AN EXPERIMENTAL STUDY OF H₂ AND CO₂ ADSORPTION BEHAVIOR OF C-MOF-5 AND T-MOF-5: A COMPLEMENTARY STUDY

Abstract

In this paper the cubic and tetragonal structure of MOF-5 were successfully synthesized and characterized by TGA and SEM analysis. Equilibrium adsorption isotherms of C-MOF-5 and T-MOF-5 for H₂ and CO₂ were measured up to 25 bar at 298 K using a volumetric method. The C-MOF-5 adsorbent synthesized in this study had a 0.107 and 79.9 wt% adsorption capacities at 298 K and 25 bar for H₂ and CO₂, respectively. T-MOF-5 had a H₂ adsorption capacity of 0.122 wt% and CO₂ adsorption capacity of 67.6 wt% at 298 K and 25 bar. This behavior was attributed to more ZnO units in the T-MOF-5 structure. The difference between H₂ and CO₂ adsorption capacity for the cubic and tetragonal structure of MOF-5, suggests that C-MOF-5 and T-MOF-5 are potential adsorbents for the separation of CO₂ and H₂ from gas mixtures, respectively. Langmuir, Freundlich and Sips isotherm models were used to correlate the adsorption isotherms. The results showed that, at 298 K, the fit of the Sips isotherm to the experimental datawas better than Langmuir and Freundlich isotherms. According to TGA results, the thermal decomposition of C-MOF-5 requires a higher temperature than T-MOF-5.

Keywords:
Adsorption; Hydrogen; Carbon dioxide; MOF-5; ZnO

INTRODUCTION

In the last decades, there has been an increasing interest in developing gas storage systems for different applications such as H₂ storage or CO₂ capture (Marco-Lozar et al., 2012; Saha and Deng, 2009; Saha et al., 2009; Lou et al., 2014).

H₂ is important as a new source of energy for automotive applications. The main challenge in developing this technology is H₂ storage. The development of high H₂ storage capacity materials and safe transportation methods are recognized as requirements for the realization of a H₂ economy. Also, CO₂ emissions resulting from the burning of fossil fuels in ground transportation (cars, public/goods transport vehicles) are among the pressing global environmental problems (Lee et al., 2006).

Metal-organic frameworks (MOFs), also known as coordination polymers, are ideal crystalline substances for catalysis and gas separation and storage (Kurmoo et al., 2005; Zheng et al., 2006). In addition MOFs generally have high internal surface area and, due to the presence of organic linkers and metal ligands, it is possible to tune their pore size and volume (Mishra et al., 2012).

One of the most important MOFs is the Zn₄O₁₃C₂₄H₁₂ framework called MOF-5, which was first synthesized in 1999 (Li et al., 1999). This framework has potential applications for H₂ storage, CO₂ capture and catalysts (Eddaoudi et al., 2002). MOF-5 consists of Zn₄O as metal clusters connected by 1,4-benzenedicarboxylate (BDC) as a linkers to form a porous Zn₄O(BDC)₃ framework (Li et al., 1999). It has been recognized that MOF-5 occupies either cubic (C-MOF-5) or tetragonal (T-MOF-5) structures (Li et al., 1999; Hafizovic et al., 2007; Kaye et al., 2007; Huang et al., 2003).

Zhang and Hu (2011) showed that the composition of cubic and tetragonal MOF-5 calculated with the formulas of Zn_4.28O_12.8C₂₄H_11.3 and Zn₄O₁₃C₂₄H_12.6(ZnO)_1.59(H₂O)_1.74 respectively. They indicated that the formula of the C-MOF-5 sample was consistent with the stoichiometric formula of novel MOF-5 (Zn₄O₁₃C₂₄H₁₂) and the formula of the T-MOF-5 sample was very different from the stoichiometrical formula of novel MOF-5, owing tothe presence of ZnO and H₂O.

Arjmandi and Pakizeh (2013) showed that T-MOF-5 had lower surface area, lower porosity, smaller and more uniform pore size, and more ZnO units compared with C-MOF-5.

Sarmiento-Perez et al. (2012) used the Grand Canonical Monte Carlo (GCMC) simulation of CO₂ adsorption on MOF-5 and found the surprising role of the BDC organic ligand in this process. They reported that the organic ligands (BDC) have an important role in CO₂ adsorption on MOF-5.

