Montmorillonite Clay Surface Research Articles

New insights into physicochemical aspects involved in the formation of chitosan@alginate biobased polyelectrolyte complexes on natural montmorillonite clay surface

The use of alginate@chitosan-based polyelectrolyte complexes (PEC) in encapsulation process is common due to the electrostatic interactions between the two oppositely charged biopolymers. However, the incorporation of montmorillonite (Mt) particles in the complex formation for improving the encapsulation efficiency as well as the physicochemical properties of PEC remains a challenge due to the competitive polymer–polymer and polymer-nanoparticle interactions. This study aimed to investigate the binding mechanism of alginate and chitosan through layer-by-layer approach in the presence of montmorillonite nanoparticles as a function of pH and the addition order of the components. Various techniques were employed to examine the formation of the alginate@chitosan PEC on the surface of Mt, such as zeta potential, conductivity and turbidity measurements. The characterization of the different PEC systems was performed using Fourier Transformed Infrared spectroscopy (FTIR), X-Ray diffraction (XRD), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and thermogravimetry analysis (TGA). The results indicate that the formation of the complex is pH-dependent. The highest intercalation of the complex was observed when chitosan was added first at a lower pH, while the intercalation was reduced at neutral pH. Additionally, the thermal stability of PEC was enhanced in the presence of montmorillonite, and was dependent on both pH and the order of addition of the biopolymers. This study provides a new understanding of the complex formation mechanism between alginate and chitosan in the presence of montmorillonite nanoparticles, showing that the combination of biopolymer-based PEC with clay particles can potentially provide a low-cost, more stable and effective nanocomposite for encapsulation and delivery of active agents.

Improvement of Poly(Lactic Acid) Properties by Ethylene-Octene Copolymer and Organoclay

The work studied the morphological, mechanical and thermal properties of poly(lactic acid) (PLA)/ethylene-octene copolymer (EOC) blends before and after adding the montmorillonite clay surface modified with 25-30% of octadecylamine (clay-ODA). The PLA/EOC blends and composites were prepared by melt mixing in an internal mixer. The EOC contents were 5, 10, 20, 30 wt% and clay-ODA contents were 1 and 3 phr. The morphology analysis showed that the addition of clay-ODA could improve the miscibility of PLA and EOC phases due to the domain size of dispersed EOC phase decreased with increasing clay-ODA content. X-ray diffraction revealed the formation of intercalated/exfoliated structure in PLA/clay-ODA and PLA blend composites. The mechanical properties showed that the impact strength of PLA/EOC blends dramatically increased with increasing EOC content up to 10 wt%. The strain at break of PLA blends increased with increasing EOC content. Moreover, the incorporation of clay-ODA increased significantly Young’s modulus of PLA and PLA/EOC blends with increasing clay-ODA content. The thermal stability of PLA/EOC blends improved with the addition of a small amount of clay-ODA.

Molecular simulation to discover rheological properties and soil‐binding ability of PHPA polymer on montmorillonite surface

Synthetic polymer fluids are increasingly being applied to support excavations in deep foundations. As these fluids are molecularly engineered, their underlying microstructure interaction with in situ soils significantly affect excavation stability and soil dispersion. However, little molecular‐scale research has been done on the rheological behavior of partially hydrolyzed polyacrylamides (PHPA) polymer fluids on the clay surface. Molecular models of the clay–polymer systems are constructed using PHPA on montmorillonite (MMT) clay surface. Initial rheological properties and soil‐binding ability at different shear rates, temperatures, and polymer concentrations are first studied using molecular dynamics (MD) simulations. It is found that the functional groups of PHPA can interact with the MMT surface and form a viscous film under the atomic interaction of hydrogen bonds, water bridges, and electrostatic attraction. The shear stress, σ increases with the shear rate and follows the power‐law model. And the viscosity, η decreases as the shear rate increases, which is consistent with the experimental trend. However, the σ and η decrease with the increase of temperature. And the action mode of PHPA concentration has been identified from the MD perspective. This work provides insight into the molecular mechanism for PHPA's rheology on the clay surface and their interaction.

