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[Mohamed Esmat](https://orcid.org/0000-0003-1465-0955), [Hamza El-Hosainy](https://orcid.org/0000-0001-8244-4382), [Masaya Miyagawa](https://orcid.org/0000-0002-3141-9440), Hiromitsu Takaba, [Nao Tsunoji](https://orcid.org/0000-0003-4919-702X), [Shinsuke Ishihara](https://orcid.org/0000-0001-6854-6032), [Yusuke Ide](https://orcid.org/0000-0002-6901-6954)

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This document is the Accepted Manuscript version of a Published Work that appeared in final form in ACS Applied Materials & Interfaces, copyright © 2024 American Chemical Society after peer review and technical editing by the publisher. To access the final edited and published work see https://doi.org/10.1021/acsami.4c08845.[In Copyright](http://rightsstatements.org/vocab/InC/1.0/)

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[Layered Silicates Exhibiting MOF-Like Gate-Opening Behaviors in Liquid-Phase Adsorptions: Experimental and Theoretical Investigations](https://mdr.nims.go.jp/datasets/00023d44-2fa4-4a01-bdd7-27ad2ae9b82c)

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Template for Electronic Submission to ACS JournalsLayered silicate exhibiting MOF-like gate opening behaviors in liquid-phase adsorptions: Experimental and theoretical investigationsMohamed Esmat,†$‡ Hamza El-Hosainy,†∫‡ Masaya Miyagawa,‖ Hiromitsu Takaba,‖* Nao Tsunoji,§ Shinsuke Ishihara,†  and Yusuke Ide†#*† Research Center for Materials Nanoarchitectonics (MANA), National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan$ Materials Science and Nanotechnology Department, Faculty of Postgraduate Studies for Advanced Sciences, Beni-Suef University, Beni-Suef 62511, Egypt∫ Institute of Nanoscience and Nanotechnology, Kafrelsheikh University, Kafrelsheikh 33511, Egypt‖ Department of Environmental Chemistry & Chemical Engineering, School of Advanced Engineering, Kogakuin University, Hachioji, Tokyo 192-0015, Japan§ Department of Applied Chemistry, Graduate School of Advanced Science and Engineering, Hiroshima University, Higashi-hiroshima 1-4-1 Kagamiyama 739-8527, Japan# Graduate School of Engineering Science, Yokohama National University, 79-5 Tokiwadai, Hodogaya-ku, Yokohama 240-8501, Japan‡ These two authors contributed equally to this workKeywords: layered silicate; microporous layered silicate; MOF; zeolite; gate opening; adsorption PAGE  2ABSTRACT:  Layered silicates including clay minerals can be used as liquid-phase adsorbents in many important applications. However, because their two-dimensional interlayer space is narrow and not entirely opened due to the presence of interlayer species, guest species are forced to penetrate while expanding the interlayer space, which limits the adsorption performances if compared with microporous materials such as MOFs and zeolites. Herein, as reported for the adsorption of gaseous species on flexible MOFs, we report a layered silicate that exhibits gate opening adsorption in liquid phases. This layered silicate, synthesized via dilute acid treatment of the parent sodium-type, exhibits the abrupt increase of the basal spacing (layer thickness + interlayer space) to reach a plateau even at an earlier stage of benzoic acid adsorption from acetonitrile, whereas a typical layered silicate, magadiite, exhibits gradual increase of the basal spacing with the progress of the adsorption under the identical conditions. The layered silicate shows an excellent adsorption capacity and rate for benzoic acid uptake from acetonitrile considerably higher than magadiite. With comprehensive adsorption tests using different adsorbates and solvents, we propose that the layered silicate has zeolite-like but distorted, flexible open microchannels within each layer and the intralayer microchannels can effectively and rapidly accommodate the solvent (acetonitrile) molecule capable of expanding the framework to initiate the adsorption of aromatic compounds. The density function theory calculation reveals the adsorption mechanism, where the layered silicate accommodates acetonitrile in the intralayer microchannel followed by the interlayer space, and the former selectively plays a role as the adsorption site of aromatic compounds via exchange with acetonitrile. INTRODUCTIONDemand for microporous materials is ever-increasing for the sake of their applications as adsorbents in emergent or important problems such as environmental and energy issues, health care, and food quality improvement. One of the most useful adsorption characteristics for high-performance microporous materials is “gate opening” typically observed when gaseous species is incorporated into flexible microporous frameworks such as metal organic frameworks (MOFs, also called porous crystalline polymers, PCPs) and zeolitic imidazole-based MOFs (ZIFs).1-6 In the gate opening, guest-driven structure transformations or lattice volume changes initiate adsorption to attain excellent adsorption capacity and/or selectivity higher than conventional adsorbents (Figure 1A). Thus, much effort has been devoted to designing the organic and inorganic frameworks with the gate