Abstract: Carbon microspheres with good morphology and structure were prepared in subcritical water by using waste cotton fiber as carbon source, and then the influence of different initial pH on the hydrothermal carbonization of cotton fiber was discussed. Subcritical water can destroy the crystal structure of cotton fiber, carbonize the fiber and turn it into a carbon material with low degree of graphitization. Whether in alkali, or neutral or acid condition, the cotton fiber can be dehydrated and carbonized. While H+ has minor influence on the dehydration and carbonization of the cotton fiber, pH has significant impact on the structural performance of the carbonized product, and when pH = 3.5, carbon microspheres with uniform particle size and carbon content up to 74.99% can be obtained. The analysis on liquid-phase product shows that the lower the pH, the higher the yield of glucose and the better the morphological structure during the hydrothermal reaction of cotton fiber, and vice versa. The high concentration of H+ is beneficial to the yield of carbonized product and the degree of carbonization. The research results in this paper provide a reference for the value-added reutilization of waste cotton fiber.

Key words: cotton fiber; pH value; hydrothermal carbonization; carbon microsphere; reutilization