Surface alteration on biochar in long-term application: Insights into pyrolysis, freeze-thaw aging, and dissipation

Biochar, a carbonaceous material produced by pyrolysis, is subject to physical and chemical changes over time in its long-term application. Pollutants (e.g., TBBPA) through the environmental fate and transport can be immobilized on the biochar surface, causing an unexpected environmental impact. The objective of this study is to investigate the alteration of surface in freeze-thaw cycles to explore the long-term behaviors of biochar interactions with pollutants. The aging process of biochar is elucidated through characterization using X-ray photoelectron spectroscopy (XPS) and surface charge density analysis. These findings indicate that the aging process promotes the redistribution and re-equilibration of surface functional groups, resulting in the emergence of carboxyl groups and the disruption of aromatic structures. Using 2D-COS approaches, it was observed that the freeze-thaw aging of biochar resulted in a sequence of aromatic alkane (CH) > hydroxyl groups (-OH) > polysaccharide groups (CH) > ether and ester groups (CO-C) > carboxyl and lipid groups (C = O). The study also revealed a dissipative process with a specific sequence, depending on the level of pyrolysis of the biochar. This research contributes to an enhanced comprehension of the long-term use of biochar, particularly in the context of freeze-thaw aging processes and contaminant dissipation. This understanding can inform applications, regulations, and policies related to biochar in the context of long-term utilization.