scholarly journals Removal Mechanisms of Cr(VI) By Redox-Active Moieties on HNO3 Modified Biochar Under Different pH and O2 Conditions

2021 ◽  
Author(s):  
Xiyan Yin ◽  
Jia Wen ◽  
Zhuangzhuang Xue ◽  
Cuilian Yang ◽  
Yangfang Li ◽  
...  
Keyword(s):  
Photoelectron Spectroscopy ◽  
Removal Rate ◽  
Dominant Role ◽  
Paramagnetic Resonance ◽  
Modified Biochar ◽  
Redox Active ◽  
Effective Removal ◽  
Porous Volume ◽  
Acidic Conditions ◽  
Electron Paramagnetic

Abstract Nitric acid (HNO3) modified biochar (NBC) has been demonstrated to be a promising sorbent. However, the roles of their redox-active moieties (RAMs, i.e., environmentally persistent free radicals (EPFRs) and oxygen-containing function groups) in Cr(VI) removal under varying pH and O2 conditions remain poorly understood. In this study, HNO3 oxidation caused an obvious increase in specific surface area, porous volume, RAMs content, and surface potential of the biochar, leading to the more effective removal of Cr(VI) (with the removal rate reached 100% at pH 2.0) than that of the untreated biochar. Kinetics experiments revealed that O2 and pH are of great importance for the reduction efficiency and rate of Cr(VI). RAMs on NBC can either directly reduce Cr(VI)(predominant pathway) or activate O2 to produce •O2− for indirect Cr(VI) reduction. In addition, we examined the changes in the compositions of RAMs during the reaction by tuning the RAMs compositions using methanol and hydrogen peroxide. The results of electron paramagnetic resonance and X-ray photoelectron spectroscopy analysis demonstrated that the main electron donors on NBC were different at different pH values: oxygen-containing groups, e.g., –OH and C–O–C, played a dominant role in reducing Cr(VI) under acidic conditions while the neutral condition was beneficial to EPFRs-dominated reduction. This study investigated the roles of the EPFRs and oxygen-containing function groups on HNO3 modified biochar, which may provide new insights into the promoted reduction of Cr(VI) by applications of biochar.

Jellyfish-like few-layer graphene nanoflakes: high paramagnetic response alongside increased interlayer interaction

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Alexander Ulyanov ◽  
Dmitrii Stolbov ◽  
Serguei Savilov
Keyword(s):  
Photoelectron Spectroscopy ◽  
High Sensitivity ◽  
Paramagnetic Centers ◽  
Interlayer Interaction ◽  
Paramagnetic Resonance ◽  
X Ray ◽  
Graphene Nanoflakes ◽  
Few Layer Graphene ◽  
Electron Paramagnetic ◽  
Hydrocarbon Pyrolysis

Abstract Jellyfish-like graphene nanoflakes (GNF), prepared by hydrocarbon pyrolysis, are studied with electron paramagnetic resonance (EPR) method. The results are supported by X-ray photoelectron spectroscopy (XPS) data. Oxidized (GNFox) and N-doped oxidized (N-GNFox) flakes exhibit an extremely high EPR response associated with a large interlayer interaction which is caused by the structure of nanoflakes and layer edges reached by oxygen. The GNFox and N-GNFox provide the localized and mobile paramagnetic centers which are silent in the pristine (GNF p ) and N-doped (N-GNF) samples. The change in the relative intensity of the line corresponding to delocalized electrons is parallel with the number of radicals in the quaternary N-group. The environment of localized and mobile electrons is different. The results can be important in GNF synthesis and for explanation of their features in applications, especially, in devices with high sensitivity to weak electromagnetic field.

