Novel liquid-like nanoparticle organic hybrid materials (NOHMs) which possess unique features including negligible vapor pressure and a high degree of tunability were synthesized and their physical and chemical properties as well as CO 2 capture capacities were investigated. NOHMs can be classified based on the synthesis methods involving different bonding types, the existence of linkers, and the addition of task-specific functional groups including amines for CO 2 capture. As a canopy of polymeric chains was grafted onto the nanoparticle cores, the thermal stability of the resulting NOHMs was improved. In order to isolate the entropy effect during CO 2 capture, NOHMs were first prepared using polymers that do not contain functional groups with strong chemical affinity toward CO 2. However, it was found that even ether groups on the polymeric canopy contributed to CO 2 capture in NOHMs via Lewis acid-base interactions, although this effect was insignificant compared to the effect of task-specific functional groups such as amine. In all cases, a higher partial pressure of CO 2 was more favorable for CO 2 capture, while a higher temperature caused an adverse effect. Multicyclic CO 2 capture tests confirmed superior recyclability of NOHMs and NOHMs also showed a higher selectivity toward CO 2 over N 2O, O 2 and N 2. © 2011 American Chemical Society.