Hydrolysis and carbonization of reactive dyes/cotton fiber in hydrothermal environment

To understand the evolution and mechanism of the hydrothermal carbonization products of colored cotton fiber, hydrothermal carbonization experiments were carried out on colored cotton fiber dyed with reactive red X-3B and reactive blue KN-R. Fourier transform infrared spectroscopy, X-ray diffraction, and elemental analysis were used to characterize the hydrochar from colored cotton fiber and the hydrothermal behavior of reactive dyes under different reaction temperatures and time conditions. The study showed that when the reaction temperature was in the range of 210–250 °C, hydrolysis of reactive dyes was complete in 6 h, and organic acid that is produced by the degradation of cotton fiber accelerates the hydrolysis of dyes. Also, the hydrolysis products of dyes were involved in the hydrothermal carbonization of cotton fiber and covered the inside of the carbon microspheres; this led to changes in the elemental composition and functional group of the hydrochar. However, the dye content in colored fabric was limited because of limited dye-uptake. Consequently, the reactive activity of dyes was not strong enough to change the hydrothermal behavior of cotton fiber.