Tunable interlayer hydrophobicity in a nanostructured high charge organo-mica

Abstract

A tunable hydrophobicity, from a fully hydrophobic medium to an amphiphilic quasi-solution, has been obtained in the interlayer space of a synthetic high charged mica by ion exchange reaction with amine cations. The structural and intercalation properties of the hybrids after the exchange with the n-alkylammonium cations: [RNH3]+, [RNH(CH3)2]+ and [RN(CH3]3+ with C16 alkyl chain length have been determined by termogravimetric/differential scanning calorimetry analysis (TGA-DSC) and mass spectrometry (MS), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Transmission electron microscopy (TEM) has been used as a complementary technique to provide new insights into the morphology of the exchanged products. Coverage and cation distribution have been correlated with layer charge and steric effects. Thus, a full organo-clay is obtained when the primary amine cations are adsorbed between the layers. However, a homogenous single phase of mixed organic/inorganic cations is formed in the same interlayer with the tertiary amine cations. Mixed ion clays combining both exchangeable inorganic and adsorbent organic ions in their interlayer space can be potential materials to be used as adsorbents for water decontamination, independently of the hydrophilic/hydrophobic nature of the pollutants. For the quaternary amine cations steric effects preclude the coexistence of both organic and inorganic species in the same interlayer of the clay so phase segregation together with a heterogeneous phase of organic and inorganic galleries in the same particle can be observed.