Novel carbothermal synthesis of Fe, N co-doped oak wood biochar (Fe/N-OB) for fast and effective Cr(VI) removal

In this study, nZVI and N-containing functional groups were simultaneously doped on oak wood biochar (Fe/N-OB) through a facile carbothermal reduction process followed by NH3 treatment, and employed for fast and effective hexavalent chromium (Cr(VI)) removal. Various techniques were employed and demonstrated the successful doping of Fe and N on biochar. The Fe/N-OB obtained at 1000 °C (Fe/N-OB1000) possessed the highest proportion of Fe and exhibited the best Cr(VI) removal compared to raw OB, N-OB, and Fe-OB. Various impacting factors were fully investigated. Fe/N-OB1000 displayed a fast removal kinetics for Cr(VI) with an excellent removal efficiency of 99.9% within 10 min, surpassing other reported nZVI supported biochar or N-doped biochar. XPS method verified the adsorption role of positively charged nitrogen group (N+) and the reduction role of Fe0 and NH on Cr(VI) elimination. After reacted with Fe/N-OB1000, the adsorbed Cr on Fe/N-OB1000 mainly existed as Cr(III) (∼73.09%). The outstanding performance of Fe/N-OB1000 on Cr(VI) elimination was exhibited in Cr(VI) adsorption, Cr(VI) reduction along with Cr(III) complexation. This study showed that the facilely synthesized Fe/N-OB1000 has a promising environmental application on fast and effective Cr(VI) elimination from aqueous solution.