Clay Minerals Montmorillonite Research Articles

Molecular insights into the temperature and pressure dependence of mechanical behavior and dynamics of Na-montmorillonite clay.

Sodium montmorillonite (Na-MMT) clay mineral is a common type of swelling clay that has potential applications for nuclear waste storage at high temperatures and pressures. However, there is a limited understanding of the mechanical properties, local molecular stiffness, and dynamic heterogeneity of this material at elevated temperatures and pressures. To address this, we employ all-atomistic (AA) molecular dynamics (MD) simulation to investigate the tensile behavior of Na-MMT clay over a wide temperature range (500 K to 1700 K) and pressures (200 atm to 100 000 atm). The results show that increasing the temperature significantly reduces the tensile modulus, strength, and failure strain, while pressure has a minor effect compared to temperature, as seen in the normalized pressure-temperature plot. Mean-square displacement (MSD) analysis reveals increased molecular stiffness with increasing pressure and decreasing temperature, indicating suppressed atomic mobility. Our simulations indicate temperature-dependent dynamical heterogeneity in the Na-MMT model, supported by experimental studies and quantified local molecular stiffness distribution. These findings enhance our understanding of the tensile response and dynamical heterogeneity of Na-MMT clay under extreme conditions, aiding the development of clay minerals for engineering applications such as nuclear waste storage and shale gas extraction.

Contribution of organic carbon to the total specific surface area of soils with varying clay mineralogy

Soil specific surface area (SA) reflects the quantity and quality of the soil mineral and organic fractions. For soil samples that have similar clay mineral types, clay content and or organic carbon (OC) contents are good predictors of SA. However, the magnitude of the OC contribution to SA for different soil types is unclear, particularly since SA varies depending on which method or probe molecule is used to measure it. Consequently, we set out to (i) quantify the contribution of soil OC to total SA for soils with varying clay mineralogy, and (ii) assess the effect of probe molecule (EGME or H2O) and water sorption direction on the contribution of OC to the total SA. We utilized 330 soil samples (clay = 1 to 89 %; silt = 2 to 78 %; OC = 0.03 to 34.9 %) that were grouped according to clay mineralogy and OC content. The total SA was measured using EGME adsorption (SAE) and water adsorption and desorption (SAH2O). The contribution of OC to SA was examined using regression and partial correlation analyses that combined clay, silt, and OC as explanatory variables. Results showed that SAE values were strongly correlated to SAH2O, except for OC-rich soils where SAE was significantly lower than SAH2O. Apart from montmorillonite-rich samples, OC contribution to SAE was smaller than for SAH2O. Organic carbon had a positive contribution to desorption SAH2O for all sample groups, except for montmorillonite-rich samples; OC contribution was 7.5, 10.7, and 13.9 m2/g per %C for illite-rich, kaolinite-rich and OC-rich samples, respectively. There was no significant effect of water sorption direction on the OC contribution to SAH2O. Partial correlation analyses that accounted for clay and silt contents confirmed a negative contribution of OC to SAE or SAH2O for soil samples dominated by montmorillonite clay minerals. We can conclude that for the soil types investigated here (except montmorillonitic soils), OC has a positive contribution to total SA, and the magnitude of the contribution depends on the clay type.

The Effect of Ca-Bentonite Aplication on Cadmium Uptake and Shoot Dry Matter of Bread Wheat

Cadmium(Cd) is a non-essential heavy metal that is highly toxic even at very low concentrations. Although Cd is a non-essential trace metal, when reached to high levels in agricultural soils, it can be easily absorbed by plants. Cadmium accumulation in wheat (Triticum aestivum L.) and its subsequent transfer to food chain is an important problem worldwide. Bentonite is a material essentially composed by montmorillonite and related clay minerals of the smectite group. The purpose of this study was to investigate the effects of bentonite (0, 3, 6 and 12%) application on Cd uptake of bread wheat growing in high Cd (0, 5 and 10 mg/kg soil) application. Plants were grown under greenhouse conditions acid soil. The experiment was conducted randomized block design with three replicates. The results revealed that shoot dry weight of bread was significantly increased with increasing doses of bentonite applications. While the dry weight of shoot without bentonite application was 480 mg/plant, it increased approximately 2 fold with 12% bentonite application. Cadmium concentration with the bentonite of control application decreased 4 times from 20.74 ppm to 5.07 ppm with application of 12% bentonite. The results show that Cd toxicity in the shoot was alleviated by bentonite treatment.

