Formation Mechanisms of Hydroxyl-Rich Carbon Layers on Carbon Nanotube Surfaces for Promoting the Hydrolysis of Cellulose to Sugar

Through analysis of the transformation of carbon sources including glucose, fructose, and 5-hydroxymethylfurfural in hydrothermal carbonization (HTC) and the adsorption of carbon tubes (CNTs) with them, the formation mechanism of a hydroxyl-rich carbon layer on the CNT surface is clearly revealed. During HTC, the adsorption of furan and aromatic clusters and even primary particles by CNTs by π–π interaction is noticed as the key condition to improve the utilization rate of carbon sources and the quality of the carbon layer. The coated CNTs own a hydroxyl-rich carbon layer with a thickness of several nanometers on its surface, which provides the ability for functional applications. With the use of the hydroxyl-rich carbon layer-coated CNTs, a low-acid aqueous system is established for the hydrolysis of cellulose to sugar. Accordingly, the cellulose conversion and glucose yield are obviously improved. The route of HTC for hydroxylation of CNTs not only fundamentally avoids the use of strong acid oxidation in traditional method but also provides the useful guidance to prepare functional carbon materials with application prospects.