opening property, which have been reported in merlinoite zeolite recently.7Layered silicates including clay minerals are the representative adsorbents widely used in industries.8 Because their two-dimensional interlayer space is narrow and not entirely opened for guest species, they are classified as non-microporous materials, and exchangeable cations for charge compensatation and/or surface hydroxy groups are distributed in the interlayer. Consequently, guest species must be introduced with expanding the interlayer space9,10 (Figure 1B), limiting the adsorption performances compared to MOFs and zeolites having open (permanent) micropores. Nevertheless, layered silicates show an excellent chemical stability superior to MOFs, and thus can be used as adsorbents in liquid phases even under harsh conditions.11,12 In addition, the nanostructures originating from the ultrathin layers allow for a potentially higher adsorption capacity than zeolites.13 Focusing on these advantages, the layered silicates exhibiting the gate opening adsorption behaviors (Figure 1C) would enhance their practical applications like MOFs and zeolites. However, such materials design has never been realized, although microporous organically pillared clays show the gate opening behaviors for gas- and liquid-phase adsorptions due to the open micropores in the interlayer separated by the pillars.14,15Herein, we report that a pure layered silicate, synthesized via dilute acid treatment of the parent sodium-type, exhibits the gate opening behaviors in the liquid-phase adsorptions. We experimentally and theoretically investigate the adsorption mechanism of two layered silicates with different structures; one is a microporous layered silicate having both flexible intralayer microchannels and interlayer spaces (Figure 1C), and the other is a conventional layered silicate showing guest uptake only in the interlayer spaces. The fomer16,17 and latter11 silicates are good adsorbents for benzoic acid (in acetonitrile) and phenol (in water), respectively, superior to zeolites. Thus, we expect that these molecules would be probes to investigate the gate opening behaviors.Figure 1. Schematic representation of the structural change during guest uptake in (A) flexible MOFs, (B) a conventional layered silicate, and (C) a layered silicate with flexible open microchannels within each layer.EEPERIMENTALPreparation of materials: Na-SiO2 was purchased from Nippon Chemical Industrial and used as received.  Na-mag was prepared by a hydrothermal reaction at 150 oC of SiO2 (Wakogel Q-63, Wako Pure Chemical), NaOH, and water according to a literature.18 The protonation of Na-SiO2 and Na-mag (sodium removal from the structures) was carried out based on a previous report.19 The Na-SiO2 or Na-mag powder was mixed with dilute HCl solution (0.2M) and mixture was stirred at room temperature for 2 days. After the treatment, the mixture was centrifuged, washed with water, and dried under reduced pressure (the products were named H- SiO2 or H-mag). The interlation of octylamine into H- SiO2 was also performed based on a previous report.20 H-SiO2 powder (2.0 g) was mixed with an aqueous mixture (400 mL) of propylamine (1.2 ml) and octylamine (2.0 ml), which pH was adjusted to 10 by 1M HCl. The mixture was stirred at room temperature for 1 h and the product was separated by centrifugation. This procedure was repeated twice and the final product was washed with ethanol and dried at room temperature.Materials characterizations: XRD patterns of powder and slurry samples were collected using a powder X-ray diffractometer (Smart Lab, RIGAKU) with Cu Kα radiation at 40 kV and 30 mA. 29Si MAS and 13C cross-polarized (CP) MAS NMR spectra were recorded at 119.17 and 150.87 MHz, respectively, on a Varian 600PS solid NMR spectrometer using a 6-mm diameter zirconia rotor. Thermogravimetric analysis was performed using a Hitachi HT-Seiko Instrument Exter 6300. The particle morphology of samples was observed using a Hitachi S-4800 scanning electron microscope. Nitrogen and water vapor adsorption isotherms were measured at 77 K and 298 K, respectively, on a BELSORP-max instrument (MicrotracBEL). Prior to the measurements, powder sample was outgassed at 300 oC for 24 h and 120 oC for 3 h, respectively. In situ XRD measurements: The XRD patterns were collected with a Rigaku RINT 2200V diffractometer with CuK radiation at a scan rate of 2 = 1o min−1. Measurements were conducted at room temperature under controlled partial pressure of benzoic acid vapor, which was tuned by mixing N2 gas and acetonitrile vapor with different flow ratios. Measurements at each partial pressure was repeated 3 times to confirm the equilibrium of acetonitrile uptake on the sample powder.Adsorption tests: 100 mg of powder sample was added to an acetonitrile or aqueous solution (5 mL) containing different amount of benzoic acid or phenol in a glass vial and the vial was sealed with a rubber septum. After the mixture was shaken at room temperature for a given time (24 h for adsorption isotherm preparation), the supernatant was collected by syringe filtration and analyzed with a Shimadzu GC-2010 plus gas