Structural and property synergistic correlations and sequential temperature-response mechanism of black carbon and dissolved black carbon.

Dissolved black carbon (DBC) exhibits significantly different environmental behavior from bulk black carbon (BC) and plays an important role in connecting two major pools of soils and organic sediments. As the soluble carbonaceous component, the properties of DBC are dependent on the BC formation temperature. However, the synergistic correlations and sequential temperature responses mechanisms of BC/DBC during biomass pyrolysis remain unclear. Herein, we systematically clarified the dynamic temperature response mechanism of BC/DBC to explain the evolution, heterogeneity and sequential temperature response of functional groups and fluorophores in DBC using spectroscopy techniques combined with generalized/hetero two-dimensional correlation spectroscopy (2D-COS) and parallel factor analysis (PARAFAC). As pyrolysis temperature increased, different functional groups exhibited different characteristics and dynamic behaviors, showing a sequential response of CO → OH functional groups for BC and COC → CC/benzene skeleton for DBC. The oxygen-containing functional groups evolved earlier than other functional groups and the CO/CO functional groups responded earlier than OH functional groups. Moreover, different fluorophores in DBC showed different evolution properties with varying pyrolysis temperature, and humic acid-like fluorophores exhibited higher temperature sensitivity than fulvic acid-like fluorophores. It is worth noting that the temperature response sequence of functional groups was slightly different for different biomass materials, which might be attributed to differences in their chemical compositions. These findings will provide an important basis for understanding the environmental behaviors of BC/DBC in water ecosystems.