The number of studies of controlled drug-release systems is growing constantly. Bionanocomposite materials which can be prepared from the combination of biopolymers with inorganic solids such as clay minerals offer interesting alternatives for use as drug-delivery systems. In the present study, new bionanocomposite drug-release systems were prepared from the intercalation of the antibiotic drug ciprofloxacin into montmorillonite using an ion-exchange reaction. In order to prepare more stable systems for oral ciprofloxacin release, this ciprofloxacin-clay intercalation compound was incorporated into i-carrageenan-gelatin biopolymer blend to produce bionanocomposite materials. Bionanocomposites of two distinct i-carrageenan and gelatin mass ratios were conformed as beads through an ionic gelification reaction with Ca2+ ions, and dried by freeze-drying where liquid nitrogen or conventional freezing was adopted in the freezing step. The resulting ciprofloxacin-clay hybrid was characterized by X-ray diffraction (XRD) analysis, Fourier-transform infrared (FTIR) spectroscopy, solid state 13C Nuclear Magnetic Resonance (NMR), thermal analysis, and scanning electron microscopy (SEM). The montmorillonite-ciprofloxacin hybrid incorporated into the bionanocomposite beads was evaluated by in vitro release studies which showed a significant difference in the release profiles in the aqueous medium used to simulate the gastrointestinal tract, depending on the blend composition and the freezing method employed in the preparation of the beads. The results point to bionanocomposite systems based on ciprofloxacin-clay hybrids and biopolymers that may be used as devices in the biomedical area.

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.

The development of nanoparticles incorporating Gd3+ has attracted interest in the field of contrasting nanomedicine for magnetic resonance (MR) and computed tomography (CT). In order to achieve an effective contrasting performance, the amount and stability of Gd incorporated as well as particle-size control of the nanoparticles should be considered simultaneously. In the current study, Gd-diethylenetriaminepentaacetate(Gd-DTPA) was incorporated into layered double hydroxide (LDH) to meet the physicochemical properties required for MR-CT dual contrasting nanomedicine. Strategically, the particle size and nanometer incorporation of Gd-DTPA into LDH (GL-R hybrid) were controlled homogeneously using the reverse micelle method. X-ray diffraction showed that the hybrid obtained possessed a hydrotalcite phase. Dynamic light scattering and electron microscopic analyses showed that the hybrid had a controlled size of <200 nm with significant homogeneity. Fast Fourier-transform of transmission electron microscopy confirmed that the platelets of the GL-R hybrids were oriented randomly to form inter-particle space, enabling the Gd-DTPA moiety to be encapsulated stably. The encapsulation efficiency of Gd-DTPA was 20.8%, which was sufficiently high compared with other Gd-DTPA-incorporatedLDH. According to X-ray photoelectron spectroscopy and Fourier-transform infrared spectroscopy, Gd-DTPA incorporated in the hybrid preserved its structure intact. Its potential as a dual modal contrast agent was demonstrated by measuring the concentration-dependent Hounsfield unit and magnetic resonance relaxivity, which were determined to be 230 at 2 mg/mL and 5.8 in the range ~0.2–1 mM-Gd, respectively.

Knowledge of clay mineralogy is essential for understanding the source areas and weathering environments of fluvial sediments, particularly in large reservoirs facing serious problems with sediment deposition, such as the Three Gorges Reservoir (TGR) in east-central China. The purpose of the present study was to identify the sediment provenances and weathering regimes contributing to the sediment load in the TGR by determining the clay-mineral and geochemical compositions of surface sediments during various seasons. X-ray diffractometry and scanning electron microscopy (SEM) were used to identify the clay minerals. The results showed that illite was the dominant mineral, followed in order by kaolinite, chlorite, and montmorillonite. From a mineralogical perspective, distal sources were the main contributors to the TGR sediments, and regional sources (surrounding tributaries) also contributed much during the three seasons, while proximal sources (hillslope soils) supplied sediment in the flood season but not in the other two seasons. The geochemical and hydrological data generally supported the mineralogical results. In the flood season, the chemical indices of the TGR sediments were >0.4, showing that the sediments contained Al-rich illite minerals and experienced intense hydrolysis. In the other two seasons the TGR sediments were enriched in Fe- and Mg-rich illite minerals, resulting from strong physical weathering. Furthermore, precipitation, rather than air temperature or latitude, was the factor that controlled weathering intensity. These findings provide deep insights into the sediment cycle and chemical weathering in this large reservoir basin.