chromatograph (GC) equipped with a barrier-discharge ionization detector (BID). The solution pH of benzoic acid in acetonitrile and water (500 mM for each) was 2.5 and 3.4, respectively. That of phenol in in acetonitrile and water (500 mM for each) was 3.0 and 4.2, respectively.Density Functional Theory (DFT) Calculations: The nanostructure and basal spacing of H-SiO2 composites were investigated by the DFT calculation. All the calculation was conducted under the periodic boundary condition by using the CASTEP module implemented in Materials Studio 7.0 supplied by BIOVIA Inc. Generalized gradient approximation (GGA) was used for the functional.21 Double numerical plus d-function (DND) was used as the basis set, and the Grimme method was used for the DFT-D correction. The k-point was set to 2×2×2.  The geometry optimization was conducted under the vertical pressure at 5 GPa to reproduce the structure reported previously.16 Otherwise, neither the basal spacing nor the distorted Si−O framework is reproduced. The inherent pressure in the order of GPa has been reported previously in layered clay minerals.22 Figure 2. (A) XRD patterns of H-SiO2 and H-mag. Diffraction peaks appearing in H-SiO2 but missing in H-mag and vice versa are marked by red arrows. Inset shows the expanded patterns at lower 2θ region. (B) Two kinds of possible structures for H-SiO2. Because the structure of H-mag is not determined yet, the schematic structure is shown by subtracting sodium cations from the known Na-mag structure and then shrinking the interlayer space along the layer stacking direction.RESULTS AND DISCUSSIONTwo Possible Structures of the Layered SilicateA layered silicate (named H-SiO2) was prepared by using a commercial layered silicate (Na-SiO2) via the acid treatment to remove sodium cations in the interlayer space and intralayer microchannel (Figure S1). This H-SiO2 material, which is later revealed to have structure model I (Figure 2B left), demonstrates the gate opening behaviors toward aromatic compounds in the liquid phase. We originally proposed Na-SiO2 is magadiite, a sodium-type layered silicate23 and its structure has been determined by X-ray pair distribution function analysis.16 However, the density of the interlayer silanol groups (SiOH/SiO－) in Na-SiO2 was higher than a widely accepted magadiite (Na-mag). The diversity of magadiite, including their silanol density, has been pointed out previously.24 Moreover, the structure of Na-mag has been recently proposed, where no intralayer microchannels exist.25 Accordingly, we now regard Na-SiO2 as a novel microporous layered silicate26 possessing both zeolite-like eight-membered ring pores and interlayer spaces, where sodium cations are distributed (Figure S1).The density of the interlayer silanol groups of H-SiO2 is smaller than that of the parent Na-SiO2, and almost consistent with that of Na-mag and its protonated form (H-mag) (Figure S2), the latter of which is prepared by removal of sodium cations from the interlayer space by the acid treatment (Figure S1). Considering that H-SiO2 and H-mag showed similar but significantly different powder X-ray diffraction (XRD) patterns (Figure 2A), the sodium cations are removed in either of the two scenarios shown in Figure S1; i) the interlayer silanol groups are partially condensed while retaining the original structure, and ii) structural transition occurs from Na-SiO2 to H-mag (Figure S1). In other words, H-SiO2 has two possible structures; one is a microporous layered structure with intralayer distorted open microchannels (Figure 2B left), and the other is a conventional layered structure identical to H-mag (Figure 2B right). Accordingly, in this study, we use both H-SiO2 and H-mag as adsorbents and monitor their adsorption-driven structural changes to discuss whether the gate opening behavior of H-SiO2 is ascribed to the intralayer microchannels or interlayer spaces.Intercalation property of the interlayer spaces in H-SiO2 was confirmed by the adsorption of octylammonium ion, C8. The basal spacing was largely increased (Figure S3), indicating that the C8 was introduced to the interlayer spaces by the exchange with the proton in the silanol group (SiOH). In other words, if H-SiO2 has the structure model I (Figure 2B left), the interlayer silanol groups are not significantly condensed during the acid treatment, and the interlayer spaces are available in H-SiO2, same as the conventional layered materials.The thermogravimetric analysis revealed that the as-prepared H-SiO2 contained the larger water content  than H-mag (Figure S4). Hence, the XRD peaks at the lowest 2θ region (d = 1.11 and 1.31 nm) are assignable to the basal spacing of the anhydrous and hydrous H-SiO2, respectively (Figure 2A inset). In the hydrated phase, the water molecules are assumed to interact with the surface silanol groups because the water molecules are unstable in the intralayer microchannels with no surface silanol groups.16 This structural water was difficult to be removed while retaining the original structure during the drying process in the sample preparation (see Experimental Section). However, as shown in Figure S3 and