Determination of water content in raw perlites: Combination of NIR spectroscopy and thermoanalytical methods.

A new approach to determination of water content in raw perlites, an industrially important material, and obsidian was proposed, utilizing diffuse reflectance spectroscopy in the near-IR region. The phase composition of the perlite of the perlite samples was over 94% rhyolitic volcanic glass, with only small admixture of other components. The observed volatile species contents detected from both thermogravimetric analysis (TG) and the loss of ignition method (LOI) varied from 3 to 7%. The samples with the highest content of volatiles released over the temperature interval 30-250 °C (based on thermogravimetric analysis) displayed sharp signals in the 1H MAS NMR spectra, with chemical shifts of 4.6-4.7 ppm attributed to water molecules of high mobility. Using IR spectra taken in the near-infrared region, the water content of perlites was evaluated using the combination mode (ν + δ)H2O near 5240 cm-1. The band area depended on the H2O content, with the highest value found for the sample which displayed the highest mass loss in the thermoanalytical experiments. The samples showed variations in properties depending on the location in the deposit they were taken from. The relationship between water content determined gravimetrically and calculated band areas showed a correlation coefficient of 0.78 and 0.74 for TG and LOI respectively. The correlation was significantly improved by adding internal standards, hexadecyltrimethylammonium bromide salt (HDTMA) or layered hydrosilicate talc, to the perlite samples, and then normalizing the spectra of the mixtures to selected bands of those standards (R2 = 0.89 and 0.88 respectively for TG methods). A better correlation between infrared and TG/LOI results was obtained for HDTMA-Br than for talc. The proposed method using standards could be a reliable way of estimating water content in raw perlites in processing plants.

Spectroscopic study of water adsorption on Li(+), TMA(+) and HDTMA(+) exchanged montmorillonite.

The potential of IR and NMR spectroscopy in characterization the interaction of water with natural and organically modified montmorillonites was introduced. Organoclays were prepared from Li-saturated montmorillonite (Li-S) and tetramethylammonium (TMA) or hexadecyltrimethylammonium (HDTMA) salts. The influence of organic cation size on the water vapour uptake was examined and a comparative study with natural clay mineral was provided. The near-IR spectra confirmed the reduced water content in TMA-S and HDTMA-S. After exposure of the samples to water vapour under various relative humidities (RH) the H2O content was determined. According to the adsorption isotherms the amount of water decreased in order Li-S>TMA-S>HDTMA-S. The intensities of the 2νOH and [Formula: see text] bands, corresponding to the vibrations of H2O, gradually increased in hydrated samples. The (13)C MAS NMR and near-IR of hydrated organoclays confirmed the presence of H2O close to the cation's headgroup. NMR signals of inner -CH2- groups in HDTMA-S were also affected by hydration: the intensity of disordered gauche conformers (31.1 ppm) overtook the intensity of ordered all-trans conformers (33.0 ppm).

Utilization of near infrared spectroscopy for studying solvation properties of Cu-montmorillonites.

The benefit of near infrared (NIR) spectroscopy to follow the adsorption of dimethylsulfoxide and acetonitrile on reduced-charge Cu-montmorillonites differing in their chemical composition is presented. A NIR UpDRIFT accessory enabling measurement of spectra directly in closed glass vials was used to determine the amounts of adsorbed solvents. The area of the complex 2νCH band correlated very well with gravimetric analysis confirming that the UpDRIFT technique is suitable for studies of total content of organic solvents adsorbed on montmorillonites. Changes of the 2νOH band revealed that acetonitrile with a lower dipole moment (DP) and Gutmann donor number (GDN) fully solvated all samples heated up to 200°C and only partially those heated at 300°C, while DMSO with a higher DP and GDN completely solvated all the samples. These results indicate that fixation of Cu(2+) cations in montmorillonites upon heating is a partially reversible process.

The effect of acid treatment on the structure and surface acidity of tetraalkylammonium-montmorillonites.

The effect of tetrabutylammonium (Bu4N+) and tetrapentylammonium (Pe4N+) cations on the modification of the organo-montmorillonite structure upon acid-treatment was investigated. Samples were treated with HCl for various times (2-12 h). Structural changes were followed by MAS NMR spectroscopy. The 29Si MAS NMR spectra of initial Na-saturated form (Na-SAz) showed gradual decrease of the intensity of the resonance assigned to SiO4 cross-linked in the tetrahedral sheets Q3(0Al) while signals arising from the reaction product Q31OH and Q4(0Al) became more pronounced upon acid treatment. The Q3(0Al) signal almost completely disappeared for Na-SAz treated for 8 h on contrary to Bu4N-SAz and Pe4N-SAz showing signal of relatively high intensity even after 12 h. The 27Al MAS NMR measurement proved that more than one half of Al remained in the reaction product of Bu4N-SAz and Pe4N-SAz after 8 h treatment, while Al content dropped below 5% for Na-SAz. Formation of acid sites was investigated via pyridine adsorption. Only physically adsorbed and H-bonded pyridine was detected for acid-untreated samples. In contrast, the IR spectra of the samples partially decomposed in HCl revealed bands of pyridine adsorbed on Brønsted acid sites. Strongly bonded pyridine was able to bear up heating even at 230°C.