Sequestered carbon on clay mineral probed by electron paramagnetic resonance and X-ray photoelectron spectroscopy

2006 ◽  
Vol 295 (1) ◽  
pp. 135-140 ◽  
Author(s):  
Kátia Cylene Lombardi ◽  
Antonio Salvio Mangrich ◽  
Fernando Wypych ◽  
Ubirajara Pereira Rodrigues-Filho ◽  
José L. Guimarães ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Clay Mineral ◽  
Photoelectron Spectroscopy ◽  
Paramagnetic Resonance ◽  
X Ray ◽  
Electron Paramagnetic

Redox-active crown ethers. Electrochemical and electron paramagnetic resonance studies on alkali metal complexes of quinone crown ethers

1992 ◽  
Vol 114 (23) ◽  
pp. 8983-8991 ◽  
Author(s):  
Milagros Delgado ◽  
Robert E. Wolf ◽  
JudithAnn R. Hartman ◽  
Gillian McCafferty ◽  
Rahmi Yagbasan ◽  
...  
Keyword(s):  
Electron Paramagnetic Resonance ◽  
Alkali Metal ◽  
Metal Complexes ◽  
Crown Ethers ◽  
Paramagnetic Resonance ◽  
Redox Active ◽  
Electron Paramagnetic ◽  
Alkali Metal Complexes

scholarly journals Interaction of iron ions with melanin

2019 ◽  
Author(s):  
Andrzej Czesław Żądło ◽  
Tadeusz Sarna
Keyword(s):  
Redox Reactions ◽  
Transition Metal Ions ◽  
Iron Binding ◽  
Iron Ions ◽  
Paramagnetic Resonance ◽  
Redox Active ◽  
Active Transition ◽  
Electron Paramagnetic ◽  
Aerobic And Anaerobic ◽  
Anaerobic System

One of the antioxidant roles of melanin is binding redox-active transition metal ions. The aim of this study was to examine the redox reactions accompanying iron binding by melanin. Two kinds of synthetic eumelanin were mixed with iron (II) and iron (III) in the presence and absence of citrate and ADP in the aerobic and anaerobic system. The iron binding was examined by electron paramagnetic resonance (EPR) spectroscopy and thiocyanate assay. Obtained results indicate that although melanin reduces iron (III) that is unbound to this polymer, binding of iron (II) is accompanied by its oxidation by melanin.

scholarly journals Electrochemically addressable trisradical rotaxanes organized within a metal–organic framework

2015 ◽  
Vol 112 (36) ◽  
pp. 11161-11168 ◽  
Author(s):  
Paul R. McGonigal ◽  
Pravas Deria ◽  
Idan Hod ◽  
Peyman Z. Moghadam ◽  
Alyssa-Jennifer Avestro ◽  
...  
Keyword(s):  
Solid State ◽  
Near Infrared ◽  
De Novo ◽  
Metal Organic Framework ◽  
Paramagnetic Resonance ◽  
Interlocked Molecules ◽  
Redox Active ◽  
Metal Organic ◽  
Electron Paramagnetic ◽  
Organic Framework

The organization of trisradical rotaxanes within the channels of a Zr6-based metal–organic framework (NU-1000) has been achieved postsynthetically by solvent-assisted ligand incorporation. Robust ZrIV–carboxylate bonds are forged between the Zr clusters of NU-1000 and carboxylic acid groups of rotaxane precursors (semirotaxanes) as part of this building block replacement strategy. Ultraviolet–visible–near-infrared (UV-Vis-NIR), electron paramagnetic resonance (EPR), and 1H nuclear magnetic resonance (NMR) spectroscopies all confirm the capture of redox-active rotaxanes within the mesoscale hexagonal channels of NU-1000. Cyclic voltammetry measurements performed on electroactive thin films of the resulting material indicate that redox-active viologen subunits located on the rotaxane components can be accessed electrochemically in the solid state. In contradistinction to previous methods, this strategy for the incorporation of mechanically interlocked molecules within porous materials circumvents the need for de novo synthesis of a metal–organic framework, making it a particularly convenient approach for the design and creation of solid-state molecular switches and machines. The results presented here provide proof-of-concept for the application of postsynthetic transformations in the integration of dynamic molecular machines with robust porous frameworks.

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