Sepiolite Clay Research Articles

From old to new inorganic materials for advanced applications: The paradigmatic example of the sepiolite clay mineral

This review article focuses on sepiolite fibrous clay mineral, which has been selected here as an example of an ancient inorganic natural material that is currently receiving much attention as excellent candidate for advanced materials and applications. Sepiolite clay is an abundant hydrated magnesium silicate whose crystal structure determines the presence of nanoporous cavities as well as large surface and rheological properties of great interest for the further design of functional materials. The present work introduces and discusses the relationship between aspects of this clay, in terms of its structural and morphological organization, and its physicochemical characteristics from which emerging applications arise. One of the sections is devoted to describe current industrial applications of commercially available sepiolite-based materials. As sepiolite can be considered a nanomaterial by itself, approaches including its controlled chemical and physical modifications intended to develop new advanced inorganic and hybrid nanostructured materials provided with pre-designed functionalities. Among them, polymer nanocomposites that include bionanocomposites and carbon-sepiolite nanomaterials, materials for adsorption of pollutants, functionalization with magnetic nanoparticles, active phase of sensors and DNA support for gene transfer are some of the examples that we refer to in the present review article.

Flame Retardant Nanocomposites of Polystyrene-Modified Sepiolite Clay

Flame retardancy is the property that is highly demanded when it comes to deal with plastics in different industries. In this research general purpose polystyrene (GPPS) and modified sepiolite clay are melt blended together to fabricate flame retardant nanocomposites. Structural analysis were performed with the help of Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) techniques. Morphological analysis of the fabricated nanocomposites were carried out using scanning electron microscope (SEM). As a result of better clay dispersion in polymer matrix and intermolecular interactions, mechanical properties are also improved. The standard procedure (ASTM D4986-20) was followed for observing the flame retardancy of the fabricated nanocomposites. Tangible decrease is noted upto 48% in burning rate of the optimum sample which reflects improvement in flame retardancy.

Cytotoxicity of Bentonite, Zeolite, and Sepiolite Clay Minerals on Peripheral Blood Mononuclear Cells

Background: Clays and clay minerals have great potential for exerting positive impacts on human health and implementation in medical applications. They are industrial minerals used in various medical applications, like drug delivery. Considering the abundance of clay resources in Iran, we decided to investigate the role of natural clays in peripheral blood mononuclear cells (PBMCs), as effective immune system cells that provide the health of the body in disease and standard times. Investigating the cytotoxicity of these minerals on PBMCs helps to understand their performance in medicine and the treatment of patients. Materials and Methods: The studied clays, including bentonite, zeolite, and sepiolite, were prepared from Iran mines, and their characterizations were scanned by x-ray fluorescence (XRF), x-ray diffraction, and cation-exchange capacity (CEC) determination. PBMCs were isolated by Ficoll-Hypaque density gradient centrifugation, and 200000 PBMC cells were exposed to different concentrations of clays (1-1000 µg/mL) for 48 h in 96-well cell culture plates. Cell cytotoxicity response was determined using 3-[4, 5-dimethylthiazole-2-yl]-2, 5-diphenyltetrazolium bromide (MTT) assay. Results: Bentonite inhibited cell proliferation after 48 h of incubation at a concentration above 0.05 mg/mL, whereas zeolite inhibited cell proliferation at 10 and 5 mg/mL. Sepiolite does not have any cytotoxic effect at all of the concentrations. CEC for bentonite, zeolite, and sepiolite were 86 cmol(+)/kg, 15.5 cmol(+)/kg, and 3.54 cmol(+)/kg, respectively, and showed a direct relationship with cell growth. Conclusion: The cytotoxicity of the investigated clays is less than those reported in the literature review. This suggests that the studied clays with beneficial properties have great potential to be used in medicine, taking into account the size, type, and concentration of clays. In vivo and long-term studies on bio-culture and biodistribution are essential to understand better the role of the studied clays. Furthermore, our results could provide a new perspective on the safety of using cheap and naturally available clays in medical and industrial applications.

