Structure Of MMT Research Articles

The immobilized Cu nanoparticles on magnetic montmorillonite (MMT@Fe3O4@Cu): As an efficient and reusable nanocatalyst for reduction and reductive-acetylation of nitroarenes with NaBH4

In this study, the immobilization of copper nanoparticles on superparamagnetic montmorillonite, MMT@Fe3O4@Cu, was studied. Magnetically nanoparticles (MNPs) of iron oxide (Fe3O4) were primarily prepared by a chemical co-precipitation method. Next, the prepared Fe3O4 MNPs were intercalated within the interlamellar spaces and external surface of sodium-exchanged montmorillonite. Finally, Cu NPs were immobilized on magnetic montmorillonite by a simply mixing of an aqueous solution of CuCl2·2H2O with MMT@Fe3O4 followed by the reduction with NaBH4. Characterization of MMT@Fe3O4 clay system represented that through the immobilization of Fe3O4 MNPs, disordered-layers structure of MMT was easily reorganized to an ordered-layers arrangement. The synthesized composite systems were characterized using FT-IR, SEM, EDX, XRD, VSM, BET and ICP-OES analyses. SEM analysis exhibited that dispersion of Cu NPs, with the size distribution of 15–25 nm, on the surface of magnetic clay was taken place perfectly. BET surface analysis indicated that after the immobilization of Fe3O4 and Cu species, the surface area and total pore volume of MMT@Fe3O4@Cu system was decreased. Next, the Cu-clay nanocomposite system showed a perfect catalytic activity towards reduction of nitroarenes to anilines as well as reductive-acetylation of nitroarenes to acetanilides using NaBH4 and Ac2O in water as a green and economic solvent. The copper magnetic clay catalyst can be easily separated from the reaction mixture by an external magnetic field and reused for six consecutive cycles without the significant loss of its catalytic activity.

Montmorillonite with unique interlayer space imparted polymer scaffolds with sustained release of Ag+

Abstract Polyglycolic acid (PGA) has been a potential scaffold material due to its good biocompatibility and processibility, but its poor mechanical properties and over fast degradation restricted its application in bone repair. Meanwhile, it is worth noticing that bacterial infection is a common problem in bone repair. In this study, montmorillonite (MMT), with unique interlayer space, was introduced to PGA scaffolds prepared via additive manufacturing to address the problems. The results indicated MMT acted as rigid reinforcements dispersing well in the PGA matrix, which effectively transferred and absorbed the stresses in the matrix, thereby significantly increasing the compressive properties and hardness of the scaffolds. Moreover, MMT played the role of impermeable barriers in the matrix, hindering the diffusion of water and its attack on the matrix, which inhibited the hydrolysis and hence significantly decreased the degradable rate. More importantly, Ag+ was loaded into the interlayer space of MMT via ion exchange and was further chemically reduced to metallic Ag with higher stability. The impermeable layered structure of MMT presented dual barrier effects on the release of Ag+ via inhibiting the attack of water on Ag from outside and the diffusion of Ag+ from inside. Hence, the scaffolds exhibited a sustained Ag+ release and a long-lasting antibacterial property.

Enhanced epoxy coating based on cerium loaded Na-montmorillonite as active anti-corrosive nanoreservoirs for corrosion protection of mild steel: Synthesis, characterization, and electrochemical behavior

