Novel membrane and sorbent materials are synthesized, characterized and evaluated for separating carbon dioxide from power-plant flue gas relative to an amine-absorption benchmark process. The cost of recovered CO2 using the amine process is about $40-50/ton. Examples of alternative separation materials are ionic liquids, ionic polymers, PEG-grafted ionic polymers, brominated polyphenylene oxide (BPPO), silica-impregnated BPPO nanocomposites, zeolites, and carbon-rich solid sorbents. These materials are characterized with respect to their capacity and selectivity relative to nitrogen. These characterization data are used to estimate the cost of recovered CO2 for a variety of separation approaches. By and large, the approaches that involve compression, high sorption heat, and expensive materials lead to high CO2 recovery costs.