Intercalation of aniline in Wyoming montmorillonite exchanged with different cations
Résumé
Intercalation and deintercalation of organic molecules in the interlayer space of phyllosilicates represent an important interest in the development of new materials with desirable properties (catalysts, sorbents, ...) and in environmental protection and rehabilitation (waste deposits, polluted soils,...). In this work, we turn one's attention to the interaction of aniline with montmorillonite. Firstly, because this compound serves as a model for the sorption of aromatic amines by expanding layer silicates, and secondly, because aniline is a very dangerous polluting molecule. The interaction of aniline with SWy2 Wyoming montmorillonite (structural formula : (Na0.14Ca0.05K0,01)(Al1,56Fe0.21 Mg0.23)(Si3.95Al0,05)O10(OH2).nH2O) exchanged with different interlayer cations (Na+, K+, Mg2+, Ca2+, Ba2+ and NH4+) is obtained by placing the sample in aniline vapour. Mass measurements of the sample versus time show that saturation of adsorption process is obtained after 16 hours of exposure. Carbon and nitrogen were quantified after interaction with a LECO CNS-2000 analyser. The results confirm that aniline molecules are adsorbed. The quantity of adsorbed molecules is more important that the CEC (Cationic Exchange Capacity) of the sample. For example, for 100g of Na-SWy2, 0,088 mole of aniline are adsorbed after 16 hours of exposure either than the CEC value equal to 0,065 mole/100g. The interlayer cation type influences the amount of aniline taken up with clay. For Mg2+ and Ba2+ cations, the proportion of adsorbed aniline is approximately equal to 4CEC, whereas this value is lower with Na+ ( 1,5CEC) and NH4+ (2,5CEC). Characteristics of the absorption (localisation of aniline molecules, type of bonding between layer and molecule) have been studied using infra-red spectroscopy. The comparison between the original material spectra, intercalated with aniline montmorillonite spectra and liquid state aniline spectra shows that all the characteristic bands of aniline are found in the intercalated with aniline montmorillonite spectra. The N-H stretching wavenumbers are lower for the aniline-montmorillonite complex than for the dilute state (or like gas state) aniline (3388 cm-1 and 3312-3324 cm-1 for the aniline-montmorillonite complex; 3480 cm-1 and 3395 cm-1 for the dilute state); this implies an increase of the N-H bonds length in the complex because of a strong hydrogen bridge formation between aniline and water molecule. Aniline anchorage appears to require the presence of interlayer water. O - H --- NH2 - C6H5 I H The C-N band wavenumber shifts from about 1275 cm-1 in the liquid state or dilute state to 1250cm-1 in the complex which proves a length increase for this bond in the complex consistent with the strong hydrogen bridge formation. The structural changes have also been investigated. For this purpose, a diffractometer equipped with a controlled atmosphere cell was used. The patterns have been recorded with the relative humidity of 50% at 30°C. For Na and NH4-samples an increase of 0,3 nm in the d-value of the 001 reflection after aniline treatment confirms clearly the fixation of the molecule in the interlayer space of the montmorillonite. A systematic decreasing of the width at mid height is observed for the adsorbed samples indicating a better stacking of the layers which can be attributed to a structural reorganisation of the interlayer space. For all the sample studied, the basal d-spacing is 1,5 nm after the adsorption. This result is compatible with an orientation in which the plane of the benzene ring is either perpendicular to the silicate surface of the sample.