Article pubs.acs.org/EF
Controlling the Pyrolysis Conditions of Microporous/Mesoporous MIL-125 To Synthesize Porous, Carbon-Supported Ti Catalysts with Targeted Ti Phases for the Oxidation of Dibenzothiophene Nicholas D. McNamara, Jongsik Kim, and Jason C. Hicks* Department of Chemical and Biomolecular Engineering, University of Notre Dame, 182 Fitzpatrick Hall, Notre Dame, Indiana 46556, United States S Supporting Information *
ABSTRACT: Metal−organic frameworks (MOFs) have been used as templates to synthesize a variety of functional materials. Pyrolysis of Zn-MOFs typically yields materials that retain the high surface area of the parent MOF while imparting mesoporosity due to carbothermal reduction and Zn evaporation. When non-Zn containing MOFs are used, significant loss in surface area and porosity after pyrolysis is observed. To overcome these limitations, a hierarchical microporous/mesoporous analogue of microporous MIL-125 (Ti) was synthesized and subjected to pyrolysis at various temperatures. By varying the pyrolysis temperature, both Ti content and phase in the final materials could be altered. The resulting materials exhibited enhanced mesoporosity and activity as catalysts in the oxidation of dibenzothiophene when compared to pyrolyzed microporous MIL-125. This increased activity was attributed to the greater mesoporosity of the hierarchical materials. This work demonstrated that the properties of MOF-templated materials can be tuned by altering the morphology of the precursor MOF. thermal stabilities.12 Via thermal transformations using different synthesis conditions, many favorable properties of MOFs (i.e., high surface area, dispersion, etc.) can be retained while imparting the high chemical and thermal stability inherent to carbon-supported materials.6,7,13,14 Thus, the utilization of MOFs as templates has been demonstrated in the recent literature as an effective method to synthesize many different functional materials.6,7,13−32 Depending on the parent MOF structure and pyrolysis conditions, high surface area metals/metal oxides/metal carbides, porous carbons, or carbon-supported metal particles can be synthesized. These materials are applicable as chemical sensors,20 capacitors,21−23 adsorbents,24−28 and heterogeneous catalysts.6,7,29−32 In previous reports, we detailed a method of preparing carbon-supported metal catalysts through the pyrolysis of a postsynthetically modified Zn-based MOF (M/ IRMOF-3).6,7 These types of materials are typically prepared using methods such as incipient wetness impregnation, electrochemical deposition, photochemical reduction, or direct thermal decomposition of metal precursors on previously prepared carbon supports.12,33 These methods, however, often yield materials with poor dispersion of metals to pore blocking and unfavorable solvent−carbon support interactions.12,33 Our MOF-templated synthetic method, however, was extremely effective at preparing high surface area materials with a high dispersion of active metal sites. However, the resulting materials suffered from low metal loadings (≤5 wt % in the case of Ti) due to the limited amount of postsynthetic modifiers that could be coordinated to the parent IRMOF-3. Furthermore, the phase of the metal active sites in the final materials could not be
1. INTRODUCTION The removal of sulfur compounds from petroleum streams is an important process in liquid fuels production due to sulfur’s deleterious effects during processing and utilization.1−3 Hydrodesulfurization (HDS) is a particularly effective method for removing most sulfur compounds from petroleum streams; however, thiophenic compounds are relatively unreactive in this process.4 In order to remove these thiophenic compounds, high temperatures, high pressures, and long reaction times are necessary in order to reach deep desulfurization levels (910 °C) must be used to ensure all Zn evaporates and exits the MOF scaffold.6,7,23,34 Therefore, Ti phases typically formed at lower pyrolysis temperatures are unattainable if Zn impurities are undesirable. The metal phase of functional materials is of paramount importance as it is generally the dominant factor controlling many critical properties such as chemical/thermal stability and catalytic activity.35 During pyrolysis of MOFs, the resultant metal phase can be altered by adjusting synthetic parameters such as atmosphere (inert, oxidizing, etc.), heating rate, and temperature.7,13−15,18,29 Furthermore, the strong temperature dependence on the carbothermal reduction of Ti species under pyrolysis conditions has been studied in detail.7,29 Guo et al. pyrolyzed the Ti-based MOF known as MIL-125 at various temperatures and were able to