Formation of hydroxyl-rich carbon layer coated silica microspheres and its application to enhance hydrolysis of cellulose to sugar

The formation of hydroxyl-rich carbon layer coated silica microspheres (SiO2-NH2@C) under hydrothermal carbonization (HTC) conditions is demonstrated for the catalytic hydrolysis of regenerated cellulose to sugar. The driving factors for the formation of the SiO2-NH2@C and the different morphologies are investigated through the surface amino modification of silica and the control of the carbon source concentration during the HTC cladding process. The surface silica atom content after hydrothermal treatment of unmodified and modified silica is 14.24% versus 1.17% respectively. This shows the introduction of amino groups can drive the formation of the carbon layer coated structure through electrostatic interactions. As can be seen from the SEM and TEM images, 2nd HTC and adjustment of the concentration of the carbon source can control the morphology of the SiO2-NH2@C. With the strong adsorption between the hydroxyl-rich hydrothermal carbon outer layer and the cellulose, it is possible to hydrolyze 96.4% of the regenerated cellulose to glucose under pure aqueous phase ultra-dilute acid conditions, with a glucose yield of 75.8%. A clearer understanding of the driving factors and control conditions for the formation of the hydroxyl-rich SiO2-NH2@C structure is provided, along with a more definite direction for the preparation of similar nanomaterials.