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Two series of alumina (Al₂O₃)⁻mesoporous organosilica (Al⁻MO) hybrid materials were synthesized using the co-condensation method in the presence of Pluronic 123 triblock copolymer. The first series of Al⁻MO samples was prepared using aluminum nitrate nanahydrate (Al⁻NN) and aluminum isopropoxide (Al⁻IP) as alumina precursors, and organosilanes with three different bridging groups, namely tris[3-(trimethoxysilyl)propyl]isocyanurate, 1,4-bis(triethoxysilyl)benzene, and bis(triethoxysilyl)ethane. The second series was obtained using the aforementioned precursors in the presence of an amine-containing 3-aminopropyltriethoxysilane to introduce, also, hanging groups. The Al⁻IP-derived mesostructures in the first series showed the well-developed porosity and high specific surface area, as compared to the corresponding mesostructures prepared in the second series with 3-aminopropyltriethoxysilane. The materials obtained from Al⁻NN alumina precursor possessed enlarged mesopores in the range of 3⁻17 nm, whereas the materials synthesized from Al⁻IP alumina precursor displayed relatively low pore widths in the range of 5⁻7 nm. The Al⁻IP-derived materials showed high CO₂ uptakes, due to the enhanced surface area and microporosity in comparison to those observed for the samples of the second series with AP hanging groups. The Al⁻NN- and Al⁻IP-derived samples exhibited the CO₂ uptakes in the range of 0.73⁻1.72 and 1.66⁻2.64 mmol/g at 1 atm pressure whereas, at the same pressure, the Al⁻NN and Al⁻IP-derived samples with 3-aminopropyl hanging groups showed the CO₂ uptakes in the range of 0.72⁻1.51 and 1.70⁻2.33 mmol/g, respectively. These data illustrate that Al⁻MO hybrid materials are potential adsorbents for large-scale CO₂ capture at 25 °C.