Postsynthetic Lithium Modification of Covalent-Organic Polymers for

Feb 13, 2012 - Zhonghua Xiang , Lin Zhu , Lei Qi , Lu Yan , Yuhua Xue , Dan Wang , Jian-Feng Chen , and Liming Dai. Chemistry of Materials 2016 28 (23...
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Postsynthetic Lithium Modification of Covalent-Organic Polymers for Enhancing Hydrogen and Carbon Dioxide Storage Zhonghua Xiang,† Dapeng Cao,*,† Wenchuan Wang,† Wantai Yang,‡ Bingyong Han,‡ and Jianmin Lu‡ †

State Key Lab of Organic−Inorganic Composites and ‡College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, P.R. China. S Supporting Information *

ABSTRACT: Recent experiment and simulation show that introduction of lithium in the frameworks can enhance the gasstorage capacities of framework materials. Here a covalentorganic polymer-1 (COP-1) has been synthesized through the self-polymerization of monomer 1,3,5-tris((4-bromophenyl)ethynyl) benzene (TBEB) by the nickel(0)-catalyzed Yamomoto reaction. To enhance gas adsorption properties of the COP-1 material, we have proposed a novel lithium-decorating approach in which the alkynyl functionalities in COP-1 are postsynthetically converted to lithium carboxylate groups with the aid of dry ultrapure CO2. In particular, the H2 uptake of lithium-modified COP material is 1.67 wt % at T = 77 K and ∼1 bar, which is increased by ∼70.4%, compared with the unmodified compounds. Besides, the enhancement effects of lithium modification on CO2 and CH4 adsorption have also been observed. It is expected that this approach proposed here would provide a new direction for lithium modification of MOFs and COFs for clean energy and environmental applications.

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INTRODUCTION Targeted synthesis is one of the most important technologies in materials science. Recently, metal−organic frameworks (MOFs, like MOF-210 and NU-100)1−9 and crystalline covalent-organic frameworks (COFs, like COF-105, 108)10−12 have been rapidly developed as gas storage and separation candidates for clean energy applications due to high specific surface area (SSA) along with functionalized pore walls. To obtain high gas storage capacities, (a) stable topology, (b) large SSA, (c) appropriate pore sizes, (d) special functional groups in frameworks, and (e) “open” metal sites (accessible unsaturated metal center or introduction of alkali elements into the frameworks, for example) should be considered on designing new materials for targeted synthesis. Both experiment and simulation show that introduction of lithium in the frameworks can enhance the gas storage capacities of MOFs and COFs.13−26 In previous lithium doping method in MOFs, the introduced lithium cations seem to localize around carboxylates rather than the reduced portions of the struts,13−15 which results in shield of many introduced lithium cations from direct interaction with targeted gas and reduces lithium cation effects. Himsl et al.16 and Mulfort et al.27 sought an alternative approach based on the conversion of pendant alcohols to lithium alkoxides to avoid catenation and anchor ions far from carboxylates or nodes. Different from the method mentioned above, herein, we propose a new lithium-modification approach based on the conversion of alkynyl functional group to lithium carboxylate group to decorate the material postsynthetically. Most of MOFs and COFs possess low hydrothermal stability, which limits their application in industries. Developing a moisture-resistant porous adsorbent is considered to be an © 2012 American Chemical Society

urgent alternative approach to meet the requirement in industry applications. Amorphous microporous organic polymers feature relatively stable covalent C−C, C−H, and C−N bonds, which contribute to its exceptional hydrothermal stability.28−31 Although these organic polymers usually do not possess the long-range crystallographic order like MOF and crystalline COF, these materials also exhibit tunable pore size and surface area by varying the length of the rigid organic linkers. Among them, conjugated microporous polymers (CMPs) were widely studied due to the fact that they are more thermally robust and more chemically stable than most MOFs. CMPs were usually obtained through copolymerization of terminal alkynes with aryl halide using Pd(0)/Cu(I)-catalyzed Sonogashira−Hagihara cross-coupling chemistry. The most recent research shows that the Yamamoto-type Ullmann cross-coupling reaction is more effective to produce high-performance porous frameworks.32,33 Ben et al. synthesized a porous aromatic framework (PAF-1) through self-polymerization of terakis(4-bromophenyl) methane with the nickel-catalyzed Yamamoto-type Ullmann crosscoupling reaction.34 PAF-1 has a Langmuir SSA of 7100 m2 g−1 and high storage capacity of CO2 (1300 mg g−1 at 298K, 40 bar). Besides, Lu et al. also used this approach to obtain the PPN-3 with Brunauer−Emmett−Teller (BET) SSA of 2840 m2 g−1. As is well-known, CC groups possess strong electron that could anchor lithium ions in the frameworks.17 Here we therefore synthesized an exceptionally high hydrothermal stability covalent-organic polymers (COP-1) through the Received: January 5, 2012 Revised: February 5, 2012 Published: February 13, 2012 5974

