Natural Clay Mineral Research Articles

Macroscopic observation of a first order one-dimensional swelling-deswelling transition in a nanolayered material

AbstractThe high purity and superior quality of the synthetic clay mineral fluorohectorite allows for studies of phenomena that are masked by imperfections and the inhomogeneous charge distribution in the case of natural clay minerals. We have exploited this opportunity offered by synthetic fluorohectorite and report here digital optical microscopy observations of salinity controlled macroscopic swelling and deswelling behavior of extra-large nanolamellar clay mineral particle accordions of various sizes. We find that clay particle accordions, immersed in a saline solution, at sufficiently high salinity, are in their crystalline swelling region, with only a few water layers hydrating the accordion interlayer nano-spaces, corresponding to an interlayer spacing of about 1.5 nm. Using a micropipette as a micro-tweezer and thereby transferring accordions carefully back and forth between high and low salinity solutions, we observe well defined macroscopic accordion transitions between the crystalline swelling regime and an osmotic swelling regime where the interlayer spacings reach tens of nanometers, calculated from accordion thicknesses measured by digital imaging. The transitions display a clear first order character as evidenced by threshold salinity levels for their abrupt onsets as well as clear hysteresis with retention of crystalline or osmotic state memory, as salinity is increased or lowered. The experimental observations are supported by a theoretical model of the accordion interlayer spacing based on a Donnan equilibrium originating from the salinity gradient between the embedding saline solution and the ionic strength in the clay interlayers in the osmotic swelling regime.

The potential cutaneous benefits of bentonites and montmorillonites.

Bentonites and montmorillonites, natural clay minerals originating from volcanic ash, possess unique properties that have traditionally been utilized in industrial applications. Recently, their potential biomedical applications, particularly in dermatology, have garnered significant interest. This review explores the cutaneous benefits of bentonites and montmorillonites, highlighting their anti-inflammatory, wound-healing, oil-absorbing, drug delivery, photoprotective, and anti-aging effects. Evidence from in vitro experiments, animal studies, and preliminary clinical trials demonstrate that these clays can significantly reduce inflammation, accelerate wound healing, absorb excess oil, enhance drug delivery, protect against ultraviolet radiation, and improve skin hydration and elasticity. Larger scale randomized clinical trials (RCTs) are needed to further establish the safety and efficacy of bentonites and montmorillonites. Given the increasing consumer demand for natural ingredients in skincare, bentonites and montmorillonites present a promising area for further research and development in dermatologic applications.

MXene-montmorillonite nanocomposites-based scaffold sensors for early pancreatic cancer diagnosis

Pancreatic cancer is increasingly prevalent and characterized by a high mortality rate. Due to the limitations of current diagnostic methods, early-stage detection remains elusive, contributing to persistently low survival rates among affected individuals. Nanomaterials have garnered significant attention in cancer research for their potential diagnostic applications. Among these, MXenes – a novel family of two-dimensional nanomaterials composed of transition metal carbides, nitrides, and carbonitrides – are of particular interest due to their unique properties. These include high electrical conductivity, hydrophilicity, thermal stability, large interlayer spacing, tunable structure, and high surface area. These characteristics make MXenes highly effective for detecting trace amounts of various analytes. In addition, their tunable structure enables precise manipulation of their properties, allowing for optimized sensing responses. Montmorillonite nanoclay (MMT), a member of the smectite group of natural clay minerals, is known for its ability to promote bone development and influence cell behavior. When combined with MXenes, MMT forms promising nanocomposites for early pancreatic cancer detection through sensing applications. The Ti3C2 MXene-MMT nanocomposites exhibit potential as scaffold sensors capable of distinguishing cancerous from non-cancerous samples by observing the distinctive patterns in resistance changes. In addition, MXenes possess excellent selectivity, allowing for the reliable identification of targeted analytes from a complex mixture of chemical and biological analytes. Due to the advanced sensing capabilities of MXene-MMT composite scaffold sensors, they hold great promise for early cancer diagnosis and tissue regeneration, providing a novel therapeutic approach to improving patient outcomes.