In this study, Na-montmorillonite (MMT) was intercalated with the cerium cations. The Ce3+ cations intercalated sodium montmorillonite (Ce-MMT) nanoreservoirs were incorporated into the epoxy coating. The active inhibitive performance of the synthesized nanoreservoirs and their effect on the protective behavior of the epoxy coating was investigated in the present study. For this purpose, field emission scanning electron microscopy, Fourier transformation infrared spectroscopy, inductively coupled plasma optical emission spectroscopy and X-ray diffraction analyses were employed to characterize the synthesized nanoreservoirs. Characterization results showed that the Ce3+ cations successfully intercalated into the MMT structure. The active anti-corrosion performance of the Ce-MMT was proved by electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, open circuit potential, and salt spray tests. In the electrolyte phase, the obtained results showed that the corrosion resistance of the steel samples significantly improved in the presence of the Ce-MMT extract and the observed corrosion efficiency was about 93%. Also, the results of surface study confirmed the subsequent effect of the active nanoreservoirs on the chemical composition and surface morphology of the steel samples. In the coating phase, the result of the EIS and salt spray tests confirmed the enhanced inhibitive behavior of the epoxy coating in the presence of the Ce-MMT nanoreservoirs.

2D-montmorillonite-dispersed g-C3N4/TiO2 2D/0Dnanocomposite for enhanced photo-induced H2 evolution from glycerol-water mixture

Montmorillonite (MMT) dispersed g-C3N4/TiO2 hybrid nanocomposite for enhanced photo-catalytic hydrogen production from glycerol-water mixture has been investigated. The newly designed composite photo-catalysts were fabricated through a sol-gel assisted hydrothermal method and were characterized by XRD, XPS, SEM, EDX, TEM, FTIR, UV–Vis, Raman and PL spectroscopy. Well-designed g-C3N4/MMT/TiO2 heterojunction composite was obtained with 2D MMT structure, which promoted both visible light absorption and hindered charges recombination rate. The modification of 2D/0D g-C3N4/TiO2 heterojunction with 2D MMT sheets enhances H2 production due to MMT works as a mediator for effective charges trapping and transportation within the composite structure. The g-C3N4/MMT/TiO2 photo-catalyst exhibits highest H2 production of 4425 ppm h−1 g−1 at pH 7.0, which was 2.12 times higher than the pure TiO2 (2085 ppm h−1 g−1). In addition, increasing catalyst loading promotes more H2 evolution and among the different sacrificial reagents, glycerol-water mixture gave highest H2 production due to the presence of α-hydrogen atoms attached to carbon atoms. The enhanced photo-catalytic efficiency can be attributed to synergistic effect of MMT with g-C3N4/TiO2 heterojunction composite, appropriate band structure and transportation of electrons–holes with their hindered recombination rate. These composite catalysts exhibited excellent photo-catalytic stability for H2 production in cyclic runs. Possible reaction mechanism for hydrogen production over g-C3N4/MMT/TiO2 composite has been explained based on the experimental results. The finding of this work would be fruitful for hydrogen production applications with all sustainable systems.

Effects of TiO2 pillared montmorillonite nanocomposites on the properties of asphalt with exhaust catalytic capacity

Titanium dioxide (TiO2) pillared montmorillonite nanocomposites (T/M) have been prepared from montmorillonite (MMT) with tetrabutyl titanate by sol-gel method, and characterized by X-ray diffraction, transmission electron microscopy together with energy dispersive X-ray. Anatase TiO2 could be intercalated into the layer structure of MMT and dispersed on the outer surface, as the basal spacing increases by 0.26 nm for T/M. The influences of different contents of T/M on the properties of matrix asphalt and catalytic capacity for automobile exhaust were also investigated. T/M modified asphalt samples showed a remarkable increase on the G∗/sinδ and improved resistance of asphalt pavement to failure for improved high temperature rheological performances. And T/M could improve the resistance of asphalt to UV aging effectively. What’ more, T/M modified asphalt samples showed superior degradation capabilities of NO, CO and HC for simulating the catalysis of actual automobile exhaust.