Skoulidas and Sholl (2005) applied the equilibrium molecular dynamics (EMD) and GCMC to calculate the diffusion and adsorption of CH₄, CO₂, N₂, and H₂ in C-MOF-5. They reported that at low pressure (1-2 bar), a significant increase in CH₄, CO₂, N₂, and H₂ adsorption was not observed and at high pressure (6-7 bar), only CO₂ adsorption was increased.

Spencer et al. (2005) used neutron powder diffraction to determine the H₂ adsorption sites in the MOF-5 structure. They reported that the ZnO cluster was primarily responsible for H₂ adsorption while the organic ligand (BDC) played only a secondary role.

Arjmandi and Pakizeh (2014) synthesized and characterized (by XRD, FTIR, N₂ adsorption technique at 77 K and particle size analysis) C-MOF-5 and incorporated it in polyetherimide (PEI) as filler to make C-MOF-5/PEI MMMs and study the effect of C-MOF-5 on CH₄, CO₂, N₂, and H₂ gas permeation through the MMMs. The results showed that C-MOF-5 nanocrystals have the potential (as filler in C-MOF-5/PEI MMMs) to enhance CO₂ separation from H₂, CH₄ and N₂.

Arjmandi et al. (2014) investigated the effect of more ZnO units in T-MOF-5 than in the C-MOF-5 structure on the gas permeation properties of T-MOF-5/PEI MMMs. For this purpose, T-MOF-5 was successfully synthesized and carefully characterized by XRD, FTIR, SEM and the N₂ adsorption technique at 77 K. The results showed that T-MOF-5 nanocrystals have the potential (as filler in MMMs) to enhance H₂ separation from CO₂, CH₄ and N₂.

Table 1 summarizes the pore textural property of C-MOF-5 and T-MOF-5 according to our previous studies.

Table 1
Pore textural properties of C-MOF-5 and T-MOF-5 samples.

Species	BET specific surface area (m2/g)	Pore diameter (Å )	Pore volume (cm3/g)	Ref.
C-MOF-5	2387	8.67	0.99	Arjmandi and Pakizeh (2014)
T-MOF-5	1280	6.30	0.58	Arjmandi et al. (2014)

In the present work, to estimate the amount of ZnO in T-MOF-5 compared to C-MOF-5, thermogravimetric analysis (TGA) was performed. To study the effect of more ZnO in the structure of T-MOF-5, the excess adsorption measurements (by the volumetric method) of H₂ and CO₂ on C-MOF-5 and T-MOF-5 were studied at 298 K up to 25 bar. The two samples were characterized for their topology by scanning electron microscopy (SEM) imaging.

EXPERIMENTAL

Synthesis of Adsorbents

The cubic and tetragonal forms of MOF-5 were synthesized based on previously reported procedures (Kaye et al., 2007; Huang et al., 2003). All chemicals used in this study were obtained from Sigma-Aldrich.

For the synthesis of C-MOF-5, 0.45 g of Zn(NO₃)₂·6H₂O (>98%) and 0.083 g of H₂BDC (>99%) were dissolved in a100 mL bottle containing 49 mL of DMF (99.8%) and 1 mL of H₂O. After heating the solution at 70 °C under vigorous stirring, it was placed in an oven at 100 °C for 15 h. The reaction flask was then cooled down to 25 °C. After removing the solvent, the white powder was washed six times with 60 mL of anhydrous DMF and six times with 60 mL of anhydrous CH₂Cl₂ (>99.8%) (each time 10 h), respectively. Finally, the C-MOF-5 crystals were dried at 125 °C for 24 h under vacuum. A schematic representation of the synthesis of C-MOF-5 is summarized in Figure 1.

Figure 1
Synthesis of C-MOF-5; (1) Zn(NO₃)₂·6H₂O, (2) H₂BDC, (3) DMF + H₂O, (4) Magnetic stir bar, (5) Magnetic hotplate, (6) Oven, (7) Reaction flask at 25 °C (with powder + solution), (8) Petri dish, (9) DMF, (10) CH₂CL₂, (11) Vacuum oven, (12) C-MOF-5 powder in a Petri dish with a porous lid.

