Next Article in Journal
Nanocomposite Photoanisotropic Materials for Applications in Polarization Holography and Photonics
Previous Article in Journal
Synthesis of Composite Titanate Photocatalyst via Molten Salt Processing and Its Enhanced Photocatalytic Properties
 
 
Search for Articles:
Title / Keyword
Author / Affiliation / Email
Journal
Article Type
 
 
Advanced Search
 
Section
Special Issue
Volume
Issue
Number
Page
 
Journals
Nanomaterials
Volume 13
Issue 22
10.3390/nano13222945
nanomaterials-logo
Submit to this Journal Review for this Journal Propose a Special Issue
► Article Menu

Article Menu

share Share announcement Help format_quote Cite question_answer Discuss in SciProfiles thumb_up
...
Endorse textsms
...
Comment
first_page
settings
Order Article Reprints
Font Type:
Arial Georgia Verdana
Font Size:
Aa Aa Aa
Line Spacing:
Column Width:
Background:
Article

Composition and Electronic Structure of La2O3/CNFs@C Core-Shell Nanoparticles with Variable Oxygen Content

by
Evgeniya V. Suslova
1,*,
Alexander N. Ulyanov
1,
Alexey P. Kozlov
1,
Denis A. Shashurin
2,
Serguei V. Savilov
1 and
Georgy A. Chelkov
3
1
Department of Chemistry, Lomonosov Moscow State University, 119991 Moscow, Russia
2
Faculty of Medicine, Lomonosov Moscow State University, 119991 Moscow, Russia
3
Joint Institute for Nuclear Research, 141980 Dubna, Russia
*
Author to whom correspondence should be addressed.
Nanomaterials 2023, 13(22), 2945; https://doi.org/10.3390/nano13222945
Submission received: 19 October 2023 / Revised: 8 November 2023 / Accepted: 10 November 2023 / Published: 14 November 2023
(This article belongs to the Topic Functional Surface Modifications of Nanostructures)
Browse Figures
Versions Notes

Abstract

:
La2O3 nanoparticles stabilized on carbon nanoflake (CNF) matrix were synthesized and graphitized to produce core-shell structures La2O3/CNFs@C. Further oxidation of these structures by nitric acid vapors for 1, 3 or 6 h was performed, and surface-oxidized particles La2O3/CNFs@C_x (x = 1, 3, 6) were produced. Bulk and surface compositions of La2O3/CNFs@C and La2O3/CNFs@C_x were investigated by thermogravimetric analysis and X-ray photoelectron spectroscopy. With increasing the duration of oxidation, the oxygen and La2O3 content in the La2O3/CNFs@C_x samples increased. The electronic structures of samples were assessed by electron paramagnetic resonance. Two paramagnetic centers were associated with unpaired localized and mobile electrons and were registered in all samples. The correlation between bulk and surface compositions of the samples and their electronic structures was investigated for the first time. The impact of the ratio between sp2- and sp3-hybridized C atoms, the number and nature of oxygen-containing groups on the surface and the presence and proportion of coordinated La atoms on the EPR spectra was demonstrated.

