably due to their decreased crystallinity, as evidenced the broadening 13C CP/MAS NMR signal (Figure S2).1e Chemical Stability. The chemical stability of the COFs was assessed by PXRD and N2 sorption after 24 hours treatment in boiling water, HCl (aq) and NaOH (aq) (Figures S13). All four



COFs exhibited good stability in boiling water, although showed slightly decreased crystallinity and surface areas. All of them kept well crystallinity in 0.1 M NaOH (aq.)

solution. The difference between the chemical stabilities of the

c)

b)

a)

d)

Page 4 of 9

e)

Figure 2. Structural representations of the four salen- and Zn(salen)-based COFs. a) An adamantine-like cage in COFs 1 and 2. b) An adamantine-like cage COFs 1-Zn and 2-Zn. c) A space-filling model of an adamantine-like cage in COFs 1 and 2. d) Interpenetration of seven diamond nets in the COFs. e) A space-filling model of the 3D structure of COFs 1 and 2 viewed along the a-axis (only the channel size of COF 1 was shown for clarity). C gray; N blue; H white; O red; the central C/Si in C/Si-THBA yellow.

frameworks derived from Si-THBA and C-THBA is striking in the case of acidic conditions. In 0.1 M HCl (aq.) solution, the CTHBA-based COFs 1 and 1-Zn were stable, whereas COFs 2 and 2-Zn were nearly dissolved and the remaining materials were rendered amorphous, as suggested by PXRD. Nevertheless, they were both capable of retaining crystallinity in 0.01 M HCl. The BET surface areas of the as-treated four COFs range from 294 to 567 m2 g-1, respectively (Figures S14). A slight decrease in signalto-noise ratio and an obvious decrease in their surface areas (about 20-40%) are indicative of just partial structural collapse upon treatment. HPLC Separations of Ethylbenzene (EB) and Xylene isomers. Inspired by the microporous features of the four 3D COFs, we utilized the COFs as the stationary phase in HPLC columns. The columns packed with the pure COF powders with sub-micrometer sizes show very high back-pressure during the HPLC separation processes, and so the SiO2 particles are added. The COF powders and silica spheres were dispersed in EtOH to get a uniform suspension under ultrasonication, and then the suspension was packed into the steel column. The COF packed columns for HPLC

were fabricated by loading the mixture of the crystalline sample (an average size of ~ 0.3 μm) and silica (an average size of ~5 μm) in EtOH into a 250 mm long and 2.1 mm internal diameter (i.d.) stainless steel column. The column was flushed with MeOH and activated with DCM to remove the guest molecules blocked in the packed materials. The COF 1 packed column was first examined to separate EB and xylene isomers. After optimizing mobile phase composition and its flow rate, all the targets in the mixture were well resolved and baseline separated from each other on the column packed with COF 1 using hexane/DCM (v/v = 95:5) as the eluent at a flow rate of 0.5 mL min-1 at r.t. (Figure 3a). The column provided good separation factors (αpx/Eb = 1.4, αmx/px = 1.3 and αox/mx = 2.0) and signal resolutions (Rpx/Eb = 1.7, Rmx/px = 1.5 and Rox/mx = 5.2) within 7 min. The elution sequence of these molecules follows the order of EB < p-xylene< m-xylene < o-xylene. The affinity of these isomers followed by the position of the substituents in isomers, ortho-isomer exhibit longer retention, while para-isomer exhibit shorted retention, indicative of the ability of the COF to adopt specific identification and shape-selective affinity to the


Page 5 of 9

adsorbates. The high preference for o-xylene was likely attributed to the molecular geometry of o-xylene that allows the interaction of both methyl groups with the polar salen groups of the

a)

EB

p-xylene m-xylene o-xylene

frameworks, giving rise to greater retention on the COF column.

b)

p-xylene m-xylene

EB

o-xylene

4

6

0

8

5

Retention time / min

m-xylene

24 g 12 g 6 g 3 g

2

4

6

40

EB

40 30

20

20

10

10

0

8

50

30

0

5

10

15

20

25

30

0

Mass of each analytes / g


e)

60 Peak Area Peak Height EB EB p-xylene p-xylene m-xylene m-xylene o-xylene o-xylene

50

o-xylene 30 g

0

15

d) 60

p-xylene EB

Peak Area / 105

c)

10


3

2

Peak Height / 5*10

0

f)

p-xylene m-xylene o-xylene

0.4

29 C 26 C 23 C

o-xylene

0.8

32 C

lnk'

