Characterization of organo-kenyaites: thermal stability and their effects on eosin removal characteristics

Abstract

Organo-kenyaites were prepared from a cetyltrimethylammonium hydroxide (C16TMAOH) solution and solid sodium kenyaite (Na2Si22O45.10H2O) mixture. The effect of the initial cetyltrimethylammonium solution on the structure of the intercalated materials was investigated by CHN analyses, X-ray diffraction (XRD), thermogravimetric analysis, SEM, and 29Si and 13C solid NMR techniques. For C16TMAOH concentration 0.25 mM, the Na+ cations were fully exchanged. Initial C16TMAOH concentrations higher than 0.25 mM had little effect on the intercalated amount of C16TMA+ cations. The organic cations content reached a plateau of 0.66 mmol/g. The arrangement model of C16TMA+ cations corresponded to a tilt of the organic cations to the silicate layers with an angle of 42° as deduced by XRD studies. The C16TMA+ cations exhibited mainly trans-configuration of the methyl chains, as was shown by solid 13C NMR. The thermal stability of the organo-silicates was studied using in situ FTIR and in situ XRD in the range 25–450°C. The C16TMA-kenyaites were stable at temperatures below 200°C. They collapsed at higher temperatures due to the decomposition of the intercalated surfactants. These organo-kenyaites were used to remove the acidic dye molecule, eosin. The removal tests were performed at varying conditions of initial dye concentrations, organic content in the organo-kenyaites and heating temperatures. In general, the organic modification improved the removal capacity of the Na-kenyaite from 2 mg of eosin/g to 60 mg of eosin/g, and this capacity was related to the organic contents and the calcination temperatures of the organo-kenyaites.

Application of Organo-Magadiites for the Removal of Eosin Dye from Aqueous Solutions: Thermal Treatment and Regeneration

“…In good agreement with the XRD data, the content of the organic cations did not affect the features of the spectra, indicating that the cations mainly adopted the trans conformation ( Figure 3). Similar data were reported for organo-kenyaites and organo-clays with closely packed organic contents [23,25,33]. …”

“…The EDX data indicated that traces of Na cations occurred with high loadings of organic surfactants. In the case of the similarly layered structure kenyaite, only a partial exchange occurred [33]. This result was not the same for clay minerals, where the uptake amount of C16TMA largely exceeded the CEC values [21].…”

“…ppm were related to C1 and the methyl groups bonded to N (CN), respectively [23,24,33]. Full assignments of the other peaks were described in previous works.…”

“…ppm that was assigned to C4-C13, corresponding to a dominant trans conformation for the CH2 groups, and an additional shoulder at 30 ppm associated with a minor degree of the gauche conformation [23,24,33] (Figure 3) The peaks at 63.7 ppm and 55.5…”

“…The carbon, nitrogen and hydrogen analysis was used to quantify the organic contents in organo-clays and other organo-silicates [24,32,33,34]. The elemental analysis of the organo-magadiites is summarized in Table 1.…”