Graphical Abstract

1. Introduction

Different lanthanum and lanthanide-containing compounds deposited on the carbon nanomaterials (CNMs) are currently considered promising materials for contrast agents for magnetic resonance imaging (MRI) [1,2] and computed tomography [3,4,5]. Oxide La2O3, in combination with reduced graphene oxide (rGO), is an effective catalyst for the synthesis of dimethyl carbonate [6] and bis(indolyl)methanes [7]. La2O3/rGO and La2O3 supported on carbon nanotubes (CNTs) can be used for energy storage devices, including asymmetric supercapacitors [8,9]. La2O3 encapsulated into the CNT cavity is a felicitous composite material for Pt-free counter electrodes of solar cells [10].
CNMs are unique supports because their surface properties depend on the allotropic modification of carbon, particle size, surface defectiveness, functional groups, etc. The CNM surface can be easily modified by hydroxyl and carboxyl groups, resulting in further coordination of Ln3+ (or other metal ions) with the formation of stable chelate complexes [11,12]. Nanodiamonds (NDs), carbon nanoflakes (CNFs) or graphene nanoflakes (GNFs), CNTs and nitrogen-doped carbon dots are described as supports of Ln3+ as well [1,3,5,13,14]. An interesting example of Ln/CNM composites is the endohedral fullerenes with a Ln@Cn structure that purports the encapsulation of Ln3+ ions or Ln metal atoms inside the fullerene sphere [15,16,17]. Ln3+ ions are coordinated with oxygen atoms to result in the C-O-Ln bond formation. The Mn+ ions are typically coordinated by two surface functional groups that are coordinately saturated with solvent molecules and anions that were originally present in the metal precursor salt [12,14]. It was, for example, shown using HRTEM in HAADF mode and EPS spectra that Tm3+ ions uniformly distribute on the oxidized CNT surface and mainly at the edges after thermal defunctionalization of CNTs [13].
Electron paramagnetic resonance (EPR) is a suitable method for the study of compounds and materials with free electrons, radicals, radical ions, particles in the triplet state, as well as paramagnetic ions of transition and rare earth metals. To summarize, both CNMs and lanthanide derivatives are suitable objects for EPR studies [17,18,19,20]. The CNTs [21,22], nitrogen-doped CNTs [23], boron-doped CNTs [24], CNFs [25,26,27], consolidate of CNTs and CNFs [28,29,30,31], GO [32,33,34], graphene [35], GO aerogels [36,37], GO quantum dots [38], carbon nanofibers [39], glass-like carbon [40], detonation diamonds and NDs [12], graphite-polystyrene composite [41], carbon films [42], natural coals [43], oxidized coals [44], carbon blacks [45], different carbon composites [46] and others [18] were investigated using the EPR. EPR signals contain information about possible paramagnetic centers of CNMs, their nature and the possible influence of oxygen-containing groups [28,47,48,49]. The temperature dependencies of the intensity of the EPR spectra are used to identify the source of the observed magnetism [34]. For example, a specific π-electronic zone, stabilized by saddle-shaped edges of nanographene, was at first predicted theoretically and then was demonstrated by the EPR method [50,51]. The EPR can be used to study the mechanism of reactions on the surface of CNMs. For example, it has been proven that F- ion reacted region-selectively with the C70 fullerene [52].
The most often rare earth elements and their compounds studied by EPR are gadolinium derivatives [20,53,54] because only ions Gd3+ and Eu2+ EPR spectra at room temperature can be observed [19]. For some Ln derivatives, for example, for Ln(OH)3 (Ln = La, Pr, Nd), EPR spectra can provide information about oxygen vacancies and the coordination environment of Ln3+ [55,56,57].
Panich, Osipov and other authors described the EPR spectra of different complexes Mn+/CNMs where CNMs are ND or detonation diamond with metal ions Cu2+, Co2+, Gd3+, Fe2+, Fe3+ and Mn2+ [11,12,58,59,60,61]. It has been shown that the EPR allows distinguishing signals from two types of spins: the carbon spins localized inside the ND particles and the spins of Mn+ ions on the surface.
In the present work, we observe and discuss the properties of La2O3/CNFs@C nanosized composite assessed by EPR and XPS. The 2–3 nm La2O3 particles deposited on the CNF surface and encapsulated with the shells from 2–3 graphene layers were studied. This material is used as a contrast agent for computed tomography [3,5]. The CNF matrix is necessary for 2–3 nm of La2O3 particles’ stabilization, preventing their agglomeration and enlargement. Graphene shells allow the functionalization of the particle surface without affecting the La2O3 core, modifying their chemical and pharmacological properties without impacting their roentgenological characteristics. Specifically, oxidative treatment of the surface leads to its modification with carboxyl and hydroxyl groups. These groups can be subsequently used to decorate the surface with various functional groups or small molecules with high affinity to specific biopolymers, forming contrasts with high selectivity to the structures of interest. Such synthetic work requires a comprehensive understanding of the composite structure and properties as well as their correlation with various factors such as duration or degree of oxidation. So, we studied the composites that underwent the post-functionalization of graphene shells with carboxyl and hydroxyl groups by HNO3 vapors during 1.0, 3.0 and 6.0 h. The different durations of oxidation treatment of La2O3/CNFs@C resulted in the different degrees of graphene shell degradation and oxygen content and change in its electronic structure. The oxidized materials were investigated by EPR to establish how the surface and volume content of La2O3, as well as the number and nature of oxygen-containing groups, influence the electronic structure of particles. The changes in composition and structure, as well as the increase in oxygen-containing groups, had the most dramatic effect on the EPR spectra. The intensity, width of spectra and number of unpaired electrons were found to be different.

