This review summarizes several aspects of the interactions between organic dyes and clay minerals, and presents some interesting properties of hybrid materials based on these components. It explains the basic phenomena and photophysical properties of dye/clay mineral hybrid systems (DCHS) while examining the role of clay minerals in them. A brief history of using dyes as tools for clay research and on traditional materials based on DCHS is presented. Metachromasy, the phenomenon of colour change related to the formation of dye molecular aggregates is described in detail and analysed from various perspectives. The properties of DCHS, including photoactivity, luminescence, photocatalytic properties, optical anisotropy and non-linear optical properties are analysed in detail. Clay minerals often play a significant role in the occurrence of specific photophysical phenomena such as resonance energy transfer and luminescence quenching and may influence various reactions, such as conformational changes in dye molecules, photochromism, photoisomerization, photosensitization and other photochemical processes. Routes to synthesize various types of hybrid materials are also described here. The relevance of DCHS for clay research, chemistry and materials science is summarized briefly.

This work describes the development of potential multi-element slow-release fertilizers obtained by mechanochemical activation of mixtures of kaolinite and ammonium or potassium monohydrogen phosphates. Preliminary results of talc amorphization have also been included. The methodology consists of milling the materials in a high-energy ball mill, where the influence of rotation and time of milling were investigated. The samples were characterized by XRD, FTIR, TGA/DTA, SEM and MAS-NMR. The experimental results explain the slow-release behaviour of the amorphous nanostructured materials in aqueous suspensions, especially the MASNMR spectra, which showed the changes in the chemical environment of the elements analysed. The materials displayed slow-release behaviour for phosphates probably because the aluminium ions in the mineral structure interact more thoroughly with phosphate than potassium or ammonium. Nevertheless, in general, all of the nutrients were released slowly.

More than 100 minerals have been reported from the Silver Coin Mine, Nevada USA; five new minerals have been discovered here, due to the unusual geochemical environment. The present study reports on the investigation of a greenish clayey sample from the Silver Coin Mine. After the separation of a fine fraction to enrich the clay minerals, sauconite, a rare Zn-rich smectite, was found by X-ray diffraction (XRD) and was further characterized by differential thermal analysis (DTA), infrared (IR) spectroscopy and scanning electron microscopy (SEM). The Zn-rich smectite is accompanied by illite, minor kaolinite/halloysite and traces of gibbsite (as was indicated by the IR spectroscopy). The occurrence indicates an acidic environment probably caused by oxidation of sulfides.

The determination of the structural formula, to further characterize the Zn-rich smectite, was difficult because of the multi-clay mineral assembly. However, different SEM-EDX (energy dispersive X-ray) approaches as well as transmission electron microscopy (TEM)-EDX analysis helped to characterize the smectite as Al-rich sauconite with some exchangeable K+.

The upper Jequitinhonha Valley is located within the Serra do Espinhaço Meridional mountain range in the State of Minas Gerais, Brazil. The topography is flat or gently undulating with large flat areas known as chapadas (‘high plains’) that are dissected by rivers forming swamps known locally as veredas (‘paths’). The present study is concerned mainly with a representative toposequence in the watershed of the Lagoa do Leandro vereda, a swamp near the city of Minas Novas on a chapada of the highlands of the Alto (Upper) Jequitinhonha region.

The soils of this sequence were studied by a variety of physical and chemical techniques, including Mössbauer, electron spin resonance (ESR) and photoacoustic (PAS) spectroscopies, as well as X-ray diffraction (XRD) and carbon isotope data. Mössbauer spectra of the silt fraction of a grey Xanthic Haplustox (Munsell 10YR 3/2) from the Lagoa do Leandro vereda, referred to here as a ‘Grey Haplustox’ (‘LAC’), proved the existence of Fe2+- and Fe3+-bearing components. Photoacoustic spectroscopy confirmed the presence of Fe2+, as shown by Mössbauer spectroscopy, probably in an octahedrally coordinated site, but the principal optical absorption bands are due to different Fe3+ sites. A ferrimagnetic contribution and three other paramagnetic lines attributed to Fe3+ and Ti3+ were demonstrated by means of ESR. The ESR and PAS results are thus in agreement with the chemical composition and Mössbauer spectroscopy, allowing a detailed characterization of the mineralogy of this silt.

Carbon isotope data indicate the climate to have varied during the past: awetter climate in the Pleistocene, with drier phases in the Late Pleistocene and Holocene, and again a more humid climate 1200 years ago. δ13C data indicate the C3 scrubland vegetation to have occupied the bottom of the vereda in the past (Bispo & Silva, 2014).

Greyish Oxisols that consist chiefly of phyllosilicate minerals of the kaolinite group (which are usually associated with binary oxides and hydroxides) are of common occurrence in tropical soils resulting from leaching and precipitation. Such Oxisols of greyish appearance and similar mineralogy have been described elsewhere from Brazil and, for example, from India. Such soils are therefore proposed here as a new hierarchical level of the Soil Classification System.