will be demonstrated below, the structural water was removed by the adsorption of guest species in the interlayer spaces, which was elucidated by XRD measurement. Therefore, we hereafter discuss the change in the basal spacing of H-SiO2 by any adsorption tests based on the anhydrous phase with the basal spacing of 1.11 nm.Figure 3. Time course of adsorption of benzoic acid on H-SiO2 and H-mag from acetonitrile containing (A) 500 mM and (B) 20 mM of benzoic acid, and XRD patterns at each adsorption stage for H-SiO2 and H-mag. Asterisk indicates the diffraction peak due to benzoic acid crystals deposited on the particle’s outer surface.Adsorption TestsFigure 3A shows time course adsorptions of 500-mM benzoic acid on H-SiO2 and H-mag. Interestingly, H-SiO2 adsorbed benzoic acid more efficiently and rapidly than H-mag despite their similar primary particle sizes (Figure S5) and XRD patterns (Figure 2A). More interestingly, the diffraction peak assigned to the 1.11-nm basal spacing of H-SiO2 got sharpened, shifted to the lower 2θ region in the early stage, and reached a plateau at 1.36 nm.  These results indicate the adsorption of benzoic acid in the structure of H-SiO2. In contrast, the basal spacing of H-mag gradually increased from 1.11 nm to 1.29 nm with the progress of the adsorption, which is commonly observed in layered inorganic solids without any structural or organic modifications.9 We note that the different adsorption behaviors indicate that the structure of H-SiO2 is not identical to that of H-mag. In other words, the structure model I is suggested for H-SiO2. Similar changes in the XRD patterns were observed even when the concentration of benzoic acid is lowered to 20 mM (Figure 3B). The basal spacing of H-SiO2 reached the plateau at 0.25 h even though the adsorbed amount is considerably small. Hence, H-SiO2 should rapidly expand the framework or interlayer space upon adsorption of either the solvent molecule (acetonitrile) or the trace amount of benzoic acid (< 0.001 mmol g−1). In contrast, H-mag did not adsorb benzoic acid at all and the basal spacing was only gradually increased. Thus, it is found that H-mag adsorbs rather the solvent molecule than benzoic acid in the interlayer space.The parent Na-SiO2 adsorbed benzoic acid from acetonitrile (500 mM) to some extent, probably because sodium cations were desorbed from intralayer microchannels to create the adsorption site (Figure S6). However, the majority of the adsorbed benzoic acid was deposited on the particle’s outer surface because the diffraction peaks due to benzoic acid and sodium benzoate crystals were observed in the recovered samples at each adsorption stage.To reveal the adsorption-induced nanostructural changes, we further investigated the adsorption behavior of H-SiO2 and H-mag toward both pure gaseous and liquid acetonitrile. Figure 4A shows the adsorption isotherms of acetonitrile vapor on H-SiO2 and H-mag. H-SiO2 showed abrupt uptake of acetonitrile in the partial pressure range lower than 0.05, whereas H-mag did not. These results indicate that the adsorption affinity of H-SiO2 toward acetonitrile is higher than that of H-mag. The changes in the basal spacing upon acetonitrile uptake on H-SiO2 and H-mag were also evaluated by in situ XRD measurements under the controlled acetonitrile vapor pressures and the powder XRD measurement in the slurry state (Figure 4B, Figure S7 and Figure S8). Despite the high affinity toward acetonitrile, the basal spacing of H-SiO2 was hardly increased under the acetonitrile atmosphere. However, the  increase was observed in the slurry state, which was consistent with that for benzoic acid adsorption from the acetonitrile solution (Figure 3). In contrast, the gradual increase in the basal spacing was observed in H-mag upon contact with acetonitrile vapors and dispersing in acetonitrile liquid. Thus, H-SiO2 should have open micropores to accommodate the acetonitrile vapor while H-mag does not. Similar abrupt uptake was also observed in N2 adsorption, supporting the presence of the open micropores in H-SiO2 (Figure S9).All the aforementioned discussions suggest that the structure of H-SiO2 is the model I (Figure 2B left), where the intralayer microchannels are assumed to be the open micropores for the the acetonitrile molecules to initiate the rapid and effective benzoic acid adsorption (Figure 3 and 4B). In addition, the framework of H-SiO2 must be flexible enough to accommodate small organic molecules in the intralayer microchannels, because the cross-section area was slightly decreased by the removal of the sodium cations via the acid treatment (Figure S1 upper). To the best of our knowledge, this is the first report of the pure layered silicate showing gate opening behaviors in liquid-phase adsorption.In order to get a deeper insight into whether H-SiO2 shows the gate opening adsorption via the intralayer flexible framework (Figure 1C) or interlayer space, we analyzed adsorption isotherms of benzoic acid and phenol on H-SiO2 and H-mag from acetonitrile and water (Figure 5A, B, D and E). We further monitored the structural change of H-SiO2 and H-mag during the adsorption tests