Synthesis of macroporous Li4SiO4 via a citric acid-based sol–gel route coupled with carbon coating and its CO2 chemisorption properties

A highly efficient lithium orthosilicate (CSG-Li 4 SiO 4 ) was synthesized using a sol–gel method combined with carbon coating. The presence of citric acid played dual roles, serving as a complexing agent that homogeneously mixed the precursors and as a carbon source, which effectively prevented the Li 4 SiO 4 crystallite from growing. The sorbent characteristics, CO 2 absorption capacity, and cyclic absorption–desorption properties of CSG-Li 4 SiO 4 were determined using X-ray diffraction, nitrogen absorption, scanning electron microscopy, thermogravimetric analysis and a fixed-bed reactor. Compared with two reference sorbents synthesized using the solid-state method and a simple sol–gel without carbon coating, CSG-Li 4 SiO 4 presented a loose shell-connected structure with higher purity, smaller grain size and larger specific surface area. This favorable structure was responsible for the sorbent׳s improved performance, as indicated by a higher capacity (a maximum absorption of 34.2   wt%), faster absorption kinetics and better stability.