Mechanism of tetracycline sorption on carbon-bentonite

Antibiotics increased industrial production is the reason of their occurrence in wastewater, soils, groundwater, and drinking water. In this regard, treating the environment for pharmaceuticals is one of the urgent environmental challenges. Synthesis of adsorbents using different types of raw materials by the methods of mechanochemical activation makes it possible to significantly increase their sorption capacity due to the accumulation of various kinds of defects in the crystal structure of the adsorbent. We obtained the bentonite-carbon composite using roller-ring vibratory mill with coal-bentonite ratio of 30 : 70 and 50 : 50. However, the nature of the interaction between carbon and bentonite correlates with changes of surface area and porosity. The porous structure parameters of the samples show the mechanochemical activation of the mixture involves their components interactions. The authors studied the structural and chemical changes during the modification of bentonite with activated carbon by analysing the vibrational spectra of carbon, initial, and modified aluminosilicate samples. According to infrared spectroscopy of adsorbents, absorption bands characteristic of Si-O-C bond vibrations occurred. The paper investigates the sorption capacity of mechanochemically modified natural clay mineral Dash-Salakhli bentonite towards tetracycline hydrochloride. Research investigates the kinetics of the process and rapid sorption of tetracycline. The paper provides possible mechanisms of chemisorption due to donor-acceptor interaction and ion-exchange processes.

Obtaining granular adsorbents based on biopolymers and clay minerals

The development of granular, low-cost adsorbents represents an important environmental challenge. Natural clay minerals show promise in this area, as they exhibit adsorption capacity a range of pollutants. Nevertheless, the high dispersion of aluminosilicates limits their widespread use. To enhance the processability of these materials, they are subjected to granulation using natural biopolymers, such as sodium alginates. Concurrently, the adsorption capacity of the granules can be increased by the application of modifiers to the surface of natural silicates, in particular iron oxyhydroxides, which are efficacious in the removal of heavy metals from water. The aim of this study is to obtain granular adsorbents based on saponite and biopolymer that are stable in water and capable of removing heavy metal ions from the water environment. The rheological behavior of the suspensions was investigated in order to ascertain the optimal conditions for high-quality granulation. The phase composition of the modified saponite was determined by X-ray diffraction analysis. The structural-sorption characteristics of the samples were investigated using the method of low-temperature nitrogen adsorption-desorption, and their thermal properties were studied by differential thermal and thermal gravimetric analyses. The present study demonstrates that the viscosity of saponite and sodium alginate-based suspensions with varying mass ratios is dependent on the clay mineral content of the mixture, at a fixed polymer quantity. The conditions for granulation were determined, and it was established that the stability of the granules in the aqueous medium is influenced by the quantity of sodium alginate incorporated into the mixture. It was established that the specific surface area of the modified sample decreases during the granulation process. This value is 109 m2/g, which is less than the 173 m2/g that observed for the powdered adsorbent. The processes and phase transformations occurring in granular materials during heating were studied. As a result of the study of the rheological characteristics of suspensions based on saponite and sodium alginate, it was found that these systems are thixotropic. It was also discovered that the stability of the granules in an aqueous medium is significantly affected by the amount of sodium alginate added to the suspension. The potential applications of the obtained adsorbents in the purification of water from heavy metal ion contamination are shown.

Impurity Ions Mn<sup>2+</sup> and Fe<sup>3+</sup> as Paired Spin Labels for the Study of Structural Transformations in Phyllosilicates by the ESR Method

Impurity paramagnetic ions Mn2+ and high spin Fe3+ (S = 5/2) are shown to be very informative “paired spin labels” to investigate structural transformations in natural aluminosilicate clay minerals by ESR spectroscopy. Second derivative ESR (SD ESR) enables to detect minor narrow lines of the ions against the background of intense broad lines of other paramagnetic impurities. Complex SD ESR spectra of the ions are explained by the Jahn-Teller effect and hyperfine interactions with OH-groups. SD ESR spectra before and after heating (620°C and 900°C) proved transformations of octahedral crystal cells accompanied by the loss of the OH-groups, displacement of the ions to equivalent positions.