by the XRD measurements (Figure 5C and F). Water was additionally selected as the solvent because it is adsorbed less effectively on both H-SiO2 and H-mag than acetonitrile. As shown in Figure S10, the basal spacing of H-SiO2 did not change in the slurry state, while that of H-mag was slightly increased. Phenol was additionally selected as the adsorbate because of the adsorption in the interlayer spaces of H-mag from the aqueous solution.11 Given that the intercalated water molecules interact with the surface silanol group,16 we expected that benzoic acid and phenol in water would preferentially adsorb in the interlayer space even for the possible structure model I of H-SiO2.Figure 5A shows the adsorption isotherms of benzoic acid on H-SiO2 from acetonitrile and water. Despite the S-type isotherm indicating relatively weak adsorbent-adsorbate interactions according to the Giles classification,27 the adsorbed amount was larger in acetonitrile than water: the maximum adsorbed amount on H-SiO2 is estimated as ~2 mmol g−1 since the recovered H-SiO2 from the 200-mM benzoic acid solution (the second largest adsorbed amount-plot in Figure 5A) had no peak due to the benzoic acid crystals deposited on particle’s outer surface unlike the recovered H-SiO2 from the 500-mM benzoic acid solution (the largest adsorbed amount-plot in Figure 5A) showing the peak of the crystals (Figure 3A, 24 h). Figure 4. (A) Adsorption isotherms of acetonitrile vapors on H-SiO2 and H-mag and (B) change in the basal spacing of H-SiO2 and H-mag when contacting with acetonitrile vapor and dispersing in acetonitrile liquid (slurry state). Inset of panel (A) shows the adsorption isotherms with the x axis of a linear scale.H-SiO2 hardly adsorbed benzoic acid in the aqueous solution (Figure 5A, square plots). Importantly, the relation between the basal spacing and the adsorbed amount on H-SiO2 was different in the acetonitrile and water systems (Figure 5C). In the former, the basal spacing did not depend on the adsorbed amount and reached a plateau even at 10−4 mmol g−1, which was gradually increased in the latter. The adsorbate species also affected the adsorption behavior of H-SiO2. Figure 5B shows the adsorption isotherms of phenol on H-SiO2 in the acetonitrile and aqueous solutions. Contrary to benzoic acid, the adsorbed amount of phenol on H-SiO2 was larger from water than acetonitrile. The basal spacing of H-SiO2 gradually increased as phenol is adsorbed from water, whereas the basal spacing is quickly increased and almost constant at the low adsorbed amount (~0.001 mmol g−1) when acetonitrile is used for the solvent (Figure 5C).These solvent- and adsorbate-dependent adsorption behaviors of H-SiO2 can be rationalized by the presence of two adsorption sites; the intralayer microchannels and interlayer spaces, both of which are contained in the structure model I (Figure 2B left). H-SiO2 has both acetonitrile-philic (more hydrophobic16) intralayer microchannels and water-philic (more hydrophilic) interlayer spaces. Thus, from acetonitrile, benzoic acid and phenol can be adsorbed in the intralayer microchannels with the aid of acetonitrile accommodated within the microchannels via hydrophobic interactions. In contrast, from water, phenol is adsorbed in the interlayer space due to its hydrophilicity. Water molecules pre-adsorbed in the interlayer space (Figure 2A inset) might initiate phenol uptake there.Solid state 13C cross-polarization (CP) nuclear magnetic resonance (NMR) measurements not only revealed the co-existing of benzoic acid and acetonitrile in the recovered H-SiO2 but suggested the state of the adsorbed benzoic acid. Figure 6 shows the 13C CP MAS NMR spectra of H-SiO2 with different adsorbed amounts of benzoic acid from acetonitrile. When the adsorbed amount is high (3.70 mmol g−1 from 500 mM solution), H-SiO2 showed one peak assigned to acetonitrile and two peaks assigned to benzoic acid. However, when the adsorbed amount is low (0.12 mmol g−1 from 10 mM solution), the peak due to the carbonyl group of benzoic acid disappeared while that due to the phenyl group was observed. Figure 5. Adsorption behaviors of (A-C) H-SiO2 and (D-F) H-mag.  Adsorption isotherms of (A) benzoic acid (BA) and (B) phenol (P) on H-SiO2 from acetonitrile and water and (C) variation of basal spacing of H-SiO2 as a function of adsorbed amounts of BA and P. Adsorption isotherms of (D) BA and (E) P on H-mag from acetonitrile and water and (F) variation of basal spacing of H-mag as a function of adsorbed amounts of BA and P. Note that BA adsorption tests from water at higher concentrations were not performed due to the poor solubility of BA in water lower than that in acetonitrile. Figure 6. 