Semiconductor photocatalysis has been regarded as one of the most promising methods for treatment of Cr(VI)-containing wastewater, but the high recombination rate of photogenerated carriers and photocorrosion have limited severely its practical application. The objective of the current study was to employ a layered double hydroxide (LDH) to mitigate these problems by designing and constructing a multiple heterojunction system of g-C3N4/LDH/Ag3PO4 (CNLDHAP) through a two-step hydrothermal route. The structures, morphologies, chemical states, and optical properties of the products were investigated systematically. The CNLDHAP composite showed superior photocatalytic activity for Cr(VI) reduction than that of the individual components under visible-light irradiation. The composite exhibited high photocatalytic reduction stability after five recycles. The enhanced photocatalytic performance may originate from the very efficient separation of photogenerated carriers of the multiple heterojunction system. Possible photocatalytic mechanisms for the reduction of Cr(VI) over the CNLDHAP composite photocatalyst are proposed.

The overuse of antibiotics in medicine has led to concerns over management of wound infections where antibiotic-resistant bacteria are involved. Wound infections exhibit both acquired and biofilm-associated antibiotic resistance; innovative non-antibiotic therapeutic and preventive treatments are needed to limit emergence of conventional antimicrobial resistance and to address biofilm-associated resistance. Toward this goal, natural antibacterial clays have been identified that are effective at killing drug-resistant human pathogens in planktonic and biofilm states, in vitro. To move toward clinical testing of antibacterial clays, the present study was conducted to evaluate the topical application of a natural antibacterial clay to wounds in mice experimentally infected with methicillin-resistant Staphylococcus aureus (MRSA). Five preliminary animal trials were conducted to test various methods of applying hydrated antibacterial clay to infected wounds. None of the experiments yielded significantly reduced MRSA infection in vivo, compared to controls. Several hypotheses were tested to explore the diminished clay antibacterial activity in vivo including: (1) pH and Eh of mineral-bacterial suspensions may differ in wound fluids compared to growth media; (2) antibacterial reactants may complex with components of the wound; (3) hydrated clays may dry out in the wound; and (4) limited dissolved oxygen may reduce Fenton reactions. Ancillary in vitro tests were performed to explore these hypotheses. Results indicate that the clay application to wounds may require enhanced oxidation and possibly a longer treatment regimen. The experimental results foster understanding of the natural clay–bacterial interactions in wounds and may improve designs for medicinal applications.

Water is essential for humans, animals, and plants; pollutants, usually derived from anthropogenic activities, can have a serious effect on its quality. Heavy metals are significant pollutants and are often highly toxic to living organisms, even at very low concentrations. Among the numerous removal techniques proposed, adsorption onto suitable adsorbent materials is considered to be one of the most promising. The objective of the current study was to determine the effectiveness of halloysite nanotubes (HNT) functionalized with organic amino or thiol groups as adsorbent materials to decontaminate polluted waters, using the removal of Hg2+ ions, one of the most dangerous heavy metals, as the test case. The effects of pH, ionic strength (I), and temperature of the metal ion solution on the adsorption ability and affinity of both materials were evaluated. To this end, adsorption experiments were carried out with no ionic medium and in NaNO3 and NaCl at I = 0.1 mol L−1, in the pH range 3–5 and in the temperature range 283.15–313.15 K. Kinetic and thermodynamic aspects of adsorption were considered by measuring the metal ion concentrations in aqueous solution. Various equations were used to fit experimental data, and the results obtained were explained on the basis of both the adsorbent’s characterization and the Hg2+ speciation under the given experimental conditions. Thiol and amino groups enhanced the adsorption capability of halloysite for Hg2+ ions in the pH range 3–5. The pH, the ionic medium, and the ionic strength of aqueous solution all play an important role in the adsorption process. A physical adsorption mechanism enhanced by ion exchange is proposed for both functionalized materials.

