Electron donation of Fe-Mn biochar for chromium(VI) immobilization: Key roles of embedded zero-valent iron clusters within iron-manganese oxide

Zibo Xu; Mingzhe Sun; Xiaoyun Xu; Xinde Cao; James A Ippolito; Sanjay K Mohanty; Bing-Jie Ni; Shuguang Xu; Daniel C W Tsang

doi:10.1016/j.jhazmat.2023.131632

Electron donation of Fe-Mn biochar for chromium(VI) immobilization: Key roles of embedded zero-valent iron clusters within iron-manganese oxide

J Hazard Mater. 2023 Aug 15:456:131632. doi: 10.1016/j.jhazmat.2023.131632. Epub 2023 May 12.

Authors

Zibo Xu¹, Mingzhe Sun¹, Xiaoyun Xu², Xinde Cao³, James A Ippolito⁴, Sanjay K Mohanty⁵, Bing-Jie Ni⁶, Shuguang Xu⁷, Daniel C W Tsang⁸

Affiliations

¹ Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China.
² School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai, China.
³ School of Environmental Science and Engineering, Shanghai Jiao Tong University, Shanghai, China. Electronic address: xdcao@sjtu.edu.cn.
⁴ Department of Soil and Crop Sciences, Colorado State University, Fort Collins, United States.
⁵ Department of Civil and Environmental Engineering, University of California Los Angeles, United States.
⁶ Centre for Technology in Water and Wastewater, School of Civil and Environmental Engineering, University of Technology Sydney, Sydney, New South Wales, Australia.
⁷ Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China; Key Laboratory of Green Chemistry and Technology, Ministry of Education, College of Chemistry, Sichuan University, Chengdu, Sichuan, China.
⁸ Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong, China. Electronic address: dan.tsang@polyu.edu.hk.

PMID: 37210785
DOI: 10.1016/j.jhazmat.2023.131632

Abstract

The dense surface passivation layer on zero-valent iron (ZVI) restricts its efficiency for water decontamination, causing a poor economy and waste of resources. Herein, we found that the ZVI on Fe-Mn biochar could afford a high electron-donating efficiency for the Cr(VI) reduction and immobilization. Over 78.0% of Fe in the Fe-Mn biochar was used for the Cr(VI) reduction and immobilization, i.e., 56.2 - 161.7 times higher than the commercial ZVI (0.5%) and modified ZVI (0.9 -1.3%), indicating that the unique ZVI species in Fe-Mn biochar offered an outstanding Fe utilization efficiency. We proposed that oxygen atoms in the FeO in the FeMnO₂ precursor were removed during pyrolysis with biochar while the MnO skeleton was preserved, forming the embedded ZVI clusters within Fe-Mn oxide. The unique structure inhibited the formation of the Fe-Cr complex on Fe(0), which would facilitate the electron transfer between core Fe(0) and Cr(VI). Moreover, the surface FeMnO₂ inhibited the diffusion of Fe and facilitated its affinity with pollutants, thus supporting higher efficiency for pollutant immobilization. The preserved performance of Fe-Mn biochar was proved in industrial wastewater and after long-term oxidation process, and the economic benefit was evaluated. This work provides a new approach for developing active ZVI-based materials with high Fe utilization efficiency and economics for water pollution control.

Keywords: Atom efficiency; Chromium reduction; Electron transfer; Engineered biochar; Mineral transformation.