2. Materials and Methods

2.1. Synthesis

Carbon nanoflakes were synthesized by pyrolysis of hexane (99.8%, Reachim) at 900 °C in the presence of MgO template [62]. MgO was dissolved in boiling 34% HCl (99.9%, Reachim) solution. Obtained CNFs were washed with dt. water and dried at 110 °C. The CNF particles replicated the template’s form and consisted of 7–15 graphene layers (Figure 1). The subsequent surface oxidation of CNFs was carried out with boiling 67–69% nitric acid (Component-Reaktiv) solution for 1 h for the most uniform subsequent distribution of La3+ ions [3,13].
The synthesis, properties and characteristics of 2–3 nm sized La2O3 particles stabilized with CNF matrix (La2O3/CNFs) have been described in detail in our earlier works [3,5]. The La2O3/CNF composite was prepared by impregnation of 0.10 g oxidized CNFs with 0.146 g of La(NO3)3·6H2O (99%, China Northern Rare Earth Group High-Tech Co., Ltd., Baotou, China) in the 100 mL ethanolic (99.99%, Merck, Darmstadt, Germany) solution with further solvent evaporation and decomposition of nitrate at 400 °C under nitrogen (99.999%, Logika Ltd., Moscow, Russia) flow. Core-shell particles La2O3/CNFs@C have been prepared by encapsulation of La2O3/CNFs with the graphene shells via methane (99.99% Moscow Gas Processing Plant, Moscow, Russia) decomposition at 400 °C [63]. Gas-phase oxidation of La2O3/CNFs@C was described elsewhere [64]. The La2O3/CNFs@C sample was placed in an open box in an atmosphere of boiling nitric acid with a temperature of 83 °C and kept for 1.0, 3.0 or 6.0 h. The vapor phase was a complex mixture of HNO3, O2, H2O and various nitrogen oxides [65]. Then, the oxidized samples La2O3/CNFs@C_x (where x is the duration of oxidation equal to 1, 3 or 6) were washed with water to delete nitric acid and partially dissolved La-containing fraction. The scheme illustrating and explaining the sequence of synthesis procedures is shown in Figure 2.

2.2. Physico-Chemical Analysis

Thermogravimetric (TG) analysis was performed on a Netzsch STA 449 PC LUXX instrument (Netzsch, Selb, Germany) with a sample heating rate of 5 °C·min−1 and a temperature range of 25–1000 °C in an air atmosphere. The error of the unburned impurity definition was less than 2%.
Transmission electron microscopy (TEM) images were recorded on a JEOL 2100F/Cs (Jeol, Tokyo, Japan) microscope operated at 200 kV and equipped with a UHR pole tip, a spherical aberration corrector (CEOS, Heidelberg, Germany) and an EEL spectrometer (Gatan, Germany).
The X-ray photoelectron spectra (XPS) were recorded on an Axis Ultra DLD spectrometer (Kratos Analytical, Milton Keynes, UK) using monochromatic AlKα radiation (1486.7 eV). The pass energies of the analyzer were 160 eV for survey spectra and 40 eV for high-resolution scans. The error in element definition was about 5%.
Electron paramagnetic resonance (EPR) measurements were performed with a BRUKER EMX 6/1 spectrometer at 9.8–9.9 GHz (X-band) at room temperature. The spectra of studied and standard/reference samples were recorded at the microwave power of 0.635 mW (well below the saturation power of ≈2.0 mW), modulation amplitude of 1.0 G, modulation frequency of 100.00 kHz, time constant of 40.960 ms, sweep time of 335.54 s, number of scans of 1 and receiver gain equal to 1.78 × 103. The EPR measurements of the studied as well as of standard samples were performed in the ampule with the outer and inner diameters of 3.9 and 2.8 mm, respectively. TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxyl) in toluene solution was used as a reference sample with the number of paramagnetic centers Nst = 2.0792 × 1016 spins. The height of the studied and reference samples in the ampule was about 5.5 mm. The N-value for the studied samples was deduced using the expression N = (Qst/Q)·(DI·Nst)/DIst, where Qst and Q are the quality factors of the resonator with the reference and studied samples, respectively, and DI and DIst are double integrated intensities of the resonance spectrum limes of the studied and reference samples, respectively. The measurements were performed using samples with almost equal mass (about 8 mg). The DI values were deduced by the integration of the initial raw experimental spectra with the consequent normalization of the sample mass. The Q/Qst ratio was ≈0.9. The background signal was subtracted using the Bruker WinEPR System Version 2.11b software.