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


m-xylene

0.0

p-xylene

-0.4

EB

20 C

-0.8 0

2

4

6

8

0.00328

0.00332

0.00336

0.00340

-1


1/T (K )

Figure 3. (a) HPLC chromatograms of EB and xylene isomers on the COF 1 packed column for five replicate experiments; (b) HPLC chromatograms of EB and xylene isomers on the COF 1-Zn packed column; (c) HPLC chromatograms of EB and xylene isomers with different injected masses on the COF 1 packed column; (d) Effects of injected mass of EB and xylene isomers on the peak area and the peak height; (e) HPLC chromatograms of EB and xylene isomers on the COF 1 packed column at 20-32 °C; (f) Van’t Hoff plots for EB and xylene isomers. Analytes were analyzed at r t. using hexane and DCM (v/v = 95:5) at a flow rate of 0.5 mL min-1 with UV detection at 254 nm.

The m- and p-xylene isomers can only interact with the salen units with one methyl group and so eluted faster than o-xylene.21c The easiest elution of EB and p-xylene is probably due to their lowest dipole moment compared to the other two xylene molecules. PXRD showed that the recovered COF 1 after HPLC measurement retained and structurally intact (Figure S18). As expected, the column packed with COF 2 can also give

high-through separation of EB and xylene isomers using hexane/DCM (v/v = 95:5) as the eluent at a flow rate of 0.25 mL min-1 (Figure S27). However, despite their isostructural analogs of the salen-COFs, the metallosalen-based COFs 1-Zn and 2-Zn cannot offer baseline separation of the mixture of EB and xylene isomers after being packed into the columns (Figures S25 and S26). This indicated that uncoordinated polar salen units in the



COFs are vital towards specific isomer recognition and separation. The capability of the COF 1 packed column was further demonstrated by high-resolution HPLC separation of five more isomer mixtures of aromatic substituted benzene derivatives including o-, m-, and p-dibromobenzene, -ethyltoluene, chlorotoluene, and -diethylbenzene, as well as EB and styrene. In all cases, the isomers were well separated from each other in a short time (Figures S20). The 3D salen-based COF 1 features 1D tubular channels with an opening of 7.8  12.3 Å2, which covers the diameters of EB and xylene isomers and other three isomer mixtures (maximum sizes: 6.0  9.8 Å2, Figure S17). It is thus likely that the separation capability of the COFs results from a combination of the microporous channels with amphiphilic channel surfaces decorated with polar salen groups, which can direct host-guest interactions favoring selectivity during the adsorption process.25 To confirm this point, three more control experiments were designed and performed on the COF 1 packed column. First, four monohalobenzenes having diameters (maximum sizes: 6.0  8.1 Å2) increased with the order of atom radius (F < Cl < Br < I) were selected as analytes. The mixture was well separated and the elution order followed with an increasing order of diameter, suggesting the binding strength of adsorbent and adsorbate followed the size of analytes (Figure S20d). Second, when the mixture of three diphenylbenzene isomers, sterically more demanding substrates with maximum sizes of 6.0  15.4 Å2, were subjected to the separation. The elution appeared with a very long retention time and almost no separation was achieved (Figure S16), probably because this bulky substrate are hard to reach the internal polar functional groups via the narrow open channels. Third, we prepared monodispersed amorphous COF 1/SiO2 hybrid particles and COF 1@SiO2 shell-core particles and evaluated their separation ability as stationary phases. The results showed they cannot separate EB and xylene isomers (Figures S28 and S29), also highlighting the critical role of the crystalline structure of the COF in isomer separation. Taken together, the above results suggested that the present separation was indeed associated with analytes being recognized in the crystalline microporous channels. DFT calculations were carried out to gain insight into the separation performance of the COFs. As shown in Table S1, the calculations of adsorption energies and the adsorption configurations shown that xylene isomers and EB stacked on the salen-COFs and Zn(salen)-COFs by an edge-to-face configuration had lower adsorption energy than those by a face-to-face configuration. Therefore, the edge-to-face configuration is thermodynamics preferred. As shown in Figure S9, only o-xylene allowed both methyl groups to interact with polar salen groups of the framework and the hydrogen bond lengths are shorter compare with the rest of isomers either on the salen-COF or the salen-ZnCOF. More importantly, the adsorption energies of xylene isomers and EB were variant on the salen-COF, probably leading to the salen-COFs capable of offering baseline separation of the mixture (Figure S10). However, the incorporation of Zn ions may slightly enhance the intermolecular interactions between the C8 aromatic molecules and the Zn(salen)-COFs through the metal sites, which play the important role for their comparable interaction enthalpies. This leads to that the adsorption energies of the four C8 aromatic isomers are almost identical on the Zn(salen)-COF, which might be the possible reason why the Zn(salen)-COFs cannot provide baseline separation of the C8 mixture. Nevertheless, further study is greatly needed to understand the separation behavior. To provide further insight into the separation of C8 isomers, an increase in EB and xylene isomers mass from 3 μg to 30 μg was

