3D to 2D Routes to Ultrathin and Expanded Zeolitic Materials

Article pubs.acs.org/cm

3D to 2D Routes to Ultrathin and Expanded Zeolitic Materials Pavla Chlubná,† Wieslaw J. Roth,† Heather F. Greer,‡ Wuzong Zhou,‡ Oleksiy Shvets,§ Arnošt Zukal,† Jiří Č ejka,*,† and Russell E. Morris‡ †

J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of Czech Republic, v.v.i., Dolejškova 3, 182 23 Prague 8, Czech Republic ‡ EaStCHEM School of Chemistry, University of St. Andrews, St. Andrews KY16 9ST, U.K. § L.V. Pisarzhevskiy Institute of Physical Chemistry, National Academy of Sciences of Ukraine, 31 pr. Nauky, Kyiv 03028, Ukraine ABSTRACT: This contribution reports new methodology we have developed for the disassembly of 3-D UTL framework into 2-D lamellae followed by structure modification including pillaring. This may be widely applicable, particularly to other zeolites that have D4R units present, and so should have great impact also on other porous solids. Specifically, controlled hydrolysis of D4R units in the interlayer space provides individual ultrathin layers with UTL structure by a chemically selective method. Further manipulation of the layers gives a completely novel approach (3D to 2D to pillared) offering hitherto unprecedented opportunities for the preparation of modified zeolites with diverse chemical and structural properties. KEYWORDS: ultrathin zeolites, UTL zeolite, IPC-1PI, two-dimensional zeolites

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INTRODUCTION In zeolite chemistry two of the most important current challenges and great opportunities are (i) improved accessibility of active sites by introducing mesoporosity and (ii) making ultrathin zeolite layers that can be modified into expanded assemblies. Here, we report on the chemically selective disassembly of a fully formed crystalline three-dimensional zeolite structure to form intact, ultrathin zeolite 2D layers, which can be further treated to prepare pillared materials. Zeolites are a dominant group of microporous crystalline aluminosilicates with extensive applications as exceptional industrial catalysts, adsorbents, and detergents.1 Their main catalytic applications are in oil refining and petrochemistry, with increasing potential for fine chemical synthesis.1 The traditional pursuit of new zeolite frameworks has focused on those with implicit 3D characteristics.2,3 The field is now being supplemented and expanded by the emergence of ultrathin and nanoscale silicate-based materials,4−8 that is, assemblies of zeolite-like layers with thicknesses of the order of one unit cell in various spatial arrangements. In contrast to standard zeolite crystals, these 2D materials, while having zeolite attributes such as porosity and strong acid activity, can be modified postsynthesis, for example, into new architectures with potential for expanded (hierarchical) and/or improved materials for study and development of applications.9 This is exemplified by the MWW zeolite family,6,10 which demonstrated novel behavior and afforded diverse materials found to have improved performance in some processes upon pillaring and delamination, such as ITQ-211 and MCM-56.12 These materials not only show enhanced catalytic activity13 but can also show interesting effects as seeds in crystal growth.14 In addition other layered silicate materials can be postsynthetically © 2013 American Chemical Society

modified to provide 3D structures, some of which even retain crystallinity after post synthetic modification.15,16 Recently, one of the most widely studied and highly profitable zeolites, MFI, was synthesized in a lamellar form suitable for structural manipulation of its zeolitic nanosheets.5,17,18 Until now 2D zeolites with modifiable architecture have only been obtained directly by standard hydrothermal zeolite synthesis methods, typically template assisted, in a process similar to that used for conventional 3D zeolites.4 The conversions from layered precursors to zeolite frameworks all occur as 2D to 3D transformations. The opposite transformation, from 3D to 2D, has never previously been unequivocally accomplished; i.e. there has never been an example of a 3D zeolite being formed and then transformed into layers without recrystallization. This is due to the inherent nature of the bonding in zeolites, where in general the “layers” in a bulk 3D zeolite comprise the same chemical bonds as the interlayer region. This makes targeting the breaking of bonds specifically in the interlayer region impossibleany chemical process that will break bonds between the layers will also break the same bonds within the layers, leading inevitably to total breakup of the zeolite structure. The key to successful 3D to 2D zeolitic transformations is to engineer weaker bonds regiospecifically in the interlayer regions, which can then be selectively targeted in order to “unzip” the zeolitic layers apart.8 Importantly, in this paper we prove, using electron microscopy, that the zeolite layers remain structurally intact during the 3D to 2D process and that the layers can be further chemically Received: October 30, 2012 Revised: January 21, 2013 Published: January 28, 2013 542

dx.doi.org/10.1021/cm303260z | Chem. Mater. 2013, 25, 542−547

Chemistry of Materials

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be used as a platform on which other chemical manipulations can be carried out.

