Quasi-homogeneous carbocatalysis for one-pot selective conversion of carbohydrates to 5-hydroxymethylfurfural using sulfonated graphene quantum dots

Graphene quantum dot (GQD), which is the latest addition to the family of nanocarbon materials, promises a wide spectrum of novel applications. Here, we for the first time demonstrate the use of GQD and sulfonated GQDs (SGQDs) as quasi-homogenous catalysts for chemo-catalysis. Specifically, we demonstrate that SGQDs are able to selectively and effectively degrade carbohydrates (eg. fructose, glucose, and cellulose) at high concentrations into 5-hydroxymethylfurfural (5-HMF). For example, dehydration of fructose (up to 20 wt% concentration) to 5-HMF with a yield of 51.7% and a conversion rate of 91.8%. SGQDs uniquely combine the merits of homogenous catalysts and heterogeneous catalysts, i.e., SGQDs resemble a homogenous catalyst in the reaction while they can be recycled just mimicking the heterogeneous catalysts. The high efficiency of SGQDs is attributed to their unique physicochemical and structural properties. The DFT calculations reveal that intra-molecular hydrogen bonded -OH groups and the adjacent -SO₃H groups on SGQDs play a synergistical role in their high catalytic efficiency. This study suggests the potential of SGQD as an efficient and green carbocatalyst for one-pot biomass transformation and more generally the unique potential of functionalized GQDs as novel quasi-homogeneous catalysts for various reactions.