Effects of additives on sucrose-derived activated carbon microspheres synthesized by hydrothermal carbonization

In the hydrothermal carbonization of carbohydrates, such as sucrose as raw material in this study, activated carbon microspheres were synthesized by two steps of hydrothermal carbonization (180 °C) and further heat treatment in nitrogen (1000 °C). The main purpose of this study was to investigate the effects of additives, such as H3PO4, ZnCl2, SnCl2, and CaCl2, on the surface characteristics and toluene adsorption ability by adding them into the two processes. The structural, chemical, and adsorption properties of sucrose-derived activated carbon microspheres were characterized using nitrogen adsorption, scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy, water contact angles, and dynamic adsorption of toluene. Results showed that additives played important roles in the synthesis process. The addition of CaCl2 in the hydrothermal process, the specific surface area of activated carbon spheres increased up to 1180 m2 g−1 compared with that of the blank sample (i.e., 724 m2 g−1). By contrast, the addition of H3PO4 in the heat treatment process increased the specific surface area to 1529 m2 g−1. Moreover, the micromorphology of activated carbon microspheres was more homogeneous when additives were added in the heat treatment process, but the activated carbon microspheres were more hydrophobic when additives were added in the hydrothermal process. These findings may help researchers to understand the influence of additives on the preparation of hydrochar-derived activated carbon.