processed to yield expanded materials, via swelling, pillaring, and calcination treatments similar to those used for other 2D to 3D transformation processes described above. Electron microscopy indicates that the zeolite layers remain structurally intact throughout the various processes. Given the structure of zeolites, the chemical selectivity shown in the disassembly process is remarkable and is wholly dependent on the chemical properties of the zeolites and on a chemical route to engineering bonds that are susceptible to hydrolysis in the interlayer region. Zeolite UTL is a 3D zeolite comprising intersecting 14- and 12-ring pores. Its structure can be described as a being “layered” but connected by double four ring (D4R) units that contain eight tetrahedral centers in the shape of a cube (Scheme 1).

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EXPERIMENTAL SECTION

The reagents used, i.e., 1,4-dibromobutane, (2R,6S)-2,6-dimethylpiperidine, germanium oxide, 25% solution of hexadecyltrimethylammonium chloride (CTMA-Cl), tetrapropylammonium hydroxide (TPAOH) as 40% solutions, and tetraethyl orthosilicate (TEOS), were purchased from Sigma-Aldrich. Preparation of the (6R,10S)-6,10dimethyl-5-azoniaspiro[4,5] decane hydroxide was performed according to the procedure described elsewhere.21 The salt after the synthesis was ion-exchanged into hydroxide form with AG 1-X8 Resin (BioRad). The synthesis of zeolite-UTL and isomorphously substituted UTL was carried out according to the procedures described elsewhere.21−23 The preparation and the postsynthesis modifications here are described for pure germanosilicate UTL. For substituted UTL zeolites similar procedures were used. A reaction gel of molar composition 0.6−1.0:0.6−0.2:0.3−0.7:30− 33 SiO2/GeO2/SDA/H2O was prepared by dissolving amorphous germanium oxide in the solution of SDA ((6R,10S)-6,10-dimethyl-5azoniaspiro[4,5] decane hydroxide). After that, silica (Cab-O-Sil M5) was added to the solution, and the mixture was stirred at room temperature for 30 min. The resulting gel was charged into 25 mL Teflon-lined steel autoclaves and heated at 175 °C for 3−9 days under agitation (∼40 rpm). The solid product was recovered by filtration, thoroughly washed with distilled water, and dried overnight at 90 °C. The as-synthesized zeolite was calcined in air at 550 °C for 6 h with a temperature ramp of 1 °C/min. Calcined UTL was hydrolyzed in 0.1 M HCl with the w/w ratio around 1/200 at 99 °C for overnight. The product was isolated by centrifugation, washed with water, and dried at 60 °C. Hydrolyzed product was denoted IPC-1P and after calcination IPC-1. The swollen material (IPC-1SW) was prepared from IPC-1P treated with a mixture of 40% tetrapropyl ammonium hydroxide (TPA-OH) and 25% hexadecyltrimethyl ammonium chloride (CTMA-Cl) (w/w = 1/9) in the ratio from 1/30 to 1/75 (w/w). The slurry was stirred at ambient temperature overnight (∼10 h). The product was isolated by centrifugation, washed with water, and dried at 80 °C. The pillaring treatment was carried out with about 0.3 g of dried swollen IPC-1SW zeolite in 15 mL of TEOS solution. The mixture was stirred and heated under reflux at 99 °C overnight. The solid was isolated by filtration and stirred with water (300−400 mL) for 7 h.

