Clay Surface Research Articles

Target-oriented element activation and functional group synthesis lead to high quality modified clay for Prorocentrum donghaiense control

Single source with series modifications (SSSM) is a new method to modify clay surfaces by activating clay mineral resources for harmful algal blooms control. In this study, the optimal preparation conditions for this method were obtained using response surface methodology. Based on the material analysis, an important way to obtain modified clay (MC) with the excellent Prorocentrum donghaiense removal performance was explored and the optimum preparation conditions were as follows: calcination temperature 750°C, alkali neutralization pH 3.7 and clay supplementation ratio 1.3:1. Under these conditions, the calcination treatment can effectively activate the aluminum element in the clay lattice and obtain the largest amount of highly active Al IV and Al V, which are readily released from the lattice as activated aluminum. When the alkali neutralization pH was adjusted to 3.7, the activated aluminum was hydrolyzed and induced into highly positively charged polyhydroxyaluminum compounds. The supplemented kaolin increased the yield of the MC product by surface convergence of the activated aluminum in the system. As a result, the optimized MC can form large particle size flocs with good regeneration and stability during the algal removal process, which greatly improved its ability to coagulate and sediment algal cells. Overall, the MC prepared by the SSSM method achieved high algal removal efficiency through targeted element activation and functional group shaping.

A mechanistic model for the complex conductivity of clay materials. I. Theory

Summary Clay materials are ubiquitous in the Earth's continental and oceanic crusts. They are characterized by a large specific surface area, and, in contact with water, they have remarkable adsorption, catalytic and containment properties. Clay materials also exhibit a high electrical conductivity response associated with their large surface. However, sedimentary clay minerals have a complex microstructure and electrochemistry that are not fully understood and make the quantitative petrophysical interpretation of geoelectrical measurements difficult. In this study, we have developed a new mechanistic model to better understand and predict the complex conductivity of clay materials from their microstructure and electrical double layer properties. For the conductive component, our model considers ion electromigration in bulk water, clay electrical diffuse layer, and interlayer space, if any. Concerning polarisation, it takes into account ion back-diffusion in the Stern layer and in the interlayer space, if any, and also Maxwell-Wagner effect. Water and clay surface conductivities, formation factor, cementation exponent and sample electrically connected porosity can be extracted from the comparison of the model to experimental data. This study is a step forward to better understand and quantify the complex conductivity of clays observed during electrical and electromagnetic measurements, from laboratory to geological formation scales.

Investigation on the development of Novel PAM structure as high-performance clay inhibitor in HT/HP conditions by using functional groups

Polyacrylamide (PAM) molecular structures are not stable at higher temperatures, limiting their effectiveness in water-based drilling fluid (WBDF) applications. This study focuses on identifying functional groups that can enhance the thermal stability of PAM structure. It presents a comprehensive and comparative analysis of the swelling inhibition capacity of both low and high molecular weight (MW) PAM-based polymers at high temperature and high pressure (HT/HP). The mechanism by which modified PAM interacts with and adsorbs to the clay (Na-MMT) surface is examined, along with an analysis of the surface properties of the clay minerals. Therefore, molecular dynamic (MD) simulation results revealed that the Novel PAM polymers with high MW containing ethyl and benzyl groups demonstrate greater stability and more controlled deformation behavior compared to conventional PAM at HT conditions. Surface modification and hydrophobic effects were observed in the interactions between polymers and Na-MMT. Low MW PAM-based polymers showed larger fluctuations in d-spacing, indicating various or more disruptive interactions. In contrast, the insertion of high MW PAM-based polymer resulted in significantly narrower and lower d-spacing fluctuation ranges. The Novel PAM exhibited superior performance, providing lower d-spacing fluctuations compared to both low MW PAM-based polymers and standard PAM. Across a temperature range from 300 to 600°K, the Novel PAM consistently improved polymer adsorption on the Na-MMT surface compared to standard PAM. Indicating that the modifications effectively reduce the interaction between Na-MMT particles and water molecules while enhancing the interaction between the polymer and Na-MMT, potentially leading to more stable structures in HT/HP environments. The enhanced stability suggests that Novel PAM is more suitable for WBDF applications, as it is less prone to structural changes and can maintain its integrity under harsh conditions. The modifications provide the polymer with better resilience, potentially leading to improved performance in practical applications.

