Next Article in Journal
Poly(butylene adipate-co-terephthalate)/Poly(lactic acid) Polymeric Blends Electrospun with TiO2-R/Fe3O4 for Pollutant Photodegradation
Next Article in Special Issue
The Methylene Spacer Matters: The Structural and Luminescent Effects of Positional Isomerism of n-Methylpyridyltriazole Carboxylate Semi-Rigid Ligands in the Structure of Zn(II) Based Coordination Polymers
Previous Article in Journal
Structural, Mechanical, and Tribological Properties of Oriented Ultra-High Molecular Weight Polyethylene/Graphene Nanoplates/Polyaniline Films
Previous Article in Special Issue
Covalent Organic Frameworks (COFs) as Multi-Target Multifunctional Frameworks
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:

Exploring the Potential of a Highly Scalable Metal-Organic Framework CALF-20 for Selective Gas Adsorption at Low Pressure

Mostafa Yousefzadeh Borzehandani
Majid Namayandeh Jorabchi
Emilia Abdulmalek
Mohd Basyaruddin Abdul Rahman
1,2 and
Muhammad Alif Mohammad Latif
Integrated Chemical BioPhysics Research, Faculty of Science, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia
Foundry of Reticular Materials for Sustainability, Institute of Nanoscience and Nanotechnology, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia
Leibniz Institute for Catalysis, Albert-Einstein-Straße 29a, D-18059 Rostock, Germany
Centre of Foundation Studies for Agricultural Science, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia
Authors to whom correspondence should be addressed.
Polymers 2023, 15(3), 760;
Submission received: 29 December 2022 / Revised: 28 January 2023 / Accepted: 29 January 2023 / Published: 2 February 2023
(This article belongs to the Special Issue Synthesis and Properties of Polymeric Frameworks)


In this study, the ability of the highly scalable metal-organic framework (MOF) CALF-20 to adsorb polar and non-polar gases at low pressure was investigated using grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations. The results from the simulated adsorption isotherms revealed that the highest loading was achieved for SO2 and Cl2, while the lowest loading was found for F2 molecules. The analysis of interaction energies indicated that SO2 molecules were able to form the strongest adsorbent-adsorbate interactions and had a tight molecular packing due to their polarity and angular structure. Additionally, Cl2 gas was found to be highly adsorbed due to its large van der Waals surface and strong chemical affinity in CALF-20 pores. MD simulations showed that SO2 and Cl2 had the lowest mobility inside CALF-20 pores. The values of the Henry coefficient and isosteric heat of adsorption confirmed that CALF-20 could selectively adsorb SO2 and Cl2. Based on the results, it was concluded that CALF-20 is a suitable adsorbent for SO2 and Cl2 but not for F2. This research emphasizes the importance of molecular size, geometry, and polarity in determining the suitability of a porous material as an adsorbent for specific adsorbates.

Graphical Abstract

1. Introduction

Metal-organic frameworks (MOFs) are a sub-class of porous materials with one-, two-, and three-dimensional networks that are constructed by metal ions/clusters and organic linkers [1]. MOFs have shown advantageous features when compared to conventional porous materials; (i) experimental measurement of BET (Brunauer, Emmett and Teller) for zirconium-based MOF, NU-1103, recorded an ultra-high surface area (6550 m2/g) [2], (ii) variable-temperature powder x-ray diffraction (VT-PXRD) and thermal gravimetric (TG) analyses for Co-based MOF, NJU-Bai62 indicated surprising thermal stability of up to 450 °C [3], (iii) D-glucose selective hydrogenation reaction tests using ruthenium-impregnated, chromium-based MIL-100 exhibited an exceptional catalytic activity, and recyclability up to 12 runs [4], and (iv) revised auto-correlations (RACs) analysis using the machine learning method has recently updated that there are more than 90,000 synthesized and 500,000 predicted MOF structures, highlighting MOFs’ high structural diversity [5].
Although MOFs have been considered for energy conversion [6], water treatment [7], catalysis [8], photodynamic therapy [9], and drug delivery [10], their applications for gas adsorption and separation have been extensively studied [11,12,13,14,15,16,17]. This can be addressed by the features and characteristics that make MOFs an ideal porous material for research and practical use for gas adsorption and separation. For example, Jian-Rong Li and colleagues designed an organic linker that resulted in two interpenetrated frameworks, BUT-43 and BUT-44, after mixing with paddlewheel Cu2(COO)4 and Zr6O4(OH)8(COO)8 clusters, respectively [18]. Adsorption isotherm showed that both frameworks had the highest uptake and selectivity for C2H2 over CO2 and CH4 due to better chemical affinity and surface contact. Moreover, combining pyridine-based acylamide-linking diisophthalate with dicopper(II)-paddlewheel clusters produced the acylamide-functionalized MOF, HNUST-8 [19]. It was found that this framework had high selectivity for CO2 over CH4 and N2 caused by its strong Lewis acid-base interactions with open metal site Cu(II) and hydrogen interactions with acylamide functional groups (-CONH … OCO). In addition, it was shown that developing the polarity of pore surface using O- and N-rich organic linkers via the pre-functionalization process could improve the adsorption of gas molecules. For instance, titanium-based MOF, NTU-9, demonstrated a one-dimensional channel containing polar oxygen atoms, and it was capable of excellent C2H2 adsorption [20]. Surface area, chemical affinity, presence of polar/non-polar functional groups, and polarity of pore surface are the most determinative factors for gas adsorption.
Regardless of MOFs being an ideal platform for gas adsorption, they must be produced on a large scale for industrial applications [21]. Recently, Shimizu et al. have synthesized a low-priced and scalable zinc-based MOF, CALF-20 (Calgary Framework 20) [22]. More than 35% of dried solid CALF-20 was extracted per total amount of solvents used, plus an extraordinary space-time yield (STY) for the precipitation step of 550 kg/m3 per day. In comparison with this achievement, it is worth noting that the STYs for zeolites are observed in the range of 50 to 150 kg/m3 per day [23]. The 3D frameworks were built by first synthesizing 2D layers of 1,2,4-triazolate-bridged zinc(II) ions, which were subsequently pillared by oxalate ions (Figure 1). The reactants are cost-effective, commercially available, and environmentally safe because the reaction can be accomplished in a water/methanol mixture (less than 25 wt% organic solvents) [22]. More attention should be paid to CALF-20 MOF since it can be synthesized using a sustainable methodology. This can be emphasized as scalability and cost-efficiency are the major parameters to consider when transitioning from academia to commercialization [21]. Concerning the environmental impacts of hazardous organic linkers, metal complexes, and solvents, focusing on green synthesized MOFs such as CALF-20 guarantees clean MOF-based technologies [24]. In terms of CALF-20 applications in gas adsorption, it demonstrated a high capacity for CO2 (up to 5.0 mmol⋅g−1 at 1.2 bar and 273 K), as well as outstanding selectivity of CO2 over water (below 40% relative humidity). In addition, for a 10:90 CO2/N2 mixture, the estimated selectivity of CO2 over N2 using the ideal adsorbed solution theory (IAST) was 230. CALF-20 was tested for the separation of CO2 from flue gas (containing CO2/N2 15:85) using the four-step vacuum swing adsorption (VSA) method under dry conditions [25]. An excellent percentage of CO2 purity (95%) and recovery (90%) was achieved using CALF-20. Although CALF-20 can be considered a promising scalable MOF for CO2 adsorption and separation, its capability for the adsorption of other toxic gases has not yet been established. Since the CALF-20′s framework is composed of abundant nitrogen and oxygen sites, comparing the adsorption of polar and non-polar gas molecules on the CALF-20 pore surface will be imperative as the surface polarity is a determinative agent for gas adsorption on the pore surface.
In this work, we have selected hydrogen sulfide (H2S), sulfur dioxide (SO2), fluorine (F2), and chlorine (Cl2) as polar and non-polar gas molecules to study. Adsorption of these gases is important in terms of the environmental and health aspects since they are among the most toxic gases with a high level of immediately dangerous to life or health (IDLH) status [26,27]. These gases are mainly released from the combustion of natural gas, biogas, and petroleum, which cause acute environmental and health problems. Halogen contaminations have been observed in some areas depending on industrial activities; for instance, a high level of fluorine pollution was found surrounding a power station in New South Wales (Australia) [28,29]. Studies have demonstrated that a sufficient concentration of H2S (e.g., above 100 ppm) damages the central nervous system in the human body [30,31]. In addition, the exposure of asthmatic people to H2S leads to bronchial constrictions [32,33]. The emission of SO2 in the air accelerates the formation of acid rain and photochemical smog [34]. Research works on the adsorption of SO2 using MOFs [35], zeolites [36], and ionic liquids [37] have attributed to the highly corrosive nature of SO2 gas, which can affect the materials. MOFs have been found to be the most widely used platform among them. [38,39,40]. Herein, two computational approaches, including grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations, were employed to study the adsorption and the mobility of the gas molecules, respectively. The details of the methods employed in this work are described in the next section. These methodologies offer a detailed, atomic-level understanding of the adsorption of both polar and non-polar gas species in CALF-20.