Page 6 of 9

injected into the COF 1 packed column for separation (Figure 3c). The results showed an unchanged retention time for each eluted analytes, and the resolution for the analyte did not decreased as the mass increased. Besides, the peak area of each analyte increased linearly with the increase in the injected mass. The RSD (relative standard deviation) for five replicate separations were 0.37-0.48%, 0.35-0.51%, 0.04-0.09% and 0.23-0.41% for the peak area, peak height, retention time and half peak width, respectively. The column efficiencies were found to be 10980, 10285, 9005 and 7097 plate/m for EB, -xylene, m-xylene and o-xylene, respectively. The COF 1 packed column service life can be at least 2 months, as evidenced by the repeating chromatograms (Table S15 and Figure S22). The repeatability of the COF column was further confirmed by fifty replicate separations of xylene isomers and EB. The RSD were found to be 1.55-1.89%, 1.57-1.77%, 0.06-0.10% and 0.19-0.36% for the peak area, peak height, retention time and half peak width, respectively. The thermodynamics of the EB and xylene isomer separation was studied at temperatures range from 20 to 32 °C (Figure 3e). It was found that as the column temperature increased, the retention times of the analytes were substantially decreased, suggesting the separation process was exothermic, while the selectivity was only slightly decreased. The van’t Hoff plots for the analytes showed good linearly correlation, suggesting no changes in the interaction mechanism during the separation process. Analysis from the values of ΔH and ΔS showed no apparent control by ΔH and ΔS individually, indicating that the separation process was controlled by both of them. Nevertheless, the adsorption enthalpy results are consistent with the order of retention times and the elution sequence of the EB and xylene isomers (Table S17). To develop a new class of chromatographic materials, MOFs have been explored as stationary phases for GC and HPLC separation of substituted aromatics.2b,21e,26 For the separation of EB and xylene isomers, the present column efficiencies and resolution and selectivity factors for COF 1 are comparable to or higher than those of reported for MOF-based stationary phases, as summarized in Table S7.21

CONCLUSIONS In summary, we have demonstrated that interpenetration of diamondoid frameworks can be an efficient strategy to design and construct microporous 3D COFs that are formed by Schiff-base condensations of tetrahedral tetra(salicylaldehydes) and ethanediamine building units. PXRD and modeling studies, together with pore size distribution analysis demonstrated all four COFs were 7-fold interpenetrated microporous frameworks containing about 7.8 Å wide tubular channels decorated with salen- or Zn(salen) functionalities. The two salen-COFs are capable of working as stationary phases of HPLC for baseline separation of xylene isomers and ethylbenzene with excellent column efficiencies and repeatability, whereas the Zn(salen)COFs cannot afford such high-resolution separation. This is the first report that demonstrated COFs to be promising porous materials for separation of the important C8 alkyl-aromatics. We expect that our effort will not only lead to the rational design and synthesis of microporous COFs but also push forward the applications of COF materials.

ASSOCIATED CONTENT

Supporting Information Experimental procedures and characterization data. This material is available free of charge via the Internet at http: //pubs.acs.org


Page 7 of 9

Journal of the American Chemical Society AUTHOR INFORMATION

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

Corresponding Author [email protected] Author Contributions J.H. and †X.H. contributed equally.

§

ACKNOWLEDGMENT This work was financially supported by the National Science Foundation of China (Grants 21431004, 21620102001, 21625604, 21875136, and 91856204), the National Key Basic Research Program of China (Grant 2016YFA0203400), Key Project of Basic Research of Shanghai (17JC1403100 and 18JC1413200), and the Shanghai “Eastern Scholar” Program.