MARTINI Coarse-Grained Force Field for Thermoplastic Starch Nanocomposites.

Thermoplastic starch (TPS) is an excellent film-forming material, and the addition of fillers, such as tetramethylammonium-montmorillonite (TMA-MMT) clay, has significantly expanded its use in packaging applications. We first used an all-atom (AA) simulation to predict several macroscopic (Young's modulus, glass transition temperature, density) and microscopic (conformation along 1-4 and 1-6 glycosidic linkages, composite morphology) properties of TPS melt and TPS-TMA-MMT composite. The interplay of polymer-surface (weakly repulsive), plasticizer-surface (attractive), and polymer-plasticizer (weakly attractive) interactions leads to conformational and dynamics properties distinct from those in systems with either attractive or repulsive polymer-surface interactions. A subset of AA properties was used to parametrize the MARTINI-2 coarse-grained (CG) force field (FF) for the melt and composite systems. The missing bonded parameters of amylose and amylopectin and the bead types for 1-4 and 1-6 linked α-D glucose were determined using two-body excess entropy, density, and bond and angle distributions in the AA TPS melt. This new MARTINI-2 CG model was also compared with the MARTINI-3 model for the TPS melt. However, the requirement of a polarizable water model necessitates the use of MARTINI-2 FF for the composite system. This liquid-liquid partitioning-based FF shows freezing and compaction of polymer chains near the clay surface, further accentuated by lowering of dispersive interactions between pairs of high-covalent-coordination ring units of TPS polymers and the montmorillonite sheet. A rescaling of the effective dispersive component of TPS-MMT cross interactions was used to optimize the MARTINI-2 FF for the composite system with structural (chain size distribution), thermodynamic (chain conformational entropy and density), and dynamic (self-diffusion coefficient) properties obtained from long AA simulations forming the constraints for optimization. The obtained CG FF parameters provided excellent estimates for several other properties of the melt and composite systems not used in parameter estimation, thus establishing the robustness of the developed model.

Mineral-associated organic matter is heterogeneous and structured by hydrophobic, charged, and polar interactions

The formation of mineral-associated organic matter (MAOM) is a key phenomenon that may explain the slow turnover rates of carbon in soil organic matter (SOM). Despite this, important details pertaining to the structure and dynamics of MAOM remain unknown. In the present study, we use replica-exchange molecular dynamics simulations to gain insight into the structure of MAOM on the surface of prototypical phyllosilicate clay and Fe-oxide minerals, montmorillonite and goethite, fine-grained minerals that strongly impact soil carbon dynamics in temperate and tropical regions, respectively. We examine the impact of aqueous chemistry through the presence of either Na[Formula: see text] or Ca[Formula: see text] charge balancing counterions. Our results are consistent with the hypothesized multilayer sorption ("onion-skin") model of MAOM and help to explain previous observations regarding the patchy distribution of SOM on mineral surfaces. In particular, the SOM coatings are partial and laterally heterogeneous, and water retains extensive access to mineral surfaces even when significant SOM sorption occurs. Low molecular weight neutral SOM molecules ([Formula: see text]200 Da) infrequently interact with the mineral surfaces nor their sorbed organic matter coatings and are increasingly labile with decreasing molecular weight. This observation is inconsistent with a central feature of the predominant soil continuum model of SOM and suggests that further iterations of the conceptual model may be required.

In Situ Stabilization of Bi Nanoparticles into the Nanopores of Modified Montmorillonite: Efficient Heterogeneous Catalysts for Reduction of 4-Nitrophenol.

Here, we report the in situ generation of Bi nanoparticles (BiNPs) into a nanoporous matrix by impregnation of bismuth chloride and subsequent reduction with sodium borohydride. The nanoporous matrix was created by acid activation of natural montmorillonite clay under controlled conditions with the aim that it may serve as a host for BiNPs. The characterization of stabilized BiNPs was done by using Fourier-transform infrared (FTIR), powder X-ray diffraction (PXRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), transmission electron microscopy (TEM), and field emission scanning electron microscopy-energy dispersive X-ray (FESEM-EDX) techniques. The TEM study reveals that the BiNPs with an average particle size of 7.16 nm are well-distributed on the surface of the acid-activated montmorillonite clay. The synthesized BiNPs exhibited excellent catalytic activity for the degradation of 4-nitrophenol (4-NP) in aqueous medium with remarkable results. The degradation of 4-NP to 4-aminophenol (4-AP) at 25 °C, in the presence of sodium borohydride, brought about almost 100% conversion in 6 min with a rate constant of 0.20098 s-1 that follows the pseudo-first-order kinetics.

