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°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 13.75wt%. 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 75.4mg 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.