Showing papers in "Clays and Clay Minerals in 2019"

Clay Minerals in Skin Drug Delivery

Abstract: Clays have played an important role in medicine since the dawn of mankind and are still applied widely as active ingredients and/or excipients in pharmaceutical formulations Due to their outstanding properties of large retention capacity, swelling and rheological properties, and relative low cost, they have been used widely as advanced carriers for the efficient delivery of drugs by modifying their release (rate and/or time), increasing the stability of the drug, improving the dissolution profile of a drug, or enhancing their intestinal permeability In addition, recent studies have shed new light on the potential of clay minerals in the nanomedicine field due to their biocompatibility, beneficial effects of clay nanoparticles on cellular adhesion, proliferation, and differentiation Use as active ingredients and excipients are exerted via the oral and topical administration pathways Skin drug delivery represents an attractive alternative to the oral route, providing local and/or systemic drug delivery Due to their complex structures, however, most drugs penetrate the human skin only with difficulty Enormous efforts have been invested, therefore, in developing advanced drug delivery systems able to overcome the skin barrier Most strategies require the use of singular materials with new properties In particular, and on the basis of their inherent properties, clay minerals are ideal candidates for the development of intelligent skin drug delivery systems In this article, the properties of clay materials and their use in the skin-addressed pharmaceutical field are reviewed A brief introduction of skin physiology and biopharmaceutical features of penetration by a drug through the skin layers is also included and is designed to shed light on the optimum properties of ideal nanosystems for advanced skin drug delivery Special attention is devoted to the pharmacological functions of clays and their biomedical applications in pelotherapy, wound healing, regenerative medicine, antimicrobial, and dermocosmetics

NovaSil clay for the protection of humans and animals from aflatoxins and other contaminants.

Abstract: Aflatoxin contamination of diets results in disease and death in humans and animals. The objective of the present paper was to review the development of innovative enterosorption strategies for the detoxification of aflatoxins. NovaSil clay (NS) has been shown to decrease exposures to aflatoxins and prevent aflatoxicosis in a variety of animals when included in their diets. Results have shown that NS clay binds aflatoxins with high affinity and high capacity in the gastrointestinal tract, resulting in a notable reduction in the bioavailability of these toxins without interfering with the utilization of vitamins and other micronutrients. This strategy is already being utilized as a potential remedy for acute aflatoxicosis in animals, and as a sustainable intervention via diet. Animal and human studies have confirmed the apparent safety of NS and refined NS clay (with uniform particle size). Studies in Ghanaians at high risk of aflatoxicosis have indicated that NS (at a dose level of 0.25% w/w) is effective at decreasing biomarkers of aflatoxin exposure and does not interfere with levels of serum vitamins A and E, or iron or zinc. A new spinoff of this strategy is the development and use of broad-acting sorbents for the mitigation of environmental chemicals and microbes during natural disasters and emergencies. In summary, enterosorption strategies/therapies based on NS clay are promising for the management of aflatoxins and as sustainable public health interventions. The NS clay remedy is novel, inexpensive, and easily disseminated.

Natural antibacterial clays: historical uses and modern advances

Abstract: Antibacterial clays in nature include a variety of clay mineral assemblages that are capable of killing certain human pathogens. Although clays have been used for medicinal applications historically, only in the last decade have analytical methods and instrumentation been developed that allow researchers to evaluate the antibacterial mechanisms of various clays applied medicinally. Comparisons of the mineralogical and chemical compositions of natural clays that kill bacteria have promoted a better understanding of the mineral properties that are toxic to a broad-spectrum of human pathogens, including bacteria that have developed resistance to antibiotics. Popular literature is filled with reports of ‘healing’ clays, that, when tested against pathogens in vitro and compared to controls, do not appear to have bactericidal properties. It is important, however, to differentiate what properties make a clay ‘healing,’ versus what makes a clay ‘antibacterial.’ Most antibacterial clays identified to date buffer pH conditions of a hydrated clay outside the range of conditions in which human pathogens thrive (circum-neutral pH) and require oxidation reactions to occur. It is the change in oxidation state and pH imposed by the hydrated clay, applied topically, that leads to a chemical attack of the bacteria. Healing clays, on the other hand, may not kill bacteria but have soothing effects that are palliative. This article reviews some of the historical uses of clays in medicine but focuses primarily on the common characteristics of natural antibacterial clays and early studies of their antibacterial mechanisms. In this era of bacterial resistance to antibiotics, mimicking the antibacterial mechanisms exhibited by natural clays could be advantageous in the development of new antimicrobial agents.

Prediction of swelling characteristics of compacted GMZ bentonite in salt solution incorporating ion-exchange reactions

Abstract: Salt solutions have complex effects on the swelling characteristics of compacted bentonite; these effects are caused by the inhibitory action of salinity and the ion-exchange reaction between the solution and bentonite. In order to characterize the swelling properties of compacted bentonite in a salt solution, swelling deformation tests were carried out for Gao-Miao-Zi (GMZ) bentonite specimens in NaCl and CaCl2 solutions. Swelling characteristics decreased with increasing salt concentration. Swelling strains in NaCl solution were larger than those in CaCl2 solution, even though the ionic concentration of 1.0 mol/L (M) NaCl solution is larger than that of 0.5 M CaCl2. According to the exchangeable cations tests, cation exchange was different for specimens immersed in different salt solutions. The swelling fractal model was used to predict the swelling strains of compacted bentonite in a concentrated salt solution. In this model, the effective stress incorporating osmotic suction was applied to take the effect of salinity into consideration, and the swelling coefficient, K, was employed to describe the swelling properties affected by the variation in exchangeable cations. In the model, fractal dimension was measured by nitrogen adsorption, and the salt solution had little effect on fractal dimension. K was estimated by the diffuse double layer (DDL) model for osmotic swelling in distilled water. Comparison of fractal model estimations with experimental data demonstrated that the new model performed well in predicting swelling characteristics affected by a salt solution.

