Synthesis of zeolite-templated carbons using oxygen-containing organic solvents

Zeolite-templated synthesis of ordered microporous carbons was performed with Ca2+ ion-exchanged Y and beta zeolites, where the conventionally used carbon source gases (e.g., ethylene and propylene) were replaced by various organic solvents, such as methanol, ethanol, isopropanol, acetone, tetrahydrofuran, and diisopropyl ether.

Microporous and Mesoporous Materials 318 (2021) 111038 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: http://www.elsevier.com/locate/micromeso Synthesis of zeolite-templated carbons using oxygen-containing organic solvents Hongjun Park a, Jisuk Bang a, b, Seung Won Han a, Raj Kumar Bera a, Kyoungsoo Kim c, Ryong Ryoo a, b, * a b c Center for Nanomaterials and Chemical Reactions, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea Department of Chemistry, Korea Advanced Institute of Science and Technology (KAIST), Daejeon, 34141, Republic of Korea Department of Chemistry, Jeonbuk National University, Jeollabuk-do, 54896, Republic of Korea A R T I C L E I N F O A B S T R A C T Keywords: Zeolite-templated carbon Organic solvent Synthesis Chemical vapor deposition Supercapacitor application Zeolite-templated synthesis of ordered microporous carbons was performed with Ca2+ ion-exchanged Y and beta zeolites, where the conventionally used carbon source gases (e.g., ethylene and propylene) were replaced by various organic solvents, such as methanol, ethanol, isopropanol, acetone, tetrahydrofuran, and diisopropyl ether The oxygen-containing solvents were fed to the zeolites as carried by N2 gas through a bubbler Mass spectrometric analyses of the carbonization stream indicated that isopropanol, acetone, tetrahydrofuran, and diisopropyl ether were converted largely to propylene and H2O vapor, while ethanol and methanol to ethylene The simultaneous generation of H2O and the olefins, without using high-pressure gas cylinders, can be merit in the Ca2+ ion-catalyzed synthesis of zeolite-templated carbons (ZTCs) The approach in this work provides a facile way to produce high quality ZTCs exhibiting excellent micropore orders and high specific capacitances in supercapacitor applications Introduction Three-dimensional (3D) graphenes refer to carbonaceous materials with a 3D interconnected porous structure made up of a single layer of sp2-bonded carbon atoms [1–3] The 3D graphenes, particularly those with a negative Gaussian curvature along the carbon surfaces, have received considerable attention in recent years Research groups have proposed saddle-like, negatively curved structure having heptagonal or octagonal carbon rings, which are expected to alter the electrical, magnetic, optical, and mechanical properties as compared to those of 2D graphenes [4–8] Especially, due to their unique properties, synthesis of negatively curved carbon materials that resemble triply periodic mini­ mal surfaces (so-called Schwarzites) have been explored for a long time [9,10] Theoretical works suggested that the 7- or 8-membered rings would cause stronger adsorption of Li ions and other adsorbates on the carbon surfaces, thereby increasing the adsorption capacity [11–13] Furthermore, it has been demonstrated that 3D graphene-based carbons exhibit new and potentially useful catalytic properties in (de)hydroge­ nation, rearrangement, and isomerization reactions [14,15] Among various routes to produce nanoporous carbons [16,17], the most effective way to generate 3D graphene-like surface structures is to use zeolite templates [18–21] The first step of the zeolite-templated carbon (ZTC) synthesis is pyrolytic carbonization of a carbon source (typically, acetylene, ethylene or propylene) in zeolite pores The second step is liberation of the deposited carbon framework by dissolution of the template using HF/HCl or NaOH/HCl [22] The carbon product has an ordered microporous structure, corresponding to a negative replica of the zeolite There are more than 200 kinds of zeolite, but