Metals free MWCNTs@TiO2@MMT heterojunction composite with MMT as a mediator for fast charges separation towards visible light driven photocatalytic hydrogen evolution

Constructing heterojunctions with low-cost materials functional under solar energy is an important way for efficient hydrogen production for energy management applications. In this study, multiwall carbon nanotubes (MWCNTs) modified TiO2 1D/0D heterojunction dispersed in 2D montmorillonite (MMT) nanoclay was designed and fabricated using a facile sol-gel and wet impregnation approach. The samples were characterized by XRD, Raman, FESEM, HRTEM, FTIR, UV–vis and PL-spectroscopy techniques. Dispersing 1D/0D MWCNTs/TiO2 on the 2D MMT structure extends visible light absorption, shorten charges migration distance and provides abundant active sites. The performance of samples was investigated for dynamic photocatalytic H2 evolution with different sacrificial reagents under visible light irradiations. The MWCNTs/TiO2/MMT heterojunction composite exhibits the highest H2 evolution rate of 1888 ppm h−1, which is about 1.49, 3.07 and 7.12 folds higher than MWCNTs/TiO2, MMT/TiO2 and pure TiO2 samples, respectively. Among the different sacrificial reagents, highest H2 production was obtained using glycerol-water mixture due to the presence of α-hydrogen atoms attached to carbon atoms. Next, the photocatalytic turn-over productivity (PTOP) was estimated which demonstrated the molecular H2 production rate with the photon-energy utilization. The maximum PTOP for H2 production was achieved over MWCNTs/TiO2/MMT heterojunction composite, 5.94 times higher than using bare TiO2 NPs. The improved charges efficiency due to the synergistic effect between MWCNTs/TiO2/MMT in 1D/OD/2D heterojunctions is critical for enhanced and dynamic H2 evolution. The ternary composite exhibited excellent and stable performance for H2 production. This study suggests that constructing heterojunction of low cost coupling materials with TiO2 can provide an efficient way for H2 production under solar energy.

Effect of intercalated and exfoliated montmorillonite clay on the structural, dielectric and electrical properties of plasticized nanocomposite solid polymer electrolytes

Abstract Plasticized nanocomposite solid polymer electrolyte (PNSPE) films, consisted of poly(ethylene oxide) (PEO) and poly(methyl methacrylate) (PMMA) polymer blend matrix (50/50 wt%) with lithium tetrafluoroborate (LiBF4) as dopant ionic salt (10 wt%), ethylene carbonate (EC) as plasticizer (10 wt%) and montmorillonite (MMT) clay as nanofiller (3 wt%), have been prepared by classical solution-cast (SC) and the ultrasonic-microwave irradiated (US–MW) solution-cast methods. X–ray diffraction (XRD) study confirms that these PNSPE films are predominantly amorphous and contain very small amount of PEO crystallites. The SC method prepared PNSPE film bears highly ordered intercalated MMT structures, whereas, the US–MW method prepared PNSPE film has large amount of disordered exfoliated MMT structures. Dielectric relaxation spectroscopy (DRS) from 20 Hz to 1 MHz has been employed for characterization of complex dielectric permittivity, alternating current electrical conductivity and complex impedance spectra of the films. Three relaxation processes corresponding to the electric double layers dynamics, polymer chain segmental motion and ionic conductivity have been explored. It has been observed that the dielectric and electrical properties of the PNSPE films change notably with the film preparation methods. Results reveal that the exfoliated MMT decreases the dielectric polarization and creates hindrance to the polymer chain segmental dynamics which causes decrease of ionic conductivity in comparison to the ion-dipolar complexes containing intercalated MMT. The room temperature dc ionic conductivity of the PNSPE films have been found about 10−5 S cm−1, which confirms these materials as potential candidate for design and development of flexible-type all-solid-state lithium-ion conducting electrochromic devices.

Enhancement clay tolerance of PCE by lignin-based polyoxyethylene ether in montmorillonite-contained paste

Abstract The dispersion ability of polycarboxylate ether (PCE) in fresh concrete is much impeded by clay impurities. To improve the dispersion of PCE in the clay-contained concrete, lignin-based polyoxyethylene ether (PEG- grafted -lignin) was synthesized through polyethylene glycol (PEG) grafted to kraft lignin (KL). The results showed that PEG- grafted -lignin increased the fluidity of MMT-contained cement paste when combined with PCE. It improved the rheological properties of MMT-contained cement paste by reducing the yield stress and the rheological behavior index. The adsorption of PEG- grafted -lignin on MMT was more quickly than KL and the equilibrium adsorption amount was 31.43 mg/g at an initial concentration of 100 mg/L. XRD revealed that PEG- grafted -lignin had inserted into the interlayer structure of MMT, while DLS disclosed the spatial effect of PEG- grafted -lignin was much stronger than PCE. This study put forward a new method in the anti-sludge study of PCE.