2. Computational Details

2.1. Model Construction

Crystal information file (.cif) was taken from Cambridge Crystallographic Data Center (CCDC) with deposition number 2084733 [22]. The .cif file was employed to perform initial geometry-based analysis, such as pore diameters using the Zeo++ program version 0.3 (, accessed on 28 December 2022) [41] and surface area using RASPA 2.0 program (, accessed on 28 December 2022) [42]. The molecular formula of CALF-20 is [Zn2(1,2,4-triazolate)2(oxalate)], and the metal centers, zinc (Zn), are fully coordinated. The unit cell lengths of a, b, and c for CALF-20 are 8.91, 9.69, and 9.48 Å, respectively, and the arrangement of the atoms in the unit cell formed a monoclinic symmetry. The CALF-20′s unit cell was then extended to a 3 × 3 × 3 supercell. Periodic boundary conditions were defined in all directions for all simulations. Lennard-Jones (LJ) and electrostatic potentials were applied uniformly to CALF-20 framework atoms, in which the LJ potential parameters were described by GenericMOFs force field (as implemented in RASPA [42]) (see Supplementary Materials (Figures S1 and S2, Tables S1 and S2)). GenericMOFs is a combined force field where the metal center (Zn) is treated by the universal force field (UFF) [43] and the non-metallic elements by Dreiding force field [44]. Atomic charges of the frameworks were calculated using the CHarges from Electrostatic Potentials using a Grid (CHelpG) method at B3LYP/6-311+G(d,p) level (Figures S1 and S2, Tables S1 and S2). Atomic van der Waals radii used for Zn, O, N, C, and H were 1.39, 1.52, 1.55, 1.70 and 1.09 Å, respectively [45,46,47]. Lorentz-Berthelot mixing rules were employed to compute the adsorbent-adsorbate and adsorbate-adsorbate interactions. The structure of gas molecules was initially created and optimized at B3LYP/6-311+G(d,p) level, and the atomic charges were extracted using the electrostatic potential (ESP) method (Figure S3, Table S3). Afterward, all gas molecules were parameterized using the general amber force field (GAFF) (Figure S3, Table S3). Quantum mechanics (QM) calculations of atomic charges were performed using the Gaussian 09 program [48], whereas GCMC and MD simulations were carried out using RASPA 2.0 [42].

2.2. GCMC Simulation

To evaluate the adsorption isotherms of pure F2, Cl2, H2S, and SO2 gases at low-pressure, the GCMC method was employed. All the simulations were performed at 293 K [49] and a range of pressure between 0 to 120 kPa. Evaluating the adsorption properties in this condition of low pressure and ambient temperature is highly important. It allows us to characterize the parameters which control the adsorbed gas affinity, such as adsorbent-adsorbate interactions, surface analysis, and porosity [50,51]. The helium (He) void fraction and accessible pore volume of CALF-20 were determined to be 0.35 and 0.22 cm3/g, respectively. Calculation of the He void fraction for CALF-20 was performed using Widom particle insertion, and the resulting value (0.35) was set in the input file for adsorption simulations. Our calculated helium void fraction was comparable with the experimental value of 0.38 [22]. Up to 2.5 × 105 Monte Carlo cycles were set for the adsorption simulations, which consisted of 5 × 104 cycles for the initial equilibrium phase and 2 × 105 cycles for the production phase. This number of cycles was sufficient for initial equilibration and production stages as used in similar works [52,53,54,55]. Each MC sampling move was set by the equal probability of attempting insertions, deletions, rotations, and translations [56]. In addition, as shown in Figures S4 and S5, the average potential energy and the number of adsorbed gases of the equilibrium phases at saturation pressure confirmed that the systems were adequately equilibrated. Each Monte Carlo (MC) move includes an equal probability of translation, rotation, insertion, and deletion. A 12.0 Å cut-off was defined in the RASPA package for the electrostatic and van der Waals interactions. To ensure the accuracy of our modeling for the framework and gas molecules, the adsorption isotherm of nitrogen (N2) gas in CALF-20 was validated with experimental values [22]. Similar to the gases used in this study, the N2 molecule was optimized at B3LYP/6-311+G(d,p) level, and the atomic charges were assigned using the ESP method. The topology for the N2 molecule was also parameterized using the GAFF force field. As depicted in Figure 2, our simulated adsorption isotherm ranging from 0 to 120 kPa is in good agreement with the experimental adsorption isotherm.

2.3. MD Simulation

MD simulations were used to characterize the movement of both polar and non-polar gases within the pores of CALF-20. An equal concentration was adopted for all the gas molecules as 1 mole per unit cell, resulting in a total of 27 moles in the 3 × 3 × 3 frameworks. The distribution of 1-mole gas per unit cell, which means loading at very low pressure, would help us to understand the impact of the CALF-20 pore surface on the gas molecule’s motion (adsorbent-adsorbate) regardless of dominant adsorbate-adsorbate interactions [57,58]. MD simulations were performed at 293 K in a canonical (NVT) ensemble using the Nose-Hoover thermostat. The cut-off was defined as 12 Å for the electrostatic and the van der Waals interactions. Ewald method with a precision of 10−6 was set for computing the long-range electrostatic interactions. A full MD run was comprised of 107 production cycles after accomplishing 104 initialization cycles and 104 equilibration cycles. The time step was set for 0.5 fs, and this resulted in a total of 5 ns of production simulation time. For our particular purpose, the total production MD simulation time is sufficient to generate the slope of mean square displacement (MSD) for gas molecules in porous materials [59,60,61,62]. However, to sample a higher frequency of MSD data during the simulation run, the order-N algorithm with 100 block elements was adopted.

3. Results and Discussion

Many attempts have been made to enlarge the pore size of MOFs with the purpose of greater gas storage [63]. So far, the pore sizes of MOFs have varied from 3 to 100 Å, and the surface area has ranged from 100 to 10,000 m2/g [64]. However, increasing the capability of MOFs for specific and selective gas adsorption required the pore size to be fine-tuned [65]. Fine-tuning MOF pores either by functionalizing the frameworks or selecting a shorter organic linker is beneficial because; (i) they promote the pore’s local charge density, thus making better adsorption at low pressure [66,67], and (ii) they discriminate gas molecules based on their three-dimensional molecular size [68,69]. Evaluation of pore diameter for CALF-20 using Zeo++ showed the largest cavity diameter (LCD) and the pore-limiting diameter (PLD) of 4.3 and 2.8 Å, respectively. The calculated N2 surface area using RASPA was determined to be 317 m2/g at 77 K, which is comparable to the experimental value of 528 m2/g at the same temperature. [22]. The two results from pore diameter and surface area gave us the expectation that CALF-20 has small enough (fine-tuned) pores for the selective adsorption of some toxic gases.

3.1. Adsorption Isotherm

The adsorption isotherms of polar (H2S and SO2) and non-polar (F2 and Cl2) gas molecules in CALF-20 at 293 K are illustrated in Figure 3. The isotherm plots are displayed using a logarithmic scale (log10) on the x-axis for clarification of the adsorptions at very low pressure (Figure 3b). The MOF pores were abruptly filled by SO2 and Cl2 at nearly zero pressure (near 0 kPa). This corresponds to the larger van der Waals surface of SO2 and Cl2 making greater contact with the MOF pore surface, resulting in higher adsorption. It is also noticeable that SO2 and Cl2 plots showed stable progression after about 20 kPa (green and red lines). The plateau state became more evident for SO2 at very low pressure after the log10 plot was drawn. These types of adsorption (having a constant isotherm) indicate that the MOF pores are completely saturated [70,71]. Shimizu et al. [22] acquired high storage of CO2 in CALF-20 at 120 kPa (up to 5.0 mmol/g at 273 K), whereas we have highlighted that CALF-20 has abrupt and selective adsorption for SO2 molecules at 293 K and nearly zero pressure. The difference implies that CO2 adsorption using CALF-20 is dependent on higher pressure (more energy-consuming), whereas SO2 adsorption relies on better fitting into the MOF pores, implying adequate molecular size and geometry. We additionally compare the adsorption isotherms of SO2 in CALF-20 to another framework, ZIF-69 [72]. ZIF-69 pore surface has a similar chemical environment to the CALF-20 pore surface since it is composed of nitrogen-containing rings, four fully coordinated Zn metals, and nitro functional groups. However, ZIF-69 was found to have a larger pore diameter, with an LCD of 8.7 Å and a PLD of 4.9 Å [73], nearly double the values observed in CALF-20. Adsorption isotherms of SO2 in ZIF-69 slightly increased at very low pressure meaning that ZIF-69 had enough empty pore space for higher loading of SO2 gas while the pressure was increasing. The adsorption isotherm for SO2 in ZIF-69 also showed that it reached a saturation loading that was nearly twice as high as that of SO2 in CALF-20, highlighting the difference in pore sizes between the two materials. By this comparison, CALF-20 has again demonstrated a fine-tuned pore size for selective adsorption of SO2 gas.
Meanwhile, F2, with the smallest molecular size, made the lowest amount of loading inside CALF-20 pores. The very slow growth of F2 adsorption at low pressures suggested that CALF-20 should not be used to adsorb and store F2 gas. H2S showed a gradually increased loading suggesting that H2S molecules were adsorbed on the MOF pore surfaces and then accumulated in the pores as the pressure increased [74]. At the end of the simulations, the maximum loading of the gas molecules at 120 kPa was observed in decreasing order of SO2 (2.89 mmol/g) > Cl2 (2.79 mmol/g) > H2S (2.55 mmol/g) > F2 (0.16 mmol/g).