Gray-black kaolinitic claystones of industrial value are abundant in Upper Carboniferous–Lower Permian coal-bearing strata of the Datong Coalfield of northern China. The main types are tonsteins and cryptocrystalline kaolinitic claystones, distinguished by the thinness and greater crystallinity of kaolinite in the former and by the presence of detrital illite and authigenic pyrite in the latter. In order to determine the formation history of these two types of kaolinitic claystone, the petrological, mineralogical, and geochemical characteristics of borehole samples from the Upper Carboniferous Taiyuan Formation which comprises siliciclastics and coal seams deposited in a coastal environment, were analyzed. In addition to kaolinite, the claystones contain subordinate illite, quartz, pyrite, anatase, feldspar, siderite, and calcite. The tonsteins and cryptocrystalline kaolinitic claystones have different sources, as shown by petrographic data, elemental ratios, and chondrite-normalized rare earth element (REE) patterns. The volcanic origin of the tonsteins is revealed by an abundance of volcanic quartz and vitric fragments as well as Al2O3/TiO2, Zr/Hf, and Nb/Ta ratios consistent with a felsic igneous source. Their REE fraction was derived from feldspars or micas of the parent rocks, and the fraction decreased with alteration of these minerals to kaolinite. The sedimentary origin of the cryptocrystalline kaolinitic claystones is revealed by an abundance of detrital quartz and illite grains derived from either granite or sedimentary upper crust, and by the total REE contents (ΣREE) and (La/Yb)N values which are consistent with granitic material. Their depositional environment was in a transitional (coastal) setting (as shown by intermediate Sr/Ba ratios) hosting an open acidic hydrologic system (as shown by high chemical index of alteration (CIA) values indicative of intensive chemical weathering) that was suboxic to anoxic (as shown by high U/Th ratios and trace-metal enrichment factors). The present chemistry of these claystones was thus controlled by a combination of parent rock type and diagenetic alteration.

Clays are used in various cosmetic formulations, such as sunscreens, toothpastes, deodorants, creams, hair cosmetics, makeups, nail polish, facial masks, and shampoos, among others, to improve the organoleptic and physicochemical characteristics, to increase the stability, or to facilitate elaboration. Together with their technological functionalities, clays are cosmetologically active ingredients with cleaning, anti-aging, anti-wrinkling, and sun-care functionalities. Talc, kaolinite, mica, and some smectites are the clay minerals used most frequently in cosmetic products, but several other phyllosilicates as well as modified and synthetic clays are also used. Sometimes, clays are useful in the design of cosmetics just because they are made of rigid, small, and anisometric particles. Kaolinite and mica are made of hard prismatic particles which are lightly abrasive over the skin, teeth, or hair. Electric charges in smectites result in ion-exchange capacities useful in the loading of active cosmetics but also adsorbing and cleaning waste substances. Intermediate net negative charges of smectites result in layer expansion in polar media and specific rheological properties that are very useful in cosmetic formulations. The absence of charged particles in talc and kaolin make them flow easily resulting in lubricant effects. Protection against radiation from the sun by clay particles and decorative effects complete the possibilities of clays in cosmetics. The nomenclature for clays used as ingredients in cosmetics follows historical use and the names of commercial products, rather than following strict compositional principles. In this sense, an effort was made here to correlate the names of the minerals that make up each of the clay-based cosmetic ingredients.