13C CP MAS NMR spectra of recovered H-SiO2 and H-mag with different amounts of the adsorbed benzoic acid.The absence of the carbonyl peak of benzoic acid in 13C CP MAS NMR spectra was reported previously, where benzoic acid was encapsulated within mesoporous silicas and showed high mobility.28-30 Considering that the former H-SiO2 sample contains benzoic acid crystal on particle’s outer surface with restricted mobility (Figure 2A), the absence of the carbonyl peak of benzoic acid for the latter H-SiO2 sample is attributed to the encapsulation with the high mobility in open microchannels, rather than narrow interlayer spaces.Unlike H-SiO2, H-mag showed the adsorption behaviors typical for the layered silicates.9,10 Figure 5D and Figure 5E shows the adsorption isotherms of benzoic acid and phenol on H-mag from acetonitrile and water. Although all the isotherms were type-S27 like those observed in H-SiO2, the basal spacing of H-mag was gradually increased as the adsorbed amounts got larger (Figure 5F). The 13C CP MAS NMR spectra of the recovered H-mag suggest that the adsorbed benzoic acid is restricted28-30 in the narrow interlayer space (Figure 6). These results are reasonable because H-mag has only the interlayer space to accommodate benzoic acid and phenol as well as acetonitrile and water. Note that the basal spacings of the recovered H-mag with no adsorption of benzoic acid and phenol for the acetonitrile systems were larger than the pristine H-mag (circles and diamonds at x = 0 in Figure 5F). This is explained by the fact that H-mag slightly increased the basal spacing upon pure acetonitrile uptake (Figure 4B).  Depending of the solvent natures (mixing ratios of acetonitrile and benzoic acid/phenol), the amount of the intercalated solvents might be different.From the comprehensive adsorption tests and analyses described above, we experimentally conclude that H-SiO2 has a zeolite-like open but distorted microchannels within each layer (structure model I in Figure 2B) and the framework is flexible enough to accommodate acetonitrile to expand the pore and initiate benzoic acid and phenol uptake from acetonitrile.Density Functional Theory (DFT) Calculation Figure 7A shows the optimized structure of H-SiO2.  The calculated basal spacing is 1.13 nm, which is consistent with the experimental value. The interlayer spaces are partly occupied by the silanol groups, and the distortion of the intralayer microchannels consisting of the zeolite-like eight-membered ring is also reproduced. Figure 7B shows the optimized structure of H-SiO2 containing two acetonitrile molecules in each intralayer microchannel. The adsorbed amount of acetonitrile is 3.14 mmol g−1, which is approximately equal to that at the saturated vapor pressure estimated from the adsorption isotherm shown in Figure 4A. By the acetonitrile adsorption, the Si−O framework gets rather symmetrical both from the front and side views, indicating that the framework is flexible similar to flexible MOFs. Changes in the distances between two oxygen atoms in the eight-membred ring are summarized in Table S1. The interlayer microchannels are slightly expanded both along the horizontal and vertical directions by the acetonitrile adsorption. The basal spacing is only slightly increased to 1.18 nm.  Because the gallery height (the height of the interlayer spaces) is not changed, it is found that the change in the basal spacing is ascribed to the flexibility of the silicate layer, not the swelling of the interlayer. Because the intralayer microchannel is already fully occupied with acetonitrile, the increase in the basal spacing experimentally observed in the slurry state (Figure 4B) is assumed to be the adsorption in the interlayer space. Figure 7C shows the optimized structure of H-SiO2 containing two and one acetonitrile molecules in each intralayer microchannel and interlayer space, respectively. The basal spacing is calculated to be 1.40 nm, which is close to the experimental value in the slurry state. Thus, it is demonstrated that H-SiO2 possesses two different adsorption sites. The acetonitrile molecules are accommodated selectively in the intralayer microchannels in the gas adsorption, and also introduced to the interlayer spaces to form the unimolecular layer when immersed in the solution. Due to the flexibility, the Si−O framework is slightly distorted by the intercalation, but the intralayer microchannel is expanded from that of the original H-SiO2 due to the presence of the acetonitrile molecules (Table S1).Figure 7. Optimized structure of (A) H-SiO2, (B) H-SiO2 containing 2 acetonitrile molecules in each intralayer, (C) H-SiO2 containing 2 and 1 acetonitrile molecules in each intralayer and interlayer, and (D) H-SiO2 containing 1 BA and 1 acetonitrile in each intralayer and interlayer, respectively.  The yellow, red, white, gray, and blue spheres represent Si, O, H, C, and N atoms, respectively.Figure 7D shows the optimized structure of H-SiO2 containing one benzoic acid and one acetonitrile molecules in each intralayer microchannel and interlayer space. Various models of benzoic acid with different orientations are calculated and the most stable structure is shown. The corresponding adsorbed amount of benzoic acid is 1.57 mmol g−1 in the range observed experimentally, shown in Figure 3A.  