Effect of mechanical activation on the pozzolanic activity of muscovite

Abstract: In order to provide a theoretical foundation for the utilization of tailings as supplementary cementitious materials, the pozzolanic activity of muscovite—a typical mineral phase in tailings—before and after mechanical activation was investigated. In this study, significant pozzolanic activity of muscovite was obtained as a result of the structural and morphological changes that were induced by mechanical activation. The activated muscovite that was obtained after mechanical activation for 160 min satisfies the requirements for use as an active supplementary cementitious material, and the main characteristics of the pozzolana were as follows: median particle size (D50) of 11.7 μm, BET specific surface area of 28.82 m2 g−1, relative crystallinity of 14.99%, and pozzolanic activity index of 94.36%. Continuous grinding led to a gradual reduction in the relative crystallinity and an increase in the pozzolanic activity index due to the dehydroxylation reaction induced by mechanical activation, which occurred despite the fact that the specific surface area showed a decreasing trend when the grinding time was prolonged. Mechanically activated muscovite exhibited the capacity to react with calcium hydroxide to form calcium silicate hydrate, which is a typical characteristic of pozzolana. This experimental study provided a theoretical basis for evaluating the pozzolanic activity of muscovite using mechanical activation.

Eighteen years of steel–bentonite interaction in the FEBEX in situ test at the Grimsel Test Site in Switzerland

Abstract: Corrosion of steel canisters containing buried high-level radioactive waste is a relevant issue for the long-term integrity of repositories. The purpose of the present study was to evaluate this issue by examining two differently corroded blocks originating from a full-scale in situ test of the FEBEX bentonite site in Switzerland. The FEBEX experiment was designed initially as a feasibility test of an engineered clay barrier system and was recently dismantled after 18 years of activity. Samples were studied by ‘spatially resolved’ and ‘bulk’ experimental methods, including Scanning Electron Microscopy, Elemental Energy Dispersive Spectroscopy (SEM-EDX), μ-Raman spectroscopy, X-ray Fluorescence (XRF), X-ray Diffraction (XRD), and 57Fe Mossbauer spectrometry, with a focus on Fe-bearing phases. In one of the blocks, corrosion of the steel liner led to diffusion of Fe into the bentonite, resulting in the formation of large (width > 140 mm) red, orange, and blue colored halos. Goethite was identified as the main corrosion product in the red and orange zones while no excess Fe2+ (compared to the unaffected bentonite) was observed there. Excess Fe2+ was found to have diffused further into the clay (in the blue zones) but its speciation could not be unambiguously clarified. The results indicate the occurrence of newly formed octahedral Fe2+ either as Fe2+ sorbed on the clay or as structural Fe2+ inside the clay (following electron transfer from sorbed Fe2+). No other indications of clay transformation or newly formed clay phases were found. The overall pattern indicates that diffusion of Fe was initiated when oxidizing conditions were still prevailing inside the bentonite block, resulting in the accumulation of Fe3+ close to the interface (up to three times the original Fe content), and continued when reducing conditions were reached, allowing deeper diffusion of Fe2+ into the clay (inducing an increase of 10–12% of the Fe content).

Surfactant-modified clay sorbents for the removal of p-nitrophenol.

Abstract: Organic pollutants are widespread and a known problem for the environment. p-nitrophenol (PNP) is one such pollutant found in effluents from various industries involved with pesticides, pharmaceuticals, petrochemicals, plastic, paper, and other materials. The objective of this research was to prepare and test organically modified clays using four different surfactants and to evaluate the removal efficiency of PNP from aqueous solutions. Organically modified clays have attracted great interest due to their wide applications in industry and environmental protection as sorbents for organic pollutants. Two natural smectite-dominated clay types from outcrops in Latvia and Lithuania as well as industrially manufactured montmorillonite (Mt) clay were modified using different nonionic (4-methylmorpholine N-oxide (NMO) and dimethyldodecylamine N-oxide (DDAO)) and cationic (benzyltrimethyl ammonium chloride (BTMAC) and dodecyltrimethyl ammonium chloride (DTAC)) surfactants. Modified clay materials were characterized by Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and the Brunauer-Emmett-Teller method (BET) for surface area analysis. Sorption of PNP was investigated under various conditions, e.g. surfactant loading, initial PNP concentration, contact time, and pH. The novelty of the present study was to prepare innovative organo-sorbents based on manufactured as well as natural clay samples using cationic surfactants and nonconventional nonionic surfactants as modifiers. The sorption data combined with FTIR and XRD supplementary results suggests that nonionic organo-clay (Mt-DDAO_2) is the most effective sorbent and may serve as a low-toxicity immobilizer of pollutants such as phenols.

