Hybrid films consisting of Sumecton SA smectite (SSA) and a diacetylenic two-photon absorptive dye; 1,4-bis(2,5-dimethoxy-4-{2-[4-(N-methyl)pyridinium]ethenyl}phenyl) butadiyne triflate (MPPBT) were fabricated. The MPPBT-clay composites were prepared by the cation exchange method in a dimethylsulfoxide (DMSO)-water mixed solvent. A low-light-scattering film, suitable for use in optical devices, was obtained by filtration of the dispersion of the MPPBT-clay composites. Estimation of the two-photon absorption cross-section (σ(2)) by means of the open-aperture Z-scan technique was performed using the present film. The σ(2) value of MPPBT in the film fabricated at the MPPBT loading levels vs. 20% cation exchange capacity was 1030 GM (1 GM= 1 × 1050 cm4 s photon−1 molecule−1) at an excitation wavelength of 800 nm. The value was 1.3 times greater than the maximum value of the σ(2) of MPPBT diss lved in DMSO with ut clay.

Due to the increased importance of bionanocomposites, protamine and papain proteins were adsorbed on Na+- and on Cs+-exchanged saponite from aqueous solution. Protein analysis of equilibrium solutions and thermogravimetric analyses of biocomposites were used to prepare adsorption isotherms. Based on the isotherm shape, and on the amounts of protein adsorbed and the amounts of Na+ and Cs+ released, the initial protein sorption apparently was due to ion exchange. Additional sorbed protein was weakly retained and could be removed by washing with water. From ion exchange, the average charge of the protamine adsorbed was estimated to be +13.1 to +13.5. Similar papain measurements could not be made due to partial decomposition. Quantitatively, protamine was adsorbed at levels up to 400 mg/g on Na+-saponite and 200 mg/g on Cs+-saponite. The maximum protamine adsorption was 650 to 700 mg/g for Na+-saponite and 350–400 mg/g for Cs+-saponite. Protamine was sorbed to edge surfaces and the basal spacing of the interlamellar region of saponite was 1.75 nm. Protamine displaced only 36% of the Cs+ in Cs+-saponite and expanded the interlamellar region by 36% for a basal spacing of 1.6 nm. Papain sorption to Na+-saponite occurred by a two-step process: (1) adsorption to saponite particle external surfaces followed, (2) by partial intercalation. Quantitatively, Papain was adsorbed up to 100 mg/g for Na+-and Cs+-saponite. Greater initial papain concentrations resulted in a 450 mg/g maximum for Na+-saponite, but no increase above 100 mg/g for Cs+-saponite. Papain apparently only sorbed to external Cs+-saponite surfaces that were estimated to be 33–40 m2/g. Step-wise thermal decomposition of the saponite-protein composites occurred between 300 and 800°C.

Sub-micrometer clay particles are of interest in clay-polymer applications, especially when transparency is important. The scattering of light can be reduced by the adjustment of the refractive index (RI) of the clays to that of the matrix. In this study, the RI of sub-micrometer illite particles was changed by treatment with 5 M HCl for treatment times ranging between 2 and 24 h. The dissolution of Fe leads to a decrease in the RI of illite from 1.587 for the unaltered material to 1.502 after 24 h. The layer structure of the illite particles was preserved during the treatment. The RI of the sub-micrometer illite particles was determined by means of a photospectrometer measuring the light intensity passing through suspensions containing the clay particles, with varying refractive indices.

Various physicochemical characteristics of a sepiolite sample from the Eskişehir area, Turkey, were investigated to help in making predictions about possible uses of the material. The sample was examined by chemical analysis (CA), thermal analysis (DTA/TGA), X-ray diffraction (XRD) analysis, particle-size analysis (PSA), linear dilatometry (LD), scanning electron microscopy (SEM), mercury porosimetry (Hg-Por.), and low-temperature nitrogen adsorption/desorption (N2-AD) techniques. The CA and XRD data indicated that the sepiolite contains only 6% dolomite by mass. The XRD patterns showed that sepiolite anhydride, enstatite, diopside, and opal-CT form upon heating the sepiolite above 600, 800, 900, and 1200°C, respectively. The maximum rate of endothermic changes in the DTA and TGA curves were observed at 82, 287, and 491°C, corresponding to the loss of external, zeolitic, and bound water from the sepiolite, respectively. Dehydroxylation and recrystallization of the sepiolite were fastest at 845°C and 862°C, respectively. The LD curve indicated that the shrinkage began at 800°C and reached 4.0% at 1000°C. The proportion of particles with diameters of <2 µm, and the external surface area of the long-term (24 h) water-treated sepiolite were determined by PSA as 79% by volume, and 8 m2g−1, respectively. The SEM view revealed discrete bundles of sepiolite fibers of various lengths. The specific surface area found from adsorption data was 316 m2g−1. The specific micro-, meso-, macro-, and total-pore volumes obtained from the combination of Hg-Por. and N2-AD results were 0.16, 0.21, 0.45, and 0.82 cm3g−1, respectively. The average macropore and micro-mesopore radii in the sepiolite were estimated (using the Hg-Por. and N2-AD data) tobe 35 and 2.4 nm, respectively.