only a few of them with pore apertures built with 12≡Si–O- units, such as FAU (X and Y), EMT and beta zeolites, have practical significance as a ZTC template The 12-membered oxygen-ring (or 12 MR) pore apertures of these ze­ olites are similar to the diameter of C60 fullerene, but too narrow for the formation of any multi-walled carbon nanotubes The only problem with the 12 MR zeolites is that the tightly fitting pores tend to cause serious diffusion limitations for the carbon sources [19,23] Consequently, the ZTC synthesis often suffers from incomplete filling of carbon in the in­ ternal micropores of the template, and also deposition of graphite-like carbon multilayers at the external surfaces [24–26] Several approaches have been proposed to resolve the diffusion limitation problem A commonly employed method is to conduct a flow- * Corresponding author Center for Nanomaterials and Chemical Reactions, IBS, Daejeon, 34141, Republic of Korea E-mail address: rryoo@kaist.ac.kr (R Ryoo) https://doi.org/10.1016/j.micromeso.2021.111038 Received 18 January 2021; Received in revised form 10 March 2021; Accepted 12 March 2021 Available online 17 March 2021 1387-1811/© 2021 The Authors Published by Elsevier Inc This is an open (http://creativecommons.org/licenses/by-nc-nd/4.0/) access article under the CC BY-NC-ND license H Park et al Microporous and Mesoporous Materials 318 (2021) 111038 type chemical vapor deposition (CVD) through a thin bed of zeolite powder, using a hydrocarbon gas diluted in N2 or by low-pressure CVD [26] Agitation of zeolite bed using a rotary tubular furnace has also been proposed for uniform infiltration of the carbon sources [23] Whereas these approaches focused on optimizing physical parameters, the laboratory of the present authors has developed a chemical method that involves the incorporation of La3+, Y3+, or Ca2+ within the zeolite template by an ion exchange process [19,27,28] A common feature of these metal cations is that they are carbide forming elements These carbide-forming cations promoted (or catalyzed) the CVD of ethylene, but the catalytic function required feeding of H2O vapor In the present work, based on the Ca2+ ion-promoted ZTC synthesis, we explored possibilities for using common laboratory organic solvents, instead of ethylene stored in a high-pressure cylinder Up to now, a few carbon sources in liquid state have already been reported in ZTC syn­ theses, such as acetonitrile, benzene, 2-methylfuran, methanol and ethanol [20,24,29–32] Each of these previous works was specialized to a particular kind of organic compound in a Na+ or H+ ion-exchanged zeolite In the present work, we sought a more generalized principle that would be useful for the selection of liquid carbon sources, through ZTC synthesis tests with methanol, ethanol, isopropanol (IPA), acetone, tetrahydrofuran (THF), and diisopropyl ether (DIPE) with Ca2+ ion-exchanged Y and β templates These oxygen-containing compounds were chosen since they were easily available, and furthermore, expected to produce H2O vapor under the carbonization conditions adsorption at − 186.15 ◦ C, X-ray powder diffraction (XRD, Cu Kα radi­ ation with λ = 0.154 nm), and transmission electron microscopy (TEM) All the characterizations were performed following the same procedures reported previously [22] Experimental section Decomposition products of the organic solvents were analyzed using an on-line installed quadrupole mass spectrometer (Pfeiffer Vacuum) The gas sampling was performed continuously from the outlet of the CVD stream through a capillary sampler to the mass spectrometer The multichannel mass signal intensities were plotted as a function of CVD time under various deposition conditions These plots were used to analyze chemical species that were generated during the CVD The flow rate and heating conditions were the same as described above, except that the organic solvents were flowed as carried in He (99.999%, Joongang gas) bubbles instead of N2, to avoid overlapping of