Removal Efficiency of Basic Blue 41 by Three Zeolites Prepared from Natural Jordanian Kaolin

Abstract: The conventional method of zeolite synthesis involves an expensive hydrothermal step whereby a mixture of a metakaolinite, sodium hydroxide, and water is preactivated by thermal treatment between 400°C and 1000°C. The objective of the current study was to determine whether Jordanian kaolinite could be converted to zeolite materials without thermal pre-activation. The alkaline hydrothermal transformation of kaolinite into hydroxysodalite (HS) was achieved, then followed by a reaction with citric acid and solid sodium hydroxide to obtain Zeolite A, or by adding solid Na2SiO3 to prepare zeolite X. These materials were tested for their ability to serve as removal agents for Basic Blue 41 (BB-41) dye from artificially contaminated water, at concentrations ranging from 25 to 1000 mg/L. The maximum removal capacities were estimated using the Langmuir model, with a value of 39 mg/g for hydroxysodalite. Zeolite-X achieved the lowest value (19 mg/g). The feasibility of BB-41 removal was deduced from the Freundlich model for the zeolites studied. The reported low-cost method is proposed as an alternative way to reduce the cost of synthesizing zeolite, and the materials were shown to be potential candidates for the removal of BB-41 dye.

Clay-based biohybrid materials for biomedical and pharmaceutical applications

Abstract: Clays have traditionally been linked to health care, being used for centuries in the fight against infections and diseases. Similarly, biohybrids produced by combinations of clays and biological species through ‘bottom-up’ approaches have been evaluated over the past decade for biomedical and pharmaceutical uses. These biohybrids show interesting features such as biocompatibility and biodegradability which make them suitable for healthcare applications. The aim of the present communication was to review recent research contributions describing progress and the role of biohybrid materials based on clays in biomedicine and pharmacy disciplines. Emphasis will be on the authors’ own experience of this topic, particularly on aspects related to controlled drug-delivery systems, adjuvants of vaccines, and vectors for non-viral gene transfection. Bionanocomposites offer several advantages for use in the design of new and efficient pharmacological formulations for cutaneous and oral administration. In these systems, the drug is typically entrapped in the clay and protected by a biopolymer matrix, and both components contribute to a gradual release of the drug. Clay-based hybrids have also shown their efficacy in vaccines as they can act as nanocarriers of viral particles, due to the biomimetic interface created on the clay surface after adsorption of suitable biomolecules such as phospholipids, while the clay acts as an adjuvant to increase the efficacy of the vaccine. Finally, a new application of clays as non-viral vectors for controlled gene delivery is attracting increasing interest in the treatment of diverse diseases; clays such as sepiolite have demonstrated their ability to act as nanocarriers of nucleic acids and facilitate their transfection in mammalian cells.

The Interaction between Surfactants and Montmorillonite and its Influence on the Properties of Organo-Montmorillonite in Oil-Based Drilling FluIDS

Abstract: The increasing demands for oil and gas and associated difficult drilling operations require oil-based drilling fluids that possess excellent rheological properties and thermal stability. The objective of the present work was to investigate the rheological properties and thermal stability of organo-montmorillonite (OMnt) modified with various surfactants and under various loading levels in oil-based drilling fluids, as revealed by the interaction between organic surfactants and montmorillonite. The influence of the structural arrangement of surfactants on the thermal stability of organo-montmorillonite (OMnt) in oil-based drilling fluids was also addressed. OMnt samples were prepared in aqueous solution using surfactants possessing either a single long alkyl chain two long alkyl chains. OMnt samples were characterized by X-ray diffraction, high-resolution transmission electron microscopy, thermal analysis, and X-ray photoelectron spectroscopy. Organic surfactants interacted with montmorillonite by electrostatic attraction. The arrangements of organic surfactants depended on the number of long alkyl chains and the geometrical shape of organic cations. In addition to the thermal stability of surfactants, intermolecular interaction also improved the thermal stability of OMnt/oil fluids. A tight paraffin-type bilayer arrangement contributed to the excellent rheological properties and thermal stability of OMnt/oil fluids. The deterioration of rheological properties of OMnt/oil fluids at temperatures up to 200°C was due mainly to the release of interlayer surfactants into the oil.

Iron Mineralogy and Magnetic Susceptibility of Soils Developed on Various Rocks in Western Iran

Abstract: The characterization of magnetic minerals and the relationship of these minerals to the magnetic susceptibility of soils that have developed on various parent materials can provide valuable information to various disciplines, such as soil evolution and environmental science. The aim of the study reported here was to investigate variations in the magnetic susceptibility (χ) of soils in western Iran due to differences in lithology and to examine the relationship of χ to ferrimagnetic minerals. Eighty samples were collected from eight parent materials taken from both intact rocks and associated soils. The soil parent materials included a range of igneous and sedimentary rocks, such as ultrabasic rocks (Eocene), basalt (Eocene), andesite (Eocene), limestone (Permian), shale (Cretaceous), marl (Cretaceous), and the Qom formation (partially consolidated fine evaporative materials, early Miocene). The 80 samples were analyzed for χ using a dual-frequency magnetic sensor and for mineralogy using X-ray diffraction (XRD). The highest χ values were found in the ultrabasic rocks and associated soils, while the lowest χ values were observed in the limestone rocks and associated soils. The pedogenic processes significantly enhanced the χ values of soils developed on the sedimentary rocks due to the formation of ferrimagnetic minerals. In contrast, χ values decreased as a result of pedogenic processes in soils developed on igneous rocks due to the dilution effects of diamagnetic materials, such as halite, calcite, phyllosilicates, and organic matter. The significant positive correlation between the XRD peak intensity of the maghemite/magnetite particles and χ values confirmed that χ values in soils are largely controlled by the distribution and content of ferrimagnetic minerals. These results show that χ measurements can be used to quantify low concentrations of ferrimagnetic minerals in the soils of semiarid regions.

