Due to the wide range of uses of water-soluble polymers in commercial products, water contamination by polymers has become a serious environmental concern. Adsorption onto an acidic clay, obtained from Tsunagi mine, Niigata, Japan, of water-soluble polymers from aqueous solutions was investigated as a means of purifying water. Poly(vinylpyrrolidone) (PVP) was used as a sample polymer in an attempt to find optimal conditions for extracting the greatest proportion of polymer from the aqueous solution. The adsorption isotherms at lower equilibrium concentrations were of type L, indicating a strong affinity between the acidic clay and PVP. A larger amount of PVP was adsorbed when a higher-molecularweight PVP (comparison between MWs of 160,000 and 10,000) was used. From the Langmuir equation, the adsorption capacity was calculated as 0.029 g/g clay for the adsorption of poly(vinylpyrrolidone) from an aqueous solution. The adsorption of PVP from a NaCl solution (simulated sea water) was also possible though the amount of adsorption was slightly less than from an aqueous solution. A polymer removal efficiency of >90% was achieved when 200 mg of the acidic clay was added to 50 mL of 0.001 wt.% PVP aqueous solution. The acidic clay was also used for adsorption of poly(ethylene glycol), poly(vinyl alcohol), and polyacrylamide from aqueous solutions.

Control of the structure and morphology of clay crystals presents a challenge in the synthesis of materials for adsorption and catalysis. In the present study, direct crystallization of a phyllosilicate grafted with organosilyl (methylsilyl and phenylsilyl) groups on the surface of monodisperse spherical silica particles (2.6 μm) is reported. Methyl- and phenyltriethoxysilanes were allowed to react hydrothermally in a Teflon-lined autoclave with silica, MgCl2, and LiF in the presence of urea for 2 or 4 days. X-ray diffraction patterns revealed that the fine platy particles formed were a trioctahedral hectorite-like layered silicate. Greater temperature (150°C) was required to achieve homogeneous coverage of the original spherical silica particles with the hectorite-like particles. The diameter of the initial silica grains increased slightly to 3.0 μm after the hydrothermal reactions, while the original spherical shape and size distribution were maintained. Solid-state 29Si nuclear magnetic resonance analyses confirmed that the presence of resonances attributed to the RSi(OMg)(OSi)2 and RSi(OMg)(OH)(OSi) (R = methyl or phenyl) environments of the silicon proved the formation of covalent bonds between phyllosilicate sheets and the organic moieties. The crystallinity of the layered silicates increased when the reactions ran for a longer time (4 days).

The molecular aggregation of organic dyes onto clay mineral particles is a very complex phenomenon including dye adsorption, the migration of dye molecules, rearrangement of initially formed aggregates, etc. Some details of this complex process are not yet fully understood. The objective of the present study was to understand the influence of dye surface concentration on the dynamic processes in dye molecular aggregation. A stopped-flow rapid mixing device was used for accurate measurements of the molecular aggregation of the cationic dye rhodamine 123 (R123) in montmorillonite (MntK) colloidal dispersions. The influence of dye surface concentration, which was changed by altering the ratio of the amount of R123 to the mass of MntK (nR123/mMntK), was examined in detail. Chemometric analysis was used to reconstruct the spectral matrix to obtain linearly uncorrelated spectral profiles of the major components and their concentrations at the respective reaction times. The conversion of isolated R123 cations into oblique J-aggregates (head-to-tail molecular assemblies) was observed over time and the existence of a J-dimers intermediate was hypothesized. The reaction kinetics followed a biphasic exponential function. An unexpected effect of dye surface concentration on R123 aggregation was observed: the initial formation of the molecular aggregates increased significantly with dye surface concentration, but an inverse trend was observed after longer reaction times. While dye aggregates were formed slowly at low dye loadings, systems with high R123/MntK ratios (nR123/mMntK) reached spectral stability after the first few seconds of the reaction. After longer reaction times, the greatest degree of dye aggregation was achieved in the dispersion of the lowest dye loading. Such a phenomenon is described for the first time. The results presented here are important for understanding the complex processes occurring in systems based on organic cations and clay minerals, and should be considered in the development of functional hybrid materials of dyes and nanoparticles with a layered structure.

