Microwave-assisted exfoliation of graphite using 1-allyl-pyridinium-based ionic liquids and application to solid acid catalysts

A novel, eco-friendly direct graphite exfoliation method was developed using 1-allyl-pyridinium-based ionic liquids (ILs) under microwave irradiation. Exfoliated graphene comprising a few layers was prepared from graphite using 1-allyl-pyridinium nitrate under 300 W microwave irradiation for 10 min, which was characterized by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Density functional theory calculations indicated that the combination of the cations and anions in the ILs led to improved adsorption on the graphite surface. High-power microwave irradiation can also allow cations to intercalate easily between the graphite layers and increase the efficiency of graphite exfoliation. Solid acid catalysts were prepared from exfoliated graphene via oxidation and sulfonation. The catalytic activity was evaluated for the saccharification of cellulose, where the highest monosaccharide yield of 15.9% was obtained after 24 h at 140 degrees C with a cellulose/solid acid catalyst/water ratio of 0.1/0.05/3 (g/g/g). This performance was superior to that of several commercial catalysts. The magnetic solid acid catalyst which was prepared to facilitate separation from cellulose residue showed constant durability in three activity tests.