Removal of trivalent chromium from aqueous solutions by natural clays: Valorization of saturated adsorbents as raw materials in ceramic manufacturing

Kaolinite/illite (KUb) and sepiolite (SEP) clays were used to study Cr(III) adsorption removal from aqueous solutions so that they could be utilized after saturation for ceramic manufacturing. SEP had a larger specific surface area and a higher PZC than KUb. The removal of Cr(III) was evaluated using a batch equilibration procedure at pHi = 4 and pHi = 6. Fast removal kinetics were observed for both clays. Maximum removal capacity was determined by changing the concentration of Cr(III) while keeping the concentration of clay constant and by altering the amount of clay while keeping the concentration of Cr(III) constant. In all situations, SEP had greater capacity than KUb, and capacity was greater for both clays at higher pHi. Not only did the pHi impact the removal capacity and efficiency, but so did the pH during adsorption and the initial concentration of Cr(III). Because of the higher PZC, the pHf for SEP was higher for the same pHi. The higher the pH and Cr(III) concentration, the higher the probability of Cr(OH)3 precipitation and the higher the removal capacity.Dried saturated clays were uniaxially pressed and sintered at 1000 °C for 2 h. The densities of the sintered materials were nearly identical to those of pure clay-based materials, but the compressive strengths were higher, which is significant for the use of saturated clays as raw materials in ceramic manufacturing. Leaching of Cr from SEP-based material was significantly higher than from KUb-based material probably due to the presence of CaCO3 in the SEP.

Synergistic effect of organically modified sepiolite clay in intumescent flame retardant polyolefin elastomer-based cable outer sheath compounds

Synergistic effect of organically modified sepiolite clay in intumescent flame retardant polyolefin elastomer-based cable outer sheath compounds

Modification of high-density polyethylene and ethylene-vinyl acetate copolymer by chain-layered silicate «sepiolite»

Composites based on high-pressure polyethylene and ethylene-vinyl acetate copolymer, containing sepiolite clay powder with a chain-layered structure have been investigated, and their physical-mechanical properties have been analyzed. When using sepiolite, the organomodification and compatibilization are not required. It is shown, that composite materials with the addition of sepiolite are superior in a number of characteristics to those containing traditionally applied layered clay powders.

Aflatoxin Adsorption by Natural and Heated Sepiolite and Palygorskite in Comparison with Adsorption by Smectite

Abstract Smectites are effective binders of aflatoxin in aqueous solutions. Unfortunately, their efficacy is reduced in guts because of interference by biomolecules and essential nutrients within the gut. Tunnel structures in palygorskite and sepiolite may function as molecular sieves and may, therefore, serve as alternatives or complements to smectites in binding aflatoxins but not larger biological compounds. The objective of the current work was to determine the effect of heat treatment on aflatoxin B1 (AfB1) adsorption and selectivity for biomolecules by two palygorskites (Plg_PK and Plg_CN), sepiolite (Sep), and a palygorskite-smectite mixture (Plg-Sm) in comparison with a smectite (Sm-37GR). The clays were heated at 250, 400, 500, and 600°C while phase and structural changes were characterized by X-ray diffraction and infrared spectroscopy. Comparative AfB1 adsorption was determined in aqueous and in simulated gastric fluids. The clay structures collapsed irreversibly in Sm-37GR and folded in fibrous clays with heating at 400°C or more. Sm-37GR adsorbed more AfB1 than all of the other clays; the estimated adsorption capacity followed the trend Sm-37GR (44 g kg–1) > Plg_PK (18.12 g kg–1) > Sep (12.7 g kg–1) > Plg_CN (11.4 g kg–1) > Plg-Sm (9.0 g kg–1). This trend appeared to be correlated with the abundance of smectite in the clays. Sepiolite had greater binding strength for AfB1 than the other clays. With intact clay structures, heating induced a negligible effect on AfB1 adsorption by the fibrous clays while in Sm-37GR and Plg-Sm, adsorption increased with heating at 250°C. Tunnel folding and structural collapse that had occurred at 400°C caused an abrupt decline in AfB1 adsorption irrespective of the clay type. The sepiolite clay adsorbed the least pepsin (370 g kg–1) while smectite adsorbed the most (1430 g kg–1). Consequently, in the simulated gastric fluid, adsorption declined by 25–30% in sepiolite, 52–60% in smectite, and remained unaffected in the palygorskites. Aflatoxin B1 adsorption probably occurred through H-bonding at the surface with the silanol group in palygorskite and sepiolite. No evidence that AfB1 molecules occupied the tunnels of the natural or heated palygorskite or sepiolite was observed in the present study. Palygorskite and sepiolite had a much smaller adsorption capacity for AfB1 than the smectite but also adsorbed less pepsin; therefore, both may be effective aflatoxin binders in gastrointestinal systems.