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Preparation of Lithium Naphthalenide. An equimolar amount of clean lithium was added to a 0.1 M solution of naphthalene in purified THF with vigorous stirring for 2 h. The concentration of the resulting dark-green solution was calibrated by the standard concentration of HCl. Synthesis of Li@COP-1. A precise quantity of prepared lithium naphthalenide was transferred by syringing 30 mL of THF with 1/3 equiv of evacuated COP-1 in dry flask. The mixture was stirred for 3 min, subsequently injected with dry ultrapure CO2 (99.994% purity; Beijing AP Beifen Gases Industry) for 30 min with a simultaneous stirring, and kept stirring for overnight. The resulting mixture was isolated by filtration and rinsing with THF and then immersed in THF for 1 day to remove the weakly adsorbed naphthalene. It was dried in vacuo at 100 °C to yield the product. ICP analysis shows the content of Li is 32 250 μg g−1 (equal to the 3.2 wt % Li content in Li@COP-1). Elemental analysis calcd (%) for C33H18O6Li3: C, 74.55; H, 3.42; O, 18.07. Found: C, 70.23; H, 2.91; O, 17.42. Experimental Characterizations. Powder X-ray diffraction (PXRD) measurements were performed with a D/MAX 2000 X-ray diffactometer with Cu Kα line (λ = 1.54178 Å) as the incident beam. Thermogravimetric analysis (TGA) data were obtained on an STA449C (NETZSCH) instrument, with a heating rate of 2 °C min−1 under flowing Ar. FT-IR spectroscopy was performed on an AC-80 MHz (Bruker) instrument with the wave range of 4000−400 cm−1. Scanning electron microscopy (SEM) images were obtained on a Cambridge S250MK3 SEM instrument. Elemental analysis (C and H) was performed on a Thermo Fisher Scientific elemental analyzer (Ea1112, Beijing Research Institute of Chemical Industry, SINOPEC). Inductively coupled plasma (ICP) spectroscopy was carried out on an ULTIMA ICP spectrometer (JY, Beijing Normal University). Solid-state NMR spectra were measured on a Bruker AV300 spectrometer operating at 75.5 MHz for 13C and 300.1 MHz for 1H. The 13C CP/MAS (crosspolarization with magic angle spinning) experiments were carried out at MAS rates of 11.0 kHz using densely packed powders of the evacuated COP-1 and Li@COP-1 in 4 mm ZrO2 rotors. The 1H π/2 pulse was 2.4 μs, and two-pulse phase modulation (TPPM) decoupling was used during the acquisition. The spectra were measured using a contact time of 3.5 ms and a relaxation delay of 5.0 s. XPS data were obtained on a ThermoFisher ESCALAB 250 X-ray photoelectron spectroscopy (XPS) equipped with twin anode Al Kα X-ray source. Because of the insulating nature of the samples, the charge shift was observed. The spectra were corrected based on C1s/285.0 eV without neutralization. Adsorption Measurements. N2 Adsorption. N2 adsorption/desorption isotherms were measured at 77 K with a Micromeritics ASAP 2020. The samples of 150 mg were degassed at 200 °C for 24 h. Pore size distribution data were calculated from the N2 sorption isotherms based on the DFT model in the Micromeritics ASAP 2020 software package (assuming slit pore geometry). Ultra-high-purity grade He (99.999%) and N2 (99.9992%) were used for all adsorption measurements. H2 Adsorption Analysis. H2 adsorption isotherms were measured at 77 and 87 K using a Micromeritics ASAP 2020 volumetric adsorption analyzer. Ultrahigh-purity grade He (99.999%) and H2 (99.999%) were used for all adsorption measurements. IGA-003 Gravimetric CO2 and CH4 Adsorption Measurements. The CO2 and CH4 isotherms at 298 K were measured

monomer 1,3,5-tris((4-romophenyl)ethynyl) benzene (TBEB) by using the Yamamoto-type Ullmann cross-coupling reaction, as shown in Figure 1a and Figure S1 in the Supporting