3.2. Radial Distribution Function (RDF)

To study the structural behavior of the different gas species in the system, the radial distribution function (RDF) was calculated using Equation (1).
g ij ( r ) = N ij   ( r ,   r   + Δ r ) V   4 π r 2 Δ r N i   N j  
In this equation, Nij (r, r + Δr) represents the number of particles j around particle i inside the area from r to r + Δr. V and N denote the volume of the system and the number of particles, respectively. Analyzing RDF allowed us to assess the distribution of F2, Cl2, H2S, and SO2 gas molecules on the interaction sites of CALF-20. In general, the highest distribution of gas molecules must follow the adsorbed amount in the CALF-20 pores. The level of distribution for the gas molecules was found in the order of F2 < H2S < Cl2 < SO2 (Figure 4). Since F2 had the least adsorption and more freely moving inside CALF-20 pores, the RDF calculation produced the lowest distribution of this molecule (about ~0.9 g(r)). Zinc and oxygen atoms in the frameworks were found to be the most favorable sites for F2 molecules. In contrast, the distribution g(r) for sulfur atoms in SO2 molecules reached the highest level (about ~3.7 g(r)) when they had interactions with zinc and hydrogen atoms of the framework.
Among the interaction sites in CALF-20, the oxygen atom was the most active site, as it formed the strongest interaction (the shortest distance of distribution) with the gas molecules. This oxygen atom belonged to the oxalate ions, which built a strong coordinative bond with zinc during the later step in the synthesis of CALF-20 (Figure 1). According to the adsorbed amounts and the van der Waals surfaces of F2, Cl2, and H2S, the RDF plots for these gas molecules exhibited a reasonable distribution of oxygen atoms in CALF-20. However, an abnormal RDF plot was seen for the sulfur atom of SO2 gas on oxygen atoms in the framework (Figure 4d). This phenomenon limited the availability of the sulfur atom to interact with oxygen atoms in the framework, which encouraged us to carry out further analysis of adsorbent-adsorbate and adsorbate-adsorbate interaction energies.

3.3. Simulation Snapshot Analysis

The simulation snapshots for the adsorption of the gas molecules F2, Cl2, H2S, and SO2 at 10, 50, and 100 kPa along the Y-axis of CALF-20 are presented in Figure 5a. As illustrated, all gas molecules were contained between the layers of 1,2,4-triazolate-bridged zinc(II). These furrows between the layers are shelved by oxalate ions, which create the active sites for gas molecule adsorption. F2 gas exhibited poor loading between triazolate sheets because of its small van der Waals surface, thus, the least contact with the surface of the pores. It could be seen that the increase in pressure had no significant impact on the adsorption of F2. The framework was also gradually loaded by H2S molecules on oxalate sites by increasing the pressure. In contrast, CALF-20 channels along the y-axis were almost saturated by the accumulation of Cl2 and SO2 gas molecules from 10 to 50 and 100 kPa. By closer exploration of the three-dimensional SO2 packing into CALF-20 pores along the x-axis, it was realized that SO2 molecules were able to construct gas packing through SO-O···SO2 intermolecular interactions since they have angular and polar structure (Figure 5b). The SO2 intermolecular interaction distances between oxygen and sulfur atoms (OSO···SO2) were found to be 3.145 and 3.474 Å in CALF-20 pores, which indicated good agreement with experimental high-resolution SPXRD measurement at 100 kPa and 293 K [75]. Intermolecular interactions of SO2 can be considered as evidence explaining the reduced distribution of sulfur atoms in SO2 molecules on oxygen atoms in the CALF-20 framework (Figure 4d). Nevertheless, this situation was not found for the other types of gases (F2, Cl2, and H2S). To show the effect of intermolecular interactions on the adsorption of all gas molecules in CALF-20, an analysis of interaction energies was carried out.

3.4. Interaction Energies

Figure 6 shows the adsorbent-adsorbate and adsorbate-adsorbate interaction energies at pressures ranging from 0 to 120 kPa at 293 K. The interaction energy was obtained by the sum of van der Waals interactions and Columbic interactions that are governed by atomic charges [76]. According to the plot in Figure 6a, framework-F2 and framework-SO2 interaction energies remained constant throughout, whereas the framework-H2S and framework-Cl2 interaction energies steadily reduced at very low pressure and reached a plateau at a higher pressure. The framework-F2 showed the highest values of interaction energies because the F2 molecule had the least van der Waals surface for the interaction with the framework surface, and the atomic charge was neutralized (no Columbic interactions). On the other hand, the framework-SO2 interaction energies were the lowest values, around −2300 kJ/mol, since the SO2 molecule provided the largest van der Waals surface and the greatest polarity (the strongest columbic interactions). The highest polarity in SO2 is the consequence of uneven charge distribution between oxygen and sulfur atoms (see Table S3 in Supplementary Materials for the values of atomic charges for all gas molecules). These characteristics in the SO2 molecules allowed them to have the strongest chemical affinity and interaction with the surface of CALF-20 pores.
This trend at very low pressure indicates that H2S and Cl2 molecules were not optimally fitted within the MOF pores (lower chemical affinity) and did not make strong interactions with the surface of the pores as compared to SO2 molecules. Although similar trends were observed for adsorbent-adsorbate and adsorbate-adsorbate interaction energies, we realized an interesting point in Figure 6b. When comparing the adsorbate-adsorbate interaction energies, the energy level of F2-F2, Cl2-Cl2, and H2S-H2S intermolecular interactions have consistent gaps. However, the difference in energy level between Cl2-Cl2 and SO2-SO2 intermolecular interactions is almost doubled. Regarding their molecular structure, Cl2 is linear and non-polar, but SO2 is an angular and highly polar molecule that can make tightly packed molecules. The tighter SO2 packing was governed by a considerable difference between the positively charged sulfur atom (+0.62 e) and the negatively charged oxygen atom (−0.31 e) of other SO2 molecules. The angular shape and charge differences between sulfur and oxygen atoms in SO2 led to a stronger attraction via electrostatic interactions among SO2 gas molecules. Therefore, we are convinced that SO2 gas molecules not only built the strongest adsorbent-adsorbate interactions but also had a much tighter gas packing inside CALF-20 pores.