Adsorption characteristics of Zn (ii), Pb (ii) and Cd (ii) ions from aqueous solution onto natural clay minerals

Adsorption characteristics of Zn (ii), Pb (ii) and Cd (ii) ions from aqueous solution onto natural clay minerals

Insights into relationship between microbial community-induced polycyclic aromatic hydrocarbons degradation and soluble organic matter transformation during vermiculite-amended sewage sludge composting

Vermiculite is a natural clay mineral with unique properties that are widely used in plant cultivation, soil remediation, and solid waste management. This study investigated the relationship between microbial community-induced polycyclic aromatic hydrocarbons (PAHs) degradation and dissolved organic matter (DOM) transformation during vermiculite-amended composting of sewage sludge. Four treatments with varying vermiculite percent compositions, 0%, 1%, 5%, and 10%, mixed with initial mix waste, were designed and then composted for 33 days. The results showed that the addition of 1% vermiculite caused the highest losses of 82.19%, 52.98%, and 69.00% for LMW-PAHs (2–3 rings), HMW-PAHs (4–6 rings), and total PAHs respectively compared to other treatments. Spectral and community analyses revealed that 1% vermiculite enhanced the PAHs losses by functional networking of key genera and promoting the aromatization and humification of DOM to format the micelles with PAHs. The transformation and utilization of DOM driven by key genera Acinetobacter, Ochrobactrum, Pseudoxanthomonas, and Bacillus were the important impact factors for the losses of PAHs. Finally, this study provides new insights and a guide for applying vermiculite to sludge composting for PAHs removal.

Heterojunction of natural clay minerals and carbon nanotubes as robust moisture electric generator

Among various sustainable energy harvesting devices, moisture electric generators (MEG) possess distinct advantages like portability, minimum human intervention, absence of moving parts, unnecessity of fuels, and potential for off-grid power generation. However, maturing this emerging technology requires the exploration of a diverse range of materials and device configurations. Here, we report the fabrication of heterojunction-based robust MEGs by using reconstructed layers of natural vermiculite clay (VM) and HNO3-treated oxidized multi-walled carbon nanotubes (o-CNT). The heterojunction of negatively charged VM and o-CNT membranes (o-CNT-VM) prepared through a facile water-assisted fusion process yielded voltages of ∼ 790 mV for more than 2000 s (at 75 % RH). Assembling multiple o-CNT-VM devices in series connection output potentials up to 98 V were achieved. The mechanistic studies revealed the junction potential between VM and o-CNT to be the major contributor to the observed potential, with minor contributions arising from evaporation-driven streaming of ions through the 2D nanofluidic channels. The o-CNT-VM devices can function in extreme conditions such as temperatures ranging from 0 to 80 °C. The practical applicability of the o-CNT-VM-based MEG devices is demonstrated by lighting LED, and powering calculators by assembling o-CNT-VM devices in simultaneous series and parallel connection.

Introducing and Boosting Oxygen Vacancies within CoMn2O4 by Loading on Planar Clay Minerals for Efficient Peroxymonosulfate Activation.

CoMn2O4 (CMO) has been recognized as an effective peroxymonosulfate (PMS) activator; however, it still shows disadvantages such as limited reactive sites and metal leakage. Herein, an effective and environmentally friendly composite catalyst, CMO/Kln, was synthesized by anchoring CMO on kaolinite (Kln), a natural clay mineral with a special lamellar structure, to activate peroxymonosulfate (PMS) for the degradation of residue pharmaceuticals in water. The abundant hydroxyl groups located on the surface of Kln helped induce rich oxygen vacancies (OVs) into composite CMO/Kln, which not only acted as additional active sites but also accelerated working efficiency. In addition, compared with bare CMO, CMO/Kln showed lower crystallinity, and the adoption of the Kln substrate contributed to its structural stability with lower metal leaching after three rounds of reaction. The universal applicability of CMO/Kln was also verified by using three other pharmaceuticals as probes. This work shed light on the adoption of natural clay minerals in modifying CMO catalysts with promoted catalytic activity for the efficient and eco-friendly remediation of pharmaceuticals in wastewater.