Polystyrene-Sepiolite Clay Nanocomposites with Enhanced Mechanical and Thermal Properties.

Polystyrene (PS)/sepiolite clay nanocomposites were prepared via the melt extrusion technique using vinyl tri-ethoxy silane (VTES) as the compatibilizer and cross-linking agent. Mechanical, thermal, and flame-retardant properties of the newly developed polystyrene-based nanocomposites were determined. Surface morphology was investigated using scanning electron microscopy (SEM), examining the distribution of the filler in various compositions of fabricated composites. Structural analysis of the samples was carried out using the Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) techniques. Thermal stability was determined by thermal gravimetric analysis (TGA), showing a maximum 30.2 wt.% increase in residue by adding sepiolite clay. The results obtained from the dynamic mechanical analyzer (DMA) in terms of the storage modulus, loss modulus and damping factor exhibited better stress transfer rate and effective interfacial adhesion between the filler and the matrix. The higher filler loaded sample showed greater flame retardancy by decreasing the burning rate up to 48%.

Sunflower Oil Ethyl Esters (Biodiesel) Production Using Extruded Catalyst Based on Potassium Carbonate, Sepiolite Clay and Magnetite

In this study, a magnetic catalyst based on potassium carbonate, sepiolite and magnetite was prepared seeking to convert efficiently sunflower oil into ethanolic biodiesel. The magnetic catalyst was attained by extrusion method and characterized by magnetic, mechanical, structural and textural properties. The catalytic performance of this catalyst was also evaluated in a reactor assisted by magnetic field. The reactor was operated in a closed loop, recycling the reaction mixture. High oil conversion to biodiesel was obtained using 2 wt% of catalyst with 1:12 oil/ethanol molar ratio at 70 °C after 2 h. The magnetic properties of this catalyst allowed the bed stabilization under magnetic field and the catalysts separation, enabling its reuse in other reaction cycles.

Ethylene scavenging film based on corn starch-gum acacia impregnated with sepiolite clay and its effect on quality of fresh broccoli florets

Ethylene scavenging film based on corn starch (CS) and gum acacia (GA) nanocomposite film impregnated with sepiolite (SP) was fabricated by the casting method and characterized. FTIR, TGA, XRD, SEM, mechanical, water vapor barrier, and ethylene scavenging properties of CS/GA films with and without SP were carried out. The addition of SP in the CS/GA films showed improved elongation and lowered water vapor permeability in comparison to the control film. Interfacial interaction between the CS/GA and SP was observed in FTIR. The SEM images showed that SP clay nanoparticles were evenly distributed in the CS/GA film matrix. Increasing the SP into CS/GA films improves tensile strength, water vapor permeability, crystallinity, and thermal stability. The CS/GA/SP film showed ethylene scavenging properties increasing with SP. Based on mechanical, water barrier permeability, and ethylene scavenging properties, CS/GA film impregnated with 20% SP was optimal and was selected for broccoli florets packaging. Broccoli packaged in a CS/GA/SP20 film and stored at 23 °C for 6 d showed a reduction in loss of weight, color, and total soluble solids of broccoli florets. CS/GA/SP nano biocomposites films show great potential in the area of active packaging due to their good mechanical, barrier, and ethylene scavenging properties.