3.5. Henry Coefficient (KH) and Isosteric Heat of Adsorption (Qst)

The Henry coefficient (KH) and the isosteric heat of adsorption (Qst) are useful metrics to measure the strength of chemical affinity of guest molecules in MOFs pores [77,78]. In this study, the KH value for each gas@CALF-20 complex system was calculated using the Widom test particle insertion method at very low pressure, and the results were compiled in Table 1. The KH value can also be used for evaluating the selectivity when it is extracted at low pressure and low concentration [79,80]. The values of KH for the corresponding gas molecules in CALF-20 follow the order of F2 > H2S > Cl2 > SO2. These results conveyed that SO2 molecules were adsorbed on CALF-20′s pore surfaces more than 20 times stronger than Cl2 (22.743/1.018). Using the KH values for each gas species, the separation ability of CALF-20 for binary gas mixture can be assessed using intrinsic thermodynamic selectivity (α) [81,82]. The α values for SO2/H2S, SO2/Cl2, SO2/F2, Cl2/H2S, H2S/F2, and Cl2/F2 mixtures were measured as 163.62, 22.34, 22,743, 7.32, 139, and 1018, respectively. Thus, it is predicted that CALF-20 is highly promising for the separation of SO2/F2 and Cl2/F2 mixtures, contrarily not recommended for Cl2/H2S and SO2/Cl2 mixtures.
The Qst value is an indication of the strength of the interactions between the frameworks and the gas molecules. The higher value of Qst means stronger interaction between the two components. The Qst value can be calculated using Equation (2),
Q st =   RT ( U N ) T , V
where the U/N is calculated as average over configurations; R, T, U, and N are the ideal gas constant, temperature, total energy of the system, and the number of adsorbed molecules, respectively. Although there are many studies in the literature that have reported high values of Qst for the adsorbed gas in different materials [83], we are interested in highlighting the values of Qst for CALF-20 against porous metallocavitand pillarplex (PPX) and a covalent organic framework (COF), COF-10. PPX is formed by pyrazole rings where connected to Gold (Au) metal. The presence of nitrogen atoms in the pyrazole rings of PPX pores provides polar sites, similar to triazole rings in CALF-20. In addition, the cavity diameter in PPX has been reported as 4.3 Å [83], which is equivalent to the LCD in CALF-20 measured by the Zeo++ program. Adsorptions of a wide variety of gas molecules inside the PPX pore were previously studied by computational tools [84]. According to the adsorption isotherms and the Qst, CS2, H2S, NO2, HBr, and Br2 were selected as the highest selective adsorption because of the greatest value of Qst among all gas molecules. Surface area and pore diameter were found to be considerably high in COF-10 (1760 m2/g and 32 Å, respectively) [85] compared to our observation for CALF-20 (317 m2/g and 4.3 Å, respectively). In this regard, Zeng et al. concluded that COF-1 had the highest uptake of H2S and SO2 compared to COF-5, COF-8, and COF-6 due to its largest surface area and pore volume [86]. However, COF-10 had smaller Qst values caused by the differences in the COF’s surface and structure. In addition, the authors stated that COFs such as COF-10 having too large a pore could not be appropriate for high selective adsorption of H2S and SO2 at low pressure. Based on Table 1, the Qst values of CALF-20 indicate that it was capable of adsorption for polar gas molecules due to having a polar surface and capture of non-polar gas molecules by providing small pore volume (high chemical affinity). Therefore, CALF-20 could be considered a highly promising material for separating polar and non-polar molecules. The polarity of a gas molecule is an advantage for higher adsorption due to stronger adsorbate-adsorbate interactions.
When the value of Qst is less than 41.84 kJ/mol, the adsorption forms via physical adsorption (physisorption) [87]; the phenomenon of adsorption of gas molecules (adsorbates) on solid materials (adsorbents) goes through two main mechanisms; chemisorption and physisorption [88]. Chemisorption is accomplished when adsorbates form strong chemical bonds to the active sites of the adsorbent surface, resulting in a unimolecular layer of adsorbates. However, physisorption takes place when adsorbates build weak van der Waals forces on the adsorbent surfaces, resulting in a multilayer of adsorbates. According to Table 1, F2 and H2S gas molecules formed physisorption onto the CALF-20 pore surface. It was found that H2S was adsorbed more than F2 (Figure 3). It is expected that H2S molecules built greater multilayer by weak van der Waals forces. This result could be considered for addressing a common problem in the use of metal oxides such as MgO, Ni-doped MgO, and ZnO to remove and separate H2S as they are irreversible transformation materials due to the strong chemical interactions with H2S [89]. Interestingly, Cl2 in CALF-20 recorded a Qst value on the border (41.84 kJ/mol), which gave the possibility of chemisorption. This could be attributed not only to the highly reactive nature of Cl2 [90] but also to fitting CALF-20 pore size to Cl2 molecules.
Concerning the possibility of chemisorption of Cl2 in CALF-20, Dinca and colleagues proved that Cl2 and Br2 gases made strong chemical bonds on the Co metal sites of MOF-74 [91]. However, the reactions between the Co metals and the halogen gases were reversible as thermal treatment of the MOF led to the breaking of the Co-halogen bonds. Adsorption of SO2 in CALF-20 went through chemisorption, and it probably happened on Zn metal sites, as demonstrated by RDF analysis (Section 3.2). In comparison, in many other frameworks that are constructed by fully coordinated Zn metals, such as MOF-5 [92] and ZIFs [93,94,95], SO2 mostly tends to be physisorbed on the pore surfaces. For example, Yazaydin et al. calculated the values of Qst for SO2 loaded in ZIF-10, ZIF-68, ZIF-69, and ZIF-71 as 26.1, 52.6, 36.7 and 26.0 kJ/mol, respectively, at low pressure and 298 K [72]. As a result, only ZIF-68 was able to provide chemisorption for SO2 due to its appropriate pore size and the presence of -NO2 functional groups. It is important to note that materials such as ZIF-68 and CALF-20, which are suitable platforms for strong adsorption (chemisorption), can be effectively utilized for capturing SO2.

3.6. Mean Square Displacement (MSD)

MD simulations were carried out to elucidate the mobility of the gas molecules in CALF-20 pores [96,97]. All MD simulations were conducted at 293 K in the NVT ensemble, and the resulting trajectories were used to extract the mean square displacement (MSD) of the gas molecules. The values of MSD were computed via the Einstein relationship [98,99] as presented in Equation (3), and they allowed us to express the average distance traveled by the gas molecules.
MSD   ( t ) = 1 N i = 1 N | r i ( t )   r i ( 0 ) | 2
According to Equation (3), N, t, and ri are the number of particles, time, and center-of-mass of the particle i, respectively. The MSD plots for one mole of F2, Cl2, H2S, and SO2 gas per unit cell of CALF-20 (a total of 27 moles in a 3 × 3 × 3 MOF system) are presented in Figure 7, and the calculated slope of MSD (red line) is correlated to the diffusion of the gas molecules. The results from MSD allowed us to measure the self-diffusion coefficient (Ds) using Equation (4) [100]:
D s = 1 2 d   lim Δ t MSD   ( Δ t )
where d is equal to 3 in the case of three-dimensional systems, the highest value of MSD slope belonged to F2 (12.400), and it suggested that F2 molecules were moving freely within the CALF-20 pores. Accordingly, the average area spent by F2 molecules was enhanced up to ~60 Å2. In contrast, the lowest values of the average area were found for Cl2 (~0.6 Å2) and SO2 (~1.0 Å2). The MSD slope for Cl2 and SO2 were recorded as −0.005 and 0.003 (almost zero), respectively. This indicates that Cl2 and SO2 gas had the slowest motion in CALF-20 pores, and they did not considerably change during the 5 ns simulation time. This can be attributed to the tightly fitted Cl2 molecules inside the pores and the strongest polar interactions of SO2. In the case of H2S, the average area value was about ~2.5 Å2 during the simulation time with a steadily increased MSD slope of 0.024. It meant that the mobility of H2S molecules in CALF-20 pores slowly progressed as the simulation time passed. The mobility of the gas molecules in the MOF pores was in the order of F2 > H2S > SO2 > Cl2. Considering the same amount of gas molecules in the framework, the values of self-diffusion coefficient (Ds) were obtained as 2.7, −0.0008, 0.004, and 0.0005 Å2 ns−1 for F2, Cl2, H2S, and SO2, respectively. These values stated that diffusion of F2 gas molecules inside the CALF-20 pores took the largest space at very low pressure, whereas the rest of the gases had much-restricted motion in their position.

4. Conclusions

In this computational study, we have presented an atomic-level understanding of the adsorption of polar (H2S and SO2) and non-polar (F2 and Cl2) toxic gases in CALF-20 at low pressure. GCMC and MD methods were employed to calculate the adsorption isotherms, radial distribution functions, mean square displacements, Henry coefficients, and heat of adsorptions for different systems. The adsorption isotherm showed the highest and constant loading for SO2 and Cl2 gas at low pressure. Gas molecules having larger contact with the framework surface (e.g., SO2 and Cl2) have higher adsorption, with polar molecules such as SO2 showing much higher adsorption due to the strongest adsorbent-adsorbate interactions. This was further confirmed by the highest amount of heat of adsorption obtained for SO2 (45.51 kJ/mol). RDF analysis elucidated that oxygen atoms of the framework belonging to the oxalate component are the most favorable interaction site with all gas species tested. As measured by MSD analysis, smaller and non-polar gas molecules such as F2 (MSD = 12.4 Å2) could not be loaded sufficiently in CALF-20 at low pressure. The adsorption of F2 in CALF-20 was very poor, and the molecules were freely moving in pores since they lacked charge and had not had enough contact surfaces with the framework. Based on the results, we have determined CALF-20 as a highly potential material for selective adsorption of SO2 and Cl2 at low pressure.

Supplementary Materials

All materials are included in the Supplementary Materials file, available online at, Figure S1: The first cluster used for CHelpG charges calculation; Figure S2: The second cluster used for CHelpG charges calculation; Figure S3: Optimized structure of the gas molecules; Figure S4: Plots for potential energy of the systems; Figure S5: Plots for number adsorbed gases; Table S1: The values for the atomic charges and the LJ potential parameters; Table S2: The values for the atomic charges and the LJ potential parameters; Table S3: The values for the atomic charges and the LJ potential parameters.

Author Contributions

Conceptualization, M.A.M.L., M.N.J., M.Y.B., E.A. and M.B.A.R.; formal analysis, M.Y.B., M.N.J. and M.A.M.L.; investigation, M.Y.B., M.N.J. and M.A.M.L.; resources, M.A.M.L. and M.B.A.R.; data curation, M.Y.B.; writing—original draft preparation, M.Y.B.; writing—review and editing, M.Y.B., M.N.J., E.A., M.B.A.R. and M.A.M.L.; visualization, M.Y.B.; supervision, M.A.M.L., E.A. and M.B.A.R.; project administration, M.A.M.L.; funding acquisition, M.A.M.L. All authors have read and agreed to the published version of the manuscript.