The configuration of hydroxyl groups around the octahedral cations of 2:1 phyllosilicate minerals has long been an important question in clay science. In the present study, 27Al multiple quantum (MQ) magic angle spinning nuclear magnetic resonance (MAS NMR) was applied to the local structural analysis of octahedral Al positions in a purified Na-montmorillonite. Three octahedral Al sites ([6]Ala, [6]Alb, and [6]Alc) are distinguished by 27Al 5QMAS NMR, whereas these sites are not differentiated by 27Al MAS and 3QMAS NMR. The isotropic chemical shift (δcs) and the quadrupolar product (PQ) were estimated to be 5.8 ppm and 2.6 MHz for [6]Ala, 6.2 ppm and 3.0 MHz for [6]Alb, and 6.7 ppm and 3.7 MHz for [6]Alc, respectively. The three Al sites originated from geometric isomers with cis and trans structures, which have mutually different configurations of the OH groups around the central Al3+ ions. From the view point of symmetry for the OH groups, [6]Ala and [6]Alb in the upfield region were assigned to cis sites, and [6]Alc in the downfield region was assigned to a trans site. The occurrence of multiple Al sites implies that Na-montmorillonite used in the present study has cis-vacant structure in the octahedral sheet. This is a reasonable insight, supported by the chemical composition and the differential thermal analysis data of the Na-montmorillonite.

Feroxyhyte (δ′-FeOOH) is a relatively uncommon Fe oxide mineral and one of the few phases in the system Fe2O3-H2O for which thermodynamic properties are not known. In natural occurrences, it is always fine-grained, although samples with larger particle sizes and better crystallinity (labeled as δ-FeOOH) can be prepared in the laboratory. This contribution presents a thermochemical study on a series of feroxyhyte samples. One is fine-grained and poorly crystalline, similar to natural materials, while the other three are of better crystallinity. The enthalpy of formation of feroxyhyte at 298.15 K is −547.4±1.3kJ mol−1 for the poorly crystalline sample (surface area 88 m2/g), and −550.6±1.4, −550.9±1.3, and −552.6±1.2 kJ mol−1 for the samples with better crystallinity. The entropy of feroxyhyte can be estimated only crudely, because it is influenced to a great extent by its magnetic properties, particle size, and structural disorder. The $S_{298}^{\text{o}}$$S_{298}^{\rm{o}}$ of feroxyhyte is estimated here to be 65±5 J K−1 mol−1. The Gibbs free energy of the reaction feroxyhyte → hematite + liquid water is −7.4 to −12.6 kJ mol−1 at 298.15 K. The Gibbs free energy of formation ($\text{Δ}{G}_{\text{f}}^{\text{o}}$${\rm{\Delta }}G_{\rm{f}}^{\rm{o}}$) of the fine-grained, poorly crystalline feroxyhyte is −478.1±2.0 kJ mol−1 at 298.15 K. Since this sample is closest in its physical properties to natural feroxyhyte, this $\text{Δ}{G}_{\text{f}}^{\text{o}}$${\rm{\Delta }}G_{\rm{f}}^{\rm{o}}$ value should be used in thermodynamic modeling related to processes involving naturally occurring feroxyhyte. In terms of Gibbs free energy and enthalpy, feroxyhyte is very similar to lepidocrocite and maghemite, and, like these two phases, has no thermodynamic stability field in the system Fe2O3-H2O, except possibly at the nanoscale.