3. Results and Discussion

The morphology and particle size were investigated by TEM and reported earlier [63,64]. According to TEM images, the La2O3 particles with 2–3 nm size are uniformly distributed on the CNF surface. Graphene shells contain 2–3 layers forming a La2O3/CNFs@C composite with a core-shell structure. After gas-phase oxidation, the carbon particles degraded with partial loss of initial structure (Figure 2) [63,64].
The La2O3 bulk content in the composition of samples La2O3/CNFs@C and La2O3/CNFs@C_x (x = 1, 3, 6) was confirmed by thermogravimetric (TG) analysis through the determination of the unburned impurities (Figure 3). According to TG data, the La2O3 content in the La2O3/CNFs@C_x was 21.08, 23.48 and 27.39 wt. % for x = 1, 2 and 3, respectively. The La2O3 content in the La2O3/CNFs@C was 36.24 wt. %. This indicates that the increase in the duration of the oxidation was accompanied by a partial loss of the carbon component in the samples.
The content of La2O3 in the samples is different for the samples with different x (Figure 4a) according to both TG (indicating the bulk composition of the sample) and XPS (reflecting the composition of approximately 10 upper layers of the surface). The extent and direction of the differences vary between TG and XPS, demonstrating different impacts of extension of the oxidation to the bulk and the surface of the samples. According to XPS data, the oxygen and carbon content differ as well. The amount of carbon decreased with the increase in oxidation duration, and oxygen understandably increased (Figure 4b). According to the C1s XPS spectra, the oxidized samples La2O3/CNFs@C_x have sp2- and sp3-hybridized carbon atoms and oxygen-bonded carbon species (Figure 5a) [64]. The O1s XPS spectra show that oxygen can present as O2− in the La-O fragments, lanthanum-bonded hydroxyl groups (OH−), and different oxygen species, C–O, C=O, etc., bonded to carbon atoms (Figure 5b) [64]. The ratio between different carbon and oxygen forms changed with a change in gas-phase oxidation duration (Figure 4c,d).
Figure 6 shows the EPR spectra of La2O3/CNFs@C and La2O3/CNFs@C_x compositions. Initial raw spectra are presented in Figure 6a,c,e,g. Absorption spectra, obtained by the integration of the raw ones, are shown in Figure 6b,d,f,h. The asymmetry of the raw spectra is caused by the fine structure of the absorption ones. EPR spectra of all samples differ in width, positions (g-factor) and number of spins (N). The absorption spectra were simulated by Gaussian, Lorentzian and Voigt functions. The best fit was obtained with the Lorentzian. All observed spectra are well fitted with two Lorentzian lines with different widths corresponding to gl- and gh-factors and located at low- and high-applied fields, respectively (Figure 6b,d,f,h). Therefore, we consider two types of paramagnetic centers attributed to these lines [29,49].
EPR spectra of La3+ are typically silent because of the absence of unpaired electrons in its electron structure, which corresponds to [Xe]6s05d0. Only La2+ ions and zero valence La atoms were characterized by EPR spectra at low temperatures [17,66]. In the EPR spectra of La(OH)3, the g-factor equaled 2.02788 and corresponded to oxygen vacancies in the La(OH)3 structure [55]. In the present study, both the gl and gh values are 2.0022–2.0047 (Figure 7a). There are no correlations observed between gl and gh and La3+ bulk and/or surface concentrations according to TG and XPS data in the La2O3/CNFs@C and La2O3/CNFs@C_x (x = 1, 3, 6), respectively (Figure S1). Due to this, we concluded that the EPR spectra were predominantly defined by the carbon matrix.
Two EPR lines (named broad and narrow as per standard terminology), associated with two g-factors and reflecting the presence of two different types of paramagnetic centers, were previously reported for different CNMs: GO [32,51], ND [67], CNFs, CNTs [25,29,30,31,47,48,50], etc. A broad line may be related to the defect states strongly coupled with itinerant spins and/or conduction electrons within the sp2-clusters [25,27,32,48,51,68]. The narrow line was attributed to the localized electrons provoked by terminal sp3-hybridized carbon atoms and various vacancies in the graphene layers [25,27,32,48,51,68,69]. These are the terminal energetically unsaturated carbon atoms combined with oxygen atoms and molecules, forming functional groups or saturated due to chemisorption. Only one line (g-factor is 2.0028) is present in the sp3-hybridized carbon atoms in the structure of the diamond. Paramagnetism of ~5 nm diamond is associated with intrinsic paramagnetic defects of the diamond crystal lattice with an unpaired electron located within the near-surface belt at the distance of 0.3–0.9 nm from the surface [70]. In the present study, the values of the g-factors are 2.0022–2.0047 (Figure 7a). The value of the gl-factor of oxidized CNFs is 2.0010 [25].
According to XPS data, the content of sp3-hybridized carbon atoms and carbon-oxygen bonds increased with the increase of oxidation duration (Figure 4c). We have also previously shown that an increase in the oxidation time of CNTs and CNFs, as well as consolidated and oxidized CNTs and CNFs, leads to an increase in oxygen groups and surface defectiveness according to Raman spectra [71] and, at the same time, the number of paramagnetic centers [25,28,29,31,48,49].
The width of EPR lines is highly sensitive to oxygen in the CNM compositions. Broadening of ∆Hh lines has a satisfactory correlation with the content of surface oxygen in the samples La2O3/CNFs@C → La2O3/CNFs@C_1 → La2O3/CNFs@C_3 (Figure 7b) that is in line with the data [47,68]. Based on this, we concluded that the line at the high applied field corresponds to the unpaired electrons on the terminal sp3-hybridized carbon atoms. This was additionally confirmed by a decrease in the number of unpaired Nh electrons (Figure 7c), caused by the increase of the C=O terminal groups that lead to the disappearance of the edge electrons and do not contribute to the EPR signal [47]. At the same time, the ∆Hl line width did not change in the row La2O3/CNFs@C_1 → La2O3/CNFs@C_3 → La2O3/CNFs@C_6 (Figure 7b), while the content of unpaired electrons Nl increased (Figure 7c). So, we concluded that the line at the low applied field corresponds to itinerant spins within the sp2-clusters.
The correlation between the ratio of sp2 and sp3-hybridized carbon atoms for samples according to XPS and EPR data is shown in Figure 8. The sp2/sp3 ratio (XPS) and Nh/Nl ratio (EPR) associated with sp2/sp3 decreased with an increase in the oxidation time according to both methods. The sp2/sp3 ratio for non-oxidized sample La2O3/CNFs@C could not be assessed by XPS due to the massive prevalence of sp2-hybridized carbon atoms. This ratio became assessable only after the oxidation of the sample. The Nh/Nl ratio could be assessed by EPR for all samples. This difference can be attributed to the higher impact of the oxidation towards the surface assessed by XPS and the preservation of the bulk sample assessed by EPR.
Another important factor affecting the EPR spectra of samples is the presence of La2O3 particles that are coordinated by the surface oxygen atoms and can also affect the electronic interaction in the system, similar to how high-polar carbon bonded with Fe2+ ions has its own manifestation in the ERP [72]. La3+ ions, coordinated by oxygen atoms with C-O-La bridge formation, are distributed over the CNF surface, mainly in the areas of localization of the oxygen-containing groups [13]. C-O-La fragments impact the surface electronic structure of the carbon matrix. To estimate the contribution of La3+, we normalized the number of spins only to the carbon-oxygen component (Figure 7d). The sum Nl + Nh increased (Figure 7c) with an increase of specific oxygen content in the composition of La2O3/CNFs@C, La2O3/CNFs@C_1 and La2O3/CNFs@C_3 samples. However, the recalculation of the number of unpaired electrons only on the carbon-oxygen component led to the decrease of Nl + Nh (Figure 7d). We believe that this trend was driven by a change in the structure of the graphene shells and CNFs caused by oxidation, i.e., significant degradation of graphene sheets due to etching with nitric acid [64]. Specifically, the oxidation during 6 h (La2O3/CNFs@C_6 sample) led to the strong damage of the carbon structure and change of the sample composition, including decrease of the carbon content (Figure 4b).
The effects of the size of the CNMs on the EPR signal were described in numerous studies [51,73,74]. It was shown that the decrease of ND size from 100 down to 18 nm led to the disappearance of the characteristic hyperfine splitting in the EPR spectrum and the appearance of the two lines [73]. The increase of the edged carbon atoms content resulted in the increase of unpaired electrons because of the fragmentation of rGO [51]. The CNF sizes in the samples were smaller than 18 nm, which allowed interlayer interaction, resulting in a high paramagnetic response. This is consistent with the statement that the interlayer interaction changes the nature of the π-wave function from 2D (single-layer) to 3D (volumetric) in multilayer graphene, which is associated with electron mobility and unique high sensitivity of the band structure and materials [75,76].