During solventless alkylation of phenol with 4-hydroxy-2-butanone under microwave irradiation, paratoluenesulfonic acid (pTSA)-modified montmorillonite clays gave, regioselectively, 4-(4′-hydroxyphenyl)-2-butanone (raspberry ketone). The duration for this reaction under microwave irradiation is much shorter than that of the conventional method. A comparative study of the alkylation reaction over a montmorillonite clay sample treated with 0.5 M-pTSA (0.5 M-pTSA clay) with that of Al-exchanged montmorillonite (Al3+-Mont) and beta-zeolite (HB) was carried out. The results show that the reaction time to reach equilibrium and the product distribution pattern for the reaction over 0.5 M-pTSA clay were similar to those values for the HB. Micropores formed on the clay surface during the pTSA treatment were found to enhance the rate of formation of C-alkylation. Micropores appear to enable better access to the active sites during the course of reaction.

The contamination of water bodies in urban areas is a serious problem, which may increase when wastewater is discharged without complete remediation. Due to their high adsorption capacity and ion-exchange properties, zeolites, such as clinoptilolite, can be used successfully to detoxify the wastewater before discharging it into the water body. In this study, experimental use of clinoptilolite is presented for water remediation. A static flow (A) and a laminar flow (B) method were applied in order to evaluate the efficiency of clinoptilolite for reducing different contaminants in the outflow wastewater of an old municipal treatment plant in Bologna District (Northern Italy). Mesocosm experiments were performed in order to achieve reduction of the microbial faecal indicators and of the excess nutrients and heavy metals in the effluent. During the experiments, pathogenic microorganisms, ammonium and heavy metals were reduced by as much as between 78 and 95% within 24 h, highlighting the great efficiency of this low-cost material for water remediation.

Dolomite and calcite in Bavarian bentonites, southern Germany, were investigated using petrography, field-emission scanning electron microscopy and stable isotope geochemistry to explore the role of authigenic carbonate formation during bentonitization. Pedogenic, palustrine and groundwater carbonates were distinguished on the basis of X-ray diffraction, micromorphological and stable isotope analysis. The δ13CV-PDB and δ18OV-PDB values of dolomite range from −8.0% to −6.1% and −5.4% to −3.4%, respectively. Calcites show a range from −11.9% to −8.1% for carbon and from −9.1% to −6.2% for oxygen. Carbon isotope compositions imply a C3-plant-dominated carbon source and repeated wetting and drying cycles. The oxygen isotope data points to an evaporation and temperature controlled δ18OV-SMOW value of meteoric water of −7.0% to −4.8%. A syngenetic to early diagenetic timing of dolomitization is indicated, suggesting both dolomite and bentonite formation in non-saline, non-arid and repeatedly partially-oxygenated and reducing soil and groundwater environments during pedogenesis.

Nucleation is much more important for clay minerals than for other authigenic cements as clay crystals are very small, so that a very large number of clay crystals must be nucleated. The role of this difficult kinetic step in the diagenesis of sandstones has not been considered adequately as a ratedetermining process. The relationship between pore-fluid supersaturation and the rate of nucleation of a mineral is very different from the relationship between supersaturation and the rate of crystal enlargement; thus the two processes will act at very different rates. A diagenetic model that predicts claymineral formation but omits the nucleation stage may make unreliable predictions. This may account partially for the discrepancy between numerical simulations of CO2 injection that predict high degrees of reaction between the CO2 and the host rock, and the results of studies of natural analogues that have much lower degrees of reaction.

Coatings with the composition of Li-Al-NO3 hydrotalcite were formed on the Al alloy 6060 using a spray system. The coatings consist of crystals with a typical hydrotalcite structure. Dense, uniform and blade-like flakes cover completely the surface of the Al substrate. The coatings display a multi-layer structure with average thickness of ∼1000 nm. The hydrotalcite-coated samples performed better than those without coatings in salt-spray and filiform-corrosion tests, and further treatment involving sealing with a Mg acetate solution and dipping in a H2O2 + Ce-based solution improved the corrosion resistance ability.

The sorption of ibuprofen by modified natural zeolite composites at three concentration levels (10, 20 and 30 mmol/100 g) of cationic surfactants – benzalkonium chloride and cetylpyridinium chloride, in a buffer solution (pH 7.4), was studied. Characterization of the composites before and after ibuprofen sorption was performed by drug sorption and isotherm studies, zeta potential and Fourier Transform infrared spectroscopic analysis. The biopharmaceutical performance of cationic surfactant-modified zeolites as drug formulation excipients was evaluated by in vitro dissolution experiments from the composites with medium surfactant contents. The drug sorption was influenced by the surfactant type and amount used for the zeolite modification. Prolonged drug release over a period of 8 h (up to ~40%) was achieved with both groups of samples. The kinetic analysis showed that the drug release profiles were best fitted with the Higuchi and the Bhaskar models, indicating a combination of drug diffusion and ion exchange as the predominant release mechanisms.

