Mechanistic insights into adsorption and reduction of hexavalent chromium from water using magnetic biochar composite: Key roles of Fe3O4 and persistent free radicals

Delai Zhong, Yanrong Zhang, Linling Wang, Jing Chen, Yi Jiang, Daniel C.W. Tsang, Zezhou Zhao, Shupeng Ren, Zhenhua Liu, John C. Crittenden

Research output: Journal article publicationJournal articleAcademic researchpeer-review

112 Citations (Scopus)


Magnetic biochar (MBC) has been used to remove hexavalent chromium (Cr(VI)) from water, but the roles of Fe3O4 and persistent free radicals (PFRs) in MBC in Cr(VI) removal are still less investigated. In this work, the MBC synthesized by microwave co-pyrolysis of solid-state FeSO4 and rice husk was employed to remove Cr(VI) from water. In comparison to the rice husk biochar (BC), the MBC exhibits the 3.2- and 11.7-fold higher adsorption and reduction efficiency of Cr(VI), resulting in the higher Cr(VI) removal efficiency (84.3%) and equilibrium adsorption capacity of MBC (8.35 mg g−1) than that (26.5% and 2.63 mg g−1) of BC. Multiple characterization results revealed that the high Cr(VI) removal performance of MBC was mainly attributed to the presence of active Fe3O4 and carbon-centered PFRs in the porous and graphitic MBC. The Fe3O4 not only provided active chemisorption/reduction sites for Cr(VI) via its Fe(II)oct and Fe(III)oct coordination, but also facilitated the generation of more active electron donating carbon-centered PFRs than carbon-centered PFRs with an oxygen atom in the graphitic structure to reduce Cr(VI). The presence of Fe3O4 also elevated 36.7 m2 g−1 of BET-surface area and 0.043 cm2 g−1 of pore volume of MBC, promoting the Cr(VI) removal. The Fe3O4 and carbon-centered PFRs contributed to ∼81.8% and ∼18.2% of total Cr(III) generation, respectively. In addition, the initial solution pH was responsible for determining the relative significance of Cr(VI) adsorption and reduction. This study provides new insights into the mechanisms of Cr(VI) removal from water by the MBC. This study shed new mechanistic lights on the key roles of Fe3O4 and persistent free radicals in the MBC in the removal of Cr(VI).

Original languageEnglish
Pages (from-to)1302-1309
Number of pages8
JournalEnvironmental Pollution
Publication statusPublished - Dec 2018


  • Hexavalent chromium
  • Magnetic biochar
  • Magnetite
  • Persistent free radicals
  • Synergistic removal

ASJC Scopus subject areas

  • Toxicology
  • Pollution
  • Health, Toxicology and Mutagenesis

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