4. Conclusions

The electronic structure of La2O3/CNFs@C was studied. The EPR spectra of core-shell structured La2O3/CNFs@C and gas-phase oxidized La2O3/CNFs@C_x (where x = 1, 3 or 6 is the duration of oxidation) composites developed as potential contrast agents for computed tomography. La2O3/CNFs@C_x composition changed under gas-phase treatment with HNO3 vapors. With an increase in oxidation duration, the surface and bulk content of La2O3 in the La2O3/CNFs@C_x increased because of carbon shell oxidation.
The EPR spectra of all samples differed in intensity, width, positions (g-factor) and number of spins (N). Two gl- and gh-factors located at low- and high-applied fields, respectively, were determined for each sample. This indicates two types of paramagnetic centers. The spin density is associated with the lines and correlated with the spin number of localized and mobile electrons. The content of oxygen in the samples and, consequently, the content of localized unpaired electrons Nl associated with terminal sp3-hybridized carbon atoms increased with an increase in the oxidation duration. In parallel, the content of unpaired electrons Nh decreased. We conclude that the line at the low-applied field corresponded to itinerant spins within the sp2-clusters. It was also shown that the number of unpaired electrons in the La2O3/CNFs@C and La2O3/CNFs@C_x structure was influenced by many factors, including (1) the ratio between sp2- and sp3-hybridized C atoms, (2) the number and nature of oxygen-containing groups on the surface, and (3) the presence and proportion of coordinated La atoms because of differences of lanthanum content between TG and XPS data.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/nano13222945/s1, Figure S1: Correlations between gl, gh, surface (TG) and bulk (XPS) La content.

