Paramagnetic Impurities in Graphene Oxide

Discussion of the origin of paramagnetic centres observed by electron paramagnetic resonance in graphene oxide (GO) and reduced graphene oxide (rGO) is done on the assumption that GO can be considered as a functionalized graphene. This leads to the conclusion that the narrow signal with g close to 2, observed for GO and thermally reduced GO, is due to paramagnetic centres localized on defects and exchange coupled to conduction electrons. Randomness of graphene modication results in variety of parameters of EPR signals. The broad signals observed in GO and rGO and ascribed to magnetic clusters on the zig-zag edge states indicate that the edge magnetism can be preserved by functionalization.

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“…2a and b. Materials prepared and studied by us are free from Mn 2+ ions, which were suggested as a possible source of this signal [12].…”

Section: Resultsmentioning

confidence: 99%

Magnetic Centres in Functionalized Graphene

et al. 2015

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“…Additionally, the concentration of manganese increased drastically from 0.14 to 2,290 ppm (Table 1). Indeed, the Hummers method is known to result in considerable amounts of residual manganese because of the use of permanganate oxidant (43)(44)(45). This Hummers GO (HU-GO) was subsequently reduced to yield RGOs (HU-RGOs) using three different methods: thermal treatment (HU-TRGO), sodium borohydride (HU-NaBH 4 ), and hydrazine (HU-N 2 H 4 ).…”

Section: Resultsmentioning

confidence: 99%

Synthetic routes contaminate graphene materials with a whole spectrum of unanticipated metallic elements

Wong

Sofer²,

Kubešová

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

145

118

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The synthesis of graphene materials is typically carried out by oxidizing graphite to graphite oxide followed by a reduction process. Numerous methods exist for both the oxidation and reduction steps, which causes unpredictable contamination from metallic impurities into the final material. These impurities are known to have considerable impact on the properties of graphene materials. We synthesized several reduced graphene oxides from extremely pure graphite using several popular oxidation and reduction methods and tracked the concentrations of metallic impurities at each stage of synthesis. We show that different combinations of oxidation and reduction introduce varying types as well as amounts of metallic elements into the graphene materials, and their origin can be traced to impurities within the chemical reagents used during synthesis. These metallic impurities are able to alter the graphene materials' electrochemical properties significantly and have wide-reaching implications on the potential applications of graphene materials.

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“…EPR studies also revealed the existence of Mn þ2 arising from the preparation procedure of rGO from GO and indicated that Mn þ2 is anchored to the graphene lattice and cannot be removed by conventional washing. 21,22 Quenching experiments through monitoring the EPR signal by Su et al 23 revealed that the catalytic activity of porous GO is related to the localized spins generated at the edge of the p-electron system. Prakash et al 24 found that EPR signals from ZnO-rGO hybrid materials occur at g-values in a range between 2.0042 and 2.0045, which is slightly higher than for "normal" graphitic EPR signals that typically resonate at g-values between 2.0022 and 2.0035, thus indicating an interaction among carbon-inherited spin species, p-electrons in condensed sp 2 -domains of graphene sheets and oxygen-vacancy-related defect centers of ZnO.…”

mentioning

confidence: 98%

Comparative electron paramagnetic resonance investigation of reduced graphene oxide and carbon nanotubes with different chemical functionalities for quantum dot attachment

Pham¹,

Krueger²,

Eck³

et al. 2014

Applied Physics Letters

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Electron paramagnetic resonance (EPR) spectroscopy has been applied to different chemically treated reduced graphene oxide (rGO) and multiwalled carbon nanotubes (CNTs). A narrow EPR signal is visible at g = 2.0029 in both GO and CNT-Oxide from carbon-related dangling bonds. EPR signals became broader and of lower intensity after oxygen-containing functionalities were reduced and partially transformed into thiol groups to obtain thiol-functionalized reduced GO (TrGO) and thiol-functionalized CNT (CNT-SH), respectively. Additionally, EPR investigation of CdSe quantum dot-TrGO hybrid material reveals complete quenching of the TrGO EPR signal due to direct chemical attachment and electronic coupling. Our work confirms that EPR is a suitable tool to detect spin density changes in different functionalized nanocarbon materials and can contribute to improved understanding of electronic coupling effects in nanocarbon-nanoparticle hybrid nano-composites promising for various electronic and optoelectronic applications.

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Paramagnetic Impurities in Graphene Oxide

Cited by 66 publications

References 26 publications

Magnetic Centres in Functionalized Graphene

Magnetic Centres in Functionalized Graphene

Synthetic routes contaminate graphene materials with a whole spectrum of unanticipated metallic elements

Comparative electron paramagnetic resonance investigation of reduced graphene oxide and carbon nanotubes with different chemical functionalities for quantum dot attachment

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