Supporting Information
Cooperative Template-Directed Assembly of Mesoporous Metal-Organic Frameworks Lin-Bing Sun, Jian-Rong Li, Jinhee Park, and Hong-Cai Zhou* Department of Chemistry, Texas A&M University, P.O. Box 30012, College Station, Texas 77842-3012 * Corresponding author. Email:
[email protected] S1
Experimental Details Chemicals. Copper nitrate hemipentahydrate (> 98%), benzene-1,3,5-tricarboxylic acid (H3BTC, > 98%), citric acid (CA, > 99%), and ammonium nitrate (> 95%) were purchased from Alfa Aesar Chemicals. Cetyltrimethylammonium bromide (CTAB, > 99%) was purchased from Acros. Ethanol and N,N-dimethylformamide (DMF) were obtained from Koptech and Mallinckrodt Chemicals, respectively. All starting materials were used without further purification. Materials Synthesis. In a typical synthesis, 0.232 g (1.0 mmol) of copper nitrate hemipentahydrate, 0.116 g (0.56 mmol) of H3BTC were dissolved in 10 mL of DMF. After a given amount of surfactant CTAB (0-0.6 g) and chelating agent CA (0-0.1 g) were added, the mixture was sonicated for 10 min to form a homogeneous solution. The solution was then heated to 75 oC and held at this temperature for 24 h under static conditions. The resulting solid was washed with DMF to remove unreacted starting materials. Finally, the as-synthesized sample was subjected to an ion-exchange process at 60 oC for 24 h with 1 M ammonium nitrate ethanol/water solution (volume ratio of 1:2) to remove the template, followed by washing with an ethanol/water mixture (volume ratio of 1:2). Mesostructured MOFs were obtained and denoted as mesoMOF(SmCn), where m and n represent the amount of surfactant and chelating agent in gram, respectively. Instrumentation. X-ray diffraction (XRD) patterns of the materials were recorded using a BRUKER D8-Focus Bragg-Brentano X-ray Powder Diffractometer equipped with a Cu sealed tube (λ = 1.54178) at 40 kV and 40 mA. Transmission electron microscopy (TEM) analysis were performed on a FEI Tecnai G2-F20 transmission electron microscope. Thermogravimetry analysis (TGA) was conducted on a TGA-50 (SHIMADZU) thermogravimetric analyzer. About 10 mg of sample was heated from room temperature to 500 °C in a N2 flow (25 mL·g−1). Fourier transform infrared (IR) measurements were performed on a SHIMADZU IRAffinity-1 spectrometer. The spectra were collected with a 2 cm−1 resolution. N2 adsorption-desorption isotherms were measured using a Micrometritics ASAP2020 system at −196 oC. The samples were degassed at 180 oC for 12 h prior to analysis. The Langmuir surface area was estimated using the adsorption data accoding to the Langmuir equation.1 The S2
Brunauer-Emmett-Teller (BET) surface area was calculated using adsorption data in a relative pressure ranging from 0.1 to 0.3. The total pore volume was determined from the amount adsorbed at a relative pressure of about 0.95. The mesopore pore volume was obtained from the Barrett-Joyner-Halenda (BJH) cumulative specific adsorption volume according to the literature.2 The mesopore size distributions were calculated using the BJH method.
Discussion on CA-Derived Crystal Phase and Synthetic Mechanism As described in manuscript, one CA molecule can interact with two CTAB molecules. Hence, the optimum CTAB/CA molar ratio is about 2. In the presence of 0.08 and 0.10 g CA, the CTAB/CA ratio is 1.4 and 1.2, respectively, and is obviously lower than 2. As a results, their XRD patterns show several new diffraction lines with the strongest one at 2 of 10.1o besides those from Cu3(BTC)2 (Figure S1). Also, their IR spectra display new bands with a typical one at 1567 cm−1 (Figure S3). Because both XRD patterns and IR spectra are apparently different from those of CA itself (Figures S7 and S8), the residue of CA in the samples can be excluded. That means, an excess of CA leads to the formation a new phase (denote as 1). This phase cannot be identified, owing to the difficulty in obtaining a pure crystal. The reaction of Cu(NO3)2 with CA, under the similar conditions as Cu3(BTC)2 synthesis except that BTC was replaced by CA, yielded a phase (denote as 2) with a strongest diffraction line at 2 of 8.5o (Figures S9), which is different from phase 1. Moreover, this sample shows a very poor porosity with a BET surface area of 16 m2·g−1 and a pore volume of 0.017 cm3·g−1 (Figure S10). Thus, phase 1 should not be a mixture of MOFs constructed from BTC and CA. It is interesting to note that a pure Cu3(BTC)2 phase can be obtained even if 0.05 g CA was introduced to the synthetic system of Cu3(BTC)2, in the absence of CTAB (Figure S2). This reveals the preferential coordination of copper ions with BTC rather than CA. Nevertheless, the introduction of small amount of CTAB (in the case of CTAB/CA molar ratios lower than 2) results in the formation of phase 1. This indicates that the existence of CTAB plays an important role in the produce of phase 1. The effect of bromine ion was evaluated by using CuBr2 with the same amount of bromine instead of CTAB. As presented in Figure S11, pure Cu3(BTC)2 phase was obtained under the same conditions as the synthesis S3