For the synthesis of T-MOF-5, 1.19 g of Zn(NO₃)₂·6H₂O (>98%) and 0.34 g of H₂BDC (>99%) were dissolved in 40 mL of DMF (99.8%) at room temperature. After adding three drops of aqueous H₂O₂ solution, 2.3 mL of triethylamine (TEA, >99.5%) was added dropwise to the reaction flask under strong agitation at 70 °C for 2 h. After placing the flask in an oven at 100 °C for 15 h, it was removed from the oven and cooled down to 25 °C. The white solid obtained was filtered and washed with DMF three times. Finally, the T-MOF-5 was dried at 125 °C for 24 h under vacuum. A schematic of the synthesis of T-MOF-5 is summarized in Figure 2.

Figure 2
Synthesis of T-MOF-5; (1) Zn(NO₃)₂·6H₂O, (2) H₂BDC, (3) DMF, (4) Magnetic stir bar, (5) Magnetic hotplate, (6) H₂O₂, (7) TEA, (8) Oven, (9) Reaction flask at 25 °C (with powder + solution), (10) Dish, (11) Filter paper, (12) DMF, (13) Petri dish containing powder, (14) Vacuum oven, (15) T-MOF-5 powder in a Petri dish with a porous lid.

Characterization of Adsorbents

As mentioned above, the XRD, FTIR, N₂ adsorption, surface area measurement and pore textural properties of MOF-5 samples/forms were presented in our previous studies (Arjmandi and Pakizeh, 2014; Arjmandi et al. 2014). In this article, thermogravimetric analysis (TGA-50 Shimadzu)in a N₂ atmosphere was used to evaluate the amount of ZnO units in T-MOF-5.Scanning electron microscopy (SEM) images of C-MOF-5 and T-MOF-5 were taken using a Cam Scan SEM model KYKYEM3200 microscope.

Gas Sorption Measurements

The H₂ and CO₂ adsorption capacities of C-MOF-5 and T-MOF-5 were determined in the apparatus based on the volumetric method shown in Figure 3.

Figure 3
Schematic diagram of the volumetric adsorption apparatus: (1) H₂ gas cylinder, (2) CO₂ gas cylinder, (3) and (4) needle valve, (5) regulator, (6)-(8) needle valve, (9) gas charge cell, (10) adsorption cell, (11) needle valve, (12) regulator, (13) needle valve, (14) vacuum pump, (15) pressure transducer, (16) pressure digital indicator, (17) computer.

The apparatus consisted of two high-pressure stainless steel vessels including the gas charge and adsorption cells (built in-house). The gas charge vessels were connected to a regulator and needle valve (Swagelok, 6DB series) to control the pressure of the gas entering the gas charge cell. Before the sorption process, C-MOF-5 and T-MOF-5 were degassed at 100 °C for about 24 h and the system was evacuated by a vacuum pump (Welch, DuoSeal 1376). Two high precision pressure transducers (Danfoss, MBS 3000 - 2611 - 1 AB04) measured the changes in pressure of the gas and adsorption cell in H₂ and CO₂ adsorption experiments. The H₂ and CO₂ adsorption experiments were conducted at pressures ranging from 0 to 25 bar at ambient temperature.

According to the material balance, the total amount of gas initially available in the gas charge and sorption cells should be equal to the amount of gas in these cells at the steady state plus the amount of gas adsorbed, based on the following equation:

where subscripts 1, 2, c and a denote the initial state, final equilibrium state, gas charge cell and adsorption cell, respectively. Also V, P, T, R and N_ads represent volume, pressure, temperature, the universal gas constant and amount of gas adsorbed by the adsorbent, respectively. As is evident from Eq. (1), compressibility factors (Z) are required for proper data analysis of the pure gases. The compressibility factors of H₂ and CO₂ were calculated from the Peng-Rabinson (PR) equation of state.

RESULTS AND DISCUSSION

Physical Properties of MOF-5s

The results of thermogravimetric analysis (TGA) are shown in Figure 4 for both tetragonal and cubic MOF-5 nanocrystals. For T-MOF-5, a 15% weight loss occurred in the range of 30-300 °C and then a 43% weight loss, beginning at about 350 ºC. For C-MOF-5, 1.5 and 51.5 wt% weight losses were also observed in the same temperature range of T-MOF-5 weight losses. According to Zhang's experimental results (Zhang and Hu, 2011) it can be said that, for both samples, the first weight loss in TGA corresponds to desorption of water and the second one is associated with the decomposition of MOF-5 to release CO₂ and benzene (Zhang and Hu, 2011). As reported by Zhang and Hu (2011) based on calculation from the chemical formula of novel MOF-5 (Zn₄O₁₃C₂₄H₁₂), the weight percent of ZnO units is around 42 wt%. The solid products from the decomposition of both MOF-5s consist of carbon and ZnO (Zhang and Hu, 2011). As shown in Figure 4, the final residual weights of T-MOF-5 and C-MOF-5 were 57 and 48.5 wt%, respectively (regardless of water). For the same amount of carbon in MOF-5s (Zhang and Hu, 2011), the decomposition products of T-MOF-5 contain 8.5 wt% more ZnO than those of C-MOF-5. In addition, C-MOF-5 is more stable than T-MOF-5 because the decomposition temperature of C-MOF-5 is higher than that of T-MOF-5.

