Synthesis and characterization of sulfonated carbon-based graphene oxide monolith by solvothermal carbonization for esterification and unsymmetrical ether formation

Abstract

Herein, we report solvothermal carbonization of biomass, such as glucose, in the presence of a small amount of graphene oxide (GO) as a structure-directing agent that yields a carbon-based graphene oxide monolith (CGO monolith). The CGO monolith was functionalized with chlorosulfonic acid under mild reaction conditions to achieve sulfated carbon-based graphene oxide (SO₃H@CGO monolith). It was used for the esterification of levulinic acid with benzyl alcohol and the etherification of benzyl alcohol with butanol as model reactions. The activity of the catalyst was compared with different solid acid catalysts, such as GO, CGO monolith, nanocrystalline sulfated titania (NCST), SO₃H@HTC (sulfated hydrothermal carbon), amberlyst-15, and SO₃H@GO for esterification of levulinic acid with benzyl alcohol. The SO₃H@CGO monolith showed excellent conversion (97%) toward benzyl levulinate at 110 °C with low catalyst loading (0.008 g/cm³) and mole ratio. The catalyst was well characterized by SEM, EDXA, TEM, XRD, FTIR, BET surface area, CHNS, and TGA analysis. The role of various parameters, such as speed of agitation, molar ratio, catalyst loading, and temperature, on the reaction rate using SO₃H@CGO monolith as catalyst was studied to establish the mechanism of the reaction, and the catalyst was reused up to five times, including the fresh one. The overall process is novel and green.