Nitrogen-Doped Porous Carbons from Ionic Liquids@MOF

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Nitrogen-doped Porous Carbons from Ionic Liquids@MOF: Remarkable Adsorbents for Both Aqueous and Non-aqueous Media Imteaz Ahmed, Tandra Panja, Nazmul Abedin Khan, Mithun Sarker, Jong-Sung Yu, and Sung Hwa Jhung ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.7b00859 • Publication Date (Web): 27 Feb 2017 Downloaded from http://pubs.acs.org on February 28, 2017

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ACS Applied Materials & Interfaces

Nitrogen-doped Porous Carbons from Ionic Liquids@MOF: Remarkable Adsorbents for Both Aqueous and Non-aqueous Media

Imteaz Ahmed, a Tandra Panja, b Nazmul Abedin Khan, a Mithun Sarker, a Jong-Sung Yu*b, Sung Hwa Jhung*a a

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

University, Daegu 41566, Republic of Korea. b

Department of Energy Systems Engineering, DGIST, Daegu 42988, Republic of Korea.

Corresponding Authors * Phone: 82-53-950-5341; Fax: 82-53-950-6330; E-mail: [email protected] * Phone: 82-53-785-6443; Fax: 82-53-785-6409; E-mail: [email protected]

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ABSTRACT Porous carbons were prepared from a metal-organic framework (MOF, named ZIF-8), with or without modification, via high temperature pyrolysis. Porous carbons with high nitrogen content were obtained from the calcination of MOF after introducing an ionic liquid (IL) (IL@MOF) via the ship-in-bottle method. The MOF-derived carbons (MDCs) and IL@MOFderived carbons (IMDCs) were characterized using various techniques and used for liquid-phase adsorptions in both water and hydrocarbon to understand the possible applications in purification of water and fuel, respectively. Adsorptive performances for the removal of organic contaminants, atrazine (ATZ), diuron, and diclofenac, were remarkably enhanced with the modification/conversion of MOFs to MDC and IMDC. For example, in the case of ATZ adsorption, the maximum adsorption capacity of IMDC (Q0= 208 m2/g) was much higher than that of activated carbon (AC, Q0= 60 m2/g) and MDC (Q0= 168 m2/g), and was found to be the highest among the reported results so far. The results of adsorptive denitrogenation and desulfurization of fuel were similar to that of water purification. The IMDCs are very useful in the adsorptions since these new carbons showed remarkable performances in both the aqueous and non-aqueous phases. These results are very meaningful because hydrophobic and hydrophilic adsorbents are usually required for the adsorptions in the water and fuel phases, respectively. Moreover, a plausible mechanism, H-bonding, was also suggested to explain the remarkable performance of the IMDCs in the adsorptions. Therefore, the IMDCs derived from IL@MOF might have various applications, especially in adsorptions, based on high porosity, mesoporosity, doped nitrogen, and functional groups. Keywords: H-bonding, Liquid phase adsorption, Metal-organic Frameworks, Nitrogen doping, MOF-derived carbons, Pyrolysis of MOFs. 2 ACS Paragon Plus Environment

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1. INTRODUCTION Carbonaceous materials have been used for a long time in a large number of chemical and electrical fields including adsorption, catalysis, and energy storage. With the improvement in modern technologies, the advancement of carbonaceous materials is also occurring rapidly, leading to several types of micro- and mesoporous, ordered, and hierarchical porous carbonaceous materials for a large number of potential applications with remarkable results.1-4 Among carbonaceous materials, nano- and mesoporous structures are attracting the most attention because of their efficiency in a large number of applications.5,6 These materials are prepared by various advanced methods including chemical vapor deposition, pyrolysis, hydrothermal carbonization, arc-discharge, and post modification.1,7 Highly porous carbonaceous materials can be obtained by using such technologies. However, these types of methods often lead to a wide range of sizes of pore openings and pore size distributions, and therefore, high efficiency cannot be maintained easily. To improve the uniformity and distribution of pore size, calcination is used to obtain carbon materials with ordered porosity. One example is using metalorganic frameworks (MOFs) as a source and templating material for high temperature treatment to obtain ordered and highly porous carbons.8-13 MOFs are a group of advanced porous materials14-17 that contain metal sites connected to each other with organic linkers,18-21 forming an ordered framework, usually with a large surface area and porosity. Carbonaceous materials may form during anaerobic, high temperature pyrolysis and eventually a highly ordered, highly porous (nano- or mesoporous) carbon material can be obtained. Several attempts have been reported to prepare MOF-derived carbons (MDCs) for a large number of applications including supercapacitors, electrodes, catalysis, catalyst supports, energy storage, and gas adsorption.1,11,22-27 3 ACS Paragon Plus Environment