Reductive Cyclization of Levulinic Acid to γ-Valerolactone over Non-Noble Bimetallic Nanocomposite

Bimetallic nanoparticles have diverse applications in catalytic processes owing to the differences in individual properties that contribute to their increased catalytic activity. To further improve the efficiency, they are dispersed in an inert support that enhances the catalytic activity toward organic transformations. In this study, we report simple, facile, and cost-effective chemical route for the fabrication of nanocomposites with Fe–Ni bimetallic nanoparticles supported on montmorillonite (MMT) possessing variation in the Fe and Ni content. These composites are characterized with X-ray diffraction, transmission electron microscopy surface area, and NH3-TPD. Fe–Ni bimetallic nanoparticles are well-dispersed within MMT structure having particle sizes of about 30–40 nm. Among various compositions of Fe–Ni/MMT catalysts, composite with 25% Fe and 25% Ni exhibits >99% LA conversion with 98% selectivity to GVL within 1 h. IPA is found to be better solvent for levulinic acid (LA) to γ-valerolactone (GVL) c...

Ionic liquids intercalated in montmorillonite as the sorptive phase for the extraction of low-polarity organic compounds from water by rotating-disk sorptive extraction

Montmorillonite (MMT) clays were modified by the intercalation into their galleries of ionic liquids (IL) based on imidazolium quaternary ammonium salts. This new eco-materials exhibited good features for use as a sorptive phase in the extraction of low-polarity analytes from aqueous samples. Spectroscopic analyses of the modified clays were conducted and revealed an increase in the basal spacing and a shifting of the reflection plane towards lower values as a consequence of the effective intercalation of organic cations into the MMT structure. The novel sorbent developed herein was assayed as the sorptive phase in rotating-disk sorptive extraction (RDSE), using polychlorinated biphenyls (PCBs), representative of low-polarity pollutants, as model analytes. The final determination was made by gas chromatography with electron capture detection. Among the synthetized sorptive phases, the selected system for analytical purposes consisted of MMT modified with the 1-hexadecyl-3-methylimidazolium bromide (HDMIM-Br) IL. Satisfactory analytical features were achieved using a sample volume of 5 mL: the relative recoveries from a wastewater sample were higher than 80%, the detection limits were between 3 ng L−1 and 43 ng L−1, the precision (within-run precision) expressed as the relative standard deviation ranged from 2% to 24%, and the enrichment factors ranged between 18 and 28. Using RDSE, the extraction efficiency achieved for the selected MMT-HDMIM-Br phase was compared with other commercial solid phases/supports, such as polypropylene, polypropylene with 1-octanol (as a supported liquid membrane), octadecyl (C18) and octyl (C8), and showed the highest response for all the studied analytes.Under the optimized extraction conditions, this new device was applied in the analysis of the influent of a wastewater treatment plant in Santiago (Chile), demonstrating its applicability through the good recoveries and precision achieved with real samples.

