Smectite Family Research Articles

Hydromechanical behavior of unsaturated swelling clays: review

Expansive soils are materials composed mainly of active minerals of the smectite family, where montmorillonite is an essential member of that group. These types of soils tend to undergo volumetric changes due to variations in moisture content. Many geotechnical engineering practices, such as dam core design or subgrade compaction, require a thorough evaluation of the response of these soils to determine placement conditions. However, the main problem in evaluating the mechanical response of this type of soil lies in the nonlinear nature, which limits the use of most classical constitutive models that apply the basic rules of elastoplasticity. In this study, an analysis is carried out to understand the hydromechanical behavior of expansive soils in saturated and unsaturated conditions. Direct and indirect physical evidence is presented and discussed to evaluate the hydraulic response of the soil structural elements responsible for these adverse dynamics from a global (expansive phenomena as a whole) and individual (swelling and shrinkage) perspective. Since the response of these soils is hydrostatic dependent, the locus of water movement in porous media is examined, starting from the Richards equation (1931), in order to consider the flow mechanisms in unsaturated media under transient conditions.

Synthesis of polymer hybrid latex polystyrene methylmethacrylate-co-butylacrylate with organo-montmorillonite as filler through miniemulsion polymerization for barrier paper application

Nanocomposite have a huge potential in the future technologies and scientific communities. It is possible to design new materials with a simple modification and new materials have different properties and improvement in its mechanical properties and application fields. Hybrid latex based on monomer styrene (St), butyl acrylate (BA) and methylmethacrylate (MMA) have been studied and used for barrier paper applications in food industries in order to replace polypropylene (PP), polyethylene (PE) or polyethylene terephthalate (PET) materials. To achieve better hybrid materials, various techniques and materials have been utilized, montmorillonite (MMT) from smectite family have been selected as filler in order to synthesize polymer clay nanocomposites (PCNs). The selection of MMT as filler due to its high aspect ratio, high modulus and high cation exchange capacity (CEC). MMT was not susceptible to common polymer due to its organophobicity, low basal spacing, and incompatible to common monomers phase. Surface modification of MMT with traditional ion exchange method can be done through ion exchange with quaternary alkyl ammonium surfactants. The objective of surface modification of MMT are to change its nature hydrophilicity to organophilicity, in the same time to increase its basal spacing. Various quaternary alkylammonium cationic surfactants have been used; in this study, three type of alkylammonium were selected to be used due to its different in alkyl carbon chain lengths. Intercalation of surfactants cation in MMT depend on the layer-charge alkyl carbon chains, selection of myristyltrimethylammonium bromide (MTAB) with C17 carbon chains, cetyltrimethylammonium bromide (CTAB) with C19 carbon chains and octadecyltrimethylammonium bromide (OTAB) with C21 carbon chains could give an answer of the selection of organoclay that compatible with St, BA and MMA. This study focuses on the microstructure of organo montmorillonite (OMMT) after surface modification and the potential to be used as filler in synthesis of hybrid latex through miniemulsion polymerization technique. The intercalation or exfoliation of MMT through ion exchange with alkylammonium surfactant were studied, interlayer spacing of OMMT were analysed with X-ray diffraction, small angle X-ray scanning (SAXS) technique, presence of cationic surfactant in the interlayer space and bond character and arrangement of surfactant ions were analysed by Fourier Transform Infrared (FTIR), Thermogravimetric analysis (TGA) and Transmission Electron Microscope (TEM). Synthesis of hybrid latex was done by miniemulsion polymerization technique with selected OMMT filler. Series of experiments were performed to study the polymerization variables such as filler loading, role of surfactant/cosurfactant and filler solubility in monomer emulsions. The results shown that water soluble surfactant SDS in miniemulsion polymerization resulted lower coagulum and smaller particle size compare to non-ionic surfactant (TX405) and cationic surfactant (OTAB). Combination of non-ionic surfactant (TX405) with ionic surfactant (SDS) with ration 1:2 showed the better results than SDS alone, with lowest coagulum, narrow particle size distribution, and lowest Broekfield Viscosity. Scale up loading level of OMMT filler in miniemulsion to 5.0 wt%, resulting instability before and after polymerization with regard to high coagulum content and low monomer conversion rate (<90%). The hybrid latex resulted from miniemulsion polymerization will be applied on paperboard with hand rod coater with coating weight 15-20 gsm. The coated paperboard tested on its water vapour transmission rate (WVTR) together with paperboard coated with PE from melt blending process. Paperboard coated with hybrid latex comparable to paperboard coated with PE, indicated improvement in its WVTR value compare to paperboard coated with latex without filler addition. The main target of this research was to synthesis polymer hybrid latex for super barrier material for food packaging in order to replace unrecyclable PP, PE or PET. The utilization of polymer hybrid latex could benefit paper and paperboard packaging industries.