Nanoscale Interactions of Humic Acid and Minerals Reveal Mechanisms of Carbon Protection in Soil.

The concentrations of terrestrially sourced dissolved organic matter (DOM) have expanded throughout aquatic ecosystems in recent decades. Although sorption to minerals in soils is one major pathway to sequestrate soil organic matter, the mechanisms of organic matter-mineral interactions are not thoroughly understood. Here, we investigated the effect of calcium phosphate mineralization on humic acid (HA) fixation in simulated soil solutions, either with or without clay mineral montmorillonite (Mt). We found that Mt in solution promoted nucleation and crystallization of calcium phosphate (CaP) due to amorphous calcium phosphate clustering and coalescence on Mt surface, which contributed to the long-term persistence and accumulation of HA. Organic ligands with specific chemical groups on HA have higher binding energies to CaP-Mt than to CaP/Mt, according to dynamic force spectroscopy observations. Moreover, CaP-Mt formed in solution showed a great capacity for HA adsorption with a maximum adsorption quantity of 156.89 mg/g. Our findings directly support that Mt is crucial for DOM sequestration by facilitating CaP precipitation/transformation. This has an impact on how effectively we understand the long-term turnover of DOM and highlights knowledge gaps that might assist in resolving essential soil C sequestration issues.

Naturally Occurring Montmorillonite-Based Polymer Monolith Composites as Stationary Phases for Capillary Liquid and Gas Chromatography

This work is associated with the preparation of capillary chromatographic columns containing inorganic-organic composites comprised of naturally occurring montmorillonite (MMT) clay mineral and polymethacrylate monolithic material. The prepared composites combine the best qualities of both constituents, offering desirable properties for use under the disparate conditions of both GC and HPLC at the same time. The stationary phases were investigated by scanning electron microscopy (SEM), the specific surface area, and thermogravimetric analysis (TGA) and examined in terms of various conditions utilized for GC and HPLC methods. The prepared columns demonstrated an excellent permeability and stability against common chromatographic conditions, such as the eluent type, flow rate, pressure, and temperature. The results confirmed that the addition of small amounts of MMT into the monolith induced significant improvement in the specific surface area, which contributed to the formation of more active sites and enhanced the retention of analytes. The registered column backpressures did not exceed 980 kPa and 16,500 kPa for the prepared GC and HPLC columns, respectively. The prepared columns were subjected to the separation of various interesting compounds possessing different chemistries and polarities, including alkanes, alkylbenzenes, polycyclic aromatic hydrocarbons (PAHs), alcohols, ketones, phenols, some common organic solvents, and isomeric mixtures. Under the optimal conditions, the efficiency of the columns fell between 4900–38,500 plates m−1 for GC and 3400–58,800 plates m−1 for capillary HPLC applications. In all cases, the measured chromatographic resolution was more than 1.38, with excellent an peak symmetry and low tailing factors. In comparison with the most commonly used commercial columns, the polysiloxane open tubular column for GC and silica-based C18 packed column for HPLC, the prepared GC columns demonstrated a faster separation with a higher efficiency, comparable resolution and tailing factors, and lower consumption of carrier gas. Regarding the capillary columns prepared for HPLC, the chromatographic experiments exposed a much lower run time with a comparable efficiency and resolution and drastically lower consumption of mobile phase solvents and samples. The results demonstrate that the MMT-based polymethacrylate monolith composites are applicable as novel and promising separation media for analyzing various mixtures of interest in different fields, such as petrochemical and environmental samples.