Figure 1. (a) Schematic representation of synthesis of COP-1 through monomers TBEB (1,3,5-tris((4-bromophenyl)ethynyl) benzene) using nickel-catalyzed Yamamoto-type Ullmann cross-coupling reaction. (b) 13C CP/MAS spectra of the COP-1. Asterisks denote spinning sidebands, and peak assignments for NMR of COP-1 were inserted.

Information. COP-1 is an orange powder that is insoluble in the usual solvents and resistant against acids and bases.

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EXPERIMENTS AND METHODS

All reagents, unless otherwise stated, were obtained from commercial sources (Alfa Aesar, Sigma Aldrich) and were used without further purification. Tetrahydrofuran (THF) was purified by distillation with sodium naphthalene.23 The sodium and lithium wires were immersed in THF to remove excess mineral oil, and any dark oxide on the surface was removed to reveal the shiny metallic surface prior to using. All procedures for preparing lithium naphthalenide and the procedures for lithium modification were performed under an argon atmosphere in a glovebox. Synthesis of COP-1. 1,5-Cyclooctadiene (cod, 0.50 mL, 3.96 mmol, dried over CaH2) was added to a solution of bis(1,5-cyclooctadiene)nickel(0) ([Ni(cod)2], 1.125 g, 4.09 mmol) and 2,2′-bipyridyl (0.640 g, 4.09 mmol) in dry dimethylformamide (DMF) (65 mL), and the mixture was stirred until completely dissolved. 1,3,5-Tris((4-bromophenyl)ethynyl) benzene (0.484 g, 0.785 mmol) was subsequently added to the resulting purple solution. The reaction vessel was heated to 105 °C overnight under a nitrogen atmosphere. After cooling to room temperature, concentrated HCl was added to the deep-purple suspension. After filtration, the residue was washed by CHCl3 (5 × 15 mL), THF (5 × 15 mL), and H2O (5 × 15 mL), respectively, and dried in vacuo to give COP-1 as an orange powder (258 mg, 78% yield). Elemental analysis calcd (%) for C30H15: C, 95.97; H, 4.03 C. Found: C, 88.86; H, 5.36. Br content: 542 μg g−1. Ni content: 5300 μg g−1. 5975

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Figure 2. FTIR spectra of the TBEB (red) and the COP-1 (black) from (a) 400−4000 and (b) 400−1000 cm−1. The characteristic absorption bands for Carbon−Bromine are highlighted via green region (see the right panel), clearly showing the lack of bromine in the COP-1 and indicating the formation of the polymeric COP-1 structure.

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RESULTS AND DISCUSSION The success of the phenyl−phenyl coupling can be proved by the FTIR and solid-state 13C/MAS NMR measurement. Figure 2 shows the disappearance of C−Br bonds in COP-1. Moreover, the residual Br content of COP-1 is only 542 μg g−1 (equal to 0.14% of the Br in TBEB), which also confirms the high efficiency of the Yamomoto reaction. It is worth mentioning that the characteristic peak of νCC (∼2200 cm−1) is invisible in FTIR spectra of COP-1 (Figure 2), indicating that COP-1 material possesses centrosymmetric structure. The signal assignments of 13C/MAS spectra for COP-1 are shown in Figure 1b. The signals at approximately δ 90 and 129 are the characteristic peak of TBEB, suggesting the presence of carbon from CC and phenyl group. The phenyl−phenyl coupling between the monomers can be reconfirmed by the peak at δ 140.5 with the combination of the above FTIR spectra. SEM images (Figure S2 in the Supporting Information) reveal that COP-1 exhibits ball-shaped morphology, which is different from the messy rough fiber textures of CMP-2.36 N2 adsorption measurement in COP-1 (Figure 3) show that the desorption