Author Contributions

Conceptualization, E.V.S. and D.A.S.; Methodology, A.N.U., A.P.K. and D.A.S.; Formal Analysis, D.A.S., E.V.S. and A.N.U.; Investigation, D.A.S., A.N.U. and A.P.K., Writing—Original Draft Preparation, E.V.S., Writing—Review and Editing, D.A.S., A.N.U. and S.V.S.; Visualization, E.V.S.; Supervision, G.A.C.; Project Administration, S.V.S. and G.A.C.; Funding Acquisition, G.A.C. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Russian Science Foundation, grant number 22-15-00072.

Data Availability Statement

Data are contained within the article and Supplementary Materials.

Acknowledgments

Authors are grateful to Konstantin Maslakov, Alexey Shumyantsev and Sergey Maximov for help in XPS, TG and TEM experiments. The authors are grateful for the support from the MSU Equipment Center “Nanochemistry and Nanomaterials” acting under the Lomonosov Moscow State University Program of Development.

Conflicts of Interest

The authors declare no conflict of interest.

References

  1. Manus, L.M.; Mastarone, D.J.; Waters, E.A.; Zhang, X.Q.; Schultz-Sikma, E.A.; MacRenaris, K.W.; Ho, D.; Meade, T.J. Gd(III)-Nanodiamond Conjugates for MRI Contrast Enhancement. Nano Lett. 2010, 10, 484–489. [Google Scholar] [CrossRef] [PubMed]
  2. Bouzas-Ramos, D.; Cigales Canga, J.; Mayo, J.C.; Sainz, R.M.; Ruiz Encinar, J.; Costa-Fernandez, J.M. Carbon Quantum Dots Codoped with Nitrogen and Lanthanides for Multimodal Imaging. Adv. Funct. Mater. 2019, 29, 1903884. [Google Scholar] [CrossRef]
  3. Suslova, E.V.; Kozlov, A.P.; Shashurin, D.A.; Rozhkov, V.A.; Sotenskii, R.V.; Maximov, S.V.; Savilov, S.V.; Medvedev, O.S.; Chelkov, G.A. New Composite Contrast Agents Based on Ln and Graphene Matrix for Multi-Energy Computed Tomography. Nanomaterials 2022, 12, 4110. [Google Scholar] [CrossRef] [PubMed]
  4. Zeng, Y.; Li, H.; Li, Z.; Luo, Q.; Zhu, H.; Gu, Z.; Zhang, H.; Gong, Q.; Luo, K. Engineered Gadolinium-Based Nanomaterials as Cancer Imaging Agents. Appl. Mater. Today 2020, 20, 100686. [Google Scholar] [CrossRef]
  5. Suslova, E.; Shashurin, D.; Kozlov, A.; Maximov, S.; Rozhkov, V.; Sotenskii, R.; Savilov, S.; Medvedev, O.; Chelkov, G. Development of La-Graphene Composite Contrasting Agents for Photon-Counting Computed Tomography. Funct. Mater. Lett. 2022, 15, 2250029. [Google Scholar] [CrossRef]
  6. Kumar, N.; Srivastava, V.C. La2O3 Nanorods-Reduced Graphene Oxide Composite as a Novel Catalyst for Dimethyl Carbonate Production via Transesterification Route. Mater. Today Commun. 2021, 29, 102974. [Google Scholar] [CrossRef]
  7. Mogha, N.K.; Kirti, S.; Masram, D.T. La2O3/Reduced Graphene Oxide Nanocomposite: A Highly Efficient, Reusable Heterogeneous Catalyst for the Synthesis of Biologically Important Bis(Indolyl)Methanes under Solvent Free Conditions. J. Nanosci. Nanotechnol. 2017, 17, 2508–2514. [Google Scholar] [CrossRef]
  8. Karthikeyan, S.; Selvapandiyan, M.; Sankar, A. Electrochemical Performance of Reduced Graphene Oxide (RGO) Decorated Lanthanum Oxide (La2O3) Composite Nanostructure as Asymmetric Supercapacitors. Inorg. Chem. Commun. 2022, 139, 109331. [Google Scholar] [CrossRef]
  9. Li, Y.; Sun, K.; Cheng, P.; Li, J.; Liu, D.; He, D. The Synergy of La2O3 Nanoparticles and Graphene for Advanced Li-S Batteries. ChemistrySelect 2022, 7, e20210432. [Google Scholar] [CrossRef]
