In this work, stable water-based zinc oxide (ZnO), titania (TiO2), and multi-walled carbon nanotube (MWCNT) nanofluids are prepared and examined as CO2 absorbents in a polypropylene hollow fiber membrane contactor. Different operating variables, such as liquid flow rate, gas flow rate, and concentration of nanoparticles, and their effects on CO2 molar flux are investigated. The long-term stability of nanofluids is monitored using ultraviolet-visible spectroscopy. Also, zeta-potential measurements and sediment photography are applied to confirm the results of nanofluid stability. Dynamic light scattering is used to determine the size distribution of dispersed nanoparticles. The results show that the increase in the nanoparticle concentration to 0.15 wt % has a favorable effect on CO2 absorption efficiency as a result of the increase in Brownian motion and other related mechanisms. However, it adversely affects the CO2 absorption by lowering the nanofluid stability at higher concentrations. The obtained results reveal that ZnO nanofluid is the most effective nanofluid in all experimental conditions. At low liquid flow rates of about 10 mL/min, ZnO nanofluid could augment CO2 absorption efficiency by 130%, while both TiO2 and MWCNT nanofluids could enhance it by 60% with respect to distilled water. Possible mechanisms regarding mass transfer augmentation are also discussed.