obtain different Ti oxide phases.29 Alternatively, Kim et al. pyrolyzed IRMOF-3 coordinated with a titanium iso-propoxide complex to synthesize Ti oxycarbide nanoparticles supported on a porous carbon support.7 To avoid the problems of low loadings of metal and lack of metal phase control, pyrolysis can be performed on MOFs containing only metal centers of the desired element.15,17,20,26,29,32 In such a way, high metal loadings can be achieved due to the high metal content inherent to the parent MOF. Furthermore, by forgoing the use of a MOF containing an undesired metal, greater control over synthetic conditions is granted and the need for postpyrolysis purification can be avoided. Avoiding the use of Zn-based MOF templates, however, can lead to alternative problems. Pyrolysis of MOFs typically results in materials with morphologies that strongly depend on the morphology of the parent MOFs, most of which typically exhibit fairly small micropores (1000 °C). XRD analysis of materials pyrolyzed at different temperatures indicated that the bulk metal phase could be altered by changing the pyrolysis temperature of MIL-125. Low temperature pyrolysis (600−800 °C) led to TiO2 phases, whereas higher pyrolysis temperatures (900−1100 °C) led to more reduced Ti phases, including a Ti oxycarbide phase. Having elucidated the bulk Ti phases present in the pyrolyzed materials, XPS was used to probe the surface phases of the Ti species (Figure 4). Similar to XRD results, pyrolysis of microporous and mesoporous analogues of MIL-125 at identical temperatures yielded the presence of identical surface phases of Ti according to the XPS results. Pyrolysis of samples at all temperatures from 600 to 900 °C resulted in Ti 2p3/2 binding energies (BEs) of 459.1 eV attributed to TiO2.43 These results indicated that, regardless of the bulk phase, all materials pyrolyzed at these temperatures contained a passivating layer of TiO2 present on the surface. When materials were pyrolyzed at 1000 °C, the X-ray photoelectron spectra showed three distinct Ti 2p3/2 features. The first feature and major component of the spectrum (at 79.3% relative abundance) was located at 458.6
Figure 4. XP spectra of the Ti 2p region of MIL-125 materials pyrolyzed at (a) 600, (b) 700, (c) 800, (d) 900, (e) 1000, and (f) 1110 °C.
eV and was assigned to a surface suboxide44 (Ti4O7 surface phase) because it exhibited a BE of the Ti 2p3/2 shell between the BEs typical of TiO2 and Ti3O5 surface phases. A second minor feature (at 14.7% relative abundance) was located at 457.0 eV and was attributed to a Ti2O3 surface phase. The spectra of these 1000 °C pyrolysis materials also displayed a small third peak at 454.8 eV with a relative abundance of 6.1%, which could be assigned to a TiCxOy surface phase.43,45−48 The X-ray photoelectron spectra of MOF materials pyrolyzed at 1100 °C exhibited the same three features seen in the 1000 °C samples at Ti 2p3/2 BEs of 458.6, 457.0, and 454.8 eV, which were assigned to the presence of Ti4O7, Ti2O3, and TiCxOy, respectively. While the peak centered at 458.6 eV still dominated the spectrum (at relative abundance of 76.7%), the peak corresponding to the TiCxOy phase did become more pronounced, resulting in a relative abundance of 8.6%. Of additional note, the XPS spectra of the C 1s region of materials pyrolyzed at 1000 and 1100 °C exhibited a BE of 281.8 eV, which corresponded to a Ti-C carbon (Figure S6).45 These XPS results corroborated the presence of phases that were observed in the XRD patterns and suggested that all materials also contained oxide phase passivating layers when pyrolyzed at temperatures below 1100 °C. N2 physisorption data were analyzed using nonlocal density functional theory (NLDFT) to determine the textural properties of all pyrolyzed MIL-125 materials (Figure S7 and Figure 5). The mesopore surface areas (SAmeso) of all materials (both micro-XXX and meso-XXX series) increased with increasing pyrolysis temperature from 600 to 1000 °C. When the pyrolysis temperature was increased from 1000 to 1100 °C, however, the resulting material experienced a loss in SAmeso. The mesopore volume (Vmeso) of the micro-XXX series of materials also increased as the pyrolysis temperature was increased from 600 to 1000 °C, followed by a slight decrease at 1100 °C. The meso-XXX series, however, showed a more parabolic trend with a slight loss in Vmeso as the pyrolysis temperature was increased 598
DOI: 10.1021/acs.energyfuels.5b01946 Energy Fuels 2016, 30, 594−602
Article
Energy & Fuels
Figure 5. (a) Mesopore surface areas and (b) mesopore volumes of (blue open squares) micro-MIL-125 and (red filled circles) meso-MIL125 pyrolyzed at different temperatures.