Effect of clay minerals on the flame retardancy of polylactic acid/ammonium polyphosphate system

The overview of the literature reveals the lack of comprehensive study on the effect of clay minerals in flame-retarded polylactic acid (PLA) composites. This research focuses on sepiolite (SEP) and montmorillonite (MMT) clay minerals and their impact on ammonium polyphosphate (APP)-based intumescent flame-retardant (IFR) system in PLA. The effects of the clay mineral types, their surface modification (O-SEP and O-MMT, respectively) and their concentration in PLA/APP composites on the flame-retardant properties were comprehensively evaluated through thermal and flammability tests. Overall, the sepiolite-containing samples showed the greatest decrease in pHRR and THR values at the 3 m/m% loading level. The sepiolites showed stronger interfacial interactions with the PLA matrix than the montmorillonites, and the organomodification proved to improve the compatibility of both types of clay minerals according to the dynamic mechanical analysis (DMA) results. Yet, the organomodification had a contradictory effect on the flame-retardant properties. In the case of sepiolites, it proved to be beneficial as the O-SEP added composite achieved a 60% decrease in the pHRR value and reduced the THR value to 60%. For montmorillonites, the improved compatibility by the organomodification with the PLA matrix seemed to hinder its flame-retardant effectiveness, as the critical point to its flame-retardant mechanism is the rapid migration and accumulation of the clay minerals towards the surface of the polymer.

Near-Infrared-II Activatable Symbiotic 2D Carbon-Clay Nanohybrids for Dual Imaging-Guided Combinational Cancer Therapy.

Two-dimensional (2D) nanomaterials hold great potential for cancer theranostic applications, yet their clinical translation faces great challenges of high toxicity and limited therapeutic/diagnostic modality. Here, we have created a kind of symbiotic 2D carbon-2D clay nanohybrids, which are composed of a novel 2D carbon nanomaterial (carbon nanochips, or CNC), prepared by carbonizing a conjugated polymer polydiiodobutadiyne, and a 2D layered aluminosilicate clay mineral montmorillonite (MMT). Intriguingly, with the formation of the nanohybrids, MMT can help the dispersion of CNC, while CNC can significantly reduce the hemolysis and toxicity of MMT. The symbiotic combination of CNC and MMT also leads to a synergistic anti-cancer theranostic effect. CNC has a strong absorption and high photothermal conversion efficiency in the second near-infrared region (NIR-II, 1000-1700 nm), while MMT contains Fe3+ that can facilitate the generation of reactive oxygen species from highly expressed H2O2 in tumor microenvironment. The nanohybrids not only enable a synergy of photothermal therapy and chemodynamic therapy to suppress the extremely rapid growth of RM1 tumors in mice but also allow for dual photoacoustic and magnetic imaging to guide the drug delivery and NIR-II irradiation execution, hence establishing a highly efficient and biosafe "all-in-one" theranostic platform for precision nanomedicine.

Raw and Purified Clay Minerals for Drug Delivery Applications.

In this study, the aim was to prepare drug-releasing clay mineral particles using raw (CaMt) and purified (PMt) montmorillonite and to compare and determine the effects of purification on the properties of montmorillonite. Montmorillonite clay minerals are used in several pharmaceutical and cosmetic products due to their many favorable properties, such as cation exchange capacity, adsorption capability, high specific surface area, and biocompatibility. Recently, several types of clay minerals have been widely studied for drug delivery applications due to their unique properties. The purification of montmorillonite is considered as a potentially useful step which may decrease the toxicity of impurities but which may increase the adsorption capacity of the montmorillonite. However, the effects on the toxicity and drug-release properties of purified montmorillonite have never been compared to that of raw montmorillonite. Montmorillonite was purified through decomposition of carbonates, dissolution of hydroxides, oxidation of organic materials, dialysis, and sedimentation. The raw and the purified montmorillonite were characterized using XRD, FTIR, and cation exchange capacities. Then, the cytotoxicity of raw and purified montmorillonite on normal hFOB cells was investigated to assess their biocompatibility in vitro. Finally, the efficacy of montmorillonite as a drug-delivering agent was investigated in vitro using cytotoxicity assays with the MCF7 cell line. The antitumor drug doxorubicin was loaded onto particles through electrostatic forces at 97.99% for CaMt and 96.79% for PMt. The drug-loading efficiency and release behavior of both clay minerals were determined. Results showed that both raw and purified montmorillonite did not significantly reduce the viability of normal cells at low concentrations (<500 μg/mL). At high concentrations, both raw and purified montmorillonite showed significant toxicity and the effect of impurities on toxicity were also more pronounced. Although drug loading was successful for both clay minerals there were differences in their controlled drug-release behavior. Doxorubicin-loaded raw and purified clay minerals significantly reduced MCF7 cell viability similar to pure DOX.