Figure 4
Thermogravimetric curves of (a) C-MOF-5 and (b) T-MOF-5 samples.

Figure 5 shows the scanning electron microscopic images of C-MOF-5 and T-MOF-5 nanocrystals synthesized in this work. The range of particle size of both the C-MOF-5 and T-MOF-5 nanocrystals was 100-150 nm, with no defined morphology. Similar SEM pictures were obtained in literature (Huang et al., 2003; Perez et al., 2009), with aggregates similar in size (70-100 nm) to the nanocrystals synthesized in this studythat showed no defined crystal morphology.

Figure 5
SEM images of (a) C-MOF-5 and (b) T-MOF-5 samples.

Adsorption Equilibrium

The adsorption isotherms of CO₂ and H₂ on both MOF-5s at 298 K and pressures in the range 0-25 bar are plotted in Figures 6 and 7, respectively.

Figure 6
CO₂ adsorption capacity at 298 K and 25 bar of C-MOF-5 and T-MOF-5.

Figure 7
H₂ adsorption capacity at 298 K and 25 bar of C-MOF-5 and T-MOF-5.

The formula of the C-MOF-5 sample (Zn_4.28O_12.8C₂₄H_11.3) is consistent with the stoichiometric formula of novel MOF-5 (Zn₄O₁₃C₂₄H₁₂). The comparison of the results for CO₂ and H₂ adsorption on C-MOF-5 in this study with those for CO₂ and H₂ adsorption on novel MOF-5 in the literature (Marco-Lozar et al., 2012), indicates the accuracy of the experimental system shown in Figure 3.

According to Figure 6, the adsorption capacity of CO₂ on C-MOF-5 at 298 K and 25 bar is 79.9 wt%, which is about 18% higher than the adsorption capacity of CO₂ on T-MOF-5 at 298 K. In contrast, as shown in Figure 7, T-MOF-5 showed an adsorption capacity of 0.122 wt% for H₂, which is about 12.3% higher than the adsorption capacity of C-MOF-5 for H₂.

For physisorptive materials (such as MOFs) and some gases (such as CH₄), the adsorption capacity has a strong correlation with the surface area and pore volume. For these gases the structure and chemical composition of the adsorbent are not important for the adsorption capacity (Coates, 2000; Zhou, 2010; Anbia et al., 2012). In contrast, for H₂ and CO₂ the structure and chemical composition of the adsorbent are important to increase the adsorption capacity.

As noted in the previous sections, the T-MOF-5 nanocrystals have lower surface area, lower porosity and smaller and more uniform pore size than C-MOF-5 nanocrystals.

Also as mentioned earlier, T-MOF-5 contains less CO₂ and organic ligand molecule and more inorganic clusters (containing ZnO units) than C-MOF-5. The difference between the amount of ZnO units in the cubic and tetragonal structures of MOF-5 brings about the difference of H₂ and CO₂ adsorption capacities. Considering that the organic ligand and inorganic clusters in the MOF-5 structure are the major sites of adsorption of CO₂ and H₂, respectively, it can be expected that CO₂ adsorption on T-MOF-5 should be less than that on C-MOF-5. As well, H₂ adsorption on T-MOF-5 is more than that on C-MOF-5.

Accordingly, the higher CO₂ adsorption capacity of C-MOF-5 was attributed to the organic ligand and the higher H₂ adsorption capacity of T-MOF-5 was attributed to the inorganic clusters.

The adsorption selectivities for H₂ and CO₂ were calculated from their adsorption isotherms. The adsorption selectivity of a gas A over gas B was calculated by using Eq. (2) (Lee et al., 2009):

where V_A and V_B are the volumes of gases A and B, respectively, adsorbed at any given pressure P and temperature T. The orders of adsorption selectivity for CO₂ and H₂ showed that CO₂/H₂ in T-MOF-5 (553.77) was lower than CO₂/H₂ in C-MOF-5 (746.73).This occurred because there were more adsorption sites for CO₂(organic ligand) in C-MOF-5 than in T-MOF-5 and more H₂ adsorption sites (inorganic clusters) in T-MOF-5 than in C-MOF-5.

