Phosphate sorption mechanisms in biochar: Insights from depth profiling of porous structure across pH and pyrolysis conditions

초록

This study examines phosphate (P(V)) sorption mechanisms in Miscanthus biochar, focusing on the effects of concentration, pH, and pyrolysis temperature. Biochars produced at 400 degrees C (B400) and 700 degrees C (B700) were analyzed using Freundlich isotherm and depth profiling X-ray photoelectron spectroscopy (DP-XPS). Four sorption mechanisms were identified: physisorption and C-P(V) complexes for both biochars, electrostatic bridging complex (EBC) in B400, and O-P(V) complexes in B700. B400 had higher sorption capacity but relied on weaker EBC, making it more prone to leaching, though it also provides greater P(V) availability for uptake. In contrast, B700 exhibited stronger inner-sphere, resulting in more stable retention. DP-XPS revealed internal enrichment of P(V) and changes in functional groups by pH. These findings indicate that pyrolysis and environmental conditions significantly influence P(V) retention characteristics, and that biochar can be tailored to balance P(V) availability and stability, thereby contributing to improved soil fertility and reduced leaching.

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