Enhanced CO2 absorption in hollow fiber membrane contactors using Amine-Functionalized ZnO nanofluids

• Amine-functionalized ZnO nanoparticles (ZnO–NH 2 ) enhance CO 2 capture in HFMC systems. • Effects of nanoparticle loading and liquid/gas flow rates are evaluated for different absorbents. • 0.1 wt% ZnO–NH 2 increases CO 2 absorption by 68.2% in water and 12.7% in MDEA. • Mass-transfer analysis identifies dominant resistances using Wilson plot correlations. Stable and efficient absorbents are critical for advancing CO 2 capture in hollow fiber membrane contactors (HFMCs). This study investigates zinc oxide nanoparticles functionalized with 3-aminopropyltriethoxysilane (ZnO–NH 2 ) as novel nanofluids for CO 2 absorption in both water (physical solvent) and N-methyldiethanolamine (MDEA, chemical solvent). Functionalization markedly improved nanoparticle dispersion stability, as validated by zeta potential and DLS, and introduced amine groups that enabled direct chemical interaction with CO 2 , confirmed by FTIR analysis. Performance tests revealed that ZnO–NH 2 nanofluids significantly outperformed bare ZnO nanofluids. At 0.1 wt% loading, CO 2 absorption flux was enhanced significantly by 68.2% in water and 12.7% in MDEA relative to the respective base fluids. Mass transfer and resistance analysis showed that in water-based systems, improvements originated primarily from reductions in liquid-film resistance, whereas in MDEA-based systems both gas- and liquid-film resistances were already minimal, leaving membrane resistance as the comparatively more influential resistance. These findings were further supported by predictive correlations, confirming the robustness of the observed trends. Overall, ZnO–NH 2 nanofluids are demonstrated to be stable, surfactant-free, and high-performance absorbents that bridge the gap between environmentally benign physical solvents and industrially relevant amines, offering a practical pathway to intensify CO 2 capture in HFMCs.