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 hydroxylrich 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 pi-pi 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.

Automated summary

By analyzing the transformation of glucose, fructose, and 5-hydroxymethylfurfural in hydrothermal carbonization (HTC) and their adsorption on carbon nanotubes (CNTs), the formation mechanism of a hydroxyl-rich carbon layer on the CNT surface is revealed. The adsorption of furan and aromatic clusters by CNTs through pi-pi interaction during HTC is found to be crucial in improving the utilization rate of carbon sources and the quality of the carbon layer. The use of hydroxyl-rich carbon layer-coated CNTs in a low-acid aqueous system significantly improves cellulose conversion and glucose yield. The HTC route for hydroxylation of CNTs provides guidance for the preparation of functional carbon materials.