Mechanochemically activated Li4SiO4-based adsorbent with enhanced CO2 capture performance and its modification mechanisms

Abstract In recent years, high-temperature post-combustion carbon capture (PCC) using regenerable lithium orthosilicate ceramics has drawn extensive attention. However, the low conversion rate of Li4SiO4 is still one of the toughest obstacles limiting its practical applications. In this work, a mechanochemical activation method was used for the modification of Li4SiO4-based adsorbents for the first time, and the physico-chemical properties of activated samples were systematically compared with that of dry-milled. It was found that the mechanochemically activated Li4SiO4 possesses higher surface area, smaller particle size and greater microstructure, resulting in a superior CO2 adsorption capacity of ~0.271 g/g after 72 min’s activation. The dry-milling has been proven to enhance the capture capacity by crushing the adsorbent and reducing its particle size. However, the modification effects of dry-milling will be limited as the increasing of milling time due to the occurrence of cold welding. In comparison, the additional modification mechanisms of mechanochemical activation process could be summarized as: (i) the water could act as the liquid agent to reduce the cold welding agglomeration and produce smaller adsorbent particles; (ii) these smaller particles provide more surface area for the occurrence of hydration reaction (Li4SiO4 + H2O ↔ Li2SiO3 + 2LiOH), resulting in a porous structure consisted with laminated LiOH crystals and thus promoting the surface area of adsorbents efficiently. In a word, the superior morphology improvement and adsorption enhancement effects of this novel activation method made it a promising method for the future modification of Li4SiO4-based adsorbents.