Modifying layered double hydroxide nanoparticles for tumor imaging and therapy

Abstract: Tumor theranostics (a portmanteau of therapeutics and diagnostics) is now achieved in various ways with complex nanoparticle systems. Layered double hydroxide (LDH) nanoparticles are effective at drug/gene delivery and as imaging agents in potential tumor theranostics. This mini-review paper summarizes recent progress in developing LDH nanoparticles as a pH-sensitive magnetic resonance imaging (MRI) contrast agent, as a positron emission tomography (PET) imaging agent, and as a co-delivery platform for two therapeutic agents for tumor diagnosis and therapy. These results have indicated clearly the potential application of LDH nanoparticles for simultaneous diagnosis and treatment of cancers.

Bentonite/Magnetite Composite for Removal of Nitrofurazone

Abstract: The presence of pharmaceutical pollutants in the environment is one of the most pressing environmental problems. Adsorption from solution is an effective way to remove pharmaceuticals from liquid media, but the problem then is to separate the adsorbent from the liquids. The objective of the present study was to remove nitrofurazone from aqueous solutions using a bentonite/magnetite composite, prepared by co-precipitation of magnetite with bentonite, which could then be collected by magnetic separation. The bentonite/magnetite composite was characterized using diverse techniques, such as X-ray diffraction, scanning electron microscopy, low-temperature N2 adsorption/desorption, laser diffraction, and magnetization measurements. The particle size of the composite material did not exceed 50 μm and the particle size distribution was mono-modal with a maximum at 3.2 μm. The strong hysteresis in the magnetization curve revealed that the bentonite/magnetite particles were ferromagnetic. Adsorption of nitrofurazone by the bentonite/magnetite composite from aqueous solutions was measured and the amount of nitrofurazone adsorbed was 3.2×10–2 mmol/g. The adsorption kinetics of nitrofurazone to the bentonite/magnetite composite followed a pseudo-second-order kinetics equation. Upon adsorption, hydrogen bonds were formed between the amide groups of nitrofurazone and oxygen groups in bentonite.

Synthesis and Adsorption Desulfurization Performance of Modified Mesoporous Silica Materials M-MCM-41 (M = Fe, Co, Zn)

Abstract: Adsorption desulfurization is a potential new method for deep desulfurization of fuel oil. The development of adsorbents with high adsorption capacity and selectivity is the core of deep adsorption desulfurization. The adsorption behavior of thiophene in MCM-41 mesoporous materials modified by various metal ions was studied in order to understand the adsorption desulfurization process of molecular sieves. The Fe-, Co-, and Zn-modified MCM-41 materials were prepared using a one-step in situ hydrothermal synthesis method. The modified MCM-41 molecular sieves maintained the mesoporous structure, and the metal ions had specific dispersion on the surface of the molecular sieves. Adsorption of thiophene on the surfaces of molecular sieves had both physical and chemical characteristics. The adsorption desulfurization performance of the modified molecular sieve was superior to that of the pure silica molecular sieve. In the simulated gasoline with sulfur content of 220 μg/g, when the amount of adsorbent used was 100 mg, the adsorptive desulfurization performance tended to be in equilibrium, and the optimum adsorption temperature was 30°C. Fe-MCM-41 and MCM-41 molecular sieves reached adsorption equilibrium after ~60 min, but the desulfurization rate of Co-MCM-41 and Zn-MCM-41 still increased slightly. The kinetic simulation results indicated that the pseudo-second-order kinetics adsorption model described well the adsorption process of thiophene on molecular sieves. The molecular sieve Fe-MCM-41 had the best desulfurization performance with an equilibrium adsorption capacity of 14.02 mg/g and the desulfurization rate was ~90%.

The Influence of Clays on Human Health: a Medical Geology Perspective

Abstract: Clay is unique especially from the perspective of medical geology, that is, the impacts of geologic materials and geologic processes on animal and human health. Clay is the only natural material that can impact human health through all routes of exposure: ingestion, inhalation, and dermal contact. Moreover, these impacts can be harmful as well as beneficial. Ingestion of clay, a form of geophagy, has been practiced for millennia and is still widely practiced today. Humanoids have been ingesting clay for at least two million years to ease indigestion and counteract poisons. Some additional benefits may accrue from eating clays such as providing some nutrients but these benefits are far outweighed by the likely negative consequences such as tissue abrasion, intestinal blockage, anemia, exposure to pathogens and toxic trace elements, and potassium overdose. Inhalation of airborne minerals including clays has impacted the heath of millions. In the 1930s thousands of people living in the Dust Bowl in the U.S. southwest inhaled copious amounts of clay contributing to deadly ‘dust pneumonia.’ Using clay as a poultice to stem bleeding and cure certain skin ailments is an age-old practice that still has many adherents. A classic recent example of the antibacterial properties of clay is the use of certain clays to cure Buruli ulcer, a flesh eating disease. However, walking barefoot on clays in certain volcanic soils can result in non-filarial podoconiosis or elephantiasis. The absence of clays in soils can have serious health consequences. In South Africa, clay-poor soils yield crops lacking in essential nutrients and may be the principal cause of Msileni joint disease. Clearly, a detailed knowledge of the clays in the environment can have significant benefits to human health and wellbeing.