Preparation and Performance Evaluation of Small-Molecule Ammonium as a Shale Hydration Inhibitor

In this paper, small-molecule quaternary ammonium salts were synthesized by N-alkylation to inhibit hydration swelling and hydration dispersion. The prepared small-molecule quaternary ammonium salt was characterized by Fourier transform infrared (FTIR) spectroscopy, Thermogravimetric analysis (TGA), particle size analysis and Scanning electron microscopy (SEM), and its performance as an inhibitor in clay was evaluated by an anti-swelling test and a linear swelling test. The results show that small-molecule quaternary ammonium salt (TEE-2) synthesized by triethanolamine and epichlorohydrin in ethanol with a molar ratio of 1:1.5 can successfully inhibit the hydration swelling and dispersion of clay. The anti-swelling rate of TEE-2 was 84.94%, the linear swelling rate was 36.42%, and the linear swelling rate of 0.5% TEE-2 was only 29.34%. The hydration swelling of clay in 0.5% TEE-2 solution was significantly inhibited. The hydration inhibition mechanism of the small-molecule quaternary ammonium salt inhibitor 0.5% TEE-2 was analyzed by FTIR, SEM and TGA. It was considered that 0.5% TEE-2 has strong hydration inhibition, which was realized by infiltration and adsorption on the clay surface. Small-molecule quaternary ammonium salts were beneficial for maintaining wellbore stability and reducing the risk of wellbore instability.

Molecular dynamics investigation of epoxy resin adsorption mechanisms on clay surfaces and the mechanical properties of epoxy resin-clay

The strength of natural clay can be improved with epoxy resins. However, nanoscale curing mechanisms remain poorly understood, which is essential for enhancing stability. In this study, molecular dynamics simulation was employed to calculate the quantity of interface hydrogen bonds, adsorption energy, radius of gyration, and mechanical properties of clay cured by diglycidyl ether of bisphenol-A epoxy resin (DGEBA), diglycidyl ether 4,4’-dihydroxy diphenyl sulfone (DGEDDS), and Aliphatic epoxidation of olefin resin (AEOR). Adsorption behavior and mechanical properties of the clay cured by three epoxy resins were investigated: (1) The chain structure of AEOR led to 18.2% more hydrogen bonds than DGEBA and 59.1% more than DGEDDS. (2) The simulated adsorption energies for DGEBA, DGEDDS, and AEOR with kaolinite were 92.59, 98.25, and 116.87 kcal·mol−1, respectively. (3) The bulk and shear modulus of kaolinite increased by 4.93% and 4.80% when using AEOR. The interface stability and mechanical properties of kaolinite were also improved through strong hydrogen bonds and high adsorption energy. (4) The improvement in Young’s modulus of kaolinite was most significant with AEOR, followed by DGEDDS. AEOR excelled in the Z direction, while DGEDDS excelled in the X and Y directions. This research provided a theoretical foundation to effectively improve the properties of clay using epoxy resins.

Elucidating Wettability Alteration on Clay Surface Contacting Mixed Electrolyte Solution: Implications to Low-Salinity Waterflooding

