Co-producing carbon dots and hydrochars via hydrothermal carbonization of microalgae: Transformation mechanisms and...

Green microalgae Chlorella pyrenoidosa (CP) was chosen to co-produce carbon dots (CDs) and hydrochar (HC) through hydrothermal carbonization, where the CDs and HC yields were 15.7 % and 14.2 % at 230 °C for 120 min, and could be used as fluorescent material and solid fuel. A reaction kinetics model for co-producing functional carbon materials was established, achieving 99.1 % agreement between simulation and experimental results. Notably, mutual conversions between CDs and micromolecules were primary reactions, intensified with increasing hydrothermal temperature. While the direct conversion of bio-oil or micromolecules into HC and the direct transformation of HC into CDs were challenging. Adding 2 g/100 mL CH₃COOH could improve the CDs yield by promoting CP hydrolysis and inhibiting CDs degradation. However, HC generation via CDs polymerization caused by excessive CH₃COOH should be regulated. This study provides valuable insights into biomass HTC kinetics and offers a framework for optimizing the co-production of CDs and HC.