Enhanced adsorption of bisphenol A in using N-doped biochar from corn kernel wastes via multiple adsorption sites

Biochar is a cost-effective adsorbent for diverse environmental pollutants. However, its adsorption capacity is fundamentally limited by intrinsically low specific surface area (SSA) and underdeveloped porosity. Moreover, the operative adsorption mechanisms require comprehensive mechanistic clarification. In this study, high-performance nitrogen-doped biochar was fabricated from corn cob wastes via a facile one-pot calcination approach, specifically tailored for efficient bisphenol A (BPA) removal. Synthesized at 800 ℃, the nitrogen-enriched biochar developed well-defined micro/mesoporous architectures, demonstrated a significantly enhanced SSA (1217.88 m²/g), considerable pore volume (PV, 0.84 cm³/g), and abundant graphitic lattice defects. Collectively, these structural merits conferred an exceptional BPA adsorption capacity of 739.5 mg/g, significantly surpassing most reported carbon-based adsorbents. Remarkably, the biochar maintained robust adsorption resilience across a wide pH spectrum and exhibited superior selectivity toward BPA against competing ions and humic acid (HA) in complex aqueous systems. The adsorption process was governed by a Langmuir isotherm model and followed pseudo-second-order kinetics, indicating monolayer chemisorption as the dominant mechanism. Definitive mechanistic analysis established that π-π electron donor–acceptor (EDA) interactions dominated the adsorption of BPA onto nitrogen-enriched biochar surfaces, with synergistic contributions from electrostatic attraction and hydrogen bonding. Integrated comparative experiments and density functional theory (DFT) calculations definitively identified oxidized-N and graphitic-N as primary active sites in nitrogen-enriched biochar, where enhanced electron transfer significantly elevated BPA adsorption through strengthened π-π EDA interactions. Collectively, this work provides unprecedented molecular-level mechanistic insights for the rational design of high-efficiency, nitrogen-engineered biochar adsorbents targeting persistent organic pollutants in environmentally sustainable water remediation applications.