Ultrasonic‐assisted activation of clay for efficient removal of U(VI) and Cr(VI)

AbstractThe natural clay mineral was activated using the acid treatment under ultrasonic conditions to improve its adsorption performance. The acid‐activated clay (AAC) was investigated to remove Cr(VI) from wasted lubricant and U(VI) from aqueous solution by batch, spectroscopy, and modeling. Batch experiments showed that the isotherms and adsorption kinetics of Cr(VI)/U(VI) on AAC were satisfactorily followed by Frenudlich and the pseudo‐second‐order model, respectively. The decreased adsorption of U(VI) on AAC with the increase of ion strength indicated the outer surface complexation of U(VI) on AAC. The interaction mechanism of Cr(VI)/U(VI) on AAC was demonstrated to be surface complexation by oxygenated functional groups (e.g., hydroxyl) according to X‐ray photoelectron spectroscopy (XPS) analysis. According to fitting of surface complexation models using three approaches, the adsorption of U(VI) on AAC at different pH can be better fitted by the double‐layer model compared to the constant‐capacitance model and triple‐layer model. These findings are great important for the application of acid activated clay in the removal of heavy metals and radionuclides from the environment.

Functionalized Palygorskite as a Delivery Platforms for Bioactive Asymmetric Beta-Diketone Dyes

Natural clay minerals are among the most versatile materials used in the biomedical field. Palygorskite has found various applications in this field, from the treatment of diarrheal diseases in the past to materials with antibacterial properties and platforms carrying bioactive compounds used in the treatment of diseases, cosmetic and healthcare products in the present. In this study, a possible delivery method of some bioactive asymmetric β-diketonic compounds is presented. Palygorskite modified with amphionic groups (P) and copper ions (PCu) was used as a platform to load bioactive curcumin derivatives (1 and 2). By varying the copper ions, the amounts of charged active compounds were monitored. Studies have shown that the hybrid materials resulting from the loading of 1 and 2 compounds on palygorskite with 30% copper ions (PCu30) can be used as delivery methods for these asymmetric curcumin derivatives, while palygorskite with 50% copper ions(PCu50) loaded with the same type of bioactive compounds has antibacterial properties.

A hybrid adsorption / ultrafiltration membrane process for removal of Cs-137 from radioactive wastewater using natural clay adsorbent

The removal of radioactive cesium element (Cs-137) from wastewater is relatively challenging due to its high diffusion coefficient, short hydration radius, and the similarity between its chemical behavior to other alkali metals having high background concentrations, leading to a competition that reduces the removal efficiency of cesium (Cs-137). This study introduces an innovative treatment process using a submerged membrane adsorption hybrid system (SMAHS) using natural Iraqi clay minerals as adsorbents. The operational conditions were studied using the (SMAHS) continuous flow operation in stirred filtration mode experiments. The maximum operational conditions were achieved for the initial radioactivity concentration of Cs-137 at 7201.8 Bq/L, clay dose 1 g/L, the stirring speed at 700 rpm, pH =6, the transmembrane pressure (TMP) under 2 bar, and temperature at 25 °C. The SMAHS rejection percentage of Cs-137 was 93.6 % and the permeate flux was 105.6 L/m2.h at the best operational conditions. This study demonstrates that utilizing raw bentonite which is both environmentally friendly and locally available as an adsorbent in the SMAHS has proven its effectiveness for removing Cs-137 from wastewater. The hybrid method effectively immobilizes radioactive waste by converting it from liquid to solid state, leading to an extended and safer storage time.

Assembly of Natural Clay Minerals as Highly Robust Evaporation-Driven Power Generator

Assembly of Natural Clay Minerals as Highly Robust Evaporation-Driven Power Generator

Dye-sensitized sepiolite clay as natural scaffolds for visible light driven photocatalytic hydrogen evolution