Organo-montmorillonite (OMnt) has wide applications in paints, clay-polymer nanocomposites, biomaterials, etc. In most cases, the dispersibility and swellability of OMnt dictate the performance of OMnt in the target products. Previous studies have revealed that the properties can be improved when multiple organic species are co-introduced into the interlayer space of montmorillonite (Mnt). In the present study, single surfactant erucylamide (EA), dual-surfactants cetyltrimethyl ammonium bromide (CTAB) and octadecyltrimethyl ammonium chloride (OTAC), and ternary-surfactants EA, CTAB, and OTAC were co-introduced into Mnt by solution intercalation. The resulting OMnts were characterized by powder X-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, thermogravimetry-differential thermogravimetry (TG-DTG), water contact-angle tests, scanning electronic microscopy (SEM), laser particle-size analysis, and swelling indices. Mnt co-modified by ternary CTAB, OTAC, and EA led to a large d001 value (4.20 nm), surface hydrophobicity with a contact angle of 95.6°, swellability (50 mL/g) with small average particle sizes (2.1−2.8 μm) in xylene, and >99% of the OMnt particles were kept as <5 μm in deionized water. The formation of EA-modified-Mnt was proposed according to hydrophobic affinity, hydrogen bonding, and van der Waals forces. The nanoplatelets of the CTA+, OTA+, and EA co-modified OMnts in xylene were assembled into a house-of-cards structure by face-to-edge and edge-to-edge associations. The electrostatic attractions, electrostatic and steric repulsions, and hydrophobic interactions were responsible for the good dispersibility of OMnt in xylene. The ternary surfactant co-modified OMnt with high dispersion and swellability will make OMnt better suited for real-world applications.

Epilepsy treatment requires anti-seizure medical formulations; available medications have various painful side effects and penetrate the brain–blood barrier poorly. A promising method is the use of natural clay nanocontainers for drug delivery through this membrane barrier. Halloysites (Hly) are biocompatible, 50-nm diameter tubes with a positively charged, hollow inner lumen and negatively charged outer shell and are available naturally. These characteristics enable them to be versatile as drug loaded ‘nano-torpedoes’ effectively penetrating cell membranes. The endothelial cells are a major cell type in the blood–brain barrier that provides for the selective permeability separating the circulating blood and allowing only the passage of glucose, water, and amino acids, but not traditional drug formulations. Nanotubes encapsulating rhodamine isothiocyanate and ionomycin penetration through the rat-brain microvascular endothelial cells followed by a prolonged 24-h drug release was demonstrated. A model membrane was set up across 0.4-μm-pore polystyrene transwell supports covered by seeding endothelial and astrocyte cells to mimic the blood–brain barrier in vivo. This barrier demonstrated a dual permeation mechanism (inter-cell accumulation and through-passing) for loaded Hlys, exploiting the potential of this nanoclay in the trans-membrane delivery of drugs. Use of Hly nanotubes as drug carriers to penetrate the brain microvascular endothelial barrier and to deliver the payload displayed a new approach for the treatment of brain diseases such as epilepsy.

As a photocatalyst with good prospects, TiO2 has the shortcomings of easy agglomeration and no catalytic performance under visible light. The purpose of the present study was to help solve these problems by employing muscovite as a carrier for N-doped TiO2 in a nanocomposite. The nanocomposites were prepared by a liquid precipitation-grinding method using muscovite as the matrix and urea as the nitrogen source. The crystal structures, chemical bonding, and micromorphology of the nanocomposites were analyzed by X-ray diffraction, infrared absorption spectrometry, and field emission scanning electron microscopy, respectively. Visible and ultraviolet (UV-Vis) light absorption of the nanocomposites was analyzed by solid ultraviolet diffuse reflectance spectroscopy. The photocatalytic effect of the nanocomposites was studied based on the degradation of rhodamine B (RhB) solution. The photocatalytic degradation product of RhB was detected by high-performance liquid chromatography-mass spectrometry, revealing that N-doping inhibits the growth of TiO2 nanoparticles. The photocatalytic performance of N-TiO2/muscovite composite nanomaterials decreased with increasing heat-treatment temperature. N-doped TiO2/muscovite nanocomposites that were heated at 400°C showed the best photocatalytic performance under visible-light illumination with an RhB degradation of 97%.