Preparation of Waterborne Polyurethane‐OMt Nanocomposites and Effect of Clay on UV Degradation

SummaryWaterborne polyurethane polymers (WPU) have gained importance for some decades because of their environmentally friendly characteristics due to low or zero content of solvents. Polyurethane properties can be modified by changing segmental structure or incorporating inorganic fillers into the polymer matrix. Montmorillonite (Mt) clay which is a member of smectite family is widely used in polymer clay composites as a filler. In this work, linear WPU nanocomposites were synthesized using different polyols as soft segment via acetone process which has many advantages over the prepolymer mixing process in terms of reliable reproducibility and convenience for obtaining linear polyurethanes. Sodium modified montmorillonite (NaMt) clay was used without any chemical pretreatment. WPU nanocomposites were prepared via in‐situ polymerization method by modification of sodium modified montmorillonite (NaMt) clay in polyol and following polyurethane reaction. Finally, spectroscopic, thermal, morphological characterizations and UV weathering tests carried out. As a result, different thermal and mechanical properties were observed due to different soft and hard segment content. Furthermore, increasing clay content caused lowering of resistance against UV degradation.

Layered Clay Aerogels by a Freeze-Drying Process for a Platinum-Supported Catalyst

We prepared a clay aerogel by freeze drying an aqueous viscous suspension of a synthetic saponite (a layered clay mineral of the smectite family). The nanostructure and texture of the resulting aerogel varied with the freezing conditions. The freeze drying resulted in microporous aerogels with well-ordered (stacked) silicate layers. A fine texture was observed after freeze drying of a starting suspension at a lower concentration. Freezing in liquid propane yielded a well-defined continuous network texture. Toluene in vapor phase was oxidatively decomposed in air flow over aerogels on which platinum was deposited by an impregnation wetness method; the decomposition was probably affected by the size distribution of micropores.

Organosilane grafted acid-activated beidellite clay for the removal of non-ionic alachlor and anionic imazaquin

Clay adsorbents were prepared via two-step method to remove nonionic alachlor and anionic imazaquin herbicides from water. Firstly, layered beidellite clay, a member of smectite family, was treated with acid in hydrothermal process; secondly, common silane coupling agents, 3-chloro-propyl trimethoxysilane or triethoxy silane, were grafted on the acid treated samples to prepare adsorbent materials. The organically modified clay samples were characterized by powder X-ray diffraction, N2 gas adsorption, and FTIR spectroscopy. It was found that the selective modification of clay samples displayed higher adsorption capacity for herbicides compared with acid activated clay. And the amount of adsorption is increased with increasing the grafting amount of silane groups. Clay grafted with 3-chloro-propyl trimethoxysilane is an excellent adsorbent for both alachlor and imazaquin but triethoxy (octyl) silane grafted clay is more efficient only for alachlor removal.

2,3,7,8-Tetrachloro dibenzo- p-dioxin can be successfully decomposed over 2:1 dioctahedral smectite—a reactivity index study

2:1 Dioctahedral smectite family has shown its capability to decompose 2,3,7,8-tetrachloro dibenzo- p-dioxin (TeCDD) using the active hydroxyl hydrogen attached with the central octahedral aluminum, as monitored using density functional theory (DFT). From the values of the local softness and the charge on the hydrogen atom of the bridging/structural (occurring on the surface) hydroxyl attached to octahedral/tetrahedral metal site present in smectite used as a first approximation to the local hardness, it is concluded that the local acidities of the inorganic material systems are dependent on several characteristics which are of importance within the framework of hard–soft acid–base (HSAB) principle. The first step in this process of decomposition is the abstraction of chlorine bound to TeCDD using surface hydrogen of smectites. This results in non-chlorinated dibenzo- p-dioxin (NCDD), which is less toxic than TeCDD. The second step is the formation of a dative bond between oxygen of NCDD and hydroxyl proton of smectite, with the breaking of CO bond of NCDD. The reaction mechanism is postulated within the helm of DFT using Fukui functions for all possible chlorinated and non-chlorinated dioxin varieties along with clay clusters. The material is identified to act for the decomposition of dioxin.