Synthesis, characterization, and application of MOF@clay composite as a visible light-driven photocatalyst for Rhodamine B degradation

Metal Organic Frameworks (MOFs) with natural clay materials is a relatively new research avenue that appears to reduce high production costs and address the instability issues of pure MOFs. A novel MOF and natural clay composites of MOF@Sp_n (n = 1–4) were fabricated by the in situ precipitation of stable MOF, Zr6O4(OH)4 (ABDC)6 (where ABDC = 2-aminobenzene-1,4-dicarboxylic acid), over natural sepiolite (Sp) clay and used as a photocatalysts for elimination of organic dyes in aqueous media. The formation of MOF@Sp_n due to its strong electrostatic interactions between the positively charged MOF and the negatively charged sepiolite. Optimizing the Sp content in the composite strongly influenced the dispersibility, crystallinity of MOFs, resulting in progressively functional hybrid materials with an excellent optoelectronic properties. The composites lessened the shortcomings of the individual components and made them suitable as a visible light-active, highly efficient, standalone photocatalyst material that can degrade RhB.

Plasma-catalytic oxidation of toluene on Fe2O3/sepiolite catalyst in DDBD reactor

The removal of toluene by sepiolite supported with Fe2O3 by plasma catalysis was studied. Fe2O3/SEP catalysts were prepared by impregnation and characterized by Brunauer–Emmett–Teller, inductively coupled plasma, x-ray diffractometer, scanning electron microscopy, x-ray photoelectron spectroscopy, and H2-TPR. Degradation efficiency of toluene under Fe2O3 loading, energy yield, carbon balance, CO2 selectivity, and residual O3 concentration were studied. The results show that sepiolite clay as a carrier can reduce the reduction temperature of Fe2O3. Fe2O3/SEP catalyst has good moisture resistance and catalytic capacity. 5Fe/SEP has the best catalytic effect due to its high lattice oxygen content and large specific surface area. After continuous discharge at constant energy density for 48 h, the catalytic ability of 5Fe/SEP does not decrease. The results indicated that sepiolite supported Fe2O3 catalyst is an efficient catalyst for toluene degradation by plasma-catalyst measure.

Development and characterization of PVA-starch incorporated with coconut shell extract and sepiolite clay as an antioxidant film for active food packaging applications

An active antioxidant film was fabricated by using polyvinyl alcohol (PVA) and corn starch (ST) and incorporated with and 3, 5, 10, and 20% (v/v) coconut shell extract (CSE) and sepiolite clay (SP) for the first time. The microstructure and physical properties of prepared films were characterized and examined. The addition of sepiolite clay to PVA improved the elongation break 15.57 to 69.24%, and water vapor permeability increased with the addition of CSE. In addition to CSE to films, the antioxidant activity properties of the films were enhanced up to 80%. Further, increasing the amount of CSE slightly affected the color of the active films. The thermal properties of films were enhanced with the addition of CSE and SP. The dispersion of SP in the PVA matrix was affected by an increase in CSE concentration in the PVA matrix. Remarkably, PVA-ST film-based sachets successfully improved the oxidative stability of packaged soybean oil. Our results suggest PVA-ST film containing CSE and sepiolite clay can be utilized as a novel antioxidant packaging material in the food processing industry.

Economic Evaluation on the Production of Poly-DADMAC and Sepiolite Nanocomposite

Some agricultural wastes are not suitable for direct disposal to standard sewage treatment plants and pre-treatment is required to avoid clogging by colloidal materials. One of the pre-treatment stages is coagulation and flocculation. In several studies, the mixture of polymer and clay fulfills the properties of coagulant and flocculant materials. A mixture of poly-DADMAC polymer and sepiolite clay can be used as a coagoflocculant at the same time. This study aims to analyze whether a project to manufacture clay polymer nanocomposites is feasible or not. By taking into account various perspectives including engineering and economic perspectives, this project is considered prospective to be carried out. This is indicated by the increase in the Profitability Index (PI) value of 5.33658 in the third year from -0.00975 which was the PI value the previous year. In twenty-four hours, the project can produce approximately 8.25 tonnes of adsorbent. The total profit earned in one year reaches 719,738.04 USD when run under ideal conditions. Apart from the results of the economic analysis mentioned, this project is also very effective in terms of time because it is simple and the raw materials needed are abundant

