In this work, a comparative study on water-stable microporous adsorbents is conducted computationally in the quest of a suitable adsorbent for post-combustion CO2 capture. In this regard, three metal-organic frameworks (MOFs), two covalent organic frameworks (COFs), and a single-wall carbon nanotube (SWCNT) are investigated under the same flue gas conditions. The simulation results show that the pure component adsorption capacity for CO2, follows the order SWCNT > InOF-1 > COF-300 > UiO-66 > COF-108 > ZIF-8 at post-combustion conditions. Further, these materials are impregnated with ionic liquids to examine the effect on the CO2, separation ability of these materials. The adsorption capacity enhances by incorporating ionic liquids, especially [EMIM] [SCN] compared to [EMIM] [BF4] as a result of a stronger interaction and being less bulky in nature. We further tested the effect of the presence of other components of flue gas on the selectivity of CO2, over N-2, and we found that the presence of SO2 and water vapor reduces the CO2, selectivity in all of the materials considered in this work. Performance in terms of CO2, selectivity of these materials is tested in the presence of all major components of flue gas, and we found that, under the same thermodynamic conditions, it follows the order InOF-1 > COF-300 > UiO-66 > SWCNT > COF-108 approximate to ZIF-8. The CO2/N-2 selectivity increases significantly after impregnating materials with ionic liquids. In the presence of water, InOF-1 completely discard N-2, showing infinitely large selectivity for CO2/N-2. In humid conditions, the difference in selectivity between pristine and composite materials decreases significantly.