Aqueous alteration in the Northwest Africa 817 (NWA 817) Martian meteorite

Samples of a new Martian meteorite of the nakhlite family (NWA 817) contain traces of an iron-rich alteration product. Textural arguments indicate that this alteration product has been formed on the parent body of the meteorite (Mars). The chemical composition and structural data (X-ray diffraction, transmission electron microscopy and vibrational spectroscopy) show that the alteration mineral is a hydrous phase from the smectite family. Major elements and rare earth elements suggest that the formation of the alteration phase is related to the circulation of an aqueous fluid which composition is controlled by the dissolution of feldspars to account for a positive Eu anomaly, olivine and possibly apatite. Hydrogen isotope data display negative δD values ranging from −60 to −280‰ in olivine and pyroxenes and from −140 to −181‰ in the alteration phase. The values of δD for the alteration product show a small scatter with a mean value of −170±14‰. These values are lower than those previously obtained on other Martian meteorites, which give mainly positive δD values. These positive values have been interpreted as resulting from the interaction of the Martian meteorites with water from the Martian atmosphere. Ruling out the effect of terrestrial alteration, it is suggested that alteration in the NWA 817 meteorite was likely produced on Mars by the circulation of an aqueous fluid originating from a chemical reservoir, such as the Martian mantle, which has not equilibrated with a fractionated Martian atmosphere.

2:1 Dioctahedral Smectites as a Selective Sorbent for Dioxins and Furans: Reactivity Index Study

A suitable sorbent from the dioctahedral smectite family for the sorption of 2,3,7,8-terachlorinated/brominated dibenzo-p-dioxins (TCDD,TBDD), tetrachlorinated/brominated dibenzo furans (TCDF, TBDF) is investigated by means of a range of reactivity index using density functional theory (DFT). From the values of the local softness and the charge on the hydrogen atom of the bridging/structural (occurring on the surface) hydroxyl attached to the octahedral/tetrahedral metal site present in smectite, used as first approximation to the local hardness, it is concluded that the local acidities of the inorganic material systems are dependent on several characteristics that are of importance within the framework of the hard and soft acids and bases (HSAB) principle. We first aimed to rationalize an understanding to locate the active site of dioxins and furans by the local softness calculation. We compared its activity with that of the OH group of both octahedrally and terahedrally substituted members of the dioctahedral smectite family. We compared the probability of surface hydrogen bonding with that which resulted from the interaction of bridging hydroxyl present at the octahedral site in clays. By the interaction between systems, we validate the proposition for designing a novel qualitative way to choose the best sorption material both in terms of isomorphous substitution of clays and the nature of the interacting molecule.

Best Dioctahedral Smectite for Nitrogen Heterocyclics AdsorptionA Reactivity Index Study

The activity of nitrogen heterocyclics present in biomacromolecules and its suitable sorbent from the dioctahedral smectite family is investigated using a range of reactivity index using density functional theory (DFT). For the first time, a novel function λ has been defined for quantitative description of weak adsorption cases, which was so far qualitative inside the domain of DFT. From the values of the local softness, it is concluded that the local acidities of the inorganic material systems are dependent on several characteristics, which are of importance within the framework of the hard and soft acids and bases (HSAB) principle. We first rationalized an understanding of the electronic structures of a range of nitrogen heterocyclics ranging from indole, imidazole, pyrrole, and pyridine, followed by the local softness calculation to locate its active site. We compared its activity with that of the OH group of isomorphously substituted (Fe3+, Mg2+, Fe2+, and Li+) dioctahedral smectite family. Two types ...

A Novel Method to Correlate Layer Charge and the Catalytic Activity of 2:1 Dioctahedral Smectite Clays in Terms of Binding the Interlayer Cation Surrounded by Monohydrate

Ab initio total energy pseudopotential calculations were performed on 2:1 dioctahedral smectite to rationalize an understanding of the structure and energetics for the same and to correlate catalytic activity of clay materials with layer charge. We have chosen two clay members from the 2:1 dioctahedral smectite family(1) beidellite and (2) montmorilloniteto monitor the effect of negative charge on the location of interlayer cation. Local softness calculation using Fukui functions generated for clusters derived from the structures of the clay matrixes in the domain of the hard-soft acid-base (HSAB) principle were performed first to locate the active site in clay. Ab initio calculations were followed to determine the most feasible orientation of the single interlayer water molecule in hydrated montmorillonite and beidellite. The role of hydroxyl hydrogen attached with the bridging oxygen connected to octahedral aluminum was also monitored. It is observed that interlayer cation (Na+) has a lesser influence o...