Photocatalytic Degradation of Methylene Blue Over Layered Double Hydroxides Using Various Divalent Metal Ions

Abstract: To apply hydrotalcites more effectively to the problem of dye wastewater, the effects of divalent metal ions on the structure and stability of hydrotalcites, especially on their photocatalytic activity, were compared. In the present study, M/Cr hydrotalcites (M3Cr-CO3-LDHs) (in which M = Mg, Co, Ni, Cu, Zn), where the M/Cr molar ratio was 3, were prepared by the co-precipitation method. The structures and properties were characterized using powder X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric-differential thermal analysis (TG-DTA), and UV-Visible diffuse reflectance spectroscopy (UV-Vis DRS). The results showed that five kinds of M3Cr-CO3-LDHs were synthesized successfully, and the layered structure of the samples obtained was regular and the crystal phase was single. When methylene blue (MB) solution was exposed to ZnCr-CO3-LDHs, H2O2, and visible light irradiation, more than 90.67% of the methylene blue (MB) was removed after 140 min. The photocatalytic activity of the samples was in the order: Co3Cr-CO3-LDHs > Mg3Cr-CO3-LDHs > Cu3Cr-CO3-LDHs > Zn3Cr-CO3-LDHs > Ni3Cr-CO3-LDHs. The results of a catalytic mechanism study showed that photocatalytic degradation of MB involved a demethylation reaction, with the reactive species containing •O2-, •OH, and h+.

Geology, Mineralogy, Geochemistry, and Genesis of Bentonite Deposits in Miocene Volcano–Sedimentary Units of the Balikesir Region, Western Anatolia, Turkey

Abstract: The widespread Balikesir bentonite deposits within the Miocene volcano-sedimentary units in western Anatolia have economic potential; they are important raw materials for the paper and bleaching industries in Turkey. No detailed geological, mineralogical, geochemical, or genesis characterizations of these bentonite deposits have been carried out to date. The present study was undertaken to close this gap. The mineralogical characteristics of the bentonites and their parent rocks were examined using polarized-light microscopy, X-ray powder diffractometry (XRD), scanning- and transmission-electron microscopies (SEM–EDX and TEM), and chemical (ICP–AES and –MS) methods. In the bentonite deposits, smectite is associated with smaller amounts of illite, chlorite, quartz, feldspar, dolomite, calcite, opal-CT, and amphibole. The smectite was identified by sharp basal reflections at 14.42–14.93 A. Plagioclase and sanidine crystals in volcanic units are altered and sericitized. Biotite and hornblende are partly to completely Fe-(oxyhydr)oxidized and chloritized. Smectite flakes occur on altered feldspar and mica grains and devitrified volcanic glass fragments in association with or without calcite ± dolomite crystals. Increasing Al+Fe+Mg/Si ratios with increasing degree of alteration reveal that hydration of volcanogenic grains (feldspar, mica, hornblende, glass shard) favored precipitation of smectite with montmorillonite composition, with an average structural formula: (Ca0.31Na0.05K0.08)(Al2.72Fe0.17Mg1.27Ti0.011Mn0.01)(Si7.94Al0.06)O20(OH)4. The concentration of Al2O3 and MgO and increase of LREE/HREE ratio, and a distinct, negative Eu anomaly show that smectite was probably formed as a result of the decomposition of volcanic feldspar, mica, amphibole, and volcanic glass. Association of carbonate rocks within the smectite-rich material and the absence of chlorite and detrital materials such as rock fragments in the bentonites suggest that the bentonite deposits formed authigenetically as ‘primary bentonites’ from volcanoclastic materials deposited in a calm lacustrine–palustrine environment during an early diagenetic process.

Giant multistep crystalline vs. osmotic swelling of synthetic hectorite in aqueous acetonitrile

Abstract: Intercalation of large organocations into 2:1 clay minerals may be hampered by two problems: on one hand, the solubility of organocations in water is limited and the resulting high selectivity for adsorption in the polar solvent may lead to non-equilibrium structures. On the other hand, the large expansion of the interlayer space will slow down kinetics of ion exchange considerably. The best workaround for these obstacles is to suspend the clay minerals in mixtures of water with more hydrophobic organic solvents that nevertheless trigger a considerable expansion of the interlayer space by swelling. This in turn fosters ion exchange. The current study, therefore, revisited pioneering work by Bradley (1945) and investigated the swelling behavior of synthetic sodium hectorite (Na-hec) as a function of the composition of the swelling solvent, a mixture of acetonitrile and water. Up to a maximum acetonitrile content of 65 vol.%, delamination by osmotic swelling occurred. At even higher acetonitrile concentrations, swelling was limited to the crystalline swelling regime where a step-like adjustment of the d value was observed. Several mixtures were identified yielding a well defined and uniform interlayer height as evidenced by rational 00l-series with the d spacing decreasing with increasing acetonitrile content. Surprisingly, for a specific acetonitrile:water ratio even an ordered interstratification of two strictly alternating interlayer heights with distinctly different solvent compositions was observed.