Zn-Al layered double hydroxides (LDH), before and after calcination, were tested for the removal of indigo carmine (IC) dye from solution. These LDH photocatalysts were characterized by powder x-ray diffraction (PXRD), Fourier transform infrared (FTIR) spectroscopy, thermogravimetry/differential thermogravimetry (TG/DTG), nitrogen physisorption at −196°C, scanning electron microscopy (SEM) and diffuse reflectance spectrophotometry (DRS). The different photocatalysts were supported on polyacrylonitrile (PAN) nanofibres, so that filtration was unnecessary.

The PXRD and FTIR analyses showed that the IC adsorption on c-Zn-Al-3-500 (LDH calcined at 500°C) was enhanced by construction of the hydrotalcite matrix intercalated with the dye. The intercalation was clearly evidenced by the appearance of a peak at low °2θ values. All of the materials prepared exhibited photocatalytic activity, which for the c-Zn-Al-3-500 was comparable to that of commercial PAN-supported ZnO nanoparticles (100% degradation after 180 min). Kinetic studies showed that the degradation of the IC followed a pseudo-first order rate. The high activity and the ease of both synthesis and separation processes rendered this photocatalyst a promising candidate for environmental remediation.

Following a round-table discussion at the Mid-European Clay Conference in Dresden 2014, new recommendations for illite ‘crystallinity’ Kübler index standardization have been agreed upon. The use of Crystallinity Index standards in the form of rock-fragment samples will be continued, along with the same numerical scale of measurement presented by Warr & Rice (1994). However, in order to be compatible with the original working definition of Kübler's (1967) anchizone, the upper and lower boundary limits of the Crystallinity Index Standard (CIS) scale are adjusted appropriately from 0.25°2θ and 0.42°2θ to 0.32°2θ and 0.52°2θ. This adjustment is based on an inter-laboratory correlation between the laboratories of Basel, Neuchâtel and the CIS scale. The details of this correction are presented in this first note, as discussed at the round-table meeting and will be further substantiated by a correlation program between CIS and former Kübler–Frey–Kisch standards.

Because of widespread tremolite and chrysotile minerals in Palaeozoic-Mesozoic metamorphic and Triassic ophiolitic units, respectively, in the Eskişehir region, Turkey, there is significant potential for development of cases of mesothelioma. Such occurrences in the Eskişehir region show a positive correlation with the concentration and dimension of tremolite crystals compared with those of chrysotile crystals. A detailed assessment of the mineralogy, geochemistry and genesis of these materials has not been carried out to date; the present study was undertaken to fill that gap. The sharp diagnostic basal reflections at 8.14 Å, 3.09 Å and at 7.30 Å, 3.63 Å, well defined fibrous crystallinity, and ideal differential thermal analysis-thermal gravimetric and Raman curves suggest the development of well crystallized fibrous/acicular tremolite and chrysotile with the average structural formulae of: (Na0.07K0.03)(Ca1.68Mg0.18Mn0.01)(Fe0.42Mg4.55Ti0.01)(Si7.60Al0.24Fe0.16)O22(OH)2, and (Mg5.55Fe0.41 Mn0.006)(Si3.79Al0.13)O10(OH)8, respectively.

Enrichment of light rare earth elements relative to medium rare earth elements and heavy rare earth elements in tremolite compared to that of chrysotile which exhibits no anomaly and negative anomalies for Ba, Sr, Ce, Nb, Yand Zr in the tremolite samples and chrysotile, are responses to the fractionation of feldspar, glaucophane, pyroxene and olivine under the high temperatures of hydrothermal-alteration processes during serpentinization and the high-pressure conditions of metamorphism. Based on H and O isotope data, the tremolite and chrysotile are thought to have developed from tectonically controlled magmatic and meteoric hydrothermal systems and the formation temperatures of the tremolite are higher than those of chrysotile.

Thirty clay samples collected from three hills in Koutaba (west Cameroon) were characterized in order to evaluate their potential use as raw materials for ceramics. After preliminary mineralogical identification by X-ray diffraction, three representative samples from the three different hills, referred to hereafter as K1M, K2M and K3M, were selected for further investigation by X-ray fluorescence, plasticity, granularity and thermogravimetric analysis. The main clay minerals are kaolinite (32–51%) and illite (up to 12%). Additional major phases are quartz (32–52%), goethite (6–7%) and feldspars (0–4%). The chemical composition showed variable amounts of SiO2 (60–72%), Al2O3 (15–20%) and Fe2O3 (1–9%), in accordance with the quartz abundance in all of the samples studied. The particle-size distribution showed a large proportion of silty fraction (64–88%) with moderate sandy (9–19%) and clayey fractions ( < 5% for K2M, 12% for K1M and 20% for K3M). All of the clays showed moderate plasticity-index values (8–11%). Because of these characteristics, K1M and K3M may be suitable for use in common bricks and hollow ceramic products. Sieving or the addition of ball clays is recommended to increase the plasticity of sample K2M for use in common bricks.

