Herein, different water-based modified magnetite nanodispersions of Fe3O4-proline (Fe3O4-P), Fe3O4-lysine (Fe3O4-L), Fe3O4@SiO2-proline (Fe3O4@SiO2-P), and Fe3O4@SiO2-lysine (Fe3O4@SiO2-L) were prepared to improve the stability and absorption capacity of bare Fe3O4 nanodispersion for selective physical/chemical carbon dioxide (CO2) separation in a polypropylene hollow fiber membrane contactor (PP HFMC). The liquid was passed through the tube side and CO2 gas was passed through the shell side concurrently. Subsequently, the impacts of varying nanoparticle (NP) loadings, gas/liquid flow rates (Q l/Q g), and NP stability on CO2 separation were elucidated. Considering the achieved results, all modified NPs revealed higher selective CO2 separation performances compared to bare Fe3O4 NPs because of functionalization with chemical reactants of CO2. Also, for the first time, to evaluate the influence of the CO2 inlet concentration and wetting parameter, a new and simple model was proposed in which the behavior of functional NPs was considered. Ultimately, the CO2 removal enhancements of 27.5, 57.14, 64.28, 72.8, and 96.42% were achieved for Fe3O4, Fe3O4-P, Fe3O4-L, Fe3O4@SiO2-P, and Fe3O4@SiO2-L at optimal NP loadings and in the best operational conditions (i.e., Q l = 10 mL·min–1 and Q g = 100 mL·min–1).

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