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Although MDCs are promising materials themselves, their properties can be further improved by using a dopant material such as nitrogen. By adding a small amount of nitrogen, the properties of carbonaceous materials including MDCs can be greatly improved and their applicability for various purposes can be enhanced.11 Although detailed study of the role of nitrogen doping (N-doping) is not revealed completely, several studies showed that the doping affects the surface of the carbonaceous material and hence improves the surface properties and activities.1, 26-30 Hazardous materials from various sources such as industrial wastewater and burning of fossil fuels are one of the biggest environmental concerns these days. Several organic wastes including pharmaceutical and personal care products (PPCPs) and pesticides/fungicides/herbicides are reported to be very harmful for ecological systems as well as human health, especially when they are present in water resources.31-34 Besides these, nitrogen and sulfur-containing compounds (NCCs and SCCs, respectively) in fuel, when burned for energy, create air pollution by releasing NOx and SOx, which mix with the air and create health hazards and acid rain. Moreover, NCCs and SCCs are very harmful for catalysts as they cause severe poisoning.35-37 Therefore, removing such harmful materials from both water and fuel is essential for the environment and our health. In this study, we prepared MDC from a MOF (ZIF-8, Zn(C4H6N2)2·(HCON(CH3)2)·(H2O)3)38 by high temperature pyrolysis. MDC with a high concentration of nitrogen was also prepared from the MOF after introduction of an ionic liquid (IL). An IL (1-butyl-3-methylimidazolium bromide) was synthesized in the presence of ZIF-8 via the ship-in-bottle (SIB) technique.39 SIB is an important technique for loading bulkier functional moieties within porous materials, especially to materials with narrow pore openings for successful loading and stability.40 The MDC obtained in this study from IL@MOF was named IMDC (ionic liquids@MOF-derived


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carbons). Although the IL-loaded MOF has been converted into MDC before for gas storage,41 to the best of our knowledge, there has been no attempt to prepare carbons (especially with a high concentration of nitrogen) from ZIF-8 containing IL (that was synthesized inside of the MOF via the SIB technique). The materials (MDC and IMDCs) were used for the liquid phase adsorption of contaminants from both aqueous and organic solutions, and remarkably removed several contaminants from both phases. Successful adsorption of organics over an adsorbent from both polar and non-polar media is very useful because hydrophobic and hydrophilic adsorbents are usually required for the adsorptions in the water and fuel phases, respectively.42

2. EXPERIMENTAL 2.1. Chemicals and preparation of materials All the chemicals used in this study were commercially available and used without further purification. Zinc nitrate (ZnNO3·6H2O, 99.0%), triethylamine (TEA, (C2H5)3N, 99%), 2-methyl imidazole (99%), quinoline (QUI, 98%), indole (IND, ≥ 99%), 2-methyl imidazole (99%), atrazine (ATZ, analytical standard), and diclofenac sodium (analytical standard) were obtained from Sigma Aldrich. Ethanol (C2H6O, >99.5%), toluene (C6H5CH3, 97%), acetone (C3H6O, >99.5%), and N,N-dimethylformamide (DMF, 99.0%), were obtained from OCI Chemicals. Sodium hydroxide (NaOH, 98%) and 1-bromobutane (98%) were purchased from Daejung Chemicals; diuron (97%) and N-methylimidazole (99%) were procured from Alfa Aesar. Synthesis of ZIF-8: ZIF-8 was synthesized over a large scale according to a reported procedure using ultrasound.43 In short, 720 mmol of ZnNO3·6H2O and 720 mmol of 2methylimidazole in 600 ml DMF were stirred vigorously until a clear solution was obtained by



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dissolving the materials. After that, 132 ml of 10 M NaOH solution and 4.5 ml triethylamine were added to the mixture and the resulting solution was quickly transferred to an ultrasound reactor (Sonics, model: VCX750) fitted to a sonicator bar, resulting in the precipitation of white ZIF-8. Preparation of IL@ZIF-8: IL was prepared inside the MOF directly using the SIB approach according to a reported recipe.39 N-methylimidazole was added to a vial containing dehydrated ZIF-8 and was magnetically stirred at room temperature for 15 h. After that, 1-bromobutane (the same molar amount as N-methylimidazole) was added to the mixture and magnetically stirred for an additional 24 h at room temperature. The resulting solid was separated via filtration and washed with ethanol several times. Finally, the filtered solid product was dried in an oven at 80 °C overnight. Carbonization procedure: Both the pristine and IL@ZIF-8s (IL-incorporated ZIF-8s) were carbonized by using a tubular furnace (MTI Corporation, model GSL-1500X). ZIF-8 or IL@ZIF8 (1 g) was loaded in a boat-shaped crucible and placed inside the tube of the furnace. After that, the temperature of the furnace was increased (with a ramping rate of 5 °C/min) up to the desired temperature, and maintained there for a fixed time (usually 10 h), and finally cooled to room temperature. Nitrogen flow was maintained at ~50 ml/min during all the stages of pyrolysis including heating and cooling. The carbonaceous material prepared from the pristine MOF was named MDC-X, where X stands for the pyrolysis temperature (in °C) of the MOF. Materials prepared from IL@ZIF-8 were named IMDC-X(Y%), where X stands for the pyrolysis temperature and Y represents the expected wt% of nitrogen (from the loaded IL) in IMDC (based on only carbon and nitrogen). 2.2. Characterization 6 ACS Paragon Plus Environment

