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, ζ-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.