from 600 to 700 °C. As the pyrolysis temperature was increased from 700 to 1100 °C, however, the Vmeso continually increased. Of significant note was that the meso-XXX series of materials always exhibited enhancements in both surface areas and pore volumes as compared to the micro-XXX series of materials in this temperature range. The enhanced mesoporosity innate to the meso-XXX materials was further evidenced by the mesopore size distribution, which revealed that the mesoXXX series contained a significant amount of mesopores in the 40−100 Å pore size region compared to the micro-XXX series (Figure 6). Thus, N2 physisorption analysis indicated that the
Figure 7. TEM images of (a) micro-600, (b) micro-1000, (c) micro1100, (d) meso-600, (e) meso-1000, and (f) meso-1100.
prisms. As the pyrolysis temperature was increased to 1000 °C in the micro-1000 material, the edges of the carbon nanoparticles appeared to become rougher in texture. Additionally, the Ti nanoparticles were agglomerated, which resulted in larger sized particles (17.5 ± 7.5 nm). Materials obtained from pyrolysis temperatures of 1100 °C resulted in further agglomeration of the Ti nanoparticles, resulting in a larger average particle size (19.4 ± 6.7 nm). In contrast to the micro-XXX series, TEM images of the meso-XXX series revealed significant differences in the particle morphologies. As previously stated, the meso-MIL-125 material was composed of small MOF nanoparticles (40 μm) (Figure S4). After pyrolysis of meso-MIL-125, images of meso-600 material showed large agglomerations of carbon-supported Ti nanoparticles (elements confirmed by EDX analysis). Determining individual sizes of Ti nanoparticles was difficult on this material due to such small particle sizes and instrumentation limits. However, an average size of 2.8 ± 0.7 nm was obtained by size analysis with reasonable confidence. Increasing the pyrolysis temperature to 1000 °C (meso-1000) caused the agglomeration of Ti species, resulting in larger, spherical Ti nanoparticles (13.8 ± 5.6 nm) supported on carbon. At higher pyrolysis temperatures of 1100 °C (meso-1100), larger Ti nanoparticles (16.5 ± 5.3 nm) were observed. The Ti nanoparticles in the meso-XXX series of materials, however, were consistently smaller than the Ti nanoparticles of the micro-XXX materials (when comparing materials synthesized at the same pyrolysis temperatures). This was attributed to the small size of MOF particles in the precursor meso-MIL-125. We suspect that these small MOF particles limited the aggregation of the Ti metal centers by keeping them in the confined volume of the small parent MOF particles. 3.2. Catalytic Activity in the Oxidation of Dibenzothiophene. Having demonstrated the significant differences in textural and morphological properties of the meso-XXX materials compared to the micro-XXX materials through extensive characterization, catalysis was then performed with all pyrolyzed materials to demonstrate their practical
Figure 6. Mesopore size distributions of the (a) micro-XXX series and (b) meso-XXX series of pyrolyzed materials.
morphology of the precursor MIL-125 subjected to pyrolysis had a significant effect on the textural properties of the resulting pyrolyzed materials. In order to investigate the root causes of these textural property differences between the micro-XXX and meso-XXX series, transmission electron microscopy (TEM) was used to image the morphology of the materials after pyrolysis. The micro-MIL-125 and meso-MIL-125 materials pyrolyzed at 600, 1000, and 1100 °C were analyzed by TEM, and the resulting images are depicted in Figure 7. Additionally, as shown in Figure S8, particle size analysis of the Ti nanoparticles on the resulting micro-XXX and meso-XXX materials was performed using these TEM images. As previously stated, TEM images of micro-MIL-125 (Figure S3) showed that the MOF was composed of mostly spherical particles in the size range of ∼0.5−10 μm. After pyrolysis, TEM images revealed that micro600 retained a similar morphology to micro-MIL-125. The micro-600 material was composed of spherical and rectangular carbon particles as seen in the parent MOF. This was expected as it has been shown that the morphology of the MOF prior to pyrolysis is a governing factor in determining the morphology of the pyrolyzed material.13,15,17−19,26,27 Embedded in these larger carbon nanoparticles were Ti nanoparticles in the size range of 7.0 ± 3.1 nm, which adopted the shape of rectangular 599
DOI: 10.1021/acs.energyfuels.5b01946 Energy Fuels 2016, 30, 594−602
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Energy & Fuels