by using a Hiden Isochema intelligent gravimetric analyzer (IGA-003). In this instrument, an ultrasensitive microbalance of resolution 0.2 μg is mounted in a thermostatted heatsink with high-precision temperature control. The IGA-003 system can operate up to the pressure of 20 bar, and it is equipped with a high vacuum turbomolecular pump with a dry (membrane) backing pump to ensure minimal contamination of the sample and microbalance chamber. Prior to the measurement, ∼30 mg of samples was loaded into the IGA-003 and degassed at ∼10−3 Pa at 200 °C for 24 h. The measurements were then carried out under water bath. The buoyanas corrections were carried out following our previous reports.6,8 The CO2 and CH4 used for the experiment were of 99.994% purity (Beijing AP Beifen Gases Industry) and were delivered via a T-purge regulator to minimize the risk of gas supply contamination. Isosteric Heat of Adsorption (Qst) Calculations. The virial equation of the form given in eq 135 was employed to calculate the enthalpies of adsorption for H2 and CO2 on COP1 and Li@COP-1. m

ln P = ln N + 1/T

∑ ai N i=0

i

n

+

∑ biN i i=0

(1)

where P is the pressure expressed in torr, N is the amount adsorbed in millimoles per gram, T is the temperature in kelvin, ai and bi are virial coefficients, and m and n represent the number of coefficients required to describe the isotherms adequately. The equation was fitted by using the least-squares method; m and n were gradually increased until the contribution of a and b coefficients toward the overall fitting was statistically trivial, as determined by the t test. The values of the virial coefficients a0...am were then used to calculate the isosteric heat of adsorption by the following expression: m

Q st = −R

Figure 3. N2 adsorption isotherms in COP-1 (red) and Li@COP-1 (black) at 77 K. Solid and open symbols represent adsorption and desorption, respectively.

∑ ai N i i=0

(2)

To determine the accuracy of fitting, we define the relative squared 2-norm of the residual Res as the criterion R es =

curve has a remarkable hysteresis loop, suggesting that COP-1 not only contains mesopores but also includes micropores (Figure S3 in the Supporting Information). The ideal 31 Å perforations within COP-1 (Figure 1a) result in the mesopores in COP-1. The micropores in COP-1 might arise from the framework interpenetration during kinetics-controlled irreversible coupling process. The BET SSA and pore volume of COP-1 are of 827 m2 g−1 and 0.71 cm3 g−1, which is larger than

∑ix= 1 |fi − Ei|2 (∑ix= 1 Ei2)1/2

(3)

where f is the fitted pressure, E is the measured pressure, and x is the number of the measured pressure. 5976

