Liquid-Phase Adsorption of Aromatics over a MetalâOrganic

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Liquid-Phase Adsorption of Aromatics over a MetalOrganic Framework and Activated Carbon: Effects of Hydrophobicity/Hydrophilicity of Adsorbents and Solvent Polarity Biswa Nath Bhadra, Kyung Ho Cho, Nazmul Abedin Khan, Do Young Hong, and Sung Hwa Jhung J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b09298 • Publication Date (Web): 10 Nov 2015 Downloaded from http://pubs.acs.org on November 14, 2015

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The Journal of Physical Chemistry

Liquid-Phase Adsorption of Aromatics over a MetalOrganic Framework and Activated Carbon: Effects of Hydrophobicity/Hydrophilicity of Adsorbents and Solvent Polarity

Biswa Nath Bhadra,a Kyung Ho Cho,b Nazmul Abedin Khan,a Do-Young Hong, b and Sung Hwa Jhung a* a

Department of Chemistry and Green-Nano Materials Research Center, Kyungpook National

University, Daegu 702-701, Republic of Korea. Fax: 82-53-950-6330; email: [email protected] b

Nanocatalyst Research Center, Division of Green Chemistry & Engineering Research, Korea Research Institute of Chemical Technology (KRICT), Republic of Korea

1

ACS Paragon Plus Environment


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ABSTRACT:

In

order

to

understand

the

effect

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of

solvent

polarity

and

hydrophilicity/hydrophobicity of adsorbents on adsorption, aromatic compounds with very low acidity or basicity were adsorbed over two highly porous adsorbents, a metal-organic framework (MOF, MIL-101) and activated carbon (AC). Thiophene, pyrrole, and nitrobenzene were tested in liquid-phase adsorptions to estimate possible applications of the adsorbents in adsorptive desulfurization (ADS), adsorptive denitrogenation (ADN), and water purification, respectively. MIL-101 adsorbed the three adsorbates more effectively with decreasing solvent polarity, and AC with increasing solvent polarity. This behavior can be explained by the hydrophilicity of MIL-101 and hydrophobicity of AC, which was confirmed by measuring the hydrophobicity indexes. The preferential adsorptions of the adsorbates over MOF might be explained by polar interactions and AC by hydrophobic interactions. Moreover, it can be concluded that MOFs, especially hydrophilic ones, can be effectively used in adsorptions in non-aqueous phases, including ADS and ADN. Finally, an increase in hydrophobicity of a MOF is necessary for the applications of MOFs in water purification.

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1. INTRODUCTION Adsorption has been widely used for the removal of hazardous materials, storage and delivery of drugs, storage of gases such as hydrogen, methane and carbon dioxide, and separation of chemicals. To date, activated carbons (ACs) have been one of the most important adsorbents because of their low cost, chemical stability, wide pore size, and high porosity. Recently, nanoporous materials applicable to adsorptions have been developed as a result of newly reported advanced materials,1-6 including metal organic frameworks (MOFs).7-17 MOFs are interesting because of their facile synthesis, high porosity, wide pore size and shape, and easy modification. Therefore, MOFs have attracted much attention based on their large number of applications, including adsorption.8-16 Removal of sulfur-containing compounds (SCCs) and nitrogen-containing compounds (NCCs) from fuel is one of the interesting adsorption applications for MOFs.18-27 Another important possibility for MOF applications is water purification.28, 29 Therefore, MOFs and ACs can be regarded as the most popular adsorbents in various fields of adsorption in both vapor and liquid phases. Moreover, the adsorptive performance of MOFs is usually compared with those of ACs (the standard) in order to estimate the competitiveness of MOFs in adsorption processes. So far, however, there has been no detailed comparison between AC and MOF in adsorptive performance. On the other hand, solvents are very important in liquid-phase adsorption because of the high probability that they occupy most of the adsorption sites. Moreover, the molecular size of solvents is important because entropy increase may be one of the driving forces for adsorption in the liquid phase.30 The choice of solvent may vary from very polar (such as water) to nonpolar (such as hydrocarbons) depending on the adsorption process used. For example, water purification28, 29 and fuel upgrading (such as adsorptive desulfurization (ADS) and adsorptive

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denitrogenation (ADN))31 are carried out mainly in water and hydrocarbons, respectively. From this viewpoint, the characteristics of not only the adsorbents/adsorbates but also the solvents must be considered for successful adsorption results. To date, however, the effect of solvent polarity and adsorbent hydrophobicity/hydrophilicity on adsorption has not been well researched. Studies till date have used only a single adsorbent, mainly AC, rather than two or more different adsorbents. Ania et al.32 reported that hydrophilicity/hydrophobicity was important in the adsorption of a non-polar compound (naphthalene) from water or hydrocarbons in a liquid phase over microporous ACs having different oxygen contents. In addition, Ania’s group suggested that competitive adsorption (between adsorbates and solvents) was also important, because adsorption capacity decreased in the presence of organic solvents such as cyclohexane and heptane. It was also concluded that solubility or affinity between solvent and adsorbate was important in the adsorption of naphthalene over AC.33 Similar conclusions were obtained by Carvalho et al. via adsorption of caffeine over AC from water (in the presence of co-solvents such as methanol and i-propyl alcohol).34 It was also reported that adsorption of polyaromatic hydrocarbons (PAHs, including naphthalene, anthrathene, and pyrene) was more effective from a polar solvent than from an aromatic solvent (benzene) because of the high affinity of aromatics for adsorbents (ACs).35 Zaera et al. pointed out that the dissolving power of a solvent was important in the adsorption of alkaloids on Pt.36 With increasing dissolving power, the equilibrium shifts to the solution, favoring desorption rather than adsorption. To the best of our knowledge, MIL-53(Fe) is the only MOF that has been used to study the influence of solvent properties on the adsorptive removal of heterocycles (having N and/or S),