Soil clay minerals abundance mapping using AVIRIS-NG data

Advanced hyperspectral remote sensing technology can identify various clay minerals in the soil. The improved spectral and spatial resolution of the airborne hyperspectral sensor can be used for a better interpretation of clay mineral abundance in the soil. This research utilizes the high-resolution image data acquired from Advanced Visible Infrared Imaging Spectrometer Next Generation (AVIRIS-NG) on an airborne platform to map the abundance of clay minerals in the Udaipur region of Rajasthan (24° 34′ 16.5720′' N, 73° 41′ 29.5584′' E). The representative soil samples for various soil clay minerals, e.g., kaolinite, montmorillonite, and illite, were classified from AVIRIS-NG data using a spectral feature fitting algorithm. A total of thirty sites were selected from agricultural and wastelands for soil sample collection. X-ray diffraction (XRD) analysis of representative soil samples was carried out to find the percentage and type of clay minerals present. Regression analysis between absorption peak depth values estimated from the hyperspectral image of the sampling sites in the spectral region from 2205 to 2214 nm and corresponding clay content value showed a significant relationship. The regression line obtained for the known pixels was used to prepare the mineral abundance map over the study area. This study significantly indicates the dominance of montmorillonite clay mineral over kaolinite and illite in the soils of the Udaipur region.

Growth and Welfare of African Catfish (Clarias gariepinus Burchell, 1822) under Dietary Supplementation with Mixed-Layer Clay Mineral Montmorillonite-Illite/Muscovite in Commercial Aquaculture

Juvenile African catfish (Clarias gariepinus Burchell, 1822) were reared within two experiments (a research facility and a local catfish farm, E1 and E2, respectively) for 102 d each under commercial recirculating aquaculture conditions. The mixed-layer clay mineral montmorillonite–illite/muscovite (1g557) was applied as a feed additive at concentrations of 0.5% and 2.0%, which were compared with an unsupplemented control (0.0%) over 70 d. For E1, feeding was automatic at night, while E2 was fed manually during the day. The growth and physiological welfare parameters of the fish were monitored, including the mortality, skin lesions, stress responses after confinement (plasma cortisol and glucose), and additional blood parameters. Tendentially, the most efficient growth in both the experiments was observed in the 0.5% groups, which performed slightly better than the controls (E1: 0.8% and E2: 3.2%) despite a lower nutrient content (p &gt; 0.05). In E1, the negative skewness of the leptokurtic distribution also revealed the highest number of larger-sized fish per batch. Mortality was low in all the treatment groups (E1 control/0.5%/2.0%: 3.6%/4.9%/2.9%; E2 control/0.5%: 2.6%/5.5%). After only 29 d in E1, the number of skin lesions per fish decreased significantly (p &lt; 0.05 between each of the 0.5% and 2.0% groups, compared to the control (E1 control/0.5%/2.0%: 1.2/0.8/0.8). In both E1 and E2, the number of lesions per fish decreased even further after 70 d, significantly between the treatment groups and the control (E1 control/0.5%/2.0%: 0.9/0.4/0.5 and E2 control/0.5%: 0.6/0.3). In E1, the cortisol and glucose concentrations increased strongly in all the groups due to the induced stress, whereas this was not evident in E2 based on the different sampling procedure. The additional blood parameters (aspartate aminotransferase, glutamate dehydrogenase, urea, calcium, phosphate, total protein, leucocytes, erythrocytes, hematocrit, cholesterol, triglycerides, sodium, potassium, and chloride) revealed no significant difference between the treatment groups in either experiment, indicating no negative effects of 1g557 on the organs or metabolism of the fish. Supplementation with 0.5% 1g557 in the common commercial feeds for African catfish increases growth performance (p &gt; 0.05), reduces size variance, and supports fish welfare under different commercial aquaculture conditions in the present study.

