Treatment of Water with Water:N, P Co‐Doped and Post‐Loaded Magnetic Hydrochar for Sustainable Water Pollution Control

Hydrochars synthesized from aquatic plants are an effective solution for waste water treatment. In this study, magnetic hydrochar (LSH‐NPFe) is prepared from lotus stalks, an N‐rich precursor with a porous structure. The N, P co‐doped hydrochar obtained via hydrothermal carbonization is loaded with Fe 3 O 4 nanoparticles (NPs). This process regulated the surface activity of the hydrochar, enhanced electrostatic attraction, and anchored Fe ions onto its surface. The sequential doping and loading methods improved the dispersion and stability of Fe 3 O 4 NPs on the hydrochar surface. LSH‐NPFe has high adsorption capacity for methylene blue (MB) and Pb 2+ even with salt ions, coexisting adsorbates, and light. LSH‐NPFe rapidly removed MB (within 15 min), and adsorption equilibrium is achieved within 30 min. During dynamic adsorption experiments, LSH‐NPFe removed >90% of MB from wastewater within ≈6 h. After adsorption, LSH‐NPFe is pyrolyzed to immobilize pollutants and mixed with high‐density polyethylene to form a carbon‐plastic composite. This research explains the interfacial interaction mechanism between heteroatom doping and loading, and proposes practical strategies for using aquatic plants in wastewater treatment and resource recycling. These findings can broaden the applications of biomass ‐ derived carbon materials and advance the industrialization of advanced carbon materials.