Summary Many mechanisms have been proposed in the literature to explain wettability alteration at low-salinity waterflooding (LSWF). Some of these mechanisms include electrical double layer (EDL) expansion, multi-ion exchange, and cation hydration. However, no consensus has been reached on which one is the key mechanism in low-salinity enhanced oil recovery (EOR). Moreover, the mechanisms by which low-salinity flooding can enhance oil recovery are poorly understood. Parameters such as salinity, electrolyte type, oil components, and presence of clay minerals are often associated with the degree to which the injection of low-salinity water increases oil production. Therefore, an investigation of the geochemistry of the clay/fluid interface is crucial to understand the role of petrophysical properties such as wettability on oil production. We use molecular dynamics (MD) to (i) quantify the impacts of different types of oil components, electrolytes, and its mixture at varying ionic strengths on interfacial properties and (ii) investigate wettability alteration by means of water adsorption quantification. We investigate the brine/clay and oil/brine/clay interfacial interactions involved in the adsorption of ions and water molecules onto the clay surface. Clay is represented by illite, and brine is composed of water molecules and different electrolyte types such as NaCl, CaCl2, and their mixtures at varied concentrations. The oil components investigated in this work include decane (C10H22), decanoic acid (CH₃(CH₂)₈COOH), and sodium decanoate (C10H19NaO2). These components were selected to represent the range of oil molecules typically found in reservoirs, which include nonpolar, polar, and charged polar molecules. Initially, we set up systems composed of different ion composition and salinity to investigate the effect of these parameters on EDL structure and water adsorption. Then, we created systems composed of mixed electrolyte and different oil components to verify the impacts of these molecules on the oil/brine/clay interface. Finally, we increased the NaCl concentration in the system containing sodium decanoate to investigate the role of Na in wettability alteration. MD simulations were performed at 330 K, and particle density profiles of water, hydrocarbon, and ions inside the illite nanopores were computed. We observed that the ion composition and salt concentration of the systems composed of clay minerals and brine do not result in significant changes in the adsorption planes of cations. For the same systems, we also computed the number of water molecules per unit cell in each hydration layer. We observed that the change in the thickness of these hydration layers is also very small. The results showed that nonpolar-charged hydrocarbon molecules have the lowest mobility, suggesting that this component has a more intense interaction with the illite surface compared with other hydrocarbons. Additionally, snapshots of the simulation indicate that calcium preferentially forms bridges with sodium decanoate molecules compared with other organic components. Despite being widely known as an efficient method for achieving EOR, the underpinning mechanism for wettability alteration at LSWF is still not fully understood. The outcomes of this work improve our understanding of the key parameters affecting interactions at the oil/rock/brine interface during LSWF.

Atomistic origin of montmorillonite clay subjected to freeze-thaw hysteresis

The freeze-thaw cycles of frozen soil could significantly affect its thermo-hydro-mechanical-chemical (THMC) properties, causing the frost heaving and thawing settlement. The microscale essence is the water-ice phase transition, but the microscale details are still poorly understood, especially at ultra-low temperatures. Nuclear magnetic resonance (NMR) technology and molecular dynamics (MD) simulation methods were performed to explore the freeze-thaw behaviors of montmorillonite clay under temperature of 210 - 293 K. Then, the water-ice phase transition, freeze-thaw hysteresis, ice nucleation mechanism, and surface effect of clay at an atomistic level were discussed. A classification method of different types of unfrozen water through NMR experiment was proposed, including bulk, capillary, and bound water. Here, it is found that: (1) the freeze-thaw process of frozen soil at the macroscale was essentially the occurrence of ice-water phase transition at the microscale. (2) The freeze-thaw hysteresis was caused by different growth and melting rates of ice crystals, where the ice growth/nucleation on clay surface was more difficult to develop. (3) The surface effect of clay was essential for the ice nucleation and the existence of bound water. For example, little unfrozen water still existed in unfrozen soil even at 213 K. (4) For unsaturated frozen soil, the quasi-liquid water was an essential component of unfrozen water that cannot be ignored. This work could provide an atomistic insight to unravel the atomistic origin of the freeze-thaw mechanism of montmorillonite clay and complement relevant experimental evidence.

Redox Properties of Structural Fe in Clay Minerals: 4. Reinterpreting Redox Curves by Accounting for Electron Transfer and Structural Rearrangement Kinetics.

Iron-bearing smectite clay minerals can act as electron sources and sinks in the environment. Previous studies using mediated electrochemical analyses to determine the reduction potential (EH) values of smectites observed that the relationship between the structural Fe2+(s)/FeTotal ratio in the smectite and EH varied based on the redox history of the smectite. We hypothesize that this behavior, referred to as redox hysteresis, results from the smectite particles not equilibrating with the applied EH over the course of the experiment (∼30 min). To test this hypothesis, we developed a model incorporating interfacial electron transfer kinetics and charge redistribution within the particle to simulate the mediated electrochemical experiments from previous studies. The simulated redox curves accurately matched the previously reported experimental redox curves of the smectite SWa-1, demonstrating that longer equilibration periods led to a decrease in redox hysteresis. We validated this experimentally by measuring the redox curve of SWa-1 after an equilibration period of at least 12 h. Furthermore, we extended the simulations to three other smectites (NAu-1, NAu-2, and SWy-2) and extracted their respective thermodynamic and kinetic parameters. This work offers a framework for interpreting and modeling redox reactions on clay surfaces, along with key parameters for four commonly studied smectites.