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X-ray powder diffraction (XRD) analysis was conducted using a D2 Phaser X-ray diffractometer (Bruker) using CuKα radiation. The nitrogen adsorptions of the adsorbents were carried out at -196 °C using a surface area and porosity analyzer (Micromeritics, Tristar II 3020) after evacuation of the samples at 170 °C for 12 h. The surface area and pore size distribution of an adsorbent were calculated by using Brunauer-Emmett-Teller (BET) and Barrett-JoynerHalenda (BJH) equations, respectively. Fourier transform infrared (FTIR) spectroscopy was performed with a Jasco FTIR-4100 spectrometer in the attenuated total reflection mode (resolution: 4.0 cm−1). Elemental analyses of the adsorbents for nitrogen content were done using an elemental analyzer (Thermo Fisher, Flash-2000) with a TCD detector. X-ray photoelectron spectroscopy (XPS) analyses were carried out using a Quantera SXM X-ray photoelectron spectrometer (ULVAC-PHI) equipped with a dual beam charge neutralizer. Field emission scanning electron microscopy (FESEM) was carried out using a Hitachi model S-4300 microscope. Transmission electron microscopy images were obtained using biological transmission electron microscopy (BioTEM) (Hitachi, HT-7700) and field emission transmission electron microscopy (FETEM) (Titan G2ChemiSTEM Cs prove). 2.3. General procedures for adsorption experiments ATZ (20 ppmw), diuron (20 ppmw), and diclofenac sodium (100 ppmw) aqueous solutions were prepared by dissolving the materials directly in deionized water using a 1 L volumetric flask. Stock solutions of NCCs (i.e., IND and QUI) and SCC (i.e., dibenzothiophene or DBT) were prepared (each at a concentration of 10,000 ppmw) by dissolving adsorbates separately in n-octane. Solutions for lower concentration of the adsorbates were prepared separately by further diluting the stock solutions with n-octane. Solutions of fixed concentration (usually 1000 ppmw of IND, QUI, and DBT) were used to determine the adsorption capacities at various adsorption 7 ACS Paragon Plus Environment


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times. To obtain adsorption isotherms, solutions with different concentrations were prepared accordingly. Prior to adsorption, the adsorbents were dried using a vacuum oven at 150 °C for 12 h and stored in a desiccator. For each adsorption experiment, an exact amount of the adsorbent (~ 5.0 mg) was added to the solution containing the contaminant (~5.0 ml) and stirred magnetically for a predetermined time (up to 12 h) while maintaining the adsorption temperature at 25 °C. After adsorption, the solvent was separated from the solid using a syringe filter (PTFE, hydrophobic, 0.5 µm) and the concentration of the adsorbates was measured using a UV visible spectrometer (UV-1800, Shimadzu). Calculations related to the adsorption experiments are described elsewhere.44 3. RESULTS AND DISCUSSION 3.1. Characterization Figures 1(a) and S1(a) (Supporting Information) show the XRD patterns of the prepared MDC/IMDCs, which have the typical wide XRD patterns of pyrolytic carbon materials.45 The diffraction peak at 2θ ∼25o (for the 002 plane) indicates π-stacking of nanographitic platelets of the graphite sheets while the peak at 2θ ∼44o (for the 100 plane) indicates their lateral size (La).46 Figures 1(b) and S1(b) show the N2 adsorption isotherms for the prepared MDC and IMDC materials from which the surface areas and porosities were calculated (Tables S1 and S2). From the tables, it can be observed that the BET surface area was the highest for MDC-1000, which is prepared at 1000 °C from the pristine ZIF-8 without IL loading. All the materials prepared from IL-loaded MOFs (IMDCs) show lesser porosity than MDC. Moreover, among the IMDCs with the same IL content (4%), as shown in Table S2, the highest porosity was obtained at a pyrolysis temperature of 1000 °C. However, the amount of IL loaded inside the MOF did not have a 8 ACS Paragon Plus Environment