N2 mass peaks with those of ethylene 2.4 Electrochemical capacitance measurements For measuring capacitance in an aqueous electrolyte, a carbon ink was prepared following the method in the literature [22] In specific, mg of ZTC was dispersed in a mixture of 0.084 mL of water, 0.1 mL of wt% Nafion (Sigma-Aldrich), and 0.316 mL of ethanol by sonication for h The working electrode was prepared through drop casting μL of the ink on an alumina-polished glassy carbon electrode (d = mm) The mass-areal loading of the carbon in the electrode was 0.4 mg cm− The capacitance was measured in negative potential window of − 0.2–0.8 V vs Ag/AgCl with three-electrode system A M Na2SO4 aqueous solu­ tion saturated with N2 gas was used as the electrolyte Cyclic voltam­ metry (CV) and Galvanostatic charge/discharge (GCD) measurements were performed using a workstation (Autolab PGSTAT30) at room temperature The CV curve was obtained after repeated scans for sta­ bilization The specific capacitance was calculated from the GCD curve, measured after CV stabilization, by following the equations in the literature [34] 2.5 Mass analysis in carbonization stream 2.1 Zeolite preparation FAU-Y zeolite with Si/Al = 2.4 was synthesized following the same procedures reported previously [33] Three samples of FAU zeolite and one sample of beta zeolite were purchased in a powder form from Tosoh The Tosoh zeolite codes of these samples are HSZ-320NAA (Y with Si/Al = 2.8), HSZ-350HUA (USY with Si/Al = 5.5), HSZ-360HUA (USY with Si/Al = 7.5), and HSZ-HOA301 (β with Si/Al = 14), respectively A FAU-X zeolite (Si/Al = 1.2, 13X) was purchased from Sigma-Aldrich All the zeolite samples were ion-exchanged into a Ca2+ ionic form prior to their use as a carbon template, following the ion-exchange procedure reported elsewhere [28] Results and discussion 3.1 Evaluation of carbon precursors for CaY-ZTC synthesis 2.2 Carbon synthesis In the present ZTC synthesis, it was important to achieve the initial deposition of carbonaceous polymers as fully as possible throughout the entire zeolite micropore system, without the deposition at external surfaces To this, the precursor concentration and the deposition temperature were optimized for each carbon precursor with a lab-made, Ca2+ ion-exchanged Y zeolite (denoted by CaY, Si/Al = 2.4, Ca/Al = 0.45) IPA, acetone, THF, DIPE, ethanol, and methanol were tested as carbon precursors because of their high volatility near room tempera­ ture The test was performed with a N2-bubbled vapor stream without additional feeding of water vapor, which is in contrast to the case of ethylene precursor [19,28] For each carbon precursor, the pyrolytic deposition conditions were optimized through the exploration of the effects of temperature and organic vapor pressure The optimized syn­ thesis conditions obtained in this manner are summarized in Table The ‘Carbon Products’ in Table indicate the resultant carbon products collected after liberation from the zeolite template using an aqueous solution of HF/HCl mixture As shown in Table 1, when IPA was used as a carbon precursor in CaY, the optimum time for the pyrolytic deposition was h at 550 ◦ C The resultant ZTC yield from IPA was 0.30 g carbon per g CaY zeolite, which was similar to the carbon yields from ethylene and propylene in the same zeolite (0.33 g g−zeolite ) On the other hand, when NaY zeolite was used as a template, the carbon yield from IPA was only 0.03 g g−zeolite Even in the case of HY zeolite, the carbon yield was only 0.15 g Isopropyl alcohol (99.5%, Sigma-Aldrich), acetone (99.9%, SigmaAldrich), tetrahydrofuran (99.5%, Daejung), diisopropyl ether (99.0%, Sigma-Aldrich), ethanol (99.9%, Merck), and methanol (99.9%, Merck) were used for carbon synthesis as purchased These organic solvents were fed as a vapor carried by N2 gas through a bubbler Typically, 0.3 g of a zeolite sample was placed on a fritted disk in a vertically mounted, fused quartz reactor (d = 15 mm) The reactor was heated to a desired temperature for