Cost-effective and green synthesized electroactive nanocomposite for high selective potentiometric determination of clomipramine hydrochloride

Cost-effective, scalable and efficient electroactive material for ion-selective electrode was developed. Facile nanocomposite composed from montmorillonite clay layers and polyaniline nanofibers (PANI-NFs) was facilely prepared at ambient condition. The polyaniline nanofibers were polymerized on the surface of montmorillonite clay. Then the prepared nanocomposite was used as efficient electroactive modifier for developing new sensitive and selective modified carbon paste electrodes (CPE) for potentiometric determination of Clomipramine hydrochloride (CLO-HCl) in pure and pharmaceutical formulations. Effects of experimental parameters such as paste composition, response time, selectivity, pH and temperature on the potential response of CLO-HCl electrode were investigated. The paste incorporating 5 (electrode I) and 10 (electrode II) mg of developed nanocomposite (MT-PANI-NF) showed the best experimental performance, exhibiting the best Nernstian slope values of 60.30 ± 0.28 and 60.00 ± 0.22 mV decade−1 over a considerable spacious concentration range from 1.0 × 10−5 to 1.0 × 10−2 mol L−1 over pH range from 3.5 to 7.5. Additionally, a fast dynamic response time of 9 and 7 s for electrode I and II, respectively, was achieved. The proposed sensors displayed good discriminating capability toward CLO-HCl with regard to a number of interfering materials. The interaction between MT-PANI-NF nanocomposite and CLO-HCl drug at the electrode surface was studied through scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX). The results were obtained using those electrodes were in a good agreement with those which were obtained using the official method. The method was validated according to IUPAC recommendation parameters.

Morphology and Properties of Poly(Lactic Acid)/Ethylene-Octene Copolymer Nanocomposites

The effects of the montmorillonite clay surface modified with 0.5-5 wt% aminopropyltriethoxysilane and 15-35% octadecylamine (Clay-APTSO) on morphology, mechanical and thermal properties of poly(lactic acid) (PLA)/ethylene-octene copolymer (EOC)/Clay-APTSO composites were investigated. The blends of PLA/EOC with and without Clay-APTSO were prepared by melt mixing in an internal mixer. Scanning electron microscopy analysis observed the morphology of PLA/EOC blends demonstrated a phase separation of minor phase and matrix phase. The addition of Clay-APTSO in PLA/EOC blends showed significant decreased in droplet size of dispersed EOC phase, thus, Clay-APTSO acted as an effective compatibilizer in the PLA/EOC blends. The results of tensile properties found the decrease of Young’s modulus of PLA when added EOC due to the low modulus and flexibility of EOC. While the incorporation of Clay-APTSO increased significantly Young’s modulus of PLA/EOC blends at low EOC and Clay-APTSO content. The strain at break of the blends increased with the increase of EOC loading, this indicated the presence of EOC enhanced the elongation at break of PLA, while the addition Clay-APTSO reduced the strain at break of PLA/EOC blends. The tensile strength of all blend compositions improved when added Clay-APTSO and the tensile strength showed the highest value at 3 phr of Clay-APTSO. The thermal stability of PLA/EOC blends did not change when compared with neat PLA, and when added Clay-APTSO in the blends could improve the thermal stability of the PLA/EOC blends.

Sorption kinetics of plutonium (V)/(VI) to three montmorillonite clays

Pu(V) adsorbed to the surface of montmorillonite clay can be reduced to Pu(IV). In this work, the role of clay structural Fe on this surface mediated reduction reaction was investigated by quantifying Pu(V)/(VI) sorption rates under atmospheric (oxic) conditions to three montmorillonite clays with variable Fe content (SWy-1: 2.6 wt % Fe; STx-1: 0.6 wt % Fe; Barasym synthetic mica-montmorillonite: 0.01 wt % Fe) at pH 4, pH 6, and pH 8. The experiments were performed over a period of one year, a timescale at which the sorption rates were expected to capture both adsorption and surface mediated reduction processes. At pH 6 and pH 8, the rate of sorption was positively correlated with structural Fe content. However, by 360 d, the extent of sorption was independent of Fe. Moreover, in the case of the synthetic montmorillonite it was not apparent that sorption equilibrium had been achieved by the end of the experiment. There was minimal difference in sorption rates between the clays at pH 4, suggesting that structural Fe content may be less important in Pu(V)/(VI) reduction at low pH. The results indicate that at circumneutral pH, structural Fe will affect the kinetics of Pu surface mediated reduction on montmorillonite clays but not necessarily the equilibrium Pu sorption affinity at environmentally relevant timescales. The differences in rates on the three clays emphasize the need to perform long-term sorption experiments (>1 year) to adequately capture the equilibrium processes controlling the uptake of Pu under atmospheric conditions. Comparison to other minerals indicates that the sorption rates can vary by as much as five orders of magnitude depending on the structure and composition of the surface.