Kaolinite is a clay mineral with diverse environmental, industrial, and agricultural applications. The influence of the crystallographic properties of kaolinite, e.g. structural disorder, on these applications is of great interest. Qualitative and quantitative analyses of kaolinite structural disordering over the last 70 years have revealed three main sources of layer-stacking disordering: (1) enantiomorphic stacking; (2) dickite-like stacking; and (3) random shift of layers. What influence do these stacking disorders have on the reactivity of kaolinite? The objective of the present study was to investigate the influence of stacking disorder on the intercalation and dissolution of kaolinite layers. To minimize the effect of particle size on reactivity, the 1–2 μm fractions of five geologic kaolinites were used. The 1–2 μm fractions varied in the degree of structural disorder. The kaolinites were: (1) intercalated with saturated CH3COOK solution at room temperature to examine the effect of stacking disorder on intercalation; and (2) dissolved in 4 M NaOH at 80°C to examine the effect of stacking disorder on kaolinite stability in alkaline solution. Samples with a low degree of stacking disorder intercalated twice as much and dissolved >1.5 times as much as the most disordered sample. The infrared spectrum of the undissolved kaolinite residue in 4 M NaOH showed relative intensities of OH-stretching bands characteristic of a kaolinite-dickite mixture. The binding strength (i.e. resistance to intercalation) of the undissolved residue by NaOH was high; the residue could not be intercalated by CH3COOK. Differences in the average interlayer binding strength were attributed to the greater proportions of dickite-like sequences in highly disordered kaolinite compared to ordered kaolinite specimens. These results suggested that the binding strength of kaolinite layers is proportional to the degree of stacking disorder. Dickite-like sequences, a type of stacking defect, contributed to the lower reactivity of highly disordered kaolinite.

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.

Lipase is an industrial enzyme, the catalytic efficiency of which is restricted by various environmental factors. To improve this efficiency, immobilization technology has been utilized in the past to improve the stability of lipase in harsh conditions. Immobilization technology can be divided into physical methods and chemical methods. Some unsolved problems remain in current immobilization technology. The interaction between enzyme and immobilization support is weak and reversible during physical adsorption, resulting in poor stability of the immobilized enzyme and the contamination of substrate solution by leached enzymes. In chemical methods, enzyme-active sites might be inactivated due to the chemical reactions between enzyme molecules and support, resulting in a decrease in the enzymes’ catalytic activity (Liu et al., 2018a). The objective of the current study was to construct a nanostructured lipase via Mg-amino-clay as a carrier and improve the catalytic activity and stability of lipase by immobilization. Lipase produced by Aspergillus oryzae was immobilized on aminopropyl functionalized magnesium phyllosilicate (a 2:1 trioctahedral talc-like silicate Mg-amino-clay) via a 1-(3-Dimethylaminopropyl)-3-ethyl-carbodiimide hydrochloride (EDC) coupling agent. The physical and chemical properties of the Mg-amino-clay and Mg-amino-clay-based nanostructured biocatalyst (Mg-clay-lipase) were characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and scanning electron microscopy. Optimal immobilization conditions were determined by taking into account the following variables: amount of initial lipase, EDC concentration, and reaction time. The results revealed that the optimum temperature, pH, and thermal stability of Mg-clay-lipase were greater than equivalent values for free lipase under optimal conditions (described below – Process for Immobilization of Lipase on Mg-amino-clay). The Michaelis-Menten constant (Km) values were 5.25 mM and 7.42 mM while the maximum reaction rates (vmax) were 30.58 mM/(L·min) and 55.87 mM/(L·min) for free lipase and Mg-clay-lipase, respectively. The present study provided a new nanostructured biocatalyst and demonstrated that the enzyme activity and stability of Mg-clay-lipase were superior to those of free lipase due to the mechanism of 'interface activation'.