carbonization under a high-purity N2 gas flow at a rate of 60 cm3 min− The N2 flow was then switched to flow through a N2 bubbler containing an organic solvent The concentration of the organic solvent in N2 was controlled by the temperature of a constanttemperature bath surrounding the bubbler The flow of the organic vapor was maintained in this manner over 2–5 h The exact time of flow was optimized, depending on the carbon source and the bubbler tem­ perature After the carbon deposition in zeolite pores was accomplished, the zeolite-carbon composite was heated for h at 900 ◦ C under a N2 flow The resultant carbon was then released from the zeolite template using a mixture of 1.0 M HF (J.T Baker) and 1.0 M HCl (Junsei), as reported elsewhere [28] 2.3 Materials characterization Characterization of carbon samples was performed by argon H Park et al Microporous and Mesoporous Materials 318 (2021) 111038 Table Optimized carbonization conditions and results for CaY zeolite and various carbon precursors Zeolite-Carbon Source Carbonization Conditions Tb ( C) N2/Organic Flow Rates (cm CaY-IPA CaY-Acetone CaY-THF CaY-DIPE CaY-Ethanol CaY-Methanol CaY-Propylene CaY-Ethylene 20 − 10 3 20 − 30h 30h 60/3 60/3 60/3 60/3 60/3 60/3 60/15 60/15 a c d e f g h a ◦ Carbon Products b − ) Tcc (◦ C) d t (h) Carbon Yielde (g g−zeolite ) SBETf (m2 g− 1) Vmicrog (cm3 g− 1) 550 550 550 550 600 600 550 600 2 3 0.30 0.31 0.31 0.30 TABLE 0.34 0.31 0.33 3600 3740 3370 3780 2780 2720 3520 2710 1.43 1.48 1.33 1.49 1.20 1.07 1.39 1.09 Bubbler temperature.b Flow rate was determined by solvent vapor pressure at corresponding bubbler temperature Carbonization temperature Carbonization time Carbon yield was determined by TGA BET specific surface area was calculated from the adsorption data in the relative pressure (P/P0) region between 0.05 and 0.15 Micropore volume was determined from the density functional theory cumulative volume in the pore size range of D < nm Temperature of bubbler used to feed water vapor g−zeolite This result indicates that Ca2+ ions in the zeolite acted as an effective catalyst or promotor for the IPA carbonization process, as compared to Na+ and H+ The resultant IPA-derived ZTC product from CaY exhibited a high Brunauer–Emmett–Teller (BET) surface area of 3600 m2 g− with a large micropore volume of 1.43 cm3 g− Similar to the case of IPA, when acetone, THF, and DIPE were used as the carbon sources, the carbon deposition in CaY was accomplished at 550 ◦ C (Table 1) The obtained ZTC products exhibited excellent BET surface areas (3370–3780 m2 g− 1) with large micropore volumes (1.33–1.49 cm3 g− 1), which were comparable to those of the IPA-based carbon However, when methanol and ethanol were used as the carbon pre­ cursors, the optimum temperature for the carbonization had to be increased to 600 ◦ C The carbon yields from methanol and ethanol were similar to those from IPA, acetone, THF, and DIPE, but there was a significant difference in the porous textural properties That is, the BET surface areas (~2700 m2 g− 1) and micropore volumes (~1.1 cm3 g− 1) of the ZTCs from both ethanol and methanol were 20–30% lower, compared with the other four organic solvents Based on the required carbonization temperature and the resultant BET areas and pore volumes, the carbon precursors could be classified into two groups, represented as IPA-group compounds (i.e., IPA, acetone, THF and DIPE) and ethanol-group compounds (i.e., ethanol and methanol) The BET surface areas and micropore volumes of the ZTCs from the IPA-group compounds were similarly high to those of the carbon from propylene (3520 m2 g− 1, 1.39 cm3 g− 1) On the other hand, the ethanol-group compounds yielded ZTC products having specific surface areas and pore volumes much alike to those of carbon from ethylene (2710 m2 g− 1, 1.09 cm3 g− 1), which were comparatively low Further details of the carbon characterization resulting from the six solvents are discussed in the following section deposition of graphite-like multilayer