The intercalation of kaolinite through the insertion of ions or molecules amongst the structural aluminosilicate layers is a vital process in numerous clay-based applications and products. Layer neutrality and hydrogen bonding limits direct intercalation into kaolinite, other than for small molecules. Synthesizing zirconia-intercalated kaolinite is not a straightforward matter. To overcome this barrier, raw Egyptian kaolin (UnK) or its acid-activated product (HK) was sonicated and impregnated in aqueous ZrOCl2·8H2O solution followed by thermal treatment at various temperatures (100, 200, 300, and 500°C). The intercalation process was confirmed using various spectroscopic and analytical techniques. The direct intercalation of ZrO2 into the kaolinite layers was observed even through a mild thermal treatment (100, 200, and 300°C). The mechanism of intercalation was suggested to occur by binding ZrO2 to the Si/AlO groups with a preference for the acid-activated HK, causing variable enlargements of the basal spacing and producing very perturbed layers. Interestingly, the surface area increased by 250% as a result of zirconia intercalation. Scanning electron microscopy (SEM) images showed a remarkable improvement in the stacking order of the kaolinite particles. The impact of ZrO2 intercalation into kaolinite also enhanced its adsorption efficiency for Pb2+, Cu2+, and Cd2+ ions. Preliminary investigations showed that the zirconia-intercalated HK demonstrated a removal efficiency, which is three times greater than that of pristine HK. The adsorption tendency toward Pb2+ ions was greater than those of Cu2+ and Cd2+ and followed the order: Pb2+ >> Cu2+ > Cd2+. The study suggests that the chemical modification of kaolin by zirconia via a direct intercalation technique, which greatly improves its functionality as demonstrated by the selective sorption of heavy metal ions, is worthy of further study.

Tracing interactions during burial-induced organic maturation and associated clay-material alteration is of prime importance for understanding both the individual and combined mineral and organic processes. In the present study the light elements B, Li, O, and H of a sample from oil-prone Eocene Kreyenhagen Shale from San Joaquin Basin (California) were examined. The natural burial-induced temperature increase was simulated by pyrolysis experiments at progressively increasing temperatures (270–365°C) and for varied durations (72–216 h) applied to the whole rock and its <2 μm fraction. The illite structure as well as the K-rich interlayers of the illite-smectite mixed layers were not affected by the pyrolysis experiments and the smectite-rich interlayers did not collapse, while the soluble minerals and the organic matter were altered. The distribution pattern of the rare-earth elements (REEs) from untreated whole rock and of its pyrolyzed equivalents are within analytical uncertainty, which confirms that the changes induced by pyrolysis experiments were minimal in the bulk sample. Conversely, the REEs from the <2 μm fractions were modified significantly, suggesting that the whole rocks and the <2 μm fractions may contain different types of organic materials. Also, only the carbonates, oxides, chlorides, and organic matter were affected together with the smectite-rich interlayers of the illite-smectite structure. Bitumen coating of the smectite interlayers probably increased the amount of B of organic origin in their sites. The δ11B and δ7Li of the successively expelled hydrocarbon phases changed with increasing pyrolysis temperatures, together with the B and Li contents of the hydrocarbon-related fluids. On the basis of the δ11B and δ7Li from pyrolyzed clay fractions, the B released successively was not isotopically homogeneous, probably depending on how the type of organic matter decomposed during the successive pyrolysis steps, and on which components were released. The δ11B of organic-B increased progressively from –2‰ at low experimental temperature up to +9‰ at the highest temperature. The calculated δ7Li that was released also increased relative to the value of the outcropping sample used as a reference, but it remained almost constant from –7‰ at 310°C for 72 h to –8‰ at 365°C for 216 h. The δ18O values of the <2 μm size fractions decreased significantly during pyrolysis above 300°C, but the δD changes were rather modest. The total organic carbon (TOC) remained statistically constant after pyrolysis to 300°C, as did the δ7Li values. The pyrolysis experiments in the present study suggest the presence of bitumen-coated smectite interlayers that could have been misidentified as dehydrated smectite in the literature. Together with abnormal illite K-Ar ages, the occurrence of such bitumen-coated illite-smectite interlayers occurring in source and reservoir rocks could indicate the timing of hydrocarbon maturation relative to illitization.