Study on the Hydration Reaction of Typical Clay Minerals under Alkali and Sulfate Compound Activation.

Sand, stone, tailings and other aggregates often contain a small amount of clay mineral and their hydration activity is low, thereby lowering concrete performance indexes while negatively affecting their resource utilisation. In this study, clay minerals, calcium hydroxide and desulfurised gypsum were used to prepare cementitious materials to examine kaolinite, montmorillonite, illite and chlorite clay mineral contents under compound activation. The effects of curing temperature and water reducer on clay samples were analysed. The results showed that the compressive strength of kaolinite samples cured at 25 °C and 55 °C reached 1.09 and 4.93 MPa in 28 days and increased by 43% and 12%, respectively, after adding a 0.3% water reducer. Montmorillonite was activated and its compressive strength reached 5.33 MPa after curing at 55 °C in 28 days. Illite exhibited some activity and its compressive strength reached 1.43 MPa after curing at 55 °C in 28 days and the strength increased slightly after adding a water reducer. The chlorite sample had no strength after activation under the same conditions. Furthermore, X-ray diffraction and scanning electron microscope and energy-dispersive spectroscopy microstructure analyses showed that after alkali and sulfate activation, the hydration products of activated clay minerals mainly included ettringite, hydrated calcium aluminate and hydrated calcium silicate. The increase in curing temperature accelerated the reaction speed and improved the early strength. However, the effect on chlorite minerals was not obvious.

Effects of clay minerals on Fe2+-induced phase transformation of ferrihydrite

Ferrihydrite (Fhy) is the initial Fe-oxyhydroxide in supergene soils, and its structural instability is affected by many environmental factors. However, little attention has been paid to how these Fe-oxyhydroxide transformations are induced by Fe2+ cations when they combine with clay minerals, especially organoclay minerals, in soil solutions. This study investigated Fhy transformation in the presence of Fe2+ with and without the clay minerals montmorillonite (Mnt) and organo-Mnt (OMnt) under anaerobic conditions at pH 6.5. X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and Mössbauer spectroscopy were used to characterize the Fhy phase transformation. The results showed that goethite (Goe), lepidocrocite (Lep), and hematite (Hem) were the main products in the pure Fhy system. While Goe and Lep were the main transformation products, and Hem was not found in the presence of Mnt and OMnt. Fhy transformation was due to Fe2+ adsorption, followed by atomic exchange and electron transfer between Fe2+ and structural Fe(III) in Fhy. The presence of Mnt and OMnt dispersed Fhy particles, and some even combined with Fhy. Particularly, the presence of organic matter increased the dispersion of Fhy to a greater extent and occupied the interlayer sites of Mnt, which thus reduced the specific surface area and the Fe2+ adsorption capacity. Moreover, the Fe2+ adsorption sites, electronic transfer pathway, and the atomic exchange level were also affected by the presence of Mnt and OMnt, which further influenced the transformation products of Fhy accordingly. The presence of Mnt was more conducive to the formation of Lep, while OMnt was more conducive to the formation of Goe. These findings provide new insights into the stability of Fhy in clay-based anaerobic environments as well as the geochemical behavior of Fe in response to Fe cycling.