carbons on the external surfaces However, the internal ZTC frameworks showed detectable differences in the long-range pore order, consistent with the quality trend of IPA ≈ acetone ≈ THF ≈ DIPE ≈ propylene ≫ ethanol ≈ methanol ≈ ethylene As shown in Fig 1b and c, both the ZTCs from IPA and ethanol exhibited lattice fringes with a d-spacing of 1.4 nm, but there was a noticeable difference in the long-range orders (see TEM images in Fig S1 for the other samples) We investigated the chemical bonding nature of the ZTC products, using 13C MAS NMR and Raman spectroscopy The 13C NMR spectra of the carbon samples showed a single broad peak centered at 120–130 ppm, which is characteristic of sp2-hybridized carbons, regardless of the choice of the carbon precursors (Fig S2) [19,36,37] The similarity in their chemical structures was again observed in the Raman spectra, which exhibited the formation of a single-layered carbon framework along the zeolite surface These results are similar to our previous work on ethylene carbonization (Fig S3) [28,38,39] The C/H/O elemental ratios of the ZTCs (i.e., 93/2/5 in weight ratio or simply C25H6⋅4O) were also very similar to each other (Table S1) In addition, the IPA-derived ZTC sample exhibited very similar thermal stability to that of ZTCs resulting from ethylene and propylene upon calcination in air (Fig S4) [19] The ZTC products in Table were further examined by micropore analyses using Ar adsorption (Fig 2) The results showed a very sharp increase of adsorption quantity in the region of P/P0 < 0.02, at which indicates that the carbons were highly microporous with an extremely narrow distribution of micropore diameters All four ZTC samples ob­ tained from IPA group possessed about a 20–35% higher volume of micropores than the volumes of ZTCs synthesized with ethanol group In addition, the former group of ZTCs exhibited a sharper distribution of micropore diameters The narrow distribution peak centered at ~0.9 nm in Fig insets can be interpreted as a result of faithful replication of the zeolite micropores into the ZTC frameworks [19,40] From the results, it was suggested that the micropores in the carbons from IPA, acetone, THF, and DIPE were more faithfully replicated than the cases of ethanol and methanol The ZTC products in Table were further examined to check whether the surface area variation would actually cause a significant difference in specific capacitance Fig shows the capacitance values measured in an aqueous solution of Na2SO4 (see Fig S5 for CV curves and Fig S6 for GCD profiles) The capacitance values show a good linear correlation with the BET surface areas This result is in good agreement with pre­ vious works supporting that the supercapacitor capacitance should be proportional to the specific surface areas when compared with carbons with similar surface chemistry under a sufficiently low discharge rate [41–44] Under these conditions, the effects of the electrical resistance 3.2 Pore structure of CaY-templated carbon products Fig 1a shows the powder XRD patterns of the ZTC products shown in Table All the XRD patterns have a sharp XRD peak centered at 2θ = 6.5◦ (i.e., d = 1.4 nm) The presence of the XRD peak indicates that the ordered microporous structure of the zeolite has been inherited to the carbons successfully [19,35] However, there is a remarkable difference in the peak intensity between the ZTCs obtained from the IPA-acetone-THF-DIPE-propylene group and those from the ethanol-methanol-ethylene group (Fig 1a) The difference is in good agreement with the aforementioned analysis of surface areas and micropore volumes Based on this analysis, we believe that the quality of the ZTCs varies in the order of IPA ≈ acetone ≈ THF ≈ DIPE ≈ pro­ pylene ≫ ethanol ≈ methanol ≈ ethylene We investigated TEM images of all the ZTC products The TEM image analysis indicated no significant H Park et al Microporous and Mesoporous Materials 318 (2021) 111038 Fig (a) Powder XRD patterns of the CaY-ZTC samples synthesized