Clay, or more precisely, certain clay typologies, have been used traditionally by humans for therapeutic, nutritional, and skin-care purposes though they may be responsible for some relatively rare but significant health and skin-care risks. For example, clay particles could adsorb and make available for elimination or excretion any potential toxic elements or toxins being ingested or produced, but they could also adsorb and make available for incorporation, through ingestion or through dermal absorption, toxic elements, e.g. heavy metals. Geophagy has been observed in all parts of the world since Antiquity, reflecting cultural practices, religious beliefs, and physiological needs, be they nutritional (dietary supplementation) or as a remedy for disease. Some clays and clay minerals are employed widely in both the pharmaceutical and cosmetics industries as active compounds/agents and as excipients. In the biomedical field, some clay minerals such as halloysite and montmorillonite are known for their effective role as carriers for the control and sustainable delivery of active drug molecules, and in the biomaterials field some clay minerals are used for scaffold, hydrogel, foam, and film production. Constraints, both chemical and microbiological, on the use of clay-based products for therapeutic and cosmetic topical applications are generally imposed by sanitary regulations, and some solutions are proposed herein to control and reduce such restrictions. Particular emphasis is placed here on peloids and pelotherapy, as well as on manipulated and modified peloids, and specifically on tailored peloids or ‘designed and engineered’ peloids, and their derivatives, bactericidal peloids and ointments. As far as the so-called ‘killer clays’ are concerned, their pre-requisites, mechanisms of action, and disinfection role are also enhanced. Podoconiosis is an environment-related or geochemical disease that occurs in tropical highland areas, and is caused by long-term exposure of bare feet to volcanic, red-clay soil and affects some people, particularly those working in agriculture in some regions of Africa, Asia, and South America.

Recent measurements from Mars document X-ray amorphous/nano-crystalline materials in multiple locations across the planet. Despite their prevalence, however, little is known about these materials or what their presence implies for the history of Mars. The X-ray amorphous component of the martian soil in Gale crater has an X-ray diffraction pattern that can be fit partially with allophane (approximately Al2O3⋅(SiO2)1.3–2⋅(H2O)2.5–3), and the low-temperature water-release data are consistent with allophane. The chemical data from Gale crater suggest that other silicate materials similar to allophane, such as Fe-substituted allophane (approximately (Fe2O3)0.01–0.5(Al2O3)0.5–0.99⋅(SiO2)2⋅3H2O), may also be present. In order to investigate the properties of these potential poorly crystalline components of the martian soil, Fe-free allophane (Fe:Al = 0), Fe-poor allophane (Fe:Al = 1:99), and Fe-rich allophane (Fe:Al = 1:1) were synthesized and then characterized using electron microscopy and Mars-relevant techniques, including infrared spectroscopy, X-ray diffraction, and evolved gas analysis. Dissolution experiments were performed under acidic (initial pH values pH0 = 3.01, pH0 = 5.04), near-neutral (pH0 = 6.99), and alkaline (pH0 = 10.4) conditions in order to determine dissolution kinetics and alteration phases for these poorly crystalline materials. Dissolution rates (rdiss), based on the rate of Si release into solution, show that these poorly crystalline materials dissolve approximately an order of magnitude faster than crystalline phases with similar compositions at all pH conditions. For Fe-free allophane, logrdiss = –10.65–0.15 × pH; for Fe-poor allophane, logrdiss = –10.35–0.22 × pH; and for Fe-rich allophane, logrdiss = –11.46–0.042 × pH at 25°C, where rdiss has the units of mol m–2 s–1. The formation of incipient phyllosilicate-like phases was detected in Fe-free and Fe-rich allophane reacted in aqueous solutions with pH0 = 10.4 (steady-state pH ≈ 8). Mars-analog instrument analyses demonstrate that Fe-free allophane, Fe-poor allophane, and Fe-rich allophane are appropriate analogs for silicate phases in the martian amorphous soil component. Therefore, similar materials on Mars must have had limited interaction with liquid water since their formation. Combined with chemical changes expected from weathering, such as phyllosilicate formation, the rapid alteration of these poorly crystalline materials may be a useful tool for evaluating the extent of aqueous alteration in returned samples of martian soils.