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even though the authors did not focus on the solvent effects in detail.37 Preferential adsorption of indole from n-heptane (compared with negligible adsorption from i-propyl alcohol) was observed for MIL-53(Fe). Solvents, however, cause very complicated adsorptions because of the breathing property of the MOF.38 For example, a higher amount of benzothiophene (BT) was adsorbed from i-propyl alcohol, especially when the BT concentration was high, than the adsorption of BT from n-heptane. Moreover, the contribution of hydrogen bonding from solvents such as i-propyl alcohol was very important in some adsorptions (such as stepwise adsorptions).37 So far, the effect of solvent polarity on liquid-phase adsorptions has been hardly studied, especially with MOFs. Therefore, it is very interesting to compare ACs with MOFs for adsorption, especially in solvents with different polarities. ACs are typical examples of hydrophobic (HPho) adsorbents, and MOFs might be regarded as typical examples of hydrophilic (HPhi) adsorbents. In this study, we used a typical and highly porous MOF, MIL-101,39 and a conventional AC in adsorption from water, n-butanol, and n-octane solvents. Thiophene (Th), pyrrole (Py), and nitrobenzene (NB) were used as adsorbates in this study to assess the possible applications of MOFs and ACs in ADS, ADN and water purification. Th, Py, and NB are typical aromatics having an N or S that do not have high acidity or basicity. Acid-base interactions might have a big influence on an adsorption process. To the best of our knowledge, this is the first work to study the effect of hydrophobicity/hydrophilicity of adsorbents on the adsorption of typical aromatics (with N or S) from typical solvents (very polar water, very non-polar n-octane, and medium-polar n-butanol).

2. EXPERIMENTAL 2.1 Materials

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Terephthalic acid (C6H4-1,4-(CO2H)2, 98%), 2-methylimidazole (C4H6N2, 99%), and thiophene (C4H4S, 99%) were purchased from Sigma-Aldrich. Chromium nitrate nonahydrate (Cr(NO3)3·9H2O, 98%) and granular activated carbon (AC, size: 2-3 mm) were procured from Duksan Pure Chemical Co. Ltd. n-Butanol (C4H10O, 99%) and nitrobenzene (C6H5NO2, 98%) were

acquired

from

OCI

chemical

company,

Korea.

Zinc

acetate

dihydrate

((CH3COO)2Zn·2H2O, 98%) was obtained from DC Chemical Co. Ltd; pyrrole (C4H5N, 98%), from Yakuri Chemical Co. Ltd.; and n-octane (C8H18, 97%), from Alfa Aesar. 2.2 Syntheses of MIL-101 and ZIF-8 The syntheses of MIL-10139, 40 and ZIF-841 were done following the procedures summarized in the Supporting Information. The physical properties of the adsorbents used in this study, such as AC and MIL-101, are shown in Table S1. 2.3 Adsorption experiments Adsorption experiments were carried out following a method reported previously.42 Briefly, Th, Py, and NB solutions in n-octane, n-butanol, and water were used in adsorption experiments. Th, Py, and NB concentrations were determined using UV spectroscopy. Adsorption experiments were done three times and the average values were reported. Detailed experimental procedures are shown in the Supporting Information. The Langmuir parameters, such as maximum adsorption capacity (Qo) and b-value, were obtained using the Langmuir equation (see Supporting Information).43, 44 2.4 Measurement of hydrophobicity indexes (HIs) of adsorbents In order to obtain HIs of the adsorbents, competitive adsorptions of water-toluene vapor mixtures were conducted with 50 mg of adsorbent in a fixed bed reactor (stainless steel tubular reactor, 4 mm inner diameter) at 298 ±1 K. The adsorbents were pressed to form pellets, which

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were then crushed and sieved to attain particle sizes between 210 and 250 µm. The adsorbents were supported in the reactor using quartz wool. Prior to conducting competitive adsorptions, adsorbent samples were activated for 6 h at 423 K under He flow (20 mL/min), and then cooled to 298 K. A constant He flow containing water and toluene vapors (20 mL/min, pwater = 1 kPa, ptoluene = 1 kPa) was introduced into the sample area. Vapors (water and toluene) with constant pressures were generated by flowing He (10 mL/min) through water or toluene at constant temperature (Twater = 290.4 K and Ttoluene = 286.2 K). The two vapor streams were mixed before passing through the reactor, and off-gases from the reactor were periodically analyzed using an on-line gas chromatograph equipped with a thermal conductivity detector. The adsorbed amounts of water and toluene were obtained by integration of the corresponding breakthrough curves. The HI was calculated using equation (1) as described by Weitkamp et al.45 HI = Qtoluene /Qwater

(1)

where, Qtoluene = amount of adsorbed toluene (gtoluene/gadsorbent) and Qwater = amount of adsorbed water (gwater/gadsorbent).