using different precursors under the synthesis conditions summarized in Table Each XRD pattern was obtained under the same measurement conditions The intensity in the XRD patterns was expressed in the same unit (i.e., counts per second, cps) Representative TEM images of the carbons from (b) IPA and (c) ethanol could be neglected, and the specific capacitance would be decided by the surface areas available for the electrolyte adsorption [45,46] Based on the present capacitance results, we believe that all the measured BET surface areas of the ZTCs could be equally utilized for the adsorption of electrolyte ions The aperture diameter (0.67 nm in β) is similar to that of FAU-Y zeolite (0.74 nm) [47], but they have markedly different pore shapes (see Fig S7 for structure models) β zeolite is a typical channel-type zeolite, with micropores perpendicularly interconnected to form a 3D porous network [48] The β zeolite template was ion-exchanged three times with Ca2+ In the case of the Ca2+ ion-exchanged β (Caβ) zeolite with Si/Al = 14, the precursor trend was completely reversed As shown in Table 2, the BET area and pore volume of the resultant Caβ-ZTCs decreased in the order of ethanol ≈ methanol ≈ ethylene (3400 m2 g− 1, 1.36 cm3 g− 1) ≫ IPA ≈ acetone ≈ THF ≈ DIPE ≈ propylene (2350 m2 g− 1, 0.93 cm3 g− 1), as shown in Table This order was consistent with the XRD data (Fig S8) As shown in Fig 4a, the XRD pattern of the ethanol-derived 3.3 Evaluation of carbon precursors for Caβ-ZTC synthesis In the case of CaY-templated carbons, the IPA group precursors gave distinctively high-quality ZTC products, compared to those synthesized with the ethanol group precursors However, this result was only a particular case for CaY zeolite The ZTC synthesis was investigated with a β zeolite with Si/Al = 14 The β zeolite also has 12 MR pore apertures H Park et al Microporous and Mesoporous Materials 318 (2021) 111038 Fig Ar adsorption-desorption isotherms of the CaY-ZTC samples synthesized using the organic precursors (solid line), which were compared to the isotherm of the carbon synthesized using ethylene (dashed line) Insets of each graph are the pore size distributions of the carbon products synthesized using each organic precursor The horizontal axis of the inset plots is pore diameter (D, nm), and the vertical axis is dV/dD (cm3 g− nm− 1) ZTC product from Caβ zeolite exhibited broad but well-distinguished The CVD conditions for β zeolite were also individually optimized for each carbon source, in the same manner as described in the synthesis of FAU-ZTC in the previous section The optimized synthesis results are presented in Fig and Table Bragg reflections at 2θ = 7.8◦ and 15◦ , indicating replication of the (101) and (201) planes in the polymorph A of beta zeolite (BEA*) [31, 49–51] The structural order of the Caβ-ZTC from ethanol was similar to that of the ethylene-based Caβ-ZTC However, in the cases of IPA and propylene, both ZTC products exhibited only a low-intensity peak at 7.8◦ The Ar adsorption analysis was consistent with the XRD data (Fig 4b and 4c) The TEM image of all the Caβ-ZTC samples (Fig S9) showed that the carbon had lattice fringes of 1.1 nm The lattice fringes in β-ZTC looked somewhat disordered This did not originate from poor template replication, but rather from the intrinsic structural disorder of three polymorph structures in β zeolite itself [48] Among the Caβ-ZTCs, the carbons obtained from ethanol-based precursors exhibited an even sharper distribution of micropore diameters than those from the IPA-group precursors As these results show, these ZTC products exhibited a very sharp peak at D ≈ nm, which is ascribed to the H Park et al Microporous and Mesoporous Materials 318 (2021) 111038 ion-exchanged templates, H2O vapor was reported to be essential to promote pore-selective carbon deposition by activating the metal ion catalyst [16,28] In the case of the organic solvent precursor, no addi­ tional feeding of water vapor was needed, which is