Synergizing graphene oxide with microwave irradiation for efficient cellulose depolymerization into glucose

The abundance in hydroxyl groups neighboring the hydrolytic site (beta-1,4 glycosidic bonds) in cellulose forms a tightly packed crystalline structure, and hence, is a major challenge in cellulose depolymerization into fermentable sugars. Herein, we report on the synergistic effect of the carbocatalyst, graphene oxide (GO) and microwave irradiation (MW) on cellulose depolymerization in the absence of pretreatment. Results showed that microcrystalline cellulose (MCC) can be effectively depolymerized into glucose in as short as 30 s at 473 K (800 W). Generated yields without pretreatments were as high as 61 +/- 4% within 60 min (200 W and 453 K), which has never been reported before to the best of our knowledge. The synergy of GO and MW was demonstrated by high heating rates and which allowed for the activation of in situ crystalline-to-amorphous transformations and suppressed immediate formation of degradation products. The activity of GO under MW was much higher than those of other solid acid catalysts such as Amberlyst 15, sulfated zirconia, and phosphotungstic acid due to the variety of surface functionalities and its high microwave absorptivity. The depolymerization mechanism was also discussed in terms of surface attrition of MCC as observed via scanning electron microscopy. On this basis, the proposed process offers an important strategy for cellulose depolymerization.