The authors would like to acknowledge the Ministry of Education (MOE) Malaysia. This research is supported by the Ministry of Education (MOE) Malaysia through Fundamental Research Grant Scheme (FRGS/1/2020/STG04/UPM/02/9).

Data Availability Statement

The datasets generated during the current study are available from the corresponding author at a reasonable request.

Conflicts of Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.


  1. Yu, J.; Xie, L.-H.; Li, J.-R.; Ma, Y.; Seminario, J.M.; Balbuena, P.B. CO2 capture and separations using MOFs: Computational and experimental studies. Chem. Rev. 2017, 117, 9674–9754. [Google Scholar] [CrossRef]
  2. Wang, T.C.; Bury, W.; Gómez-Gualdrón, D.A.; Vermeulen, N.A.; Mondloch, J.E.; Deria, P.; Zhang, K.; Moghadam, P.Z.; Sarjeant, A.A.; Snurr, R.Q. Ultrahigh surface area zirconium MOFs and insights into the applicability of the BET theory. J. Am. Chem. Soc. 2015, 137, 3585–3591. [Google Scholar] [CrossRef]
  3. Gao, Y.; Zhang, M.; Chen, C.; Zhang, Y.; Gu, Y.; Wang, Q.; Zhang, W.; Pan, Y.; Ma, J.; Bai, J. A low symmetry cluster meets a low symmetry ligand to sharply boost MOF thermal stability. Chem. Commun. 2020, 56, 11985–11988. [Google Scholar] [CrossRef]
  4. Xu, W.; Zhang, Y.; Wang, J.; Xu, Y.; Bian, L.; Ju, Q.; Wang, Y.; Fang, Z. Defects engineering simultaneously enhances activity and recyclability of MOFs in selective hydrogenation of biomass. Nat. Commun. 2022, 13, 2068. [Google Scholar] [CrossRef] [PubMed]
  5. Moosavi, S.M.; Nandy, A.; Jablonka, K.M.; Ongari, D.; Janet, J.P.; Boyd, P.G.; Lee, Y.; Smit, B.; Kulik, H.J. Understanding the diversity of the metal-organic framework ecosystem. Nat. Commun. 2020, 11, 4068. [Google Scholar] [CrossRef]
  6. Zhu, J.; Chen, X.; Thang, A.Q.; Li, F.; Chen, D.; Geng, H.; Rui, X.; Yan, Q. Vanadium-based metal-organic frameworks and their derivatives for electrochemical energy conversion and storage. SmartMat 2022, 3, 384–416. [Google Scholar] [CrossRef]
  7. Haldar, D.; Duarah, P.; Purkait, M.K. MOFs for the treatment of arsenic, fluoride and iron contaminated drinking water: A review. Chemosphere 2020, 251, 126388. [Google Scholar] [CrossRef]
  8. Zhu, L.; Liu, X.-Q.; Jiang, H.-L.; Sun, L.-B. Metal–organic frameworks for heterogeneous basic catalysis. Chem. Rev. 2017, 117, 8129–8176. [Google Scholar] [CrossRef]
  9. Lismont, M.; Dreesen, L.; Wuttke, S. Metal-organic framework nanoparticles in photodynamic therapy: Current status and perspectives. Adv. Funct. Mater. 2017, 27, 1606314. [Google Scholar] [CrossRef]
  10. Lázaro, I.A.; Forgan, R.S. Application of zirconium MOFs in drug delivery and biomedicine. Coord. Chem. Rev. 2019, 380, 230–259. [Google Scholar] [CrossRef] [Green Version]
  11. Szczęśniak, B.; Choma, J.; Jaroniec, M. Gas adsorption properties of hybrid graphene-MOF materials. J. Colloid Interface Sci. 2018, 514, 801–813. [Google Scholar] [CrossRef]
  12. Petit, C. Present and future of MOF research in the field of adsorption and molecular separation. Curr. Opin. Chem. Eng. 2018, 20, 132–142. [Google Scholar] [CrossRef]
  13. Ghanbari, T.; Abnisa, F.; Daud, W.M.A.W. A review on production of metal organic frameworks (MOF) for CO2 adsorption. Sci. Total Environ. 2020, 707, 135090. [Google Scholar] [CrossRef]
  14. Li, J.-R.; Kuppler, R.J.; Zhou, H.-C. Selective gas adsorption and separation in metal–organic frameworks. Chem. Soc. Rev. 2009, 38, 1477–1504. [Google Scholar] [CrossRef] [PubMed]
  15. Qin, L.; Li, Y.; Liang, F.; Li, L.; Lan, Y.; Li, Z.; Lu, X.; Yang, M.; Ma, D. A microporous 2D cobalt-based MOF with pyridyl sites and open metal sites for selective adsorption of CO2. Microporous Mesoporous Mater. 2022, 341, 112098. [Google Scholar] [CrossRef]
  16. Liu, J.; Wang, W.; Luo, Z.; Li, B.; Yuan, D. Microporous metal–organic framework based on ligand-truncation strategy with high performance for gas adsorption and separation. Inorg. Chem. 2017, 56, 10215–10219. [Google Scholar] [CrossRef] [PubMed]
  17. Liu, J.; Liu, G.; Gu, C.; Liu, W.; Xu, J.; Li, B.; Wang, W. Rational synthesis of a novel 3,3,5-c polyhedral metal–organic framework with high thermal stability and hydrogen storage capability. J. Mater. Chem. A 2016, 4, 11630–11634. [Google Scholar] [CrossRef]
  18. Kong, X.-J.; Zhang, Y.-Z.; He, T.; Wu, X.-Q.; Xu, M.-M.; Wang, S.-N.; Xie, L.-H.; Li, J.-R. Two interpenetrated metal–organic frameworks with a slim ethynyl-based ligand: Designed for selective gas adsorption and structural tuning. CrystEngComm 2018, 20, 6018–6025. [Google Scholar] [CrossRef]
  19. Zheng, B.; Luo, X.; Wang, Z.; Zhang, S.; Yun, R.; Huang, L.; Zeng, W.; Liu, W. An unprecedented water stable acylamide-functionalized metal–organic framework for highly efficient CH4/CO2 gas storage/separation and acid–base cooperative catalytic activity. Inorg. Chem. Front. 2018, 5, 2355–2363. [Google Scholar] [CrossRef]
  20. Cai, Y.; Zou, L.; Ji, Q.; Yong, J.; Qian, X.; Gao, J. Two dimensional Ti-based metal-organic framework with polar oxygen atoms on the pore surface for efficient gas separation. Polyhedron 2020, 190, 114771. [Google Scholar] [CrossRef]
  21. Teo, W.L.; Zhou, W.; Qian, C.; Zhao, Y. Industrializing metal–organic frameworks: Scalable synthetic means and their transformation into functional materials. Mater. Today 2021, 47, 170–186. [Google Scholar] [CrossRef]
  22. Lin, J.-B.; Nguyen, T.T.T.; Vaidhyanathan, R.; Burner, J.; Taylor, J.M.; Durekova, H.; Akhtar, F.; Mah, R.K.; Ghaffari-Nik, O.; Marx, S. A scalable metal-organic framework as a durable physisorbent for carbon dioxide capture. Science 2021, 374, 1464–1469. [Google Scholar] [CrossRef] [PubMed]
  23. Czaja, A.U.; Trukhan, N.; Müller, U. Industrial applications of metal–organic frameworks. Chem. Soc. Rev. 2009, 38, 1284–1293. [Google Scholar] [CrossRef] [PubMed]
  24. Julien, P.A.; Mottillo, C.; Friščić, T. Metal–organic frameworks meet scalable and sustainable synthesis. Green Chem. 2017, 19, 2729–2747. [Google Scholar] [CrossRef]
  25. Nguyen, T.T.T.; Lin, J.-B.; Shimizu, G.K.H.; Rajendran, A. Separation of CO2 and N2 on a hydrophobic metal organic framework CALF-20. Chem. Eng. J. 2022, 442, 136263. [Google Scholar] [CrossRef]
  26. Barea, E.; Montoro, C.; Navarro, J.A.R. Toxic gas removal–metal–organic frameworks for the capture and degradation of toxic gases and vapours. Chem. Soc. Rev. 2014, 43, 5419–5430. [Google Scholar] [CrossRef]
  27. Korica, M.; Balić, I.; van Wyk, L.M.; van Heerden, D.P.; Nikolayenko, V.I.; Barbour, L.J.; Jednačak, T.; Đilović, I.; Balić, T. Inclusion of CO2, NH3, SO2, Cl2 and H2S in porous N4O4-donor macrocyclic Schiff base. Microporous Mesoporous Mater. 2022, 332, 111708. [Google Scholar] [CrossRef]
  28. Fuge, R. Sources of halogens in the environment, influences on human and animal health. Environ. Geochem. Health 1988, 10, 51–61. [Google Scholar] [CrossRef]