Results reported so far in the literature on CO₂ and H₂ adsorption are summarized in Table 2.

The equilibrium adsorption isotherm is the basis for describing the interaction between adsorbent and adsorbate. In this study, the Langmuir (1916), Freundlich (1906) and Sips (1948) models were used to correlate the adsorption isotherms.

Table 2
High-pressure CO₂ and H₂ excess adsorption data at 298 K for selected porous MOFs.

MOFs	BET surface area (m2/g)	Pressure (bar)	H2 uptake (wt%)	H2 uptake (mol/m3)	CO2 uptake (wt%)	CO2 uptake (mol/m3)	Ref.
MIL-53-Ala	-	25	-	-	44.04	10122.52	Bourrelly et al. (2005)
MIL-53-Cra	-	25	-	-	44.04	10122.52	Bourrelly et al. (2005)
MIL-100b	1900	50	-	-	79.27	12596.92	Llewellyn et al. (2008)
MIL-101b	4230	50	-	-	176.16	17545.71	Llewellyn et al. (2008)
MIL-47a	-	20	-	-	484.84	11247.25	Bourrelly et al. (2005)
MOF-5	2296	35	-	-	95.57	13046.81	Millward and Yaghi (2005)
IRMOF-6	2804	40	-	-	87.20	12866.85	Millward and Yaghi (2005)
MOF-177	4750	42	-	-	147.53	14396.48	Millward and Yaghi (2005)
MIL-100	-	90	0.15	515.91	-	-	Latroche et al. (2006)
MIL-101	-	80	0.43	912.76	-	-	Latroche et al. (2006)
PCN-10c	1407	45	4.2	15973.17	-	-	Wang et al. (2008)
PCN-11c	1931	45	5.04	18751.12	-	-	Wang et al. (2008)
PCN-6	-	50	0.93	-	-	-	Furukawa et al. (2007)
HKUST-1	1154	65	0.35	-	-	-	Panella et al. (2006)
IRMOF-8	-	30	0.40	1150.86	-	-	Dailly et al. (2006)
MOF-5	3800	100d	0.57e	-	-	-	Kaye et al. (2007)
MOF-5c	3800	100d	7.60	20884.18	-	-	Kaye et al. (2007)
IRMOF-8 + Pt/AC	-	100	4.0	-	-	-	Li and Yang (2006)
MOF-5 + Pt/AC	-	100	3.0	-	-	-	Li and Yang (2006)
C-MOF-5	2387	25	0.107	296.71	79.90	10148.63	This study
T-MOF-5	1280	25	0.122	347.38	67.56	8811.51	This study

• ^a
  Measured at 302 K
• ^b
  Measured at 304 K
• ^c
  Measured at 77 K
• ^d
  Absolute pressure
• ^e
  Absolute adsorption

The Langmuir isotherm is written as:

where q_e is the H₂ and CO₂ adsorbed amount on MOF-5s, p is the gas pressure, a_m and b are the Langmuir isotherm equation parameters.

The Freundlich isotherm is given by:

where k_F and n are the Freundlich isotherm equation parameters that can be determined from the experimental H₂ and CO₂ adsorption isotherms.

The Sips isotherm is a combined form of the Langmuir and Freundlich equations deduced for heterogeneous adsorption systems circumventing the limitation of the increasing adsorbate concentration associated with the Freundlich isotherm model. At low adsorbate concentrations, the Sips isotherm reduces to the Freundlich isotherm; while at high concentrations, it predicts a monolayer adsorption capacity characteristic of the Langmuir isotherm. The Sips isotherm is given by:

where k_s, α_s and β are the Sips isotherm constants. These three isotherms were fitted to each of the adsorption data. The adsorption isotherm equation parameters for the Langmuir, Freundlich and Sips equations are listed in Table 3.

Table 3
Summary of adsorption isotherm model parameters for H₂ and CO₂ in C-MOF-5 and T-MOF-5.