L-serine-functionalized montmorillonite decorated with Au nanoparticles: A new highly efficient catalyst for the reduction of 4-nitrophenol

The conversion of nitroarenes to aminoarenes is of great industrial interest since they are prevalent pollutants in water and aminoarenes are important intermediates in the synthesis of pharmaceuticals, natural products and in bulk chemical production. In this work, two new catalysts for the reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) were prepared by immobilization of gold nanoparticles onto the surface of K10 montmorillonite clay (K10) functionalized with two new l-serine derivative organosilanes. Transmission electron microscopy showed the presence of 4–5 nm gold nanoparticles after catalysis. The reduction reaction of 4-NP to 4-AP at 25 °C, using NaBH4 as reducing agent, led to nearly 100% conversion in only 1 minute, presenting pseudo-first-order rate constants normalized for Au loading of K = 630 and 430 mmol−1 s−1. The catalysts showed high stability, leading to substrate conversions of 95–100% after 10 consecutive cycles, with negligible Au leaching.

Experimental and MD simulation study on the physical and mechanical properties of organically modified montmorillonite clay and compatibilized linear low density polyethylene nanocomposites

ABSTRACTUnderstanding the interfacial interactions plays a key role in controlling mechanical and physical properties of polymer/clay nanocomposites (PCNs). In this work, the surface interactions between constituents of experimentally prepared PCNs which are the pristine linear low density polyethylene (PE) chains, PE compatibilizers, montmorillonite clay surface layer, and surfactants were studied quantitatively by employing molecular dynamics simulation technique. The interaction energy between the polymer and the clay was found to be inversely proportional with the volume of the surfactant which decreases the electrostatic interactions between the compatibilizer and the hydrophilic clay surface. However, the van der Waals (vdW) interactions between alkyl tails of surfactants and the PE chains increase with the tail length of the surfactants. The most attractive interaction was between the surfactant's head group and the clay surface. We showed that there existed fine balance between the electrostatic and vdW type forces on the stability and the enhanced properties of the PE–organoclay nanocomposites. Calculated interaction energies were then correlated to the experimentally measured mechanical properties. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45817.

Pesticide interaction with environmentally important cations: A molecular dynamics and DFT study of metamitron and fenhexamid

Metamitron (Meta), 4-amino-3-methyl-6-phenyl-1,2,4-triazin-5-one, and fenhexamid (Fen), N-(2,3-dichloro-4-hydroxyphenyl)-1-methylcyclohexanecarboxamide, are active substances of herbicide and fungicide products, respectively, employed in agriculture. When these molecules are spread on crops, an important amount reaches the soil and diffuse through water to deep layers of the soil structure and thus to groundwater tables. To get some insight into the interaction of pesticides with soil, in particular clay surfaces, we have run theoretical calculations. This paper presents preliminary results of this wide and challenging work. Metamitron, fenhexamid and their complexes with one or two Ca2+ and Na+, which are among the most abundant cations into soils, are under investigation. Conformational searches have been performed thanks to Car-Parrinello molecular dynamics (CPMD) simulations from which geometries as well as relative, complexation and interaction energies have been extracted. Thermodynamical complexation values have been calculated for complexes of Meta or Fen with one or two cation(s) in order to understand the complex stability. We found that complexation free energies are comparable for Meta and Fen: around −32kcal/mol with one sodium cation, ≈−130kcal/mol with one Ca2+, and −7kcal/mol with two Na+. With two Ca2+, complexation free energy is four times larger in absolute value for Fen (−40kcal/mol) than for Meta due to longer inter-cation distances in Fen-(Ca2+)2 complexes. The larger values obtained with Ca2+ in the gas phase suggest a strong adsorption of Meta and Fen with Ca2+-montmorillonite clay surfaces.