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significant influence on the porosity of IMDCs (Table S1). The micropore volume (PVmic) and the total pore volume (PVtot) also showed a similar trend as that of the surface area. The pore size distributions of the prepared materials are illustrated in Figure 2, which shows a prominent mesoporosity for all the materials. Figure 3 and Figure S2 show the N 1s XPS patterns of the materials. Three types of nitrogen were observed on the surface of the IMDC samples. Based on the binding energies, the three nitrogen species can be interpreted as pyridinic nitrogen (N-6), pyrrolic/pyridonic nitrogen (N-5), and quarternary nitrogen (N-Q).29 Deconvoluted XPS spectra to show the three nitrogen species are illustrated in Figure S3. The nitrogen content of the samples MDC-1000, IMDC-900(4%), IMDC-1000(4%), IMDC-1100(4%), IMDC-1000(8%), and IMDC-1000(12%) obtained from XPS and elemental analyses (EA), are shown in Table S3. Based on these analyses, it can be assumed that MDC-1000 contains almost no surface nitrogen even though its total or bulk nitrogen content is considerable, similar to a previous report.47 On the other hand, all the IMDC materials have prominent surface nitrogen, which is necessary for imparting chemical functionality to the carbonaceous materials. Importantly, from the XPS spectra in Figure 3(b), it is evident that the nitrogen content of the IMDCs as surface N-6 and N-5 increased monotonously with increasing content of introduced IL. On the other hand, the nitrogen content of the IMDCs (for 4% N) as surface N-6 decreases with increasing pyrolysis temperature, as shown in Figure S2. The bonding state of nitrogen atoms can also be estimated from FTIR spectroscopy (Figures 4 and S4), which shows sp3 and sp2 hybridized N configurations. The C-N (sp3) stretching was observed at ∼1116 and ∼1184 cm-1, while C=N (sp2) stretching was observed at ∼1405 cm-1.48 The FTIR spectra show that nitrogen atoms are attached to the graphite structure through the 9 ACS Paragon Plus Environment


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formation of single or double bonds. This indicates successful doping of nitrogen atoms within the graphite structure among the carbon atoms since stretching, compared to other types of movements, is easier in a 2D layer.49 These observations agree with previously described XPS results showing surface nitrogen doped onto the graphite sheets. To study the morphology of the prepared MDC and IMDCs in detail, a few electron microscopy techniques were applied. The SEM images presented in Figure S5 showed that the MDC and IMDC materials do not show much difference in physical appearance from the original MOF, ZIF-8. Therefore, BioTEM analyses were carried out to obtain a deeper understanding. The obtained BioTEM images for the different materials are shown in Figure 5. A partially crumpled layer separation50 was observed for the MDC and IMDC materials, which increased their surface area. The layer separation was further confirmed by higher resolution FETEM images, shown in Figure S6. This layer separation is one of the reasons for the improved surface area compared to the original MOF. As stated earlier, while the initial surface area of the MOF was 804 m2/g, the MDC and IMDC samples show more or less double the surface area of the original MOF (Tables S1 and S2). 3.2. Adsorption results The chemical structures of the six adsorbates used are shown in Scheme S1. Adsorption results from water and fuel are described separately in the following sections. Adsorption of organic contaminants from water: The prepared MDC and IMDCs were used for the adsorptive removal of hazardous organics, including ATZ, diuron, and diclofenac sodium from aqueous solutions. Figure 6(a), 6(b), and 6(c) show the adsorption results of ATZ, diuron, and diclofenac sodium, respectively, over AC, MDC-1000, and IMDC-1000(12%). It


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was found that MDC-1000 showed better performance compared to commercial AC; and IMDC1000(12%) was the best adsorbent for all the three cases. Similarly, the kinetics of adsorption was slightly increased in MDC and IMDC compared to commercial AC in case of ATZ (Table 1). To investigate the adsorption results in detail, ATZ as an adsorbate was studied further. Figure S7(a) shows the adsorption isotherms of ATZ over various adsorbents. From the isotherms, the Langmuir plots44 were obtained as shown in Figure S7(b). The maximum adsorption capacities (Qo) were calculated from the Langmuir plots and are listed in Table 1. It was found that the Qo of ATZ increased from 60 mg/g in AC to 173 mg/g in MDC-1000 and 208 mg/g in IMDC-1000(12%). Additionally, the b-values44 of the isotherms show a favorable adsorption over the adsorbents, especially for IMDC-1000(12%), which shows the maximum bvalue. The reported adsorption results of ATZ are shown in Table S4, and it can be seen that the current adsorption capacity of IMDC-1000(12%) is the highest among the reported results. Adsorptive denitrogenation and desulfurization from fuel: The prepared carbonaceous materials were used for the adsorptive removal of NCCs and SCCs as well. As shown in Figure 7(a) and 7(b), adsorption was carried out for IND and QUI-containing model fuels over MDC/IMDCs as well as for commercial AC. The effects of the N-content of the materials on the adsorbed quantities of IND and QUI are shown in Figure S8. In both cases, the adsorption increased with increasing N-content of the prepared materials. Therefore, we tried to prepare IMDC from ZIF-8 with a higher IL content; however, degraded materials with a very low surface area were obtained (for example, 16% nitrogen leads to a surface area of 266 m2/g). Therefore, all the experiments were carried out up to 12% nitrogen content. To calculate the Qo, adsorption isotherms were obtained for both IND and QUI, and these are shown in Figure 8. The Langmuir plots (Figure S9) and Qo of IND and QUI over different adsorbents were obtained (Table S5).