activity could be attributed to the enhancement in mesoporosity in the 800 °C materials. Increasing the pyrolysis temperature once again to 900 °C led to materials with enhanced activity. This increase in activity could have been due to the enhancement in SAmeso, the phase transition from anatase and rutile to Ti2O3 and TiCxOy, or a combination of both. Casarin and co-workers performed DFT studies on the adsorption of H2S and SO2 on rutile and Ti2O3 surfaces and found that, in both cases, Ti2O3 bound the sulfur substrates more strongly.50,51 Furthermore, the S species were significantly altered upon adsorption on a Ti2O3 surface. H2S experienced dissociative adsorption, and SO2 exhibited S−O bond lengths that were dramatically lengthened upon adsorption.50,51 All of these results suggest the possibility of different active sites for catalysis on TiO2 and Ti2O3 surfaces. Utilization of the materials pyrolyzed at 1000 °C yielded a significant improvement in reaction kinetics. Once again, this could have been due to the enhanced mesoporosity of the 1000 °C materials (both sets of which showed a significant increase in SAmeso). Additionally, XPS experiments showed that the surface phases were altered from TiO2 to a combination of Ti4O7, Ti2O3, and TiCxOy phases when the pyrolysis temperature was increased from 900 to 1000 °C. Furthermore, while both the 900 and 1000 °C materials showed the same bulk metal phases (Ti2O3 and TiCxOy), quantitative XRD analysis of the 1000 °C materials showed stronger diffractions of TiCxOy compared to the Ti2O3 diffractions than those seen in the 900 °C materials. It is possible that the Ti oxycarbide phase has sites that are more active for this oxidation catalysis than the Ti2O3 phase as the Ti oxycarbide has been shown to have promising catalytic capabilities in density functional theory (DFT) studies.52,53 However, more studies are needed in order to conclusively determine this result. Both the micro-1100 and meso-1100 materials showed significant reductions in initial reaction rate. This drastic loss in activity could be due to a combination of lower mesopore surface areas and larger nanoparticle sizes of the 1100 °C materials. Additionally, the nature of the active sites on the 1100 °C materials could be different than the samples synthesized at lower pyrolysis temperatures. XRD results suggested that the 1100 °C materials have less oxygen content in the carbide phase than the 900 and 1000 °C materials. Liu et al. performed a DFT study on the activity of different Mo- and Ti-based carbides and found that, as the C coordination number of the metal atoms increased, the materials exhibited a significant loss in chemical activity.52 In the 1100 °C materials, it is reasonable to hypothesize that the C coordination number of the metal atoms is higher as there is less oxygen content in these materials, which could be the cause of the loss in activity. Vojvodic et al. also performed a DFT study on the activity of transition metal carbides and found that, when O was used to replace a C vacancy in a Ti carbide, electronic surface states and resonances arose at these sites.53 These resonances are known to appear at steps and defects and play an important role in the catalytic activity of a material.53 Furthermore, they discovered that the density of states of these resonances was depleted upon adsorption of a reactant molecule. Therefore, more oxygen substitutions could lead to more active sites in these pyrolyzed Ti oxycarbide materials. Overall, trends in activities of the materials followed the trends in mesopore surface areas of the materials, which indicated that the activity of these materials was most likely a strong function of the mesoporosity.
applications. These Ti nanoparticle-incorporated materials were hypothesized to have catalytic activity in this reaction as the precursor MIL-125 has already been reported as an active catalyst for sulfur oxidation reactions.9,37,49 All pyrolyzed materials (micro-XXX and meso-XXX) were utilized as catalysts in the oxidation of DBT by TBHP in an organic medium (decane). Although materials contained different Ti content, all reactions were conducted with the same total moles of Ti present in the reactant solution. In this reaction, the sulfur atom of DBT was oxidized to yield the corresponding sulfoxide and then sulfone of DBT. The concentration of DBT was monitored throughout the reaction as a function of time by analyzing reaction samples in a GC-FID. Only the corresponding sulfone of DBT was observed as a product in all reactions. The concentration of DBT as a function of time was used to determine apparent reaction rate constants (kapp) by fitting data to a pseudo-first-order rate model, which was used to calculate initial rates (Figure 8). The meso-XXX series of materials
Figure 8. Initial reaction rates of the oxidation of dibenzothiophene by tert-butyl hydroperoxide catalyzed by the (blue, patterned) micro-XXX series of materials and the (red, filled) meso-XXX series of materials. Reaction conditions: 88 μmol of Ti, 21.9 g of decane, 0.5 g dodecane, 0.065 g of DBT (500 ppmw sulfur), TBHP in a 10:1 molar ratio of TBHP:DBT, 80 °C, 1 atm.
