Synthesis of Nitrogen‐Metal Co‐doped Biochar and its performance in removing methylene blue

A nitrogen-metal co-doped corn stem biochar (SMCUB) was successfully prepared to enhance Methylene blue (MB) adsorption performance. The addition of Mg and Ca into the biochar matrix with the help of urea-assisted N doping enhanced its pH, ash content, specific surface area and pore volume, thus increasing the adsorption properties. Adsorption experiments showed SMCUB exhibited a maximum adsorption capacity of 379.28 mg/g for MB, which was significantly higher than that of unmodified corn stem biochar (SB, 166.43 mg/g). The adsorption processes of MB on SB and SMCUB followed the PSO kinetic model and were better described by the Langmuir isotherm model. Characterization analyses confirmed that Mg and Ca-containing mineral phases and enriched oxygen- and nitrogen-containing functional groups played important roles in MB adsorption through pore filling, electrostatic attraction, hydrogen bonding, π–π interaction, and surface complexation. This study demonstrates that nitrogen-metal co-doped stem biochar is an effective and low-cost adsorbent for MB removal.