N-doped biochar synthesized by a facile ball-milling method for enhanced sorption of CO2 and reactive red.

Graphical abstract Highlights • A facile approach to prepare N-doped carbon materials was developed. • N-doped biochar was synthesized by simply ball milling pristine biochar with NH 3 ·H 2 O. • NH 2 and C N were loaded on biochar through the dehydration of COOH and OH. • N-doped biochar showed enhanced sorption for CO 2 and reactive red in comparison to N-free biochar. Abstract Doping of nitrogen (N) on carbon materials often requires complicated synthetic steps or specific machinery. In this study, N-doped biochar was successfully synthesized by simply ball milling pristine biochar with ammonium hydroxide. The content and species of N in the resulting N-doped biochars were carefully characterized, the formation mechanisms of N-related groups were illustrated, and their applications in CO 2 uptake and reactive red removal were evaluated. Most of N introduced to biochar was loaded on its surface in forms of NH 2 and C N, resulting from the dehydration of COOH and OH. Biochars produced at 450 °C were doped with more N on the surface (XPS, 2.41%–2.65%) than those produced at 600 °C (XPS, 1.18%–1.82%) because the content of O-containing functional groups in biochar decreases with increasing pyrolysis temperature. The basic properties of N-related groups enhanced the sorption performance of biochar to both acidic CO 2 and anionic reactive red. For example, the CO 2 uptake of the N-doped, 450 °C hickory biochar was 31.6%–55.2% higher than the corresponding pristine and ball-milled biochars. The maximum sorption capacity of the N-doped, 600 °C bagasse biochar to reactive red was about 3.66–16.2 times of the corresponding biochars without N doping. This paper provides an alternative and facile approach to prepare N-doped biochar that can be extended to other carbon materials to meet the specific needs in different applications, especially adsorption. [ABSTRACT FROM AUTHOR]