This review demonstrates that high-resolution transmission electron microscopy (HRTEM) imaging of clay minerals or phyllosilicates with an incident electron beam along the major zone axes parallel to the constituting layers, in which the contrast corresponds to individual cation columns in the images obtained, is indispensable for elucidating the enigmatic structures of these minerals. Several kinds of variables for layer stacking, including polytypes, stacking disorder and the interstratification of various kinds of unit layers or interlayer materials, are common in phyllosilicates. Local and rigorous determination of such variables is possible only with HRTEM, although examination as to whether the results obtained by the HRTEM images from limited areas represent the whole specimen should be made using other techniques, such as X-ray diffraction. Analysis of these stacking features in clay minerals provides valuable insights into their origin and/or formation processes. Recent state-of-the-art techniques in electron microscopy, including incoherent imaging, superior resolutions of ~0.1 nm and low-dose imaging using new recording media, will also contribute significantly to our understanding of the true structures of clay minerals.

The synthesis of copper citrate complex supported on acid-activated vermiculite was investigated with a view to preparing an efficient, mild, robust and recyclable catalyst for the Biginelli reaction. The new catalyst was characterized by X-ray fluorescence (XRF), infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), X-ray powder diffraction (XRD), and scanning electron microscopy (SEM) coupled with energy dispersive X-ray spectroscopy (EDS). Copper citrate supported over activated vermiculite (AAVrm-Cu2) showed good catalytic activity in the synthesis of 3,4-dihydropyrimidinones. The catalyst can be separated easily from the reaction mixture by filtration and retains its catalytic activity for up to five cycles of reaction with no apparent decrease in yield.

The aim of this study was to help drive the Tunisian construction industry towards a more sustainable approach given the existence of abundant local raw material deposits that could be exploited for the production of low-CO2 binders. Various clay sediments from the Kebili region (southern Tunisia) were characterized by chemical analysis, X-ray diffraction, thermal analysis and geotechnical tests to determine their suitability for the preparation of geopolymer binders. The clays consist of illite and kaolinite with other accessory minerals. To test the possibility of using these materials as precursors for the production of low-CO2 and low-cost geopolymers, the raw samples were calcined and activated by addition of solid sodium silicate. Compressive strength tests performed on four alkali-activated clays show that promising mechanical performance may be achieved, with mechanical strength values as high as 25 MPa after 7 days, depending on the clay composition. The mechanical strength is related to the SiO2:Al2O3 and Al2O3:(NaO2 + K2O) ratios. Careful selection of the raw materials is, therefore, an essential step in the exploitation of clay deposits to be used for the production of ecological materials such as geopolymers.

The addition of clay minerals in drilling fluids modifies the dispersion's viscosity. In this article, scientific advances related to the use of clays and clay minerals (bentonite, palygorskite, sepiolite and mixtures of clay minerals) in drilling fluids are summarized and discussed based on their specific structure, rheological properties, applications, prevailing challenges and future directions. The rheological properties of drilling fluids are affected by the temperature, type of electrolytes, pH and concentration of clay minerals. Bentonites are smectite-rich clays often used in drilling fluids, and their composition varies from deposit to deposit. Such variations significantly affect the behaviour of bentonite-based drilling fluids. Palygorskite is suitable for use in oil-based drilling fluids, but the gelation and gel structures of palygorskite-added drilling fluids have not received much attention. Sepiolite is often used in water-based drilling fluids as a rheological additive. Dispersions containing mixtures of clays including bentonite, kaolin, palygorskite and sepiolite are used in drilling fluids requiring specific features such as high-density drilling fluids or those used in impermeable slurry walls. In these cases, the surface chemistry–microstructure–property relationships of mixed-clay dispersions need to be understood fully. The prevailing challenges and future directions in drilling fluids research include safety, ‘green’ processes and high-temperature and high-pressure-resistant clay minerals.

Tannic acid-stabilized silver nanoparticles were synthesized in situ on halloysite clay nanotubes. The synthesis strategy included simple steps of tannic acid adsorption on clay nanotubes and further particle formation from silver salt solution. Pristine halloysite nanotubes as well as amino-modified clays were used for silver stabilization in water or ethanol. The materials were tested for antibacterial performance using three different methods. All of the materials produced showed antimicrobial activity. The pristine halloysite-based material with ~5 nm particles produced using ethanol as the solvent and tannic acid as the reducing agent showed the greatest antibacterial activity against Serratia marcescens. The materials were tested in vivo on Caenorhabditis elegans nematodes to ensure their safety, and they showed no negative effects on nematode growth and life expectancy.

