The development of novel absorbents is essential for improving CO2 separation technology. In this study, 1-hexyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide/titanium dioxide/water ([Hmim][NTf2]/TiO2-H2O) was developed to separate CO2, where the thermodynamic and kinetic experiments were conducted, and Henry's constant and the liquid-side mass-transfer coefficient were determined accordingly. Furthermore, CO2 separation performance in a bubble tower was validated. A previously proposed index named “absorption ability” (AA) was used to predict and compare the experimental results. Additionally, the cost of biogas upgrading (i.e., CO2 removal for biogas purification) using [Hmim][NTf2]/TiO2-H2O was estimated. The results showed that for the developed [Hmim][NTf2]/TiO2-based technology, the average CO2 mass-transfer rate was increased by 20.0% compared with the current commercialized technology, and the contributions from the thermodynamic and kinetic aspects were 2.5% and 17.5%, respectively. The cost of biogas upgrading was 16.6% lower. In addition, AA successfully predicted the performance of CO2 separation technologies, achieving an average relative deviation of 8.1%.