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For both IND and QUI, the adsorptive performance was in the order AC < MDC-1000 < IMDC1000(12%), which is similar to the previously obtained trend in the case of ATZ (Figure 6(a), Figure S7). This result is also agreeable with the adsorbed amounts of diuron and diclofenac sodium (Figure 6(b) and 6(c)). Compared to commercial AC and MDC, IMDC showed a very high adsorption capacity for NCCs. As shown in Table S5, the adsorption capacity of IMDC1000(12%) for IND and QUI were 258% and 169%, respectively, of that of the AC. After successful use in the removal of organics and NCCs, from water and fuel, respectively, the prepared materials were also used for the adsorption of an SCC named DBT. As shown in Figure 7(c), IMDC-1000(12%), compared to the pristine MOF (ZIF-8), commercial AC and MDC-1000, showed the best performance for the adsorption of DBT as well. In other words, similar to previous adsorptions, the adsorptive performances for DBT increased in the order ZIF8 < AC < MDC-1000 < IMDC-1000(12%). Therefore, IMDC-1000(12%) showed the best performance for adsorptive desulfurization, very similar to the results of water purification and adsorptive denitrogenation of the model fuel. Reusability of the adsorbent materials: The commercial use of an adsorbent relies on its reusability so that it can be used for long time. Therefore, we investigated the reusability of the IMDC-1000(12%) in the case of ATZ adsorption. The applied adsorbent was reused by a simple solvent washing with ethanol up to four cycles. As shown in Figure S10, the adsorption of ATZ was negligibly reduced even after the fourth cycle, which indicates that the material can be used several times through solvent washing without any significant reduction in its performance. 3.2. Adsorption mechanism


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As compared in Table S1 and S2, IMDC materials are less porous than MDC; however, IMDCs showed better performance compared to MDC in all the adsorption studies. This implies that the IL loading in ZIF-8 (and hence, increased nitrogen content in the carbonaceous materials) has a significant influence on the adsorption, considering that porosity generally determines the adsorptive performance, especially when there is no special adsorption mechanism (excluding van der Waals interaction).51 To understand this remarkable observation, we utilized the properties of the surface nitrogen species observed by XPS and FTIR analyses. As stated earlier, doped nitrogen exists in three major forms (N-6, N-5, or N-Q) on the surface of a graphitic carbon material.29,52 Among these three types of nitrogens, the N-Q sites of doped nitrogen do not have much effect on the adsorptions because of the inertness of these sites.53 However, N-6 and N-5 nitrogen sites are chemically active and are found mainly at the edge of a graphite sheet.55 Moreover, the N-6 and N-5 nitrogen sites show basic and H-bonding (as hydrogen donor) functionality,28 respectively. Therefore, these sites might be useful for acid-base and H-bonding interactions. These are two of the most important mechanisms in the case of liquid phase adsorption of organics, which has recently been shown in various studies.34,37,54-56 However, acid-base interactions cannot be applied to explain the enhanced performances since the improvements do not have any dependence on the acidity or basicity of adsorbates. Moreover, Hbonding, which can be obtained, for example, from the nitrogen doping of the graphite surface or by the introduction of oxygen/nitrogen in the adsorbents, is reported to be one of the most significant adsorption mechanisms for several hazardous materials.55,56 Additionally, in previous studies, it was found that surface functionality of the graphite surface of carbonaceous materials enhanced the adsorption of a few NCCs such as IND and QUI through H-bonding.51 Several 13 ACS Paragon Plus Environment


