Removing waste gas, more particularly carbon dioxide, from a gaseous medium and producing gaseous oxygen, a recovered waste constituent, more particularly solid carbon, heat and electrical power, by means of chemical reaction of waste gas with a metal oxide, more particularly dodecatungstophosphoric acid, immobilized in a porous matrix, more particularly tetraethylorthosilicate sol gel, enclosed in a gas permeable membrane. Regeneration of the metal oxide, more particularly by heating, and reconstitution of the porous matrix containing same by periodic introduction of base materials, and in some cases with externally supplied energy.