Clays as Micro-Electrodes in Environmental Detoxification

AbstractIn-situ reduction of contamination in soil and groundwater is an ongoing challenge that often requires a multi-pronged approach for effective and efficient clean-up. Spontaneous or assisted electrochemical reactions that break down certain pollutants held on clay surfaces can render natural clays a unique and powerful ally in environmental mitigation of contaminated soils. Application of a low-level DC electric field (mV/cm) has been shown to facilitate transformation of some compounds and ionic species through redox reactions in addition to transporting them through the pores in wet clay soils. Results from previous tests suggest that the natural electrochemical processes that promote pollutant sloughing or chemical breakdown can be enhanced for targeted treatment by applying low-level electric field to the contaminated soil with clay content. The central idea of this hypothesis is that clay, due to its surface charge and electrostatic interaction with adjacent pore fluid, acts as a “micro-electrode” through the diffused double layer (DDL) interactions when subjected to an external electric field. This hypothesis, proven viable, may unlock potential ability of natural clays to generate beneficial reactions for detoxification of contaminated sub-surfaces. Evidence from past laboratory experiments accompanied by a proposed electrical model of clay behaving as a micro-electrode are presented in this paper. The laboratory experiment results support the proposed electrical model.

Green Engineered CuO/SnO2/HNT Composites: Illuminating the Photocatalytic Path for Organic Pollutant Remediation and Zebrafish Embryo Toxicity Evaluation.

Photocatalysis stands out as a promising technique for treating organic contaminants, yet the quest for visible light active composite materials, crafted through cost-effective, eco-friendly, and uncomplicated processes, poses formidable challenges. Here, we introduce a successful endeavor, the synthesis of a CuO/SnO2 (CS) composite via a microwave method, employing Carissa edulis fruit extract as a reducing as well as capping agent. Various loadings of CS-HNT composites were prepared by ultrasonically incorporating CS onto nanotubular halloysite (HNT) clay. Employing a suite of types of characterization, including XRD, XPS, FT-IR, FE-SEM, HR-TEM, ζ potential, UV-vis-DRS, TGA, BET, and EIS, we meticulously explored the morphology, structure, stability, surface area, electrochemical, and optical properties of the developed CS-HNT composites. HR-TEM observations unveiled the formation of a heterojunction between cubic CuO and spherical SnO2 on the HNT clay surface. Optical and EIS analysis highlighted that the 20CS-HNT composite displayed significant absorption in the visible region, efficient electron-hole pair separation, and enhanced interfacial charge transport relative to other loadings. Photocatalytic evaluations and optimization studies revealed that the 20CS-HNT photocatalyst achieved notable removal efficiencies, eliminating 85% of Congo red (CR) and 80% of tetracycline (TC) within 90 min and 74% of ATZ in 3 h under visible light conditions. Scavenging investigations, the fluorescence probe method, and a NBT transformation study underscored the pivotal roles of hydroxyl and superoxide radicals in pollutant removal. The reusability trials highlighted the exceptional stability and recyclability of the photocatalyst, even after five cycles. In addition, zebrafish embryo toxicity tests revealed improved survival and hatching rates in photocatalyst-treated samples compared to those of controls. Moderate toxicity was observed in treated TC, while the treated CR sample showed non-lethal toxicity. In essence, this study unveils a straightforward and efficacious approach for developing photocatalysts for large-scale wastewater treatment. Furthermore, it proposes the adoption of safe clay-based bimetal oxide photocatalysts in diverse environmental applications.