The present study deals with accurate identification of polytypes, twins, and allotwins – oriented crystal associations of more than one polytype. The trioctahedral 1:1 layered silicate cronstedtite was studied using single-crystal X-ray diffraction data collected with a four-circle diffractometer equipped with a CCD detector. The sample from the skarn occurrence, Ouedi Beht, El Hammam, Morocco, was explored. It contains cronstedtite in fibrous massive aggregates in the central part, and euhedral crystals in surrounding veinlets and druses. The reciprocal space (RS) sections created by the diffractometer software and presented here were used to determine the OD (ordered-disordered) subfamilies (Bailey’s group A, B, C, D) and to identify polytypes. The chemical compositions of some crystals were determined thereafter by electron probe microanalysis (EPMA-WDS). Some crystals studied are more or less complicated allotwins. Polytypes were thus separated by cleaving crystals into smaller parts in many cases. All polytypes found belong to subfamilies A or D. The following polytypes of the subfamily A were identified: 2M1 (a = 5.49, b = 9.51, c = 14.40 Å, β = 97.30°, space group Cc), 1M (a = 5.51, b = 9.54, c = 7.33 Å, β = 104.5°, Cm), 3T (a = 5.51, c = 21.32 Å, P31), 6T2 (a = 5.50, c = 42.60 Å, P31). 2M1 and 3T were present as isolated crystals or separated by cleaving, otherwise all these polytypes are parts of allotwins. The 2M1 polytype is sometimes twinned by reticular pseudo merohedry with twin index n = 3 and 120° rotation about the chex axis as the twin operation. Allotwins of 1M + twinned 2M1 polytypes are also present. Another kind of twinning, with rotation by (2n+1)×60° about chex is rare. The subfamily D is represented mostly by 2H1 and 2H2 polytypes, a = 5.50, c = 14.25 Å, space groups P63cm (2H1), P63 (2H2). In addition, several six-layer (a = 5.49, c = 42.80 Å), mostly non-MDO polytypes were separated from allotwins by cleaving. In order to identify them, 24 possible stacking sequences were modeled, diffraction patterns calculated, graphical identification diagrams constructed, and comparisons made with actual RS sections. This simulation revealed that five pairs of sequences provided identical diffraction patterns. Polytypes actually found correspond to the following sequences: 1 (6T1), 5 (proposed Ramsdell’s symbol 6T3), 8+10 (6T5), 11+12 (6T4), 24 (6T6, trigonal polytypes, space group type P3), 22 (6R1), and 23 (6R2, rhombohedral polytypes, space group type R3c and R3, respectively). The RS section corresponding to the hexagonal polytype 6H2 (sequence 14) was also found. However, diffraction patterns geometrically indistinguishable can be produced by the twin with rotation by 180° about chex as a twin operation of the rhombohedral polytype 6R2 (sequence 23). Several aggregates with fiber texture of polytype 2H2 were separated from the central part. Use of EPMA-WDS revealed Fe and Si along with significant amounts of Mn and Mg. Crystals from veins were more Mn- and Mg-rich than these from the central part. Traces of Cl, S, and Al are present also.

Halloysite nanotubes (HNTs) have attracted much attention as delivery carriers for various drugs, but the loading of one such drug, quercetin, on HNTs has been investigated only rarely and usually involved cyclic vacuum pumping. The main objective of the present study was to develop a novel carrier system based on HNTs for quercetin delivery without a vacuum process and to investigate the effect of chemical modification of HNTs on the loading and release of quercetin. For this purpose, comparative studies of five chemical modification reagents (sodium lauroamphoacetate, cocoamidopropyl betaine, 1-hydroxyethyl 2-nonyl imidazoline betaine, triethanolamine, and dipicolinic acid) functionalized on HNTs were investigated for quercetin loading and in vitro release. Characterization of raw halloysite, modified halloysite, and quercetin-loaded halloysite were done by X-ray diffraction (XRD), Fourier-transform infrared spectrometry (FTIR), thermogravimetric analysis (TGA), and transmission electron microscopy (TEM). The results indicated that chemical modification could improve the interactions between HNTs and quercetin. After chemical modification, quercetin was anchored to both the inner and outer surfaces of HNTs by electrostatic attraction, hydrogen bonding, and van der Waals forces. Sodium lauroamphoacetate-modified HNTs were given the highest loading of 1.96 wt.% among the five reagents. Cocamidopropyl betaine-modified HNTs exhibited the best sustained-release profile with only 29.07% for initial burst release and 480 h of consecutive release. Carboxyl groups of the modification reagent improved the loading capacity of quercetin. Amide groups prolonged drug release due to the strong affinity between amine and phenolic hydroxyl groups of quercetin. The release of quercetin from the cocamidopropyl betaine-modified HNTs fitted a first-order kinetics model well. The present study suggested that cocamidopropyl betaine-modified HNTs offer promise as vehicles for delivery of quercetin and for extending the application of quercetin.

