Abstract
The effect of the counteranion of hexadecyltrimethylammonium salts on the physico-chemical properties of organoclays was investigated, using a selected natural clay mineral with a cation exchange capacity of 95 meq/100 g. The uptake amount of C16 cations was dependent on the hexadecyltrimethylammonium (C16) salt solution used, the organoclay prepared from C16Br salt solution exhibited a value of 1. 05 mmole/g higher than those prepared from C16Cl and C16OH salt solutions. The basal spacing of these organoclays was in the range of 1.81 nm to 2.10 nm, indicating a similar orientation of the intercalated surfactants, and could indicated that the excess amount of surfactants, above the cation exchange capacity of 0.95 meq/g could be adsorbed on the external surface of the clay mineral sheets. These organoclays were found to be stable in neutral, acidic, and basic media. The thermal stability of these organoclays was carried out using thermogravimetric analysis and in-situ X-ray diffraction (XRD) techniques. The decomposition of the surfactant occurred at a maximum temperature of 240 °C, accompanied with a decrease of the basal spacing value close to 1.42 nm. The application of these organoclays was investigated to remove an acidic dye, eosin. The removal amount was related to the initial used concentrations, the amount of the surfactants contents, and to the preheated temperatures of the organoclays. The removal was found to be endothermic process with a maximum amount of 55 mg of eosin/g of organoclay. The value decreased to 25 mg/g, when the intercalated surfactants were decomposed. The reuse of these organoclays was limited to four regeneration recycles with a reduction of 20 to 30%. However, noticeable reduction between 35% to 50% of the initial efficiency, was achieved after the fifth cycle, depending of the used organoclays.
Highlights
The demand for water, especially fresh water for the comfort of human society, is sharply increasing due to the rapid increase in population and industrial activities [1,2,3]
This study was carried out to test the hypothesis that the nature of the C16 solutions might affect the uptake amount of C16 cations for another type of clay mineral, leading to organoclays with different physiochemical properties, and determine if the resulting materials would be effective in the removal of the acidic dye eosin
The in-situ PXRD of the C16 Cl-cloisite Na (CN) precursor showed that the basal spacing of 2.00 nm was maintained at temperatures up to 150 ◦ C, and indicating that the removal of water molecules did not affect the layered expansion, and the water molecules were mainly adsorbed onto the external surface of the organoclays, as described in the TGA section
Summary
The demand for water, especially fresh water for the comfort of human society, is sharply increasing due to the rapid increase in population and industrial activities [1,2,3]. The most common modification consists of the use of cationic surfactant solutions that generate organoclay adsorbents that combine both the properties of the inorganic layered material and hydrophobic environment with the intercalation of the organic cations These materials adsorb a large range of pollutants, such as pesticides [27], phenolic compounds [28], various pharmaceutical products [29] and acidic dyes [23,24]. This study was carried out to test the hypothesis that the nature of the C16 solutions (in term of their anions) might affect the uptake amount of C16 cations for another type of clay mineral, leading to organoclays with different physiochemical properties, and determine if the resulting materials would be effective in the removal of the acidic dye eosin. Regeneration tests were carried out to study further valorization of these organoclays, and an economical and friendly method was used in this regard [33,48]
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