Influence of Curing Temperature on the Synthesis of a Phosphate-Waste-Based Geopolymer for CO₂ Capture and Separation

A promising approach to combating global warming is the capture, storage, and reuse of greenhouse gas emissions. Adsorption processes can capture up to 90% of the CO₂ emissions. However, CO₂ storage requires significant investment and may not always be feasible, making it essential to improve capture efficiency and reduce costs. Geopolymeric adsorbents have shown potential for separating CO₂ from gaseous mixtures. Additionally, captured CO₂ can be utilized in processes such as electrochemical reduction, photocatalytic reduction, and catalytic methanation. This study compares the potential of four geopolymers synthesized from phosphate waste and metakaolin as precursors under different curing conditions by analyzing the adsorption equilibrium isotherms of CO₂, H₂, and CO at various temperatures. The samples were characterized using XRF, XRD, FTIR, SEM, EDS, XPS, NMR, micro-CT, density, BET surface area, and porosity analyses. The best performance was observed for the submerged samples, which exhibited a CO₂ adsorption capacity of 2.24 mmol/g at 80 °C and 2.00 mmol/g at 65 °C, highlighting the significance of the submerged-cured process. BET surface area analysis revealed values of 301 and 337 m²/g for the submerged G65s and G80s samples, with corresponding porosity values of ∼0.130 cm³/g. Additionally, FTIR and NMR analyses confirmed the successful geopolymerization and identified key aluminosilicate peaks. These findings highlight the potential of industrial waste-based geopolymers as sustainable and cost-effective adsorbents for CO₂ separation, with key characteristics such as reusability and compatibility with cyclical processes further enhancing their suitability for practical applications in gas separation technologies.