Ionic Polyacrylamides as Stability-Modifying Substances of Soil Mineral Suspensions Containing Heavy Metal Impurities

The accumulation of heavy metal in soils is a serious environmental problem. The aim of this paper was to compare the adsorption mechanism of ionic polyacrylamides (PAMs)—anionic and cationic with different contents of functional groups, on the surface of clay minerals—montmorillonite (type 2:1) and kaolinite (type 1:1), without and with the presence of heavy metal ions (Cr(VI) or Pb(II)). The dependence of solution pH, structure of mineral, type of PAM, ionic form of heavy metal, as well as order of adsorbates addition on the adsorption efficiency and stability of the clay mineral-polymer-heavy metal system was determined. In addition to adsorption and stability studies, electrokinetic and potentiometric titration measurements were performed. It was shown that the mixed PAM+heavy metal adsorption layers modify the surface properties of clay minerals significantly, which in many cases leads to the effective destabilization of the solid suspension and its separation from the liquid phase. Moreover, the most important factor, which influences the adsorbed amount of ionic polyacrylamide, turned out to be the internal structure of layered aluminosilicates and the presence of inter-package spaces capable of adsorbate molecules accumulating. For this reason the obtained adsorption capacity of montmorillonite is about 100 times higher in comparison to kaolinite.

Improvement of Geo-engineering Properties of Expansive Clayey Soil by using Sodium Chloride and Bagasse Ash

Expansive soils contain minerals such as smectite clays that are capable of absorbing water accompanied by shrink and swell behavior and thus change in volume. The swell–shrink behavior of these soils could lead to instability of the structures found on them, specifically the light-weight structures and pavements. Expansive clay soil is encountered in most parts of Egypt. A comprehensive study was made in Sixth of October city to investigate the impact of lime sludge and bagasse ash as an industrial solid waste from sugar-cane factory and sodium chloride salt on geotechnical engineering properties of expansive soil. The macrostructural properties are quantified through laboratory testing for Free swell index, Plasticity index and infiltration tests. The microstructural aspects of the treated soil are observed through X-ray diffraction studies and SEM micrographs. The laboratory results showed that by increasing the lime sludge, Bagasse ash and NaCl concentrations the liquid limit decreased from 100% to 60% while the plastic limit increased from 100% to 90% respectively. In addition, the infiltration tests showed an increase in the infiltration rate from 10% to 80% when LS and Bagasse ash were added to the soil also the free swell decreased from 100% to 70 % sufficiently. XRD patterns showed the formation of new kaolin cementitious compound as the change of montmorillonite to kaolinite mineral took place due to the reaction of high amount of calcium ions produced from the stabilizer, the cation exchange took place between the calcium cation of the lime associated with the surfaces of the clay particles. The effect of cation exchange and attraction causes clay particles to became close to each other, this process is called flocculation which is accompanied by a series of pozzolanic reactions resulting in the formation of clay aggregates that are bound together by the new cementitious products such as calcium aluminate. Scanning Electron Microscopic images (SEM) and SEM micrographs determined the formation of organized dense clay matrices of aggregations that showed the reduction of Montmorillonite clay mineral peak intensities and an increase in kaolinite clay mineral peak intensities due to the change of expansive soil texture and reduction of interplanar spacing of the treated soil.

Removal of methylene blue from water by ultrasound-assisted adsorption using low-cost bentonites