High-Performance Poly(vinyl alcohol) Nanocomposites Filled with Individual Montmorillonite Nanolayers

ABSTRACTFilling poly(vinyl alcohol) (PVA) with clay, typically montmorillonite (MMT), has been proven to be an attractive option to meet the high-performance requirements of PVA-based materials. In previous reports MMT or organophilic MMT (OMMT) were directly used as fillers. As a result, both exfoliated and intercalated MMT structures coexisted in the resultant nanocomposites. However, there is still a large gap between these nanocomposites and ideally designed ones where individual clay nanolayers (CNLs) are expected to be uniformly dispersed in the PVA. With this in mind, an ameliorative solution casting process is proposed here to prepare PVA nanocomposites. For this purpose the CNLs were prepared ahead of time by exfoliation of MMT in water and then used as fillers. Assessment of the dispersion state of the CNLs in PVA revealed that they (≤5.0 wt%) were randomly and uniformly dispersed (down to the level of individual silicate layers) in and formed strong interfacial interactions with the PVA. This resulted in significantly enhanced physical properties of the resultant nanocomposites relative to neat PVA. In particular, a 104.7% increment in the yield stress was achieved with 5.0 wt% CNLs, much larger than the 15–70% increments of previous PVA nanocomposites using MMT or OMMT as fillers. Additionally, excellent optical clarity of the PVA was obtained for the nanocomposites.

Molecular dynamics simulation of gas diffusion in polyethylene-clay nanocomposites with different silicate layers configurations

Barrier properties of pristine polyethylene (PE) and polyethylene/montmorillonite-clay (PE/MMT) nanocomposite films with different MMT layers configurations were studied using molecular dynamics simulation within NVT ensemble. The force field parameters were optimized for bond lengths, bond angles and torsion angles of the MMT structure. A special simulation box was designed to simulate the diffusion of oxygen, nitrogen and methane, through pristine PE and PE/MMT nanocomposite films. The diffusion coefficients of these gases and the tortuosity values were calculated and analyzed. Results showed that the configuration of clay nanoparticles has strong effect on the barrier properties of the nanocomposite films. The parallel configuration for layered silicates was predicted to have a low diffusion coefficient and a high tortuosity parameter for gas diffusive molecules. The simulation could also indicate that the diffusion coefficient of oxygen is higher than those of nitrogen and methane gases in the examined systems which can be attributed to the smaller kinetic diameter of oxygen.

Dielectric Dispersion and Relaxation in Polymer Blend Based Nanodielectric Film

SummaryPolymer nanodielectrics is the exponential growing field of advanced materials sciences. Such flexible materials have recognized their suitability as substrate and insulator in fabrication of microelectronic devices, and also in preparation of ion conducting solid polymer electrolytes. The nanodielectric film consisted of poly(ethylene oxide) and poly(methyl methacrylate) (PEO–PMMA; 75/25 wt/wt%) blend with 5 wt% montmorillonite (MMT) clay as nanofiller has been prepared by solution‐casting method followed by melt‐pressed technique. The X‐ray diffraction study of the film confirms the intercalated MMT structures in the semicrystalline phase of PEO–PMMA blend. The scanning electron microscopic images confirm the significant variation in morphology of the PEO–PMMA blend on addition of MMT nanofiller. The dielectric relaxation spectroscopy has been employed for measurement of complex dielectric function, ac electrical conductivity and electric modulus spectra of the nanodielectric film in the frequency range 20 Hz–1 MHz. The value of real part of dielectric function of the film is found high at low frequencies due to contribution of electrode polarization effect, but it decreases non‐linearly with the increase of frequency and finally approaches the high frequency limiting value of 2.3 at 1 MHz. The relaxation peak in dielectric loss spectra corresponding to polymer segmental motion is found above 10 kHz, and the peak positions have a shift towards higher frequency side with the increase of temperature. The dc conductivity increases and the relaxation time of the polymer segmental motion decreases with increasing temperature of the nanodielectric film according to the Arrhenius behaviour.

Catalytic Ethanol Dehydration over Different Acid-activated Montmorillonite Clays.