The hydrolysis of sodium borohydride (NaBH4) is a promising reaction with a possible practical application as a means of generating hydrogen. The efficiency of hydrogen production can be enhanced significantly by use of a catalyst during the reaction. Cobalt borides show significant catalytic activity, but unsupported CoB particles aggregate easily and are difficult to separate from the reaction medium for re-use. The objectives of the present study were to use halloysite (Hly) as a support material to increase the catalytic activity and reusability of a Co metal-based system and to investigate the binary effect of metal loading and reaction parameters on the hydrolysis of NaBH4. Catalysts were prepared by wet impregnation and chemical reduction. The surface morphology and structural properties of the prepared catalysts were characterized using N2 adsorption-desorption and the Brunauer-Emmet-Teller (BET) method, field emission scanning electron microscopy (FE-SEM), with energy dispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma mass spectrometry (ICP-MS). Response surface methodology (RSM) was used to optimize metal loading and reaction conditions for the hydrogen-generation rate. Optimum reaction conditions were determined (using Design Expert 7.0 software) as 5.01 wt.% Co loading using a Co-B/Hly-supported catalyst, 0.44 M NaBH4, 10.66 mg catalyst, and at a reaction temperature of 39.96°C. The maximum hydrogen generation rate was 33,854 mL min−1 gCo−1 under these conditions.

The organization of organic species on the ordered structures of clays and clay minerals is one way to produce inorganic-organic hybrids with controlled microstructures and properties. The reactions of the adsorbed species and their arrangement on the clay surfaces can be guided by the choice of clay and of adsorbed species. The purpose of the present study was to intercalate alkylammonium ions into a Thai bentonite and to study the effect on dye-adsorption efficiency. A series of alkylammonium ions, CnH2n+1NH3+ (n = 8, 10, 12, or 18), was incorporated into the interlayer spaces of a natural bentonite by mixing an aqueous dispersion of bentonite with an aqueous solution of protonated alkylamines at room temperature. The basal spacings of the intercalation compounds varied depending on the alkyl chain lengths and the amount of alkylammonium ions. The alkylammonium ions adsorbed formed lateral monolayer, bilayer, pseudo-trimolecular layer, paraffin-type monolayer, and/or paraffin-type bilayer structures. The adsorption efficiency of alkylammonium-bentonites was determined using batch adsorption experiments of rhodamine 6G from a water-ethanol solution; the greatest efficiency was 87% while that of the bare bentonite was 47%. The loading amount and the arrangement of the intercalated alkylammonium ions in the interlayer spaces, as well as the specific surface area and pore volume, played important roles in the adsorption efficiency of alkylammonium-bentonite. The adsorption equilibrium data for rhodamine 6G on the best adsorbent were interpreted using the Langmuir isotherm model and a pseudo-second order kinetics model. The adsorption efficiency of the adsorbent decreased by only 17% after five runs.

Polymer–filler interactions play a major role in determining the antibacterial activity of organoclay in nanocomposites. The objective of the current study was to determine the effect of polymer type on the antibacterial properties of an organically modified clay – cloisite 10A (C10A) – using poly-ε-caprolactone (PCL) and poly-L-lactic acid (PLA) polymeric systems. Nanocomposite characterization using atomic force microscopy (AFM) showed an increase in roughness upon addition of the clay mineral, and X-ray diffraction (XRD) showed intercalation of the selected polymers into the interlayer spaces of the clay. Transmission electron microscopy (TEM) analysis supported the XRD findings. C10A in PCL thin films enhanced the bactericidal activity against Staphylococcus aureus when compared to the C10A in PLA. The observed change could be the result of pronounced levels of interaction between the filler and polymer matrix in the C10A-PLA nanocomposite when compared to C10A-PCL. The higher interaction levels could hinder the diffusion of bactericidal agents from the nanocomposite membranes. The present study provided insight into the nature of interaction between nanocomposite components and its impact on bioactivity, which can have applications in terms of generating engineered antibacterial materials.

The poor environmental stability of natural anthocyanin hinders its usefulness in various functional applications. The objectives of the present study were to enhance the environmental stability of anthocyanin extracted from Lycium ruthenicum by mixing it with montmorillonite to form an organic/inorganic hybrid pigment, and then to synthesize allochroic biodegradable composite films by incorporating the hybrid pigment into sodium alginate and test them for potential applications in food testing and packaging. The results of X-ray diffraction, Fourier-transform infrared spectroscopy, and use of the Brunauer–Emmett–Teller method and zeta potential demonstrated that anthocyanin was both adsorbed on the surface and intercalated into the interlayer of montmorillonite via host–guest interaction, and the hybrid pigments obtained allowed good, reversible, acid/base behavior after exposure to HCl and NH3 atmospheres. The composite films containing hybrid pigments had good mechanical properties due to the uniform dispersion of the pigments in a sodium alginate substrate and the formation of hydrogen bonds between them. Interestingly, the composite films also exhibited reversible acidichromism. The as-prepared hybrid pigments in composite films could, therefore, serve simultaneously as a reinforced material and as a smart coloring agent for a polymer substrate.

