Exploring the realm of advanced membranes with customizable separation capabilities holds great promise in CO2 separation. A particularly exciting path is the utilization of mixed matrix membranes (MMMs) to surpass the performance of commonly used polymeric membranes. In recent times, there has been a surge of interest in hafnium (Hf) metal–organic frameworks (MOFs) due to their multiple potential sites for CO2 adsorption. These MOFs feature four bridging hydroxyl groups (μ3-OH) positioned at the corners of the tetrahedral cavity, electronegative linker moieties, and Bronsted acid sites arising from undercoordinated metals. In this study, we synthesized task-specific UiO-66(Hf) and UiO-66-NH2(Hf) MOFs and integrated them into a chitosan (CS) matrix to explore their effects on CO2 separation performance of MMMs. Comprehensive analyses using various analytical techniques were conducted on synthesized MOFs and MMMs. At an optimal loading of 5 wt% of UiO-66-NH2(Hf) under humid conditions, the MMMs demonstrated a remarkable 408 % increment in CO2 permeance and a 113 % improvement in CO2/N2 selectivity compared to unfilled CS membranes. Notably, the UiO-66-NH2(Hf) MOF, enriched with amino ligands, exhibited superior dispersibility and enhanced CO2 separation ability compared to the UiO-66(Hf) MOF within the CS matrix. These findings not only approach the 2008 Robeson upper bound curve but also demonstrate consistency in the CO2 separation performance for over 120 hours of exposure at elevated temperatures (85°C) and a feed pressure of 2.21 bar under humid conditions. These challenging conditions, mirroring real-world applications, highlight the stability of the synthesized MMMs as efficient gas separation technologies.