A Novel Way To Design Suitable Inorganic Material from the Smectite Family for Sorption of 2,3,7,8-Tetrachlorinated Dibenzo-p-dioxin

The activities of 2,3,7,8-tetrachlorinated dibenzo- p-dioxin (2,3,7,8-TCDD), a highly toxic pollutant, and its suitable sorbent from the dioctahedral smectite family are investigated using a range of reactivity indexes using density functional theory (DFT). From the values of the local softness and the charge on the hydrogen atom of the bridging hydroxyl attached to the octahedral metal site present in smectite, used as a first approximation to the local hardness, it is concluded that the local acidities of the inorganic material systems are dependent on several characteristics which are of importance within the framework of the hard and soft acids and bases principle. We first rationalized an understanding of the electronic structure of 2,3,7,8-TCDD, followed by the local softness calculation, to locate its active site. We compared its activity with that of the OH group of the isomorphously substituted (Fe 3+ ,M g 2+ ,F e 2+ , and Li + ) dioctahedral smectite family. The recently proposed local hard-soft acid-base principle characterizes the reactive centers of two systems on the basis of equal local softness. We validate the proposition by considering the interaction between systems with different global softnesses, which further paves the way for proposing a novel qualitative way to choose the best sorption material. The results were compared with the interaction energy calculations using DFT. The ordering for best sorption follows the order Mg 2+ > Fe 2+ > Fe 3+ > Li + .

B9 A DFT study to design suitable material from smectite family for sorption of 2,3,7,8-tetrachlorinated Dibenzo-p-dioxin

B9 A DFT study to design suitable material from smectite family for sorption of 2,3,7,8-tetrachlorinated Dibenzo-p-dioxin

In situ Measurements of Tetraphenylboron Degradation Kinetics on Clay Mineral Surfaces by IR

An attenuated total reflectance Fourier transform infrared (ATR-IR) spectroscopic method has been developed to quantitatively measure, in situ, the surface-facilitated degradation of tetraphenylboron (TPB) in fully aquated clay pastes. Two pathways for degradation of TPB could be studied both independently and simultaneously. Surface-facilitated oxidation of TPB to diphenylboric acid (DPBA) at Lewis acid sites on clay mineral surfaces was investigated on three members of the smectite family of clays. No degradation of TPB occurred on hectorite, which contains no structural Fe. TPB degraded to DPBA on montmorillonite and nontronite. A color change in nontronite indicated the production of mixed valence Fe[sup 3+]-O-Fe[sup 2+] states and clearly demonstrates the reduction of structural iron during the course of the reaction. The degradation of TPB to triphenylboron (TriPB) at Bronsted acid sites could also be measured on aluminum-saturated clays either independently on hectorite or simultaneously to the Lewis acid reaction on montmorillonite by the ATR-IR method. First-order rate models are developed for both reactions and describe the data well. 28 refs., 4 figs., 1 tab.

Oxide and Metal Intercalated Clay Nanocomposites

ABSTRACTTruly nanocomposite materials that are stable to about 400 to 700°C can be prepared by intercalating oxides or metal clusters of about 0.4 to 2.0 nm in between ∼1.0 nm layers of smectite clays. Both the chemistry and size of intercalates (pillars) can be varied to introduce unique catalytic, molecular sieving, dehumidifying and adsorption properties in these materials. The intercalated clays also provide opportunities to prepare compositionally and stoichiometrically diverse nanocomposite precursors to high temperature structural and electronic ceramics. Although montmorillonite is the most widely used host, further designing in properties can be achieved by using other members of smectite family having subtle crystal chemical and compositional variations, such as beidellite, nontronite, saponite or hectorite. The sol-gel chemistry involving the preparation of positively charged mono- or multiphasic solution-sol or colloidal-sol particles is a viable approach to introduce chemically diverse oxide particles in the interlayers of smectite. Reduction of transition metal ions or complexes in the interlayers of smectite to zerovalent metal clusters/particles using polar liquids is another novel approach to develop catalytically active, high surface area materials.