Edible clays are consumed by diverse groups of people, especially of African descent, living in Africa and abroad, in a behavior known as geophagy. The clays are used topically as an emollient and drying agent and internally to control diarrhea. Scientific information concerning the chemical constituents and toxicity of edible clays is scarce. The aims of the present study, therefore, were to ascertain the chemical composition of white edible clays (WEC) and gray edible clays (GEC); to determine their toxicity profiles using analytical chemical methods; to test the acute and sub-acute toxicity of edible clays in their natural form as consumed; and to compare the raw and processed clays, and also to compare the latter to a proprietary drug known as ‘Mist kaolin’ (Moko®) which contains some clay along with other chemicals. Atomic absorption spectroscopy (AAS) and gas chromatography/mass spectrometry (GC/MS) were used to determine the elements present. White female Wistar mice and rats were used for the acute and sub-acute toxicity analyses, respectively. The results from AAS showed the presence of heavy metals and metalloids in both GEC and WEC, and the GC/MS revealed the presence of contaminants such as indomethacin and ethyl benzene, but quantities were below human toxicity levels. Doses of 100–500 mg/kg of either clay type could be harmful to the digestive system, but all of the tests revealed that edible clay is not toxic to humans unless very large amounts (500–1000 mg/kg of body weight) are consumed.

Ion-exchange modeling is used widely to describe and predict ion-adsorption data on clay minerals. Although the model parameters are usually optimized by curve fitting experimental data, this approach does not confirm the identity of the adsorption sites. The purpose of the present study was to extend to divalent cations a previous study on the retention of monovalent cations on Na-saturated montmorillonite (NaMnt) which optimized some of the model parameters using density functional theory (DFT) simulations. The adsorption strength of divalent cations increased in the order Mg2+ < Cd2+ < Ca2+ < Sr2+ < Ba2+. After adding adsorption of metal hydroxide species (MOH+), the three-site ion-exchange model was able to describe adsorption data over a wide pH range (pH 1–10) on NaMnt. X-ray diffraction (XRD) analyses were conducted to investigate the interlayer dimension of clay samples under various conditions. The cation retention strengths of divalent cations did not correlate with interlayer dimensions. The XRD analyses of the Mnt showed a d001 value of 19.6 Å when saturated with alkaline earth cations, 22.1 Å with Cd2+, 15.6 Å with Na+, and 15.2 Å with H+. In the case of Na+, the 15.6 Å peak decreased gradually and disappeared, and new peaks at 22.1 and 19.6 Å appeared when the percentages of Mg2+ and Ba2+ adsorbed increased on NaMnt. The peak shifted from 22.1 to 20.3 and 19.6 Å when the pH increased for all cations except Cd2+, which stayed constant at 22.1 Å. The coexistence of multiple d001 peaks in the XRD patterns suggested that the interlayer cations were segregated, and that the interlayer ion–ion interactions among different types of ions were minimized.

Among all iron oxides, hematite (α-Fe2O3), goethite (α-FeOOH), and ferrihydrite (FeOOH⋅nH2O) are the most common mineral species. While immobilization of Mo6+ by surface adsorption on ferric oxides has been studied extensively, the mechanisms of incorporation in their structure have been researched little. The objective of this study was to investigate the relation between Mo content and its structural incorporation in hematite, goethite, and six-line ferrihydrite by a combination of X-ray absorption spectroscopy (XAS), powder X-ray diffraction (pXRD), and inductively-coupled plasma optical emission spectrometry (ICP-OES). Synthesized in the presence of Mo, the hematite, goethite, and six-line ferrihydrite phases incorporated up to 8.52, 0.03, and 17.49 wt. % Mo, respectively. For hematite and goethite, pXRD analyses did not indicate the presence of separate Mo phases. Refined unit-cell parameters correlated with increasing Mo concentration in hematite and goethite. The unit-cell parameters indicated an increase in structural disorder within both phases and, therefore, supported the structural incorporation of Mo in hematite and goethite. Analysis of pXRD measurements of Mo-bearing six-line ferrihydrites revealed small amounts of coprecipitated akaganéite. X-ray absorption near edge structure (XANES) measurements at the Mo L3-edge indicated a strong distortion of the MoO6 octahedra in all three phases. Fitting of extended X-ray absorption fine structure (EXAFS) spectra of the Mo K-edge supported the presence of such distorted octahedra in a coordination environment similar to the Fe position in the investigated specimen. Incorporation of Mo6+ at the Fe3+-position for both hematite and goethite resulted in the formation of one Fe vacancy in close proximity to the newly incorporated Mo6+ and, therefore, charge balance within the hematite and goethite structures.