Functionalized Sepiolitic Clay Nanofibers as a Natural Ingredient in Medical Cosmetics

Medical clay also known as medicinal clay was first used in Mesopotamia around 2500 B.C and is still a relevant topic today. Among typical medical clays, sepiolite, a fibrous clay in the family of palygorskite is often ignored by cosmetic brands as it is not found abundantly in nature as much as other clays like bentonite. However, much of the world reserves of this clay are in Turkey. In this study, antibacterial sepiolite clay was prepared from nanosilver added dispersed sepiolite samples. These Ag-nanoparticles (Ag-NPs) were formed according to green synthesis under microwave heating using the additives like alginate polymer and ascorbic acid later these fibers were put through serial dilution antibacterial tests using gram +/- bacteria (ATCC 25922 and ATCC 25923) for general quality control and determining minimum inhibitory concentrations. Although the best antibacterial clay samples (Ag-NPs have theoretically 30mg/L of silver content) were washed at least five times with distilled water, it was observed that their antibacterial stability was still maintained. Finally, the morphology of sepiolite fibers smaller than 40 nm was characterized by AFM images show that highly dispersed single fibers can be used as a natural raw material and have a great opportunity in the development of new products in the cosmetic and medical sector.

Hydrophobic composite foams based on nanocellulose-sepiolite for oil sorption applications

TEMPO (2,2,6,6-tetramethylpiperidin-1-oxyl)-oxidized cellulose nanofibers (CNF) were assembled to fibrous clay sepiolite (SEP) by means of a high shear homogenizer and an ultrasound treatment followed by lyophilization using three different methods: normal freezing, directional freezing, and a sequential combination of both methods. Methyltrimethoxysilane (MTMS) was grafted to the foam surface by the vapor deposition method to introduce hydrophobicity to the resulting materials. Both the SEP addition (for the normal and directional freezing methods) and the refreezing preparation procedure enhanced the compressive strength of the foams, showing compressive moduli in the range from 28 to 103 kPa for foams loaded with 20% w/w sepiolite. Mercury intrusion porosimetry shows that the average pore diameters were in the range of 30–45 µm depending on the freezing method. This large porosity leads to materials with very low apparent density, around 6 mg/cm3, and very high porosity >99.5%. In addition, water contact angle measurement and Fourier-transform infrared spectroscopy (FTIR) were applied to confirm the foam hydrophobicity, which is suitable for use as an oil sorbent. The sorption ability of these composite foams has been tested using olive and motor oils as models of organophilic liquid adsorbates, observing a maximum sorption capacity of 138 and 90 g/g, respectively.

Sepiolite clay: A review of its applications to immobilize toxic metals in contaminated soils and its implications in soil–plant system

High reactivity, reliable properties and positive environmental impacts of sepiolite clay in environment make it an important adsorbent for soil and water applications. Present review critically evaluates the applications of sepiolite in contaminated soils to adsorb toxic metals with an emphasis on cadmium (Cd) and lead (Pb). Research data has been compiled from about 140 publications reporting lab simulation studies, greenhouse experiments, and field trials. First section of this review describes the properties of sepiolite due to their role in dictating the efficiency of this mineral. In the next sections, we evaluate research advancements on the use of sepiolite for soil decontamination with a brief description about the underlying mechanisms. The properties and remediation efficiency of sepiolite can be tuned by its modification by physical or chemical strategies. In addition to its prominent metal adsorption capacity, sepiolite has the potential to increase soil pH which reduces the metal availability in soils and uptake by plants. The impacts of sepiolite on soil properties and plant growth are illustrated in soil–plant system. This extensive review highlights the strong remediation potential of sepiolite in metal-contaminated soils and positive impacts on soil–plant​ systems. Future studies need to focus on finding suitable methods to modify sepiolite and to explore its use in composite amendments for an improved efficiency under field conditions.