of mesoMOF(S0.05C0.05). That means, bromine does not favor the generation of phase 1. In other words, the micelles derived from cetyltrimethylammonium ions (CTA+), together with CA, are responsible for the generation of phase 1. It is possible that micelles produce some available microspace, so that CA has the opportunity to react with copper ions. It is worthy of noting that further increasing CTAB dosage, the amount of phase 1 decreases gradually and disappears finally. This gives evidence of the strong interaction between CTAB and CA, which decline the interaction of CA with copper ions, and subsequently pure Cu3(BTC)2 phase is created. Further evidence can be provided by the results shown in Figure S9. The reaction of Cu(NO3)2 with CA leads to the formation of phase 2 in the absence of CTAB. However, the diffraction lines were weakened after the introduction of 0.05 g CTAB, and no diffraction can be observed in the presence of 0.2 g CTAB. On the basis of the description above, it can be tentatively concluded that the formation of phase 1 is derived from CA, while the presence of CTAB is also necessary. The molar ratio of CTAB-to-CA affects the content of phase 1 in the final samples. A low CTAB/CA ratio favors the generation of phase 1, while a high CTAB/CA ratio is beneficial to the formation of pure Cu3(BTC)2 phase. Aiming to obtain mesostructured MOFs with pure Cu3(BTC)2 phase, a CTAB/CA molar ratio higher than 2 is suggested, from the standpoint of avoiding an excess of CA. It is worth noting that Qiu et al. reported the fabrication of mesoporous MOFs in the presence of CTAB individually.2 In the present study, we employed DMF as solvent and conducted the reaction at 75 oC. The mesoporous MOFs reported by Qiu et al. were synthesized in ethanol/H2O mixed solvents at 120 oC. It is known that DMF can favor the deprotonation of carboxylic acid; in the meanwhile, dimethylammonium
cations
are
produced.
These
cations
may
compete
with
surfactants
(cetyltrimethylammonium cations from CTAB) to interact with MOF precursors. As a result, the structure-directing role of surfactants is seriously degraded, which will certainly affect the formation of mesopores. However, there is no competition existed in the ethanol/H2O synthetic system, so surfactants can interact with MOF precursors despite that the direct interaction is relatively weak. Therefore, different solvents should be responsible for the difference between Qiu’s results and ours. Due to the S4
strong interaction between template and MOF precursors established by chelating agent, our strategy might be applicable in synthetic systems with different solvents.
References (1) Yuan, D.; Lu, W.; Zhao, D.; Zhou, H.-C. Adv. Mater. 2011, 23, 3723. (2) Qiu, L.-G.; Xu, T.; Li, Z.-Q.; Wang, W.; Wu, Y.; Jiang, X.; Tian, X.-Y.; Zhang, L.-D. Angew. Chem. Int. Ed. 2008, 47, 9487; Complete reference 2g: Horcajada, P.; Chalati, T.; Serre, C.; Gillet, B.; Sebrie, C.; Baati, T.; Eubank, J. F.; Heurtaux, D.; Clayette, P.; Kreuz, C.; Chang, J.-S.; Hwang, Y. K.; Marsaud, V.; Bories, P.-N.; Cynober, L.; Gil, S.; Ferey, G.; Couvreur, P.; Gref, R. Nat. Mater. 2010, 9, 172;
S5
Table S1. Structural Properties of mesoMOFs Synthesized with Different Amount of CTAB and CA Sample a
a
CTAB/CA
BET Surface
Langmuir
Pore
Mesopore
Mesopore
molar ratio
area
surface area
volume
diameter
volume
(m2·g−1)
(m2·g−1)
(cm3·g−1)
(nm)
(cm3·g−1)
mesoMOF(S0C0)
−
1261
1957
0.696
−
−
mesoMOF(S0.2C0)
−
1181
1831
0.650
−
−
mesoMOF(S0.2C0.01)
11.6
1183
1848
0.657
4.7
0.044
mesoMOF(S0.2C0.02)
5.8
1112
1744
0.620
4.7
0.052
mesoMOF(S0.2C0.05)
2.3
1162
1915
0.694
19.6
0.103
mesoMOF(S0.2C0.08)
1.4
940
1569
0.566
19.6
0.090
mesoMOF(S0.2C0.10)
1.2
783
1297
0.465
19.6
0.069
mesoMOF(S0C0.05)
0
1260
1954
0.696
−
−
mesoMOF(S0.05C0.05)
0.6
1084
1754
0.628
16.7
0.055
mesoMOF(S0.1C0.05)
1.1
1202
1877
0.672
14.5
0.060
mesoMOF(S0.4C0.05)
4.6
1273
1966
0.701
19.6
0.071
mesoMOF(S0.6C0.05)
6.9
1229
1940
0.692
17.6
0.056
mesoMOF(SmCn) denotes mesostructured metal-organic frameworks, where m and n represent the amount of
surfactant and chelating agent in gram, respectively.
