The mineralogical and physicochemical characteristics of various types of modified smectites exchanged with inorganic (Ca and Na) and organic cations such as Hexadecyltrimethylammonium (HDTMA), Benzyldimethyltetradecylammonium (BDTDA), and Cetylpyridinium (CP) by the ionic exchange reaction were investigated for the suggestion of new industrial application. The smectites satutated with inorganic cations (Ca and Na) show quite different mineralogical and chemical properties in basal spacing (d001), pH, viscosity, swelling and flocculation and dispersion behaviors according to interlayer cation types. Confirmed factors controlling mineralogical and chemical properties of smectite are layer charge and interlayer cation type of smectite as well as smectite (montmorillonite) content. Inorganic satutared smectites show an the excellent adsorption of heavy metals such as Cu, Pb, and Cd, but are less efficient and unstable for the adsorption of actinides (U and Th) and lanthanide elements (Ce and Eu). HDTMA-, BDTDA-, and CP-exchanged organo-smectites show the strong interlayer expansion to 40.1Å, 30.8Å and 40.9Å, respectively when 400% CEC equivalent amount is reacted. Their intercalation structures are similar to double layered paraffin complexes (Deng and Dixon, 2002). Three kinds of organo-smectites begin to decompose at about 250°C and end at 400°C. Considering all the investigated results, the interlayer cation type of natural smectites is very important mineralogical characteristics for the industrial utilization. CP exchanged organic-smectite of the investigated organo-smectites is the most economic and efficient organo-smectite in the viewpoint of price of chemicals, adsorption capacity, adsorption behavior, and stability for the new industrial application.
The adsorption of an anion such as oxalate and phosphate at low concentration by soils is important because their contents in the soils are usually low. The adsorption of oxalate and phosphate on allophane at initial concentrations up to 200üM showed that the amount of adsorption of phosphate was higher than that of oxalate, while the adsorption energy of oxalate estimated by the Freundlich parameter n was higher than that of phosphate. The high adsorption energy for oxalate was also suggested by molecular orbital calculations, where changes in the total energy of the adsorption reactions of oxalate were compared with that of phosphate. The amount of adsorption of oxalate or phosphate increased with raising the concentration of the background electrolyte (i.e. NaCl). This was ascribed to development of anion exchange site on allophane under the high concentration of NaCl. The amount of adsorption of oxalate coexisting with 200μM of phosphate decreased as compared to that of oxalate alone. However, the adsorption strength of oxalate estimated by the Langmuir K and Freundlich n parameters was enhanced by the coexisting phosphate. For the adsorption of phosphate in coexisting oxalate, oxalate also had the effect on the adsorption strength of phosphate. Especially for the adsorption of oxalate, it was clearly observed that the amounts of Si and Al released from allophane with the adsorption abruptly increased at the equilibrium oxalate concentration of about 100μM. This means that, at the equilibrium concentration, the adsorption schema of oxalate changed from the ligand exchange reaction between hydroxyl group and oxalate to the replacement reaction of silicate with oxalate. The critical equilibrium concentration shifted to about 70μM with the addition of 200μM phosphate. This indicates that the coexisting phosphate also consumed hydroxyls (Al-OH) leading oxalate to begin replacement with silicate at lower equilibrium concentration. It is concluded that, at low concentration, coexisting phosphate affect not only amount and strength but also mechanism of the adsorption of oxalate, and vice versa.
Twelve profiles of ferralitic soils derived from different igneous rocks were collected from hilly and mountainous areas in the Northern, North of Central, Coastal Area of Southern Central and High Plateau Tay Nguyen regions of Vietnam, and were subjected to clay mineral analysis. The main clay minerals detected were kaolin (kaolinite and halloysite (0.7nm)), 2: 1-type silicate (mainly mica, vermiculite, smectite, the mica/vermiculite/smectite-mica/smectite mixed-layer mineral, and chlorite-vermiculite intergrade), and oxide/hydroxide (gibbsite and goethite) minerals. Based on the abundance of kaolin and oxide/hydroxide minerals in the clay fraction, twelve profiles were grouped into 3 groups. The mineralogical difference of soils among the three groups was explained by the difference in rock-forming minerals of igneous rocks rather than by advancement of ferralitization, different from soils derived from sedimentary and metamorphic rocks in the previous study (Nguyen and Egashira, 2007). Inherent potentiality of the soils was assessed based on the type and amount of clay minerals and varied with soils depending mainly on the amount of 2: 1-type silicate minerals in the clay fraction.