Comparison of Organoclay and PE-g-MA on Properties of Poly(Lactic Acid) and Acrylonitrile-Butadiene Rubber Blends

The effects of the montmorillonite clay surface modified with 0.5-5 wt% aminopropyltriethoxysilane and 15-35 wt% octadecylamine (Clay-ASO) and polyethylene-g-maleic anhydride (PE-g-MA) on morphology and mechanical properties of poly (lactic acid) (PLA)/acrylonitrile-butadiene rubber copolymer (NBR) blends were investigated and compared. The PLA/NBR blends and composites were prepared by melt mixing in an internal mixer and molded by compression molding. The ratio of PLA and NBR was 80/20 by weight and the Clay-ASO and PE-g-MA contents were 3, 5 and 7 phr. The morphology analysis showed that the addition of Clay-ASO and PE-g-MA at high content could improve the miscibility of PLA and NBR to be homogeneous blends due to the voids in the polymer matrix were decreased. The tensile properties showed Young’s modulus of the PLA/NBR/Clay-ASO composites was more than that of the PLA/NBR blends and Young’s modulus of composites increased with increasing Clay-ASO content, while the tensile strength and strain at break decreased with increasing Clay-ASO content. The incorporation of PE-g-MA 3 phr could improve the tensile strength, stress at break and strain at break of PLA/NBR blends.

Theoretical study of the atrazine pesticide interaction with pyrophyllite and Ca(2+) -montmorillonite clay surfaces.

Atrazine, a pesticide belonging to the s-triazine family, is one of the most employed pesticides. Due to its negative impact on the environment, it has been forbidden within the European Union since 2004 but remains abundant in soils. For these reasons, its behavior in soils and water at the atomic scale is of great interest. In this article, we have investigated, using DFT, the adsorption of atrazine onto two different clay surfaces: a pyrophyllite clay and an Mg-substituted clay named montmorillonite, with Ca2+ compensating cations on its surface. The calculations show that the atrazine molecule is physisorbed on the pyrophyllite surface, evidencing the necessity to use dispersion-corrected computational methods. The adsorption energies of atrazine on montmorillonite are two to three times larger than on pyrophyllite, depending on the adsorption pattern. The computed adsorption energy is of about -30 kcal mol-1 for the two most stable montmorillonite-atrazine studied isomers. For these complexes, the large adsorption energy is related to the strong interaction between the chlorine atom of the atrazine molecule and one of the Ca2+ compensating cations of the clay surface. The structural modifications induced by the adsorption are localized: for the surface, close to substitutions and particularly below the Ca2+ cations; in the molecule, around the chlorine atom when Ca2+ interacts strongly with this basic site in a monodentate mode. This study shows the important role of the alkaline earth cations on the adsorption of atrazine on clays, suggesting that the atrazine pesticide retention will be significant in Ca2+ -montmorillonite clays. © 2016 Wiley Periodicals, Inc.

Morphology and Mechanical Properties of Poly (Lactic Acid) and Acrylonitrile-Butadiene Rubber Blends with Organoclay

The effects of the montmorillonite clay surface modified with 25-30 wt% of methyl dihydroxyethyl hydrogenated tallow ammonium (Clay-MHA) on morphology and mechanical properties of poly(lactic acid) (PLA)/acrylonitrile-butadiene rubber copolymer (NBR)/Clay-MHA composites were investigated. The composites of blends of PLA/NBR with Clay-MHA were prepared by melt mixing in an internal mixer and molded by compression molding. The ratio of PLA and NBR was 80/20 by weight and the Clay-MHA content was 1, 3, 5 and 7 phr. The results showed Young’s modulus and stress at break of the composites increased with increasing Clay-MHA content. While the tensile strength and strain at break of the composites decreased with increasing Clay-MHA content. Scanning electron microscopy analysis showed that the addition of Clay-MHA could improve the miscibility of PLA and NBR to be homogeneous blends and the pore in polymer blends was disappeared.