REFERENCES (1) (a) Côté, A. P.; Benin, A. I.; Ockwig, N. W.; O'Keeffe, M.; Matzger, A. J.; Yaghi, O. M. Porous, Crystalline, Covalent Organic Frameworks. Science. 2005, 310, 1166. (b) Kandambeth, S.; Mallick, A.; Lukose, B.; Mane, M. V.; Heine, T.; Banerjee, R. Construction of Crystalline 2D Covalent Organic Frameworks with Remarkable Chemical (Acid/Base) Stability via a Combined Reversible and Irreversible Route. J. Am. Chem. Soc. 2012, 134, 1952. (c) Jin, E.; Asada, M.; Xu, Q.; Dalapati, S.; Addicoat, M. A.; Brady, M. A.; Xu, H.; Nakamura, T.; Heine, T.; Chen, Q.; Jiang, D. Two-Dimensional sp2 Carbon-conjugated Covalent Organic Frameworks. Science. 2017, 357, 673. (d) Parent, L. R.; Flanders, N. C.; Bisbey, R. P.; Vitaku, E; Evans, A. M; Kirschner, M. S; Schaller, R. D; Chen, L. X; Gianneschi, N. C; Dichtel, W. R. Seeded Growth of SingleCrystal Two-Dimensional Covalent Organic Frameworks. Science, 2018, 361, 52-57. (e) Ma, T.; Kapustin, E. A.; Yin, S. X.; Liang, L.; Zhou, Z.; Niu, J.; Li, L.; Wang, Y.; Su, J.; Li, J.; Wang, X.; Wang, W. D.; Wang, W.; Sun, J.; Yaghi, O. M. Single-Crystal X-ray Diffraction Structures of Covalent Organic Frameworks. Science. 2018, 361, 48. (2) (a) Sun, Q.; Aguila, B.; Perman, J.; Earl, L. D.; Abney, C. W.; Cheng, Y.; Wei, H.; Nguyen, N.; Wojtas, L.; Ma, S. Postsynthetically Modified Covalent Organic Frameworks for Efficient and Effective Mercury Removal. J. Am. Chem. Soc. 2017, 139, 2786. (b) Qian, H.; Yang, C.; Yan, X. Bottom-up Synthesis of Chiral Covalent Organic Frameworks and Their Bound Capillaries for Chiral Separation. Nat. Commun. 2016, 7, 12104. (c) Ning, G.; Chen, Z.; Gao, Q.; Tang, W.; Chen, Z.; Liu, C.; Tian, B.; Li, X.; Loh, K. Salicylideneanilines-Based Covalent Organic Frameworks as Chemoselective Molecular Sieves. J. Am. Chem. Soc. 2017, 139, 8897. (d) Ji, W.; Xiao, L.; Ling, Y.; Ching, C.; Matsumoto, M.; Bisbey, R. P.; Helbling, D. E.; Dichtel, W. R. Removal of GenX and Perfluorinated Alkyl Substances from Water by Amine Functionalized Covalent Organic Frameworks. J. Am. Chem. Soc. 2018, 140, 12677. (3) (a) Li, L.; Feng, X.; Cui, X.; Ma, Y.; Ding, S.; Wang, W. SalenBased Covalent Organic Framework. J. Am. Chem. Soc. 2017, 139, 6042. (b) Han, X.; Xia, Q.; Huang, J.; Liu, Y.; Tan, C.; Cui, Y. Chiral Covalent Organic Frameworks with High Chemical Stability for Heterogeneous Asymmetric Catalysis. J. Am. Chem. Soc. 2017, 139, 8693. (c) Yang, S.; Hu, W.; Zhang, X.; He, P.; Pattengale, B.; Liu, C.; Cendejas, M.; Hermans, I.; Zhang, X.; Zhang, J.; Huang, J. 2D Covalent Organic Frameworks as Intrinsic Photocatalysts for Visible Light-Driven CO2 Reduction. J. Am. Chem. Soc. 2018, 140, 14614. (4) (a) Bertrand, G. H. V.; Michaelis, V. K.; Ong, T.; Griffin, R. G.; Dincă, M. Thiophene-based Covalent Organic Frameworks. Proc. Natl. Acad. Sci. U. S. A. 2013, 110, 4923. (b) Bessinger, D.; Ascherl, L.; Auras, F.; Bein, T. Spectrally Switchable Photodetection with Near-InfraredAbsorbing Covalent Organic Frameworks. J. Am. Chem. Soc. 2017, 139, 12035. (c) Haldar, S.; Chakraborty, D.; Roy, B.; Banappanavar, G.; Rinku, K.; Mullangi, D.; Hazra, P.; Kabra, D.; Vaidhyanathan, R. AnthraceneResorcinol Derived Covalent Organic Framework as Flexible White Light Emitter. J. Am. Chem. Soc. 2018, 140, 13367. (5) (a) Ascherl, L.; Evans, E. W.; Hennemann, M.; Di Nuzzo, D.; Hufnagel, A. G.; Beetz, M.; Friend, R. H.; Clark, T.; Bein, T.; Auras, F. Solvatochromic Covalent Organic Frameworks. Nat. Commun. 2018, 9, 3802. (b) Rao, M.R.; Fang,Y.; DeFeyter, S.; Perepichka, D. F. Conjugated Covalent Organic Frameworks via Michael Addition-Elimination. J. Am. Chem. Soc. 2017, 139, 2421.

