An adsorption-desorption material, in particular, crosslinked organo-amine polymeric materials having a weight average molecular weight of from about 500 to about 1×106, a total pore volume of from about 0.2 cubic centimeters per gram (cc/g) to about 2.0 cc/g, and an adsorption capacity of at least about 0.2 millimoles of CO2 adsorbed per gram of adsorption-desorption material, and linear organo-amine polymeric materials having a weight average molecular weight of from about 160 to about 1×106, a total pore volume of from about 0.2 cubic centimeters per gram (cc/g) to about 2.0 cc/g, and an adsorption capacity of at least about 0.2 millimoles of CO2 adsorbed per gram of adsorption-desorption material. This disclosure also relates in part to processes for preparing the crosslinked organo-amine materials and linear organo-amine materials. This disclosure further relates in part to the selective removal of CO2 and/or other acid gases from a gaseous stream containing one or more of these gases using the adsorption-desorption materials.