Dye molecular aggregation and other interactions on clay mineral surfaces cause phenomena such as methachromasy (change in color), fluorescence enhancement, or quenching, which represent significant changes in the spectral properties of the dye. These phenomena can be used to control the photophysical properties of hybrid systems based on cationic organic dyes. In the present study, the aggregation of two structurally similar cyanine dyes, 3,3’-diethyl-oxocyanine iodide (OxCy) and 3,3’-diethyl-2,2’-thiacyanine iodide (ThCy), in colloidal dispersions of three smectites (saponite, hectorite, and montmorillonite) was studied by absorption and fluorescence spectroscopy for a broad range of dye/smectite loadings. Spectral data were analysed by chemometric methods (principal component analysis, PCA, and multivariate curve resolution, MCR). Detailed analysis of the OxCy absorption spectra by the chemometric methods revealed the formation of two types of oblique aggregates exhibiting light absorption in both H- and J-bands. The existence of such similar aggregates, with similar splitting of excitation energies, appears to be related to the existence of two stable conformational isomers of this dye. On increasing the smectite CEC and dye/smectite loading, fluorescence quenching occurred. The ThCy dye exhibited a stronger tendency for molecular aggregation than OxCy. On increasing the smectite CEC, the formation of oblique aggregates with dominant H-bands also increased. On aging of the hybrid dispersions, equilibria of ThCy aggregates were shifted to the species with dominant J-bands. This behavior had a significant impact on the shape and intensity of the fluorescence emission of the hybrid dispersions. Using different smectites enables control of the dye aggregation and significant change to the photophysical properties of the hybrid systems. These systems can be used for the detailed study of the photophysical properties of cyanine dyes in various states. The colloidal systems with cyanine dyes can be used as precursors for the preparation of novel hybrid materials. In addition, the sensitive response of the photophysical properties of cyanine dyes to the clay mineral surface can be applied to the characterization of clay minerals.

Because inorganic nanosheets, such as clay minerals, are anisotropic, the manipulation of nanosheet orientation is an important challenge in order to realize future functional materials. In the present study, a novel methodology for nanosheet manipulation using laser radiation pressure is proposed. When a linearly polarized laser beam was used to irradiate a niobate (Nb6O174-) nanosheet colloid, the nanosheet was trapped at the focal point so that the in-plane direction of the nanosheet was oriented parallel to the propagation direction of the incident laser beam so as to minimize the scattering force. In addition, the trapped nanosheet was aligned along the polarization direction of the linearly polarized laser beam.

Numerous occurrences of asbestos minerals, notably chrysotile and tremolite, are to be found on fracture surfaces in thrust fault deformation zones of Cretaceous dunite-harzburgite and pyroxenite in the Çankırı and Ankara regions, central Anatolia, Turkey. Consequently, potential exists for the development of regional malignant mesothelioma. The means of serpentinization, such as reaction of seawater during accretion of the upper ophiolitic mantle crust in a subduction zone and/or following uplift of ophiolitic units and the influence of hydrothermal/meteoric fluids along fractures, were investigated. Cretaceous dunite-harzburgite and localized pyroxenite rocks are mainly composed of serpentinized olivine and pyroxene associated with opaque minerals and Fe-(oxyhydr)oxide phases. Smectite, chlorite, illite, kaolinite, hydromagnesite, goethite, quartz, and opal-CT are also present. Chrysotile and localized tremolite occur either as a mesh, a suboriented to oriented long-fiber bundle, or as fiber-filling millimetric micro-vein textures on relicts of olivine and pyroxene (enstatite, augite). The chrysotile and tremolite have non-pseudomorphic textures developed under high pressure and temperature. The textures suggest authigenic formation of chrysotile and tremolite via a dissolution and precipitation mechanism. Additionally, spherical structures of opal-CT and locally platy hydromagnesite crystals either enclose or are developed within chrysotile/tremolite fiber bundles. The leaching of MgO, Fe2O3, Al2O3, Ni, Cr, and Nb, an increase in the LREE/HREE ratio, and negative Eu anomalies in the dunite-harzburgite and pyroxenite, and asbestos samples suggest that the chrysotile and tremolite were derived from the serpentinization of olivine and pyroxene. The chrysotile and tremolite were developed along fractures by hydrothermal fluid alteration during accretion and/or following the uplift of ophiolitic units of the region under high pressure and temperature conditions. This interpretation is also supported by isotope data and the calculated formation temperature of 170–555°C for chrysotile and tremolite. The average structural formulae for chrysotile and tremolite are (NanK0.03)(Mg5.54Fe0.09Al0.05Ca0.01Mn0.001) (Si3.96Al0.03)O10(OH)8 and (Na0.17K0.07)(Ca1.59Mg0.19Mn0.002)(Mg4.72Fe0.28)(Si7.86Al0.1Fe0.06)O22(OH)2, respectively.