(6) (a) Du,Y.;Yang, H.; Whiteley, J. M.; Wan, S.; Jin, Y.; Lee, S.; Zhang, W. Ionic Covalent Organic Frameworks with Spiroborate Linkage. Angew. Chem., Int. Ed. 2016, 55, 1737. (b) Lv, J.; Tan, Y.-X.; Xie, J.; Yang, R.; Yu, M.; Sun, S.; Li, M.-D.; Yuan, D.; Wang, Y. Direct Solar-toElectrochemical Energy Storage in a Functionalized Covalent Organic Framework. Angew. Chem., Int. Ed. 2018, 57, 12716. (c) Peng, Y.; Xu, G.; Hu, Z.; Cheng, Y.; Chi, C.; Yuan, D.; Cheng, H.; Zhao, D. Mechanoassisted Synthesis of Sulfonated Covalent Organic Frameworks with High Intrinsic Proton Conductivity. ACS Appl. Mater. Interfaces, 2016, 8, 18505. (7) (a) Fang, Q.; Wang, J.; Gu, S.; Kaspar, R. B.; Zhuang, Z.; Zheng, J.; Guo, H.; Qiu, S.; Yan, Y. 3D Porous Crystalline Polyimide Covalent Organic Frameworks for Drug Delivery. J. Am. Chem. Soc. 2015, 137, 8352. (b) Mitra, S.; Sasmal, H. S.; Kundu, T.; Kandambeth, S.; Illath, K.; Díaz Díaz, D.; Banerjee, R. Targeted Drug Delivery in Covalent Organic Nanosheets (CONs) via Sequential Postsynthetic Modification. J. Am. Chem. Soc. 2017, 139, 4513. (8) (a) Côté, A. P.; El-Kaderi, H. M.; Furukawa, H.; Hunt, J. R.; Yaghi, O. M. Reticular Synthesis of Microporous and Mesoporous 2D Covalent Organic Frameworks. J. Am. Chem. Soc. 2007, 129, 12914. (b) Ding, S.; Wang, W. Covalent Organic Frameworks (COFs): From Design to Applications. Chem. Soc. Rev. 2013, 42, 548. (9) Xuan, W.; Zhu, C.; Liu, Y.; Cui, Y. Mesoporous Metal-Organic Framework Materials. Chem. Soc. Rev. 2012, 41, 1677. (10) (a) Das, S.; Heasman, P.; Ben, T.; Qiu, S. Porous Organic Materials: Strategic Design and Structure-Function Correlation. Chem. Rev. 2017, 117, 1515. (b) Lohse, M. S.; Bein, T. Covalent Organic Frameworks: Structures, Synthesis, and Applications. Adv. Funct. Mater. 2018, 28, 1705553. (11) (a) He, Y.; Krishna, R.; Chen, B. Metal-Organic Frameworks with Potential for Energy-Efficient Adsorptive Separation of Light Hydrocarbons. Energy Environ. Sci. 2012, 5, 9107. (b) Zeng, Y.; Zou, R.; Luo, Z.; Zhang, H.; Yao, X.; Ma, X.; Zou, R.; Zhao, Y. Covalent Organic Frameworks Formed with Two Types of Covalent Bonds Based on Orthogonal Reactions. J. Am. Chem. Soc. 2015, 137, 1020. (c) Ma, T.; Li, J.; Niu, J.; Zhang, L.; Etman, A. S.; Lin, C.; Shi, D.; Chen, P.; Li, L.; Du, X.; Sun, J.; Wang, W. Observation of Interpenetration Isomerism in Covalent Organic Frameworks. J. Am. Chem. Soc. 2018, 140, 6763. (12) (a) Tilford, R. W.; Mugavero III, S. J.; Pellechia, P. J.; Lavigne, J. J. Tailoring Microporosity in Covalent Organic Frameworks. Adv. Mater. 2008, 20, 2741. (b) Ma, H.; Ren, H.; Meng, S.; Yan, Z.; Zhao, H.; Sun, F.; Zhu, G. A 3D Microporous Covalent Organic Framework with Exceedingly High C3H8/CH4 and C2 Hydrocarbon/CH4 Selectivity. Chem. Commun. 2013, 49, 9773. (13) (a) Xu, H.; Gao, J.; Jiang, D. Stable, Crystalline, Porous, Covalent Organic Frameworks as a Platform for Chiral Organocatalysts. Nat. Chem. 2015, 7, 905. (b) Yang, H.; Du, Y.; Wan, S.; Trahan, G. D.; Jin, Y.; Zhang, W. Mesoporous 2D Covalent Organic Frameworks Based on ShapePersistent Arylene-Ethynylene Macrocycles. Chem. Sci. 2015, 6, 4049. (c) Fang, Q.; Zhuang, Z.; Gu, S.; Kaspar, R. B.; Zheng, J.; Wang, J.; Yan, Y. Designed Synthesis of Large-Pore Crystalline Polyimide Covalent Organic Frameworks. Nat. Commun. 2014, 5, 4503. (d) Nagai, A.; Chen, X.; Feng, X.; Ding, X.; Guo, Z.; Jiang, D. A Squaraine-Linked Mesoporous Covalent Organic Framework. Angew. Chem., Int. Ed. 2013, 52, 3770. (e) Baldwin, L. A.; Crowe, J. W.; Pyles, D. A.; McGrier, P. L. Metalation of a Mesoporous Three-Dimensional Covalent Organic Framework. J. Am. Chem. Soc. 2016. 138, 15134. (f) Zhou, T.; Xu, S.; Wen, Q.; Pang, Z.; Zhao, X. One-Step Construction of Two Different Kinds of Pores in a 2D Covalent Organic Framework. J. Am. Chem. Soc. 2014, 136, 15885. (14) (a) Wu, X.; Han, X.; Liu, Y.; Liu, Y.; Cui, Y. Control Interlayer Stacking and Chemical Stability of Two-Dimensional Covalent Organic Frameworks via Steric Tuning. J. Am. Chem. Soc. 2018, 140, 16124. (b) Yang, Y.; Faheem, M.; Wang, L.; Meng, Q.; Sha, H.; Yang, N.; Yuan, Y.; Zhu, G. Surface Pore Engineering of Covalent Organic Frameworks for Ammonia Capture through Synergistic Multivariate and Open Metal Site Approaches. ACS Cent. Sci. 2018, 4, 748. (c) Fang, Q.; Gu, S.; Zheng, J.; Zhuang, Z.; Qiu, S.; Yan, Y. 3D Microporous Base-Functionalized Covalent Organic Frameworks for Size-Selective Catalysis. Angew. Chem., Int. Ed., 2014, 126, 2922. (d) Luo, Z.; Liu, L.; Ning, J.; Lei, K.; Lu, Y.; Li, F.; Chen, J. A Microporous Covalent-Organic Framework with Abundant Accessible Carbonyl Groups for Lithium-Ion Batteries. Angew. Chem., Int. Ed. 2018, 57, 9443.



