Pore reconstruction mechanism of wheat straw-templated Li₄SiO₄ pellets for CO₂ capture

The traditional Li₄SiO₄-based CO₂ sorbent pellets prepared from mechanical granulation methods usually presented densified microstructures. Hence, wheat straw, an agricultural waste featured with huge production and low cost, was used as porosity creator to improve the microstructures and CO₂ capture performance of Li₄SiO₄ pellets. The results indicated that wheat straw effectively enhanced the cyclic CO₂ sorption capacity of the pellets. In particular, 30 wt% wheat straw-templated Li₄SiO₄ pellets (LA-WS30) exhibited the capacity of ~0.15 g/g that is almost twice as high as that of unmodified pellets. The enriched porosity and improved porous structures resulted from the quick release of burning gases was considered as the main reason for the performance enhancement. In addition, the alkaline (K and Na) salts in wheat straw played a positive role in CO₂ sorption of Li₄SiO₄ pellets due to the reduced diffusion resistance. However, the pore plugging of residual wheat straw ashes after high-temperature treatment decreased the contact areas and, thus, led to the capacity reduction. To conclude, the comprehensive performance of wheat straw-templated Li₄SiO₄ pellets is the result of the combined effects of porosity creation, alkali doping and pore plugging by ashes.