Carbon dioxide levels in the atmosphere are related to global warming and climate change. Materials to be used for CO2 capture are an important factor in assisting humanity in overcoming this challenge. The goals of this study are to look into the synthesis of adsorbents from red mud (RM), fly ash (FA), and metakaolin (MK). The initial composition was chosen to induce in situ crystallization of zeolites dispersed together with a geopolymer matrix. Two aging steps were used, which combined temperature (25; 95 °C) and atmosphere (air; water). The MK + FA system crystallized zeolite sites dispersed throughout the geopolymer matrix. These crystals were identified as faujasite-Na. They were responsible for the surface area ranging from 23.2 to 238.4 m2.g−1, and CO2 adsorption from 0.83 to 2.32 mmol.g−1 at 35 °C and 1 atm. The best results were obtained by first aging at 95 °C for 120 h, followed by water aging at 25 °C for 120 h.
