A review on N-doped biochar for enhanced water treatment and emerging applications

N-doped biochar as high efficiency adsorbent to mitigate heavy metal and organic pollutants from wastewater has received extensive attentions, because of its specific surface structure and advantages in low cost and environmental friendliness. In this review, we first summarized the preparation technologies of N-doped biochar from both N-rich and N-poor biomass, followed by discussions on the determinants of N content in N-doped biochar. The N content and the content of N-containing functional groups, the two most important factors of the N-doped biochar, can be regulated through the selection of biomass, activation agents and N dopants together with the controlling of the doping ratio of activation agent and N dopants, pyrolysis temperature and holding time. In addition, this review systemically discussed the application of N-doped biochar in adsorption of heavy metals and organic pollutants. Furthermore, the adsorption mechanisms and specific roles of N-containing functional groups were further explained. Also, several emerging applications of N-doped biochar were introduced, including supercapacitors, CO2 adsorption, catalysts, soil remediation and soil fertilizer. Finally, several challenges in the wastewater treatment by N-doped biochar were presented, and the future outlook on the precise regulate the N functional groups and synergistic effect between N and O functional groups were proposed.