Unique characteristics of MWCNT such as high porosity and high surface area make MWCNT as potential material to be explored in-depth through research. The role of MWCNT as CO2 adsorbent will be more efficient after modification with 3-Aminopropyl triethoxysilane (APTS) in order to obtain amine functional group. However, direct functionalization is not permissible due to the hydrophobic problem faced by pristine MWCNT. This complication can be resolved by liquid oxidation treatment using different types of oxidants such as nitric acid (HNO3), sulfuric acid (H2SO4), and mixture of nitric and sulfuric acid (HNO3/H2SO4). The characteristics of pristine MWCNT and modified MWCNT were investigated by analyzing the samples using scanning electron microscopy and energy dispersive X-ray spectroscopy (FESEM-EDXs), fourier transform infra-red (FTIR), and Raman spectroscopy technique. Higher degree of functionalization implies higher attachment of amine functional group for higher CO2 adsorption. Here, MWCNT sample treated with HNO3/H2SO4 and APTS recorded the highest degree of functionalization. © (2014) Trans Tech Publications, Switzerland.