The basal spacing is 1.33 nm, which is consistent with the experimental value. One may think that the acetonitrile molecules in the interlayer space are possibly desorbed during the drying process before the XRD measurement, but this scenario is unlikely to occur. The basal spacing of the corresponding structure is calculated to be 1.19 nm, which is significantly smaller than the experimental value. We note that the nanostructure containing one acetonitrile and one benzoic acid molecules in one intralayer microchnnel was not optimized due to the limited pore volume even though the framework is flexible. From the interatomic distances shown in Table S1, it is found that the intralayer microchannels are further expanded by exchanging the two acetonitrile molecules for one benzoic acid molecule.  The fact that intralayer microchannels are preliminarily expanded by the acetonitrile adsorption and benzoic acid is adsorbed in exchange for acetonitrile supports our assumption, where the rapid and effective adsorption observed in H-SiO2 is initiated by the flexible framework containing open microchannels. Therefore, it is concluded that the interlayer microchannels are expandable by the adsorptions due to the flexible Si−O framework, and benzoic acid is adsorbed in the microchannel in exchange for pre-adsorbed acetonitrile. CONCLUSIONS We have reported the gate opening adsorption behaviors of a layered silicate, prepared via dilute acid treatment of a commercially available sodium-type layered silicate, toward aromatic compounds (benzoic acid and phenol) in acetonitrile. Our comprehensive liquid-phase adsorption tests demonstrated, as reported for the adsorption of gaseous species on flexible MOFs, that the layered silicate has zeolite-like open microchannels within each layer and the framework is flexible enough to expand and accommodate the solvent molecule to initiate further aromatic compound uptake. Thanks to this gate opening behaviors, the layered silicate exhibited an excellent adsorption performance (amounts and rates) toward aromatic compounds from acetonitrile considerably higher than a widely studied layered silicate (magadiite after the removal of sodium cations from the interlayer space). DFT calculations supported the estimated adsorption site and reproduced the flexibility of the intralayer microchannel induced by the adsorption reactions. It was also revealed that one benzoic acid molecule is adsorbed in the intralayer microchannel in exchange for two acetonitrile molecules. Further adsorption tests on this microporous layered silicate in liquid and gas phases are under investigation in our laboratory, which will make the material more attractive and practical for important applications in energy, environments, and healthcare issues.  ASSOCIATED CONTENT Structures of Na-SiO2, Na-mag and their protonated forms, full experimental procedures and characterization data, including 29Si NMR, TG-DTA, SEM, in situ XRD, N2 adsorption, and water vapor adsorption, and details of calculation method and results.   This material is available free of charge via the Internet at http://pubs.acs.org.AUTHOR INFORMATIONCorresponding AuthorHiromitsu Takabatakaba@cc.kogakuin.ac.jpYusuke IdeIDE.Yusuke@nims.go.jpAuthor ContributionsAll authors have given approval to the final version of the manuscript.  ‡M.E. and H.E. contributed equally to this paper. Funding SourcesThis work was supported by JSPS KAKENHI (Grant Numbers 21H02034).NotesThe authors declare no competing financial interest.ACKNOWLEDGMENT This work was supported by JSPS KAKENHI (Grant Numbers 21H02034).REFERENCESCussen, E. J.; Claridge, J. B.; Rosseinsky, M. J.; Kepert, C. J. Flexible Sorption and Transformation Behavior in a Microporous Metal-Organic Framework. J. Am. Chem. Soc. 2002, 124 (32), 9574–9581. doi/10.1021/ja0262737Dybtsev, D. N.; Chun, H.; Kim, K.; Dybtsev, D N; Chun, H.; Kim, K. Rigid and Flexible: A Highly Porous Metal–Organic Framework with Unusual Guest-Dependent Dynamic Behavior. Angew. Chem. Int. Ed. 2004, 43 (38), 5033–5036. doi.org/10.1002/anie.200460712Sato, H.; Kosaka, W.; Matsuda, R.; Hori, A.; Hijikata, Y.; Belosludov, R. V.; Sakaki, S.; Takata, M.; Kitagawa, S. Self-Accelerating CO Sorption in a Soft Nanoporous Crystal. Science 2014, 343 (6167), 167–170. doi/10.1126/science.1246423Sakaida, S.; Otsubo, K.; Sakata, O.; Song, C.; Fujiwara, A.; Takata, M.; Kitagawa, H. Crystalline Coordination Framework Endowed with Dynamic Gate-Opening Behaviour by Being Downsized to a Thin Film. Nat. Chem. 2016 8:4 2016, 8 (4), 377–383. doi.org/10.1038/nchem.2469Fairen-Jimenez, D.; Moggach, S. A.; Wharmby, M. T.; Wright, P. A.; Parsons, S.; Düren, T. Opening the Gate: Framework Flexibility in ZIF-8 Explored by Experiments and Simulations. J. Am. Chem. Soc. 2011, 133 (23), 8900–8902. doi.org/10.1021/ja202154jGücüyener, C.; Van Den Bergh, J.; Gascon, J.; Kapteijn, F. Ethane/Ethene Separation Turned on Its Head: Selective Ethane Adsorption on the Metal-Organic Framework ZIF-7 through a Gate-Opening Mechanism. J. Am. Chem. Soc.2010, 132 (50), 17704–17706. doi.org/10.1021/ja1089765Georgieva, V. M.; Bruce, E. L.; Verbraeken, M. C.; Scott, A. R.; Casteel, W. J.; Brandani, S.; Wright, P. A. Triggered Gate Opening and Breathing Effects during Selective CO2 Adsorption by Merlinoite Zeolite. J. Am. Chem. Soc.2019, 141 (32), 12744–12759. doi/10.1021/jacs.9b05539Okada, T.; Ide, Y.; Ogawa, M. Organic–Inorganic Hybrids Based on Ultrathin Oxide Layers: Designed Nanostructures for Molecular Recognition. Chem. Asian J. 2012, 7 (9), 1980–1992. doi.org/10.1002/asia.201101015Watanabe, T.; Sato, T. Expansion characteristics of montmorillonite and saponite under various relative humidity conditions. Clay Sci. 1988, 7, 129–138. doi.org/10.11362/jcssjclayscience1960.7.129Ishihara, S.; Iyi, N.; Tsujimoto, Y.; Tominaka, S.; Matsushita, Y.; Krishnan, V.; Akada, M.; Labuta, J.; Deguchi, K.; Ohki, S.; Tansho, M.; Shimizu, T.; Ji, Q.; Yamauchi, Y.; Hill, J. P.; Abe, H.; Ariga, K. Hydrogen-Bond-Driven ‘Homogeneous Intercalation’ for Rapid, Reversible, and Ultra-Precise Actuation of Layered Clay Nanosheets. Chem. Commun. 