Adsorption and catalytic oxidation removal of Mn2+ by MnO2 with different crystal structures: Structure-activity relationship and mechanism

Fengkai Shi; Biao Yang; Zikang Xiong; Ya Cheng; Caiyun Ma; Tinglin Huang; Gang Wen

doi:10.1016/j.watres.2024.123027

Adsorption and catalytic oxidation removal of Mn²⁺ by MnO₂ with different crystal structures: Structure-activity relationship and mechanism

Water Res. 2024 Dec 21:273:123027. doi: 10.1016/j.watres.2024.123027. Online ahead of print.

Authors

Fengkai Shi¹, Biao Yang¹, Zikang Xiong¹, Ya Cheng², Caiyun Ma¹, Tinglin Huang³, Gang Wen¹

Affiliations

¹ Key Laboratory of Northwest Resource, Environment and Ecology, MOE, Xi'an University of Architecture and Technology, Xi'an 710055, PR China; Shaanxi Key Laboratory of Environmental Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, PR China; Collaborative Innovation Center of Water Pollution Control and Water Quality Security Assurance of Shaanxi Province, Xi'an University of Architecture and Technology, Xi'an 710055, PR China.
² Key Laboratory of Northwest Resource, Environment and Ecology, MOE, Xi'an University of Architecture and Technology, Xi'an 710055, PR China; Shaanxi Key Laboratory of Environmental Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, PR China; Collaborative Innovation Center of Water Pollution Control and Water Quality Security Assurance of Shaanxi Province, Xi'an University of Architecture and Technology, Xi'an 710055, PR China. Electronic address: chengya.xauat@outlook.com.
³ Key Laboratory of Northwest Resource, Environment and Ecology, MOE, Xi'an University of Architecture and Technology, Xi'an 710055, PR China; Shaanxi Key Laboratory of Environmental Engineering, Xi'an University of Architecture and Technology, Xi'an 710055, PR China; Collaborative Innovation Center of Water Pollution Control and Water Quality Security Assurance of Shaanxi Province, Xi'an University of Architecture and Technology, Xi'an 710055, PR China. Electronic address: huangtinglin@xauat.edu.cn.

PMID: 39721507
DOI: 10.1016/j.watres.2024.123027

Abstract

This study investigates the impact of MnO₂ crystal structures on Mn²⁺ removal in drinking water for the first time. α-, γ-, and δ-MnO₂ phases were synthesized, showing a removal process involving adsorption (Mn²⁺ was adsorbed as the state of Mn(OH)₂), saturation, and catalytic oxidation. The adsorption capacity followed δ- > γ- > α-MnO₂, aligning with the Mn oxidation state. Electron transfer between MnO₂ and Mn(OH)₂ led to the formation of Mn₂O₃ (α-MnO₂) and Mn₅O₈ (γ- and δ-MnO₂), enhancing catalytic activity, especially for γ-MnO₂ with increased hydroxyl groups, oxygen vacancies, and polyvalent Mn. Combined with EIS tests, a reduction in charge transfer resistance of the active MnO₂ was confirmed. The structural-activity relationship of catalytic oxidation and removal of Mn²⁺ was established, and the crystal form transformation between Mn²⁺ and MnO₂ during groundwater treatment was revealed.

Keywords: Adsorption; Catalytic oxidation; Crystal structure; Manganese dioxide; Manganese removal.