Vectorized Clay Nanoparticles in Therapy and Diagnosis

Abstract: Over the past several decades, clay minerals have been applied in various bio-fields such as drug and drug additives, animal medicine and feed additives, cosmetics, biosensors, etc. Among various research areas, however, the medical application of clay minerals is an emerging field not only in academia but also in industry. In particular, cationic and anionic clays have long been considered as drug delivery vehicles for developing advanced drug delivery systems (DDSs), which is the most important of the various research fields including new drugs and medicines, in vitro and in vivo diagnostics, implants, biocompatible materials, etc., in nanomedicine. These applications are obviously related to global issues such as improvements in welfare and quality of life with life expectancy increasing. Many scientists, therefore, in various disciplines, such as clay mineralogy, material chemistry, molecular biology, pharmacology, and medical science, have been endeavoring to find solutions to such global issues. One of the strategic approaches is probably to explore new drugs possessing intrinsic therapeutic effects or to develop advanced materials with theranostic functions. With this is mind, discussions of examples of cationic and anionic clays with bio- and medical applications based on nanomedicine are relevant. In this tutorial review, nanomedicine based on clay minerals are described in terms of synthetic strategies of clay nanohybrids, in vitro and in vivo toxicity, biocompatibility, oral and injectable medications, diagnostics, theranosis, etc.

Medicine Beneath Your Feet: A Biocultural Examination of the Risks and Benefits of Geophagy

Abstract: Geophagy is the intentional consumption of earth. Although widely documented among vulnerable populations, including children and pregnant women, the causes and consequences of geophagy remain poorly understood. Relevant literature was, therefore, reviewed to describe geophagy across species, geographies, life stages, and disease states. After a brief consideration of hypothesized etiologies, the potential harmful and beneficial consequences of geophagy are described, considering current evidence for each. Data available to date suggest that the greatest potential risks of geophagy include toxicity or heavy metal poisoning, and diseases resulting from consumed clays binding nutrients and beneficial pharmaceuticals in the gut. Evidence also suggests that geophagy may be beneficial by protecting against harmful pathogens and toxins through two distinct physiological pathways. Future research should explore causal relationships between geophagy and iron deficiency, as well as investigate the biological and psychosocial conditions that govern geophagy.

Characterization of altered mica from sokli, northern finland

Abstract: Vermiculite is a mineral with many potential uses in various industrial areas, such as in insulation, horticulture, and environmental applications. The regolith of the Sokli carbonatite intrusion in northern Finland consists of weathered micas which reportedly contain vermiculite. The aim of the present study was to characterize the weathered mica in order to determine if the weathered regolith contains vermiculite. If so, the value of the apatite-rich Sokli intrusion may increase, because the vermiculite could be classified as an ore in Sokli. For the characterization, mica fractions were investigated using electron probe microanalysis (EPMA), X-ray diffraction (XRD), and thermogravimetric analysis (TGA). The EPMA results show that the potassium (K2O) content of the mica investigated varies between 6.20 and 0.31 wt.%. The XRD results provided evidence that the interlayer distances in the mica vary between 10.1 and 14.7 A. The TGA shows that the dehydration of the samples varies between 6 and 12 wt.% for temperatures up to 170°C. Dehydroxylation takes place in three steps, as is characteristic for vermiculite. The results from this study revealed that mica in the weathered parts of the Sokli carbonatite is mostly vermiculite, and that the vermiculite was formed by the weathering of phlogopite. These results can be used to determine whether vermiculite is a possible future commodity at the Sokli carbonatite complex.

Simultaneous Immobilization of Zn(II) and Cr(III) in Spinel Crystals from Beneficial Utilization of Waste Brownfield-Site Soils

Abstract: Waste brownfield-site soils contaminated with heavy metals such as Zn and Cr are of critical environmental concern because of the rapid urbanization and industrialization that is occurring in China. Thermal treatment can fix heavy metals in specific mineral structures, which might be a promising technology for remediation and reutilization of the metal-contaminated soils. The objective of the present study was to elucidate the stabilization mechanisms of Zn and Cr through thermal treatment of mixtures of ZnO + Cr2O3 to form ZnCr2O4 and to confirm that Zn and Cr were incorporated simultaneously into the spinel structure. The incorporation efficiency for Zn was quantified, with the value ranging from 70.6 to 100% over the temperature range 700–1300°C. Leaching results further confirmed that ZnCr2O4 spinel was a superior product for Zn and Cr immobilization. Then, by artificially sintering Zn- and Cr-enriched soils, both Zn and Cr were immobilized effectively (with three orders of magnitude reduction in Zn leachability) in the ZnCr2O4 spinel as the predominant product phase. In addition, multiple heavy metals such as Zn, Cu, and Cr in the actual brownfield-site soils were well immobilized after sintering, which confirmed the potential for practical application of the thermal treatment technology utilized in this study.