convenient in terms of the experimental apparatus All the IPA-group compounds were decomposed to produce propylene as a major acting carbon source rather than ethylene On the other hand, in the case of the ethanol-group compounds, ethylene was a major decomposition product The product difference clarified why the IPA-group compounds exhibited carbon deposition behavior similar to that of propylene, while ethanol and methanol behaved similar to ethylene To understand the difference in the carbonization characteristics of ethylene and propylene within Y and β zeolites, we reinvestigated the effect of zeolite Si/Al ratios on the structural quality of the carbon products from propylene and ethylene [20,54,55] Fig S11 shows XRD patterns of the ZTC products that were synthesized using X zeolite (Si/Al = 1.2), Y zeolite (Si/Al = 2.4), and two USY zeolite (Si/Al = 5.5 and 7.5, respectively) templates The four zeolites have the same FAU structure, except for the differences in the Si/Al ratio and corresponding changes in the lattice parameter [56] The XRD patterns indicate that the structural order of the ZTC products depended not only on the zeolite Si/Al ratios but also on the carbon sources When propylene was the carbon precursor (Fig S11a), the zeolites with both Si/Al = 1.2 and 2.4 gave ZTC products exhibiting a very sharp XRD peak centered at 2θ = 6.5◦ However, the zeolites with Si/Al = 5.5 and 7.5 yielded ZTC products exhibiting much lower structural orders The higher the Al content in the series of FAU zeolite templates was, the more highly or­ dered were the carbon structures In particular, the USY zeolite with Si/Al = 7.5 provided a carbon product almost without structural order, and the carbon yield was only 0.13 g g−zeolite In this zeolite, Ca2+ ions appeared to exist too sparsely to form interconnected carbon frame­ works When ethylene was the carbon source in the FAU template, the carbon deposition yield in the USY zeolite with Si/Al = 7.5 was increased to 0.27 g g−zeolite , but the resultant carbon product still exhibited a very poor structural order (Fig S11b) The other FAU zeo­ lites with Si/Al = 1.2, 2.4, and 5.5 all yielded ZTC products exhibiting an ordered microporous structure One notable point in the ethylene-based synthesis is that the ZTC structural order decreased as the zeolite Al content increased within the series of FAU templates with Si/Al = 1.2, 2.4, and 5.5, while the trend was the opposite in the case of propylene According to these results, when choosing an appropriate precursor for Ca2+-assisted ZTC synthesis, it would be helpful to consider the Si/Al ratio of the zeolite template This consideration for zeolite template will be useful for adsorption, catalysis, and electrochemical applications of the synthesized nanoporous carbon materials [57–61] Fig Specific capacitance of CaY-ZTC electrodes (with dashed line as a guide to the eye) measured in an aqueous M Na2SO4 electrolyte at discharge current density of 0.1 A g− as a function of the BET surface area of the carbons The ZTC samples synthesized using (a) DIPE, (b) acetone, (c) IPA, (d) propylene, (e) THF, (f) ethanol, (g) methanol, and (h) ethylene as the carbon source zeolite-inherited primary micropores The shoulder peaks appearing at around 1.5 nm (i.e., secondary micropores due to defective templating [19]) were low in intensity, similar to the case of CaY-ZTCs from the IPA-group precursors in Fig Based on these product characterization results, we could conclude that the ethanol-group compounds were more suitable as a carbon precursor for ZTCs than the IPA-group com­ pounds when Caβ zeolite was the template 3.4 Mechanistic investigation of ZTC synthesis For better understanding of the different trends in carbonization behavior of different solvent precursors, we investigated how the com­ pounds are utilized as the carbon source, by analyzing the vapor stream outflowing from the CaY-loaded carbonization reactor, using an on-line mass spectrometer The reactor temperature was