scholarly journals Insight to Microbial Fe(III) Reduction Mediated by Redox-Active Humic Acids with Varied Redox Potentials

2021 ◽  
Vol 18 (13) ◽  
pp. 6807
Author(s):  
Jingtao Duan ◽  
Zhiyuan Xu ◽  
Zhen Yang ◽  
Jie Jiang
Keyword(s):  
Molecular Weight ◽  
Electron Transfer ◽  
Humic Acids ◽  
Weight Fraction ◽  
Electrochemical Analysis ◽  
Microbial Reduction ◽  
Redox Potentials ◽  
Groundwater Environment ◽  
Redox Active ◽  
Different Molecular Weight

Redox-active humic acids (HA) are ubiquitous in terrestrial and aquatic systems and are involved in numerous electron transfer reactions affecting biogeochemical processes and fates of pollutants in soil environments. Redox-active contaminants are trapped in soil micropores (<2 nm) that have limited access to microbes and HA. Therefore, the contaminants whose molecular structure and properties are not damaged accumulate in the soil micropores and become potential pollution sources. Electron transfer capacities (ETC) of HA reflecting redox activities of low molecular weight fraction (LMWF, <2.5) HA can be detected by an electrochemical method, which is related to redox potentials (Eh) in soil and aquatic environments. Nevertheless, electron accepting capacities (EAC) and electron donating capacities (EDC) of these LMWF HA at different Eh are still unknown. EDC and EAC of different molecular weight HA at different Eh were analyzed using electrochemical methods. EAC of LMWF at −0.59 V was 12 times higher than that at −0.49 V, while EAC increased to 2.6 times when the Eh decreased from −0.59 V to −0.69 V. Afterward, LMWF can act as a shuttle to stimulate microbial Fe(III) reduction processes in microbial reduction experiments. Additionally, EAC by electrochemical analysis at a range of −0.49–−0.59 V was comparable to total calculated ETC of different molecular weight fractions of HA by microbial reduction. Therefore, it is indicated that redox-active functional groups that can be reduced at Eh range of −0.49–−0.59 are available to microbial reduction. This finding contributes to a novel perspective in the protection and remediation of the groundwater environment in the biogeochemistry process.

scholarly journals Too Much of a Good Thing? Assessing Performance Tradeoffs of Two-Electron Compounds for Redox Flow Batteries

2021 ◽  
Author(s):  
Bertrand Neyhouse ◽  
Alexis Fenton Jr ◽  
Fikile Brushett
Keyword(s):  
Electron Transfer ◽  
Systems Engineering ◽  
Mass Transfer Rate ◽  
Electrode Polarization ◽  
Redox Potentials ◽  
Electron Transfer Mechanism ◽  
Redox Flow Batteries ◽  
Redox Active ◽  
Flow Batteries ◽  
Electron Compounds

<p>Engineering redox-active compounds to support stable multi-electron transfer is an emerging strategy for enhancing the energy density and reducing the cost of redox flow batteries (RFBs). However, when sequential electron transfers occur at disparate redox potentials, increases in electrolyte capacity are accompanied by decreases in voltaic efficiency, restricting the viable design space. To understand these performance tradeoffs for two-electron compounds specifically, we apply theoretical models to investigate the influence of the electron transfer mechanism and redox-active species properties on galvanostatic processes. First, we model chronopotentiometry at a planar electrode to understand how the electrochemical response and associated concentration distributions depend on thermodynamic, kinetic, and mass transport factors. Second, using a zero-dimensional galvanostatic charge / discharge model, we assess the effects of these key descriptors on performance for a single half-cell. Specifically, we examine how different properties (i.e., average of the two redox potentials, difference between the two redox potentials, charging rate, mass transfer rate, and comproportionation rate) affect the electrode polarization and voltaic efficiency. Finally, we extend the galvanostatic model to include two-electron compounds in both half-cells, demonstrating compounding voltage losses for a full cell. These results evince limitations to the applicability of multi-electron compounds—as such, we suggest new directions for molecular and systems engineering that may improve the prospects of these materials within RFBs.<b></b></p>

scholarly journals Electrochemical Analysis of Architecturally Enhanced LiFe0.5Mn0.5PO4 Multiwalled Carbon Nanotube Composite