We fabricated novel hybrid films consisting of a clay and cationic tetrathiafulvalene (TTF). The average distance between the TTF molecules adsorbed onto the clay sheet was controlled by changing the fabricating condition. The obtained films showed the absorption bands at around 450, 750 and 2000 nm, which were assigned to an intramolecular transition of TTF+, and intermolecular transitions between TTF+s and between TTF+ and TTF0, respectively. The relative absorbances of the bands were found to vary depending on the average distance between the TTF molecules adsorbed onto the clay sheet. This fact indicates that the electronic properties of the TTF molecules in the present films can be controlled by changing the fabricating condition.
The present paper deals with the heavy metal contamination of soil and rice grain in the paddy field subjected to the irrigation water polluted with wastes from various industrial plants in Hanoi. Soil and rice grain samples were taken at different distances (0-50m) from the edge of the paddy field. The retention and potential mobility of heavy metals were assessed based on the contents of total and fractionated heavy metals in the soil and their leachability. The concentration of the fractionated heavy metals was determined by selective sequential extraction method. Heavy metal contents in the rice grain were also assessed. The average concentration of the metals in the soil was in the order: Cu (202mg kg-1)>Zn (192mg kg-1)>Cr (185mg kg-1)>Pb (159 mg kg-1)>Ni (45mg kg-1)>Cd (4mg kg-1). The heavy metal concentrations in the soil exceeded the permissible level of the Vietnamese standard for Cd, Cu, Pb and Zn. The results of selective sequential extraction procedure indicated that dominant fractions were oxide, organic and residual materials for Cd, Ni, Pb and Zn, and organic and residual materials for Cr, and an organic material for Cu. Leaching tests with deionized water and acid solutions indicated that the ratio of leached metal concentration to total metal concentration in the soil decreased in the order: Cd>Ni>Cr>Pb>Cu>Zn. By leaching with deionized water and acid solutions, all heavy metals were released fully from exchangeable fraction, and Cd and Ni were fully from carbonate and oxide fractions. The average concentration of heavy metals in the rice grain was in the order: Zn (14.4mg kg-1)>Cu (6.9 mg kg-1)>Cr (3.1mg kg-1)>Pb (2.1mg kg-1)>Ni (1.4mg kg-1)>Cd (0.1mg kg-1). The concentrations of Cu, Ni, and Zn in the rice grain met the WHO standard while the concentrations of Cr and Pb exceeded the permissible level of the standard. The concentrations of Cd met the Vietnamese standard while those of Pb exceeded the permissible level of the standard. Transfer coefficient for the metals was in the order: Zn>Ni>Cu>Cd≈Cr>Pb.
The authors produced novel radical-trapping sheets mainly from an environmentally friendly material, natural bentonite clay. Using two identical radical-trapping reagents, their effectiveness was confirmed for high performance in active radical trapping. Radical-trapping sheets were prepared using casting from dispersion pastes including clay and radical-trapping reagents. Purified natural bentonite clay that had been treated by quaternary ammonium ions was used along with one of two radical-trapping reagents, a spin-trap reagent (α-phenyl-N-tert-butyl nitrone; PBN) or a radical-scavenging reagent (4-Oxo-2, 2, 6, 6-tetramethylpiperidine 1-Oxyl; 4-Oxo-TEMPO), yielding 40-üm-thick flexible self-standing sheets. The sheets' radical-trapping performance was investigated using electron spin resonance (ESR). Results confirmed the radical-trapping sheets' capability for capturing active radical species that were observed neither in the original radical trap reagents nor in the clay. The PBN spin-trapping sheet trapped hydroxyl radicals and hydroxyethyl radicals. The sheet provides long-term stabilization of radical species. The trapped radicals remained active more than one month after the trapping experiment. The 4-Oxo-TEMPO radical scavenging sheet also trapped both radicals. New basal-plane reflection was observed in the X-ray diffraction (XRD) pattern of the radical-trapping sheets, suggesting intercalation of radical-trapping reagents between the clay platelet crystals. These radical-trapping sheets might be applicable to packaging, catalytic sheets for radical reactions, and environmental analyses.
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