In the present study, the catalytic dehydration of ethanol to obtain ethylene over montmorillonite clays (MMT) with mineral acid activation including H2SO4 (SA-MMT), HCl (HA-MMT) and HNO3 (NA-MMT) was investigated at temperature range of 200 to 400°C. It revealed that HA-MMT exhibited the highest catalytic activity. Ethanol conversion and ethylene selectivity were found to increase with increased reaction temperature. At 400°C, the HA-MMT yielded 82% of ethanol conversion having 78% of ethylene yield. At lower temperature (i.e. 200 to 300°C), diethyl ether (DEE) was a major product. The highest activity obtained from HA-MMT can be attributed to an increase of weak acid sites and acid density by the activation of MMT with HCl. It can be also proven by various characterization techniques that in most case, the main structure of MMT did not alter by acid activation (excepted for NA-MMT). Upon the stability test for 72 h during the reaction, the MMT and HA-MMT showed only slight deactivation due to carbon deposition. Hence, the acid activation of MMT by HCl is promising to enhance the catalytic dehydration of ethanol.

Effects of Gamma Irradiation on Clay Membrane with Poly(vinyl alcohol) for Fire Retardancy

Clay membrane hybrid composites were prepared by facile solution-casting of aqueous precursor suspensions of poly(vinyl alcohol) (PVOH) and montmorillonite clay (MMT), then cross-linked by gamma irradiation. The influences of absorbed dose and polymer loading on composite structure and properties were investigated. A moderate amount of PVOH (P4C6) is found to be optimum for fabricating mechanically strong PVOH composites; however, gamma irradiation has a positive influence on strengthening composites only with low PVOH content. Scanning electron microscopy (SEM) observation shows a layered structure from the cross-section of a cryo-fractured surface for all composites, and a comparatively smooth surface. The wide-angle X-ray diffraction (WAXD) characterization shows an intercalated MMT structure with incorporation of PVOH. Cross-linking and the increase of clay content lead to a decreased onset decomposition temperature but an increase in the temperature at the maximum decomposition rate and enhancement o...

Preparation of Acid-Activated Montmorillonite and Its Application

The natural Na-type montmorillonite (Na-MMT) was treated with HNO3 to obtain acid-activated montmorillonite (acid-MMT). The materials were characterized by XRD, XRF, SEM, and N2 adsorption–desorption at low temperature. Results indicated that the structure and textural properties of MMT were significantly changed via acid activation. Meanwhile, the potential use of acid-MMT as adsorbent for the removal of phenol from aqueous solution was evaluated. Important parameters which affected adsorption, such as contact time, pH of solution, and mass of acid-MMT had been investigated. The removal of phenol was decreased with the increase of pH value, and increased with the increase of contact time and mass of acid-MMT. The equilibrium data in aqueous solutions were well represented by the Freundlich isotherm.

NIR‐Mediated Antibacterial Clay Nanocomposites: Exfoliation of Montmorillonite Nanolayers by IR825 Intercalation

We report the exfoliation of montmorillonite (MMT) by IR825, a near infrared (NIR) active hyper‐thermal antibacterial nanocomposite, constructed using polyvinylpyrrolidione‐q‐catechol with sultones (C‐PVPS) through ionic exchange reactions. Studying this nanocomposite revealed a sharp increase in photothermal heat as a function of irradiation time, and the layered MMT structure is promising for optimizing the required thermal stability to increase the photothermal heat. Only 5 min of exposing an in vitro suspension of bacteria to NIR‐triggered local nanocomposite resulted in rapid killing of bacteria. Due to their considerable potential for photothermal applications, thermo‐stable MMT‐based materials have attracted tremendous attention for designing nanocomposites of pathogenic bacteria.

