An adsorption-desorption material, in particular, crosslinked organo-amine polymeric materials having an Mw from about 500 to about 1×106, a total pore volume from about 0.2 cc/g to about 2.0 cc/g, and an adsorption capacity of at least about 0.2 millimoles adsorbed CO2 per gram of adsorption-desorption material, and linear organo-amine polymeric materials having an Mw from about 160 to about 1×106, a total pore volume from about 0.2 cc/g to about 2.0 cc/g, and an adsorption capacity of at least about 0.2 millimoles adsorbed CO2 per gram of adsorption-desorption material. This disclosure also relates to processes for preparing the crosslinked and linear organo-amine materials, as well as to selective removal of CO2 and/or other acid gases from a gaseous stream using the adsorption-desorption materials.