  29. Pena-Pereira, F.; García-Figueroa, A.; Lavilla, I.; Bendicho, C. Nanomaterials for the detection of halides and halogen oxyanions by colorimetric and luminescent techniques: A critical overview. Trac Trends Anal. Chem. 2020, 125, 115837. [Google Scholar] [CrossRef]
  30. Tian, K.; Wang, X.-X.; Yu, Z.-Y.; Li, H.-Y.; Guo, X. Hierarchical and hollow Fe2O3 nanoboxes derived from metal–organic frameworks with excellent sensitivity to H2S. ACS Appl. Mater. Interfaces 2017, 9, 29669–29676. [Google Scholar] [CrossRef]
  31. Dong, X.; Su, Y.; Lu, T.; Zhang, L.; Wu, L.; Lv, Y. MOFs-derived dodecahedra porous Co3O4: An efficient cataluminescence sensing material for H2S. Sens. Actuators B Chem. 2018, 258, 349–357. [Google Scholar] [CrossRef]
  32. Yang, X.-F.; Zhu, H.-B.; Liu, M. Transition-metal-based (Zn2+ and Cd2+) metal-organic frameworks as fluorescence “turn-off” sensors for highly sensitive and selective detection of hydrogen sulfide. Inorg. Chim. Acta 2017, 466, 410–416. [Google Scholar] [CrossRef]
  33. Vikrant, K.; Kailasa, S.K.; Tsang, D.C.W.; Lee, S.S.; Kumar, P.; Giri, B.S.; Singh, R.S.; Kim, K.-H. Biofiltration of hydrogen sulfide: Trends and challenges. J. Clean. Prod. 2018, 187, 131–147. [Google Scholar] [CrossRef]
  34. Liu, D.; Quan, X.; Zhou, L.; Huang, Q.; Wang, C. Utilization of waste concrete powder with different particle size as absorbents for SO2 reduction. Constr. Build. Mater. 2021, 266, 121005. [Google Scholar] [CrossRef]
  35. Carter, J.H.; Han, X.; Moreau, F.Y.; Da Silva, I.; Nevin, A.; Godfrey, H.G.W.; Tang, C.C.; Yang, S.; Schröder, M. Exceptional adsorption and binding of sulfur dioxide in a robust zirconium-based metal–organic framework. J. Am. Chem. Soc. 2018, 140, 15564–15567. [Google Scholar] [CrossRef]
  36. Chen, X.; Shen, B.; Sun, H. Ion-exchange modified zeolites X for selective adsorption desulfurization from Claus tail gas: Experimental and computational investigations. Microporous Mesoporous Mater. 2018, 261, 227–236. [Google Scholar] [CrossRef]
  37. Li, J.; Kang, Y.; Li, B.; Wang, X.; Li, D. PEG-linked functionalized dicationic ionic liquids for highly efficient SO2 capture through physical absorption. Energy Fuels 2018, 32, 12703–12710. [Google Scholar] [CrossRef]
  38. Xing, S.; Liang, J.; Brandt, P.; Schäfer, F.; Nuhnen, A.; Heinen, T.; Boldog, I.; Möllmer, J.; Lange, M.; Weingart, O. Capture and Separation of SO2 Traces in Metal–Organic Frameworks via Pre-Synthetic Pore Environment Tailoring by Methyl Groups. Angew. Chem. Int. Ed. 2021, 60, 17998–18005. [Google Scholar] [CrossRef]
  39. Brandt, P.; Nuhnen, A.; Lange, M.; Möllmer, J.; Weingart, O.; Janiak, C. Metal–organic frameworks with potential application for SO2 separation and flue gas desulfurization. ACS Appl. Mater. Interfaces 2019, 11, 17350–17358. [Google Scholar] [CrossRef]
  40. Rodríguez-Albelo, L.M.; López-Maya, E.; Hamad, S.; Ruiz-Salvador, A.R.; Calero, S.; Navarro, J.A.R. Selective sulfur dioxide adsorption on crystal defect sites on an isoreticular metal organic framework series. Nat. Commun. 2017, 8, 14457. [Google Scholar] [CrossRef] [Green Version]
  41. Willems, T.F.; Rycroft, C.H.; Kazi, M.; Meza, J.C.; Haranczyk, M. Algorithms and tools for high-throughput geometry-based analysis of crystalline porous materials. Microporous Mesoporous Mater. 2012, 149, 134–141. [Google Scholar] [CrossRef]
  42. Dubbeldam, D.; Calero, S.; Ellis, D.E.; Snurr, R.Q. RASPA: Molecular simulation software for adsorption and diffusion in flexible nanoporous materials. Mol. Simul. 2016, 42, 81–101. [Google Scholar] [CrossRef]
  43. Rappé, A.K.; Casewit, C.J.; Colwell, K.S.; Goddard III, W.A.; Skiff, W.M. UFF, a full periodic table force field for molecular mechanics and molecular dynamics simulations. J. Am. Chem. Soc. 1992, 114, 10024–10035. [Google Scholar] [CrossRef]
  44. Mayo, S.L.; Olafson, B.D.; Goddard, W.A. DREIDING: A generic force field for molecular simulations. J. Phys. Chem. 1990, 94, 8897–8909. [Google Scholar] [CrossRef]
  45. Bondi, A. van van der Waals volumes and radii. J. Phys. Chem. 1964, 68, 441–451. [Google Scholar] [CrossRef]
  46. Boyd, P.G.; Moosavi, S.M.; Witman, M.; Smit, B. Force-field prediction of materials properties in metal-organic frameworks. J. Phys. Chem. Lett. 2017, 8, 357–363. [Google Scholar] [CrossRef]
  47. Bristow, J.K.; Tiana, D.; Walsh, A. Transferable force field for metal–organic frameworks from first-principles: BTW-FF. J. Chem. Theory Comput. 2014, 10, 4644–4652. [Google Scholar] [CrossRef] [PubMed]
  48. Frisch, M.J.; Trucks, G.W.; Schlegel, H.B.; Scuseria, G.E.; Robb, M.A.; Cheeseman, J.R.; Scalmani, G.; Barone, V.; Mennucci, B.; Petersson, G.A. Gaussian, 09 Program; Gaussian Inc.: Wallingford, CT, USA, 2009. [Google Scholar]
  49. Savage, M.; Yang, S.; Suyetin, M.; Bichoutskaia, E.; Lewis, W.; Blake, A.J.; Barnett, S.A.; Schröder, M. A Novel Bismuth-Based Metal–Organic Framework for High Volumetric Methane and Carbon Dioxide Adsorption. Chem. Eur. J. 2014, 20, 8024–8029. [Google Scholar] [CrossRef]
  50. Burtch, N.C.; Jasuja, H.; Dubbeldam, D.; Walton, K.S. Molecular-level insight into unusual low pressure CO2 affinity in pillared metal–organic frameworks. J. Am. Chem. Soc. 2013, 135, 7172–7180. [Google Scholar] [CrossRef]
  51. Brandt, P.; Xing, S.-H.; Liang, J.; Kurt, G.; Nuhnen, A.; Weingart, O.; Janiak, C. Zirconium and Aluminum MOFs for Low-Pressure SO2 Adsorption and Potential Separation: Elucidating the Effect of Small Pores and NH2 Groups. ACS Appl. Mater. Interfaces 2021, 13, 29137–29149. [Google Scholar] [CrossRef]
  52. Xia, X.; Hu, G.; Li, W.; Li, S. Understanding reduced CO2 uptake of ionic liquid/metal–organic framework (IL/MOF) composites. ACS Appl. Nano Mater. 2019, 2, 6022–6029. [Google Scholar] [CrossRef]
  53. Anderson, R.; Schweitzer, B.; Wu, T.; Carreon, M.A.; Gómez-Gualdrón, D.A. Molecular simulation insights on Xe/Kr separation in a set of nanoporous crystalline membranes. ACS Appl. Mater. Interfaces 2018, 10, 582–592. [Google Scholar] [CrossRef] [PubMed]
  54. Avci, G.; Velioglu, S.; Keskin, S. High-throughput screening of MOF adsorbents and membranes for H2 purification and CO2 capture. ACS Appl. Mater. Interfaces 2018, 10, 33693–33706. [Google Scholar] [CrossRef]
  55. Qian, J.; Chen, G.; Xiao, S.; Li, H.; Ouyang, Y.; Wang, Q. Switching Xe/Kr adsorption selectivity in modified SBMOF-1: A theoretical study. RSC Adv. 2020, 10, 17195–17204. [Google Scholar] [CrossRef] [PubMed]
  56. Rogge, S.M.J.; Goeminne, R.; Demuynck, R.; Gutiérrez-Sevillano, J.J.; Vandenbrande, S.; Vanduyfhuys, L.; Waroquier, M.; Verstraelen, T.; Van Speybroeck, V. Modeling Gas Adsorption in Flexible Metal–Organic Frameworks via Hybrid Monte Carlo/Molecular Dynamics Schemes. Adv. Theory Simul. 2019, 2, 1800177. [Google Scholar] [CrossRef]