  10. Wu, K.; Zhao, J.; Xiong, Y.; Ruan, B.; Wu, M. Synthesis and Performance of La2O3@MWCNT Composite Materials as Pt-Free Counter Electrodes for Dye-Sensitized Solar Cells. Ionics 2018, 24, 4055–4061. [Google Scholar] [CrossRef]
  11. Panich, A.M.; Sergeev, N.A. Towards Determination of Distances Between Nanoparticles and Grafted Paramagnetic Ions by NMR Relaxation. Appl. Magn. Reson. 2018, 49, 195–208. [Google Scholar] [CrossRef] [PubMed]
  12. Osipov, V.Y.; Romanov, N.M.; Suvorkova, I.E.; Osipova, E.V.; Tsuji, T.; Ishiguro, Y.; Takai, K. Magnetic Resonance Tracking of Copper Ion Fixation on the Surface of Carboxylated Nanodiamonds from Viewpoint of Changes in Carbon-Inherited Paramagnetism. Mendeleev Commun. 2022, 32, 132–135. [Google Scholar] [CrossRef]
  13. Savilov, S.V.; Egorov, A.V.; Ivanov, A.S.; Lunin, V.V. Staining of Light Heteroatoms in Modified Carbon Nanomaterials for Direct Surveying by TEM and Related Techniques. Procedia Eng. 2014, 93, 25–33. [Google Scholar] [CrossRef]
  14. Osipov, V.Y.; Aleksenskiy, A.E.; Takai, K.; Vul’, A.Y. Magnetic studies of a detonation nanodiamond with the surface modified by gadolinium ions. Phys. Solid State 2015, 57, 2314–2319. [Google Scholar] [CrossRef]
  15. Chen, Z.; Ma, L.; Liu, Y.; Chen, C. Applications of Functionalized Fullerenes in Tumor Theranostics. Theranostics 2012, 2, 238–250. [Google Scholar] [CrossRef]
  16. Cao, B.; Wakahara, T.; Maeda, Y.; Han, A.; Akasaka, T.; Kato, T.; Kobayashi, K.; Nagase, S. Lanthanum Endohedral Metallofulleropyrrolidines: Synthesis, Isolation, and EPR Characterization. Chem. Eur. J. 2004, 10, 716–720. [Google Scholar] [CrossRef]
  17. Koltover, V.K. Preservation of Endometallofullerene La@C82 in Polycarbonate: EPR, ENDOR, and NMR Studies. J. Mol. Liq. 2005, 120, 151–154. [Google Scholar] [CrossRef]
  18. Tomaszewski, D.; Tadyszak, K. Electron Spin Relaxation in Carbon Materials. Materials 2022, 15, 4964. [Google Scholar] [CrossRef]
  19. McPeak, J.E.; Eaton, S.S.; Eaton, G.R. Electron Paramagnetic Resonance of Lanthanides. Methods Enzymol. 2021, 651, 63–101. [Google Scholar]
  20. Ivanin, S.N.; Buz’ko, V.Y.; Panyushkin, V.T. Research of the Properties of Gadolinium Stearate by EPR Spectroscopy. Russ. J. Coord. Chem. 2021, 47, 219–224. [Google Scholar] [CrossRef]
  21. Dhami, A.K.; Bhat, S.; Sharma, A.; Bhat, S.V. Spin Probe ESR Studies of Dynamics of Single Walled Carbon Nanotubes. Spectrochim. Acta Part A Mol. Biomol. Spectrosc. 2008, 69, 1178–1182. [Google Scholar] [CrossRef]
  22. Shieh, Y.T.; Wang, W.W. Radical Scavenging Efficiencies of Modified and Microwave-Treated Multiwalled Carbon Nanotubes. Carbon 2014, 79, 354–362. [Google Scholar] [CrossRef]
  23. Sun, D.; Shen, B.; Yang, S.; Cheng, X.; Zhong, Q.; Azhar Abbas, S.; Dai, Y.; Liu, Y.; Xu, C.; Qi, C.; et al. Nitrogen-Doped CNTs Enhance Heterogeneous Fenton Reaction for IOH Removal by FeOCl: Role of NCNTs and Mechanism. Sep. Purif. Technol. 2023, 326, 124763. [Google Scholar] [CrossRef]
  24. Mondal, K.C.; Strydom, A.M.; Erasmus, R.M.; Keartland, J.M.; Coville, N.J. Physical Properties of CVD Boron-Doped Multiwalled Carbon Nanotubes. Mater. Chem. Phys. 2008, 111, 386–390. [Google Scholar] [CrossRef]
  25. Ulyanov, A.; Stolbov, D.; Savilov, S. Jellyfish-like Few-Layer Graphene Nanoflakes: High Paramagnetic Response alongside Increased Interlayer Interaction. Z. Für Phys. Chem. 2022, 236, 79–86. [Google Scholar] [CrossRef]