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other studies also showed the significance of H-bonding for the adsorption of hazardous materials including PPCPs.54,57,58 Even though it is generally understood that sulfur, unlike nitrogen and oxygen, is not capable of making H-bonds, recent studies have shown that a weak H-bond is possible between the H of the adsorbents and the S of SCC such as H2S (or in reverse mode, i.e., H-donor from H2S and Hacceptor from adsorbents).57,59 Therefore, the improved performance of IMDC with N doping in DBT adsorption might also be explained by the weak H-bond between the S atom and the N-5 sites having hydrogen. Based on the above observations, we suggest that H-bonding is one of the important mechanisms for the enhanced adsorptive performances for all of the adsorbates. A plausible mechanism for the adsorption is illustrated in Scheme 1. It should be mentioned that there might be more than one way of H-bond in some cases. For example, ATZ can make H-bond via the (i) N-H of ATZ and N-6 (as shown in Scheme 1) and (ii) the N (of the ATZ ring) and H of N-5. Detailed mechanisms, together with the detailed experimental results for the adsorption of hazardous organics over IMDC will be reported in a separate paper. As observed in earlier studies, adsorptive removal of hazardous organics from aqueous and non-aqueous phases usually requires hydrophobic and hydrophilic adsorbents, respectively.42 The effective adsorption/removal of organics both in water and fuel systems using the IMDCs, especially using doped nitrogen (as N-5 and N-6) in porous carbons, is, therefore, very advantageous. Because of the possibility of adsorption in both aqueous and non-aqueous phases, IMDCs might have various applications in adsorption. For example, vapor or gas-phase adsorptions (such as H2S, CO2, NOx, SOx, and NH3) based on H-bonding need further research.


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Moreover, acidic contaminants might also be removed via acid-base interactions by using basic nitrogen or N-6 in the IMDCs. 4. CONCLUSION Highly porous MDC and IMDCs were prepared by pyrolysis of a pristine MOF and ILintroduced MOF (via SIB technique), respectively, and characterized thoroughly using various methods including XRD, XPS, FTIR, SEM, and TEM. IMDCs have a higher nitrogen content (especially on the surface) than MDC. The pyridinic (N-6) or pyrrolic (N-5) nitrogen content of IMDCs increased with increasing the introduced IL content in MOF (before pyrolysis) or decreasing the pyrolysis temperature. Even though the porosities of the IMDCs were generally lower than that of MDC, IMDCs showed the highest adsorption capacities for all of the studied organics both in aqueous (ATZ, diuron, diclofenac sodium) and non-aqueous phases (IND, QUI, DBT). This is remarkable considering that hydrophilic and hydrophobic adsorbents are generally required for fuel and water purification, respectively. Moreover, the adsorption capacity of IMDC for ATZ was the highest among any adsorbents reported so far. These remarkable adsorptive performances might be explained using H-bonding because of the N-6 and/or N-5 nitrogen in the IMDCs. IMDC has potential applications in various fields, especially in adsorptions, based on functionality (basic or H-donating/accepting sites), high porosity, doped nitrogen, and mesoporosity.



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Funding Sources: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT and future Planning (grant number: 2015R1A2A1A15055291). ASSOCIATED CONTENT Supporting Information Supporting information is available for additional characterization data including atomic composition, structure of adsorbate materials, additional XRD patterns, XPS, FTIR spectra, SEM images, and adsorption-related results. “This material is available free of charge via the Internet at http://pubs.acs.org.” AUTHOR INFORMATION Corresponding Authors *Sung Hwa Jhung. Phone: 82-53- 950-5341; Fax: 82-53-950-6330; E-mail: [email protected] *Jong Sung Yu. Phone: 82-53- 785-6443; Fax: 82-53- 785-6409; E-mail: [email protected] ABBREVIATIONS AC, activated carbon; ATZ, attrazine; BET, Brunauer-Emmett-Teller; BJH, Barrett-JoynerHalenda; IL, ionic liquid; IMDC, IL@MOF-derived carbons; IND, indole; MDC, MOF derived carbon; MOF, metal-organic framework; NCC, nitrogen containing compound; QUI, quinoline; SCC, sulfur containing compound; PPCP, pharmaceutical and personal care products.


