Arrangement Models, Evolution And Conformation Of Alkylammonium-cations In The Interlayers Of HDTMA～+ Pillared Montmorillonite

Pillaring reaction has been well known as one of the significant methods to prepar porous materials and inorganic-organic nanocomposites. Montmorillonite is a major host mineral for the pillaring reaction because of its 2:1 sandwich-like structure and the exchangeable cations between the layers. Organic pillaring reaction has an important signification for researching the montmorillonite micro structure and understanding the reaction mechanism between natural organic matters and minerals. Organic pillared montmorillonite possesses not only the unique adsorptivity, dispersivity, porosity, rheological behavior and surface acidity of the clay mineral but also the multivariate functional groups and the reactivity of the organic compound. As a new type of mineral materials, it has extensive potential application in catalysts, functional supporter, adsorbents, filler and layered silicate nanocomposites.In this paper, HDTMA+ pillared montmorillonite hybridizations were prepared by pillaring Hexadecyltrimethylammonium bromide into Hebei montmorillonite (HM) in water solution. The hybridization's structure, conformation of HDTMA+ and the pillaring mechanism were studied by the powder X-ray diffraction analysis (XRD), 13C MAS NMR, FTIR, and thermal analysis (DTA-TG). The influence of pillaring reagent concentration on the organic cations' arrangement was studied by changing the reagent concentrations.Main conclusions of this work are drawn as follows:1) Some mineralogical characteristics of Hebei montmorillonite were studied2) On the basis of XRD and stereochemical analyses of organic molecules, the "M" and "L" type of arrangement model for monolayer were firstly proposed.3) The orientation of organic cations may be influenced significantly by the concentration of pillaring reagent. Different arrangement model can be formed under different concentration. With the increase of the concentration of pillaring reagent, the stack density of organic cations in the interlayer space increases, and the change of the arrangement of organic cations can be sammarized as the following: Lateral monolayer → Lateral bilayer → Paraffin-type monolayer → Paraffin-type monolayer+ pseudotrilayer → Paraffin-type bilayer+(pseudotrilayer).4) FTIR and NMR techniques have been used to study two kinds of conformation (Trans and Gauche) in hybridization. With the increasing of the concentration of pillaring reagent, a wide range of molecular environments, varying from liquid-like to solid-like was found. The NMR spectra clearly demonstrate that the relative contents of the phases formed by different conformations variy from liquid-like state to solid-like state.5) Thermal analysis demonstrate that the quantity of organic surfactant cations pillared into montmorillonite was more than the CEC. The reaction of HDTMA+ intercalated into interlayer proceeded in by two stages: the exchange of ions and adsorption reaction. The reaction between organic matters and minerals result in new phases and materials during thermal degradation process.This work was supported by the National Natural Science Foundation of China (Grant No. 49972018), the Natural Science Foundation of Guangdong Province (Grant No. 990522), the Guangdong Technological linnovation Funds (Grant No. 013101).