Porous N-doped carbon converted from protein-rich shrub enables record-high removal of p-nitrophenol: superior performance and mechanism

The complete removal of harmful phenolic contaminants from water remains huge challenge because of the lack of cost-effective and powerful adsorbents. Herein, a sustainable nitrogen self-doped biochar (named KBC750N) with large specific surface area (1398.44 m2/g), high adsorption capacity (606.06 mg/g) and removal ratio (99.99%) for p-nitrophenol (PNP) in real waters (Seawater, Yangtze River water, and Yellow River water) was prepared from a naturally abundant protein-rich psammophyte Caragana korshinskii (CK) by a facile one-step pyrolysis process. The in-situ nitrogen-doped biochar shows much better adsorption removal efficiency of 99.99% toward PNP than expensive commercial adsorbents (only 77.52%). The biochar still keeps high adsorption efficiency after reused more than five times. Site energy distribution analysis revealed that the biochar captures PNP mainly through n–π and π–π electron-donor–acceptor interactions among the electron-rich functional groups (N-containing moieties, –COOH, and –OH), graphite carbon, and PNP. Density functional theory (DFT) calculations confirmed that the nitrogen site in biochar helps to strengthen its adsorption capability to PNP. This work provides a sustainable platform for the development of high-performance, cost-effective materials for efficient elimination of organic pollutants from water.