(15) (a) Uribe-Romo, F. J.; Hunt, J. R.; Furukawa, H.; Klöck, C.; O’Keeffe, M.; Yaghi, O. M. A Crystalline Imine-Linked 3-D Porous Covalent Organic Framework. J. Am. Chem. Soc. 2009, 131, 4570. (b) Zhang, Y.-B.; Su, J.; Furukawa, H.; Yun, Y.; Gándara, F.; Duong, A.; Zou, X.; Yaghi, O. M. Single-Crystal Structure of a Covalent Organic Framework. J. Am. Chem. Soc. 2013, 135, 16336. (c) Lin, G.; Ding, H.; Yuan, D.; Wang, B.; Wang, C. A Pyrene-Based, Fluorescent ThreeDimensional Covalent Organic Framework. J. Am. Chem. Soc. 2016, 138, 3302. (d) Baldwin,L. A.; Crowe, J. W.; Pyles, D. A.; McGrier, P. L. Metalation of a Mesoporous Three-Dimensional Covalent Organic Framework. J. Am. Chem. Soc. 2016, 138, 15134. (e) Ma, Y.; Li, Z.; Wei, L.; Ding, S.; Zhang, Y.; Wang, W. A Dynamic Three-Dimensional Covalent Organic Framework. J. Am. Chem. Soc. 2017, 139, 4995. (f) Yahiaoui, O.; Fitch, A. N.; Hoffmann, F.; Fröba, M.; Thomas, A.; Roeser, J. 3D Anionic Silicate Covalent Organic Framework with srs Topology. J. Am. Chem. Soc. 2018, 140, 5330. (g) Han, X.; Hung, J.; Yuan, C.; Liu, Y.; Cui. Y. Chiral 3D Covalent Organic Frameworks for High Performance Liquid Chromatographic Enantioseparation. J. Am. Chem. Soc. 2018, 140, 892. (h)Yan, S.; Guan, X.; Li, H.; Li, D.; Xue, M.; Yan, Y.; Valtchev, V.; Qiu, S.; Fang, Q. Three-dimensional Salphen-based Covalent–Organic Frameworks as Catalytic Antioxidants. J. Am. Chem. Soc., 2019, 141, 2920. (16) (a) Meyers, R. Handbook of Petroleum Refining Processes, 3rd ed.; McGraw-Hill: New York, 2003; pp247-253. (b) Sholl, D. S.; Lively, R. P. Seven Chemical Separations to Change the World. Nature. 2016, 532, 435. (17) Arpe, H. J. Industrielle Organische Chemie., 6th Ed.; Wiley-VCH: Weinheim, 2007. (18) Ruthven, D.; Goddard, M. Sorption and Diffusion of C8 Aromatic Hydrocarbons in Faujasite Type Zeolites. I. Equilibrium Isotherms and Separation Factors. Zeolites. 1986, 6, 275. (19). Cottier, V.; Bellat, J. P.; Simonot-Grange, M. H. Adsorption of pXylene/m-Xylene Gas Mixtures on BaY and NaY Zeolites. Co-adsorption Equilibria and Selectivities. J. Phys. Chem. B. 1997, 101, 4798. (20) (a) Minceva, M.; Rodrigues, A. E. Understanding and Revamping of Industrial Scale SMB Units for p-xylene Separation. AIChE J. 2007, 3, 138. (b) Lima, R. M.; Grossmann, I. E. Optimal Synthesis of p-xylene Separation Processes Based on Crystallization Technology. AIChE J. 2009, 55, 