consistently catalyzed the reaction at a higher rate than their micro-XXX series counterparts when materials were synthesized at the same pyrolysis temperature. This enhanced activity was attributed to a combination of greater mesoporosity (as evidenced by N2 physisorption analysis) and smaller Ti nanoparticles (as evidenced by TEM analysis) in the mesoXXX materials than that present in the micro-XXX materials. These results demonstrated how the properties of the precursor MOF provided pyrolyzed materials with properties that are more effectively tuned for practical applications. Both sets of pyrolyzed materials (micro-XXX and mesoXXX) displayed the same trends in activity as the pyrolysis temperature was altered. Increasing the pyrolysis temperature from 600 to 700 °C resulted in a loss in activity. The SAmeso of the 700 °C materials was enhanced over the SAmeso of 600 °C, but the 600 °C materials only contained a bulk anatase phase, whereas the 700 °C materials contained both bulk anatase and rutile. These results suggested that the anatase phase in the 600 °C pyrolyzed material was more active for this oxidation reaction than the anatase/rutile phases of the 700 °C material. Increasing the pyrolysis temperature from 700 to 800 °C led to materials with increased activities. These materials both contained anatase and rutile; however, the 800 °C materials had a higher mesopore surface area. Thus, this increase in 600
DOI: 10.1021/acs.energyfuels.5b01946 Energy Fuels 2016, 30, 594−602
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Energy & Fuels Notes
4. CONCLUSION In an effort to produce hierarchically microporous/mesoporous carbonaceous material supporting a high loading of Ti nanoparticles, the Ti-based metal−organic framework (MOF), MIL-125, was used as a template and subjected to thermal conversion through pyrolysis at a series of temperatures from 600 to 1100 °C. MIL-125 materials with two different morphologies were synthesized: one using a typical solvothermal method which yielded large particles of microporous MIL-125 (micro-MIL-125) and one using a vaporassisted technique which yielded agglomerations of microporous MOF nanoparticles exhibiting interparticle mesoporosity (meso-MIL-125). As the pyrolysis temperature was increased, the Ti content (>40 wt %) also increased in the final materials. Varying the pyrolysis temperature could also be used to alter the bulk metal phase of the resulting Ti nanoparticles (i.e., increasing the pyrolysis temperature led to reduced Ti oxide phases and even a Ti oxycarbide phase). All materials, however, contained passivating Ti oxide phases on the surface. Analysis of N2 physisorption data collected on these materials showed that altering the MIL-125 morphology to contain significant interparticle mesoporosity yielded materials with significantly enhanced mesoporosity when pyrolyzed compared to pyrolysis of a strictly microporous MIL-125 material. TEM images revealed that the morphology of the pyrolyzed materials mimicked the morphology of the precursor MOF. Furthermore, pyrolysis of the hierarchically microporous/mesoporous MIL-125 yielded a carbonaceous material with smaller Ti nanoparticles compared to pyrolysis of the microporous MIL-125, which was attributed to the confined environment of the Ti particles embedded in smaller carbon particles. Finally, catalytic activity tests in the oxidation of the sulfur-containing dibenzothiophene revealed that the mesoXXX materials exhibited enhanced activities over the microXXX materials. This enhancement was attributed to the increased mesoporosity and smaller Ti nanoparticle sizes contained in the meso-XXX materials when compared to the micro-XXX materials. The above results demonstrated that, by effectively tuning the morphology of the precursor MOFs, the properties of the pyrolyzed materials could be tailored to suit specific applications.
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The authors declare no competing financial interest.
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ACKNOWLEDGMENTS Acknowledgement is made to the donors of the American Chemical Society Petroleum Research Fund for support of this research (PRF# 53874-DNI10). We thank the ND Energy Materials Characterization Facility for the use of the Bruker D8 Advanced diffractometer and PHI VersaProbe II X-ray photoelectron spectrometer. TEM images were acquired using the Notre Dame Integrated Imaging Facility’s FEI Titan microscope.