Engineering properties of asphalt binders containing nanoclay and chemical warm-mix asphalt additives

In the effort to promote the construction of green pavement the asphalt concrete industry has been making consistent effort to use warm-mix asphalt (WMA) in their construction. The objective of this study was to improve the properties of the asphalt binders through the addition of nanoclays and chemical WMA additive. An asphalt binder of 80/100 penetration grade was modified with different percentages of Nanoclay A (montmorillonite clay surface modified with 35–45wt.% dimethyl dialkyl (C14–C18) amine), Nanoclay B (montmorillonite clay surface modified with 35–45wt.% octadecylamine, and 0.5–5.0wt.% aminopropyl-triethoxysilane), and chemical WMA additive (fatty polyamines polymer non-ionic component). After modification, the asphalt binders were named Nanoclay A modified asphalt binder (NCMB A), Nanoclay B modified asphalt binder (NCMB B), and chemical WMA modified asphalt binder (CWAA). The rheological characteristics of the unmodified and modified asphalt binders were evaluated using the rotational viscosity, dynamic shear rheometer, and bending beam rheometer tests. Results of the tests showed that NCMB B and CWAA significantly reduced mixing and compaction temperatures. However, only NCMB B showed a significant increase in rutting and fatigue resistance when compared with base asphalt binder. A change in chemical bond was also observed in the tested binders after long-term aging, which suggests that the addition of modifier could delay the aging process.

Mechanical and Morphological Properties of Poly(Methyl Methacrylate)/Ethylene-Octene Copolymer/Clay Composites

The effects of the montmorillonite clay surface modified with 25-30 wt% octadecylamine (clay) on mechanical and morphological properties of poly (methyl methacrylate) (PMMA)/ ethylene-octene copolymer (EOC)/clay composites were investigated. The composites of blends of PMMA/EOC with clay were prepared by melt mixing in an internal mixer. The results showed that the Young’s modulus of the composites increased with increasing clay content. The ratio of PMMA and EOC was 80/20 by weight and the clay content was 3 and 5 phr. The results showed Young’s modulus of the composites increased with increasing clay content. While the impact strength, tensile strength and percent strain at break of the composites decreased with increasing clay content. Scanning electron microscopy analysis showed that the droplet of dispersed EOC phase in PMMA matrix was changed to the elongated structure after adding clay.

A facile method to synthesize the photocatalytic TiO2/montmorillonite nanocomposites with enhanced photoactivity

A new method for immobilizing nano-scaled TiO2 on the surface of montmorillonite (Mt) clay has been developed. First, cationic surfactants were introduced into the Mt galleries through ion exchange and physical adsorption processes. Next a titanium precursor with negative charges was allowed to hydrolyze and condense around the nature clay to form meso-phase assemblies on the external and internal surface of the Mt. After the removal of the surfactant, a highly porous TiO2 pillared clay with mesopores was formed. The cationic surfactant has a templating role, which not only tailored the formation of TiO2 but also controlled the TiO2 content in the composite. The photocatalytic performances of these new porous materials were evaluated by using methylene blue degradation. The photocatalytic activity of these TiO2 composite is higher than that of P25 although TiO2 only accounts for about one-third of the sample's mass in the composite samples.

In Memoriam: Max Merle Mortland (1923–2013)

Max M. Mortland, retired Distinguished Professor of Soil Science and Geology at Michigan State University, passed away peacefully on July 29, 2013, at the age of 90. Max was recognized internationally for his pioneering studies of clay-mineral-intercalation chemistry. Using infrared spectroscopy and X-ray powder diffraction as his primary instrumental methods of analysis, he elucidated the acid–base chemistry of inorganic and organic exchange cations on the interlayer surfaces of smectite clays, particularly Wyoming montmorillonite, his ‘favorite’ clay. He was the first to report electron-transfer reactions between transition-metal cations ( e.g . Cu2+) and physically adsorbed aromatic molecules ( e.g . benzene) on montmorillonite clay surfaces. These fundamental studies provided the basis for understanding the role of clay minerals in soil fertility and the development of new materials for environmental protection and clean-up based on smectitic clays. In recognition of …

Stearyl Amine Ethoxylate (SAM) Grafted Montmorillonite Clay-Styrene Butadiene Rubber (SBR) Nanocomposites

The present study describes the modification of montmorillonite clay (kunipia F) surface by grafting Stearyl Amine Ethoxylate (SAM). Wide-angle X-ray diffraction (WAXD) and transmission electron microscopy (TEM) provided the evidence of formation of a nanocomposite. The interlayer spacing of the kunipia clay was increased from 1.22 nm (unmodified) to 1.53 nm (modified). The TEM study revealed the intercalated and partially exfoliated nature of the nanocomposites. When the modified clay was compounded with SBR rubber, the interlayer spacing was further increased to 1.88 nm. Remarkable improvements in the mechanical properties were found by the addition of a small amount of modified clay.

