Hydrothermal preparation and characterization of biochar from Sargassum Horneri

Biochars were prepared by hydrothermal carbonization (HTC) of Sargassum Horneri. Orthogonal method was used to determine the optimal preparation conditions, by examining the effect of factors, including the reaction time and temperature, the weight ratio of Sargassum Horneri to deionized water, on the yield of hydrochars and the carbon recovery rate. Results showed that the optimal preparation conditions are reaction time of 2 h, reaction temperature of 180°C and weight ratio of 1/4. Under the optimal conditions, the carbon recovery rate could reach 65.0%, with the yield of 51.4%. The obtained hydrochars were analyzed by element analysis, Brunauer-Emmet-Tller (BET) surface area, pH value, contact angle and FT-IR. The results indicated that the surface area could reach 26.6 m²·g^-1, with pH value of 4.8, higher O/C value and lower C/N value. Compared with biochars produced by dry pyrolysis, hydrochars were found to have more hydrophilic surface and oxygen-and nitrogen-containing functional groups, with lower ash content and higher carbon recovery rate. Besides, the yield and the carbon recovery rate of hydrochars increased by 53.4% and 33.5%, respectively.