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(1) Campos-Martin, J. M.; Capel-Sanchez, M. C.; Perez-Presas, P.; Fierro, J. L. G. Oxidative processes of desulfurization of liquid fuels. J. Chem. Technol. Biotechnol. 2010, 85, 879−890. (2) Chandra Srivastava, V. An evaluation of desulfurization technologies for sulfur removal from liquid fuels. RSC Adv. 2012, 2, 759−783. (3) Mjalli, F. S.; Ahmed, O. U.; Al-Wahaibi, T.; Al-Wahaibi, Y.; AlNashef, I. M. Deep oxidative desulfurization of liquid fuels. Rev. Chem. Eng. 2014, 30, 337−378. (4) Ismagilov, Z.; Yashnik, S.; Kerzhentsev, M.; Parmon, V.; Bourane, A.; Al-Shahrani, F. M.; Hajji, A. A.; Koseoglu, O. R. Oxidative desulfurization of hydrocarbon fuels. Catal. Rev.: Sci. Eng. 2011, 53, 199−255. (5) Stanislaus, A.; Marafi, A.; Rana, M. S. Recent advances in the science and technology of ultra low sulfur diesel (ULSD) production. Catal. Today 2010, 153, 1−68. (6) Kim, J.; McNamara, N. D.; Her, T. H.; Hicks, J. C. Carbothermal reduction of Ti-modified IRMOF-3: An adaptable synthetic method to support catalytic nanoparticles on carbon. ACS Appl. Mater. Interfaces 2013, 5, 11479−11487. (7) Kim, J.; McNamara, N. D.; Neumann, G. T.; Hicks, J. C. Exceptional control of carbon-supported transition metal nanoparticles using metal-organic frameworks. J. Mater. Chem. A 2014, 2, 14014− 14027. (8) Corma, A.; Garcia, H.; Llabres i Xamena, F. X. Engineering metal organic frameworks for heterogeneous catalysis. Chem. Rev. 2010, 110, 4606−4655. (9) McNamara, N. D.; Neumann, G. T.; Masko, E. T.; Urban, J. A.; Hicks, J. C. Catalytic performance and stability of (V) MIL-47 and (Ti) MIL-125 in the oxidative desulfurization of heterocyclic aromatic sulfur compounds. J. Catal. 2013, 305, 217−226. (10) Nelson, A. P.; Farha, O. K.; Mulfort, K. L.; Hupp, J. T. Supercritical processing as a route to high internal surface areas and permanent microporosity in metal-organic framework materials. J. Am. Chem. Soc. 2009, 131, 458−460. (11) Farha, O. K.; Hupp, J. T. Rational design, synthesis, purification, and activation of metal-organic framework materials. Acc. Chem. Res. 2010, 43, 1166. (12) Rodriguez-Reinoso, F. The role of carbon materials in heterogeneous catalysis. Carbon 1998, 36, 159−175. (13) Masoomi, M. Y.; Morsali, A. Applications of metal−organic coordination polymers as precursors for preparation of nano-materials. Coord. Chem. Rev. 2012, 256, 2921−2943. (14) Sun, J.-K.; Xu, Q. Functional materials derived from open framework templates/precursors: synthesis and applications. Energy Environ. Sci. 2014, 7, 2071−2100. (15) Das, R.; Pachfule, P.; Banerjee, R.; Poddar, P. Metal and metal oxide nanoparticle synthesis from metal organic frameworks (MOFs): finding the border of metal and metal oxides. Nanoscale 2012, 4, 591− 599. (16) Hall, A. S.; Kondo, A.; Maeda, K.; Mallouk, T. E. Microporous brookite-phase titania made by replication of a metal-organic framework. J. Am. Chem. Soc. 2013, 135, 16276−16279.