Sodium smectite clays were enriched with ferric ions (Argel-Fe and Volclay-Fe) to convert the surface charge of the clays from negative to positive and to use the clays in the discolouration of a synthetic effluent composed of seven anionic dyes (mixed from tartrazine, Brilliant Blue FCF and amaranth). The iron content increased from 5.99% to 11.02% for Argel-Fe and from 5.39% to 10.54% for Volclay-Fe. The efficiency of the discolouration of the anion dye mixture was evaluated by measuring the absorbance of the mixture at 562 nm, where the band with the greatest intensity was found. The contact time required for the system to reach equilibrium was ~5 min for both adsorbents. The kinetic adsorption data supported a pseudo-second-order kinetic model. The experimental data support the dual-site Langmuir–Freundlich isotherm model. The maximum adsorption capacities were 88.68 mg g–1 for Argel-Fe and 392.21 mg g–1 for Volclay-Fe. The enrichment of clays with Fe(III) added functionality to the clays and generated adsorbents with rapid adsorption abilities and high discolouration capacities.

This paper deals with the adsorption of an essential oil (EO) on a kaolinite-rich clay and a smectite-rich clay. The two clays were modified with a quaternary alkyl ammonium surfactant to create a lipophilic environment for better adsorption of the EO. The preparation of the clay/EO hybrids avoided the use of a slurry and organic solvent. The selected EO was that of Lippia multiflora. This EO has insecticidal properties. The surfactant was trioctyl methylammonium (TOMA). The modified clays were characterized by X-ray diffraction (XRD) and infrared (IR) spectroscopy. The smectite-rich clay displayed greater adsorption of the L. multiflora EO compared to the kaolinite-rich clay. The interlayer space of the kaolinite-rich clay was not affected by the adsorption of the TOMA and/or EO molecules, which suggests that the adsorption in this clay took place on the external surface. By contrast, a significant increase in the interlayer space of the smectite-rich clay was observed, suggesting that the adsorption process of TOMA and/or EO took place on both the external and internal surfaces. The IR analysis showed that the surfactant loading in the interlayer space of the smectite-rich clay introduces a gauche conformation in the alkyl chains. A formulation mixing this local smectite-rich clay and the L. multiflora EO has potential for the manufacture of new biopesticides.

Thermoplastic polyurethane (TPU) matrix was reinforced with polyhedral oligomeric silsesquioxane (POSS) and halloysite nanotubes (HNT), both separately and combined. Composite samples were fabricated using a melt-compounding method. Characterization of the composites obtained was performed via tensile and hardness tests, melt-flow index measurements (MFI), abrasion tests, dynamic mechanical analysis (DMA) and scanning electron microscopy (SEM) to investigate the mechanical performance, flow behaviour, tribological characteristics, thermo-mechanical response and morphological properties. The greatest tensile strength value was obtained for the smallest HNT content. Further addition of HNT resulted in agglomerations for both POSS and HNT particles. The shore hardness of TPU was enhanced by filler inclusions. The TPU/POSS composites displayed significant improvement in terms of abrasion resistance compared to TPU at lower loading levels. The DMA study showed that composites containing 0.5% POSS and 1.0% HNT displayed the greatest storage modulus. The glass-transition temperature of TPU shifted to smaller values with the addition of both nanoparticles. The HNT inclusions increased the MFI value of TPU because of their large aspect ratio. Homogeneous mixing of nanoparticles in the TPU matrix was confirmed by a SEM study of the composites. Their dispersion decreased as the concentrations of POSS and HNT increased. An adjuvant effect of POSS with HNT was achieved in their hybrid composites.

