Reusable magnetite nanoparticles-biochar composites for the efficient removal of chromate from water

Md Samrat Alam; Brendan Bishop; Ning Chen; Salman Safari; Viola Warter; James M Byrne; Tyler Warchola; Andreas Kappler; Kurt O Konhauser; Daniel S Alessi

doi:10.1038/s41598-020-75924-7

Reusable magnetite nanoparticles-biochar composites for the efficient removal of chromate from water

Sci Rep. 2020 Nov 4;10(1):19007. doi: 10.1038/s41598-020-75924-7.

Authors

Md Samrat Alam^{1

2}, Brendan Bishop^{3

4}, Ning Chen⁵, Salman Safari³, Viola Warter⁶, James M Byrne⁶, Tyler Warchola³, Andreas Kappler⁶, Kurt O Konhauser³, Daniel S Alessi⁷

Affiliations

¹ Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Alberta, T6G 2E3, Canada. mdsamrat@ualberta.ca.
² Department of Earth Sciences, University of Toronto, 22 Russell Street, Toronto, ON, M5S 3B1, Canada. mdsamrat@ualberta.ca.
³ Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Alberta, T6G 2E3, Canada.
⁴ Department of Geology, University of Regina, 3737 Wascana Parkway, Regina, SK, S4S 0A2, Canada.
⁵ Canadian Light Source Inc., University of Saskatchewan, 114 Science Place, Saskatoon, SK, S7N 0X4, Canada.
⁶ Geomicrobiology, Center for Applied Geoscience, University of Tübingen, 72076, Tübingen, Germany.
⁷ Department of Earth and Atmospheric Sciences, University of Alberta, 1-26 Earth Sciences Building, Alberta, T6G 2E3, Canada. alessi@ualberta.ca.

Abstract

Biochar (BC) and magnetite (Fe₃O₄) nanoparticles (MNP) have both received considerable recent attention in part due to their potential use in water treatment. While both are effective independently in the removal of a range of anionic metals from aqueous solution, the efficacy of these materials is reduced considerably at neutral pH due to decreased metal adsorption and MNP aggregation. In addition to synthetic metal oxide-biochar composites for use in treatment and remediation technologies, aggregates may also occur in nature when pyrolytic carbon is deposited in soils. In this study, we tested whether magnetite synthesized in the presence of biochar leads to increased removal efficiency of hexavalent chromium, Cr(VI), at the mildly acidic to neutral pH values characteristic of most natural and contaminated aqueous environments. To do so, magnetite nanoparticles and biochar produced from ground willow were synthesized to form composites (MNP-BC). Batch studies showed that MNP-BC markedly enhanced both adsorption and reduction of Cr(VI) from aqueous solution at acidic to neutral pH as compared to MNP and BC separately, suggesting a strong synergetic effect of hybridizing Fe₃O₄ with BC. Mechanistically, the Cr(VI) removal processes occurred through both adsorption and intraparticle diffusion followed by reduction to Cr(III). Synchrotron-based X-ray absorption spectroscopy analyses confirmed that Cr(VI) was reduced at the surface of MNP-BC, with electrons derived directly from both biochar and magnetite at low pH, while at near-neutral pH, biochar increased Cr(VI) reduction by inhibiting MNP aggregation. Extended X-ray absorption fine structure fitting results confirmed that the Cr(III) precipitates consist of Cr(OH)₃ and chromite (Cr₂FeO₄) nanoparticles. Our results demonstrate that MNP-BC composites have great potential as a material for the treatment of chromate-containing aqueous solutions across a wide range of pH values, and provide information valuable broadly relevant to soils and sediments that contain biochar.

Publication types

Research Support, Non-U.S. Gov't

Grants and funding

CIHR/Canada