354. (21) (a) Holcroft, J. M.; Hartlieb, K. J.; Moghadam, P. Z.; Bell, J. G.; Barin, G.; Ferris, D. P.; Bloch, E. D.; Algaradah, M. M.; Nassar, M. S.; Botros Y. Y.; Thomas K . M.; Long, J. F.; Snurr, R. Q.; Stoddart. J. F. Carbohydrate-Mediated Purification of Petrochemicals. J. Am. Chem. Soc. 2015, 137, 5706. (b) Finsy, V.; Verelst, H.; Alaerts, L.; De Vos, D. E.; Jacobs, P. A.; Baron, G. V.; Denayer, J. F. Pore-Filling-Dependent Aelectivity Effects in the Vapor-Phase Separation of Xylene Isomers on the Metal-Organic Framework MIL-47. J. Am. Chem. Soc. 2008, 130, 7110. (c) Alaerts, L.; Maes, M.; Giebeler, L.; Jacobs, P. A.; Martens, J. A.; Denayer, J. F.; Kirschhock, C. E.; De Vos, D. E. Selective Adsorption and Separation of Ortho-Substituted Alkylaromatics with the Microporous Aluminum Terephthalate MIL-53. J. Am. Chem. Soc. 2008, 130, 14170. (d) Nicolau, M. P.; Bárcia, P. S.; Gallegos, J. M.; Silva, J. A.; Rodrigues, A. E.; Chen, B. Single-and Multicomponent Vapor-Phase Adsorption of Xylene Isomers and Ethylbenzene in a Microporous Metal-Organic Framework. J. Phys. Chem. C. 2009, 113, 13173 (e) Yang, C.; Yan, X. Metal-Organic Framework MIL-101 (Cr) for High-Performance Liquid Chromatographic Separation of Substituted Aromatics. Anal. Chem. 2011, 83, 7144. (f) Moreira, M. A.; Santos, M. P.; Silva, C. G.; Loureiro, J. M.; Chang, J. S.; Serre, C.; Ferreira, A. F. P.; Rodrigues, A. E. Adsorption Equilibrium of Xylene Isomers and Ethylbenzene on MIL-125(Ti)_NH2: the Temperature Influence on the para-Selectivity. Adsorption. 2018, 24, 715. (g) Moreira, M. A.; Santos, J. C.; Ferreira, A. F.; Loureiro, J. M.; Ragon, F.; Horcajada, P.; Yot, P. G.; Serre, C.; Rodrigues, A. E. Effect of Ethylbenzene in p-Xylene Selectivity of the Porous Titanium Amino Terephthalate MIL-125(Ti)_NH2. Microporous and Mesoporous Mater. 2012, 158, 229. (h) Moreira, M. A.; Santos, J. C.; Ferreira, A. F.; Loureiro, J. M.; Ragon, F.; Horcajada, P.; Shim, K. E.; Hwang, Y. K.; Lee, U. H.; Chang, J. S.; Serre, C.; Rodrigues, A. E. Reverse Shape Selectivity in the Liquid-Phase Adsorption of Xylene Isomers in Zirconium Terephthalate MOF UiO-66. Langmuir. 2012, 28, 5715. (i) Moreira, M. A.; Santos, J. C.; Ferreira, A. F.; Loureiro, J. M.; Ragon, F.; Horcajada, P.; Yot, P. G.; Serre, C.; Rodrigues, A. E. Toward Understanding the Influence of Ethylbenzene in p-Xylene Selectivity of the Porous Titanium Amino Terephthalate MIL125(Ti): Adsorption Equilibrium and Separation of Xylene Isomers.