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the results of CMP-2 (BET SSA: 624 m2 g−1 and pore volume: 0.53 cm3 g−1).36,37 The PXRD was performed to investigate the crystallinity of COP-1, indicating its amorphous texture (Figure S4 in the Supporting Information). The amorphous texture could be formed by the distortion and interpenetration of the phenyl rings.38 The TGA (Figure S5 in the Supporting Information) shows that COP-1 can keep its thermal stability up to 350 °C. To introduce lithium into the structure, we propose a scheme for converting alkynyl groups to lithium carboxylate group, as shown in the scheme S1 in the Supporting Information. The alkyne bond is a weak link in the COP-1’s conjugated system, which would tend to provide active sites to combine with lithium ions. Here we used lithium naphthalenide (Li+C10H8−), which makes the electron transfer possible from the naphthalenide to alkynyl functionalities owing to the strong nucleophilicity of lithium naphthalenide. Alkynyl functional groups first react with lithium naphthalenide (Li+C10H8−) in THF and form the active −C−Li group in the step 2 in the Scheme S1 in the Supporting Information. This chemical process can be completed because the electron transfer from the naphthalenide radical anion to the conjugated struts can happen easily, especially for the large conjugated system in COP-1 materials in this work, the naphthalenide radical anions form naphthalene after loss of electron, which could be dissolved in THF and easily separated by filtration, while active sites (CC bonds) are then converted into the −C−Li groups after receiving the electrons transferred from the naphthalenide. This mechanism is similar to the case of styrene polymerization using alkali metal naphthalene complex as initiator.39 Because −C−Li groups in this system are unstable and easy to react with hydrate or oxide. We, here, used dry ultrapure CO2 to react with −C−Li groups to convert the active −C−Li group into more stable −COOLi groups.40 After CO2 was injected into the complex in the step 2 in the Scheme S1, the color of solution is changed from wine to dark orange (Figure S6 in the Supporting Information). In particular, all procedures in Scheme S1 in the Supporting Information were carried out in a strict inert atmosphere, and the dry ultrapure CO2 was injected as quickly as possible after adding Li+C10H8− complex to avoid −C−Li groups reacting with peroxide spontaneously produced from the solvent THF. This hypothesis is proved by the FTIR, 13C CP/MAS, and XPS spectra. For simplification, we marked the lithiummodified COP-1 as Li@COP-1. The peaks at 1326 and 1632 cm−1 in the FTIR spectra of Li@COP-1 can be assigned as the characteristic peaks of νCC and carboxyl groups, respectively (Figure 4a and Figure S7 in the Supporting Information). Additionally, the 13C CP/MAS spectra of Li@COP-1 (Figure 4b) show the disappearance of the characteristic peak of CC groups at δ 90.3 and the existence of the carbonate characteristic peak at 171.2 ppm, compared with the spectra of COP-1. These results indicate that the CC groups in COP-1 were transferred into CC groups accompanying with the formation of carboxylate after introducing lithium. Furthermore, the XPS spectra also suggest the formation of carbonate in the Li@COP-1 (Figure 5a and Figure S8 in the Supporting Information). The peak at 290.4 eV of Li@COP-1 suggests the existence of carbonate, which reconfirms the formation of −COOLi groups in our lithium modification approach.41 The peak at 288.2 eV of COP-1 can be assigned to the guest DMF in COP-1. Because the as-synthesized COP-1 sample has not been evacuated prior to XPS measurement, the

Figure 4. (a) FTIR spectra of the COP-1 (red) and the Li@COP-1 (black) from 900 to 1800 cm−1. (b) 13C CP/MAS spectra of the COP1 and Li@COP-1. Asterisks denote spinning sidebands and peak assignments for NMR of Li@COP-1 were inserted.

sample may contain same occluded guests in pores. The peak at 55.7 eV in the Li@COP implies that Li is in an ionic state with one positive charge per Li atom (Figure 5b). Although it is very difficult to characterize the exact position of the Li centers owing to the inherent technical difficulty of obtaining single crystal of lithium-decorating materials, we believed that the alkyne bonds may have been converted into −COOLi groups following the exploited scheme S1 in the Supporting Information by analyzing those results above. The effect of lithium decoration on porous properties of COP-1 was studied by N2 adsorption isotherms at 77 K (Figure 3). The BET SSA of lithium-modified materials is only about two-thirds of unmodified materials (827 for COP-1 vs 573 m2 g−1 for Li@COP-1). Furthermore, the pore volume of COP-1 drops from 0.71 to 0.37 cm3 g−1 after lithium modification. The comparison of porosity properties between COP-1 and Li@ COP-1 was listed in Table 1. The pore size of COP-1 has been slightly reduced after introducing lithium carboxylate groups into COP-1 (Figures S9 and S10 in the Supporting Information), owing to the formation of longer lithium carboxylate groups in Li@COP-1, compared with CC groups. To investigate the effects of lithium carboxylate groups on gas adsorption, we measured H2 uptake at 77 K and CO2 and CH4 uptake at 298 K in COP-1 and Li@COP-1. All of the H2, CO2, and CH4 isotherms show good reversibility without hysteresis between adsorption and desorption, suggesting that H2, CO2, and CH4 are reversibly physisorbed in the lithium carboxylate system (Figures 6 and 7), like many other cases.14,15,23,42 As shown in Figure 6, at 77 K and 1.13 bar, 5977

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Figure 5. (a) X-ray photoelectron spectroscopy (XPS) spectra of assynthesized COP-1 (red) and Li@COP-1 (black). The peak at 290.4 eV of Li@COP-1 suggests the existence of carbonate, which reconfirm the formation of −COOLi groups in our lithium modification approach.41 The peak at 288.2 eV of COP-1 can be assigned to the guest DMF in COP-1. Because the as-synthesized COP-1 sample has not been evacuated prior to XPS measurement, the sample may contain same occluded guests in pores. (b) Li1s XPS spectra of the Li@COP-1. The peak at 55.7 eV implies that lithium is in an ionic state with one positive charge per Li atom.