Adsorbent	Gas	Isotherm model parameters
		Langmuir	Freundlich	Sips
C-MOF-5	H2	am= 0.2242 b= 0.0356 R2= 0.9981	kF= 0.0114 n= 1.4340 R2= 0.9992	ks = 0.0105 ɑs = 0.0186 β = 0.7863 R2= 0.9995
	CO2	am= 712.9 b= 0.0055 R2= 0.9870	kF= 3.9780 n= 1.0460 R2= 0.9854	ks = 1.1560 ɑs = 0.0088 β = 1.6340 R2= 0.9939
T-MOF-5	H2	am= 0.2441 b= 0.0396 R2= 0.9981	kF= 0.0139 n= 1.4720 R2= 0.9986	ks = 0.0123 ɑs = 0.0272 β = 0.8140 R2= 0.9993
	CO2	am= 2352 b= 0.0013 R2= 0.9870	kF= 2.8 n= 0.9878 R2= 0.9869	ks = 0.9186 ɑs = 0.0074 β = 1.6080 R2= 0.9930

Figure 8(a),(b) compares the experimental H₂ and CO₂ adsorption isotherm on the cubic and tetragonal structures of MOF-5 through the Langmuir, Freundlich and Sips isotherms.

Figure 8
(a) Correlation of CO₂ adsorption isotherm on C-MOF-5 and T-MOF-5 and (b) Correlation of H₂ adsorption isotherm on C-MOF-5 and T-MOF-5 with Langmuir, Freundlich and Sips isotherm models.

It can be seen from these figures that all three isotherm models can reasonably describe the H₂ and CO₂ adsorption isotherms on the two MOF-5 adsorbents, but none of them is accurate enough to predict all isotherms without any error.

The criteria associated with the selection of the best isotherm model were essentially based on the correlation coefficient and R². The correlation coefficient shows the fit between experimental data and the isotherm model, while the value of R² quantifies the goodness of fit between the experimental data and calculated data used for plotting the isotherm curves. The results presented in Table 3 show that the Sips isotherm fits better than the Langmuir and Freundlich isotherms at 298 K (especially for CO₂ adsorption on both MOF-5s).

CONCLUSIONS

There are two structures of MOF-5: one with the cubic structure (C-MOF-5) and the other tetragonal (T-MOF-5). T-MOF-5 had a lower surface area, lower porosity, smaller and more uniform pore size, and more ZnO units than C-MOF-5. Both the cubic and tetragonal structures of MOF-5 were synthesized and characterized by TGA and SEM and used as adsorbents for H₂ and CO₂ adsorption studies. We found that the CO₂ adsorption capacity of C-MOF-5 at 298 K and 25 bar is greater than that of T-MOF-5, with capacities of 79.9 and 67.5 wt%, respectively. Also we found that the H₂ adsorption capacity of C-MOF-5 at 298 K and 25 bar is less than that of T-MOF-5, with capacities of 0.107 and 0.122 wt%, respectively. This behaviour was attributed to more ZnO units in T-MOF-5 than C-MOF-5. The difference between the H₂ and CO₂ adsorption capacities of T-MOF-5 and C-MOF-5 shows that T-MOF-5 is a better adsorbent for H₂ storage and C-MOF-5 is a better adsorbent for CO₂ capture. The Sips isotherm fit better to the experimental data than the Langmuir and Freundlich isotherms.

Thermal decomposition of T-MOF-5 and C-MOF-5 produced the same products: benzene, CO₂, carbon and ZnO. However, the thermal decomposition of C-MOF-5 required a higher temperature than that of T-MOF-5, indicating that C-MOF-5 is more stable than T-MOF-5.

• *
  To whom correspondence should be addressed

ACKNOWLEDGEMENT

The authors acknowledge the Iran Nanotechnology Initiative Council for financial support.

