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.

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The state-of-the-art technology for CO 2 capture is an amine-based absorption process, which requires substantial investment costs and high energy in addition to the instability and corrosion problems. Natural gas purification techniques to meet the pipeline quality can also include adsorption, cryogenic separation, and membrane separation. More specifically, adsorption over solid adsorbents is more effective and less expensive than liquid absorption using amine solvents. [1][2][3][4][5][6] Gas separation using porous solid adsorbent (especially activated carbon) is the most effective and applicable method in terms of selectivity, large-scale of CO 2 capture, less energy requirement, and simplicity in addition to the high thermal and chemical stability of activated carbon in acidic and basic media. [1][2][3][4][5][6] Using natural charcoal as nonrenewable raw materials with the long conventional process to produce activated carbons is considered as relatively expensive substances. Recently, using biological and other cheap raw materials, several studies were reported on the synthesis of carbon-based materials with high adsorption capacity and economic impact. [3] In addition, activated carbon can also be prepared from industrial wastes such as olive cake [7] or sewage sludge. [8] Activated carbon is now considered as a valuable material for many applications in the industry (mainly as an adsorbent for gas separation) because of its superior properties like high surface area and high adsorption capacity.Moon et al. [1] investigated the use of activated carbon in the separation of CH 4 /CO 2 using the electric swing adsorption method. The adsorption capacity of CO 2 was 40 mg g −1 , and the separation factor of CH 4 /CO 2 was two at 293 K and 1 bar. Kacem et al. [9] used commercial activated carbon to study the separation of CO 2 /N 2 and CO 2 /CH 4 using pressure swing adsorption technique at different operating temperatures and pressures. Selectivity, adsorption capacity, and reusability were among the studied parameters of each adsorbent sample. High purity separation of binary gas mixtures of CH 4 -CO 2 with 95% of CH 4 in the purified gas was achieved. Shen et al. [10] investigated the adsorption of N 2 and CH 4 at different temperatures (303-423 K) and pressure (0-100 kPa) on activated carbon beads. The adsorption capacity of CH 4 and N 2 was 1.9 and 0.27 mol kg −1 , respectively, at 303 K and 100 kPa. Yi A porous fluorocarbon sorbent is synthesized from rice husk (RH) in a microwave reactor and then evaluated for the adsorption of different gases (CH 4 , CO 2 , and N 2 ). The fluorocarbon is characterized by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), Raman spectroscopy, Thermal gravimetric analysis (TGA), and X-ray photoelectron spectroscopy (XPS). Significant enhancement in the surface area of activated carbon material is obtained from 29 to 531 m 2 g −1 after removing naturally present silica in RH. Results reveal that rice husk fluorocarbon (RHF)...

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