Mechanochemical preparation and performance regulation mechanism of highly durable and multifunctional iron red nanocomposite pigments derived from natural mixed-dimensional palygorskite clay

Iron oxide red pigments are one of the most widely used inorganic red pigments around the world. It is always pursed to improve their physicochemical properties. Herein, a continuous mechanochemical method was employed to fabricate high-performance iron red nanocomposite pigments via anchoring α-Fe2O3 nanoparticles on the surface of natural mixed-dimensional palygorskite clay (MDPal). The mechanical force of twin-screw extrusion promoted the Si-OH groups of MDPal to coordinate with Fe3+ to form the precursor, while MDPal was activated with the residual H+ of the involved nitrate to accelerate the thermal diffusion of Al3+ into α-Fe2O3 crystal lattice, thus the nanocomposite pigments presented a bright yellowish-red color (L∗ ​= ​35.61, a∗ ​= ​33.10, b∗ ​= ​35.86, C∗ ​= ​48.80). Furthermore, the mixed-dimensional nanostructure of MDPal served as a good substrate for chemical bonding of α-Fe2O3 nanoparticles to improve the dispersion and environmental stability of iron red pigments. Due to the synergistic effect of each component and the excellent thermal and chemical stability, the obtained nanocomposite pigments exhibited excellent application prospect as functional inorganic pigments for anti-corrosion coating, overglaze ceramic and coloring and reinforcing of polypropylene, respectively. It provided a facile strategy for preparation of high-performance multifunctional iron red pigments based on MDPal.

Olivine alteration and the loss of Mars' early atmospheric carbon.

The early Martian atmosphere had 0.25 to 4 bar of CO2 but thinned rapidly around 3.5 billion years ago. The fate of that carbon remains poorly constrained. The hydrothermal alteration of ultramafic rocks, rich in Fe(II) and Mg, forms both abiotic methane, serpentine, and high-surface-area smectite clays. Given the abundance of ultramafic rocks and smectite in the Martian upper crust and the growing evidence of organic carbon in Martian sedimentary rocks, we quantify the effects of ultramafic alteration on the carbon cycle of early Mars. We calculate the capacity of Noachian-age clays to store organic carbon. Up to 1.7 bar of CO2 can plausibly be adsorbed on clay surfaces. Coupling abiotic methanogenesis with best estimates of Mars' δ13C history predicts a reservoir of 0.6 to 1.3 bar of CO2 equivalent. Such a reservoir could be used as an energy source for long-term missions. Our results further illustrate the control of water-rock reactions on the atmospheric evolution of planets.

Brazilian bentonite/MgO composites for adsorption of cationic and anionic dyes.

Industrial effluents, especially those containing dyes, have become the main cause of contamination of water resources. In this context, Brazilian bentonite/MgO composites, with excellent adsorptive properties, were prepared and investigated for their effectiveness in removing cationic and anionic dyes from aqueous solutions. The new adsorbents were obtained using Brazilian bentonites and MgO using the mechanochemical method followed by heat treatment (at 700°C for 4h). Different characterization techniques were used for the chemical, mineralogical, thermal, surface, and morphological analysis of the raw clays and the composites. The experimental adsorption isotherms were quantified under different conditions of initial concentration, contact time, pH, adsorbent dosage, and temperature variation to interpret the adsorption mechanism of the crystal violet (CV) and Congo red (CR) dyes. The modeling results were obtained from the empirical Sips equation and Pseudo Second Order (PSO) kinetics, indicating that the adsorption of molecules is a heterogeneous phenomenon that occurs in a monolayer on the surface (ns > 1), with the adsorption rate determined by chemisorption. The composites showed the best removal efficiency performance compared to the raw bentonites, with an increase of 12% for the CV dye and 46% for the CR dye. In addition, the qmax values obtained were 423.02mg/g and 479.86mg/g (AM01). This research underscores the potential of Brazilian bentonite/MgO composites as a promising solution for the removal of cationic and anionic dyes from water, offering hope for future applications in the field of environmental engineering and materials science.

Development of a natural ingredient based on phenolic compounds from propolis extract and bentonite and its application in carrageenan hydrogels

Nowadays, there is an increasing consumer demand for more natural and environmentally friendly food additives. The current research aimed to produce and characterize a new additive based on bentonite and the phenolic compounds from green propolis extract, as well as to characterize the effect of this additive on the rheological properties of carrageenan hydrogels. The new additive (biohybrid) was obtained after the adsorption of phenolic compounds on the clay platelets. The adsorption mechanism was explained by Langmuir and Freundlich models, which suggested that adsorbed phenolic compounds form a monolayer and multilayers on the clay surface. Despite phenolic adsorption, the physico-chemical attributes of the bentonite remained unchanged. The incorporation of the biohybrid (BH) increased the sol-gel transition temperature of carrageenan hydrogels. This research reports for the first time the development and application of a new natural ingredient with potential food applications.