Effect of Hydration on Polytypism and Disorder in the Sulfate-Intercalated Layered Double Hydroxides of Li and Al

Abstract: The double hydroxide of Li+ and Al3+ is an anionic clay comprising positively charged metal hydroxide layers and intercalated anions. While the structure of the iono-covalently bonded metal hydroxide layer is well known, relatively less knowledge is available regarding the manner in which the anions and water molecules are packed in the interlayer region. The sulfate ion is of special interest as it can potentially intercalate in a multiplicity of orientations and grow an extended hydration sphere. The sulfate-intercalated double hydroxide was synthesized by the imbibition of Li2SO4 into both the gibbsite and bayerite forms of Al(OH)3 to obtain layered double hydroxides with the nominal formula Li2Al4(OH)12SO4·nH2O (n = 4–8). The as-prepared compounds were poorly ordered and did not yield any structural information. Temperature-induced partial dehydration yielded ordered phases of different structures in the two systems. Simulation of the powder patterns of different model structures, followed by structure refinement in both direct and reciprocal spaces, showed that the gibbsite-derived phase yielded a two-layer polytype of hexagonal symmetry (space group P63/m). The local symmetry of the sulfate ion was close to D2d with one of the C2 axes of the SO42− being nearly parallel to the c axis of the crystal. The bayerite-derived phase yielded a one-layer polytype of monoclinic symmetry (space group C2/m). The sulfate ion was oriented with its C3 axes tilted away from the stacking direction. Cooling and rehydration (relative humidity ~70%) resulted in a reversible expansion of the basal spacing due to the ingress of water molecules from the ambient humidity into the interlayer region. Hydration in both cases resulted in turbostratic disorder. The disorder in the bayerite-derived phase was a result of random intergrowth of motifs with rhombohedral and monoclinic symmetries.

Competitive Adsorption of Uranyl and Toxic Trace Metal Ions at MFe2O4-montmorillonite (M = Mn, Fe, Zn, Co, or Ni) Interfaces

Abstract: Adsorption of uranyl (UO22+) ions to mineral surfaces is a potentially effective method for removing this hazardous metal from water, but other toxic trace metal ions (Xn+: Rb+, Sr2+, Cr3+, Mn2+, Ni2+, Zn2+, Cd2+) in uraniferous wastewaters compete with UO22+ for adsorption sites and thus may diminish the capacity of adsorbents to sequester UO22+. A better understanding of competitive adsorption among these metal ions and the development of better adsorbents are, therefore, of critical importance. The purpose of the present study was to synthesize and characterize magnetic adsorbents, consisting of MFe2O4 (M = Mn, Fe, Zn, Co, or Ni) nanoparticles synthesized on montmorillonite (Mnt) edge sites, and to investigate their use as adsorbents for UO22+, including competitive adsorption with trace metal ions. Selective adsorption was studied using Langmuir, Freundlich, and Dubinin-Radushkevich isotherms, and the results showed that Xn+ ions were adsorbed primarily on MFe2O4-montmorillonite surfaces, and the UO22+ ions were adsorbed on the interfaces between montmorillonite edge surfaces and MFe2O4 nanoparticles. Using the Freundlich model, the interface adsorption capacity of UO22+ reached 25.1 mg·g–1 in mixed solution. Further, the UO22+ and Cr3+ ions had a redox reaction on the interfaces with synergistic adsorption. Herein, the adsorption capacity of Cr3+ was 60.2 mg·g–1 using the Freundlich isotherm. The results demonstrated that the MFe2O4-montmorillonite with highly selective adsorption of UO22+ ions is applicable to UO22+ treatment in the presence of toxic trace metal ions.

Grafted Sepiolites for the Removal of Pharmaceuticals in Water Treatment

Abstract: The increased detection of pharmaceuticals in finished drinking water has become a growing cause of concern in recent years. The removal of atenolol, ranitidine, and carbamazepine by sepiolite, following functionalization of its surface by organosilane grafting, constituted the subject of this investigation. Silylated surfaces include octyl, γ-aminopropyl, 3-chloropropyl, and triphenyl moieties. The sorption of atenolol and ranitidine was higher on sepiolite functionalized with 3-chloropropyl, while carbamazepine showed a higher sorption on sepiolite with triphenyl groups. Filtration experiments of both ranitidine and carbamazepine on octyl- and triphenyl-sepiolite, respectively, showed a higher retention of ranitidine in comparison to carbamazepine, in spite of the fact that the number of sorption sites was lower due to its higher binding rate.

Preparation of a Hierarchical Pore Zeolite with High-Temperature Calcination and Acid-Base Leaching

Abstract: Microporous structure in zeolite leads to diffusion limitation, which causes coke formation and is harmful to catalytic reactions. Hierarchical zeolite containing primary microporosity and secondary porosity at the meso- and macroscales has received much attention due to its enhanced mass transport. Hierarchical Y zeolites were obtained by treating NH4-Y zeolite with high-temperature calcining and acid-base leaching. The results demonstrated that the calcined zeolite showed great crystallinity after acid-base leaching. The mechanism of introduction of mesopores was demonstrated in detail. The calcination transformed framework Al to extra-framework Al and enlarged the defect by acid and alkali. The mesopores increased with the calcining temperature and holding time. The relationship between the heating rate and the removal of Al species was non-linear; a heating rate of 100°C/h exhibited good protection for the zeolite structure.