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25. Jiang, H -L.; Liu, B.; Lan, Y -Q.; Kuratani, K.; Akita, T.; Shioyama, H.; Zong, F., Xu, Q. From Metal-Organic Framework to Nanoporous Carbon: Toward a Very High Surface Area and Hydrogen Uptake. J. Am. Chem. Soc. 2011, 133, 11854–11857. 26. Kang, D. -Y.; Moon, J. H. Carbon Nanotube Balls and Their Application in Supercapacitors. ACS Appl. Mater. Interfaces 2014, 6, 706–711. 27. Lin, K. -Y. A.; Chang, H. -A.; Chen, B. -J. Multi-functional MOF-Derived Magnetic Carbon Sponge. J. Mater. Chem. A 2016, 4, 13611–13625. 28. Yan, Y.; Kuila, T.; Kim, N.; Lee, S. H.; Lee, J. H. N-Doped Carbon Layer Coated Thermally Exfoliated Graphene and its Capacitive Behavior in Redox Active Electrolyte. Carbon 2015, 85, 60–71. 29. Jeong, H. M.; Lee, J. W.; Shin, W. H.; Choi, Y. J.; Shin, H. J.; Kang, J. K.; Choi, J. W. Nitrogen-Doped Graphene for High-Performance Ultracapacitors and the Importance of Nitrogen-Doped Sites at Basal Planes. Nano Lett. 2011, 11, 2472–2477. 30. Tian, Z.; Dai, S.; Jiang, D. -E. Stability and Core-Level Signature of Nitrogen Dopants in Carbonaceous Materials. Chem. Mater. 2015, 27, 5775–5781. 31. Jung, C.; Son, A.; Her, N.; Zoh, K. D.; Cho, J.; Yoon, Y. Removal of Endocrine Disrupting Compounds, Pharmaceuticals, and Personal Care Products in Water Using Carbon Nanotubes: a Review. J. Ind. Eng. Chem. 2015, 27, 1−11. 32. Miller, E. L.; Nason, S. L.; Karthikeyan, K. G.; Pedersen, J. A. Root Uptake of Pharmaceuticals and Personal Care Product Ingredients. Environ. Sci. Technol. 2016, 50, 525−541. 33. 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, 444–456.


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42. Bhadra, B. N.; Cho, K. H.; Khan, N. A.; Hong, D. -Y.; Jhung, S. H. Liquid-Phase Adsorption of Aromatics Over a Metal–Organic Framework and Activated Carbon: Effects of Hydrophobicity/Hydrophilicity of Adsorbents and Solvent Polarity. J. Phys. Chem. C 2015, 119, 26620–26627. 43. Cho, H. Y.; Kim, J.; Kim, S. N.; Ahn, W. S. High Yield 1-L Scale Synthesis of ZIF-8 via a Sonochemical Route. Micropor. Mesopor. Mater. 2013, 169, 180–184. 44. Ahmed, I.; Tong, M.; Jun, J. W.; Zhong, C.; Jhung, S. H. Adsorption of Nitrogen-Containing Compounds from Model Fuel over Sulfonated Metal–Organic Framework: Contribution of Hydrogen-Bonding and Acid–Base Interactions in Adsorption. J. Phys. Chem. C 2016, 120, 407–415. 45. Bonino, F.; Brutti, S.; Reale, P.; Scrosati, B.; Gherghel, L.; Wu, J.; Müllen, K. A Disordered Carbon as a Novel Anode Material in Lithium‐Ion Cells. Adv. Mater. 2005, 17, 743−746. 46. Zhong, M.; Kim, E. K.; McGann, J. P.; Chun, S. -E.; Whitacre, J. F; Jaroniec, M.; Matyjaszewski,

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Kowalewski,

T.

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49. Fan, H. S.; Wang, H.; Zhao, N.; Xu, J.; Pan, F. Nano-Porous Architecture of N-Doped Carbon Nanorods Grown on Graphene to Enable Synergetic Effects of Supercapacitance. Sci. Rep. 2014, 4, 7426. 50. Banerjee, A.; Upadhyay, K; Puthusseri, K. D.; Aravindan, V.; Madhavi, S.; Ogale, S. MOFderived Crumpled-Sheet-Assembled Perforated Carbon Cuboids as Highly Effective Cathode Active Materials for Ultra-High Energy Density Li-Ion Hybrid Electrochemical Capacitors (Li-HECs). Nanoscale 2014, 6, 4387–4394. 51. Ahmed, I.; Khan, N. A.; Jhung, S. H. Graphite Oxide/Metal–Organic Framework (MIL-101): Remarkable Performance in the Adsorptive Denitrogenation of Model Fuels. Inorg. Chem. 2013, 52, 14155–14161. 52. Lu, Y. -F.; Lo, S. -T.; Lin, J. -C.; Zhang, W.; Lu, J. -Y.; Liu, F. -H. Tseng, C. -M.; Lee, Y. -H.; Liang, C. -T.; Li, L. -J. Nitrogen-Doped Graphene Sheets Grown by Chemical Vapor Deposition: Synthesis and Influence of Nitrogen Impurities on Carrier Transport. ACS Nano 2013, 7, 6522–6532. 53. Lai, L.; Potts, J. R.; Zhan, D.; Wang, L.; Poh, C. K.; Tang, C.; Gong, H.; Shen, Z.; Lin, J.; Ruoff, R. S. Exploration of the Active Center Structure of Nitrogen-Doped Graphene-Based Catalysts for Oxygen Reduction Reaction. Energy Environ. Sci. 2012, 5, 7936–7942. 54. Song, J. Y.; Ahmed, I.; Seo, P. W.; Jhung, S. H. UiO-66-Type Metal–Organic Framework with Free Carboxylic Acid: Versatile Adsorbents via H-bond for Both Aqueous and Nonaqueous Phases. ACS Appl. Mater. Interfaces 2016, 8, 27394–27402. 55. Ahmed, I.; Jhung, S. H. Remarkable Adsorptive Removal Of Nitrogen-Containing Compounds From a Model Fuel by a Graphene Oxide/MIL-101 Composite Through a



