Dendrimers-containing organoclays: Characterisation and interaction with methylene blue

The structure of organoclays composed of synthesized phosphorus-based dendrimers, which was endowed with peripheral ammonium groups, and stevensite- or montmorillonite-rich clays was examined using X-ray diffraction, high resolution transmission electron microscopy, thermal analysis and solid-state nuclear magnetic resonance. The interactions between methylene blue (MB) and the organoclays or Na+-saturated clay minerals were investigated. The results showed that both dendrimers adsorbed on Na+-saturated clay minerals by cation exchange, and that the organoclays, particularly those of the first generation dendrimers, were mainly composed of intercalated nanocomposites. As a result of the adsorption of the dendrimers, the clay hydrophilicity reduced and the dehydroxylation temperature of the clay minerals increased. Regarding the adsorption of MB on the organoclays, the results pointed out that MB mainly adsorbed as MB+ and MBH2+, and the electronic environments of Al-IV of montmorillonite and that of Al-VI of stevensite were disturbed. For some organoclays, ordered structures were formed, and the Si4+ substituent (Al3+) left the tetrahedral sheet. The thermodynamic data indicated that MB adsorbed spontaneously (- 11.3 < Delta G < -0.9 kJ/mol) and the uptake of MB by montmorillonite-based organoclays was believed to occur by chemisorption. In contrast, for stevensite-based organoclays MB adsorption seemed to be accomplished by physisorption. (C) 2016 Elsevier B.V. All rights reserved.