Reflectance spectroscopy is a rapid, non-destructive technique capable of characterizing mineral and organic components within geologic materials at spatial scales that range from μm to km. The degree to which reflectance spectra can be used to provide quantitative information about organic compounds remains poorly understood, particularly for rocks with low organic content that are common in the Earth’s ancient rock record and that may be present on other planetary bodies, such as Mars. In the present study, reflectance spectra (0.35–25 μm) were acquired for a suite of Proterozoic shales and the kerogen was isolated to assess how spectral properties of aliphatic and aromatic C-H absorption bands can be used to predict organic matter abundance (total organic content, TOC, and H/C ratio). A number of spectral parameters were evaluated for organic absorption bands observed in the 3–4 μm wavelength region for comparison with independently measured TOC and H/C values. Ratios of the strengths of aliphatic to aromatic absorption bands were directly correlated to H/C values, but the reflectance spectra for pure kerogens with H/C < 0.2 lacked clear evidence for C-H absorption bands in this spectral region. Organic absorption bands are routinely observed for bulk rock powders with >1 wt.% TOC, but the detection limits of reflectance spectra for TOC may be <1 wt.% or as high as 10 wt.%. Organic detection limits for reflectance spectra are, thus, controlled by both TOC and H/C values, but these parameters can be predicted for clay-rich, kerogen-dominated samples for a range of values that are relevant to drill cores, outcrops, meteorites, and planetary surfaces.

Limonite is mainly derived from weathering of Fe sulfide, iron-bearing carbonate, or silicate minerals. The weathering of Fe sulfide or carbonate minerals to yield limonite from the Tongling mineralization cluster has been studied extensively. Knowledge of the mineralogical and geochemical characteristics of the limonite from weathering of Fe-bearing silicate minerals is still incomplete, however. To address this, black limonite containing ilvaite (a silicate mineral) found in Yeshan iron deposit, Tongling, China, was studied using mineralogical and chemical analysis. The mineralogical characteristics indicated that Mn goethite was present as nano-granular (<15 nm) or acicular (50–100 nm long, ~10 nm wide, i.e. high length/width ratio) crystals with low crystallinity. Groutite, ramsdellite, and pyrolusite were identified in the limonite as ~5 nm nanoparticles, and coated on the goethite surface. Amorphous Fe-Mn phases and silica were highly developed in the limonite studied. Ilvaite crystals showed idiomorphic granular morphology and were replaced by Fe-Mn oxides/hydroxides; pyrite was also present as inclusions within the ilvaite and the ilvaite structural formula calculated was Ca1.04(Fe1.57Mn0.31Mg0.04)(Fe1.09Al0.01)[Si1.95O]O(OH). According to the relatively high CuO and ZnO values and the low Al2O3 value in the black limonite, the negative correlations between (Fe2O3+MnO) and (CuO+ZnO+BaO), (Fe2O3+MnO) and Al2O3, high Mn and Si contents, and the characteristics of the textural relationships and compositions between the black limonite and ilvaite, a semi-enclosed environment with acidic to weakly alkaline conditions was deduced; ilvaite was found to be responsible for the formation and enrichment of limonite.