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Table 1. Kinetic constants and Langmuir parameters for the adsorption of ATZ from water over different adsorbents. Adsorbents

Kinetics

Langmuir parameters R2

k2

Q0 (mg/g)

b (mg/L)

R2

(g mg-1 h-1) Commercial AC

8.7 × 10-3

0.999

60

2.2 × 10-1

0.998

MDC-1000

1.1×10-2

0.998

173

3.0 × 10-1

0.995

IMDC-1000(12%)

1.2 ×10-2

0.999

208

15.2 × 10-1

0.996



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

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Scheme 1. Plausible adsorption mechanism of the six adsorbates over IMDC through H-bonding (shown as dotted lines). N-5 and N-6 nitrogen sites are highlighted in blue.


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(a)

1000

MDC-1000 IMDC-1000(4%) IMDC-1000(8%) IMDC-1000(12%)

Intensity (a.u.)

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


Commercial AC MDC-1000 IMDC-1000(4%) IMDC-1000(8%) IMDC-1000(12%)

(b)

750

500

250

002 100 15

30

45

0 0.0

60

0.2

0.4

0.6

0.8

1.0

P/Po

2 theta (deg)

Figure 1. (a) XRD patterns and (b) N2 adsorption isotherms of MDC and IMDCs. The materials were obtained by pyrolysis at 1000 oC.



50

50

(a)

(b)


40


40

30

dV/dlog(D)

dV/dlog(D)

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

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20 10

30 20 10

0

0 30

35

40

45

50

55

30

35

Pore Diameter (Å)

40

45

50

55

Pore Diameter (Å)

Figure 2. Pore size distribution curve with respect to (a) pyrolysis temperature and (b) N-content of the different materials.


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800

900

(a)

(b)


N-6 N-5 N-Q

700

c/s

800

c/s

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


700

600

600

500

500

410

405

400

410

395

405

400

395

Binding energy (eV)

Binding energy (eV)

Figure 3. XPS spectra of MDC and IMDCs in N 1s region with respect to N-content of the samples: (a) raw data and (b) smoothened graphs. The materials were obtained by pyrolysis at 1000 oC.



3

C-N (sp ) stretching 2

C=N (sp ) stretching

Transmittance (a.u.)

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

IMDC-1000(12%) IMDC-1000(8%) IMDC-1000(4%)

MDC-1000

3000

2500

2000

1500

1000

-1

Wavelength (cm )

Figure 4. FTIR spectra of MDC and IMDCs obtained by pyrolysis at 1000 oC.


Page 30 of 35

Page 31 of 35

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


Figure 5. BioTEM images for (a) commercial AC, (b) ZIF-8, (c) MDC-1000, and (d) IMDC1000(12%).



200

200

(b)

(a) 150

150

Commercial AC MDC-1000 IMDC-1000(12%)

100

qt (mg/g)

qt (mg/g)

100

50

50

0

0 0

3

6

9

0

12

3

6

9

12

Time (hr)

Time (hr)

300

(c) 240

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

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180

120

60

0 0

3

6

9

12

Time (hr)

Figure 6. Adsorption of (a) ATZ, (b) diuron, and (c) diclofenac sodium at 25 oC with time over different adsorbents.


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90

(a)

qt (mg/g)

60

ZIF-8 Commercial AC MDC-1000 IMDC-1000(4%) IMDC-1000(8%) IMDC-1000(12%)

30

0 0

(b)

90

qt (mg/g)

1

2

3

4

5

60

ZIF-8 Commercial AC MDC-1000 IMDC-1000(4%) IMDC-1000(8%) IMDC-1000(12%)

30

0 6

0

1

2

Time (hr)

3

4

5

6

Time (hr)

(c) 150

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


100

Commercial AC ZIF-8 MDC-1000 IMDC-1000(12%)

50

0 0

3

6

9

12

Time (hr)

Figure 7. Adsorption of (a) IND (b) QUI and (c) DBT at 25 oC with respect to time over different adsorbents.



150

150

(a)

(b)

100

100

Commercial AC MDC-1000 IMDC-1000(12%)

qe (mg/g)

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

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50

0

0

500

1000

1500

2000

50

0

0

Ce (ppm)

500

1000

1500

Ce (ppm)

Figure 8. Adsorption isotherms for (a) IND and (b) QUI over different adsorbents.


2000

Page 35 of 35

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Table of Contents (TOC) Image


Nitrogen-Doped Porous Carbons from Ionic Liquids@MOF

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