Photo-assisted Catalytic Removal of NOx Over La1–xPrxCoO3/Palygorskite Nanocomposites: Role of Pr Doping

Abstract: Photo-assisted selective catalytic reduction (photo-SCR) has been considered as a promising strategy for NOx removal in recent decades. The purpose of the present work was to test the effectiveness of La1–xPrxCoO3, supported on the surface of natural palygorskite (Pal) by a facile sol-gel method, as a photo-SCR for the removal of NOx from wastewaters. The structure, acidity, and the redox property of the prepared La1–xPrxCoO3/Pal nanocomposite were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV-Visible diffuse reflectance spectroscopy (UV-Vis DRS), and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) calculations were employed to determine the valence bands. The La1–xPrxCoO3/Pal catalysts were then tested for SCR removal of NOx with the assistance of photo-irradiation. The photo-SCR results revealed that the NOx conversion and the N2-selectivity were greatly improved by this method and reached >95% when carried out at the relatively low temperature of 200°C and with the Pr doping at x = 0.5. The improvements were attributed to the co-precipitation of a PrCoO3 phase as in a solid solution forming a coherent heterojunction of PrCoO3/La0.5Pr0.5CoO3 on the Pal surface.

Synthesis, structure, and ferroelectricity of a kaolinite-p--aminobenzamide intercalation compound

Abstract: The construction of organic-inorganic hybrid ferroelectric materials with larger, high-polarity guest molecules intercalated in kaolinite (K) faces difficulties in terms of synthesis and uncertainty of structure-property relationships. The purpose of the present study was to optimize the synthesis method and to determine the mechanism of ferroelectric behavior of kaolinite intercalated with p-aminobenzamide (PABA), with an eye to improving the design of intercalation methods and better utilization of clay-based ferroelectric materials. The K-PABA intercalation compound (chemical formula Al2Si2O5(OH)4∙(PABA)0.7) was synthesized in an autoclave and then characterized using X-ray diffraction (XRD), infrared spectroscopy (IR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The experimental results showed that PABA expanded the kaolinite interlayer from 7.2 A to 14.5 A, and the orientation of the PABA molecule was ~70° from the plane of the kaolinite layers. The amino group of the PABA molecule was close to the Si sheet. The presence of intermolecular hydrogen bonds between kaolinite and PABA and among PABA molecules caused macro polarization of K-PABA and dipole inversion under the external electric field, resulting in K-PABA ferroelectricity. Simulation calculations using the Cambridge Sequential Total Energy Package (CASTEP) and the ferroelectricity test revealed the optimized intercalation model and possible ferroelectric mechanism.

On the thermodynamic stability of illite and i-s minerals

Abstract: A review of the models proffered to advance the notion of the metastability of illite shows that these models are not supported by the various data groups that have become available. Given that clay minerals are products of water–rock interactions, low-temperature hydrothermal experiments provide singular insights into their relative stabilities; such experiments with natural materials of contrasting pedigree (illites, sericites, muscovites, and chlorites) show that clay-mineral behaviors in low-temperature hydrothermal solutions are amenable to equilibrium thermodynamic conventions. The data from hydrothermal experiments coupled with data from geothermal fields indicate that muscovite is not a stable phase in the P-T-X range in which authigenic illite occurs; given that experimental data and field occurrence suggest that muscovite and illite have different P-T stability regimes, the continued use of muscovite as a proxy for illite in thermodynamic models is of questionable utility. Furthermore, morphometric studies of clays undergoing illitization show that crystal-size distributions exhibit log-normal patterns. Because log-normal distributions derive from maximum entropy effects, these crystal-size distributions may reflect the effects of entropy production during crystallization rather than kinetically driven Ostwald ripening of illitic phases; the small crystal size of clay minerals may derive from constraints imposed by the physicochemical conditions of their environments of formation. Presumably, irreversible thermodynamics provides the framework for a quantitative understanding of the evolution of complex clay minerals in space and time.

A New Kaolin Deposit in Western Africa: Mineralogical and Compositional Features of Kaolinite from Caluquembe (Angola)

Abstract: Large kaolin deposits developed by weathering on Precambrian granitic rocks have been discovered in the Caluquembe area, Huila province, Angola. To determine accuracy of analysis and to evaluate the kaolinite grade, a full-profile Rietveld refinement by X-ray Powder Diffraction (XRPD) and Thermal Gravimetric Analysis (TGA) was used. Caluquembe kaolin is composed mainly of kaolinite (44–93 wt.%), quartz (0–23 wt.%), and feldspar (4–14 wt.%). The Aparicio-Galan-Ferrell index (AGFI), calculated by XRPD profile refinement, indicates low- and medium-defect kaolinite. Kaolinite particles show a platy habit and they stack together forming ‘booklets’ or radial aggregates; they also occur as small anhedral particles in a finer-grained mass. Muscovite-kaolinite intergrowths have also been found. Whole-rock chemical analysis included major, trace, and Rare Earth Elements (REE). Chondrite-normalized REE patterns show the same tendency for all samples, with a significant enrichment in Light Rare Earth Elements (LREE). Mineralogical and compositional features of the Caluquembe kaolin indicate that it is a suitable material for the manufacture of structural products, such as bricks, paving stones, and roofing tiles. In addition, the significant REE contents of the Caluquembe kaolin can be considered as a potential future target of mining exploration.