In this present work, we successfully prepared aminated silica (ASiO2) from rice husk ash (RHA) and functionalized with 3-aminopropyltriethoxysilane (APTES). Physical and chemical properties of the synthesized material were investigated by various techniques SEM-EDX, XPS, FTIR, TGA. The surface area of RHA was 223 m2/g, while for ASiO2 was 101 m2/g. Molecular level DFT calculations revealed that the functionalization of ASiO2 resulted in a significant decrease in the HOMO-LUMO energy gap, a reduction in hardness, and a consequent increase in charge transfer characteristics. The adsorption behavior at low pressure (1 atm.) of aminated silica on different gases CO2, CH4, H2, and N2 at temperatures 77, 273, 298 K was studied. The adsorption of hydrogen was reported for the first time on aminated silica with an excellent adsorption capacity of 1.2 mmol/g. The ASiO2 exhibited excellent performance in terms of gas separation in binary mixtures of CO2/CH4, CO2/N2 and CO2/H2 at 273, and 298 K, respectively. The catalyst further exhibits high stability during three cycles with less than 10% variation in the separation capacity.