N-doping effectively enhances the adsorption capacity of biochar for heavy metal ions from aqueous solution

N-doping was successfully employed to improve the adsorption capacity of biochar (BC) for Cu2+ and Cd2+ by direct annealing of crop straws in NH3. The surface N content of BC increased more than 20 times by N-doping; meanwhile the content of oxidized-N was gradually diminished but graphitic-N was formed and increased with increasing annealing temperature and duration time. After N-doping, a high graphitic-N percentage (46.4%) and SBET (418.7...