Mesoporous silica-amine beads from blast furnace slag for CO₂ capture applications

Steel slag, abundantly available at a low cost and containing over 30 wt% silica, is an attractive precursor for producing high-surface-area mesoporous silica. By employing a two-stage dissolution-precipitation method using 1 M HCl and 1 M NaOH, we extracted pure SiO₂, CaO, MgO, etc. from blast furnace slag (BFS). The water-soluble sodium silicate obtained was then used to synthesize mesoporous silica. The resulting silica had an average surface area of 100 m² g^-1 and a pore size distribution ranging from 4 to 20 nm. The mesoporous silica powder was further formed into beads and post-functionalized with polyethyleneimine (PEI) for cyclic CO₂ capture from a mixture containing 15% CO₂ in N₂ at 75 °C. The silica-PEI bead was tested over 105 adsorption-desorption cycles, demonstrating an average CO₂ capture capacity of 1 mmol g^-1. This work presents a sustainable approach from steel slag to cost-effective mesoporous silica materials and making CO₂ capture more feasible.