3. RESULTS 3.1. Adsorbed quantity at various conditions Figure 1 shows the adsorbed quantities of Th, Py, and NB from water and n-octane as solvents over AC and MIL-101 at various adsorption times. It should be noted that the scale of the y-axes are not the same in each of the parts of Figure 1. Figures 1a and 1d represent highly adsorbed amounts. The adsorbed quantities increase with time up to 24 h; however, the quantities are nearly saturated after 12 h of adsorption in all cases. The adsorbed quantity shows very complicated dependences on adsorbents and solvents. For example, the adsorbed quantity over

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AC from water follows the order Th > NB > Py (Figure 1a). However, the quantity over AC from n-octane decreases in the order NB >> Th~Py (Figure 1b). Figure 1c shows that the adsorbed amount over MIL-101 (from water) follows the order NB > Py > Th. Finally, the amount over MIL-101 from n-octane decreases in the order Py > NB > Th (Fig. 1d). Therefore, no simple trend is observed for the preferential or effective adsorption for the two adsorbents in the two solvents. In order to understand better the adsorptions, the adsorbed quantities of selected adsorbates over AC and MIL-101 were measured from three solvents, including n-butanol (having medium polarity), after 12 h (q12h). These quantities were plotted against solvent polarity (based on the dielectric constant, DEC, of solvents). As shown in Figure 2a, q12h over AC for the three adsorbates increased with increasing DEC of the solvents. On the contrary, a reverse tendency was observed with MIL-101 (Figure 2b). The relative ratio of q12h values for two different solvents (q12h from n-octane/q12h from water) are summarized in Table 1. The table shows that, irrespective of the adsorbate, AC preferentially adsorbs the three aromatics from water compared with adsorption from n-octane. However, MIL-101 is very effective in adsorbing the aromatics from n-octane compared with adsorption from water. 3.2. Adsorption isotherms Adsorption isotherms were obtained after adsorption for 12 h to confirm preferential adsorptions under equilibrium conditions. Figure 3 shows the adsorption isotherms for Th from water (Figure 3a) and from n-octane (Figure 3b) for the two adsorbents. As shown in Figure 3a, AC is more effective than MIL-101 for adsorbing Th from water. In contrast, MIL-101, compared with AC, is very efficient in the adsorption of Th from n-octane as shown in Figure 3b. Figure S1 shows the performance of AC (Figure S1a) and MIL-101 (Figure S1b) in different

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solvents for the adsorption of Th. Figure S1a confirms again that AC adsorbs Th much more effectively from water than from n-octane. On the contrary, from Figure S1b, it can be concluded that MIL-101 is much more effective at adsorbing Th from n-octane than from water. As shown in Figures 4 and S2, adsorption of Py is very similar to that of Th (Figures 3 and S1) in adsorptive preferences and tendencies. The NB adsorptions (Figures S3 and S4) are quite similar to the adsorptions of Th and Py, even though selectivities for NB (with adsorbents or solvents) are less than those for Th and Py. Table 2 summarizes the Langmuir parameters, such as maximum adsorption capacities (Q0) and b-values, which were obtained from Langmuir plots (Figures S5-S7). The correlation factors show that Langmuir isotherms can be satisfactorily applied to interpret the adsorptions even though saturated adsorptions were not obtained for noctane. Once again, AC shows higher Q0 and b-values for Th, Py, and NB from water than from n-octane (Table 2). In constrast, adsorption of the three adsorbates using MIL-101 is much more effective from n-octane than from water, as confirmed by higher Q0 and b-values from n-octane than from water (Table 2). Therefore, it can be concluded that AC is very effective for adsorbing aromatics used in this study from water while MIL-101 efficiently adsorbed such aromatics from n-octane.

4. DISCUSSION Figures 3, 4, and S1-S4 show that AC and MIL-101 are very effective for adsorbing Th, Py, and NB from water and n-octane, respectively. Figure 1 shows a similar tendency (note the different maximum values on the y-axes). Moreover, Figure 2 shows that the adsorbed amounts for AC increase with increasing DEC, and for MIL-101 increase with decreasing DEC of the solvents.

