Abstract
Chemical grafting of (3-aminopropyl) triethoxysilane on Na-montmorillonite in ethanol-water mixture or ethylene glycol as solvent resulted in two organoclays (NaMt-S-EW and NaMt-S-EG, respectively). The latter were characterized through X-ray diffraction, Fourier transform infrared spectroscopy, thermal analysis, differential scanning calorimetry and 29Si solid-state nuclear magnetic resonance (NMR). Nitrogen adsorption isotherms measurements revealed lower specific surface area as compared to the starting clay mineral. This was explained by the formation of compact lamella stacks bound by silylation at the edges of the clay sheets. Thermal programmed desorption analyses (TPD) revealed an improved affinity towards carbon dioxide (CO2) as compared to the starting clay mineral. NaMtS-EW displayed higher affinity towards CO2 than NaMt-S-EG, with retention efficiency factor exceeding 16 μmol.m-2 for high amine content. Differential scanning calorimetry gave desorption enthalpy ranging from 148 to 467 kcal.mol-1, suggesting that only chemical interactions are involved between the amino groups grafted and CO2. CO2 retention capacity exceeding 1.0 mmol.g-1 with efficiency factor higher than 16 micromol.m-2 can be obtained for higher amine content, in optimum content, when no CO2 removal through forced convection takes place.
Highlights
A growing interest is devoted to clay-based nanocomposites obtained through chemical grafting of organic silane moieties [1,2,3,4] and to the features of the silylating agents to be grafted [5,6]
FT-IR analyses revealed a shift of the Si-O stretching band from 1032 cm-1 for NaMt to 1038 cm-1 for both NaMt-S-EW-1 and NaMt-S-ethylene glycol (EG) (Figure 1)
The presence of APTES on the clay mineral surface was supported by new bands observed at 1521, 2885 and 2945 cm−1, and assigned to the deformation of -CH2 and to both the asymmetric and symmetric stretching of the -CH belonging to the -CH2 groups respectively
Summary
A growing interest is devoted to clay-based nanocomposites obtained through chemical grafting of organic silane moieties [1,2,3,4] and to the features of the silylating agents to be grafted [5,6]. Ethanol/water mixtures were found to enhance hydrolysis and polymerization of the silane molecules into siloxane bonds [7,11,12] These two processes can occcur even before clay pillaring [13], leading to the formation of a wide variety of polymer sizes and shapes. The grafting process of silane species should strongly depend on the surface density of the terminal OH groups These sites should be relatively more accessible for silylation than those arising from structural defects, if any, or clay sheet edges sandwiched within the interlayer space. The accessibility to these potential interlayer silylation sites could be more or less accentuated by using different solvents that promote clay exfoliation For this purpose, the present study was achieved in order to clarify the role of the two solvents used, namely ethylene glycol and a water-ethanol mixture. The results obtained will certainly be very useful for designing effective silylation processes on lamellar crystalline matrices
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