Organo cationic dyes adsorption on charged nano-clay: Revealing dual mechanisms through GCS modeling and DFT molecular simulations

This study investigates the adsorption mechanisms of organic cationic dyes, specifically malachite green (MG) and toluidine blue (TB), on sodium montmorillonite clay (Na-MMC). Using montmorillonite sourced from the Nador deposit in Northern Morocco, we aim to model cation exchange with the Gouy-Chapman-Stern (GCS) model. The adsorption capacities are found to be 192.5 meq/100 g for TB and 175.8 meq/100 g for MG at room temperature and uncontrolled pH. X-ray diffraction (XRD) analysis was employed to determine the interlayer spacing of the montmorillonite, contributing to the understanding of adsorption mechanisms. GCS modeling provided insight into the adsorption constants for both dyes, alongside parameters related to the solid/solution interface such as the amount adsorbed per layer, ion concentration in the solution, and clay surface potential. These findings confirmed a significant affinity between the dyes and the clay, aligning with the literature. Moreover, Density Functional Theory (DFT) simulations indicated a stronger affinity of toluidine blue for negatively charged surfaces compared to other dyes.

Tailor-made polymer tracers reveal the role of clay minerals on colloidal transport in carbonate media

HypothesisHost rock weathering and incipient pedogenesis result in the exposition of minerals, e.g., clay minerals in sedimentary limestones. Once exposed, these minerals provide the surfaces for fluid–solid interactions that control the fate of dissolved or suspended compounds such as organic matter and colloids. However, the functional and compositional diversity of organic matter and colloids limits the assessment of reactivity and availability of clay mineral interfaces. Such assessment demands a mobile compound with strong affinity to clay surfaces that is alien to the subsurface. ExperimentWe approached this challenge by using poly(ethylene glycol) (PEG) as interfacial tracer in limestone weathering experiments. FindingsPEG adsorption and transport was dependent on the availability of clay mineral surfaces and carbonate dissolution dynamics. In addition, PEG adsorption featured adsorption–desorption hysteresis which retained PEG mass on clay mineral surfaces. This resulted in different PEG transport for experiments conducted consecutively in the same porous medium. As such, PEG transport was reconstructed with a continuum-scale model parametrized by a Langmuir-type isotherm including hysteresis. Thus, we quantified the influence of exposed clay mineral surfaces on the transport of organic colloids in carbonate media. This renders PEG a suitable model colloid tracer for the assessment of clay surface exposition in porous media.

Specific ion effects on the soil shear strength and clay surface properties of collapsing wall in Benggang.

Benggangs are a special type of soil erosion in the hilly granite regions of the tropical and subtropical areas of Southern China. They cause severe soil and water loss, which can severely deteriorate soil quality and threat to the local ecological environment. Soils (red soil, sandy soil and detritus soil) were collected from collapsing wall of a typical Benggang in Changting County of Fujian Province, and their physicochemical and mineralogical properties were analyzed. Five different monovalent cations were used to saturate the soil samples to examine the specific ion effects on the shear strength and clay surface properties. Red soil had a higher clay content, plastic limit, liquid limit and shear strength than sandy soil and detritus soil. The studied soils mainly consisted of kaolinite, hydroxy-interlayer vermiculite, illite and gibbsite clay minerals. The soils saturated with K+, NH4 +and Cs+ had greater cohesion than the Li+- and Na+-saturated soils, e.g., the cohesion of the red soil saturated with Li+, K+, NH4 + and Cs+ cations were 1.05, 1.23, 1.45 and 1.20 times larger than that of the Na+-saturated soil, respectively. While the internal friction angle was slightly different, which indicated that different monovalent cations affected the shear strength differently. K+-, NH4 +- and Cs+-saturated clay particles had higher zeta potentials and thinner shear plane thicknesses than Li+- and Na+-saturated clay particles and showed strong specific ion effects on the clay surface properties. The changes in clay surface properties strongly affected the soil mechanical properties. Soils saturated with K+, NH4 + and Cs+ could increase the shear strength, and then increase the stability of the collapsing wall, thus might decrease the erosion intensity of Benggang. The results provide a scientific basis for the interpretation of and practical treatment of Benggang.