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In liquid phase adsorptions, hydrophobicity/hydrophilicity of adsorbents, or solvent polarity, may be important considering possible pre-adsorption by solvents, or hydrophobic/polar interactions. For example, hydrophobic interactions were applied by Krishnakumar and Somasundaran to explain adsorptions of surfactants over metal oxides46 in highly polar solvents. In nonpolar solvents, conversely, polar interactions were important to explain the adsorption of surfactants on oxides.46 Similarly, polar interactions were used to explain the adsorption of surfactants over graphite from less polar solvents.47 AC is a typical HPho material48, 49 because of its nonpolar C-C bonds. On the contrary, MOFs, including MIL-101, may be a HPhi material considering that metals or metal clusters are one of the components of MOFs.50,

51

Hydrophobicity indexes (HI), suggested by Weitkamp,45 for AC and MIL-101 were measured to understand the hydrophilicity/hydrophobicity of the adsorbents. As shown in Figure 5, AC adsorbs very little water compared with MIL-101, and AC adsorbs about half of the amount of toluene that MIL-101 adsorbs, probably due to the low porosity of AC (see Table S1). Based on the adsorbed amounts of water and toluene, the HI of AC is calculated to be 296, which is much higher than that of MIL-101 (HI=11.0). The HI of MIL-101 is similar to that of zeolites beta45 and ZSM-552 that are considered to be HPhi materials. The HI of AC is higher than that of allsilica beta (HI=66),45 which is an HPho materials. Therefore, it is confirmed that AC and MIL101 are typical HPho and HPhi materials, respectively. In

the

present

work,

two

very

different

adsorbents

(in

composition

and

hydrophilicity/hydrophobicity) with high porosity were used for the adsorption of various chemicals.

In

particular,

AC

and

MOF

materials

were

compared

in

terms

of

hydrophobicity/hydrophilicity. A fundamental conclusion was made indicating the importance of interactions between adsorbents and adsorbates (and/or solvents). Based on the competitive

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adsorption and hydrophilicy/hydrophobicity of adsorbents, it is presumed that the interaction between HPhi materials and polar adsorbates (including water) will be highly favorable (due to polar interactions). Similarly, interactions between low-polar adsorbates (including n-octane) and HPho materials will be strong (because of hydrophobic interactions).46, 47 Therefore, interaction between n-octane and HPho AC will be strong. Similarly, interaction between water and HPhi MIL-101 will also be strong. Finally, the adsorbed amounts of Th, Py, and NB on AC from noctane will be low because of pre-adsorbed n-octane on AC. Similarly, the adsorption of Th, Py, and NB on MIL-101 from water will be difficult owing to pre-adsorbed water on MIL-101. On the other hand, because of the hydrophobicity of AC, the adsorption capacities should increase with increasing DEC of the solvents (or switching from n-octane to n-butanol, and finally to water). Adsorption capacities for MIL-101 probably increase with decreasing DEC of the solvents (or changing from water to n-butanol and finally to n-octane) considering the hydrophilicity of MIL-101. These expected trends are clearly seen in Figure 2. In accordance with these facts, adsorption on AC (from water) and MIL-101 (from n-octane) are very favorable as shown in Figures 3 and S1. Even though the polarities of Th, Py, and NB are not very high, polar interactions with MIL-101 may be possible because the DECs of the three adsorbates are higher than that of n-octane (DECTh=2.74; DECPy=8.0; DECNB=35.6; DECn-octane=2.0). Similarly, the hydrophobic interaction between Th, Py, and NB, and AC may be possible even though the polarities of the three adsorbates are not very low because the DECs of the adsorbates are lower than that of water (DECwater =80). ZIF-8,53 a typical zeolitic imidazolate framework (ZIF) material (a sub-group of MOF), is well known for its high stability53 and hydrophobicity.54-56 Adsorption of Th (from solvents such as n-octane, n-butanol, and water) on ZIF-8 was done and compared with the results of AC and

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MIL-101. As shown in Figure 6, the effect of the DECs of solvents on the adsorption of Th on ZIF-8 is very similar to that on HPho AC. However, it is very different from that on HPhi MIL101. Therefore, again, HPho materials (such as AC and ZIF-8) and HPhi materials (such as MIL101) can be effective adsorbents for chemicals from water and n-octane (as solvent), respectively. This conclusion is also agreeable with the studies on the adsorption/removal of organic contaminants, including methyl-t-butyl ether and trichloroethylene, from water using ACs.57 Li et al.57 suggested applying HPho adsorbents for such adsorptions because HPhi adsorbents, if used, will effectively adsorb water and, therefore, organic materials cannot easily approach the adsorption sites. These results, favorable adsorptions of Th over AC from polar solvents, and MIL-101 from non-polar solvents, can be observed in adsorption of other adsorbates such as Py and NB. However, the results for NB are a bit different from those of Th and Py. Substantial amounts of NB were adsorbed over AC from n-octane, or over MIL-101 from water (Figures 1 and 2). Moreover, the adsorbed amounts at equilibrium (qe) of NB from n-octane over AC and MIL-101 do not differ much from each other (Figure S3b). Similarly, the qe values of NB from n-octane and water over MIL-101 are not vastly unlike each other (Figure S4b). This difference of NB from Th and Py might be due to the relatively high polarity of NB (DECNB: 35.6; DECTh: 2.74; DECPy: 8.0) or coordination by NB. MIL-101 has coordinatively unsaturated sites (CUSs) on which coordination by ligands is possible.39 Therefore, coordination of NB (via the nitro group) on the CUSs of MIL-101 may be expected, which may lead to a slight adsorption of NB on MIL101, even from water. Removal of organics with MOFs has been reported in liquid-phase adsorption from aqueous solutions via coordination on CUSs.58 Because of the polarity of NB and the presence of low concentrations of polar functional groups in AC,59 a polar interaction