Scheme 1. Schematic view of the 3D to 2D Transformation of UTLa

The “layers” in the 3D UTL structure (left) are shown in yellow, and the double four ring (D4R) units that connect the layers are shown in green (Ge/Si) and red (O).

a

UTL can be prepared with a relatively high content of Ge, which is well-known to preferentially locate in D4R units.8,19,20 Since Si−O−Ge and Ge−O−Ge linkages are more hydrothermally sensitive to degradation than Si−O−Si ones,8 this implies that the interlayer D4R units are more sensitive to hydrolysis than are the layers themselves, and this “weakness” can be exploited to selectively break the layers apart without compromising the integrity of the layers (Scheme 1). This new material, which now comprises ultrathin zeolite layers, can then

Figure 1. Characterization of the solids. (a) Powder XRD patterns from 0 to 30° 2θ for the original calcined UTL, hydrolyzed IPC-1P, its calcined form IPC-1, swollen IPC-1SW, its calcined form, and pillared calcined IPC-1PI showing the significant changes in the locations of the reflections after each chemical treatment. The intensities are arbitrarily adjusted for clarity. (b) Powder XRD patterns from 3 to 15° 2θ of IPC-1P products after different times of hydrolysis. The parent UTL structure is shown in red. Even after 5 min of hydrolysis there is no evidence of any remaining UTL, and the peaks for IPC-1P show maximum shift and smallest fwhm after 10 h of hydrolysis. (c) Nitrogen adsorption isotherms at −196 °C of UTL zeolite (1), its lamellar form IPC-1 (2), swollen calcined IPC-1SW (3), and pillared calcined IPC-1PI (4) illustrating the significantly enhanced porosity of the final expanded solid IPC-1PI. Open points denote desorption. 543



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The product was centrifuged again, washed with water, and dried at 60 °C. Calcination was carried out at 540 °C for 6 h with 2 °C/min of temperature ramp. The pillared material was denoted IPC-1PI. Powder X-ray diffraction was carried out using a Bruker AXS D8 Advance diffractometer. Adsorption isotherms of nitrogen at −196 °C were determined using an ASAP 2020 (Micromeritics) static volumetric apparatus. In order to attain sufficient accuracy in the accumulation of the adsorption data, the ASAP 2020 was equipped with pressure transducers covering the 133 Pa, 1.33 kPa, and 133 kPa ranges. Before adsorption, zeolites were outgassed at 110 °C under turbomolecular pump vacuum until the residual pressure of 0.5 Pa was obtained. After further heating at 110 °C for 1 h the temperature was increased until the temperature 250 °C of was achieved. This temperature was maintained for 8 h. The morphologies of the specimen particles were examined by scanning electron microscopy (SEM) using a Jeol JSM-6700F fieldemission gun scanning electron microscope operating at 1−5 kV. To reduce the beam charge problem, the samples were coated with gold. The microstructures were investigated using high resolution transmission electron microscopy (HRTEM) on a Jeol JEM-2011 electron microscope operating at an accelerating voltage of 200 kV. The Jeol JEM-2011 electron microscope is equipped with an Oxford Link ISIS SemiSTEM EDX system, which was used for confirming chemical compositions of the samples. The HRTEM images were recorded using a Gatan 794 CCD camera. The camera length, sample position, and magnification were calibrated using standard gold film methods.

