Localization of conduction electrons in hydrothermally reduced graphene oxide: electron paramagnetic resonance studies

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

doi:10.1016/j.carbon.2020.07.023

Cited by 26 publications

(27 citation statements)

References 68 publications

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“…33 Recently, an unusually strong temperature dependence of the intensity of the narrow EPR line in prGO was observed and explained by Anderson localization of conduction electrons in the strongly defected structure of graphene flakes. 34 This type of localization in rGO was earlier deduced from impedance measurements 15 in addition to the expected and more frequently observed Mott localization on graphene flakes. 9,26,35−37 The pulsed EPR techniques are useful for studying the isolated PCs in graphene-related materials.…”

Section: ■ Introductionsupporting

confidence: 55%

“…The width of the broader Lorentzian line is larger than that obtained earlier from the deconvolution of the CW spectrum into two Lorentzian lines. 34 The Gaussian CW line is observable only at low temperatures and becomes invisible at 50 K. The best fit of the CW spectrum at 50 K is obtained with three Lorentzian lines (Figure 3b). We suppose that the third Lorentzian line appears due to RKKY interactions between conduction electrons and the PCs.…”

Section: ■ Results and Discussionmentioning

confidence: 87%

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Electron Spin Echo Studies of Hydrothermally Reduced Graphene Oxide

et al. 2021

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Ecofriendly hydrothermal reduction of graphene oxide is widely used for producing hydrogels and aerogels, but it yields partly reduced graphene oxide (prGO) containing oxygen groups and some number of paramagnetic centers (PCs). In order to identify structural changes introduced by the reduction process, these PCs are studied by electron spin echo spectroscopy in the temperature range of 5–160 K. Two types of PCs with different spin–lattice (T 1) and phase memory (T m) relaxation times observed below 20 K result from a nonuniform distribution of magnetic defects. Above 20 K, only the PCs with the shorter T 1 and T m persist. Temperature dependences of T 1 and the distribution of T 1 for each type of the PCs reveal lattice distortions around the PCs and structural disorder in prGO. The unusually strong temperature dependence of the spin echo intensity is explained by the localization of conduction electrons. The localization is destroyed at high temperature, and exchange interactions decrease the number of the observed PCs. Every such PC is created by the sp 3 defect induced by hydrogen covalently bonded to graphene. The obtained results indicate that the hydrothermal reduction is accompanied by partial hydrogenation of graphene. The presence of such hydrogen atoms is confirmed by infrared spectroscopy.

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Section: ■ Introductionsupporting

confidence: 55%

Section: ■ Results and Discussionmentioning

confidence: 87%

Electron Spin Echo Studies of Hydrothermally Reduced Graphene Oxide

et al. 2021

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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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“…Based on the temperature dependence of EPR response in oxidized graphene, the broad line was earlier associated with the spin interaction between delocalized (mobile) electrons and localized π-electrons trapped in the extended aromatic structure [ 48 , 49 , 50 , 51 , 52 ]. At the same time, the wide and narrow lines were respectively assigned to localized and mobile electrons [ 53 ]. The intensities of both these lines increased with the oxidation time reflecting the increase in the number of paramagnetic centers, which correlates with the oxygen content and catalyst performance (see below).…”

Section: Resultsmentioning

confidence: 99%

Conversion of Secondary C3-C4 Aliphatic Alcohols on Carbon Nanotubes Consolidated by Spark Plasma Sintering

et al. 2021

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We analyze how the changes in the dimension of carbon nanomaterial (CNM) affect their catalytic conversion of secondary aliphatic alcohols. Carbon nanotubes (CNTs) consolidated by spark plasma sintering (SPS) were inactive in the conversion of secondary C3-C4 aliphatic alcohols because of the «healing» of defects in carbon structure during SPS. Gas-phase treatment of consolidated CNTs with HNO3 vapors led to their surface oxidation without destruction of the bulk structure of pellets. The oxygen content in consolidated CNTs determined by X-ray photoelectron spectroscopy increased from 11.3 to 14.9 at. % with increasing the oxidation time from 3 to 6 h. Despite the decrease in the specific surface area, the oxidized samples showed enhanced catalytic activity in alcohol conversion because of the increased number of oxygen radicals with unpaired electrons, which was established by electron paramagnetic resonance spectroscopy. We conclude that the structure of CNM determines the content and/or ratio of sp2 and sp3-hybridized carbon atoms in the material. The experimental and literature data demonstrated that sp3-hybridized carbon atoms on the surface are probably the preferable site for catalytic conversion of alcohols.

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Localization of conduction electrons in hydrothermally reduced graphene oxide: electron paramagnetic resonance studies

Cited by 26 publications

References 68 publications

Electron Spin Echo Studies of Hydrothermally Reduced Graphene Oxide

Electron Spin Echo Studies of Hydrothermally Reduced Graphene Oxide

Electron Spin Relaxation Studies of Polydopamine Radicals

Conversion of Secondary C3-C4 Aliphatic Alcohols on Carbon Nanotubes Consolidated by Spark Plasma Sintering

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