ASSOCIATED CONTENT
S Supporting Information *
The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.energyfuels.5b01946. XRD patterns, N2 physisorption isotherms, TEM images, and TGA profiles of micro-MIL-125 and meso-MIL-125; total surface areas and total pore volumes of the microXXX and meso-XXX materials; representative XP spectrum of C 1s region of materials; and particle size distributions of pyrolyzed materials (PDF)
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REFERENCES
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The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. 601
DOI: 10.1021/acs.energyfuels.5b01946 Energy Fuels 2016, 30, 594−602
Article
Energy & Fuels (17) Xu, X.; Cao, R.; Jeong, S.; Cho, J. Spindle-like mesoporous αFe2O3 anode material prepared from MOF template for high-rate lithium batteries. Nano Lett. 2012, 12, 4988−4991. (18) Cho, W.; Park, S.; Oh, M. Coordination polymer nanorods of Fe-MIL-88B and their utilization for selective preparation of hematite and magnetite nanorods. Chem. Commun. 2011, 47, 4138−4140. (19) Lim, S.; Suh, K.; Kim, Y.; Yoon, M.; Park, H.; Dybtsev, D. N.; Kim, K. Porous carbon materials with a controllable surface area synthesized from metal-organic frameworks. Chem. Commun. 2012, 48, 7447−7449. (20) Lu, Y.; Zhan, W.; He, Y.; Wang, Y.; Kong, X.; Kuang, Q.; Xie, Z.; Zheng, L. MOF-templated synthesis of porous Co3O4 concave nanocubes with high specific surface area and their gas sensing properties. ACS Appl. Mater. Interfaces 2014, 6, 4186−4195. (21) Chaikittisilp, W.; Hu, M.; Wang, H.; Huang, H. S.; Fujita, T.; Wu, K. C.; Chen, L. C.; Yamauchi, Y.; Ariga, K. Nanoporous carbons through direct carbonization of a zeolitic imidazolate framework for supercapacitor electrodes. Chem. Commun. 2012, 48, 7259−7261. (22) Hu, J.; Wang, H.; Gao, Q.; Guo, H. Porous carbons prepared by using metal−organic framework as the precursor for supercapacitors. Carbon 2010, 48, 3599−3606. (23) Liu, B.; Shioyama, H.; Jiang, H.; Zhang, X.; Xu, Q. Metal− organic framework (MOF) as a template for syntheses of nanoporous carbons as electrode materials for supercapacitor. Carbon 2010, 48, 456−463. (24) Almasoudi, A.; Mokaya, R. Preparation and hydrogen storage capacity of templated and activated carbons nanocast from commercially available zeolitic imidazolate framework. J. Mater. Chem. 2012, 22, 146−152. (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) Kim, T. K.; Lee, K. J.; Cheon, J. Y.; Lee, J. H.; Joo, S. H.; Moon, H. R. Nanoporous metal oxides with tunable and nanocrystalline frameworks via conversion of metal-organic frameworks. J. Am. Chem. Soc. 2013, 135, 8940−8946. (27) Pachfule, P.; Biswal, B. P.; Banerjee, R. Control of porosity by using isoreticular zeolitic imidazolate frameworks (IRZIFs) as a template for porous carbon synthesis. Chem. - Eur. J. 2012, 18, 11399− 11408. (28) Yang, S. J.; Kim, T.; Im, J. H.; Kim, Y. S.; Lee, K.; Jung, H.; Park, C. R. MOF-derived hierarchically porous carbon with exceptional porosity and hydrogen storage capacity. Chem. Mater. 2012, 24, 464− 470. (29) Guo, Z.; Cheng, J. K.; Hu, Z.; Zhang, M.; Xu, Q.; Kang, Z.; Zhao, D. Metal-organic frameworks (MOFs) as precursors towards TiOx/C composites for photodegradation of organic dye. RSC Adv. 2014, 4, 34221−34225. (30) Ma, S.; Goenaga, G. A.; Call, A. V.; Liu, D. J. Cobalt imidazolate framework as precursor for oxygen reduction reaction electrocatalysts. Chem. - Eur. J. 2011, 17, 2063−2067. (31) Palaniselvam, T.; Biswal, B. P.; Banerjee, R.; Kurungot, S. Zeolitic imidazolate framework (ZIF)-derived, hollow-core, nitrogendoped carbon nanostructures for oxygen-reduction reactions in PEFCs. Chem. - Eur. J. 2013, 19, 9335−9342. (32) Wang, W.; Li, Y.; Zhang, R.; He, D.; Liu, H.; Liao, S. Metalorganic framework as a host for synthesis of nanoscale Co3O4 as an active catalyst for CO oxidation. Catal. Commun. 2011, 12, 875−879. (33) Yang, Y.; Chiang, K.; Burke, N. Porous carbon-supported catalysts for energy and environmental applications: A short review. Catal. Today 2011, 178, 197−205. (34) Liu, B.; Shioyama, H.; Akita, T.; Xu, Q. Metal-organic framework as a template for porous carbon synthesis. J. Am. Chem. Soc. 2008, 130, 5390−5391. (35) Sang, L.; Zhao, Y.; Burda, C. TiO2 nanoparticles as functional building blocks. Chem. Rev. 2014, 114, 9283−9318.