  57. Seehamart, K.; Nanok, T.; Kärger, J.; Chmelik, C.; Krishna, R.; Fritzsche, S. Investigating the reasons for the significant influence of lattice flexibility on self-diffusivity of ethane in Zn (tbip). Microporous Mesoporous Mater. 2010, 130, 92–96. [Google Scholar] [CrossRef]
  58. De Toni, M.; Jonchiere, R.; Pullumbi, P.; Coudert, F.; Fuchs, A.H. How can a hydrophobic MOF be water-unstable? Insight into the hydration mechanism of IRMOFs. ChemPhysChem 2012, 13, 3497–3503. [Google Scholar] [CrossRef]
  59. Polat, H.M.; Zeeshan, M.; Uzun, A.; Keskin, S. Unlocking CO2 separation performance of ionic liquid/CuBTC composites: Combining experiments with molecular simulations. Chem. Eng. J. 2019, 373, 1179–1189. [Google Scholar] [CrossRef]
  60. Altundal, O.F.; Altintas, C.; Keskin, S. Can COFs replace MOFs in flue gas separation? high-throughput computational screening of COFs for CO2/N2 separation. J. Mater. Chem. A 2020, 8, 14609–14623. [Google Scholar] [CrossRef]
  61. Luna-Triguero, A.; Sławek, A.; Sánchez-de-Armas, R.; Gutiérrez-Sevillano, J.J.; Ania, C.O.; Parra, J.B.; Vicent-Luna, J.M.; Calero, S. π-Complexation for olefin/paraffin separation using aluminosilicates. Chem. Eng. J. 2020, 380, 122482. [Google Scholar] [CrossRef]
  62. Altintas, C.; Avci, G.; Daglar, H.; Gulcay, E.; Erucar, I.; Keskin, S. Computer simulations of 4240 MOF membranes for H2/CH4 separations: Insights into structure–performance relations. J. Mater. Chem. A 2018, 6, 5836–5847. [Google Scholar] [CrossRef] [PubMed]
  63. Fan, W.; Zhang, X.; Kang, Z.; Liu, X.; Sun, D. Isoreticular chemistry within metal–organic frameworks for gas storage and separation. Coord. Chem. Rev. 2021, 443, 213968. [Google Scholar] [CrossRef]
  64. Li, H.; Li, L.; Lin, R.-B.; Zhou, W.; Zhang, Z.; Xiang, S.; Chen, B. Porous metal-organic frameworks for gas storage and separation: Status and challenges. EnergyChem 2019, 1, 100006. [Google Scholar] [CrossRef]
  65. Xue, D.-X.; Belmabkhout, Y.; Shekhah, O.; Jiang, H.; Adil, K.; Cairns, A.J.; Eddaoudi, M. Tunable rare earth fcu-MOF platform: Access to adsorption kinetics driven gas/vapor separations via pore size contraction. J. Am. Chem. Soc. 2015, 137, 5034–5040. [Google Scholar] [CrossRef]
  66. Nugent, P.; Belmabkhout, Y.; Burd, S.D.; Cairns, A.J.; Luebke, R.; Forrest, K.; Pham, T.; Ma, S.; Space, B.; Wojtas, L. Porous materials with optimal adsorption thermodynamics and kinetics for CO2 separation. Nature 2013, 495, 80–84. [Google Scholar] [CrossRef] [PubMed]
  67. Mohideen, M.I.H.; Pillai, R.S.; Adil, K.; Bhatt, P.M.; Belmabkhout, Y.; Shkurenko, A.; Maurin, G.; Eddaoudi, M. A fine-tuned MOF for gas and vapor separation: A multipurpose adsorbent for acid gas removal, dehydration, and BTX sieving. Chem 2017, 3, 822–833. [Google Scholar] [CrossRef]
  68. Li, K.; Olson, D.H.; Seidel, J.; Emge, T.J.; Gong, H.; Zeng, H.; Li, J. Zeolitic imidazolate frameworks for kinetic separation of propane and propene. J. Am. Chem. Soc. 2009, 131, 10368–10369. [Google Scholar] [CrossRef]
  69. Cai, J.; Yu, J.; Xu, H.; He, Y.; Duan, X.; Cui, Y.; Wu, C.; Chen, B.; Qian, G. A doubly interpenetrated metal–organic framework with open metal sites and suitable pore sizes for highly selective separation of small hydrocarbons at room temperature. Cryst. Growth Des. 2013, 13, 2094–2097. [Google Scholar] [CrossRef]
  70. Cho, K.H.; Borges, D.D.; Lee, U.; Lee, J.S.; Yoon, J.W.; Cho, S.J.; Park, J.; Lombardo, W.; Moon, D.; Sapienza, A. Rational design of a robust aluminum metal-organic framework for multi-purpose water-sorption-driven heat allocations. Nat. Commun. 2020, 11, 5112. [Google Scholar] [CrossRef]
  71. Hanikel, N.; Prévot, M.S.; Fathieh, F.; Kapustin, E.A.; Lyu, H.; Wang, H.; Diercks, N.J.; Glover, T.G.; Yaghi, O.M. Rapid cycling and exceptional yield in a metal-organic framework water harvester. ACS Cent. Sci. 2019, 5, 1699–1706. [Google Scholar] [CrossRef] [PubMed]
  72. Ding, L.; Yazaydin, A.O. The effect of SO2 on CO2 capture in zeolitic imidazolate frameworks. Phys. Chem. Chem. Phys. 2013, 15, 11856–11861. [Google Scholar] [CrossRef] [PubMed]
  73. Canturk, B.; Kurt, A.S.; Gurdal, Y. Models used for permeability predictions of nanoporous materials revisited for H2/CH4 and H2/CO2 mixtures. Sep. Purif. Technol. 2022, 297, 121463. [Google Scholar] [CrossRef]
  74. Liu, Y.; Ma, X.; Li, H.A.; Hou, J. Competitive adsorption behavior of hydrocarbon(s)/CO2 mixtures in a double-nanopore system using molecular simulations. Fuel 2019, 252, 612–621. [Google Scholar] [CrossRef]
  75. Li, L.; Da Silva, I.; Kolokolov, D.I.; Han, X.; Li, J.; Smith, G.; Cheng, Y.; Daemen, L.L.; Morris, C.G.; Godfrey, H.G.W. Post-synthetic modulation of the charge distribution in a metal–organic framework for optimal binding of carbon dioxide and sulfur dioxide. Chem. Sci. 2019, 10, 1472–1482. [Google Scholar] [CrossRef]
  76. Borzehandani, M.Y.; Abdulmalek, E.; Abdul Rahman, M.B.; Latif, M.A.M. Elucidating the Aromatic Properties of Covalent Organic Frameworks Surface for Enhanced Polar Solvent Adsorption. Polymers 2021, 13, 1861. [Google Scholar] [CrossRef] [PubMed]
  77. Kareem, F.A.A.; Shariff, A.M.; Ullah, S.; Mellon, N.; Keong, L.K. Adsorption of pure and predicted binary (CO2:CH4) mixtures on 13X-Zeolite: Equilibrium and kinetic properties at offshore conditions. Microporous Mesoporous Mater. 2018, 267, 221–234. [Google Scholar] [CrossRef]
  78. Hefti, M.; Marx, D.; Joss, L.; Mazzotti, M. Adsorption equilibrium of binary mixtures of carbon dioxide and nitrogen on zeolites ZSM-5 and 13X. Microporous Mesoporous Mater. 2015, 215, 215–228. [Google Scholar] [CrossRef]
  79. Saha, D.; Bao, Z.; Jia, F.; Deng, S. Adsorption of CO2, CH4, N2O, and N2 on MOF-5, MOF-177, and zeolite 5A. Environ. Sci. Technol. 2010, 44, 1820–1826. [Google Scholar] [CrossRef]
  80. Moghadam, P.Z.; Fairen-Jimenez, D.; Snurr, R.Q. Efficient identification of hydrophobic MOFs: Application in the capture of toxic industrial chemicals. J. Mater. Chem. A 2016, 4, 529–536. [Google Scholar] [CrossRef]
  81. Wu, X.; Shahrak, M.N.; Yuan, B.; Deng, S. Synthesis and characterization of zeolitic imidazolate framework ZIF-7 for CO2 and CH4 separation. Microporous Mesoporous Mater. 2014, 190, 189–196. [Google Scholar] [CrossRef]
  82. Zacharia, R.; Gomez, L.F.; Chahine, R.; Cossement, D.; Benard, P. Thermodynamics and kinetics of CH4/CO2 binary mixture separation by metal-organic frameworks from isotope exchange and adsorption break-through. Microporous Mesoporous Mater. 2018, 263, 165–172. [Google Scholar] [CrossRef]
  83. Martínez-Ahumada, E.; He, D.; Berryman, V.; López-Olvera, A.; Hernandez, M.; Jancik, V.; Martis, V.; Vera, M.A.; Lima, E.; Parker, D.J. SO2 capture using porous organic cages. Angew. Chem. Int. Ed. 2021, 60, 17556–17563. [Google Scholar] [CrossRef] [PubMed]
  84. Mohanty, B.; Venkataramanan, N.S. Sustainable metallocavitand for flue gas-selective sorption: A multiscale study. J. Phys. Chem. C 2019, 123, 3188–3202. [Google Scholar] [CrossRef]