dominant peak has a peak almost as narrow (0.246° 2θ) as the original UTL structure. As these changes in peak width are evolving, the peaks also show a gradual shift to higher angles, indicating a continual, steady contraction of the interlayer space in the materials. This study is consistent with a very fast hydrolysis process followed by a slower ripening stage where the individual ultrathin layers begin a pseudocrystallization process, which increases the ordering in their relative arrangement, e.g., perhaps by eluting debris from degraded D4R pillars from interlayer space and/or formation of interlayer hydrogen bonds. A final feature to note is that after about 6 h of hydrolysis an extra peak begins to appear slightly to the low angle side of the main peak, centered at around 7.5° 2θ. This shows that, as the ripening process occurs, the order in the material is increasing so that some of the intralayer diffraction peaks are beginning to become visible, which suggests that the layers themselves retain their structure. This is however difficult to prove from the X-ray diffraction alone but can be proved by the electron diffraction studies reported below. If the material is left to hydrolyze longer than 10 h the diffraction peaks begin to broaden again and there is a shift in the main diffraction to lower angle, indicating that the optimum hydrolysis time under the described conditions is about 10 h. After 10 h of hydrolysis the product showed physical and chemical characteristics of a lamellar 2D solid. This represents a 3D framework to 2D transformation affording a novel lamellar product directly from a fully formed zeolite. The typical dominant peak position is at around 8.3° 2θ (d-spacing of 1.06 nm), corresponding to contraction from 2.9 to 2.1 nm upon the 3D to 2D transformation. Calcination produced a further contraction of the material to give an interlayer spacing of 1.8 nm signified by the most intense X-ray diffraction peak moving to a higher angle at 9.9° 2θ (Figure 1a). This is similar behavior to many directly synthesized lamellar materials, which also contract on calcination (e.g., Sub-NSI24). The most notable novelty in this paper is the chemically selective disassembly of the zeolite to form ultrathin layers, as described above. This provides a completely new route to ultrathin zeolite layers that retain their zeolitic structure throughout the 3D to 2D transformation, which was also applied on substituted UTL with catalytic active sites. However, it is also important to recognize that further structural manipulation is possible, enabling preparation of additional new materials with zeolitic properties in part or entirely. A compelling characteristic of lamellar solids is their ability to structurally expand under appropriate conditions with a great increase in the interlayer space (and distance).4,7,16,25 This may subsequently lead to successful pillaring, i.e., introduction of permanent props, affording solids with increased porosity.26 The IPC-1P solid is amenable to swelling with cationic surfactant, hexadecyltrimethyl ammonium (CTMA), to yield a swollen material which we call IPC-1SW (Si/Ge ratio 37). The corresponding XRD pattern is in Figure 1a, where the dominant reflection now moves to lower angle, indicating a significant expansion of the interlayer spacing caused by intercalation of the organic surfactant. In the next step, the swollen product was treated with TEOS, a pillaring agent for many layered materials.26 The XRD of the product after another calcination (Figure 1a) confirmed successful pillaring with further expanded interlayer distance compared to the swollen material (3.8 nm, see Table 1). Such increases upon pillaring are not very common occurrences but

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RESULTS AND DISSCUSION The transformation from 3D UTL to a 2D material we call IPC-1P occurs upon relatively mild treatment. Zeolite UTL with molar Si/Ge = 4.5 (determined from chemical analysis) was transformed into the lamellar IPC-1P derivative with structural degradation by treatments in 0.1 M HCl at temperatures near 100 °C.8 The transformation was diagnosed by X-ray powder diffraction (XRD), which revealed patterns consistent with contraction due to destruction of D4R bridges separating the layers. Removal of Ge, located mainly in D4Rs, was also confirmed by chemical analysis as the Si/Ge ratio increased to 22. The initial XRD pattern of UTL (Figure 1a) has the most intense peak in the pattern at ∼6.2° 2θ (Cu Kα radiation will be used throughout) indexed as the (200) reflection, giving directly the spacing between the D4Rconnected layers of 2.9 nm. On hydrolysis, the XRD pattern of the material changes considerably to one consisting of a single dominant peak together with a number of small intensity diffraction maxima attributed to intralayer reflections. The position of the most intense peak shifts to a higher angle indicating a contraction entirely consistent with the removal of the D4R units from the structure. A study of the effect of hydrolysis time on the material shows that the within 5 min there is no evidence for any remaining unhydrolyzed UTL zeolite. Such rapid hydrolysis is remarkable but may be explained by the excellent accessibility of the Gecontaining D4R units via the pores in the UTL material. However, samples that have been hydrolyzed for different lengths of time, from 5 min to 10 h, show significant differences in XRD patterns (Figure 1b). After 5 min the position of the major peak has shifted to higher angles but is significantly broader (full width at half-maximum, fwhm, of 0.647° 2θ) than in the parent UTL XRD pattern (fwhm 0.177° 2θ). This indicates a significantly shorter coherence length in the direction perpendicular to the layers; i.e., the stacking of the layers is not very regular. As the hydrolysis time increases there is a slight increase in fwhm to 0.708° 2θ after 30 min, but it then drops sharply over the next few hours until after 10 h the 544



