Abstract:
Molten salt-assisted photothermal pyrolysis has emerged as a promising approach due to the
ability of molten salts to ensure uniform heat distribution and store thermal energy. The thermodynamic
properties of these materials, such as thermal stability and high thermal conductivity,
facilitate efficient heat transfer and continuous thermal transient, which is typically constrained
in concentrated solar pyrolysis. During pyrolysis, the salts undergo phase transition, converting
into a liquid at their melting point. This results in the dispersion of biomass particles throughout
the salt reaction medium, facilitating efficient heat transfer. At the same time, the biomass can
engage with the inorganic constituents present within a molten salt environment. This interaction
can result in a distinct catalytic effect, which is contingent upon the chemical composition
of the salt. However, despite its indispensable role in practical molten salts pyrolysis technology,
the catalytic effect of molten salts on biomass remains poorly understood due to a paucity of
information. This study investigated the physicochemical characteristics of biochar produced
through molten NaOH-Na2CO3-based photothermal pyrolysis. The results demonstrated that
the molten salts promoted the development of a porous structure with increased BET surface
area, enhanced aromatic condensation, and enriched the oxygen-containing functional groups
on the biochar surface. These modifications of biochar are closely related to improved adsorption
performance, which results in biochar being endowed with chemically active sites and enhanced
pore fillings. The adsorption capacity of the molten salt-assisted pyrolysed biochar was
therefore evaluated against a range of pollutants, including methylene blue, sulfamethazine, and
heavy metal ions (Pb(II), Cu(II), and Cd(II)). The molten salt-derived biochar exhibited superior
adsorption performance compared to conventional pyrolysed biochar, thereby understanding its
versatility as a multifunctional bio-adsorbent. Finally, a life cycle assessment (LCA) was conducted
to assess the sustainability of molten salts-assisted photothermal pyrolysis, using the
experimental adsorption data as a basis. This study offers novel insights into the potential of
molten salt-based photothermal pyrolysis as a sustainable alternative to conventional pyrolysis,
enhancing adsorption performance and evaluating its sustainability through a life cycle assessment.