Adsorption and stacking behaviour of zwitterionic porphyrin on the clay surface

AbstractZwitterionic porphyrin (tetrakis {4-(2-carboxyethyl)pyridinio}porphyrin (TPyCP)) with four pyridinium and carboxyl groups in the molecule was synthesized. The adsorption behaviour of TPyCP on the montmorillonite clay surface was examined in an aqueous colloidal solution. While the adsorption maximum λmax of TPyCP was 424 nm in water, it shifted to longer wavelengths on complex formation with clay. The λmax on the exfoliated clay surface was 450 nm, and that in the stacked clay sheets was 471 nm, respectively. Under alkaline conditions ([NaOH] = 2 × 10–4 M), the stacking behaviour of the clay was completely suppressed. It emerged that anionic parts in the porphyrin molecule can suppress the stacking of clay sheets. Judging from the quantitative analysis, the maximum adsorption amount of TPyCP was 100% vs. cation exchange capacity (CEC) of the clay. As the adsorption density of TPyCP increased, λmax shifted slightly to longer wavelengths due to the interactions between adjacent porphyrins. When the loading level of TPyCP was 200% vs. CEC, the stacking of TPyCP was indicated. The average stacking layer number was calculated to be 1.48. On the other hand, it is known that tetra cationic porphyrins without anionic parts do not form such stacking structures. Thus, it seems that zwitterionic porphyrin has the potential to form a three dimensional structure through electrostatic interactions between porphyrins on the clay surface.

Mechanical and Gas Barrier Properties of Nylon 6/Clay Nanocomposite Blown Films

Nylon 6/clay nanocomposite films were prepared by melt mixing nylon 6 with organoclay using a twin screw extruder attached to a blown film die. The type of surfactant used in the pretreatment of organoclay was expected to affect the degree of clay dispersion, which would in turn affect the degree of crystallinity, crystalline phase and bulk properties of the polymer composite. Two different surfactants used to treat the surface of montmorillonite clay were trimethyl tallow quaternary ammonium chloride (M 3 T, a single-chain surfactant) and dimethyl bis (hydrogenated-tallow) ammonium chloride (M 2 (HT) 2 , a double-chain surfactant). The addition of the resulting organoclay into nylon 6 was found to enhance the formation of γ-phase and increase the degree of crystallinity and crystallization temperature of the nylon 6. In fact nanocomposite films containing the single-chain surfactant showed a higher degree of clay dispersion in nylon 6 matrix, up to 148% higher stiffness and up to 100% lower oxygen permeability than those films containing the corresponding double-chain surfactant at the same inorganic loadings investigated. As expected, the nanocomposite films exhibited 58% higher stiffness in the machine direction than the transverse direction.

Effect of Clay on the Properties of Polyoxymethylene/Clay Nanocomposites

This work investigated the effect of montmorillonite clay surface modified with 25-30 wt% trimethyl stearyl ammonium (clay) on mechanical, thermal and morphological properties of polyoxymethylene (POM)/clay nanocomposites were investigated. The results showed that POM/clay nanocomposites could maintain or decrease their tensile strength for a certain clay loading range. The Young’s modulus of the nanocomposites increased by adding clay in a range of 0.5-4 wt% while the impact strength showed an increase in a range of 0.5-2 wt%. The percent strain at break of the nanocomposites decreased with increasing filler content. The thermal degradation temperature decreased with an increase of clay content thus the addition of clay did not improve the thermal stability of POM. The microstructure of neat POM and POM/clay nanocomposites was observed that the dispersion of clay was a good in POM matrix at low clay content. The nanocomposites formed the intercalated structure with clay, and the intercalated clay stacks were distributed uniformly in the nanocomposite. The increase of clay content observed increasing of brittleness in POM/clay nanocomposites.