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.

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.

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.

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.

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%.

In 2019, BYK Additives (Widnes, UK; www.byk.com) marked the 55th anniversary of the discovery by Dr Barbara Zsusanna (Susanna) Neumann of the extraordinary product known as Laponite®. The range of Laponite® products developed in the UK during the early 1960s is one of the first examples of truly nanodimensional materials manufactured on an industrial scale, at a time when the field of nanotechnology was only being hinted at (Feynman, 1959). These hectorite-like synthetic nanoclays with very unusual properties have been an enduring commercial success for the UK company that first patented and introduced them to the market, Laporte Industries, which is now a part of the BYK company. The Laponite® brand has proved tremendously popular with academic and industrial scientists worldwide, being cited in >3000 patents and >2500 published academic articles.

A Na-montmorillonite (Na-MMT) was activated with HNO3 (20 wt.%) solution at various temperatures and times to obtain acid-activated MMT (Acid-MMT). Zinc (4 wt.%) was supported on Acid-MMT via the impregnation method using Zn(NO3)2⋅6H2O as a precursor. The catalytic performance of the Zn/Acid-MMT for the aromatization of heptane was investigated. The amount and distribution of acidity of Acid-MMT, which could be adjusted by changing the acid activation time and temperature, significantly affected the heptane conversion and aromatics content. As a result, an efficient Zn/Acid-MMT catalyst for the aromatization reaction was obtained by optimizing the acid-treatment conditions of Na-MMT.