Page 8 of 9

Langmuir. 28, 3494. (j) Moreira, M. A.; Santos, J. C.; Ferreira, A. F.; Loureiro, J. M.; Rodrigues, A. E. Influence of the Eluent in the MIL-53 (Al) Selectivity for Xylene Isomers Separation. Ind. Eng. Chem. Res. 2011, 50, 7688. (k) Moreira, M. A.; Santos, J. C.; Ferreira, A. F.; Müller, U.; Trukhan, N.; Loureiro, J. M.; Rodrigues, A. E. Selective Liquid Phase Adsorption and Separation of ortho-Xylene with the Microporous MIL53(Al). Sep. Sci. Technol. 2011, 46, 1995. (22) (a) Liu, L. H.; Yang, C. X.; Yan, X. P. Methacrylate-Bonded Covalent-Organic Framework Monolithic Columns for High Performance Liquid Chromatography. J. Chromatogr. A. 2017, 1479, 137. (b) Zhang, K.; Cai, S. L.; Yan, Y. L.; He, Z. H.; Lin.; H. M.; Huang, X. L.; Zheng, S. H.; Fan, J.; Zhang, W. G. Construction of a Hydrazone-Linked Chiral Covalent Organic Framework-Silica Composite as the Stationary Phase for High Performance Liquid Chromatography. J. Chromatogr. A. 2017, 1519, 100. (23) Yang, J.; Zhang, Z.; Qin, Y. A Molecular Tetrapod for Organic Photovoltaics. ACS Appl. Mater. Interfaces. 2016, 8, 22392. (24) Mastalerz, M.; Hauswald, H. J. S.; Stoll, R. Metal-Assisted Salphen Organic Frameworks (MaSOFs) with High Surface Areas and Narrow Pore-Size Distribution. Chem. Commun. 2012, 48, 130. (25) Peng, Y.; Gong, T.; Zhang, K.; Lin, X.; Liu, Y.; Jiang, J.; Cui, Y. Engineering Chiral Porous Metal-Organic Frameworks for Enantioselective Adsorption and Separation. Nat. Commun. 2014, 5, 4406. (26) (a) Gu, Z. Y.; Yan, X. P. Metal-Organic Framework for HighResolution Gas-Chromatographic Separation of Xylene Isomers and Ethylbenzene. Angew. Chem., Int. Ed. 2010, 49, 1477. (b) Xie, S.; Zhang, Z.; Wang, Z.; Yuan, L. Chiral Metal-Organic Frameworks for HighResolution Gas Chromatographic Separations. J. Am. Chem. Soc. 2011, 133, 11892. c) Nuzhdin, A. L.; Dybtsev, D. N.; Bryliakov, K. P.; Talsi, E. P.; Fedin, V. P. Enantioselective Chromatographic Resolution and OnePot Synthesis of Enantiomerically Pure Sulfoxides over a Homochiral ZnOrganic Framework. J. Am. Chem. Soc. 2007, 129, 12958.


Page 9 of 9 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


Topic of Content


Microporous 3D Covalent Organic Frameworks for Liquid

Recommend Documents