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.

The present study introduces an overview of gentamicin-clay mineral systems for applications in biomedicine and then focuses on the development of a series of gentamicin/clay hybrid materials to be used as the bioactive phase of hydroxypropylmethylcellulose (HPMC) to produce bionanocomposite membranes possessing antimicrobial activity of interest in wound-dressing applications. Gentamicin (Gt) was adsorbed from aqueous solutions into a montmorillonite (Cloisite®-Na+) to produce intercalation compounds with tunable content of the antibiotic. The hybrids were characterized by CHN chemical analysis, energy-dispersive X-ray analysis, X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric analysis, confirming the intercalation of Gt by an ion-exchange mechanism. The release of Gt from the hybrids was tested in water and in buffer solution to check their stability. Hybrids with various amounts of Gt were incorporated into a HPMC matrix at various loadings and processed as films by the casting method. The resulting Gt-clay/HPMC bionanocomposites were characterized by means of field-emission scanning electron microscopy, and were also evaluated for their water-adsorption and mechanical properties to confirm their suitability for wound-dressing applications. The antimicrobial activity of the bionanocomposite films was tested in vitro toward various microorganisms (Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant Enterococcus faecium, Acinetobacter baumannii, and Klebsiella pneumonia), showing a complete bacterial reduction even in films with small Gt contents.

Minerals such as quartz, present widely in various volcanic ashes, remain unaltered throughout the low-temperature hydrothermal process currently used in industry to obtain zeolites, causing an incomplete hydrothermal transformation of the starting solid. This study presents a novel and cost-effective procedure which improves the reactivity of ash toward the generation of zeolite by increasing the availability of silica and alumina components. This method leads to a final product with a large zeolite content. The transformation consisted of an ash-activation step followed by hydrothermal zeolitization. The influence of the structural, chemical, and morphological characteristics of the volcanic ash as well as the effect of the activation procedure on the ash reactivity were studied. A collected sample (VA) and an amorphous fraction obtained after VA sieving (VA40, retained on #40 mesh) were used for zeolite production. These solids were alkaline-treated separately, aged, and reacted under controlled conditions of temperature at autogenous pressure. Throughout the process, the solid phases were characterized by X-ray diffraction, energy dispersive X-ray microanalysis, scanning electron microscopy, Fourier-transform infrared spectroscopy, and N2adsorption-desorption porosimetry measurements. After activation and alkaline aging, the presence of quartz and plagioclase minerals in the natural ash seemed to improve the growth of NaAlSiO4 polymorphs, which in turn were transformed easily to zeolite structures. Even under adequate pretreatment and suitable synthesis conditions, the coarse non-crystalline fraction led to low conversion, while the highest conversions to zeolites A and X were obtained from the natural ash. The outcomes of the present study could be used to improve the conversion levels of other non-conventional aluminosiliceous minerals into zeolites.

