α-Fe2O3 (hematite) and CuO nanoparticles were synthesized, characterized, and utilized to construct water-based nanofluids capable of CO2 absorption enhancement. The structure, morphology, surface, and bulk properties of the synthesized materials were investigated using field-emission scanning electron microscopy (FE-SEM), scanning electron microscopy (SEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), ζ, dynamic light scattering (DLS), pH, and viscosity analyses and measurements. The unclear and mysterious nature of the mass transfer mechanisms of nanofluids were investigated and confirmed by developing several approaches including new parameters for optimum and equilibrium conditions. The investigations revealed the maximum CO2 absorption enhancement of 63.79 and 38.72% for water–Fe2O3 and water–CuO nanofluids, respectively. A new observation about absorption trends was hypothesized and rationalized to be caused by the variation of surface charges and named the “electrostatic bulk effect”. The approach made it possible to categorize the reported mechanisms into bulky and interfacial groups and gave a concise, clear, and integrated insight into the mass transfer mechanisms, stability concept, and nanofluid component selection standards.