Figure 6. (a) H2 uptake and (b) isosteric heat of adsorption curves for H2 adsorption in COP-1 (red) and Li@COP-1 (black) at 77 K. Solid and open symbols represent adsorption and desorption, respectively.

conditions. The enhancement of H2 uptake by the Li+ can be also explained by the isosteric heat of H2 adsorption at near zero loading (7.56 kJ mol−1 for Li@COP-1, 6.70 kJ mol−1 for unmodified COP-1; see Figure 6b). Similarly, the enhancement effects of lithium modification on CO2 and CH4 uptakes have also been observed, and the corresponding isotherms are shown in Figure 7a,b. Obviously, the fact that lithium modification can improve the gas adsorption capacity of porous materials is consistent with the previous results.23 In particular, at 18 bar and 298 K, the CO2 uptake in Li@COP-1 is increased from 194 to 220 mg g−1, whereas CH4 uptake is enhanced from 29 to 39 mg g−1 compared with unmodified COP-1 (Figure 7a,b). Likewise, the Qst for CO2 at near zero loading in Li@COP-1 is also increased from 30.71 to 33.03 kJ mol−1 (Figure 7c), which is similar to the enhancement of CO2 isosteric heat by incorporating carboxylic group in CMP.50

Table 1. Summary of Porosity and Adsorption Properties of COP-1 and Li@COP-1 materials

COP-1

Li@COP-1

Li content (wt %) BET SSA (m2 g−1)a Langmuir SSAs (m2 g−1) pore volume (cm3 g−1)b H2 uptake (wt %)c Qst for H2 (kJ mol−1)d CO2 uptake (mg g−1)e Qst for CO2 (kJ mol−1)d CH4 uptake (mg g−1)e

0 827 1259 0.71 0.98 6.70 194 30.71 29

3.2 573 866 0.37 1.67 7.56 220 33.03 39

a

BET SSA calculated in the region of P/P0 = 0.05 to 0.3. bDetermined at P/P0 = 0.9997. cHydrogen uptake at 77 K and 1.13 bar. dIsosteric heat at close to the zero loading. eUptake at 298 K and 18 bar.

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the H2 uptake in COP-1 is 0.98 wt %, which is larger than the uptakes of analogues: polyanilines (0.38, 0.85 wt %),43 polypyrole (0.63 wt %),44 CMP-2 (0.91 wt %),37 CMP-3 (0.85 wt %),37 CMP-5 (0.59 wt %),37 EOF-1 (0.94 wt %),45 P1 (0.95 wt %),46 PIM-1 (0.95 wt %),47 PSN-1 (0.89 wt %),48 COF-5 (0.89 wt %),10 COF-8 (0.86 wt %),10 COF-10 (0.84 wt %),10 and so on and is comparable to CMP-1 (1.01 wt %)37 under equivalent conditions. After introducing the lithium carboxylate, the H2 uptake in Li@COP-1 is improved to 1.67 wt % with 70.4% increment. The H2 uptake in Li@COP-1 (1.67 wt % at 77 K and ∼1 bar) overpasses those uptakes in COFs (1.22 wt % for COF-11 Å,49 1.23 wt % for COF-14 Å,49 1.40 wt % for COF-16 Å,49 1.55 wt % for COF-18 Å,49 1.18 wt % for COF-102,10 1.25 wt % for COF-10310) under similar

CONCLUSIONS

In summary, a porous material COP-1 has been synthesized by the nickel-catalyzed Yamomoto reaction, and a new postsynthetic lithium-modification approach, in which the alkynyl groups were converted to lithium carboxylate groups with the aid of dry ultrapure CO2, has been proposed in this work. Furthermore, experimental measurements indicate that lithiumdecoration definitely improves H2, CO2, and CH4 uptakes of the synthesized materials. In particular, at T = 77 K and ∼1 bar, the H2 uptake of lithium-modified COP material is 1.67 wt %, which is increased by ∼70.4% compared with the unmodified compounds. It is expected that this approach would provide a 5978