Increasing use of irrigation in India has exacerbated the problems of soil salinity and sodicity. The present study was undertaken on shrink-swell soils from Maharastra State to determine if changes in soil chemistry due to irrigation have affected the clay mineralogy. Twenty six samples (15 locations) of irrigation-induced, saline-sodic, shrink-swell soils and 27 samples (22 locations) of normal un-irrigated (rain-fed) shrink-swell soils were studied using X-ray powder diffraction (XRPD), infrared spectroscopy (FTIR), and scanning and transmission electron microscopy (SEM, TEM). The XRPD analysis of the <0.2 µm fraction of rain-fed, shrink-swell soils indicates a predominance of dioctahedral smectite with minor to trace amounts of kaolinite and chlorite. Traces of palygorskite (1–4%) were detected in three samples. In contrast, palygorskite is a common component (1–20%) of the fine-clay fraction of saline-sodic soils. Quantitative analysis of palygorskite by XRPD in whole-soil (<2 mm) samples showed that saline-sodic soils contain up to 20 wt.% of palygorskite, whereas palygorskite was only detectable (1.5 wt.%) in one sample of the rain-fed set. The SEM, TEM, and FTIR confirm the presence of Fe-rich palygorskite in saline-sodic soils and demonstrate that the fibrous palygorskite crystals are exceedingly small (∼0.5 µm long). Delicate palygorskite fibers radiate from the margins of smectite plates suggestive of a pedogenic origin and a close genetic relationship between smectite and palygorskite. The compositions of saturation-paste extracts display a shift from the stability field of smectite in rain-fed soils to that of palygorskite in saline-sodic soils. Thus the occurrence and formation of palygorskite appears to be related to the change in land management from rain-fed to irrigated agriculture. This change has occurred over a period of no more than 40–50 y, implying that palygorskite formation in the irrigated, saline-sodic soils has been an extremely rapid process.

Montmorillonite modified with the cationic biopolymer, chitosan, has, in weak acidic solutions, protonated amine groups which act as anion-adsorption sites. Due to the specific surroundings of the adsorption sites and diffusion paths in the interlayer of chitosan-montmorillonite, preferential adsorption of certain anions is likely. In the present study, the adsorption properties for the inorganic anions Cr(VI) and As(V) were determined, taking into account solution pH and competitive adsorption in the presence of Cl− and ${\text{SO}}_4^{2-}$${\rm{SO}}_4^{2 - }$. Chitosan-montmorillonite was prepared by adding an amount of chitosan equivalent to 500% of the cation exchange capacity (CEC) at pH 5 and 75°C. The resulting anion exchange capacity was ∼0.34 molc/kg. The adsorption properties for As(V) and Cr(VI) were determined with the batch technique at pH 3 to 9. Adsorption isotherms were fitted to the Langmuir and Dubinin-Radushkevich equations and judged quantitatively by the correlation coefficient. To describe the competitive adsorption, the selectivity (S) was determined by the ratio of amounts of anions A and B adsorbed (qA/qB) in a binary system. The ionic species adsorbed, i.e. either Cr(VI) or As(V), depended on the pH, as did the degree of protonation of the amine groups, and this played a decisive role in the amount of anions adsorbed. The maximum amount of Cr(VI) adsorbed was 180 mmol/kg at pH 3.5, whereas for As(V) it was 120 mmol/kg at pH 4.0 to 5.0. The adsorption process of Cr(VI) and As(V) fit well to the Langmuir isotherm. By increasing the concentration of the competitive anion, Cl−, in solution, the amount of Cr(VI) and As(V) adsorbed remained almostconstant, whereas ${\text{SO}}_4^{2-}$${\rm{SO}}_4^{2 - }$ had a more pronounced competitive effect. At concentration ratios of 0.5 and 1 for ${\text{SO}}_4^{2-}$${\rm{SO}}_4^{2 - }$ to Cr(VI) and As(V), respectively, the sorption capacity decreased by 10 and 25%, respectively. The sequence of the selectivity was: $\text{Cr}\left(\text{VI}\right)>{\text{SO}}_4^{2-}>\text{As}\left(\text{V}\right)>{\text{Cl}}^{-}$${\rm{Cr}}\left( {{\rm{VI}}} \right) > {\rm{SO}}_4^{2 - } > {\rm{As}}\left( {\rm{V}} \right) > {\rm{C}}{{\rm{l}}^ - }$. Chitosan-montmorillonite showed a high selectivity for Cr(VI), which adsorbed chemically. Despite the lower affinity for As(V) and physical adsorption, the adsorption capacity was relatively high.