Natural clay minerals are increasingly used as superior support materials for various photocatalysts due to their excellent adsorption capacity, negative surface charge, suitable thermal/chemical stability, large specific surface area, and strong surface reactivity, resulting in low agglomeration and suppression of charge recombination. However, they are still insufficient for photocatalysis due to their low efficiency. Therefore, sensitization of clay minerals with dyes to improve the efficiency and specificity of catalysts is considered a promising route for photocatalytic applications. In this work, the effect of dye sensitization on visible light-driven photocatalytic water splitting of microfibrous sepiolite scaffolds as natural photocatalyst supports was investigated for the first time by using various xanthene dyes (eosin Y, rhodamine B and eryhtrosine B (ErB)) and triethanolamine as photosensitizers and sacrificial agents, respectively, in the absence and presence of platinum as a co-catalyst. The clay/dye system was characterized using various techniques such as X-ray photoelectron spectroscopy, transmission electron microscopy, scanning electron microscopy and energy dispersive X-rays. Sep/ErB photocatalysts produced the highest amount of hydrogen among the other Sep/dye scaffold systems because they act as an effective matrix by preventing nanoparticle aggregation and promoting electron transfer due to their excellent crystal structures and physicochemical properties.

The Catalytic Potential of Modified Clays: A Review

The need for innovative catalysts and catalytic support materials is continually growing due to demanding requirements, stricter environmental demands, and the ongoing development of new chemical processes. Since about 80% of all industrial processes involve catalysts, there is a continuing need to develop new catalyst materials and supports with suitable qualities to meet ongoing industrial demands. Not only must new catalysts have tailored properties, but they must also be suitable for large-scale production through environmentally friendly and cost-effective processes. Clay minerals, with their rich history in medicine and ceramics, are now emerging as potential catalysts. Their transformative potential is exemplified in applications such as hydrogenating the greenhouse gas CO2 into carbohydrate fuel, a crucial step in meeting the rising electrical demand. Moreover, advanced materials derived from clay minerals are proving their mettle in diverse photocatalytic reactions, from organic dye removal to pharmaceutical pollutant elimination and photocatalytic energy conversion through water splitting. Clay minerals in their natural state show a low catalytic activity, so to increase their reactivity, they must be activated. Depending on the requirements of a particular application, selecting an appropriate activation method for modifying a natural clay mineral is a critical consideration. Traditional clay mineral processing methods such as acid or alkaline treatment are used. Still, these have drawbacks such as high costs, long processing times, and the formation of hazardous by-products. Other activation processes, such as ultrasonication and mechanical activation routes, have been proposed to reduce the production of hazardous by-products. The main advantage of ultrasonication and microwave-assisted procedures is that they save time, whereas mechanochemical processing is simple and efficient. This short review focuses on modifying clay minerals using various new methods to create sophisticated and innovative new materials. Recent advances in catalytic reactions are specifically covered, including organic biogeochemical processes, photocatalytic processes, carbon nanotube synthesis, and energy conversion processes such as CO2 hydrogenation and dry reforming of methane.

Comparison of Synthetic Pathways for Obtaining Fluorescent Nanomaterials Based on Halloysite and Carbon Dots for Potential Biological Sensing.

Recently, fluorescent sensors have gained considerable attention due to their high sensitivity, low cost and noninvasiveness. Among the different materials that can be used for this purpose, carbon dots (CDs) represent valuable candidates for applications in sensing. These, indeed, are easily synthesized, show high quantum yield and are highly biocompatible. However, it was pointed out that the photoluminescence properties of these nanomaterials are strictly dependent on the synthetic and purification methods adopted. The presence of halloysite nanotubes (HNTs), a natural, low cost and biocompatible clay mineral, has been found to be efficient in obtaining small and highly monodispersed CDs without long and tedious purification techniques. Herein, we report the comparison of synthetic pathways for obtaining halloysite-N-doped CDs (HNTs-NCDs) that could be used in biological sensing. One was based on the synthesis of N-doped CDs by a bottom-up approach on HNTs' surface by a MW pyrolysis process; the other one was based on the post-modification of pristine N-doped CDs with halloysite derivatives. The evaluation of the best synthetic route was performed by different physico-chemical techniques. It was found that the bottom-up approach led to the formation of N-doped CDs with different functional groups onto the HNTs' surface. This evidence was also translated in the different fluorescence quantum yields and the existence of several functional groups in the obtained materials was investigated by potentiometric titrations. Furthermore, the ability of the synthesized nanomaterials as sensors for Fe3+ ions detection was assessed by spectroscopic measurements, and the cellular uptake was verified by confocal/fluorescence microscopies as well.

