Multi-walled carbon nanotubes modified with (3-aminopropyl)triethoxysilane for effective carbon dioxide adsorption

Multi-walled carbon nanotubes (MWCNTs) were modified with (3-aminopropyl)triethoxysilane (APTES) solution in a two-step process. In the first step, the MWCNTs were pre-treated with sulfuric acid and nitric acid (5 molar each mixed at ratio of 3:1, v/v) with the aims to remove metal catalysts impurities and to introduce carboxyl groups on the MWCNT surface. In the second step, the acid pre-treated MWCNTs were functionalized with APTES at 105 degrees C under various reflux durations. The characteristics of the functionalized MWCNTs were studied by Fourier transform infrared (FT-IR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and Raman spectroscopy. TG analysis shows an increase in APTES loading with increasing reflux duration, giving the maximum loading of 13.75 wt%. This result suggests that as reflux duration increased, more amine groups were attached covalently on the MWCNT surface, forming effective mechanism sites for CO2 adsorption. The highest CO2 uptake of 75.4 mg CO2 adsorbed/g adsorbent was achieved by the amine-functionalized MWCNTs, indicating its superior performance than some other commonly used adsorbents such as SBA-15. (C) 2013 Elsevier Ltd. All rights reserved.