Facile construction of cellulose/montmorillonite nanocomposite biobased plastics with flame retardant and gas barrier properties

Plastics with good flame retardant and gas barrier properties have been widely applied in the electrical industry. On the basis of the affinity between clay and cellulose, cellulose/montmorillonite (MMT) biobased plastics were constructed via a simple hot pressing of cellulose/MMT hydrogels prepared from a mixture of the cellulose solution and MMT suspension solution. The results of Fourier transform infrared spectra, X-ray diffraction and X-ray photoelectron spectroscopy (XPS) indicated that the MMT thin lamellae with about 4 nm thickness were uniformly dispersed in cellulose/MMT nanocomposite plastics. Moreover, transmission electron microscopy confirmed that an intercalated structure of MMT appeared in the cellulose/MMT. The experimental results revealed that MMT was well fixed in the cellulose matrix by the hydrogen bonding interaction and affinity between MMT and cellulose, leading to good miscibility. The tensile strength of the nanocomposite increased with an increase of MMT content. Moreover, the flame retardant of cellulose/MMT biobased plastic was improved with an increase of MMT content, while the biobased plastic with 20 wt% MMT achieved the highest limiting oxygen index of 29.3 %. Because of their good limiting oxygen index and gas barrier properties, these cellulose/MMT biobased plastics have potential applications in fields such as gas resistance, flame retardant, packaging material, etc.

A combined X-ray absorption spectroscopy and molecular dynamic simulation to study the local structure potassium ion in hydrated montmorillonite

Atomistic local structure of potassium ion adsorbed in hydrated montmorillonite (MMT) was investigated based on a combination of an extended X-ray absorption fine structure (EXAFS) spectroscopy and classical molecular dynamics (MD) simulation. The accuracy of the representative MMT atomistic model with PCFF-INTERFACE force field was validated. MD-simulated EXAFS spectra were calculated from trajectories of hydrated MMT atomic coordinates and the results were in satisfactory agreement with corresponding experimental EXAFS spectra. Interlayer spacing determined by X-ray diffraction was consistent with the mono-layer hydrated MMT structure. The first coordination shell of K+ ion in monohydrated MMT was formed by 5 water oxygen atoms at an average K–OW distance of 2.85 A and the second coordination shell of 6 oxygen atoms from both sides of the closest silicate tetrahedral sheet at K–OMMT = 3.41 A. For hydrated K+-MMT, MD and EXAFS results confirm that K+ counter ions form the inner-sphere surface complex and that the adsorbed sites were located with the vicinity edge of a basal oxygen hexagonal cavity in the silicate tetrahedral sheets of MMT. For higher-layer hydrated MMT, K+ ions can form surface complexes that are inner-sphere, outer-sphere, and transient diffuse-layer species depending on the number of intercalated water in the clay. Water molecules are of less ordered arrangement in the monohydrated MMT due to the confinement effect from the clay surface. K+ counter ions in the single layer hydrates are almost trapped within the cavities of the basal planes surface.

First principles characterization of silicate sites in clay surfaces.

Aluminosilicate clays like Montmorillonite (MMT) and Muscovite Mica (MT) have siloxane cavities on the basal plane. The hydroxyl groups localized in these cavities and van der Waals (vdW) forces contribute significantly to adsorption processes. However, the basal sites are found to be difficult to characterize experimentally. Here, (001) surfaces of MMT and MT clays were investigated using first-principles calculations to understand how these silicate surface sites are influenced by hydroxyl groups and the effective role of inner layer vdW interactions. Based on density-functional theory (DFT) within the generalized gradient approximation (GGA), different types of exchange-correlation functionals were tested to check the effect of vdW dispersion correction. Noncontact atomic force microscopy (nc-AFM), X-ray absorption spectroscopy (XAS) in the near-edge region and solid-state nuclear magnetic resonance (SS-NMR) spectroscopy were simulated. In both clays, the oxygen surface sites are directly affected by the intralayer interaction through hydroxyl groups. Our results indicated that the chemical environment of the hydroxyl groups is distinct in the MMT and MT structures. The vdW correction was essential for a better description of the surface oxygen sites and correctly describes the similarity between both clays. Particularly, the bulk apical oxygen sites in the MT structure are less influenced by vdW interaction. Compared to MMT, the silicon surface sites of MT are more sensitive to the intralayer changes in Si-Oapical-Al and with less effect of the hydroxyl groups. These results provide a clear understanding of influence of the siloxane cavity on the oxygen and silicon surface sites in aluminosilicates.