Sorption of CO2 on NaBr co-doped Li4SiO4 ceramics: Structural and kinetic analysis

Structurally modified and improved NaBr-co-doped Li4SiO4 ceramics were developed for CO2 absorption in low-CO2-concentration atmospheres. Pure and NaCl-doped Li4SiO4 ceramics were also prepared for comparison. The samples were analyzed by X-ray diffraction, Scanning Electron Microscopy, N2 adsorption, X-ray photoelectron spectroscopy, differential scanning calorimetry, and thermogravimetric analyses (dynamic and isothermal). The sorption kinetics were obtained using a double exponential model. The results showed that both Na and Br can be introduced into the Li4SiO4 structure and doped on Li and oxygen sites, respectively. The doped sample presented a Li2O-enriched surface, guaranteeing abundant LiO sites and are significantly different from previous anionic (CO3, F and Cl) doping of Li4SiO4, Br doping also generated macroporous features with small particle size, these favorable characteristics promoted the surface chemisorption kinetics. Moreover, DSC analysis confirmed the formation of the molten phases during CO2 absorption, which helps improve the lithium diffusion kinetics. Here, 0.1 mol NaBr doping was used to reach a maximum absorption capacity (>30.0 wt%) in 15 vol% CO2, suggesting that NaBr-doped Li4SiO4 ceramics have great potential for CO2 capture at high temperature.