Series Of Montmorillonites Research Articles

Structure and performance of clay composite membranes with improved sodium conductivity for salinity gradient batteries

Low-cost cation exchange membranes with improved ionic conductivity and permselectivity are needed for the deployment of efficient large-scale energy storage technologies or separation technologies such as electrodialysis. In this work, a series of montmorillonite (Mt) clays and sulfonated poly(ether ether ketone) (SPEEK) composite membranes with 1 to 20 weight percentage (wt%) additives are studied. Two types of clays are investigated, a generic K30 Mt and an aluminum pillared (Al-pil) Mt with larger interlayer spacing owing to the inorganic crosslinks between the clay platelets. The addition of inorganic clays with two-dimensional geometries enables the formation of percolating sodium diffusing pathways with reduced tortuosity. As a result, the conductivity of the membranes increases with an increasing clay loading fraction, reaching up to 1.4 times that of the pure SPEEK with 20 wt% K30 Mt. The permselectivity of the native SPEEK membrane also improves with the addition of set amounts of K30 Mt, while the Al-pil Mt composites suffer from a slightly reduced permselectivity due to their higher water uptake. The voltaic efficiency of a concentration gradient flow battery shows that the addition of 20 wt% K30 Mt clay to the SPEEK polymer matrix can improve the voltaic efficiency by up to 10%.

Effect of montmorillonite on PEBAX® 1074-based mixed matrix membranes to be used in humidifiers in proton exchange membrane fuel cells

Abstract To meet the increasing requirements of membrane humidification in proton exchange membrane fuel cells (PEMFCs), a series of montmorillonite (MMT)/PEBAX® 1074 mixed matrix membranes (MMMs) were fabricated using the solvent casting method. Pristine MMT and poly(oxyalkylene)amine (APOP)-modified MMT were added as the filler. Using the XRD, FT-IR, SEM, and TEM, the morphology and chemical structure of MMT during modification were investigated. Using the tests of water vapor permeability, air permeability, water contact angle, and crystallinity, the effects of montmorillonite on membrane properties were investigated. The results showed that surface hydrophilicity and crystallinity of MMMs increased as the MMT content increases, which leads to higher vapor permeability and selectivity than the pure PEBAX® 1074 membrane. After modification, APOP-MMT/PEBAX® 1074 MMMs showed better performance in vapor permeability and vapor/air selectivity. The best selectivity was 1.7 × 105, which is three times higher than that of pure PEBAX® 1074 membrane.

Structural effect of imidazolium-type ionic liquid adsorption to montmorillonite

The adsorption of 1-alkyl-3-methylimidazolium-type ionic liquids (ITILs) coupled with different counteranions (Tf2N−, PF6−, BF4−, and Cl−) with variational cation alkyl chain lengths (n = 2, 4, 6, and 8) to montmorillonite was investigated to explore the structural effect of ITILs on their adsorption. A series of montmorillonite with different cation exchange capacities (CECs) and possessing a set of homoionic K- and Cs-exchanged interlayer cations were also examined to assess the influence of montmorillonite structure and characteristics. The adsorption of ITILs to Na-saturated montmorillonite (Na-MAz) was counteranion-independent but increased with the increase in the alkyl chain length of the imidazolium cation. X-ray diffraction results indicated that ITIL cations with different alkyl chains lay flat between the montmorillonite interlayers with different contact angles. The uptake of ITILs by Na-MAz increased with the increase in the solution pH and decrease in ionic strength. Na-MAz exhibited greater adsorption than K- and Cs-saturated MAz due to the larger hydrated radii of Na+ than those of K+ and Cs+. The uptake of ITILs to Na-MZj (CEC = 64 mmol/100 g) was almost half compared with that of Na-MAz (CEC = 117 mmol/100 g). Consequently, this work demonstrated that the ITIL adsorption to montmorillonite was dependent on the structures of both adsorbate and adsorbent.