Smectite interlayer water plays a key role in the mobility of elements and molecules and affects a variety of geological processes. In trioctahedral smectites, in contrast to saponite and hectorite, the layer charge of which originates from isomorphic substitutions, the stevensite layer charge originates from the presence of octahedral vacancies. Despite its common occurrence in lacustrine environments, stevensite hydration has received little attention compared to saponite and hectorite. Early reports mention a specific hydration behaviour, however, with the systematic presence of a low-angle reflection attributed to the regular interstratification of various hydration states. The present study aims to revisit this specific hydration behaviour in more depth. Within this scope, the hydration behaviour of the three smectite varieties above are compared using synthetic trioctahedral smectites of similar layer charge and various compositions of their octahedral sheets. The chemical composition of the octahedral sheet does not appear to influence significantly smectite hydration for saponite and hectorite. Compared to its saponite and hectorite equivalents, H2O content in stevensite is lower by ~2.0 mmol H2O per g of dry clay. Consistent with this lower H2O content, Zn-stevensite lacks a stable monohydrated state, with dehydrated layers prevailing from 60% to 0% relative humidity. The presence of the regular interstratification of 0W and 1W layers is responsible for the low-angle reflection commonly observed for stevensite under air-dried conditions. Finally, the stevensite identification method based on X-ray diffraction of heated and ethylene glycol-solvated samples is challenged by the possible influence of the octahedral sheet chemical composition (Zn or Mg in the present study) on hectorite swelling behaviour in synthetic Zn-smectites. The origin of this effect remains undetermined and further work is needed to propose a more general identification method.

In this study, for the first time Bacillus methylotrophicus Y37 cellulase was purified and recovered in a single step by three-phase partitioning (TPP). The optimal purification parameters for TPP were 40% ammonium sulfate saturation (m/v) with a 1.0:1.0 (v/v) ratio of crude extract:t-butanol, which gave 5.8-fold purification with 155% recovery of cellulase. Non-covalent immobilization of the partitioned cellulase was performed using bentonite as a support material. The activity observed in the 20th experiment was 100%. The optimal pH values and temperatures determined for the free enzyme and the immobilized enzyme were 5.0 and 6.0 and 45°C and 50°C, respectively. The Arrhenius activation energy (Ea) of the immobilized enzyme was lower than that of the free enzyme, whereas the Michaelis–Menten constant (Km) and maximum velocity (Vm) of the immobilized enzyme increased. The turnover number (kcat) and the catalytic performance (kcat/Km) demonstrated the improved catalytic properties of the immobilized enzyme compared to the free enzyme. Immobilization of cellulase is thermodynamically preferred.

An effective method that combines solvent extraction with ultrasonic irradiation was developed to recycle spent bleaching clay (SBC) from modern oil refinery plants. The principle of ‘waste to treasure’ was used to achieve the regenerated SBC. Various characterization techniques were applied to analyse and compare regenerated SBC and commercial bleaching clay (CBC). The structure of the regenerated SBC did not show any obvious change compared with that of CBC, but the Brunauer–Emmett–Teller-specific surface area (SBET) and pore-volume values of the regenerated SBC increased. At the same time, the parameters of the regenerated SBC reached national standards. In addition, the samples were used as low-cost adsorbents for the adsorption of methylene blue (MB) from water. The regenerated SBC had greater adsorption efficiency and cycle performance for MB than CBC. Hence, the SBC may be treated by ultrasonic radiation combined with extraction, and the regenerated SBC has better properties than CBC. This work opens up a new approach to the regeneration and utilization of SBC and raises the potential of ultrasonic irradiation as an environmentally friendly method to be applied to various regeneration systems.

To produce an optimized matrix for the in situ crystallization of zeolite Y, a commercial kaolin chemically treated with NaOH solution at 97°C for 24 h and thermally transformed from 750 to 1100°C was studied. The kaolin calcined at 750°C has 20% more reactive tetrahedral aluminium species for the synthesis of zeolite Y than kaolin calcined at 865°C. The kaolin calcined at 1000°C has amorphous silica zones that may be extracted using caustic solution; this increases the surface area by a factor of 16 and generates mesopores ~5 nm in diameter. These structural changes in the calcined and treated kaolins were combined to prepare microspheres of the mesoporous matrix, upon which well-dispersed crystals of zeolite Y crystallized.

