Aminosilanes grafting on FAU/EMT zeolite: Effect on CO 2 adsorptive properties

Abstract

In this work, the grafting reaction of as-synthesized template-free FAU/EMT intergrowth zeolite with 3-aminopropyltriethoxysilane (APTES), 3-aminopropylmethyldiethoxysilane (APMDES), and 3-aminopropyldimethylethoxysilane (APDMES) containing tri-hydrolyzable ethoxy groups (3E), di-hydrolyzable ethoxy groups (2E), and mono-hydrolyzable ethoxy group (1E), respectively, were investigated in solvents expressing different polarities. The grafting reaction via APMDES was studied in n-hexane (HEX), toluene (TOL), t-butanol (TBUT), isopropanol (IPA), isopropanol/water mixture, 95/5 V/V (IPAW), acetone (ACT) and ethanol (ETN) with dielectric constants of 1.88, 2.4, 12.4, 19.9, 19.9, 21, and 24, respectively. The samples grafting with APDMES and APTES was only conducted in TOL and IPA as examples of non-polar and polar solvents, respectively. The samples were characterized using nitrogen sorption at 77 K (BET), X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetric analysis (TG), cross polarization magic angle spinning 29Si NMR and 13C NMR (nuclear magnetic resonance) spectroscopy, FTIR and carbon dioxide (CO 2) adsorption. The obtained results showed that the polarity and dielectric constant of the solvent used for grafting aminosilanes on zeolites strongly affect the amounts of grafted amine groups, the surface area and micropore volume, as well as CO 2 adsorptive properties of the resulting materials. Non-polar solvents resulted in larger concentrations of grafted amine groups, lower surface area materials, and lower CO 2 capacity of adsorption. On the contrary, polar solvents resulted in smaller concentrations of amine groups, higher surface area materials, and larger CO 2 capacity of adsorption. The obtained results also showed that the lower the number of ethoxy groups in the aminosilane, the higher the surface area and CO 2 capacity of adsorption of the samples.