Antibiotic-resistant genes (ARGs) have been regarded as emerging contaminants that threaten public health worldwide. Poultry excreta, often used as a fertilizer in agriculture, are a major route for the proliferation and dissemination of ARGs in the environment. The aim of the present study was to assess the potential of dietary palygorskite (Plg) supplementation as nutritional manipulation for the modulation of microbial community structure and the attenuation of ARGs in the cecal contents of broilers fed with chlortetracycline (CTC). In total, 256 one-day-old, mixed-sex, broiler chicks were allocated randomly into a 2 × 2 factorial design of four treatments, which consisted of two levels of CTC (0 or 50 mg/kg) and Plg (0 or 10 g/kg). By employing in vivo feeding and slaughter experiments, after collecting the cecal contents and extracting the total genomic DNA, 16S rRNA V3-V4 hypervariable amplicon pyrosequencing and quantitative PCR-based approaches were used to address the impact of Plg on microbiota and the abundance of ARGs in broilers. The results showed that broilers given a diet supplemented with Plg had greater α-diversity indices including Chao1, phylogenetic diversity tree, and observed-species index calculations, when compared with those without Plg supplementation. Birds given a diet supplemented with Plg had fewer Firmicutes at the phylum level, but a greater abundance of Alistipes at the bacterial genus level. Dietary Plg counteracted the CTC-induced increased abundance of ARGs, among which tet(K) had a pronounced decrease, along with a similar decreased tendency for other measured ARGs and intI1. Overall, the results indicated that Plg supplementation caused pronounced changes in cecal microbial diversity and microbiota community composition of broilers, and effectively reduced ARGs, indicating that Plg supplementation is a potential alternative measure for the attenuation of ARGs in the cecal contents of broilers.

Mesoporous materials have a wide range of applications in the fields of nanotechnology, biotechnology, information technology, and medicine, but historically, the resource materials used for their synthesis have been expensive. Natural silicate minerals are characterized by their abundance, low cost, and large SiO2 contents, making them an alternative silicon source for mesoporous silica. The objective of the present study was to determine the utility of natural chlorite as the source of Si for synthesizing hexagonal mesoporous silica materials (MCM-41). The natural chlorite was pretreated by acid leaching and calcination, followed by a hydrothermal reaction with cetyltrimethylammonium bromide (CTAB) as the template, and subsequent calcination to prepare MCM-41. The structures and the porosity of MCM-41 were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), 29Si magic-angle spinning solid-state nuclear magnetic resonance spectroscopy (29Si MAS NMR), and N2 adsorption–desorption measurements. The mechanism of structural evolution from natural chlorite to MCM-41 was investigated using these techniques. Calcination of chlorite results in amorphization and partial structural breakdown, while subsequent acid leaching dissolves the Mg and Al in the octahedral sheets to leave the Si–O framework as a silicon source. 29Si MAS NMR results revealed that the ratio of Q4/Q3 increased from 0.91 to 1.21 after hydrothermal synthesis of MCM-41 from leached chlorite, demonstrating more polymerization of the Si–O structure in MCM-41. The final MCM-41 products were amorphous SiO2, with a large surface area of 630 m2/g, a pore volume of 0.46 mL/g, and a narrow pore-size distribution of 2.8 nm. MCM-41 showed favorable adsorption toward methylene blue (MB) with a monolayer adsorption capacity of up to 302 mg/g, indicating potential for application in adsorption.

Soil salinity is one of the most critical environmental stresses that affects crop productivity. In a context in which world demand for food is growing continuously, this problem requires urgent attention. Actions that go beyond traditional agricultural practices are needed. The objective of the current study was to develop a bioactive, economic, and sustainable compound that can increase the tolerance of cultivated plants in saline-stress situations by combining the hosting capacity of natural bentonite nanoclay (Bent) with a phytoactive osmoprotective compound, L-Proline (Pro). The Bent-Pro nanocomposite synthesis method, its final chemical structure, and in vitro bioactivity were addressed here. The results indicated that Bent can retain a maximum of 14.4% (w/w) of Pro. The (001) X-ray diffraction (XRD) peak of Bent shifted to smaller angles in the pattern of Bent-Pro, indicating that Pro has a monolayer arrangement between the Bent layers. The results of transmission electron microscopy (TEM) also supported this result. Pro was also retained on the edges or external surfaces of Bent, as indicated by thermogravimetric analysis (TGA) and scanning electron microscopy (SEM). In addition, Pro functional groups identified by Fourier-transform infrared (FTIR) spectroscopy indicated that it was present in its zwitterionic form. The role of Bent-Pro as a protector against plant saline stress was assayed using Arabidopsis thaliana (A. thaliana) as a model, demonstrating that it mitigates the detrimental effects of NaCl-mediated salt stress on seed germination and the leaf chlorophyll level, thus highlighting the relevance of this contribution and the versatility and broad applicability of clays.

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.

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%.

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.

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.