REFERENCES

• Anbia, M., Hoseini, V., Sheykhi, S., Sorption of methane, hydrogen and carbon dioxide on metal-organic framework, iron terephthalate (MOF-235). Journal of Industrial and Engineering Chemistry, 18, 1149-1152 (2012).
• Arjmandi, M., Pakizeh, M., Effects of washing and drying on crystal structure and pore size distribution (PSD) of Zn₄O₁₃C₂₄H₁₂ framework (IRMOF-1). Acta Metallurgica Sinica (English Letters), 26, 597-601 (2013).
• Arjmandi, M., Pakizeh, M., Mixed matrix membranes incorporated with cubic-MOF-5 for improved Polyetherimide gas separation membranes: Theory and experiment. Journal of Industrial and Engineering Chemistry, 20, 3857-3868 (2014).
• Arjmandi, M., Pakizeh, M., Pirouzram, O., The role of Tetragonal-MOF-5 loadings with extra ZnO molecule on the gas separation performance of mixed matrix membrane. Korean Journal of Chemical Engineering, Accepted (2014).
• Bourrelly, S., Llewellyn, P. L., Serre, C., Millange, F., Loiseau, T., Férey, G., Different Adsorption behaviors of methane and carbon dioxide in the isotypic nanoporous metal terephthalates MIL-53 and MIL-47. Journal of the American Chemical Society, 127, 13519-13521 (2005).
• Coates, J., Interpretation of Infrared Spectra, A Practical Approach. John Wiley and Sons Ltd., New York, 10815 (2000).
• Dailly, A., Vajo, J. J., Ahn, C. C., Saturation of hydrogen sorption in Zn benzenedicarboxylate and Zn naphthalenedicarboxylate. The Journal of Physical Chemistry, B, 110, 1099-1101 (2006).
• Eddaoudi, M., Kim, J., Rosi, N., Vodak, D., Wachter, J., O'Keeffe, M., Yaghi, O. M., Systematic design of pore size and functionality in isoreticular MOFs and their application in methane storage. Science, 295, 469-472 (2002).
• Freundlich, H. M. F., Over the adsorption in solution. Journal of Physics and Chemistry, 57(385), e470 (1906).
• Furukawa, H., Miller, M. A., Yaghi, O. M., Independent verification of the saturation hydrogen uptake in MOF-177 and establishment of a benchmark for hydrogen adsorption in metal-organic frameworks. Journal of Materials Chemistry, 17, 3197-3204 (2007).
• Hafizovic, J., Bjorgen, M., Olsbye, U., Dietzel, P. D. C., Bordiga, S., Prestipino, C., Lamberti, C., Lillerud, K. P., The inconsistency in adsorption properties and powder XRD data of MOF-5 is rationalized by framework interpenetration and the presence of organic and inorganic species in the nanocavities. Journal of the American Chemical Society, 129, 3612-3620 (2007).
• Huang, L., Wang, H., Chen, J., Wang, Z., Sun, J., Zhao, D., Yan, Y., Synthesis, morphology control, and properties of porous metal-organic coordination polymers. Microporous and Mesoporous Materials, 58, 105-114 (2003).
• Kaye, S. S., Dailly, A., Yaghi, O. M., Long, J. R., Impact of preparation and handling on the hydrogen storage properties of Zn₄O(1,4-benzenedicarboxylate)₃ (MOF-5). Journal of the American Chemical Society, 129, 14176-14177 (2007).
• Kurmoo, M., Kumagai, H., Chapman, K. W., Kepert, C. J., Reversible ferromagnetic-antiferromagnetic transformation upon dehydration-hydration of the nanoporous coordination framework, [Co₃(OH)₂(C₄O₄)₂].₃H₂O. Chemical Communications, 24, 3012-3014 (2005).
• Langmuir, I., The constitution and fundamental properties of solids and liquids. Part I. solids. Journal of the American Chemical Society, 38, 2221-2295 (1916).
• Latroche, M., Surblé, S., Serre, C., Mellot-Draznieks, C., Llewellyn, P. L., Lee, J., Chang, J., Jhung, S. H., Férey, G., Hydrogen storage in the giant-pore metal-organic frameworks MIL-100 and MIL-101. Angewandte Chemie International Edition, 45, 8227-8231 (2006).
• Lee, J. Y., Wood, C. D., Bradshaw, D., Rosseinsky, M. J., Cooper, A. I., Hydrogen adsorption in microporous hyper cross linked polymers. Chemical Communications, 25, 2670-2672 (2006).
• Lee, J. S., Jhung, S. H., Yoon, J. W., Hwang, Y. K., Chang, J. S., Adsorption of methane on porous metal carboxylates. Journal of Industrial and Engineering Chemistry, 15, 674-676 (2009).
