Structural characteristics of dissolved black carbon and its interactions with organic and inorganic contaminants: A critical review

Biochar (BC) is a sustainable and renewable carbonaceous material, and its soluble component, dissolved black carbon (DBC), is the key to understanding BC's geological and environmental processes. Although the relationship between the changes in DBC structure and its properties, functions, and associated environmental risks has been explored, a gap remains in our understanding of DBC's fate and behavior in the natural environment. Thus, in this review, we have highlighted the molecular and chemical compositions and the structural evolution of DBC during pyrolysis, the influence of DBC's physicochemical properties on its fate and transport, DBC's interaction with soil and its contaminants, and DBC stability in soil and water environments along with potential risks. Based on our in-depth assessment of DBC and its biogeochemical roles, we believe that future studies should focus on the following: (1) using advanced techniques to understand the chemical and molecular structure of DBC deeply and concisely and, thus, determine its fundamental role in the natural environment; (2) investigating the multi-functional properties of DBC and its interaction mechanisms; and (3) evaluating the environmental behaviors of and risks associated with DBC after BC application. In future, it is necessary to gain a deeper insight into the fate and transport of DBC with contaminants and study its associated risks under BC application in the environment.