title: Impact of Fe(III) as an effective electron-shuttle mediator for enhanced Cr(VI) reduction in microbial fuel cells: Reduction of diffusional resistances and cathode overpotentials.
abstract: The role of Fe(III) was investigated as an electron-shuttle mediator to enhance the reduction rate of the toxic heavy metal hexavalent chromium (Cr(VI)) in wastewaters, using microbial fuel cells (MFCs). The direct reduction of chromate (CrO4-) and dichromate (Cr2O72-) anions in MFCs was hampered by the electrical repulsion between the negatively charged cathode and Cr(VI) functional groups. In contrast, in the presence of Fe(III), the conversion of Cr(VI) and the cathodic coulombic efficiency in the MFCs were 65.6% and 81.7%, respectively, 1.6 times and 1.4 folds as those recorded in the absence of Fe(III). Multiple analytical approaches, including linear sweep voltammetry, Tafel plot, cyclic voltammetry, electrochemical impedance spectroscopy and kinetic calculations demonstrated that the complete reduction of Cr(VI) occurred through an indirect mechanism mediated by Fe(III). The direct reduction of Cr(VI) with cathode electrons in the presence of Fe(III) was insignificant. Fe(III) played a critical role in decreasing both the diffusional resistance of Cr(VI) species and the overpotential for Cr(VI) reduction. This study demonstrated that the reduction of Cr(VI) in MFCs was effective in the presence of Fe(III), providing an alternative and environmentally benign approach for efficient remediation of Cr(VI) contaminated sites with simultaneous production of renewable energy.
authors.affiliation: Key Laboratory of Industrial Ecology and Environmental Engineering, Ministry of Education (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Wang
authors.affiliation: Key Laboratory of Industrial Ecology and Environmental Engineering, Ministry of Education (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China. Electronic address: lipinghuang@dlut.edu.cn.
authors.forename: Liping
authors.initials: L
authors.lastname: Huang
authors.affiliation: College of Chemistry, Dalian University of Technology, Dalian 116024, China.
authors.forename: Yuzhen
authors.initials: Y
authors.lastname: Pan
authors.affiliation: Key Laboratory of Industrial Ecology and Environmental Engineering, Ministry of Education (MOE), School of Environmental Science and Technology, Dalian University of Technology, Dalian 116024, China.
authors.forename: Xie
authors.initials: X
authors.lastname: Quan
authors.affiliation: Environmental Nanocatalysis & Photoreaction Engineering, Department of Chemical Engineering, Loughborough University, Loughborough LE11 3TU, United Kingdom. Electronic address: g.lipuma@lboro.ac.uk.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Li Puma
mesh_terms: D000465:Algorithms; D001674:Bioelectric Energy Sources; D002857:Chromium / Q000737:chemistry*; D004058:Diffusion; D004563:Electrochemistry; D004566:Electrodes; D004583:Electrons; D007501:Iron / Q000737:chemistry*; D010084:Oxidation-Reduction; D062065:Wastewater / Q000032:analysis
chemical_list: D002857:Chromium; D007501:Iron; D062065:Wastewater; C074702:chromium hexavalent ion
keywords: Cathode overpotential; Cr(VI) reduction; Diffusion resistance; Fe(III) mediator; Microbial fuel cell