Mechanochemical construction of mesoporous silicon-supported organocatalysts with alkylol-amine cooperative sites for CO2 fixation into cyclic carbonates under halogen-free conditions

In this work, we demonstrated a mechanochemical method to quickly fabricate mesoporous SiO2-supported organocatalysts with alkylol-amine cooperative sites. The detailed characterizations of solid-state NMR, FTIR, XPS, TGA, as well as electron microscope confirmed that the organocatalysts were successfully grafted on the surface of SiO2 by mechanically ball-milling without any solvent. These SiO2-supported organocatalysts exhibit medium to remarkable activity for the cycloaddition of CO2 and epoxides under halogen- and solvent-free conditions, and the activity of the catalysts can be also adjusted by controlling the pore size of the support SiO2 and the structure of organocatalysts. Further mechanistic studies suggest that the good activity originates from the synergistic effect between the alkylol and amine sites. Furthermore, SiO2-supported organocatalysts can be easily recovered and recycled. This work not only provides an efficient method for the agile construction of multifunctional organic-inorganic hybrid materials, but also provides an alternative halogen-free catalyst for CO2 conversion.