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Adsorption and catalytic oxidation removal of Mn2+ by MnO2 with different crystal structures: Structure-activity
Fengkai Shi1, Biao Yang1, Zikang Xiong1
1Key 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.
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.
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