  85. Furukawa, H.; Yaghi, O.M. Storage of hydrogen, methane, and carbon dioxide in highly porous covalent organic frameworks for clean energy applications. J. Am. Chem. Soc. 2009, 131, 8875–8883. [Google Scholar] [CrossRef]
  86. Wang, H.; Zeng, X.; Wang, W.; Cao, D. Selective capture of trace sulfur gas by porous covalent-organic materials. Chem. Eng. Sci. 2015, 135, 373–380. [Google Scholar] [CrossRef]
  87. Zhang, J.; Wang, J.; Zhang, C.; Li, Z.; Zhu, J.; Lu, B. Molecular simulation of gases competitive adsorption in lignite and analysis of original CO desorption. Sci. Rep. 2021, 11, 11706. [Google Scholar] [CrossRef] [PubMed]
  88. Ramanayaka, S.; Vithanage, M.; Sarmah, A.; An, T.; Kim, K.-H.; Ok, Y.S. Performance of metal–organic frameworks for the adsorptive removal of potentially toxic elements in a water system: A critical review. RSC Adv. 2019, 9, 34359–34376. [Google Scholar] [CrossRef] [PubMed]
  89. Rodriguez, J.A.; Maiti, A. Adsorption and decomposition of H2S on MgO (100), NiMgO (100), and ZnO (0001) surfaces: A first-principles density functional study. J. Phys. Chem. B 2000, 104, 3630–3638. [Google Scholar] [CrossRef]
  90. Britt, D.; Tranchemontagne, D.; Yaghi, O.M. Metal-organic frameworks with high capacity and selectivity for harmful gases. Proc. Natl. Acad. Sci. USA 2008, 105, 11623–11627. [Google Scholar] [CrossRef]
  91. Tulchinsky, Y.; Hendon, C.H.; Lomachenko, K.A.; Borfecchia, E.; Melot, B.C.; Hudson, M.R.; Tarver, J.D.; Korzyński, M.D.; Stubbs, A.W.; Kagan, J.J. Reversible capture and release of Cl2 and Br2 with a redox-active metal–organic framework. J. Am. Chem. Soc. 2017, 139, 5992–5997. [Google Scholar] [CrossRef] [Green Version]
  92. Tranchemontagne, D.J.; Hunt, J.R.; Yaghi, O.M. Room temperature synthesis of metal-organic frameworks: MOF-5, MOF-74, MOF-177, MOF-199, and IRMOF-0. Tetrahedron 2008, 64, 8553–8557. [Google Scholar] [CrossRef]
  93. Lai, L.S.; Yeong, Y.F.; Ani, N.C.; Lau, K.K.; Shariff, A.M. Effect of synthesis parameters on the formation of zeolitic imidazolate framework 8 (ZIF-8) nanoparticles for CO2 adsorption. Part. Sci. Technol. 2014, 32, 520–528. [Google Scholar] [CrossRef]
  94. Åhlén, M.; Jaworski, A.; Strømme, M.; Cheung, O. Selective adsorption of CO2 and SF6 on mixed-linker ZIF-7–8s: The effect of linker substitution on uptake capacity and kinetics. Chem. Eng. J. 2021, 422, 130117. [Google Scholar] [CrossRef]
  95. Lgaz, H.; Lee, H. Computational investigation on interaction mechanism of sulfur mustard adsorption by zeolitic imidazolate frameworks ZIF-8 and ZIF-67: Insights from periodic and cluster DFT calculations. J. Mol. Liq. 2021, 344, 117705. [Google Scholar] [CrossRef]
  96. Amirjalayer, S.; Tafipolsky, M.; Schmid, R. Molecular dynamics simulation of benzene diffusion in mof-5: Importance of lattice dynamics. Angew. Chem. Int. Ed. 2007, 46, 463–466. [Google Scholar] [CrossRef]
  97. Farzi, N.; Salehi, N.; Mahboubi, A. Molecular dynamics simulation of acetylene diffusion in MOF-508a and MOF-508b. Microporous Mesoporous Mater. 2017, 248, 246–255. [Google Scholar] [CrossRef]
  98. Allen, M.P.; Tildesley, D.J. Computer Simulation of Liquids; Oxford University Press: Oxford, UK, 2017; ISBN 0192524704. [Google Scholar]
  99. Mongalo, L.; Lopis, A.S.; Venter, G.A. Molecular dynamics simulations of the structural properties and electrical conductivities of CaO–MgO–Al2O3–SiO2 melts. J. Non. Cryst. Solids 2016, 452, 194–202. [Google Scholar] [CrossRef]
  100. Wang, S.; Zhou, G.; Sun, Y.; Huang, L. A computational study of water in UiO-66 Zr-MOFs: Diffusion, hydrogen bonding network, and confinement effect. AIChE J. 2021, 67, e17035. [Google Scholar] [CrossRef]
Figure 1. Schematic diagram for the synthesis of CALF-20.
Figure 1. Schematic diagram for the synthesis of CALF-20.
Polymers 15 00760 g001
Figure 2. Comparison of experimental [22] and simulated adsorption isotherms of N2 in CALF-20.
Figure 2. Comparison of experimental [22] and simulated adsorption isotherms of N2 in CALF-20.
Polymers 15 00760 g002
Figure 3. Simulated adsorption isotherms of gas molecules in CALF-20 MOF: (a) linear plot and (b) log10 plot. The square symbols represent the adsorption isotherms of SO2 in ZIF-69 [72].
Figure 3. Simulated adsorption isotherms of gas molecules in CALF-20 MOF: (a) linear plot and (b) log10 plot. The square symbols represent the adsorption isotherms of SO2 in ZIF-69 [72].
Polymers 15 00760 g003
Figure 4. Radial distribution plots for (a) F2, (b) Cl2, (c) H2S, and (d) SO2 gases in CALF-20.
Figure 4. Radial distribution plots for (a) F2, (b) Cl2, (c) H2S, and (d) SO2 gases in CALF-20.
Polymers 15 00760 g004
Figure 5. (a) Simulation snapshots of F2, Cl2, H2S, and SO2 adsorption in CALF-20 framework at 10, 50, and 100 kPa as visualized along the Y-axis, (b) magnified SO2 packing in CALF-20 pores, presented along X-axis of the framework.
Figure 5. (a) Simulation snapshots of F2, Cl2, H2S, and SO2 adsorption in CALF-20 framework at 10, 50, and 100 kPa as visualized along the Y-axis, (b) magnified SO2 packing in CALF-20 pores, presented along X-axis of the framework.
Polymers 15 00760 g005
Figure 6. Interaction energy for (a) adsorbent-adsorbate and (b) adsorbate-adsorbate.
Figure 6. Interaction energy for (a) adsorbent-adsorbate and (b) adsorbate-adsorbate.
Polymers 15 00760 g006
Figure 7. Mean square displacements for (a) F2, (b) Cl2, (c) H2S, and (d) SO2 in CALF-20 during 5 ns of MD simulations.
Figure 7. Mean square displacements for (a) F2, (b) Cl2, (c) H2S, and (d) SO2 in CALF-20 during 5 ns of MD simulations.
Polymers 15 00760 g007
Table 1. The values for Henry coefficient (KH) and isosteric heat of adsorption (Qst).
Table 1. The values for Henry coefficient (KH) and isosteric heat of adsorption (Qst).
GasKH CALF-20Qst PPX 1Qst COF-10 2Qst CALF-20 3
KH: mol/kg/kPa and Qst: kJ/mol; 1 100 kPa 298 K, 2 100 kPa 303 K, 3 100 kPa 293 K.
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Borzehandani, M.Y.; Jorabchi, M.N.; Abdulmalek, E.; Abdul Rahman, M.B.; Mohammad Latif, M.A. Exploring the Potential of a Highly Scalable Metal-Organic Framework CALF-20 for Selective Gas Adsorption at Low Pressure. Polymers 2023, 15, 760.

AMA Style

Borzehandani MY, Jorabchi MN, Abdulmalek E, Abdul Rahman MB, Mohammad Latif MA. Exploring the Potential of a Highly Scalable Metal-Organic Framework CALF-20 for Selective Gas Adsorption at Low Pressure. Polymers. 2023; 15(3):760.

Chicago/Turabian Style

Borzehandani, Mostafa Yousefzadeh, Majid Namayandeh Jorabchi, Emilia Abdulmalek, Mohd Basyaruddin Abdul Rahman, and Muhammad Alif Mohammad Latif. 2023. "Exploring the Potential of a Highly Scalable Metal-Organic Framework CALF-20 for Selective Gas Adsorption at Low Pressure" Polymers 15, no. 3: 760.

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop