Abstract
Na-magadiite exchanged with cetyl-trimethylammonium cations provided organophilic silicate materials that allowed for the effective removal of the acidic dye “eosin”. The organic cations were intercalated into the interlayer spacing of the layered silicate via an exchange reaction between the organic cations from their bromide salt and the solid Na-magadiite at room temperature. Different techniques were used to characterize the effect of the initial concentration of the surfactant on the structure of the organo-magadiites. The C, H, and N analysis indicated that a maximum of organic cations of 0.97 mmol/g was achieved and was accompanied by an expansion of the basal spacing of 3.08 nm, with a tilted angle of 59° to the silicate layers. The conformation of the organic surfactants was probed using solid-state 13C, finding mainly the trans conformation similar to that of the starting cetyl trimethylammonium bromide salt (C16TMABr). Thermal gravimetric analysis was carried out to study the thermal stability of the resulting organo-magadiites. The intercalated surfactants started to decompose at 200 °C, with a mass loss percentage of 8% to 25%, depending on the initial loading of the surfactant, and was accompanied by a decrease of the basal spacing from 3.16 nm to 2.51 nm, as deduced from the in situ X-ray diffraction studies. At temperatures below 220 °C, an expansion of the basal spacing from 3.15 to 3.34 nm occurred. These materials were used as a removal agent for the anionic dye eosin. The maximum amount of the dye removed was related to the organic cation content and to the initial concentration of eosin, with an improvement from 2.5 mg/g to 80.65 mg/g. This value decreased when the organo-magadiite was preheated at temperatures above 200 °C. The regeneration tests indicated that an 85% removal efficiency was maintained after six cycles of use for the organo-magadiite using Ci of 200 mg/L.
Highlights
Layered materials have attracted great attention due to their wide application in different fields and due to their characteristic cation exchange capacity, acceptance of intercalated guest molecules, exfoliation in different polymer matrixes, and catalytic properties [1]
The later value was lower than the expected cation exchange capacity, and it indicated that the modification of the Na-magadiite occurred mainly via a cation exchange process
The electron dispersive X-ray analysis (EDX) data indicated that traces of Na cations occurred with high loadings of organic surfactants
Summary
Layered materials have attracted great attention due to their wide application in different fields and due to their characteristic cation exchange capacity, acceptance of intercalated guest molecules, exfoliation in different polymer matrixes, and catalytic properties [1]. The acidic properties of the magadiite could be enhanced by the insertion of other cations into the layered silicate, achieved during the synthesis by adding the cations precursors to the mixture of the silica source and NaOH. A clay mineral modified with a long-chain surfactant exhibited a higher removal capacity than did short-chain surfactant For this purpose, cetyl trimethyl ammonium (C16TMA) was the most commonly used cation, obtained from the corresponding salt; the bromide form was used to prepare organo-clays or silicates [23,24]. In the case of a layered silicate, such as magadiite, a previous study reported that the maximum amount of intercalated organic surfactants was achieved using a C16TMAOH solution [27,28]. The resulting spent materials were regenerated by a process friendly to the environment, and their reuse was studied after different consecutive cycles
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