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between NB and AC in n-octane may be possible. Therefore, the polarity of adsorbates should also be considered in adsorptive performance. MOFs have been used widely in adsorptions both in gas/vapor and liquid phases.9-17, 28-31, 60 Typical applications are storage/separation, fuel upgrading including ADS/ADN, and water purification. Based on the discussion above, applications of MOFs in fuel upgrading are easily understood if MOFs are HPhi materials. Applications of MOFs in water purification might not be very efficient if HPhi MOFs were used, even though there are several reports on water purification using HPhi MOFs.61-65 For efficient purification of water, a specific interaction mechanism (such as electrostatic interaction, acid-base interaction, π-π interaction, coordination, or hydrogen-bonding)

29, 66

is needed when HPhi MOFs are used. On the other hand, HPho

MOFs, including ZIF-8, might be efficient for water purification. Therefore, it can be presumed that HPhi and HPho MOFs can be used effectively in fuel upgrading31,

67

and water

purification,28, 29 respectively.

5. CONCLUSION Liquid-phase adsorption of Th, Py, and NB was done over porous AC and MIL-101 from the solvents water, n-butanol, and n-octane. Highly porous AC and MIL-101 were found to have HPho and HPhi characteristics, respectively, by measuring hydrophobicity indexes. From this study, the following conclusions can be drawn: -

MOFs such as MIL-101 are very effective for adsorbing aromatics from non-polar solvents because of polar interactions between adsorbates and HPhi MIL-101.

-

HPho AC or ZIF-8 is useful for adsorptions from water or polar solvents due to hydrophobic interactions between adsorbates and HPho AC or ZIF-8.

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-

HPhi MOFs can be used very effectively in fuel upgrading, such as ADS and ADN.

-

MOFs may be used effectively in adsorptions from polar solvents if the hydrophobicity can be increased or a specific functional group is available for selective adsorptions.

ASSOCIATED CONTENT Supporting information Preparation of MOFs, adsorption procedure, calculation of maximum adsorption capacity (Q0), physical properties of adsorbents, adsorption isotherms and Langmuir plots. This information is available free of charge via the internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author * Phone: 82-10-28185341; Fax: 82-53-950-6330; E-mail: [email protected] Funding Sources This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) (grant number: 2013R1A2A2A01007176). ABBREVIATIONS AC, activated carbon; ADS, adsorptive desulfurization; ADN, adsorptive denitrogenation; DEC, dielectric constant; HIs, hydrophobicity indexes; HPho, hydrophobic; HPh, hydrophilic; MOFs, metal organic frameworks; NB, nitrobenzene; NCCs, nitrogen-containing compounds; Py, pyrrole; SCCs, sulfur-containing compounds; Th, thiophene.

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17. Burtch, N. C.; Jasuja, H.; Walton, K. S. Water Stability and Adsorption in Metal–Organic Frameworks. Chem. Rev. 2014, 114, 10575–10612. 18. van de Voorde, B.; Boulhout, M.; Vermoortele, F.; Horcajada, P.; Cunha, D.; Lee, J. S.; Chang, J.-S.; et al. N/S-Heterocyclic Contaminant Removal from Fuels by the Mesoporous Metal–Organic Framework MIL-100: The Role of the Metal Ion. J. Am. Chem. Soc. 2013, 135, 9849−9856 19. Cychosz, K. A.; Wong-Foy, A. G.; Matzger, A. J. Enabling Cleaner Fuels: Desulfurization by Adsorption to Microporous Coordination Polymers. J. Am. Chem. Soc. 2009, 131, 14538-14543. 20. Cychosz, K. A.; Wong-Foy, A. G.; Matzger, A. J. Liquid Phase Adsorption by Microporous Coordination Polymers: Removal of Organosulfur Compounds. J. Am. Chem. Soc. 2008, 130, 6938-6939. 21. Khan, N. A.; Jhung, S. H. Remarkable Adsorption Capacity of CuCl2‐Loaded Porous Vanadium Benzenedicarboxylate for Benzothiophene. Angew. Chem. Int. Ed. 2012, 51, 1198 -1201. 22. Achmann, S.; Hagen, G.; Hämmerle, M.; Malkowsky, I.; Kiener, C.; Moos, R. Sulfur Removal from Low-sulfur Gasoline and Diesel Fuel by Metal-Organic Frameworks. Chem. Eng. Technol. 2010, 33, 275-280. 23. Khan, N. A.; Jun, J. W.; Jeong, J. H.; Jhung, S. H. Remarkable Adsorptive Performance of a Metal–Organic Framework, Vanadium-benzenedicarboxylate (MIL-47), for Benzothiophene. Chem. Commun. 2011, 47, 1306-1308.

