Molten Salt Carbonization and Activation of Biomass to Functional Biocarbon

Functional carbon materials are useful for energy storage, catalysis, and pollutant adsorption, and are in high demand, for which biomass has become a valuable raw material. Molten salt carbonization and activation (MSCA) is a promising approach to converting biomass to functional biocarbon and reducing or neutralizing carbon impact on the environment. It uses a single thermal treatment and features high-efficiency conversion, rapid production, and low resource and processing costs. More importantly, in this process, the unmatched purely ionic environment at high temperatures can lead to in situ activation (pore generation) of the biocarbon and introduce desired ions into the carbon to enable unique functionalities. The obtained biocarbon possesses a fairly large specific surface area (SSA), balanced pore structure, and specific surface oxygen-containing groups for diverse applications. This review explains the fundamental and technological aspects of MSCA of biomass, focusing on the approaches, salt compositions (mixtures), processing conditions, and products. The properties of the obtained biocarbon are analyzed and compared in the context of practical applications. Areas for further investigation are also explored with the hope of this molten salt route becoming optimized and industrialized for a circular economy.