Identification of a Slowly Relaxing Paramagnetic Center in Graphene Oxide

Augustyniak, Maria; Fedaruk, R.; Strzelczyk, Roman; Majchrzycki, Łukasz

doi:10.1007/s00723-018-1058-2

Cited by 17 publications

(20 citation statements)

References 34 publications

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“…Signal belongs to oxygen species located outside the graphene ring. 62 − 64 After reduction, much shorter relaxation times were observed. Probably, the radical with a longer relaxation time is also separated from the carbon ring and located on an oxygen group.…”

Section: Results and Discussionmentioning

confidence: 99%

Electron Spin Relaxation Studies of Polydopamine Radicals

2021

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We present a thoroughgoing electron paramagnetic resonance investigation of polydopamine (PDA) radicals using multiple electron paramagnetic resonance techniques at the W-band (94 GHz), electron nuclear double resonance at the Q-band (34 GHz), spin relaxation, and continuous wave measurements at the X-band (9 GHz). The analysis proves the existence of two distinct paramagnetic species in the PDA structure. One of the two radical species is characterized by a long spin–lattice T 1 relaxation time equal to 46.9 ms at 5 K and is assigned to the radical center on oxygen. The obtained data revealed that the paramagnetic species exhibit different electron spin relaxation behaviors due to different couplings to local phonons, which confirm spatial distancing between two radical types. Our results shed new light on the radical structure of PDA, which is of great importance in the application of PDA in materials science and biomedicine and allows us to better understand the properties of these materials and predict their future applications.

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Section: Results and Discussionmentioning

confidence: 99%

Electron Spin Relaxation Studies of Polydopamine Radicals

2021

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“…The results obtained in this work show that GQDs and N-GQDs provide EPR spectra that are superposition of contributions attributed to different paramagnetic centers, with different intensities and characteristics. Likely, due the presence of Mn(II), an effective relaxant, some signals are unobservable, because broadened out by the interaction with the metal ion [36]. Those observed are due to unpaired electrons non-interacting with Mn(II) ions.…”

Section: Analysis Of Cw and Pulse Epr Spectramentioning

confidence: 99%

“…While inhomogeneous contributions can be revealed by pulse EPR, the isolation of the signals attributed to homogeneous contributions is more difficult to achieve. The cw-EPR spectra of both samples were simulated by a single Lorentzian line, but in parent materials (GO) a Lorentzian-like lineshape was fitted as sum of Gaussians [36]. The response to saturation is a way to determine if the line is homogeneously, or inhomogeneously broadened, but we anticipate that the presence of the two generates a complex saturation profile.…”

Section: Analysis Of Cw and Pulse Epr Spectramentioning

confidence: 99%

“…Spin-echo pulse techniques, instead, allow the cancelation of these fast-relaxing contributions, whose spin-echo intensities decay to almost zero within the instrumental dead time. At the same time, spin-echo pulse techniques enable the separation and the identification of the species with slow relaxing spin; previously, the method has been used to identify slow-relaxing species in GO and reduced GO (RGO) [36,48,49]. Beside the HD experiments to measure the phase memory time, ED-EPR spectra can reveal the spectral components; they are characterized by inhomogeneously broadened components (Gaussian lineshape) [50,51], and hyperfine spectroscopies (mostly ESEEM and ENDOR) can be used to extract hyperfine interactions.…”

Section: Analysis Of Cw and Pulse Epr Spectramentioning

confidence: 99%

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N-Doped Graphene Oxide Nanoparticles Studied by EPR

et al. 2020

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Graphene-derived materials attract a great deal of attention because of the peculiar properties that make them suitable for a wide range of applications. Among such materials, nano-sized systems show very interesting behaviour and high reactivity. Often such materials have unpaired electrons that make them suitable for electron paramagnetic resonance (EPR) spectroscopy. In this work we study by continuous wave and pulse EPR spectroscopy undoped and nitrogen-doped graphene quantum dots (GQD) with a size of about 2 nm. The analysis of the spectra allows identifying different types of paramagnetic centers related to electrons localized on large graphenic flakes and molecular-like radicals. By hyperfine spectroscopies on nitrogen-doped samples, we determine the hyperfine coupling constant of paramagnetic centers (limited-size π-delocalized unpaired electrons) with dopant nitrogen atoms. The comparison of the experimental data with models obtained by density functional theory (DFT) calculations supports the interpretation of doping as due to the insertion of nitrogen atoms in the graphene lattice. The dimension of the delocalized regions in the flakes observed by pulse EPR is of about 20–25 carbon atoms; the nitrogen dopant can be classified as pyridinic or graphitic.

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“…Because of oxygen rich moieties it is a promising material for sensing in biology and medicine: high-contrast bio-imaging and bio-sensing applications [3,4], e.g., biosensors (glucose, mechanical stress, magnetic field) [3,4], anticancer therapies [5,6], as well as for flexible electronic applications, e.g., supercapacitors [7], FET transistors [8,9], electrical wires [10], or as active elements in mechanical energy harvesters [11]. Well reduced fibers with flake ordered composition are reaching superior physical properties with electrical conductivity of σ = 10 6 S•m −1 , thermal conductivity of 1557 W•m −1 •K −1 , tensile strength of 1.9 GPa, and a Young's modulus of 309 GPa [12]. A stronger connection between flakes changes the flake arrangement and alters the above-mentioned properties in comparison to previously studied graphene oxide structures formed by hydrothermal methods [2,13].…”

Section: Introductionmentioning

confidence: 99%

Tuning Properties of Partially Reduced Graphene Oxide Fibers upon Calcium Doping

et al. 2020

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The arrangement of two-dimensional graphene oxide sheets has been shown to influence physico-chemical properties of the final bulk structures. In particular, various graphene oxide microfibers remain of high interest in electronic applications due to their wire-like thin shapes and the ease of hydrothermal fabrication. In this research, we induced the internal ordering of graphene oxide flakes during typical hydrothermal fabrication via doping with Calcium ions (~6 wt.%) from the capillaries. The Ca2+ ions allowed for better graphene oxide flake connections formation during the hydrogelation and further modified the magnetic and electric properties of structures compared to previously studied aerogels. Moreover, we observed the unique pseudo-porous fiber structure and flakes connections perpendicular to the long fiber axis. Pulsed electron paramagnetic resonance (EPR) and conductivity measurements confirmed the denser flake ordering compared to previously studied aerogels. These studies ultimately suggest that doping graphene oxide with Ca2+ (or other) ions during hydrothermal methods could be used to better control the internal architecture and thus tune the properties of the formed structures.

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Identification of a Slowly Relaxing Paramagnetic Center in Graphene Oxide

Cited by 17 publications

References 34 publications

Electron Spin Relaxation Studies of Polydopamine Radicals

Electron Spin Relaxation Studies of Polydopamine Radicals

N-Doped Graphene Oxide Nanoparticles Studied by EPR

Tuning Properties of Partially Reduced Graphene Oxide Fibers upon Calcium Doping

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