2021 ◽  
Vol 2021 ◽  
pp. 1-8
Author(s):  
Sabelo Sifuba ◽  
Shane Willenberg ◽  
Usisipho Feleni ◽  
Natasha Ross ◽  
Emmanuel Iwuoha
Keyword(s):  
Electron Transfer ◽  
Carbon Nanotube ◽  
Electrode Materials ◽  
Electrochemical Impedance ◽  
Electrochemical Analysis ◽  
Multiwalled Carbon Nanotube ◽  
Spectroscopic Techniques ◽  
Redox Potentials ◽  
Multiwalled Carbon ◽  
Iron Manganese

In this work, the effect of carbon on the electrochemical properties of multiwalled carbon nanotube (MWCNT) functionalized lithium iron manganese phosphate was studied. In an attempt to provide insight into the structural and electronic properties of optimized electrode materials, a systematic study based on a combination of structural and spectroscopic techniques was conducted. The phosphor-olivine LiFe0.5Mn0.5PO4 was synthesized via a simple microwave synthesis using LiFePO4 and LiMnPO4 as precursors. Cyclic voltammetry was used to evaluate the electrochemical parameters (electron transfer and ionic diffusivity) of the LiFe0.5Mn0.5PO4 redox couples. The redox potentials show two separate distinct redox peaks that correspond to Mn2+/Mn3+ (4.1 V vs Li/Li+) and Fe2+/Fe3+ (3.5 V vs Li/Li+) due to interaction arrangement of Fe-O-Mn in the olivine lattice. The electrochemical impedance spectroscopy (EIS) results showed LiFe0.5Mn0.5PO4-MWCNTs have high conductivity with reduced charge resistance. This result demonstrates that MWCNTs stimulate faster electron transfer and stability for the LiFe0.5Mn0.5PO4 framework, which demonstrates to be favorable as a host material for Li+ ions.

scholarly journals Geothrix fermentans Secretes Two Different Redox-Active Compounds To Utilize Electron Acceptors across a Wide Range of Redox Potentials

2012 ◽  
Vol 78 (19) ◽  
pp. 6987-6995 ◽  
Author(s):  
Misha G. Mehta-Kolte ◽  
Daniel R. Bond
Keyword(s):  
Electron Transfer ◽  
Redox Potential ◽  
Electron Acceptor ◽  
Extracellular Electron Transfer ◽  
Redox Potentials ◽  
Active Compounds ◽  
Content Type ◽  
Electron Shuttles ◽  
Redox Active ◽  
Geothrix Fermentans

ABSTRACTThe current understanding of dissimilatory metal reduction is based primarily on isolates from the proteobacterial generaGeobacterandShewanella. However, environments undergoing active Fe(III) reduction often harbor less-well-studied phyla that are equally abundant. In this work, electrochemical techniques were used to analyze respiratory electron transfer by the only known Fe(III)-reducing representative of theAcidobacteria,Geothrix fermentans. In contrast to previously characterized metal-reducing bacteria, which typically reach maximal rates of respiration at electron acceptor potentials of 0 V versus standard hydrogen electrode (SHE),G. fermentansrequired potentials as high as 0.55 V to respire at its maximum rate. In addition,G. fermentanssecreted two different soluble redox-active electron shuttles with separate redox potentials (−0.2 V and 0.3 V). The compound with the lower midpoint potential, responsible for 20 to 30% of electron transfer activity, was riboflavin. The behavior of the higher-potential compound was consistent with hydrophilic UV-fluorescent molecules previously found inG. fermentanssupernatants. Both electron shuttles were also produced when cultures were grown with Fe(III), but not when fumarate was the electron acceptor. This study reveals thatGeothrixis able to take advantage of higher-redox-potential environments, demonstrates that secretion of flavin-based shuttles is not confined toShewanella, and points to the existence of high-potential-redox-active compounds involved in extracellular electron transfer. Based on differences between the respiratory strategies ofGeothrixandGeobacter, these two groups of bacteria could exist in distinctive environmental niches defined by redox potential.

