Structure and Magnetic Properties of Pristine and Fe-Doped Micro- and Nanographenes

Panich, A. M.; Shames, Alexander I.; Tsindlekht, M. I.; Osipov, V. Yu.; Patel, Mehulkumar; Savaram, Keerthi; He, Huixin

doi:10.1021/acs.jpcc.5b11732

Cited by 30 publications

(35 citation statements)

References 21 publications

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“…The J value of 2.41 higher than 0.5 is described in the literature [18], as a result of interactions between 4-5 spins (forming clusters). Similar values of J = 2, or with alternative fitting 5/2 were obtained by Panich et al for nanographites doped with iron [49]. Further, it is stated that the increased annealing temperature > 200 K destroys large clusters and leads to a decreased value of J (0.5 at 1000 K) [45].…”

Section: Magnetic Properties Of Goqdssupporting

confidence: 83%

Unraveling Origins of EPR Spectrum in Graphene Oxide Quantum Dots

et al. 2020

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Carbon nanostructures are utilized in a plethora of applications ranging from biomedicine to electronics. Particularly interesting are carbon nanostructured quantum dots that can be simultaneously used for bimodal therapies with both targeting and imaging capabilities. Here, magnetic and optical properties of graphene oxide quantum dots (GOQDs) prepared by the top-down technique from graphene oxide and obtained using the Hummers’ method were studied. Graphene oxide was ultra-sonicated, boiled in HNO3, ultra-centrifuged, and finally filtrated, reaching a mean flake size of ~30 nm with quantum dot properties. Flake size distributions were obtained from scanning electron microscopy (SEM) images after consecutive preparation steps. Energy-dispersive X-ray (EDX) confirmed that GOQDs were still oxidized after the fabrication procedure. Magnetic and photoluminescence measurements performed on the obtained GOQDs revealed their paramagnetic behavior and broad range optical photoluminescence around 500 nm, with magnetic moments of 2.41 µB. Finally, electron paramagnetic resonance (EPR) was used to separate the unforeseen contributions and typically not taken into account metal contaminations, and radicals from carbon defects. This study contributes to a better understanding of magnetic properties of carbon nanostructures, which could in the future be used for the design of multimodal imaging agents.

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Section: Magnetic Properties Of Goqdssupporting

confidence: 83%

Unraveling Origins of EPR Spectrum in Graphene Oxide Quantum Dots

et al. 2020

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“…The very weak signal is identical to the cavity background. Therefore, the absence of Cu 2+ signal in this spectrum can be explained by the very strong Cu 2+ ‐Cu 2+ dipolar interaction, which increases the signal linewidth, making EPR detection difficult . This result is consistent with the Cu 2+ ‐Cu 2+ distances that range from 1.148 to 1.393 Angstroms as determined in crystalline state, by X‐ray diffraction …”

Section: Resultssupporting

confidence: 85%

Magnetic resonance studies of copper (II) sorbitol complex, in solution, reveal a supramolecular structure compatible to the crystal structure

Kock

Higuera-Padilla

Vigatto

et al. 2019

Magnetic Reson in Chemistry

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Although the Cu2+‐sorbitol complex [Cu2+‐Sorb] structure in crystalline state has been determined by X rays, it is not known in solution, where most studies of this complex are performed. Therefore, the goal of this work was to obtain information about the structure of this complex in aqueous solution using nuclear magnetic resonance and electron paramagnetic resonance spectroscopies. The magnetic resonance results indicate that the complex is formed at approximately pH 12. In this pH the sorbitol 1H relaxation times were so short (broad line) that was not possible to use standard nuclear magnetic resonance parameters (nuclear Overhauser effect and spin–spin coupling constants values) to solve the three‐dimensional structure. However, valuable structural information about the complex in solution was obtained. The relaxation results indicate that the Cu2+ ions are buried in the structure and not accessible to solvent; the 1H and 13C spectra shows strong paramagnetic shift effect indicating short distance between these nuclei and Cu2+ in the structure. No electron paramagnetic resonance signal was observed in pH 12 indicating strong Cu2+‐ Cu2+ dipolar interaction, compatible to Cu2+‐Cu2+ distances measured in crystal, from 1.148 to 1.393 Angstroms. The complex self‐diffusion coefficient (D) of 1.58 × 10−10 m2/s value, determined by Diffusion‐Ordered Spectroscopy, is compatible to a molecular weight of 3–6 KDa. Therefore, these results corroborate that the [Cu2+‐Sorb] complex is assembled in solution, at pH 12, with several structural parameters compatible to the toroidal hexadecacuprate supramolecular structure determined in solid state.

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“…Not unrelated to the present study, Lyon and coworkers [38] investigated electron spin resonance in a monolayer of graphene on a Si/SiO 2 substrate in which the g factor was 1.952 ± 0.002 and insensitive to charge carrier type, concentration and mobility. A recent study by Panich et al [39] attributed the EPR signal in graphenes as originating either from the π-electronic edge-localized spins interacting with molecular oxygen, or to some stable defects in graphene that are insensitive to the oxygen environment. In our present case, the obtained g factor value is more relevant to stable carbon radicals produced by defects in p-C/TiO 2 .…”

Section: Electron Paramagnetic Resonance Spectroscopymentioning

confidence: 99%

Pyrolytic Formation of TiO2/Carbon Nanocomposite from Kraft Lignin: Characterization and Photoactivities

et al. 2020

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This article reports on the formation of pyrolytic carbon/TiO 2 nanocomposite (p-C/TiO 2 ) by pyrolysis of a mixture of the P25 TiO 2 and kraft lignin at 600 • C. The result was characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, UV-visible spectroscopy, electron paramagnetic resonance spectrometry (EPR), thermogravimetry (TGA) and SEM microscopy. Its photocatalytic activity was ascertained using three classes of chemical probes, namely (i) degradation of methylene blue (MB) and rhodamine-B (RhB) dyes in UV light-irradiated aqueous suspensions, (ii) depletion of phenol and (iii) degradation of antibiotics. The p-C/TiO 2 nanocomposite is a strong phisisorbent of both MB and RhB nearly twofold with respect to neat TiO 2 . Although it is nearly twofold more photoactive toward the degradation of MB (0.091 min −1 versus 0.047 min −1 ), it is not with regard to RhB degradation (0.064 min −1 versus 0.060 min −1 ). For the degradation of phenol in aqueous media (pH 3), pristine TiO 2 was far more effective than p-C/TiO 2 for oxygenated suspensions (17.6 × 10 −3 mM min −1 versus 4.3 × 10 −3 mM min −1 ). Under an argon atmosphere, the kinetics were otherwise identical. The activity of the material was tested also for a real application in the degradation of a fluoroquinolone antibiotic such as enrofloxacin (ENR) in tap water. It is evident that the photoactivity of a semiconductor photocatalyst is not a constant, but it does depend on the nature of the substrate used and on the experimental conditions. It is also argued that the use of dyes to assess photocatalytic activities when suspensions are subjected to visible light irradiation is to be discouraged as the dyes act as electron transfer photosensitizers and or can undergo photodegradation from their excited states.

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Structure and Magnetic Properties of Pristine and Fe-Doped Micro- and Nanographenes

Cited by 30 publications

References 21 publications

Unraveling Origins of EPR Spectrum in Graphene Oxide Quantum Dots

Unraveling Origins of EPR Spectrum in Graphene Oxide Quantum Dots

Magnetic resonance studies of copper (II) sorbitol complex, in solution, reveal a supramolecular structure compatible to the crystal structure

Pyrolytic Formation of TiO2/Carbon Nanocomposite from Kraft Lignin: Characterization and Photoactivities

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