Fabrication of Redox Active Mn3O4 on Douglas fir Biochar for Aqueous Arsenic(III) Oxidation and Remediation

ORCID

Olabode: https://orcid.org/0000-0001-7966-1212; Oguntuyi: https://orcid.org/0000-0001-8784-0843; Abdulraheem: https://orcid.org/0000-0002-3863-0070; Gaur: https://orcid.org/0009-0006-2533-6389; Mlsna: https://orcid.org/0000-0002-4858-1372

MSU Affiliation

College of Arts and Sciences; Department of Chemistry

Creation Date

2026-07-30

Abstract

Aqueous As(III) is more toxic than As(V). Its remediation from wastewater is challenging due to its neutral charge at neutral water pH. Hausmannite (Mn3O4) is the most stable Mn-oxide in geological settings. However, Mn3O4 supported on biochar or any carbon matrix remains unexplored for As(III) redox remediation. In this study, Mn3O4-modified Douglas fir biochar (Mn3O4@DFBC), designed to adsorb and oxidize As(III) to As(V), was prepared by NaOH-induced precipitation, followed by passive air oxidation. Mn3O4@DFBC was characterized by XRD, FTIR, XPS, SEM, SEM-EDX and elemental analysis. Batch adsorption studies at As(III) concentrations of 100 µg/L to 250 mg/L revealed maximum uptake at pH 5-7. The adsorption kinetics best fit the pseudo-second-order kinetic model, while the equilibrium data fitted the Langmuir isotherm best, with a maximum monolayer adsorption capacity of 14.1, 13.0, and 13.1 mg/g at 5, 25, and 40 oC, respectively. Only negligible As uptake occurred on pristine DFBC. The effects of Mn3O4@DFBC dose, ionic strength, and lake water matrices on As(III) removal were studied. Ionic strength did not affect As(III) uptake while the co-existing ions in the lake water slightly decreased As(III) uptake at 1 g/L Mn3O4@DFBC dose. Regeneration experiment restored ∼76% of the As(III) removal capacity after three cycles. XPS analysis revealed 65.5% of the adsorbed As(III) was oxidized to As(V), accompanied by Mn(III) reduction to Mn(II). A new As-O XPS peak confirmed the formation of chemisorbed Mn-O-As complexes. In the near-neutral water pH range, As(V) could form monodentate-mononuclear (1V), bidentate-binuclear (2C) and bidentate-mononuclear (2E) Mn-O-As chemisorbed complexes.

Publication Date

6-15-2026

Publication Title

Journal of Industrial and Engineering Chemistry

Publisher

Elsevier

Creative Commons License

Creative Commons Attribution 4.0 International License
This work is licensed under a Creative Commons Attribution 4.0 International License.

Rights

© 2026 The Author(s)

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Digital Object Identifier (DOI)

https://doi.org/10.1016/j.jiec.2026.06.015