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24. Maes, M.; Trekels, M.; Boulhout, M.; Schouteden, S.; Vermoortele, F.; Alaerts, L.; Heurtaux, D.; et al. Selective Removal of N-Heterocyclic Aromatic Contaminants from Fuels by Lewis Acidic Metal–Organic Frameworks. Angew. Chem. Int. Ed. 2011, 50, 4210-4214. 25. Ahmed, I.; Hasan, Z.; Khan, N. A.; Jhung, S. H. Adsorptive Denitrogenation of Model Fuels with Porous Metal-Organic Frameworks (MOFs): Effect of Acidity and Basicity of MOFs. Appl. Catal. B: Environ. 2013, 129, 123−129. 26. Wu, Y.; Xiao, J.; Wu, L.; Chen, M.; Xi, H.; Li, Z.; Wang, H. Adsorptive Denitrogenation of Fuel over Metal-Organic Frameworks: Effect of N-Types and Adsorption Mechanisms. J. Phys. Chem. C 2014, 118, 22533-22543. 27. Ahmed, I.; Khan, N. A.; Jhung, S. H. Graphite Oxide/Metal-Organic Framework (MIL101): Remarkable Performance in the Adsorptive Denitrogenation of Model Fuels. Inorg. Chem. 2013, 52, 14155-14161. 28. Khan, N. A.; Hasan, Z.; Jhung, S. H. Adsorptive Removal of Hazardous Materials Using Metal-Organic Frameworks (MOFs): a Review. J. Hazard. Mater. 2013, 244-245, 444456. 29. Hasan, Z.; Jhung, S. H. Removal of Hazardous Organics from Water Using MetalOrganic Frameworks (MOFs): Plausible Mechanisms for Selective Adsorptions. J. Hazard. Mater. 2015, 283, 329-339.

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37. van de Voorde, B.; Munn, A. S.; Guillou, N. Millange, F.; De-Vos, D.; Walton, R. I. Adsorption of N/S Heterocycles in the Flexible Metal–Organic Framework MIL-53 (Fe III) Studied by in Situ Energy Dispersive X-ray Diffraction. Phys. Chem. Chem. Phys. 2013, 15, 8606-8615. 38. Llewellyn, P. L.; Horcajada, P.; Maurin, G.; Devic, T.; Rosenbach, N.; Bourrelly, S.; Serre, C.; et al. Complex Adsorption of Short Linear Alkanes in the Flexible MetalOrganic-Framework MIL-53 (Fe). J. Am. Chem. Soc., 2009, 131, 13002–13008. 39. Hong, D. -Y.; Hwang, Y. K.; Serre, C.; Ferey, G.; Chang, J. -S. Porous Chromium Terephthalate

MIL-101

with

Coordinatively

Unsaturated

Sites:

Surface

Functionalization, Encapsulation, Sorption and Catalysis. Adv. Funct. Mater. 2009, 19, 1537–1552. 40. Khan, N. A.; Jhung, S. H. Phase-transition and Phase-selective Synthesis of Porous Chromium-benzenedicarboxylates. Cryst. Growth Des. 2010, 10, 1860-1865. 41. Torad, N. L.; Hu, M.; Kamachi, Y.; Takai, K.; Imura, M.; Naito, M.; Yamauchi, Y. Facile Synthesis of Nanoporous Carbons with Controlled Particle Sizes by Direct Carbonization of Monodispersed ZIF-8 Crystals. Chem. Commun. 2013, 49, 2521-2523. 42. Khan, N. A.; Jhung, S. H. Low-temperature Loading of Cu+ Species over Porous MetalOrganic Frameworks (MOFs) and Adsorptive Desulfurization with Cu+-loaded MOFs. J. Hazard. Mater. 2012, 237-238, 180-185.

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43. Haque, E.; Lee, J. E.; Jang, I. T.; Hwang,Y. K.; Chang, J.-S.; Jegal, J.; Jhung, S. H. Adsorptive Removal of Methyl Orange from Aqueous Solution with Metal-Organic Frameworks, Porous Chromium-Benzenedicarboxylates. J. Hazard. Mater. 2010, 181, 535–542. 44. Hasan, Z.; X Jeon, J.; Jhung, S. H. Adsorptive Removal of Naproxen and Clofibric acid from Water Using Metal-Organic Frameworks. J. Hazard. Mater. 2012, 209, 151–157. 45. Stelzer, J.; Paulus, M.; Hunger, M.; Weitkamp, J. Hydrophobic Properties of all-Silica Zeolite Beta. Microporous Mesoporous Mater. 1998, 22, 1–8. 46. Krishnakumar, S.; Somasundaran, P. Role of Surfactant-Adsorbent Acidity and Solvent Polarity in Adsorption-Desorption of Surfactants from Nonaqueous Media. Langmuir 1994, 10, 2786-2789. 47. Krishnakumar, S.; Somasundaran, P. Adsorption of Aerosol-OT on Graphite from Aqueous and Non-aqueous Media. Colloids Surfaces A: Physicochem. Eng. Aspects 1996, 117, 227-233. 48. Serre, C.

Superhydrophobicity in Highly Fluorinated Porous Metal–Organic

Frameworks. Angew. Chem. Int. Ed. 2012, 51, 6048 – 6050. 49. de Ridder, D. J.; Villacorte, L.; Verliefde, A. R. D.; Verberk1, J. Q. J. C.; Heijman, S. G. J.; Amy, G. L.; van Dijk, J. C. Modeling Equilibrium Adsorption of Organic Micropollutants onto Activated Carbon. Water Res. 2010, 44, 3077 – 3086.