Investigation of electrochemical oxidation mechanism, rapid and low-level determination for whitening cosmetic: arbutin in aqueous solution by nano sepiolite clay

Arbutin (AR) is one of the important chemical agents that has the lack of adverse effects in cosmetic applications, which has still biological importance and the increasing interest toward arbutin in the cosmetic industry. Electrochemical sensors have received much attention because of their high sensitivity, simplicity, and fast. In this work, an electroanalytical method has been developed and validated for the quantification of AR on nano sepiolite-clay carbon paste electrode. The electrochemical oxidation mechanism of AR was also investigated in the aqueous medium. Nano-sepiolite clay modified carbon paste electrode was used as rapid and the low-level electrochemical sensor for determination of AR. The electrochemical responses of AR were compared on the surfaces of the bare and nano sepiolite modified carbon paste electrode using the cyclic voltammetric method in the BR buffer solution. The results showed the superior electrocatalytic performance on the peak current of AR at the modified carbon electrode. The stripping conditions and experimental parameters (pH, the effect of modifier content, accumulation potential, and time) were optimized to obtain the best oxidation signal of AR. Under the optimized conditions, linear calibration curves were obtained in the concentration range of 0.0362–80.0 µM (with the detection limit of 10.8 nM) with square-wave adsorptive stripping voltammetry. The method was successfully applied for the determination of AR in the cosmetic Tritone cream sample. This work confirms thus that electrochemical sensors may be the potential future candidate for rapid, sensitive, low-level, and reproducible analysis.

Fabrication, morphological, structural and electrochemical characterization of sulfonated polyimide/clay-based hybrid nanocomposite membranes for energy application

Sulfonated polyimide (SPI) using 1, 4, 5, 8-Naphthalenetetracaboxylic Dianhydride was fabricated by a one-step high-temperature direct imidization method in the presence of organo-modified clay (sepiolite) as reinforcement in the polymer matrix. Different sets of SPI and clay sepiolite (in different content 1–7 wt. %) in the form of thin films were fabricated by the solution casting method. These films were cast at a temperature of 80 °C for 12 h followed by curing at 150 °C and 180 °C for 1 and 6 h, respectively. Several physicochemical parameters and analytical techniques were performed to characterize the newly fabricated nanocomposite membranes. Ion exchange capacity and hydrolytic study results showed the impact of clay content on the hydrolytic stability and morphology of hybrid membranes. Lowering in ion exchange capacity with higher hydrolytic stability was observed by increasing the clay contents in the polymeric matrix. The as-synthesized membranes were tested for its oxidative stability by Fenton reagent and observed that membrane with 5-wt (%) clay presented the maximum oxidative stability. The SPI-clay hybrid membrane with 7 wt.% of clay exhibited a water-uptake of 3.03% at 40 °C and proton conductivity of 2.45 mmol/g at 25 °C, while the pure SPI showed the values of 3.62% and 3.12 mmol/g in the same experimental conditions. FT-IR analysis investigated the structural aspects of neat SPI and all other synthesized nanocomposite membranes. The thermogravimetric analysis examined the presence of inorganic materials in the synthesized membranes along with their thermal stability profile. X-ray diffraction patterns were used to scrutinize the crystalline nature of neat sulfonated polyimide and the SPI-Clay composites membrane. In conclusion, these nanocomposite membranes can be applied as proton exchange films in fuel cells for energy application due to their interesting physicochemical, morphological, structural, and electrochemical properties.

The Hunt for Maya Purple: Revisiting Ancient Pigments Syntheses and Properties

Syntheses of analogues of historical indigo and Maya blue pigments using an inquiry-based approach are presented. Derivatives of indigo were synthesized (in particular Tyrian purple) and used as vat dyes for dyeing cotton or wool fabrics or mixed with a sepiolite clay to create new hues or colors of Maya blues using a green chemistry hydrothermal microwave synthesis. The hydrothermal approach allows a very quick preparation of Maya analogue pigments (typically 1 h) while illustrating a green chemistry approach. The obtained Maya pigments can have very different colors (or not) from their initial indigo derivative and furthermore undergo color change under annealing (thermochromism) or mechanical grinding (tribochromism). In particular, the Tyrian purple/sepiolite chromism allows a direct visual illustration for students of the structural changes in sepiolite host-matrix associated with its pores closure and water loss.