scholarly journals The Influence of Secondary Structure on Electron Transfer in Peptides

2013 ◽  
Vol 66 (8) ◽  
pp. 848 ◽  
Author(s):  
Jingxian Yu ◽  
John R. Horsley ◽  
Andrew D. Abell
Keyword(s):  
Electron Transfer ◽  
Secondary Structure ◽  
Chain Length ◽  
Intramolecular Hydrogen Bonding ◽  
Electrochemical Analysis ◽  
Helical Conformation ◽  
Intramolecular Electron Transfer ◽  
Helical Structures ◽  
Redox Active ◽  
Intramolecular Hydrogen

A series of synthetic peptides containing 0–5 α-aminoisobutyric acid (Aib) residues and a C-terminal redox-active ferrocene was synthesised and their conformations defined by NMR and circular dichroism. Each peptide was separately attached to an electrode for subsequent electrochemical analysis in order to investigate the effect of peptide chain length (distance dependence) and secondary structure on the mechanism of intramolecular electron transfer. While the shorter peptides (0–2 residues) do not adopt a well defined secondary structure, the longer peptides (3–5 residues) adopt a helical conformation, with associated intramolecular hydrogen bonding. The electrochemical results on these peptides clearly revealed a transition in the mechanism of intramolecular electron transfer on transitioning from the ill-defined shorter peptides to the longer helical peptides. The helical structures undergo electron transfer via a hopping mechanism, while the shorter ill-defined structures proceeded via an electron superexchange mechanism. Computational studies on two β-peptides PCB-(β3Val-β3Ala-β3Leu)n–NHC(CH3)2OOtBu (n = 1 and 2; PCB = p-cyanobenzamide) were consistent with these observations, where the n = 2 peptide adopts a helical conformation and the n = 1 peptide an ill-defined structure. These combined studies suggest that the mechanism of electron transfer is defined by the extent of secondary structure, rather than merely chain length as is commonly accepted.

scholarly journals Electrochemical Analysis of Architecturally Enhanced Life0.5Mn0.5PO4 Multi-Walled Carbon Nanotube Composite

2021 ◽  
Vol 66 ◽  
pp. 1-11
Author(s):  
Sabelo Sifuba ◽  
Shane Willenberg ◽  
Usisipho Feleni ◽  
Natasha Ross ◽  
Emmanuel Iwuoha
Keyword(s):  
Electron Transfer ◽  
Carbon Nanotube ◽  
Electrode Materials ◽  
Electrochemical Impedance ◽  
Electrochemical Analysis ◽  
Spectroscopic Techniques ◽  
Redox Potentials ◽  
Manganese Phosphate ◽  
Multi Walled Carbon Nanotube ◽  
Iron Manganese

In this work, the effect of carbon on the electrochemical properties of multi-walled carbon nanotube (MWCNT) functionalized Lithium iron manganese phosphate was studied. In an attempt to provide insight into the structural and electronic properties of optimized electrode materials a systematic study based on a combination of structural and spectroscopic techniques. The phosphor-olivine LiFe0.5Mn0.5PO4, was synthesized via a simple microwave synthesis using LiFePO4 and LiMnPO4 as precursors. Cyclic voltammetry was used to evaluate the electrochemical parameters (electron transfer and ionic diffusivity) of the LiFe0.5Mn0.5PO4 redox couples. The redox potentials show two separate distinct redox peaks that correspond to Mn2+/Mn3+ (4.1 V vs Li/Li+) and Fe2+/Fe3+ (3.5 V vs Li/Li+) due to interaction arrangement of Fe-O-Mn in the olivine lattice. The electrochemical impedance spectroscopy (EIS) results showed LiFe0.5Mn0.5PO4-MWCNTs having high conductivity with reduced charge resistance. This result demonstrates that MWCNTs stimulates faster electron transfer and stability for the LiFe0.5Mn0.5PO4 framework, which demonstrates favorable as a host material for Li+ ions.

