Contribution of different iron species in the iron-biochar composites to sorption and degradation of two dyes with varying properties

• Published in: Chemical engineering journal (Lausanne, Switzerland : 1996) Switzerland : 1996), 2020-06, Vol.389, p.124471, Article 124471
• Main Authors: Qiu, Yewen, Xu, Xiaoyun, Xu, Zibo, Liang, Jun, Yu, Yulu, Cao, Xinde
• Format: Article
• Language: English
• Subjects: Degradation; Dyes; Fe species; Iron-biochar composites; Sorption
• ISSN: 1385-8947; 1873-3212
• DOI: 10.1016/j.cej.2020.124471

[Display omitted] •Pyrolysis temperature for iron-biochar composite production affected Fe species.•Fe0 and Fe3+ in composite facilitated degradation while Fe3O4 showed less effect.•Degradation accounted for MB removal while AO7 removal was mainly due to sorption.•MB and AO7 degradation was more complete by biochar composite than pristine biochar. Iron-modified biochar has been demonstrated as an effective sorbent for the removal of aqueous organic contaminants. However, the effects of different iron species in the iron-biochar composites on the sorption and degradation of organic contaminants remain unclear. In this study, the iron-biochar composites containing different iron species were produced by one-pot pyrolysis of peanut shell with Fe2O3 at 400 °C and 700 °C, and then were used to remove two model dyes of different properties, methylene blue (MB) and acid orange 7 (AO7). The main Fe species in the biochar composites generated at 400 °C were Fe2O3, Fe3O4, FeO, and Fe0, while Fe3O4, FeO, and Fe0 were dominant in the biochar composites produced at 700 °C. Compared to the pristine biochar, the iron-biochar composites possessed higher ability to remove both MB and AO7 with the removal efficiency increasing from 33%–72% to 48%–92% and from 49%–70% to 72%–85%, respectively. The removal efficiency increased as Fe contents increased and biochar produced at 400 °C was more effective in removing MB and AO7 than biochar produced at 700 °C. Fe2O3, Fe0, and Fe3+ facilitated the degradation of MB, while FeO, Fe0, and Fe3+ had significant positive impact on AO7 degradation. The degradation was more obvious than sorption in MB removal by the biochar composites, while the opposite trend was observed for the removal of AO7. Degradation of MB by iron-biochar composites underwent the aromatic ring cleavage and oxidation, whereas hydroxylation, oxidization and decarboxylation were found in AO7 degradation. This study indicated that the iron-biochar composites were effective in removing the dyes and iron species played important roles in the dye removal.