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.