The role of mechanochemical treatment of carbon nanotubes in promoting glycerol etherification

High-purity and technical-grade carbon nanotubes (CNTs) were functionalized and compared, for the first time applying various mechanochemical methods to endow their surfaces with strongly acidic features. The as-prepared samples were used as catalysts in glycerol etherification performed with tert -butyl alcohol at 110 °C under autogenous pressure, converting glycerol to glycerol tert -butyl ethers, i.e. , important fuel additives, in a green way. The best-performing catalyst was the CNT sample ball-milled with glucose and hydrothermally treated with fuming H 2 SO 4 , which showed a 52.4% glycerol conversion just after 6 h. The catalytic performance of the sample was ascribed to its improved functionalization when using glucose which worked as a "binding agent" for the active functional groups, facilitating the grafting of the -SO 3 H sites on the CNT surface in a relatively short time and at a low temperature of modification. Furthermore, it was found that acidic oxygen functionalities, co-introduced with sulfonic groups during the modification, cooperated with -SO 3 H sites and jointly worked to enhance the CNT activity in glycerol etherification. Finally, it was shown that adequately tailored technical-grade CNTs could act as promising and much cheaper solid acids than functionalized expensive high-purity CNTs typically used for industrial applications. Carbon nanotubes (CNTs) were functionalized and compared, for the first time applying various mechanochemical methods to endow their surfaces with strongly acidic features. The as-prepared samples were used as catalysts in glycerol etherification.