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50. Küsgens, P.; Rose, M.; Senkovska, I.; Fröde, H.; Henschel, A.; Siegle, S.; Kaskel, S. Characterization of Metal-Organic Frameworks by Water Adsorption. Microporous Mesoporous Mater. 2009, 120, 325–330. 51. Nguyen, J. G.; Cohen, S. M. Moisture-Resistant and Superhydrophobic Metal−Organic Frameworks Obtained via Postsynthetic Modification. J. Am. Chem. Soc. 2010, 132, 4560–4561. 52. Hwang, Y. K.; Chang, J.-S.; Park, S.-E.; Kim, D. S.; Kwon, Y.-U.; Jhung, S. H.; Hwang, J.-S.; Park, M. S. Microwave Fabrication of MFI Zeolite Crystals with a Fibrous Morphology and their Applications. Angew. Chem. Int. Ed. 2005, 44, 556–560. 53. Park, K. S.; Ni, Z.; Cote, A. P.; Choi, J. Y.; Huang, R.; Uribe-Romo, F. J.; Chae, H. K.; O’Keeffe, M.; Yaghi, O. M. Exceptional Chemical and Thermal Stability of Zeoliticimidazolate Frameworks. Proc. Natl. Acad. Sci. USA 2006, 103, 10186–10191. 54. Zhang, K.; Zhang, L.; Jiang, J. Adsorption of C1−C4 Alcohols in Zeolitic Imidazolate Framework-8: Effects of Force Fields, Atomic Charges, and Framework Flexibility. J. Phys. Chem. C 2013, 117, 25628−25635. 55. Tian, F.; Mosier, A. M.; Park, A.; Webster, E. R.; Cerro, A. M.; Shine, R. S.; Benz, L. In Situ Measurement of CO2 and H2O Adsorption by ZIF-8 Films. J. Phys. Chem. C 2015, 119, 15248–15253. 56. Zhang, K.; Lively, R. P.; Zhang, C.; Koros, W. J.; Chance, R. R. Investigating the Intrinsic Ethanol/Water Separation Capability of ZIF-8: An Adsorption and Diffusion Study. J. Phys. Chem. C 2013, 117, 7214–7225.

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57. Li, L.; Quinlivan, P. A.; Knappe, D. R. U. Effects of Activated Carbon Surface Chemistry and Pore Structure on the Adsorption of Organic Contaminants from Aqueous Solution. Carbon 2002, 40, 2085-2100. 58. Jun, J. W.; Tong, M.; Jung,B. K.; Hasan, Z.; Zhong, C.; Jhung, S. W. Effect of Central Metal Ions of Analogous Metal–Organic Frameworks on Adsorption of Organoarsenic Compounds from Water: Plausible Mechanism of Adsorption and Water Purification. Chem. Eur. J. 2015, 21, 347-354. 59. Jung, B. K.; Jhung, S. H. Adsorptive Removal of Benzothiophene from Model Fuel, Using Modified Activated Carbons, in Presence of Diethylether. Fuel 2015,145, 249-255. 60. Ahmed, I.; Jhung, S. H. Composites of Metal-Organic Frameworks: Preparation and Application in Adsorption. Mater. Today 2014, 17, 136-146. 61. Lin, K. Y. A.; Yang, H.; Petit, C.; Hsu, F. K. Removing Oil Droplets from Water Using a Copper-based Metal Organic Frameworks. Chem. Eng. J. 2014, 249, 293-301. 62. Cychosz, K. A.; Matzger, A. J. Water Stability of Microporous Coordination Polymers and the Adsorption of Pharmaceuticals from Water. Langmuir 2010, 26, 17198–17202. 63. Li, L.; Liu, X. L.; Geng, H. Y.; Hu, B.; Song, G. W.; Xu, Z. S. A MOF/Graphite Oxide Hybrid (MOF: HKUST-1) Material for the Adsorption of Methylene Blue from Aqueous Solution. J. Mater. Chem. A 2013, 1, 10292-10299. 64. Tong, M.; Liu, D.; Yang, Q.; Devautour-Vinot, S.; Maurin, G.; Zhong, C. Influence of Framework Metal Ions on the Dye Capture Behavior of MIL-100 (Fe, Cr) MOF Type Solids. J. Mater. Chem. A 2013, 1, 8534-8537.

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65. Xiao, Y.; Han, T.; Xiao, G.; Ying, Y.; Huang, H.; Yang, Q.; Liu, D.; Zhong, C. Highly Selective Adsorption and Separation of Aniline/Phenol from Aqueous Solutions by Microporous MIL-53(Al): A Combined Experimental and Computational Study. Langmuir 2014, 30, 12229–12235. 66. Hasan, Z.; Tong, M.; Jung, B. K.; Ahmed, I.; Zhong, C.; Jhung, S. H. Adsorption of Pyridine over Amino-Functionalized Metal–Organic Frameworks: Attraction Via Hydrogen Bonding Versus Base–Base Repulsion. J. Phys. Chem. C 2014, 118, 21049−21056. 67. Ahmed, I.; Jhung, S. H. Adsorptive Desulfurization and Denitrogenation using MetalOrganic Frameworks. J. Hazard. Mater. 2016, 301, 259–276.

