In the present study, we have compared the adsorption behavior of as-prepared and amine-functionalized MIL-100 and MIL-101 in the selective adsorption process. The synthesized adsorbents by the hydrothermal method were investigated by the different methods of analysis and identification. The volumetric method was used to investigate CO2 and CH4 adsorption at the different temperatures and P < 10 bar. Also, the selectivity of CO2 to CH4 was studied. The surface area and pore volume of MIL-101 were higher than those of MIL-100; consequently, the CO2 adsorption capacity of MIL-101 was higher than that of MIL-100. Although the surface area and pore volume of MIL-100 and MIL-101 significantly decreased after amine functionalization, the adsorbents showed the enhanced CO2 adsorption capacity at ambient temperature. The amine-modified adsorbents displayed ultrahigh selectivity for CO2 over CH4. Also, an increase in the temperature decreased the adsorption capacity of CO2. According to the results, modified MIL-101 can be a promising adsorbent for the purification and separation of gases.

A hybrid composite of NaY zeolite and amine modified multi-walled carbon nanotube (MWCNT) has been synthesized by hydrothermal method. The obtained NaY/CNT composite (NC composite) was characterized by X-ray diffraction (XRD), Fourier transform infrared (FTIR), scanning electron microscopy (SEM), and BET analysis. CO2, CH4 and N2 adsorption at two different temperatures and P < 5 bar on the composite was investigated by the volumetric method. The selectivity of the NC composite for CO2/CH4 and CO2/N2 has been studied and compared with pure NaY zeolite. Crystal structures of NC composite were similar to those of pure NaY zeolite, but the surface area and pore volume of the NC composite are enhanced. Incorporation of MWCNTs into NaY zeolite increases nucleation sites for the formation of NaY zeolite crystals, resulting in the smaller size of NaY zeolite crystals. Gas adsorption capacity and selectivity of NC composite increased because of enhancement of micropore volume. The results confirm that NC composite is a promising material for the separation and purification of gases.

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In order to improve the adsorption capacity and selectivity of CO 2 /CH 4 and CO 2 /N 2 , we have functionalized multi-walled carbon nanotubes (MWCNT) with 3-aminopropyltriethoxysilane (APTES). The functionalized MWCNT was characterized by Fourier transform infrared (FT-IR), energy dispersive X-ray spectroscopy (EDX) and BET analysis. CO 2 , CH 4 and N 2 adsorption at two different temperatures and P < 5 bar on the functionalized MWCNTs was investigated by the volumetric method. The selectivity of the functionalized MWCNTs for CO 2 /CH 4 and CO 2 /N 2 was studied and compared with MWCNTs. The functionalized MWCNTs show higher adsorption capacity of CO 2 and selectivity of CO 2 /CH 4 and CO 2 /N 2 in comparison with the MWCNTs at different pressures. The highest CO 2 /CH 4 and CO 2 /N 2 selectivities for the functionalized MWCNTs were 6.78 and 26.14, respectively, at a pressure of 0.2 bar and at 298 K. Two of the most common adsorption models, the Langmuir and Sips isotherms, were used to correlate the experimental data of CO 2 and CH 4 adsorption on the adsorbents. The results confirm that the functionalized MWCNTs are promising materials for the separation and purification of gases.