Organic, ionic soil stabilizers (OISS) are designed to regulate directly the hydration properties of clay minerals to improve their engineering behavior. The steps involved in this regulation by OISS are unclear and this might limit their application in the current construction environment in China. The purpose of the present study was to reveal the origin of changes in hydration properties of four typical clay samples (with clay mineral contents of >90 wt.%: Na-bentonite, Ca-bentonite, illite, and kaolinite) as affected by OISS. The water-retention capacity of each clay was measured first through liquid limit and water-vapor adsorption tests. Then, the changes in hydration sites, such as exchangeable cations and the surfaces of minerals, were investigated by a series of microscopic measuring and testing techniques. Finally, infrared spectroscopy (IR) and thermal analysis were performed to verify the regulation of hydration properties by OISS. The results suggested that the exchangeable cation and surface changes controlled the regulation of hydration properties. OISS could cause some of the exchangeable cations to become free ions and disrupt the interaction between some cations and water molecules by its long organic chains; thus, the amount of hydrated cations decreased. In addition, the long organic chains covered the mineral surface and weakened its adsorption capacity. Furthermore, the long chains had cementitious qualities, connecting them to the crystalline layer and resulting in more aggregated clay particles and a smaller specific surface area (SSA). With the decrease in the number of cations and in the SSA by OISS, the hydration of the four clay samples decreased, especially in the case of bentonite.

DNA manipulation is crucial for many biotechnological prospects and for medical applications such as gene therapy. This requires the amplification and extraction of DNA from bacteria and the transfer of these DNA molecules into cells, including bacterial and mammalian cells. The capacity of the natural magnesium silicate clay mineral sepiolite to bind to DNA makes it a potentially useful tool for biotechnological/medical strategies. In addition, sepiolite is inexpensive and classified as non-toxic and non-carcinogenic. This review will first describe the physicochemical interactions between sepiolite and DNA. Then, the leverage of sepiolite/DNA interactions for DNA extraction from bacteria, to optimize DNA transfer into bacteria and DNA transfection into mammalian cells, are presented. Finally, the putative toxicity of sepiolite and its advantages and perspectives for future prospects, such as the improvement of immunotherapy, are also discussed.

CaMnt is much less important than NaMnt due to its limited commercial applications. The time-dependent property of NaMnt gel has been studied extensively as it is exploited in many applications such as drilling mud and viscosity-modifier applications. In contrast, the time-dependent property of CaMnt suspension and the factors affecting it are largely unknown. The speciation of Ca2+ ions is one such factor to be evaluated. In the current study, pH and solids concentration were examined and then used to validate a recent theory on clay gel time dependency. The results supported the theory that a strong electrostatic double layer (EDL) repulsion in the 3-D network is needed to reorganize the structure and drive it toward the state of minimum free energy. The 12 wt.% CaMnt (STx-1b) gel displayed time-dependent behavior at pH 5 but not at its natural pH of 8.4. At pH 5, the interlayer Ca2+ ions became fully hydrated and desorbed from the platelet surface. This enhanced the EDL repulsion between the platelets. At pH >6.5, the positively charged hydrolysis product Ca(OH)+ began to form and was adsorbed, partially neutralizing the permanent layer charge and weakening the repulsion. However, at 19.4 wt.% solids, the gel displayed pronounced time-dependent behavior despite the high natural pH of 8. The platelets were much closer together, allowing the EDL force to operate and effect structural reorganization. The microstructure of these CaMnt gels showed high platelet concentrations interacting to form a relatively open structure. The microstructure of a kaolin (KGa-2) suspension which showed no time-dependent behavior even after 1 day of ageing revealed the importance of particle morphology and layer charge on time dependency. Its 3-D structure was formed by relatively thick, layered platelets with a low layer charge.