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


Table 1. The relative adsorbed amounts (from n-octane and water) of thiophene, pyrrole and nitrobenzene over two adsorbents, AC and MIL-101. Ratio of q 12 h (q 12h from C8/q 12 h from

H2O)

Adsorbates AC

MIL-101

Th

0.012

7.2

Py

0.027

11

NB

0.29

2.6

a: adsorption condition: 0.005 g adsorbents in 20 mL (n-octane, n-BuOH and H2O: 100 ppm) of solution shaked for 12 h.

25



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

Page 26 of 33

Table 2. Langmuir parameters (Q0 and b values) for thiophene, pyrrole and nitrobenzene adsorptions from water and n-octane over two adsorbents, AC and MIL-101. Q0 values (mg/g) Adsorbents

Solvents Th

Py

NB

Th

Py

NB

Th

Py

NB

H2O

2.5×102

1.3×102

1.7×102

6.4×10-2

1.8×10-2

6.0×10-1

0.998

0.997

0.999

n-octane

3.7×100

4.3×100

6.6×101

2.7×10-2

8.3×10-3

2.7×10-2

0.994

0.982

0.989

H2O

6.3×100

1.2×101

3.3×101

1.5×10-2

1.3×10-2

3.3×10-2

0.997

0.987

0.987

n-octane

4.5×101

1.0×102

9.1×101

1.6×10-2

4.2×10-2

3.8×10-1

0.998

0.999

0.987

AC

MIL-101

26

R2 (Langmuir plots)

b values (L/mg)


Page 27 of 33

240

AC-H2O

(a)

60

Th Py NB

200

50 3

30

80

20

40

10

0

0

1

0

0

5

10

15

20

25

0

5

10

15

20

20

25

Time, h 100

Th Py NB

MIL-101-H2O

(c)

0

10

Time, h

35

Th Py

2 qt, mg/g

qt, mg/g

qt, mg/g

40

120

Th Py NB

AC-n-octane

(b)

160

30

MIL-101-n-octane

(d)

90

Th Py NB

80

25

70 60

20

qt, mg/g

qt, mg/g

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


15

50 40 30

10

20

5

10 0

0 0

5

10

15

20

25

0

5

10

15

20

25

Time, h

Time, h

Figure 1. Effect of adsorption time on the adsorbed amounts of thiophene, pyrrole and nitrobenzene over AC and MIL-101 from water and n-octane. Inset of (b) shows the enlarged parts for thiophene and pyrrole.


27


200

AC

(a)

Th Py NB

160

q12 h, mg/g

120

80

40

0 0

20

40

60

80

Dielectric constant of solvents 100

MIL-101

(b)

Th Py NB

80 60 q12 h, mg/g

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

Page 28 of 33

40 20 0 0

20

40

60

80

Dielectric constant of solvents

Figure 2. Effect of dielectric constants of solvents on the adsorbed quantities (after 12 h of adsorption) of thiophene, pyrrole and nitrobenzene over (a) AC and (b) MIL-101.


28

Page 29 of 33

210

water

(a) 180

AC

qe, mg/g

150 120 90 60 30 MIL-101 0 0

10

20

30

40

50

60

70

80

90

100

Ce, ppm

30

n-octane

(b) 25

MIL-101 20 qe, mg/g

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


15 10 5

AC

0 0

20

40

60

80

100

Ce, ppm

Figure 3. Adsorption isotherms of thiophene from (a) water and (b) n-octane over AC and MIL101.


29


80

water

(a)

AC

qe, mg/g

60

40

20 MIL-101 0 0

20

40

60

80

100

Ce, ppm

80

n-octane

(b)

70

MIL-101 60 50 qe, mg/g

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

Page 30 of 33

40 30 20 10 AC 0 0

20

40

60

80

100

Ce, ppm

Figure 4. Adsorption isotherms of pyrrole from (a) water and (b) n-octane over AC and MIL101.


30

Page 31 of 33

2.0

(a)

AC

H2O Toluene

p/pO

1.5

1.0

0.5

Loading (wt.%) HI H2O

Toluene

0.14

41.2

296

0.0 0

20

40

60

80

100

Time, min

1.6

MIL-101

(b)

1.4

H2O Toluene

1.2 1.0 p/po

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


0.8 0.6 0.4

Loading (wt.%)

0.2

H2 O

Toluene

6.55

71.8

HI 11.0

0.0 0

20

40

60

80

100

Time, min

Figure 5. Breakthrough curves for competitive adsorption of water and toluene over (a) AC and (b) MIL-101.


31


30

AC ZIF-8 MIL-101

160

24

120

18

80

12

40

q12 h, mg/g

200

q12 h, mg/g

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

Page 32 of 33

6

0

0 0

20 40 60 Dielectric constant of solvents

80

Figure 6. Effect of dielectric constant of solvents on the adsorbed quantity of Th (q 12 h) over AC, MIL-101 and ZIF-8. The dotted lines were added to show the general tendency of the results.


32

Page 33 of 33

Table of Contents (TOC) Image

Liquid-phase adsorption

Qadsorbed

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


MOF

Activated carbon

non-polar Polarity of solvents

polar


33

Liquid-Phase Adsorption of Aromatics over a MetalâOrganic

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