set to 550 ◦ C or 600 ◦ C, according to the carbonization temperatures given in Table The mass spectrum of the outflowing gas was continuously monitored until the carbon deposition was completed after h Fig shows the mass spectra taken in an early stage of the carbon deposition, where the zeolite color changed to gray-black, but the deposited amount was still less than 0.03 g g−zeolite In this early stage, the mass spectra obtained from all six organic compounds were decomposed into H2O (mass-to-charge ratio, m/z = 18) and olefins, including ethylene (m/z = 28) and propylene (m/ z = 39 and 41) The organic decomposition into olefins occurred cata­ lytically by the zeolite, except for IPA and ethanol [31,52,53], as confirmed by the mass spectral analysis of the solvent stream passed through an empty reactor at the same temperature (Fig S10) It is notable that in situ generation of H2O was observed for all six solvent compounds used in this study In the ZTC synthesis employing Ca2+ Conclusions We report a facile synthesis of ZTCs using common organic solvents, IPA, acetone, THF, DIPE, ethanol, and methanol, as a carbon source Under the present synthesis conditions, all the organic solvents were decomposed into H2O and hydrocarbons (mainly ethylene and propyl­ ene) The IPA and ethanol solvents were thermally decomposed before Table Optimized carbonization conditions and results for Caβ zeolite and various carbon precursors Zeolite-Carbon Source Carbonization Conditions Tb (◦ C) N2/Organic Flow Rates (cm3 min− 1) Tc (◦ C) t (h) Carbon Products Carbon Yield (g g−zeolite ) SBET (m2 g− 1) VMicro (cm3 g− 1) Caβ-IPA Caβ-Acetone Caβ-THF Caβ-DIPE Caβ-Ethanol Caβ-Methanol Caβ-Propylene Caβ-Ethylene 20 − 10 3 20 − 30 30 60/3 60/3 60/3 60/3 60/3 60/3 60/15 60/15 650 650 650 650 650 700 700 650 13 2 13 0.28 0.29 0.30 0.29 0.31 0.32 0.30 0.33 2350 2030 2160 2330 3220 2910 2730 3400 0.93 0.76 0.84 0.88 1.29 1.12 1.09 1.36 H Park et al Microporous and Mesoporous Materials 318 (2021) 111038 Fig (a) XRD patterns of the carbon samples synthesized with Caβ zeolite, using IPA, ethanol, propylene, and ethylene under the synthesis conditions in Table Ar adsorption-desorption isotherms and the QSDFT pore size distributions (insets) of the carbons obtained with (b) IPA and (c) ethanol Fig Mass spectra of the solvent vapor including (a) IPA, (b) acetone, (c) THF, (d) DIPE, (e) ethanol and (f) methanol passing through CaY zeolite at 550 ◦ C The green dashed line (m/z = 18) corresponds to H2O, the red dashed line (m/z = 28) represents ethylene, and the blue dashed lines (m/z = 39 and 41) correspond to + C3H+ and C3H5 , respectively Microporous and Mesoporous Materials 318 (2021) 111038 H Park et al reaching the zeolite in the reactor The other solvents were catalytically decomposed upon contact with the Ca2+ ion-embedded zeolite template Regardless of whether the decomposition occurred thermally or cata­ lytically inside the zeolite, all the resultant carbon products exhibited well-ordered microporous structures However, the porous textural properties (e.g., specific surface area and 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Wang, R Othman, M Choi, Scalable synthesis of zeolitetemplated ordered microporous carbons without external carbon deposition for capacitive energy storage, Microporous Mesoporous Mater 307 (2020) 110481, https://doi.org/10.1016/j.micromeso.2020.110481 ... synthesis employing Ca2+ Conclusions We report a facile synthesis of ZTCs using common organic solvents, IPA, acetone, THF, DIPE, ethanol, and methanol, as a carbon source Under the present synthesis. .. isotherms of the CaY-ZTC samples synthesized using the organic precursors (solid line), which were compared to the isotherm of the carbon synthesized using ethylene (dashed line) Insets of each... cej.2015.06.055 [24] Y Xia, R Mokaya, D.M Grant, G.S Walker, A simplified synthesis of N-doped zeolite-templated carbons, the control of the level of zeolite-like ordering and its effect on hydrogen storage