Volcanic tuffs are important in determining the stratigraphic age of sedimentary sequences, which is closely related to the tectonic, sedimentological, geomorphological, palaeoclimatic, and palaeo-ecological evolution of the sequences. However, it may be difficult practically to identify tuffs in stratigraphic sections, especially when they are altered after deposition. In this study, a series of petrographic, mineralogical, and geochemical analyses was deployed in the tuff layers cropping out in the Lunpola Basin of the central Tibetan Plateau, which is a crucial site for studying the dynamics and processes of the Cenozoic uplift of the Tibetan Plateau and its environmental impacts. In these pyroclastic layers, authigenic analcime is the main volcanic glass alteration product. The analcime-bearing samples are Na-enriched, in contrast to the K-abundant magmatic rocks in the central Tibetan Plateau. The distribution patterns of the rare earth elements (REEs) of the bulk analcime-bearing samples are similar to those of the magmatic rocks but different from those of the analcime-poor sediments and analogues of well-mixed upper continental material (e.g. the upper continental crust and post-Archaean Australian average shales). The distinct distributions of Na and REEs among analcime-bearing samples, analcime-poor sediments, and volcanic rocks reveal that analcime formed both from alteration of volcanic material and from mixing processes with non-volcanic sediments. It is proposed, therefore, that the discrimination plot of Na2O/Al2O3-(La/Yb)N may be used to distinguish the analcime-related pyroclastic rocks from the basin sedimentary sequence, and thus it may provide a means of discriminating between various volcanic material and of supporting age dating by tephrochronology in the central Tibetan Plateau.

This study reports on the effects of dielectric barrier discharge-like (DBD-like) plasma jet treatment at atmospheric pressure on Ag cation-exchanged clinoptilolite. In the plasma treatment process, argon plasma was applied to the surface of pellet samples prepared with Ag-clinoptilolite. After DBD-like plasma jet treatment for 30 and 60 min, remarkable colour changes were observed in the pellet samples. These changes indicate that the DBD-like plasma jet application led to the successful reduction of Ag+ to its metallic forms, which was further confirmed by the results of ultraviolet–visible diffuse reflectance spectroscopy. The structural, composition and morphological properties of the DBD-like plasma jet-treated samples were characterized using Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscopy and energy-dispersive X-ray analyses, and they were compared to the untreated Ag-clinoptilolite. The DBD-like plasma jet treatment caused no detectable structural changes in clinoptilolite within the analytical limitations of the methods used. The FTIR spectra show that the plasma treatment causes discharge-induced functional changes in the hydroxyl stretching region. The peaks appearing in the XRD patterns confirmed the reduction of Ag+ to Ag0 after exposure to the plasma. The present study indicates that the reduction of Ag+ cations to their metallic forms can be performed successfully using the proposed method without collapsing the crystal structure of the Ag-clinoptilolite.

Hydrotalcites with heterogeneous distributions of anions between their layers were synthesized. Some synthesis parameters were studied to verify their influence on the anionic segregation properties of the hydrotalcites. The nature of the divalent cation and the crystallization method were most relevant. Zinc, in contrast to magnesium, assisted in discriminating carbonates and attracting nitrates to form hydrotalcites with heterogeneous distributions using microwave irradiation. Furthermore, the identification of this kind of hydrotalcite could be easily verified by determining the presence of a double reflection in the 003 X-ray diffraction (XRD) maximum, which definitively characterized a heterogeneous anion distribution. Finally, the reason as to why in some cases the hydrotalcite presented two reflections in the 003 XRD peak was elucidated.

In this investigation, Maghnia (Ma) and Mostaganem (Ms) bentonite clays, mined from west Algeria, with no prior affinity for anionic dyes, were modified by simple ion exchange with aqueous Fe3+ solutions, followed by calcination at 500°C. The resulting materials, Fe-Ma and Fe-Ms, respectively, were employed as adsorbents for methyl orange. The starting materials and the two adsorbents were characterized by X-ray diffraction, N2 adsorption–desorption isotherms, Brunauer–Emmett–Teller specific surface area and X-ray fluorescence and by determining the point of zero charge. The effects of various variables, such as initial dye concentration, contact time, adsorbent dose, initial pH and adsorption temperature, were studied. The kinetics were well described by the pseudo-second-order model and the mechanism was determined from the intraparticle diffusion model, while corresponding isotherms fitted better to the Freundlich model. Thermodynamic parameters showed that the adsorption process was endothermic, spontaneous and physical in nature, accompanied by an increase of entropy.

