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. Quirk , J.P. , 1955 . Significance of surface areas calculated from water vapor sopption isotherms by use of the BET equation . Soil Science . 80 ( 6 ). 423 – 430
Abstract
For the first time a combination of B.E.T. gas adsorption method and neutron or photon activation analysis has been successfully applied to metal surfaces as well as to metal and ceramic powders (more than 50 cases). Increasing oxide film thickness was observed with increasing Al particle size. Speciation may be performed by the analysis of dehydratation. Even double-layers in the nanometer ranges may be specified. The method satisfactorily compares with TEM.
Abstract
HPLC columns were packed with quasi-spherical montmorillonite particles which were prepared by spray-drying and then thermally treated. Separations of phenylureas (linuron, neburon, diuron and monuron), phosphothioate phenyl esters (parathion, methyl parathion and paraoxon) and other smaller substituted benzenes were performed on the columns. The relative retention of the substituted phenyl pesticides demonstrated the important role polar substituents play in the eluate-surface interactions and the strong influence of steric factors on these interactions. The retention of the pesticides decreased sharply as the polarity of the mobile phase increased. The retention of the smaller substituted benzenes showed a similar trend, but for these smaller molecules this trend was partially counteracted by the increased accessibility of interlayer spaces due to swelling as the polarity of the liquid phase increased. The role of the exchangeable cation (Na+, Co2+ and Cu2+) in the adsorption was found to be complex. The cations determine both the strength of interaction, which increases with the valence of the cation, and the accessibility of the interlayer adsorption sites which decreased with the valence.
–Emmett–Teller (BET) [ 25 ], Park [ 26 ] and n -layer BET [ 27 ] models have been used to fit the experimental data and used to generally describe the water sorption behaviour between 0.1 and 0.9 of water activity. The quality of each model has been computed in terms
diffractometer, using Ni-filtered CuKα-radiation. Room temperature diffractograms were recorded at a scanning speed of 0.002° 2θ s −1 from 5° to 50°. BET specific surface areas were determined by nitrogen adsorption at the temperature of liquid nitrogen on a
Thermal destruction of rice hull in air and nitrogen
A systematic study
chemical compositions, structures, morphologies, BET surface areas, and pore characteristics of RHA samples by means of XRD, FT-IR, SEM, EDS, and nitrogen adsorption analyses. RHA presents different physico-chemical and pore characteristics in different
Abstract
Organoclays are the adsorption products of organic matter by clay minerals. In modern technology, organoclay-based nanocomposites obtained by modifying Na-clay by primary adsorption of organic ammonium cations or long-chain cationic surfactants are widely used in different industries. They are potential candidates for serving as sorbents of different organic compounds by secondary adsorption. Organoclays are widely spread in the environment and are responsible for the colloid behavior of different environmental elements such as soils. This manuscript summarizes some of the basic knowledge on thermal analysis of organoclays and reviews some of the recent studies carried out in our laboratory on organoclays which occur in the environment, those applied in industry and of those obtained by secondary adsorption processes. Complexes in the environment or those used in industry are mainly of the smectite clay mineral montmorillonite and their thermal analysis in air is treated here.
Thermal analyis of hexadecyltrimethylammonium–montmorillonites
Part 1. Thermogravimetry, carbon and hydrogen analysis and thermo-IR spectroscopy analysis
Abstract
Na-montmorillonite (Na-MONT) was loaded with hexadecyltrimethylammonium cations (HDTMA) by replacing 41 and 90% of the exchangeable Na with HDTMA, labeled OC-41 and OC-90, respectively. Na-MONT, OC-41, and OC-90 were heated in air up to 900 °C. Unheated and thermally treated organoclays heated at 150, 250, 360, and 420 °C are used in our laboratory as sorbents of different hazardous organic compounds from waste water. In order to get a better knowledge about the composition and nature of the thermally treated organoclays Na-MONT and the two organo-clays were studied by thermogravimetry (TG) in air and under nitrogen. Carbon and hydrogen contents in each of the thermal treated sample were determined and their infrared spectra were recorded. The present results showed that at 150 °C both organoclays lost water but not intercalated HDTMA cations. At 250 °C, many HDTMA cations persisted in OC-41, but in OC-90 significant part of the cations were air-oxidized into H2O and CO2 and the residual carbon formed charcoal. After heating both samples at 360 °C charcoal was present in both organo clays. This charcoal persisted at 420 °C but was gradually oxidized by air with further rise in temperature. TG runs under nitrogen showed stepwise degradation corresponding to interlayer water desorption followed by decomposition of the organic compound, volatilization of small fragments and condensation of non-volatile fragments into quasi-charcoal. After dehydroxylation of the clay the last stages of organic matter pyrolysis and volatilization occurred.