This study focused on the comparison of ultrasound-assisted (UA) and conventional (shaking or stirring) adsorption techniques, taking into account the time-dependent adsorption capacities. Six different bentonite samples were used as adsorbents, and methylene blue (MB) was used as adsorbate. Effects of pH, contact time, MB initial concentration, and temperature on the UA-adsorption were also investigated. XRD analyzes showed that all the bentonite samples were mostly composed of montmorillonite clay minerals, while XRF analyzes showed that the samples contained high percentage of silicon and aluminum oxides (≥70 wt%). Maximum zeta potential values (37.1–42.1 mV) were measured at pH 12 and, to confirm this, maximum adsorption capacities were also determined at this point. Ultrasound irradiation significantly increased the adsorption capacities of all bentonite samples in the early stages. For example, the adsorption capacity of the B-1 bentonite sample was measured as 388 mg/g by UA-adsorption at the first 5th minute, while it was 286 mg/g by conventional (C) adsorption technique at the same time. All bentonite samples showed increasing adsorption capacity with increased temperature confirming endothermic reaction. Maximum adsorption capacities of B-1, B-2, B-3, B-4, B-5, and B-6 bentonite samples with the 96–100 % MB removal percentages at selected conditions (pH: 11–12, temperature: 25 °C, contact time: 60 min, and MB initial concentrations for B-1: 800, B-2: 700, B-3,4: 650, B-5: 600, and B-6: 500 mg/L) were measured as 398, 342, 320, 296, 288, and 243 mg/g, respectively. Pseudo-second-order kinetic model and Langmuir isotherm model with higher correlation coefficients were found to be more suitable to explain the adsorption of MB cations onto bentonites. In addition, maximum adsorption capacities of B-1, B-2, B-3, B-4, B-5, and B-6 samples at 25 °C calculated from Langmuir isotherm data determined as 500, 454.5, 400, 384.6, 370, and 357.1 mg/g, respectively.

Methylene blue test and adsorption capacity of clays

This article presents results of experimental measurements focused on an ability of clay to adsorb Methylene Blue dye. This adsorption capacity is determined by a methylene blue test. Adsorption capacity could be a specific characteristics of individual types of clay which are basic component of earth. Therefore, the methylene blue test could be a good method to identify the composition of an unknown earth. Composition of earth is very important for example for final properties of unfired earth structures. The basic common element in all experiments was at least one of the elementary clay minerals (montmorillonite, kaolinite, illite). In the case of adsorption ability measurements, it was determined what is the maximum ability of a given clay to adsorb the Methylene Blue dye. The highest adsorption capacity was determined for montmorillonite clay, lower for kaolinite clay and the lowest for illite clay.

The effect of ionic strength, pH and natural organic matter on heteroaggregation of CeO2 nanoparticles with montmorillonite clay minerals

An accurate assessment of the fate and transport of engineered nanoparticles (ENPs) in aquatic environments hinges on developing an understanding of interaction between ENPs and natural colloids. In this study, we investigated the effects of pH and natural organic matter (NOM) on homoaggregation of CeO2 nanoparticles and their heteroaggregation with montmorillonite clay minerals. Time-resolved dynamic light scattering (TR-DLS) was employed to investigate the aggregation kinetics as function of electrolyte concentration in both homo- and heteroaggregation scenarios. The surface charge of CeO2 nanoparticles changed from positive to negative with pH increase while montmorillonite was negatively charged over the range of pH 4−11. At low pH, the critical coagulation concentration (CCC) of the montmorillonite-CeO2 mixtures shifted to a lower electrolyte concentration when compared to the homogenous system, indicating the negatively charged montmorillonite reduced the stability of positively charged CeO2 via heteroaggregation. In contrast, at high pH, the mixtures were stable because both montmorillonite and CeO2 nanoparticles were negatively charged. The presence of humic acid stabilized the systems against homo- and heteroaggregation. Our results suggest that the complex interactions between ENPs, natural colloids, and NOM should be considered to better understand the fate and transport of ENPs in realistic aquatic environments.

New functional hybrid materials based on clay minerals for enhanced electrocatalytic activity