To resolve the existing ambiguities in the interpretation of the OH-stretching vibrations of kaolinites, relationships were, for the first time, established between the structural and Fourier-transform infrared (FTIR) spectroscopic features for a set of kaolinite samples which differed in terms of their relative amounts of coexisting high- and low-ordered phases. For this purpose, a representative collection of kaolinites differing in origin, particle size, and degree of disorder was studied by powder X-ray diffraction (XRD) and FTIR spectroscopy. Modeling of the experimental XRD patterns based on the orthogonal layer unit cell having a mirror plane showed each sample to be a mixture of nearly defect-free high-ordered (HOK) and low-ordered (LOK) kaolinite phases, with HOK varying from 86 to 4%. The wavenumbers, heights, areas, and full widths at half-maximum (FWHM) were determined for the OH-stretching bands at ~3697 (ν1), ~3670 (ν2), ~3652 (ν3), and 3620 cm–1 (ν4) by decomposition and fitting of the FTIR spectra. The FWHM(ν1)/FWHM(ν4) and FWHM(ν3)/FWHM(ν2) values were related linearly to the HOK content, which may be associated with the in-phase and out-of-phase character of the corresponding pairs of vibrations, respectively. A novel interpretation was suggested for the variations in the relative integrated intensities of the OH bands with the amount of the HOK phase. The intensity distribution of the ν2 and ν3 bands is controlled by the triclinic structure symmetry in the defect-free kaolinite and the mirror symmetry of the layers in low-ordered structures, in agreement with the observed evolution of the corresponding band intensities. The ν1 and ν2 band positions for the low-ordered samples are within the wavenumber range for the high-ordered samples. In contrast, the ν3 and ν4 band positions for the low-ordered samples are shifted toward higher wavenumbers, indicating that some of the low-ordered kaolinites should contain dickite-like structural fragments distributed among kaolinite layers.

The immobilization of antimicrobial drugs can be used to expand the application of antibacterial properties to consumer products. The purpose of this study was to stabilize an antimicrobial agent, levofloxacin (LVX), for sustained antibacterial activity by immobilizing the drug molecules in a layered double hydroxide (LDH) and embedded in a polyurethane substrate. As-prepared MgAl-LDH was calcined at 400°C and reconstructed with LVX for intercalation. The X-ray diffraction patterns and cross-sectional transmission electron microscopy images showed lattice expansion along the crystallographic c axis upon LVX intercalation, suggesting successful loading of the drug. Fourier-transform infrared spectra revealed that the structure of LVX was well preserved between LDH layers. Elemental analysis indicated that the loading capacity of LVX in the hybrid was 41.7%. Bacterial-colony forming inhibitory assay on Bacillus subtilis exhibited ~100% antibacterial activity of both LVX alone and LVX-LDH hybrid (LL). To determine sustainability of antibacterial activity by the hybrid, either LVX alone or LL hybrid was loaded in the polyurethane (PU) substrate for which antibacterial activity was evaluated before and after immersion in a phosphate-buffered saline for 3 days. The LVX-composited PU showed a dramatic decrease in antibacterial activity, down to 0% after buffer treatment; LL-composited PU still contained antibacterial activity (~34% of colony suppression) after phosphate-buffered saline immersion.

Sulfonated carbon is a ‘green,’ solid-acid catalyst. For applications purposes, its surface area needs to be improved and its preparation needs to be made environmentally friendly. The objective of the present study was to provide a green and economical method of preparing a sulfonated carbon catalyst by using palygorskite (Plg) fiber as a support for sulfonated carbon. Sulfonated carbon/palygorskite solid-acid catalyst (SC-Plg) was synthesized via one-step carbonization-sulfonation by mixing palygorskite with sucrose as the carbon source and p-toluenesulfonic acid as the sulfonating agent. The catalyst was characterized by SEM, EDX, TEM, FTIR, and nitrogen adsorption-desorption isotherms. The results indicated that sucrose-derived carbon was loaded uniformly on the surface of Plg fibers and formed the SC-Plg catalyst. The inexpensive Plg fibers could replace sucrose-derived carbon and increase the surface area of the resulting catalyst. The SC-Plg shows significant catalytic performance and excellent stability when used in the esterification of oleic acid with methanol. The conversion of oleic acid reached 68.09%, even after five cycles. This work paves the way for the development of highly active, carbon-based, solid-acid composite catalysts using a natural Plg nanofiber template.