Simple and scalable preparation of lignin based porous carbon coated nano-clay composites and their efficient removal for the diversified iodine

Here, lignin and nano-clay were used to prepare novel composite adsorbents by one-step carbonization without adding activators for radioactive iodine capture. Specially, 1D nano-clay such as halloysite (Hal), palygorskite (Pal) and sepiolite (Sep) were selected as skeleton components, respectively, enzymatic hydrolysis lignin (EHL) as carbon source, lignin based porous carbon/nano-clay composites (ELC-X) were prepared through ultrasonic impregnation, freeze drying, and carbonization. Characterization results indicated lignin based porous carbon (ELC) well coated on the surface of nano-clay, and made its surface areas increase to 252 m2/g. These composites appeared the micro-mesoporous hierarchical structure, considerable N doping and good chemical stability. Results of adsorption experiments showed that the introduction of ELC could well promote iodine vapor uptake of nano-clay, and up to 435.0 mg/g. Meanwhile, the synergistic effect between lignin based carbon and nano-clay was very significant for the adsorption of iodine/n-hexane and iodine ions, their capacity were far exceed those of a single material, respectively. The relevant adsorption kinetic and thermodynamics, and mechanism of ELC-X composites were clarified. This work provided a class of low-cost and environmentally friendly adsorbents for radioactive iodine capture, and opened up ideas for the comprehensive utilization of waste lignin and natural clay minerals.

Effect and Mechanism of NH4H2PO4/Montmorillonite Composite Powder on Al-Mg Alloy Dust Explosion

ABSTRACT The explosion of energetic metal dusts represents a major threat to the machining industry. It is therefore crucial to develop inexpensive, high-performance explosion inhibitors. For better protection of production, by using solvent-antisolvent approach, we prepare a uniquely clustered composite inhibitor by combining a natural clay mineral – Montmorillonite. In a 20-L spherical explosion apparatus and a vertical combustion tube, our examination shows that adding 80 wt% NH4H2PO4/Montmorillonite composite powder inhibitor can fully inhibit the explosion of Al-Mg alloy dust; adding 60 wt% composite powder inhibitor can inhibit the flame propagation. And that our new composite powder inhibitor outperforms pure monomer powder inhibitors. Through XRD, XPS, etc analysis, we gain a deeper insight into the inhibitory mechanism of NH4H2PO4/Montmorillonite. On the one hand, the decomposition of NH4H2PO4 and the resulting products combine to inhibit reaction; on the other hand, Montmorillonite contains plenty of voids that not only limits the propagation of flames, but also well absorbs the products generated from explosion reaction. Through research and experiments, we obtain a cheap, environmentally friendly and efficient composite dust explosion-proofing agent, which provides new ideas for the design of dust explosion-proofing materials and broadens the application prospects of natural clay minerals as dust explosion-proofing agents.

Effective microwave regeneration of natural sepiolite and montmorillonite as adsorbents for tetracycline removal and mechanism insight

Natural clay minerals such as sepiolite (Sep) and montmorillonite (Mt) are used as low-cost adsorbents to remove tetracycline (TC) in water, and the spent adsorbents saturated with TC are regenerated under microwave (MW) irradiation. The adsorption and regeneration properties of Sep and Mt are compared. The possible adsorption and MW regeneration mechanisms are proposed. The results show that 11.25 mg·g−1 and 20.74 mg·g−1 adsorption capacities of Sep and Mt are obtained, respectively, within 120.0 min at 298 K. Mt has higher adsorption capacity, faster adsorption rate and shorter adsorption time for TC than that of Sep. The adsorption processes using Sep and Mt are well-fitted to pseudo-second-order kinetics and Langmuir models. The two adsorption reactions are spontaneous and endothermic, with increased randomness at solid–liquid interfaces. Moreover, 89.76 % and 114.45 % maximum regeneration ratios are obtained for Sep and Mt, respectively. Mt exhibits superior regeneration performance than Sep. After eight adsorption-regeneration cycles, the two adsorbents can maintain excellent adsorption and regeneration performance. This work provides new perspectives on the adsorption technology using natural clay minerals to remove antibiotics and the MW regeneration technology to regenerate spent natural clay minerals saturated with organic pollutants in organic wastewater treatment.