X-ray diffraction is one of the most effective tools for the characterization of the stacking defects which occur frequently in clay minerals. Modelling of the diffraction patterns of oriented mounts is often used for obtaining structural information about the nature of stacking order. Manual matching of calculated and observed patterns is time consuming and the results are user dependent and especially troublesome if a consistent model of the same mineral measured under different conditions needs to be obtained. It was shown recently that the Rietveld method could be applied successfully for the evaluation of the X-ray patterns of oriented mounts. Nevertheless, this automatic refinement procedure can also lead to inconsistent results if independent refinements are performed that describe the same sample measured under different conditions. One way to solve this problem is the application of parametric Rietveld refinement. For this approach a set of different measurements of the same sample was collected and fitted in one combined refinement by the connection of the structural models via external parameters. These conditions may involve different pre-treatments (e.g. different intercalations), different temperatures or relative humidities and/or different experimental setup (powder or oriented samples). All patterns were fitted in one overall refinement process by the BGMN software.

This approach was demonstrated on a mixture of two disordered reference materials and on a set of geological samples. Two different states for each sample were refined independently and parametrically and it was shown that this approach leads to consistent results, saves computation time and may even resolve small structural differences.

The Eocene İslambeyli Formation in the Lalapaşa region (NW Thrace, Turkey) consists predominantly of siliciclastic clayey clastics at the bottom and of claystone, tuff and tuffaceous claystone/ sandstone/limestone in the middle and uppermost parts of this formation. Some tuff-tuffaceous beds of the middle–upper parts of the formation are economically viable bentonite depoits. The İslambeyli Formation exhibits vertical variations in the mineralogy, elemental compositions, and smectite-forming processes. Smectite was formed by weathering and diagenetic processes in the fluvial-shore environments in the lower part and by diagenetic alteration in a shallow-marine environment in the middle–upper parts of the formation. Ca-smectite flakes were formed by two processes: direct precipitation; and by means of a dissolution-precipitation mechanism from feldspar and mica. Dissolution-precipitation was most prevalent in the siliciclastic lower part of the formation. The amounts of Al, Fe, Mg and Ca required to form smectite and accessory illite were supplied mainly from the alteration of feldspars, mica and glass shards. The origin of smectite can also be explained by the inferred solution compositions given the parent phases in this formation, and the devitrification of glass shards in pyroclastic-rich middle–upper parts of the formation. In the upper beds, the observed decrease of K and Fe in the smectite structure coincided with both the increase in the amount of smectite and the increase in solution pH suggesting that precipitation of smectite developed over a prolonged period and under arid conditions.

Phillipsite was crystallized from a high siliceous aluminosilicate mixture containing Zn cations and methylene blue (MB). The presence of MB did not affect the crystallization, but it resulted in a substantial amount of dye being anchored to the zeolite, despite its narrow channels. Dye-free synthetic phillipsite modified with MB solution showed markedly lower dye content, which, however was considerably higher than those in the MB-treated natural phillipsite and mordenite. The ultra violet/visible (UV-vis) spectra of the dye-modified synthetic phillipsites indicated the presence of MB monomers and oligomers, whereas the spectra of the modified natural zeolites showed protonated MB also. The electron spin resonance spectra of samples crystallized with MB indicated the presence of paramagnetic species.

Previous work on the structural and thermal properties of various types of kaolinite have led to different conclusions, rendering comparison of analytical results difficult. The objectives of the present study were to investigate the thermal behaviour of kaolinite and to carry out a kinetic analysis of the decomposition of kaolinite at high temperatures. X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and thermogravimetry-differential scanning calorimetry (TG-DSC) were used to study the mechanism of the thermal decomposition. The modified Coats–Redfern, Friedman, Flynn–Wall–Ozawa and Kissinger decomposition models were used to determine the decomposition mechanism of the kaolinite sample. The dehydroxylation of kaolinite occurred at ∼600°C with the formation of metakaolin, which then transformed into either γ-alumina or aluminium-silicon spinel together with amorphous silica. The results of the XRD and FTIR analyses indicated that the γ-alumina, or aluminium-silicon spinel and amorphous silica phases, transformed into mullite and α-cristobalite, respectively, after decomposition at 900°C. Good linearity was observed with the modified Coats–Redfern, Flynn–Wall–Ozawa and Kissinger models from room temperature to 1400°C and the range of the activation energy determined was 120–180 kJ/mol.