N2/Ar plasma-induced surface sulfonation on graphene nanoplatelets for catalytic hydrolysis of cellulose to glucose

Abstract

The surface functionalization of graphene nanoplatelets catalysts (GNPs) with OH, COOH, and SO3H groups for cellulose hydrolysis was investigated via gas–liquid interfacial plasma (GLIP) sulfonation system under 1 M H2SO4. The sulfonation chemistry of the GLIP process was examined under different gas ratios of N2/Ar (100%N2, 70%N2–30%Ar, 30%N2–70%Ar). The balance between plasma-induced physical activation and chemical reaction plays an essential part in the sulfonation performance. Experiments on acidic group determination and catalysis ability test demonstrated that the addition of 30% Ar to N2 exerts a positive effect on enhancing the sulfonation activity and catalytic stability of GNPs. The 70%N2–30%Ar-GNPs shown higher total acid and sulfonic acid density of 5.56 and 0.45 mmol g−1, respectively. The optimized catalyst achieved a conversion rate of 41.5% with high glucose selectivity of 84.3%. Sulfonation of GNPs over traditional hydrothermal method under 18 M H2SO4 at 200 °C for 24 h further reflected the “less hazardous” and “high efficiency” properties of GLIP sulfonation in 1 M H2SO4 for 1 h. Significantly, the GLIP-GNPs also exhibited superior recyclability of 95.9% in 3 times cycle tests for cellulose hydrolysis, which is much higher than that of H-GNPs (49.5%).