Wettability studies of reduced-charge montmorillonites modified by quaternary ammonium salts using capillary rise test

A series of montmorillonites with systematically reduced layer charge were prepared by a standard method of different fractions of Li+-fixation in montmorillonite, which could be used to mimic an oil reservoir. Three kinds of quaternary ammonium salts (QASs) with different cationic charges and structure sizes were used singularly or in compound form to modify the reduced-charge montmorillonites (RCMs). The wettability alterations of the organo-RCMs for deionized water and cyclohexane were studied based on capillary rise method and were compared using the Lipophilic to Hydrophilic Ratio (LHR). The results indicate that RCMs singularly modified by three kinds of QASs show different wettability characteristics, whereas compound modified by QASs have a synergistic effect on the wettability. Moreover, the compound type of the QASs plays a more important role on LHR values than the mix proportion. The results of this work also indicate that it is possible to regulate the wettability of the organo-RCMs by simultaneous control of the type, the compound ratio of QASs and the layer charge characteristics, which is helpful in providing theoretical guidance for the oil production.

Application of XPS method in the research into Ni ion-modified montmorillonite as a SO2 sorbent

A series of montmorillonites with adsorbed nickel ions was prepared through adsorption of nitrates from water solutions; there were four methods adopted. The surface of the sample under modification was investigated with the method of argon adsorption and XPS (X-ray photoelectron spectroscopy). SO2 was investigated on nickel-modified montmorillonites. Nickel cations were adsorbed on the montmorillonite surface as Ni2+ in Ni(OH)2 or NiO. Montmorillonite — after nickel adsorption — adsorbs SO2 physically. An addition of Mont–Ni to hard coal in a ratio 1:500 reduces SO2 emissions in the combustion process by 75–85%. Waste bentonite can be utilized for reducing SO2 emissions after processing.

Fluorescence resonance energy transfer between two cationic laser dyes in presence of the series of reduced-charge montmorillonites: Effect of the layer charge

Series of montmorillonites with systematically reduced layer charges represent a suitable model for studying various properties and interactions of layered inorganic compounds. The reduced-charge montmorillonites (RCMs) used in this study were prepared by a standard method of Li +-fixation in Nanocor montmorillonite at 100–300 °C. The layer charge gradually decreased with increasing temperature of RCM preparation. Li +-fixation led in some cases to the loss of expandability due to the formation of mixed swelling/nonswelling and homogeneous nonswelling phases. The interaction of two cationic dyes—rhodamine 3B (R3B) and oxazine 4 (Ox4)—with reduced-charge montmorillonites in dispersions was studied by means of UV/vis absorption and fluorescence spectroscopy. Montmorillonite with the highest charge density induced the formation of H-aggregates of the dye cations characterized by a sandwich-type structure. As the layer charge decreased, the amount of the H-aggregates was reduced in favor of H-dimers and monomers. RCMs with low charge density suppressed dye cation aggregation and mainly monomeric forms were detected. The process of energy transfer from R3B to Ox4 was detected as decreasing the emission from the energy donor and increasing the emission from the energy acceptor. The energy transfer was clearly influenced by the properties of RCM templates. The dye cations adsorbed at the surface of the highest-charge specimen formed H-aggregates, which were efficient luminescence quenchers. Fluorescence resonance energy transfer (FRET) gradually increased with the charge reduction to be optimal at the templates with medium layer charge. Substantial decrease of the layer charge and reduction of clay mineral swelling led to the decrease of both the luminescence and the efficiency of FRET. The relations of energy transfer processes to the layer charges and swelling properties of montmorillonite are analyzed in detail.