The properties that might influence the sequestration of aflatoxin B1 (AfB1) were examined. Laser-diffraction, particle-size analysis (LDPSA) indicated that the particle size of the smectite influences the amount of AfB1 adsorbed. Effective adsorbent smectites disperse well under combined sodium hexametaphosphate solution and ultrasonic agitation. Particle size explained 66% of the variability for most of the samples investigated in an ‘as-received’ state. One effective adsorbent smectite was especially well aggregated and required additional physical dispersion, thus raising the correlation to 73%. Transmission electron microscope (TEM) images show typical smectites and reveal the very diverse morphology of smectites in bentonites. Thin, cloud-like smectite, in TEM images, related positively to AfB1-adsorption capacity. Particles that often fold and are usually ∼0.5 µm across seem to be optimal. The selection of criteria for evaluating these smectites provides a scientific basis for their selection to obtain reliable performance. Particle size is of particular importance as outlined below, and use of LDPSA makes it possible to perform the analysis efficiently and with precision.

The fungus Aspergillus flavus Link ex Fries can infect grains and oil seeds and develop Aflatoxin B1 (AfB1) in the fieldor in storage. Aflatoxin contamination is a serious health hazard — it is extremely toxic and hepatocarcinogenic for animals and humans. A practical approach to solve this problem is to use smectite clay as an amendment to animal feed. The objective of this research is to investigate smectite clay—AfB1 interactions by employing Fourier transform infrared (FTIR) spectroscopy to determine how clay composition influences AfB1 adsorption by smectites. When AfB1 was present in the clay, the spectral region from 1800 to 1300 cm−1 was altered, and the regions between 4000 and 1800 and 1300 and 400 cm−1 were unchanged except for the intensity in the broad region near 3400 cm−1 related to the abundance of water. The 1300–400 cm−1 region is attributed only to smectite clay properties, and it relates to the relative adsorption potential of the different smectites. Bonding between AfB1 and smectite clay appears to be in the furan rings. Other possible bonding is with the two oxygens in the coumarin ring of AfB1 and interlayer cations or their associated water molecules. The FTIR evidence of octahedral Fe in smectite and amorphous silica in the clays both indicate greater AfB1 adsorption potential. Other smectites with spectral absorption indicating predominantly Al in the octahedral positions adsorbed less AfB1.

Smectite formation in alkaline-saline environments has been attributed to direct precipitation from solution and/or transformation from precursor minerals, but these mechanisms are not universally agreed upon in the literature. The objective of this work was to investigate the mineralogy of smectites in the soils surrounding a representative alkaline-saline lake of Nhecolândia, a sub-region of the Pantanal wetland, Brazil, and then to identify the mechanisms of their formation.

Soils were sampled along a toposequence and analyzed by X-ray diffraction, transmission electron microscopy-energy dispersive X-ray analysis, and inductively coupled plasma-mass spectrometry. Water was collected along a transect involving the studied toposequence and equilibrium diagrams were calculated using the databases PHREEQC and AQUA.

The fine-clay fraction is dominated by smectite, mica, and kaolinite. Smectites are concentrated at two places in the toposequence: an upper zone, which includes the soil horizons rarely reached by the lake-level variation; and a lower zone, which includes the surface horizon within the area of seasonal lake-level variation. Within the upper zone, the smectite is dioctahedral, rich in Al and Fe, and is classified as ferribeidellite. This phase is interstratified with mica and vermiculite and has an Fe content similar to that of the mica identified. These characteristics suggest that the ferribeidellite originates from transformation of micas and that vermiculite is an intermediate phase in this transformation. Within the lower zone, smectites are dominantly trioctahedral, Mg-rich, and are saponitic and stevensitic minerals. In addition, samples enriched in these minerals have much smaller rare-earth element (REE) contents than other soil samples. The water chemistry shows a geochemical control of Mg and saturation with respect to Mg-smectites in the more saline waters. The REE contents, water chemistry, and the presence of Mg-smectite where maximum evaporation is expected, suggest that saponitic and stevensitic minerals originate by chemical precipitation from the water column of the alkaline-saline lake.