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Figure 7. (a) CO2, (b) CH4 uptake, and (c) isosteric heat of adsorption curves for CO2 adsorption in COP-1 (red) and Li@COP-1 (black) at T = 298 K. Solid and open symbols represent adsorption and desorption, respectively. (4) Caskey, S. R.; Wong-Foy, A. G.; Matzger, A. J. Am. Chem. Soc. 2008, 130, 10870. (5) Sumida, K.; Brown, C. M.; Herm, Z. R.; Chavan, S.; Bordiga, S.; Long, J. R. Chem. Commun. 2011, 47, 1157. (6) Xiang, Z. H.; Lan, J. H.; Cao, D. P.; Shao, X. H.; Wang, W. C.; Broom, D. P. J. Phys. Chem. C. 2009, 113, 15106. (7) Xiang, Z. H.; Cao, D. P.; Lan, J. H.; Wang, W. C.; Broom, D. P. Energy Environ. Sci. 2010, 3, 1469. (8) Xiang, Z. H.; Cao, D. P.; Shao, X. H.; Wang, W. C.; Zhang, J. W.; Wu, W. Z. Chem. Eng. Sci. 2010, 65, 3140. (9) Xiang, Z. H.; Peng, X.; Cheng, X.; Li, X. J.; Cao, D. P. J. Phys. Chem. C. 2011, 115, 19864. (10) Furukawa, H.; Yaghi, O. M. J. Am. Chem. Soc. 2009, 131, 8875. (11) Cote, A. P.; Benin, A. I.; Ockwig, N. W.; O’Keeffe, M.; Matzger, A. J.; Yaghi, O. M. Science 2005, 310, 1166. (12) EI-Kaderi, H. M.; Hunt, J. R.; Mendoza-Cortes, J. L.; Cote, A. P.; Taylor, R. E.; O’Keeffe, M.; Yaghi, O. M. Science 2007, 316, 268. (13) Yang, S. H.; Lin, X.; Blake, A. J.; Walker, G. S.; Hubberstey, P.; Champness, N. R.; Schroder, M. Nat. Chem. 2009, 1, 487. (14) Mulfort, K. L.; Hupp, J. T. J. Am. Chem. Soc. 2007, 129, 9604. (15) Mulfort, K. L.; Wilson, T. M.; Wasielewski, M. R.; Hupp, J. T. Langmuir 2009, 25, 503. (16) Himsl, D.; Wallacher, D.; Hartmann, M. Angew. Chem., Int. Ed. 2009, 48, 4639. (17) Li, A.; Lu, R. F.; Wang, Y.; Wang, X.; Han, K. L.; Deng, W. Q. Angew. Chem., Int. Ed. 2010, 49, 3330. (18) Cao, D. P.; Lan, J. H.; Wang, W. C.; Smit, B. Angew. Chem., Int. Ed. 2009, 48, 4730. (19) Lan, J. H.; Cao, D. P.; Wang, W. C.; Ben, T.; Zhu, G. S. J. Phys. Chem. Lett. 2010, 1, 978. (20) Han, S. S.; Goddard, W. A. III. J. Am. Chem. Soc. 2007, 129, 8422. (21) Han, S. S.; Goddard, W. A. III. J. Phys. Chem. C. 2008, 112, 13431. (22) Lan, J. H.; Cao, D. P.; Wang, W. C. Langmuir 2009, 26, 220. (23) Xiang, Z. H.; Hu, Z.; Cao, D. P.; Yang, W. T.; Lu, J. M.; Han, B. Y.; Wang, W. C. Angew. Chem., Int. Ed. 2011, 50, 491.

new direction for lithium modification of MOFs and COFs for clean energy and environmental applications.

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ASSOCIATED CONTENT

S Supporting Information *

Exploited schematic representation of the lithium introduction; FTIR spectra; SEM images; PXRD data; TG analysis; pore size distributions; XPS spectra; 87K H2 uptake; and virial equation fits for calculation H2 and CO2 adsorption isosteric heat. This material is available free of charge via the Internet at http:// pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work is supported by the Huo Yingdong Foundation (121070), National 973 Program (2011CB706900), NSF of China (21121064), Doctoral Program from MOE (20100010110001), and Chemical Grid Program from BUCT.

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REFERENCES

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dx.doi.org/10.1021/jp300137e | J. Phys. Chem. C 2012, 116, 5974−5980