The production of pottery in the traditional manner using local raw materials can provide insights into the provenance of ancient artefacts. This study uses mineralogical analysis to evaluate the raw clays and tempers used for pottery production in Zlakusa (western Serbia). Particle-size distribution, plasticity, X-ray fluorescence spectroscopy, X-ray powder diffraction, scanning electron microscopy/energy-dispersive X-ray spectrometry and differential thermal analysis techniques were applied. The mineral phases identified in the raw clay sample are kaolinite/halloysite, mica/illite, smectite, quartz, paragonite, feldspar, calcite and hematite. The clay body sample is a mixture of raw clay and crushed calcite in a ~50:50 ratio, which was confirmed using various techniques. We have also considered and investigated the technological potential of the sampled materials, taking into consideration their actual and potential applications. It was confirmed that the clay body may be used in the manufacture of bricks and pottery, but its industrial application is limited by the paste recipe.

Fly ash zeolites are economically and ecologically attractive alternatives to synthetic and natural zeolites. Their use as sulfur dioxide sorbents is one of the possible applications of these materials. During the process of fly ash zeolite synthesis, a light powder is formed, which is not acceptable in practical applications due to technical problems, such as a marked drop in pressure, diffusion limits, hydraulic resistance, clogging in the packed beds and the possibility of losing a bed. It is therefore necessary to perform a pelletization process. Thickening of the material during pelletization influences sorption capacity negatively due to diffusing limitations, while the lack of an additional binder may result in a material of low mechanical durability. In this study, pressure pelletization experiments with fly ash zeolite were performed. Binders were selected on the basis of economic considerations as well as their potential to exert a positive influence on the sorption properties of the produced pellets. Cyclic sorption experiments were conducted (on sulfur dioxide) in which one zeolite powder sample was subjected to pelletization without a binder and another sample was subjected to the process with selected binders added. The results of the experiments were then analysed to ascertain the influence of the pelletization process on sulfur dioxide sorption capacity.

Sepiolite powder was hydrothermally solidified into a cemented, designed to function both in humidity regulation and volatile organic compound (VOC) removal. The solidification process mimicked the cementation of sedimentary rocks. The formation of the calcium aluminium silicate hydrate (C-A-S-H) or Al-tobermorite enhanced the strength (maximum flexural strength >17 MPa) and improved the porosity of the solidified materials. Due to the low temperature of hydrothermal solidification (≤473.15 K), most sepiolite remained in the matrix of the solidified specimens. The cemented sepiolite aggregate shows outstanding humidity-regulating performance (moisture adsorption of 430 g m–2), and the synergistic effects of the residual sepiolite and neoformed Al-tobermorite exerted a positive influence on the humidity regulation performance of the material. Similarly to the behaviour of sepiolite, the solidified material also displayed good formaldehyde-removal capacity (60–68%). The pore dimensions controlled the humidity regulation and formaldehyde removal. The humidity regulation depends on the mesopores, which originate mainly from both the original sepiolite and the neoformed C-A-S-H phases and Al-tobermorite, while the formaldehyde removal depends on the micropores from the original sepiolite in the matrix. As such, the cemented sepiolite aggregate might be hydrothermally synthesized and might be used to improve the comfort and safety of indoor environments for human beings.

Adsorption kinetic and thermodynamic tests were conducted using non-irradiated and γ-irradiated (400 kGy) NaOH-modified Philippine natural zeolites for the removal of Cu2+ ions in aqueous solution. The effects of γ-radiation on zeolites were investigated. Samples were equilibrated with binary systems of Cu2+ ↔ 2Na+ at room temperature. There were no significant changes in the elemental composition of the irradiated zeolite. Irradiation primarily results in the shrinking of the zeolite framework and improvements in the crystallinity. The γ-irradiation increases the sorption uptake according to the kinetic study in which the adsorption kinetics followed a pseudo-second-order model. Thermodynamic tests show that the adsorption isotherms of the two samples are best described by the Langmuir model. The maximum adsorption capacities of the non-irradiated and γ-irradiated NaOH-modified zeolites are 33.00 and 43.22 mg Cu2+ g–1, respectively, suggesting that γ-irradiation might enhance the maximum adsorption capacity by up to 30.8%.