Mechanistic study of bisphenol A removal from water using Fe and HNO3 co-modified clay-based biochar: Adsorption, in situ pyrolytic degradation, and DFT insights.

Bisphenol A (BPA), a typical endocrine-disrupting pollutant, poses a threat to human health. In this study, an Fe and HNO3 co-modified adsorbent was synthesized through the co-pyrolysis of lignin and spent bleaching clay for BPA removal. The effects of initial pollutant concentration, pH, coexisting substances, and regeneration cycles on adsorption performance were systematically investigated. The results showed that 1 M HNO3 treatment enhanced Fe dispersion, and introduced abundant oxygen-containing functional groups. The Fe/Ads-1N exhibited a maximum theoretical adsorption capacity of 44.94 mg/g for BPA. DFT calculations revealed the formation of stable coordination complexation interactions between the electron-rich phenolic hydroxyl oxygen of BPA and the electron-deficient Fe active sites, as well as the role of oxygen-containing functional groups as excellent hydrogen bond donors/acceptors. After three regeneration cycles, Fe/Ads-1N retained an adsorption capacity of 25.1 mg/g. Furthermore, 49.7 mg/g of phenol and methane-rich gas were recovered during the regeneration process, demonstrating the potential for converting pollutants into resource recovery. Pyrolysis regeneration of spent adsorbents offered higher stability and lower per-run operating costs compared to solvent regeneration. This study provides a viable strategy for the high-value utilization of pyrolysis residues and the efficient removal and recovery of BPA from aqueous systems.