Bentonite is used as a catalyst in the removal of olefins from aromatic compounds and the present study was designed to investigate how its performance might be improved by various treatments. Bentonite from Semnan mine, Iran, was used in the study following initial characterization. In order to investigate the effect of acid and thermal treatments on the removal of olefins from aromatic compounds, bentonite samples were modified using HNO3 at different concentrations (0.15, 0.3, 0.5, 0.7, 1, and 2 M) and were also at temperatures between 100 and 340°C for 3 h. To examine the catalytic activity of bentonite-based catalysts, the samples were evaluated after running batch and continuous experiments. The optimum catalyst was characterized using thermo-programmed desorption (TPD) of NH3 to examine the acidic sites. Scanning Electron Microscopy (SEM) images, nitrogen adsorption-desorption isotherms (BET analysis), and X-ray diffraction (XRD) patterns were used to study the structural changes of the bentonite produced by the acid and thermal activation. The removal of olefins by the catalysts in batch and continuous systems revealed that the sample modified with 0.3 M Nitric acid at 150°C had superior catalytic activity, with olefin conversion remaining at >50% for up to 20 h. Nitrogen adsorption-desorption isotherms showed that acid treatment can produce a mesoporous structure. On the other hand, the TPD analysis indicated that during weak acid treatment, some cations, such as Al3+ and Fe3+, were leached from octahedral sheets and the interlayers of the clay mineral resulting in weak acid sites being generated. Finally, a novel method was proposed and tested for measuring the Bromine Index (BI) using potentiometric titration.

Two-dimensional montmorillonite nanolayers (2D Mnt) are excellent adsorbents for methylene blue due to the fully exposed active sites, but the separation of 2D Mnt from water is difficult. The objective of the present study was to assemble 2D Mnt and graphene oxide sheets into a three-dimensional aerogel (3D Mnt-rGO Gel) to achieve easy solid–liquid separation. Structural characterization demonstrated that the Mnt-rGO Gel has a porous 3D structure with Mnt nanolayers distributed uniformly within; the introduction of 2D Mnt could reduce significantly the degree of restacking of graphene sheets. Adsorption tests indicated that 2D Mnt enhances the methylene blue (MB) removal performance of Mnt-rGO Gel with a large adsorption capacity of 207 mg g–1, which may be attributed to the adsorption of MB onto 2D Mnt and the increased adsorption surface of rGO resulting from the reduced restacking of graphene sheets. The MB was removed completely by 300 mg L–1 of Mnt-rGO Gel-3 in 180 min. The adsorption process of MB onto Mnt-rGO Gel followed the pseudo-second order kinetic model and the Langmuir isotherm model. Mnt-rGO Gel also showed good reusability. Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results suggested that the adsorption of MB onto Mnt-rGO Gel may be attributed to the π–π interactions between aromatic rings of MB and graphene, hydrogen bonding, and the electrostatic interactions between the nitrogen groups on the MB and oxygen-containing groups on the Mnt-rGO Gel.

Isomorphous substitutions of Mg and Fe for Al generally appear in the octahedral sheets of montmorillonite, whereas they are infrequent in kaolinite. Therefore, the release of Mg and Fe from the octahedral sheets probably happens during the transformation of montmorillonite into kaolinite, which could affect the migration of Mg and Fe from clay minerals into surrounding environments. The objective of the current study was to investigate the relationship between Mg and Fe release during the transformation of montmorillonite into kaolinite. The results showed that the d060 value of clay minerals decreased slightly, and the intensities of both the AlMg–OH and AlFe–OH bending vibrations also decreased gradually. In addition, the (Mg+Fe)/Al (major octahedral ions) atomic ratio of kaolinite was lower than that of montmorillonite, especially in identical hydrothermal products. These results indicated that Mg and Fe ions were released progressively from the octahedral sheets during the transformation of montmorillonite into kaolinite. Moreover, the changed relative concentrations of Mg and Fe ions in the supernatant solutions after hydrothermal reactions suggested a random distribution of Mg and/or Fe in the octahedral sheets of the montmorillonite. These results improve understanding of the release relationship between Mg and Fe during clay mineral evolution and of the distribution of these two ions in the octahedral sheets, as well as the chemical composition of clay minerals as an indicator of geological environments.