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original UTL zeolite exhibits much higher BET surface area (458 m2/g) compared with the swollen (216 m2/g) and hydrolyzed (270 m2/g) IPC zeolites. As expected, the latter shows low porosity and surface area (Vmicro = 0.095 cm3/g, BET = 270 m2/g) indicating formation of a low porosity product as the layers apparently condense on destruction of the linking D4R units. The pillared zeolite (IPC-1PI) exhibits the highest BET surface area (1085 m2/g) and shows mesoporous character (Vmeso = 0.52 cm3/g). The isotherm on IPC-1PI displayed in Figure 1c in linear coordinates is plotted in Figure 2a together with the isotherm on MCM-41 in semilogarithmic coordinates in order to magnify the low pressure region. An inspection of the isotherm and comparison with isotherms on mesoporous molecular sieves MCM-4128,29 clearly reveal purely mesoporous structure of the sample IPC-1PI. The steep increase in the adsorbed amount in the region of relative pressures p/p0 < 0.01 corresponds to the formation of adsorbed layer on the inner pore surface. In the case of microporous material, the characteristic feature of the isotherm is the long horizontal plateau at p/p0 > 0.01, which extends up to relatively high p/p0 (a typical example represents the isotherm on UTL zeolite in Figure 1c). However, for mesoporous materials with mesopores below 4 nm a reversible pore-filling process is accompanied by successive increase in adsorbed amount in the limits of p/p0 from 0.01 to 0.3.28 The isotherm on the sample IPC-1PI in Figure 1c is an example of such adsorption behavior. The structure parameters of this sample were evaluated by means of the DFT method using standard Micromeritics software. The pore size distribution displayed in Figure 2b is centered at 3.1 nm; this value roughly corresponds to the interlayer spacing of 3.7 nm determined from HRTEM images. A shoulder centered at 1.4 nm reveals the presence of a very small volume (0.014 cm3/g) of micropores. In the case of pillared IPC materials prepared from isomorphously substituted UTL (B-UTL, Al-UTL, Fe-UTL), the isotherms plotted in Figure 2c correspond with their shapes to the pure germanosilicate IPC-1PI. The BET surface areas for B-IPC-1PI, Al-IPC-1PI, and FeIPC-1PI are 1090, 970, and 1119 m2/g, respectively (see Table 1). The pillared materials do not exhibit any microporosity while having significant mesoporous character as well as the pure IPC-1PI. Scanning and transmission electron microscopy studies were carried out to confirm the interlayer spacings and integrity of

Table 1. Interlayer d-Spacing and Textural Data for the UTL Zeolite and Its Modified Derivativesa low angle line XRD material UTL (calcd) IPC-1P IPC-1 IPC-1SW IPC-1SW (calcd) IPC-1PI (calcd) B-IPC-1PI (calcd) Fe-IPC-1PI (calcd)

2θ (deg)

d-spacing (nm)

BET (m2/g)

Vmicro (cm3/g)

Vmeso (cm3/g)

6.15 8.3 9.9 2.6 10.0

1.44 1.06 0.90 3.40 0.90

458

0.193

270

0.095

216

0.007

0.123

2.3

3.80

1085

0.014

0.520

2.1

4.20

1090

0.785

2.0

4.41

1119

0.843

a

For comparison, representative values of the micropore volume (Vmicro) in zeolites MFI and FAU are 0.15 and 0.28 cm3/g, respectively.

may indicate additional expansion of the interlayer region due to high temperature soaking in TEOS. The Si/Ge ratio in IPC1PI was increased to 61 due to addition of amorphous silica pillars. The same principles of postsynthesis modifications were applied also on isomorphously substituted UTL with boron, aluminum, or iron. In all cases it led to new pillared materials with the interlayer distance around 4−4.4 nm (see Table 1) and very similar textural properties as in the case of pure germanosilicate IPC-1PI. The textural parameters of the materials under study were evaluated by nitrogen isotherms presented in Figure 1c and Table 1. The shape of N2 isotherms of the parent UTL and hydrolyzed calcined IPC-1 are typical for microporous materials: type I according to IUPAC classification.27 The swollen and calcined IPC-1SW, which is related to calcined IPC-1 except for first undergoing swelling under relatively severe conditions, exhibits a small hysteresis loop indicating the presence of interparticle adsorption and little in the way of microporosity. In contrast, the pillared material IPC-1PI yields an isotherm with a similar hysteresis loop but with a steep rise from 0 to 0.3 p/p0 to a much higher plateau (increased volume), clear evidence of mesoporosity in the material. The

Figure 2. Nitrogen isotherm at −196 °C on the sample IPC-1PI and MCM-41 in semilogarithmic coordinates (a). Mesopore size distribution of the sample IPC-1PI (b). (c) The comparison of nitrogen isotherms at −196 °C of pillared Fe-IPC-1PI (1), B-IPC-1PI (2), IPC-1PI (3), and Al-IPC-1PI (4). 545



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the UTL layers. SEM images in Figure 3a,b from IPC-1 and IPC-1PI, respectively, show little in the way of changes to the

Figure 4. (a) HRTEM image from IPC-1, viewed down the [100] axis showing intact layered component. (b) The corresponding FFT pattern and the inversed FFT image of IPC-1 (c), showing the intact crystal structure of the (bc) plane with d-spacings of (A) 0.58 nm and (B) 0.68 nm, indexed to (002) and (020), respectively.

Owing to the rather beam sensitive nature of the sample, the crystal fringes are difficult to see in the direct image (Figure 4a), although they are visible in the inverse FFT image. However, the FFT shows clear evidence of 2D ordering in the material, with measurable spacing consistent with the UTL structure remaining intact. However, there is a gradual loss of regularity when moving from the original UTL to the pillared material, indicating that some loss of register between layers has been introduced. Such disorder is to be expected when the layers are separated by a considerable distance of >2.5 nm and supported by pillars. The loss of register upon swelling and pillaring was a diagnostic feature for MCM-22P manifesting in the coalescence of the intralayer reflections (101) and (102) into a broad band.6 The work reported here demonstrates that a 3D zeolite can be disassembled into monolayers with retention of their zeolite structure. The key to the process is the chemical composition of the zeolite, which engineers hydrolytically sensitive D4R units regioselectively into the material, which then allows the chemically more robust layers to be unzipped from the structure. The results show new possibilities in the synthesis of novel materials starting from a fully formed zeolite solid and carefully manipulating the structure to achieve 3D to 2D transformation, followed by formation of a new 3D material, e.g., pillared. Properties of the UTL layers were recently described also using quantum chemical calculations, showing the role of silanols formed in the interaction of individual layers, in particular.34 Ultrathin zeolite layers can increase accessibility to important reactive sites and offer catalytic applications, especially for bulkier molecules not able to enter pores of most zeolites, including commercially used ones. It is well-known that zeolite UTL, for example, can be prepared with any number of aliovalent dopants that can provide active sites for catalysis etc. Indeed, our initial work on such materials shows that the disassembly process is fundamentally unaffected by the inclusion of aliovalent dopants, although the actual conditions required may be altered (this work will be published in the future). We believe that the methodology we have developed for the disassembly of UTL zeolite is widely applicable, particularly to the several other zeolites that have D4R units present, and so

Figure 3. SEM images of (a) IPC-1 and (b) IPC-1PI. (c) HRTEM image and the corresponding FFT pattern (inset) from IPC-1 viewed down the [001] zone axis, showing the d-spacing of (A) 0.9 nm and (B) 0.65 nm, indexing to (200) and (020). (d) HRTEM image from IPC-1PI, showing the typical d-spacing where (A) shows the thicknesses of two unit cells (7.5 nm) and (B) the thickness of one unit cell (3.7 nm).

microplate morphology of the particles. The microstructures of the samples were investigated by HRTEM. A low-dose method was used due to the sensitivity of the materials to the electron beam.30,31 The crystal structure is closely related to that of zeolite UTL, which has a monoclinic unit cell with a = 2.90, b = 1.40, c = 1.245 nm, and β = 104.9°. The layered component on the (bc) plane of UTL is maintained, while the a axis is significantly changed. The HRTEM images of IPC-1 (Figure 3c) and IPC-1PI (Figure 3d) show a clear correlation between the interlayer spacing measured from XRD and that seen in the images. For instance, the interlayer spacing for IPC-1 is measured at 0.9 nm, which is in excellent agreement with the dspacing from XRD. For the pillared material, IPC-1PI, there is a clear increase in interlayer spacing to 3.7 nm, with a slight variation (±0.1 nm) depending on the crystallite measured. Again, this agrees well with both the measured d-spacing from the diffraction maximum in the XRD and also with the fact that this particular peak is considerably broader in this material than in the others, indicating a wider range of interlayer spacing. Some very thin plates were also observed in the image (Figure 3d) from this sample as indicated by (B), showing a region two unit cells thick, and (C) showing a region only one unit cell thick. These plates were likely exfoliated from the thicker particles. These ultrathin plates are quite rigid, unlike other thin layers, which may roll up into nanotubes, e.g., niobium oxide layers from K4Nb6O17,32 or become crumpled, e.g., nanosheets of bismuth telluride.33 HRTEM images also indicate that the UTL layers remain intact during the whole treatment. One example for IPC-1 is given in Figure 4a with its fast Fourier transform (FFT) (Figure 4b) and inversed FFT images (Figure 4c). 546



