Effects of Iron Oxidation State and Organic Cations on Dioctahedral Smectite Hydration

Abstract

Abstract--Reduction of structural Fe in Na-exchanged dioctahedral smectites decreases swellability in water, but because clay interlayers also collapse in the process the concomitant effect on surface hydration energy is uncertain. This study examined the hydration behavior of oxidized and reduced dioctahedral smectite clays exchanged with polar (Na) and weakly-polar (organic) cations to determine the nature of the surface before and after Fe reduction, and to determine if clay surfaces are hydrophilic or hydrophobic. The H20 content in various dioctahedral smectites decreased if Na was replaced by tetramethylammonium (TMA), trimethylphenylammonium (TMPA), or hexadecyltrimethylammonium (HDTMA). Among the organo-clays, H20 adsorption decreased with increasing complexity of the cation. For oxidized smectites, those exchanged with TMPA retained less H20 than those exchanged with Na at all pressures. The extent of this difference depended on the clay and decreased with increasing applied pressure. Reduction of Fe(III) to Fe(II) in the octahedral sheets decreased the swelling of Na-saturated smectites, apparently causing some previously swelling interlayers to collapse. If the Na interlayer cation was exchanged to alkylammonium after reduction, but prior to swelling-pressure measurements, the swelling increased or remained near constant, suggesting that the organo-cation disrupted the collapse process of the interlayers associated with the reduced smectite layers. Reduced TMPA-saturated smectite surfaces are more strongly hydrated if the octahedral sheet is reduced than if oxidized. Thus, reduction of structural Fe increases the hydration energy of smectite basal surfaces, but swellability could decrease or increase depending on the extent of interlayer collapse occurring with different exchangeable cations.

Adsorption of Acid Blue 193 from aqueous solutions onto DEDMA-sepiolite

“…These kinds of adsorbents are termed organoclays since the exchangeable inorganic cations (e.g. H + , Na + , Ca 2+ ) are replaced by organic cations such as quaternary ammonium compounds by ionexchange reaction [16,17]. Hence, organoclays are powerful adsorbents for a wide variety of environmental applications [18].…”

Organofunctionalized Amazon smectite for dye removal from aqueous medium—Kinetic and thermodynamic adsorption investigations

“…The immobilization of the 2-aminomethylpyridine (AMP) has been explored by different immobilization methodologies in the preparation of hybrid materials with high adsorptive capacity [7], although some of these amino-functionalized adsorbents can exhibit specific interactions with hard Lewis acids, the selectively of these materials are usually unremarkable, because many dyes have great ability to bind amine ligands. The possibility of an organofunctionalization reaction prior to dye adsorption would increase the capacity of adsorption by the chemically modified materials [8][9][10][11][12][13]. For this purpose, natural Amazon smectite was chosen as a source of layered silicate, since its surface contains a high degree of regularly distributed silanol groups in the space interlayer that favor organomodification reactions [3].…”

The effect of layer charge and exchangeable cations on sorption of biphenyl on montmorillonites

“…Such materials are ineffective adsorbents of non-polar organic compounds that frequently pollute surface water because these compounds cannot effectively compete with the highly polar water molecules for adsorption sites on the smectite surface. Inorganic cations, however, can be replaced with various organic species such as quaternary alkylammonium cations, to modify properties of smectite and to increase its surface hydrophobicity [1][2][3]. The amount, configuration and mechanism of interaction of the organic cations with the smectite surface depend on the layer charge, on the type of alkylammonium cation used, on the molar ratio clay mineral/organic cation and the method of preparation [4][5][6][7][8][9][10][11][12].…”