Nano-ZnO/ nitrogen self-doped hierarchically porous graphite-like carbon derived from Astragalus residue toward effective removal of phenol

Background: Preparing porous carbon with rich pore structure and heteroatom doping is still the key issue for developing and utilizing biomass-based carbon materials. Methods: Nano-ZnO/nitrogen self-doped hierarchically porous graphite-like carbon (AZC-700) was prepared from Astragalus residue by pyrolysis and used to adsorb phenol. Significant Findings: AZC-700 showed a specific surface area of 1149 m2 g-1, hierarchical micro-/mesoporous structure, and adsorption capacity of 163.36 mg g-1 on phenol, which was better than those of reported biochar. AZC-700 could remove 90.09 % phenol with low initial concentration (5 mg L-1) in spiked Nanhu water to reach discharge standard, and it could maintain 89 % of the initial adsorption capacity after five cycles. ZnO nanoparticles anchored on AZC-700 as the spacer inhibited the stack of graphite-like. Self-doped nitrogen adsorbed phenol via n-n EDA, Lewis acid-base, hydrogen bond, and complexation. This study not only effectively utilized Astragalus residue, but also provided an efficient adsorbent for removing phenol.