Experimental Investigation of CO2 Uptake and Absorption Kinetics in APTES-Modified Fe3O4/Water Nanofluids

This study experimentally investigated CO2 absorption in APTES-modified Fe3O4/water nanofluids under continuous bubbling at nanoparticle concentrations of 0–0.1 wt% and temperatures of 10, 20, and 30 °C. Performance was evaluated using effective CO2 uptake and the apparent absorption rate constant, with enhancements calculated relative to deionized (DI) water at the same temperature. Effective uptake decreased with increasing temperature and exhibited a nonmonotonic concentration dependence, whereas normalized uptake profiles generally indicated a more rapid approach to the final uptake at higher temperatures. The highest uptake was 2.084 g L−1 at 10 °C and 0.01 wt%. The largest uptake enhancement was approximately 13.2% at 30 °C and 0.05 wt%, although the apparent rate constant decreased by approximately 4.1% under this condition. The greatest kinetic enhancement occurred at 10 °C and 0.1 wt%. Enhancement ranges across concentrations widened with increasing temperature for both metrics, while the largest ranges across temperatures occurred at different concentrations for uptake and kinetics. Normalized performance maps showed that conditions favoring uptake did not necessarily maximize the kinetic benefit of nanoparticle addition. These results support selecting nanoparticle concentration in relation to operating temperature and the relative importance of uptake and absorption rate.