Alterations of the surface and morphology of tetraalkyl-ammonium modified montmorillonites upon acid treatment.

The effect of short alkyl chain cations on the modification of the structure, surface and textural properties of organo-montmorillonites upon their acid treatment was investigated. Samples prepared from Ca-SAz montmorillonite and tetramethylammonium (Me(4)N(+)-), tetraethylammonium (Et(4)N(+)-), tetrapropylammonium (Pr(4)N(+)-) and tetrabutylammonium (Bu(4)N(+)-) salts were treated in 6 M HCl at 80 °C for 2-8 h and analyzed by different methods. Acid treatment of organo-montmorillonites caused gradual release of Al and Mg from the octahedral sheets and destruction of their layered structure. The extent of the changes depended significantly on the size of organo-cation. While large plate-like particles of Ca-SAz and Me(4)N-SAz were disintegrated during acid treatment and smaller fine grains were created, the morphology of Bu(4)N-SAz was modified only slightly. Pore size analysis showed generation of pore network upon organo-montmorillonites dissolution. After longer acid attack, pore volume increased and pore size distribution curves were shifted to pores with diameter above 25 Å. The surface area of acid-treated samples increased due to destruction of the montmorillonite layers and formation of the SiO(2)-rich reaction product. The highest value 475 m(2)/g was observed for Me(4)N-SAz treated 4 h. Surface area of Et(4)N-SAz, Pr(4)-SAz and Bu(4)N-SAz was 441, 419 and 293 m(2)/g, respectively, after 8 h treatment. Similar decomposition level was observed for Ca-SAz and Me(4)N-SAz, and less destruction was found for Et(4)N-SAz, Pr(4)-SAz and very low for Bu(4)N-SAz. Though Bu(4)N(+) is short alkyl chain cation, its size is large enough to cover the inner and outer surfaces of montmorillonite and thus to protect the clay layers from acid attack.

Synthesis and characterization of low dimensional ZnS- and PbS-semiconductor particles on a montmorillonite template.

Low dimensional metal sulfide particles have been prepared in the interlayers of montmorillonites via reactions of the metal ion-exchanged clay minerals in aqueous dispersions with gaseous hydrogen sulfide. The montmorillonites separated from the Wyoming (USA) and Jelsový Potok (Slovakia) bentonites were saturated with Pb(2+) or Zn(2+). In the final nanohybrids, the smectite mineral can be incorporated with metal sulfide pillars and/or nanoparticles. Properties of the prepared materials were investigated by various analytical techniques. The formation of metal sulfide nanoparticles in the interlayer galleries was indicated by X-ray diffraction and energy dispersive X-ray analysis. About 50% of Pb(2+) or Zn(2+) present in montmorillonite has formed metal sulfide semiconducting units. Infrared spectroscopy and thermogravimetric analysis were used for characterization of starting materials and products. Ultraviolet-visible absorption and photoluminescence spectroscopies confirmed that final composite systems acquired the optical properties of the incorporated quantum low dimensional systems exhibiting blue shift of the energy gap and higher oscillator strength excitonic peaks. Larger amounts of metal sulfide nanoparticles were formed in montmorillonite Jelsový Potok probably as a consequence of its higher cation exchange capacity.

Dry grinding of Ca and octadecyltrimethylammonium montmorillonite.

Structural changes in Ca and octadecyltrimethylammonium (ODTMA) montmorillonite induced by dry grinding in a high-energy planetary ball mill were investigated by X-ray powder diffraction (XRD) analysis, infrared (IR) spectroscopy, and scanning electron microscopy (SEM). The organomontmorillonite is more resistant toward mechanical destruction than the Ca form. Both XRD and IR analyses indicate a complete breakdown of the mineral layers after 5 min of grinding of Ca-JP. The XRD pattern of the ODTMA clay shows disappearance of the layer ordering along the c axis after 40 min of grinding, while persistence of the layered structure for all tested samples is proven by the IR spectroscopy. The grinding process affects chemical bonds in the OH, SiOAl, and SiOSi groups of montmorillonite; however, no changes are observed for CH bonds of the organocations. In contrast to the Ca form, all absorption bands typical for montmorillonite appear in the IR spectrum of the ODTMA montmorillonite even after 40 min of grinding. The majority of the bands are undetectable in the spectrum of Ca montmorillonite ground for 5 min. Amorphization of the montmorillonite caused by an intense grinding process is markedly slower after replacing the inorganic cations with the long-chain alkylammonium cations.