S6
CTAB = 0.2g
CA
Intensity (a.u.)
0 0.01 0.02 0.05 0.08 0.10
4
8
12
16
20
2 (degrees)
Figure S1. XRD patterns of mesoMOFs synthesized with different amount of CA.
CA = 0.05g
CTAB
Intensity (a.u.)
0 0.05 0.1 0.2 0.4 0.6
4
8
12
16
20
2 (degrees)
Figure S2. XRD patterns of mesoMOFs synthesized with different amount of CTAB.
S7
Transmittance (a.u.)
CA 0
CTAB = 0.2g
0.01 0.02 0.05 0.08 0.10
4000
3000
2000
1000 -1
Wavenumber (cm )
Figure S3. IR spectra of mesoMOFs synthesized with different amount of CA.
Transmittance (a.u.)
CTAB 0
CA = 0.05g
0.05 0.1 0.2 0.4 0.6
4000
3000
2000
1000 -1
Wavenumber (cm )
Figure S4. IR spectra of mesoMOFs synthesized with different amount of CTAB.
S8
CTAB = 0.2g
50%
Weight (a.u.)
CA 0 0.01 0.02 0.05 0.08 0.10
100
200
300
400
500
o
Temperature ( C)
Figure S5. TGA curves of mesoMOFs synthesized with different amount of CA.
CA = 0.05g
50%
Weight (a.u.)
CTAB 0 0.05 0.1 0.2 0.4 0.6
100
200
300
400
500
o
Temperature ( C)
Figure S6. TGA curves of mesoMOFs synthesized with different amount of CTAB.
S9
Intensity (a.u.) 4
8
12
16
20
2 (degrees)
Transmittance (a.u.)
Figure S7. XRD pattern of pure CA.
4000
3000
2000
1000 -1
Wavenumber (cm )
Figure S8. IR spectrum of pure CA.
S10
Intensity (a.u.)
CTAB 0 0.05 0.2
4
8
12
16
20
2 (degrees)
Figure S9. XRD patterns of the samples derived from the reaction of Cu(NO3)2 and CA in the presence
3 -1 Volume adsorbed (cm .g , STP)
of 0-0.2 g of CTAB.
15
10
5
0 0.0
0.2
0.4
0.6
0.8
1.0
Relative pressure (p/p0)
Figure S10. N2 adsorption-desorption isotherm of the sample derived from the reaction of Cu(NO3)2 and CA. The reaction conditions are similar to the synthesis of Cu3(BTC)2 except that the ligand BTC was replaced by CA.
S11
Intensity (a.u.) 4
8
12
16
20
2 (degrees)
Figure S11. XRD pattern of the sample derived from the reaction of Cu(NO3)2 and BTC in the presence of CA and CuBr2. The reaction conditions are similar to the synthesis of mesoMOF(S0.05C0.05) except that CTAB was replaced by CuBr2 with the same molar amount of Br.
(a)
(b)
(c) CTAB = 0.2g
CTAB = 0.2g
0.08
0.15 0.05
0.10 0.02
0.05
0.01
0.10
0.20
0.08
0.15 0.05
0.10 0.02
0.05
CA 3 -1 Pore volume (cm .g )
0.20
3 -1 Pore volume (cm .g )
3 -1 Pore volume (cm .g )
0.10
CA
0.25
CA
0.25
CTAB = 0.2g
0.10
0.3
0.08
0.2 0.05
0.1
0.02
0.01 0.01
0
0
0.00 20
100
300 o
Pore diameter (A)
0.00 20
100
300 o
Pore diameter (A)
0.0 20
0
100
300 o
Pore diameter (A)
Figure S12. Pore size distributions of mesoMOFs synthesized in the presence of different amount of CA. Pore size distributions were calculated from adsorption braches by using (a) BJH, (b) BJH-KJS, and (c) DFT models. S12
(a)
(c)
(b) CA = 0.05g
0.6 0.4
0.15 0.2
0.10
0.1 0.05
0.05 0.00 20
0
100
300 o
Pore diameter (A)
0.25
CTAB
0.20
0.6 0.4
0.15 0.10
0.2
CTAB
0.3 0.6 0.4
0.2
0.2
0.1
0.1
0.1 0.05
0.05 0.00 20
3 -1 Pore volume (cm .g )
CTAB
3 -1 Pore volume (cm .g )
3 -1 Pore volume (cm .g )
0.25 0.20
CA = 0.05g
CA = 0.05g
0
100
300 o
Pore diameter (A)
0.05
0.0 20
0
100
300 o
Pore diameter (A)
Figure S13. Pore size distributions of mesoMOFs synthesized in the presence of different amount of CTAB. Pore size distributions were calculated from adsorption braches by using (a) BJH, (b) BJH-KJS, and (c) DFT models.
S13