Lattice vibrations of montmorillonite: an FT Raman and X-ray diffraction study

The lattice vibrations of a series of dioctahedral montmorillonitic clay minerals were studied using FT Raman spectroscopy. The lattice vibrations are assigned in terms of the molecular vibrations of (a) the distorted octahedron MO 6 with symmetry S 6 in the region 50–200 cm −1, (b) the OHO isosceles triangle of C 2v symmetry in the 200 to 270 cm −1 and (c) distorted SiO 4 tetrahedra of symmetry C 3v in the region 300 to 1200 cm −1. The application of FT Raman spectroscopy to the analysis of montmorillonitic clay structure is elucidated. A series of montmorillonites with different weathering profiles from the Cressfield deposit in Australia were analysed by both FT Raman and X-ray diffraction. The FT Raman spectra of the Cressfield bentonites are shown to be a function of clay crystallinity. X-ray diffraction identified the changes in the montmorillonitic lattice as weathering occurs. The variation in the 001 d spacing changed from 17.53 to 17.36 Å and the CDS value increased from 126 to 148 Å, indicating an increase in both the order and crystallinity of the montmorillonite on ageing. FT Raman spectroscopy identified changes in the lattice vibrational modes as this weathering is taking place.

Synthesis and characterization of montmorillonite-(Ce or Zr) phosphate crosslinked compounds

A series of montmorillonite-(Ce or Zr) phosphate crosslinked compounds has been synthesized by reaction of a cerium or zirconium cation exchanged montmorillonite (diameter ⩽ 2 μm) with phosphoric acid under appropriate conditions of concentration, addition rate and temperature. The materials thus obtained were characterized by chemical and thermal analyses, X-ray diffraction, IR spectroscopy and SEM-EDX. The results show that tetravalent metal phosphate acts as a cement among the clay particles, hindering material dispersion in aqueous media. At the same time, this framework limits the cerium or zirconium hydrolysis. The surface area of the metal(IV) phosphate crosslinked montmorillonite obtained increases, relative to that reported for the individual precursors. On the other hand, micrographs and microanalyses of the samples show that a fraction of the Ce(IV) or Zr(IV) ions remain as exchange cations in the clay particles.

A STUDY ON CONDUCTANCE AND STRUCTURE OF MONTMORILLONITE SOLID ELECTROLYTES

The ionic conductance of series of montmorillonite which have different submicroscopic structure have been studied after seperating from associated minerals. The absorption bands at 915cm-1 and 840cm-1 in the IR spectra and the resonance with g≈4.3 in the ESR spectra vary with the submicroscopic structure. The influence of the structure on the conductance of the montmorillonites have been discussed.

Indications of fluid immiscibility in glass from West Clearwater Lake impact crater, Quebec, Canada

Glass from the West Clearwater Lake hypervelocity impact crater contains numerous spheroids, 10 to 500 μm across, which appear to have formed at high temperatures as fluids immiscible in the enclosing melt. The spheroids are distinguished from small, normal, largely void gas vesicles, which are also present, by being completely filled in all cases; by having fillings which vary in composition from spheroid to spheroid, even between spheroids in close association; and by indications that the present fillings are representative of the contents present before the matrix melt chilled. Most of the spheroids are classified petrographically into three types. Type I, the most numerous, includes all spheroids>100 μm and are filled with uncommon pale brown to yellow montmorillonites with an unusual structure intermediate between dioctahedral montmorillonite and saponite. Type II, brown and green, are filled with Fe-rich montmorillonites, while Type III are aluminia-rich montmorillonites crystallized into mica-like sheaves. Rare, small spheroids are filled with calcite or silica. In a few cases one spheroid encloses another of similar or different type. Electron microprobe analyses indicate that with few exceptions Types I and III spheroids belong to a Mg series of montmorillonites in which the main chemical variation is the substitution of Mg for Al. A second Fe-K series includes Type II and a few Type I spheroids and shows substitution of Fe by Al, relatively high K2O and, in the alumina-rich members, low SiO2. The close association of spheroids with deformed, embayed lechatelierite inclusions indicates that they formed while the latter were liquid, i.e. at temperatures above 1700°C, as rapidly moving impact melt engulfed highly shocked inclusions of quartz-bearing country rock. The preservation of spheroids in the West Clearwater Lake glass is attributed mainly to the position of the glass masses within the breccias lining the crater floor. It is considered that the glass in this location did not achieve free flight but, as part of a large mass, cooled relatively slowly through the high temperature regime in which the spheroids were generated, and then, when detached, chilled rapidly to preserve a record of this transient stage in their history.