Hydrothermal-calcination synthesis of lithium orthosilicate microspheres for high-temperature CO2 capture

In recent years, the Li₄SiO₄ adsorbent has become a promising candidate for high-temperature CO₂ capture. The fabrication of micro-structured Li₄SiO₄ could enhance the capture performance effectively. However, there exists a conflict between the purity and the morphology of prepared micro-structured Li₄SiO₄. This study proposed a novel hydrothermal-calcination method, which could produce Li₄SiO₄ microspheres with great morphology and relatively high purity. The physicochemical properties, CO₂ capture performance and forming mechanisms of Li₄SiO₄ microspheres are evaluated and investigated systematically. It is found that the hydrothermal process could fabricate micro-spherical LiOH@Li₂SiO₃ precursor, which was further converted to Li₄SiO₄ microspheres during the subsequent calcination process. The LiOH@Li₂SiO₃ precursor could not only maintain the microstructure but also reduce the Li₄SiO₄ generation temperature, thus improving the morphology as well as the purity of obtained Li₄SiO₄ microspheres. As a result, the adsorbents could reach a CO₂ capture capacity of 0.167–0.222 g/g within 30 min's adsorption under 15 vol.% CO₂, and their cyclic stability are diverse depending on the used calcination temperatures. The hydrothermal-calcination contributes to the future preparation of high-performance Li₄SiO₄-based CO₂ adsorbents.