Hybrid materials based on montmorillonite functionalized with LaMnO3 perovskitic structures were obtained for the first time by ultrasonic method with sonotrode immersed in the reaction medium, followed by heat treatment at a temperature of 600 °C. The clay mineral montmorillonite (Mmt), sodium montmorillonite (Mmt-Na+) and functionalized material (Mmt-LMO) were characterized by X-ray diffraction (XRD), Fourier transform-infrared spectroscopy (FT-IR), and scanning electron microscopy (SEM/Edx) techniques. The XRD patterns of Mmt-LMO composites show both the presence of the perovskitic phase with orthorhombic structure, and a mixture of aluminosilicates, corresponding to the montmorillonite clay minerals. The (Mmt), (Mmt-Na+) minerals and (Mmt-LMO) hybrid material were used to manufacture modified electrodes whose catalytic properties for the oxygen and hydrogen evolution reactions were investigated in alkaline medium.Based on electrochemical experimental results, some of these electrodes are catalytically active toward the hydrogen evolution reaction and the more performant ones were investigated further and it was found that the electrode modified with the composition containing 6 mg LaMnO3 functionalized montmorillonite and 10 µL Nafion solutions have the best electrocatalytic properties. At the current density of −10 mA/cm2 the electrode exhibits an over potentialfor hydrogen evolution of −0.48 V and its Tafel slope was measured to be 70 mV/dec. This study complements the extant scientific knowledge relevant to the water splitting domain.

Comparative Acid Leaching Study of Mongolian Muscovite and Montmorillonite Clay Minerals

Acid activation is the most commonly used method to enhance the chemical and physical properties of clay minerals. Porous structure formation behavior depends on the crystal structure of clay minerals. Within the same structure of clay minerals, their resistance to acid also varies. Acid leaching has been used to increase the surface area of clay minerals and obtain solids with high porosity and many acidic sites. This paper is focused on the results of acid leaching of Mongolian clay minerals (montmorillonite and muscovite). Both clay minerals belong to a group of phyllosilicates with the 2:1 crystal structure. The influence of acid concentration and leaching time on the porous properties of silica was studied. Initially, the montmorillonite was pre-treated by a simple physical purification methods. The montmorillonite and muscovite were acid leached by a 10% hydrochloric acid solution in an autoclave at 120°C for 10h. X-ray diffraction (XRD), X-ray fluorescence analysis (XRF), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and the surface area used for characterization of the raw and leached samples. The surface area of leached montmorillonite increased up to 77% and muscovite up to 63%. Clay mineral’s swelling character and isomorphic substitution of the octahedral layer show the main influence on porous structure formation.

Montmorillonite colloid plates with adsorbed cytochrome c: in vitro cytotoxic effect on colon cancer cell culture

BackgroundThe apoptosis (a cascade of biochemical reactions leading to suicide of damaged biological cells) is blocked in the cancer cells because of impossibility of cytochrome c (cytC) go out from the mitochondria. However, the apoptosis can be started by introducing of exogenous cytC into cytoplasm using colloid particles as a protein carrier due to ability of the cancer cells to phagocytize extracellular particles with submicron size.ResultsThe clay mineral montmorillonite (MM) were used to prepare aqueous suspension of protein/mineral composite particles by electrostatic adsorption of the positively charged cytC globules on the negatively charged MM colloid plates, and then added to colon cancel culture. The results shows out that separately cytC and MM have no effect but the composite cytC-MM particles kill 95% of the cancer cells after 96 h treatment using equine cytC which is 97% structurally identical with the human cytC. To reach this high cytotoxicity we have formulated requirements to: (a) bare colloid particles (electric charge, form and size), (b) conditions for protein adsorption (concentrations, pH, ionic strength), and (c) suspension with the composite particles (positive total charge and optimal concentration). Due to satisfying these requirements we have reached cytotoxicity which is 1/3 higher than the reached by other authors using different artificial particles. The cytotoxicity rapidly increases with concentration of the cytC-MM particles but further it shows tendency to saturation.MethodsThe optimal pH 6.5 and the 10:3 mg/mg cytC/MM concentration ratio at adsorption were found out by employing computer (protein electrostatics) and physicochemical methods (microelectrophoresis and colloid electrooptics) to prepare cytC-MM suspension. The anticancer capability of cytC-MM nanoplates were investigated using cell culture of metastasizing colon cancer.ConclusionThe in vitro experiments with colon cancer cell culture disclose that cytC-MM composite particles have potential for application in anticancer therapy of superficial neoplasms of the skin and the alimentary system (mouth cavity, esophagus, stomach, jejunum and colon).Graphic abstract