• Li, H., Eddaoudi, M., O'Keeffe, M., Yaghi, O. M., Design and synthesis of an exceptionally stable and highly porous metal-organic framework. Nature, 402, 276-279 (1999).
• Li, Y., Yang, R. T., highly selective asymmetric synthesis of homoallylic amines with and without a .β.-substituent by the reaction of allylic titanium compounds with chiral imines. Journal of the American Chemical Society, 128, 8136-8137 (2006).
• Llewellyn, P. L., Bourrelly, S., Serre, C., Vimont, A., Daturi, M., Hamon, L., Weireld, G. D., Chang, J., Hong, D., Hwang, Y. K., Jhung, S. H., Férey, G., High uptakes of CO₂ and CH₄ in mesoporous metal-organic frameworks MIL-100 and MIL-101. Langmuir, 24, 7245-7250 (2008).
• Lou, W., Yang, J., Li, L., Li, J., Adsorption and separation of CO₂ on Fe(II)-MOF-74: Effect of the open metal coordination site. Journal of Solid State Chemistry, 213, 224-228 (2014).
• Marco-Lozar, J. P., Juan-Juan, J., Suarez-Garcia, F., Cazorla-Amoros, D., Linares-Solano, A., MOF-5 and activated carbons as adsorbents for gas storage. International Journal of Hydrogen Energy, 37, 2370-2381 (2012).
• Millward, A. R., Yaghi, O. M., Metal-organic frameworks with exceptionally high capacity for storage of carbon dioxide at room temperature. Journal of the American Chemical Society, 127, 17998-17999 (2005).
• Mishra, P., Mekala, S., Dreisbach, F., Mandal, B., Gumma, S., Adsorption of CO₂, CO, CH₄ and N₂ on a zinc based metal organic framework. Separation and Purification Technology, 94, 124-130 (2012).
• Panella, B., Hirscher, M., Putter, H., Muller, U., Hydrogen adsorption in metal-organic frameworks: Cu-MOFs and Zn-MOFs Compared. Advanced Functional Materials, 16, 520-524 (2006).
• Perez, E. V., Balkus, J. K. J., Ferraris, J. P., Musselman, I. H., Mixed-matrix membranes containing MOF-5 for gas separations. Journal of Membrane Science, 328, 165-173 (2009).
• Saha, D., Deng, S., Synthesis, characterization and hydrogen adsorption in mixed crystals of MOF-5 and MOF-177. International Journal of Hydrogen Energy, 34, 2670-2678 (2009).
• Saha, D., Wei, Z., Deng, S., Hydrogen adsorption equilibrium and kinetics in metal-organic framework (MOF-5) synthesized with DEF approach. Separation and Purification Technology, 64, 280-287 (2009).
• Sarmiento-Perez, R. A., Rodriguez-Albelo, L. M., Gomez, A., Autie-Perez, M., Lewis, D. W., Ruiz-Salvador, A. R., Surprising role of the BDC organic ligand in the adsorption of CO₂ by MOF-5. Microporous and Mesoporous Materials, 163, 186-191 (2012).
• Sips, R., On the structure of a catalyst surface. Journal of Chemical Physics, 16, 490-495 (1948).
• Skoulidas, A. I., Sholl, D. S., Self-diffusion and transport diffusion of light gases in metal-organic framework materials assessed using molecular dynamics simulations. Journal of Physical Chemistry, B, 109, 15760-15768 (2005).
• Spencer, E. C., Howard, J. A. K., McIntyre, G. J., Rowsell, J. L. C., Yaghi, O. M., Determination of the hydrogen absorption sites in Zn₄O(1,4-benzenedicarboxylate) by single crystal neutron diffraction. Chemical Communications, 3, 278-280 (2006).
• Wang, X., Ma, S., Rauch, K., Simmons, J. M., Yuan, D., Wang, X., Yildirim, T., Cole, W. C., López, J. J., Meijere, A., Zhou, H., Metal-organic frameworks based on double-bond-coupled Di-Isophthalate linkers with high hydrogen and methane uptakes. Chemistry of Materials, 20, 3145-3152 (2008).
• Zhang, L., Hu, Y. H., Structure distortion of Zn₄O₁₃C₂₄H₁₂ framework (MOF-5). Materials Science and Engineering, B, 176, 573-578 (2011).
• Zheng, Y., Tong, M., Zhang, W., Chen, X., Assembling magnetic nanowires into network: A layered Co(II)-carboxylate coordination polymer exhibiting the robust single-chain-magnet behavior. Angewandte Chemie International Edition, 45, 6310-6314 (2006).
• Zhou, W., Methane storage in porous metal−organic frameworks: Current records and future perspectives. The Chemical Record, 10, 200-204 (2010).

Publication Dates

• Publication in this collection
  Jan-Mar 2016

History

• Received
  28 Oct 2014
• Reviewed
  04 Apr 2015
• Accepted
  21 Apr 2015