(36) Bradshaw, D.; El-Hankari, S.; Lupica-Spagnolo, L. Supramolecular templating of hierarchically porous metal-organic frameworks. Chem. Soc. Rev. 2014, 43, 5431−5443. (37) McNamara, N. D.; Hicks, J. C. Chelating agent-free, vaporassisted crystallization method to synthesize hierarchical microporous/ mesoporous MIL-125 (Ti). ACS Appl. Mater. Interfaces 2015, 7, 5338− 5346. (38) Dan-Hardi, M.; Serre, C.; Frot, T.; Rozes, L.; Maurin, G.; Sanchez, C.; Ferey, G. A new photoactive crystalline highly porous titanium(IV) dicarboxylate. J. Am. Chem. Soc. 2009, 131, 10857− 10859. (39) Fu, Y.; Sun, D.; Chen, Y.; Huang, R.; Ding, Z.; Fu, X.; Li, Z. An amine-functionalized titanium metal-organic framework photocatalyst with visible-light-induced activity for CO2 reduction. Angew. Chem., Int. Ed. 2012, 51, 3364−3367. (40) Shen, Y. Carbothermal synthesis of metal-functionalized nanostructures for energy and environmental applications. J. Mater. Chem. A 2015, 3, 13114−13188. (41) Yu, T.; Deng, Y. H.; Wang, L.; Liu, R. L.; Zhang, L. J.; Tu, B.; Zhao, D. Y. Ordered mesoporous nanocrystalline titanium-carbide/ carbon composites from in situ carbothermal reduction. Adv. Mater. 2007, 19, 2301−2306. (42) Jiang, Z.; Rhine, W. E. Preparation of TiN and TiC from a polymeric precursor. Chem. Mater. 1991, 3, 1132−1137. (43) McCafferty, E.; Wightman, J. P. Determination of the concentration of surface hydroxyl groups on metal oxide films by a quantitative XPS method. Surf. Interface Anal. 1998, 26, 549−564. (44) Mizuno, Y.; King, F. K.; Yamauchi, Y.; Homma, T.; Tanaka, A.; Takakuwa, Y.; Momose, T. Temperature dependence of oxide decomposition on titanium surfaces in ultrahigh vacuum. J. Vac. Sci. Technol., A 2002, 20, 1716−1721. (45) Zhang, L.; Koka, R. V. A study on the oxidation and carbon diffusion of TiC in alumina-titanium carbide ceramics using XPS and Raman spectroscopy. Mater. Chem. Phys. 1998, 57, 23−32. (46) Chen, X.; Glans, P.-A.; Qiu, X.; Dayal, S.; Jennings, W. D.; Smith, K. E.; Burda, C.; Guo, J. X-ray spectroscopic study of the electronic structure of visible-light responsive N-, C- and S-doped TiO2. J. Electron Spectrosc. Relat. Phenom. 2008, 162, 67−73. (47) Hassan, M.; Rawat, R. S.; Lee, P.; Hassan, S. M.; Qayyum, A.; Ahmad, R.; Murtaza, G.; Zakaullah, M. Synthesis of nanocrystalline multiphase titanium oxycarbide (TiCxOy) thin films by UNU/ICTP and NX2 plasma focus devices. Appl. Phys. A: Mater. Sci. Process. 2008, 90, 669−677. (48) Rüdiger, C.; Maglia, F.; Leonardi, S.; Sachsenhauser, M.; Sharp, I. D.; Paschos, O.; Kunze, J. Surface analytical study of carbothermally reduced titania films for electrocatalysis application. Electrochim. Acta 2012, 71, 1−9. (49) Kim, S.-N.; Kim, J.; Kim, H.-Y.; Cho, H.-Y.; Ahn, W.-S. Adsorption/catalytic properties of MIL-125 and NH2-MIL-125. Catal. Today 2013, 204, 85−93. (50) Casarin, M.; Ferrigato, F.; Maccato, C.; Vittadini, A. SO2 on TiO2(110) and Ti2O3(1012) nonpolar surfaces: A DFT study. J. Phys. Chem. B 2005, 109, 12596−12602. (51) Casarin, M.; Vittadini, A. A theoretical study of the chemisorption of H2O and H2S on the Ti2O3(1012) non-polar surface. Phys. Chem. Chem. Phys. 2003, 5, 2461−2468. (52) Liu, P.; Rodriguez, J. A. Effects of carbon on the stability and chemical performance of transition metal carbides: a density functional study. J. Chem. Phys. 2004, 120, 5414−5423. (53) Vojvodic, A.; Hellman, A.; Ruberto, C.; Lundqvist, B. I. From electronic structure to catalytic activity: A single descriptor for adsorption and reactivity on transition-metal carbides. Phys. Rev. Lett. 2009, 103, 146103.
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DOI: 10.1021/acs.energyfuels.5b01946 Energy Fuels 2016, 30, 594−602