2013, 49 (35), 3631–3633. doi/10.1039/c3cc40398jIde, Y.; Torii, M.; Sano, T. Layered Silicate as an Excellent Partner of a TiO2 Photocatalyst for Efficient and Selective Green Fine-Chemical Synthesis. J. Am. Chem. Soc. 2013, 135 (32), 11784–11786. doi/pdf/10.1021/ja406855eIde, Y.; Ochi, N.; Ogawa, M.; Ide, Y.; Ochi, N.; Ogawa, M. Effective and Selective Adsorption of Zn2+ from Seawater on a Layered Silicate. Angew. Chem. Int. Ed. 2011, 50 (3), 654–656. doi/10.1002/anie.201002322Honda, K.; Ide, Y.; Tsunoji, N.; Torii, M.; Sadakane, M.; Sano, T. An Efficient Way to Synthesize Hiroshima University Silicate-1 (HUS-1) and the Selective Adsorption Property of Ni2+ from Seawater. Bull. Chem. Soc. Jpn. 2014, 87 (1), 160–166. doi:10.1246/bcsj.20130251Bärwinkel, K.; Herling, M. M.; Rieß, M.; Sato, H.; Li, L.; Avadhut, Y. S.; Kemnitzer, T. W.; Kalo, H.; Senker, J.; Matsuda, R.; Kitagawa, S.; Breu, J. Constant Volume Gate-Opening by Freezing Rotational Dynamics in Microporous Organically Pillared Layered Silicates. J. Am. Chem. Soc. 2017, 139 (2), 904–909. doi.org/10.1021/jacs.6b11124Okada, T.; Yoshida, T.; Iiyama, T. Kinetics of Interlayer Expansion of a Layered Silicate Driven by Caffeine Intercalation in the Water Phase Using Transmission X-Ray Diffraction. J. Phys. Chem. B 2017, 121 (28), 6919–6925. doi.org/10.1021/acs.jpcb.7b03200Ide, Y.; Tominaka, S.; Kono, H.; Ram, R.; Machida, A.; Tsunoji, N. Zeolitic Intralayer Microchannels of Magadiite, a Natural Layered Silicate, to Boost Green Organic Synthesis. Chem. Sci. 2018, 9 (46), 8637–8643. doi/10.1039/c8sc03712dDoustkhah, E.; Ide, Y. Bursting Exfoliation of a Microporous Layered Silicate to Three-Dimensionally Meso-Microporous Nanosheets for Improved Molecular Recognition. ACS Appl. Nano Mater. 2019, 2 (12), 7513–7520. doi.org/10.1021/acsanm.9b01508Kosuge, K.; Yamazaki, A.; Tsunashima, A.; Otsuka, R. Hydrothermal synthesis of magadiite and kenyaite. J. Ceram. Soc. Jpn. 1992, 100, 326−331.Asakura, Y.; Hosaka, N.; Osada, S.; Terasawa, T.; Shimojima, A.; Kuroda, K. Interlayer condensation of protonated layered silicate magadiite through refluxing in N methylformamide. Bull. Chem. Soc. Jpn. 2015, 88, 1241−1249.Ide, Y.; Ogawa, M. Surface modification of a layered alkali titanate with organosilanes. Chem. Commun. 2003, 1262−1263.Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 1996, 77, 3865−3868.Tominaga, M.; Nishioka, Y.; Tani, S.; Suzuki, Y.; Kawamata, J. Tunable high-pressure field operating on a cationic biphenyl derivative intercalated in clay minerals. Sci. Rep. 2017, 7(1), 1–6.Eugster, H. P. Hydrous Sodium Silicates from Lake Magadi, Kenya: Precursors of Bedded Chert. Science 1967, 157 (3793), 1177–1180. doi/10.1126/science.157.3793.1177Scholzen, G.; Beneke, K.; Lagaly, G. Diversity of magadiite. Z. Anorg. Allg. Chem. 1991, 597, 183–196. doi.org/10.1002/zaac.19915970121Krysiak, Y.; Maslyk, M.; Silva, B. N.; Plana-Ruiz, S.; Moura, H. M.; Munsignatti, E. O.; Vaiss, V. S.; Kolb, U.; Tremel, W.; Palatinus, L.; Leitão, A. A.; Marler, B.; Pastore, H. O. The Elusive Structure of Magadiite, Solved by 3D Electron Diffraction and Model Building. Chem. Mater. 2021, 33 (9), 3207–3219. doi.org/10.1021/acs.chemmater.1c00107Doustkhah, E.; Ide, Y. Microporous Layered Silicates: Old but New Microporous Materials. New J. Chem. 2020, 44 (24), 9957–9968. doi/10.1039/c9nj06222jGiles, C. H.; MacEwan, T. H.; Nakhwa, S. N.; Smith, D. Studies in adsorption. Part XI. A system of classification of solution adsorption isotherms, and its use in diagnosis of adsorption mechanisms and in measurement of specific surface areas of solids. J. Chem. Soc. 1960, 3973–3993. doi.org/10.1039/JR9600003973Azais, T.; Hartmeyer, G.; Quignard, S.; Laurent, G.; Babonneau, F. Solution State NMR Techniques Applied to Solid State Samples: Characterization of Benzoic Acid Confined in MCM-41. J. Phys. Chem. C 2010, 114 (19), 8884–8891. doi/10.1021/jp910622mTozuka, Y.; Sasaoka, S.; Nagae, A.; Moribe, K.; Oguchi, T.; Yamamoto, K. Rapid Adsorption and Entrapment of Benzoic Acid Molecules onto Mesoporous Silica (FSM-16). J. Colloid Interface Sci. 2005, 291 (2), 471–476. doi:10.1016/j.jcis.2005.05.009Babonneau, F.; Yeung, L.; Steunou, N.; Gervais, C.; Ramila, A.; Vallet-Regi, M. Solid State NMR Characterisation of Encapsulated Molecules in Mesoporous Silica. J. Solgel Sci. Technol. 2004, 31, 219–223. doi.org/10.1023/B:JSST.0000047991.73840.8b14image1.tiffimage2.tiffimage3.pngimage4.tiffimage5.tiffimage6.tiffimage7.tiffimage8.tiff