This paper presents the mineralogical and textural characteristics – as well as preliminary results of determining the CO₂ sorption capacity – of synthetic zeolite materials derived from F class fly ash in hydrothermal reactions. Concerning the reaction products, three types of zeolite materials were obtained as follows: Na-X, Na-P1, and Na-A. The comparative material was a natural zeolite-clinoptilolite from the Sokirnica deposit (Ukraine). In order to enhance the sorption capacity of the tested zeolites with respect to carbon dioxide, they were activated by means of the organic compound polyethyleneimine (PEI). The untreated and activated materials were examined by XRD, SEM-EDS analysis for the purpose of determining the effect of activation on the structure of the zeolites. For all zeolites, CO₂ sorption experiments were performed under static conditions. The studies showed that the PEI did not change the mineral composition of the zeolites; it only created a form of coating on the surfaces of the tested materials. Sorption capacity experiments showed better results for the CO₂ sorption of PEI activated zeolite (up to six times higher). The best results were noted for the Na-X zeolite with PEI, where sorption capacity was at a level of 2.6 mmol/g, though it is too low a result to apply these materials on an industrial scale. Therefore, the need for further modification methods is necessary to increase the CO₂ sorption capacity of the tested materials.