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(20) Corma, A.; Díaz-Cabañas, M. J.; Rey, F.; Nicolopoulus, S.; Boulahya, K. Chem. Commun. 2004, 12, 1356−1357. (21) Shvets, O. V.; Zukal, A.; Kasian, N.; Ž ilková, N.; Č ejka, J. Chem.Eur. J. 2008, 14, 10134−10140. (22) Shvets, O. V.; Shamzhy, M. V.; Yaremov, P. S.; Musilová, Z.; Procházková, D.; Č ejka, J. Chem. Mater. 2011, 23, 2573−2585. (23) Shamzhy, M. V.; Shvets, O. V.; Opanasenko, M. V.; Yaremov, P. S.; Sarkisyan, L. G.; Chlubná, P.; Zukal, A.; Č ejka, J. J. Mater. Chem. 2012, 22, 15793−15803. (24) Roth, W. J.; Kresge, C. T. Microporous Mesoporous Mater. 2011, 144, 158−161. (25) Intercalation Chemistry; Whittingham, M. S., Jacobson, A. J., Eds.; Academic Press: New York, 1982. (26) Landis, M. E.; Aufdembrink, B. A.; Chu, P.; Johnson, I. D.; Kirker, G. W.; Rubin, M. K. J. Am. Chem. Soc. 1991, 113, 3189−3190. (27) Sing, K. S. W.; Everett, D. H.; Haul, F. A. W.; Mouscou, L.; Pierotti, R. A.; Rouquerol, J.; Siemieniewska, T. Pure Appl. Chem. 1985, 57, 603−619. (28) Kruk, M.; Jaroniec, M.; Sayari, A. J. Phys. Chem. B 1997, 101, 583−589. (29) Zukal, A.; Thommes, M.; Č ejka, J. Microporous Mesoporous Mater. 2007, 104, 52−58. (30) Greer, H. F.; Zhou, W. Z. Crystallogr. Rev. 2011, 17, 163−185. (31) Xiao, B.; Byrne, P. J.; Wheatley, P. S.; Wragg, D. S.; Zhao, X. B.; Fletcher, A. J.; Thomas, M.; Peters, L.; Evans, J. S. O.; Warren, J. E.; Zhou, W. Z.; Morris, R. E. Nat. Chem. 2009, 1, 289−294. (32) Du, G. H.; Chen, Q.; Yu, Y.; Zhang, S.; Zhou, W. Z.; Peng, L. M. J. Mater. Chem. 2004, 14, 1437−1442. (33) Zhao, Y. M.; Hughes, R. W.; Su, Z. X.; Zhou, W. Z.; Gregory, D. H. Angew. Chem., Int. Ed. 2011, 50, 10397−10401. (34) Grajciar, L.; Bludsky, O.; Roth, W. J.; Nachtigall, P. Catal. Today 2013, 204, 15−21.

should have great impact also on other porous solids. It is noteworthy that the journal Science has listed the modification of zeolites as one of its ten most important recent areas of science.18 This finding opens up new avenues of research that are not possible with zeolites themselves.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. Author Contributions

The manuscript was written through contributions of all authors. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Czech researchers acknowledge the financial support of the Czech Science Foundation (203/08/0604 and 106/12/0189). H.F.G. thanks St. Andrews University for a Ph.D. studentship. R.E.M is a Royal Society Industry Fellow. J.Č . thanks also Micromeritics for a support in the frame of the Instrument Grant Program.

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REFERENCES

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