scholarly journals Fractionation of lignin produced from the Earleaf Acacia tree by sequential industrial organic solvents

2021 ◽  
Vol 24 (1) ◽  
pp. 1835-1841
Author(s):  
Thong Hoang Le ◽  
Khanh B. Vu ◽  
Quynh-Thy Song Nguyen ◽  
Phat Van Huynh ◽  
Khanh-Ly T. Huynh ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Organic Solvent ◽  
Ethyl Acetate ◽  
Organic Solvents ◽  
Weight Fraction ◽  
Ft Ir ◽  
Catalytic Applications ◽  
Light Medium ◽  
Acacia Tree ◽  
Different Molecular Weight

Introduction: Understanding the fractions of lignin is important for further conversion of lignin into valuable products. Herein, the “home-made” lignin from Earleaf Acacia tree was extracted by sequential industrial organic solvent and characterized each fraction to reveal its properties for further catalytic applications. Methods: In this work, lignin was prepared from the Earleaf Acacia tree using the soda method. Then, the prepared lignin was fractionated by sequential solvents of ethyl acetate, ethanol, methanol, and acetone. Each lignin fractions were characterized by FT-IR and GPC. Results: The FT-IR results confirmed the soda method can produce lignin from woodchips. The fractionation of lignin separated the lignin mixture into different molecular weight fraction from light – medium into heavy compounds. Conclusion: Lignin was produced from woodchips using the soda method successfully. The fractionation using the sequential organic solvents showed the separation of different molecular weight of lignin, which allow to apply for the further conversion into useful products.

scholarly journals Too Much of a Good Thing? Assessing Performance Tradeoffs of Two-Electron Compounds for Redox Flow Batteries

2021 ◽  
Author(s):  
Bertrand Neyhouse ◽  
Alexis Fenton Jr ◽  
Fikile Brushett
Keyword(s):  
Electron Transfer ◽  
Systems Engineering ◽  
Mass Transfer Rate ◽  
Electrode Polarization ◽  
Redox Potentials ◽  
Electron Transfer Mechanism ◽  
Redox Flow Batteries ◽  
Redox Active ◽  
Flow Batteries ◽  
Electron Compounds

<p>Engineering redox-active compounds to support stable multi-electron transfer is an emerging strategy for enhancing the energy density and reducing the cost of redox flow batteries (RFBs). However, when sequential electron transfers occur at disparate redox potentials, increases in electrolyte capacity are accompanied by decreases in voltaic efficiency, restricting the viable design space. To understand these performance tradeoffs for two-electron compounds specifically, we apply theoretical models to investigate the influence of the electron transfer mechanism and redox-active species properties on galvanostatic processes. First, we model chronopotentiometry at a planar electrode to understand how the electrochemical response and associated concentration distributions depend on thermodynamic, kinetic, and mass transport factors. Second, using a zero-dimensional galvanostatic charge / discharge model, we assess the effects of these key descriptors on performance for a single half-cell. Specifically, we examine how different properties (i.e., average of the two redox potentials, difference between the two redox potentials, charging rate, mass transfer rate, and comproportionation rate) affect the electrode polarization and voltaic efficiency. Finally, we extend the galvanostatic model to include two-electron compounds in both half-cells, demonstrating compounding voltage losses for a full cell. These results evince limitations to the applicability of multi-electron compounds—as such, we suggest new directions for molecular and systems engineering that may improve the prospects of these materials within RFBs.<b></b></p>

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