  26. Vozniakovskii, A.A.; Voznyakovskii, A.P.; Kidalov, S.V.; Osipov, V.Y. Structure and Paramagnetic Properties of Graphene Nanoplatelets Prepared from Biopolymers Using Self-Propagating High-Temperature Synthesis. J. Struct. Chem. 2020, 61, 826–834. [Google Scholar] [CrossRef]
  27. Ziatdinov, A.M.; Saenko, N.S.; Skrylnik, P.G. Molecular and Electronic Structures and Magnetic Properties of Multilayer Graphene Nanoclusters and Their Changes under the Influence of Adsorbed Molecules. Russ. Chem. Bull. 2017, 66, 837–848. [Google Scholar] [CrossRef]
  28. Savilov, S.V.; Ulyanov, A.N.; Desyatov, A.V.; Suslova, E.V. Temperature Dependences of Paramagnetic Response in Oxidized Spark Plasma Sintered Carbon Nanotubes: The Way of Understanding the Local Electronic Structure. Solid State Sci. 2022, 132, 106996. [Google Scholar] [CrossRef]
  29. Ulyanov, A.N.; Suslova, E.V.; Maslakov, K.I.; Fionov, A.V.; Kuznetsova, N.N.; Singh, P.K.; Savilov, S.V. Paramagnetic Response of Carbon Nanotubes: Temperature Dependences. Russ. J. Phys. Chem. A 2022, 96, 1185–1189. [Google Scholar] [CrossRef]
  30. Ulyanov, A.N.; Suslova, E.V.; Maslakov, K.I.; Singh, P.K.; Savilov, S.V. Local Electronic Structure of Carbon Nanotubes Consolidated by Spark Plasma Sintering. Funct. Mater. Lett. 2022, 15, 2251040. [Google Scholar] [CrossRef]
  31. Ulyanov, A.N.; Suslova, E.V.; Savilov, S.V. Electronic Structure of Carbon Nanotube Network. Mendeleev Commun. 2023, 33, 127–129. [Google Scholar] [CrossRef]
  32. Diamantopoulou, A.; Glenis, S.; Zolnierkiwicz, G.; Guskos, N.; Likodimos, V. Magnetism in Pristine and Chemically Reduced Graphene Oxide. J. Appl. Phys. 2017, 121, 043906. [Google Scholar] [CrossRef]
  33. Wang, B.; Fielding, A.J.; Dryfe, R.A.W. Electron Paramagnetic Resonance Investigation of the Structure of Graphene Oxide: pH-Dependence of the Spectroscopic Response. ACS Appl. Nano Mater. 2019, 2, 19–27. [Google Scholar] [CrossRef]
  34. Augustyniak-Jabłokow, M.A.; Strzelczyk, R.; Fedaruk, R. Localization of Conduction Electrons in Hydrothermally Reduced Graphene Oxide: Electron Paramagnetic Resonance Studies. Carbon 2020, 168, 665–672. [Google Scholar] [CrossRef]
  35. Ryabikin, Y.A.; Baitimbetova, B.A.; Lebedev, I.A.; Serikkanov, A.S.; Dmitrieva, E.A. EPR of Graphenic Structures Obtained by the Ultrasound Field on Graphite in Organic Reagents. Combust. Plasma Chem. 2018, 16, 103–108. [Google Scholar]
  36. Tadyszak, K.; Chybczyńska, K.; Ławniczak, P.; Zalewska, A.; Cieniek, B.; Gonet, M.; Murias, M. Magnetic and Electric Properties of Partially Reduced Graphene Oxide Aerogels. J. Magn. Magn. Mater. 2019, 492, 165656. [Google Scholar] [CrossRef]
  37. Tadyszak, K.; Wereszczyńska, B.; Gonet, M. CT, MR and EPR Imaging of Graphene Oxide Aerogels. Solid State Sci. 2020, 109, 106402. [Google Scholar] [CrossRef]
  38. Buatong, N.; Ruttanapun, C.; Sriwong, C. Synthesis of Reduced Graphene Oxide Quantum Dots from Graphene Oxide via Hydrothermal Process and Theirs Structural, Luminescence and Magnetic Properties. J. Taiwan Inst. Chem. Eng. 2023, 142, 104667. [Google Scholar] [CrossRef]
  39. Kempiński, M. Resistivity Switching in Activated Carbon Fibers. Mater. Lett. 2018, 230, 180–182. [Google Scholar] [CrossRef]
  40. Fedaruk, R.; Strzelczyk, R.; Rusetsky, G.A.; Barbon, A.; Majchrzycki, Ł.; Augustyniak-Jabłokow, M.A. Continuous-Wave and Pulsed EPR Studies of Glass-like Carbon with High Spin Concentration: Evidence for Triplet States. Carbon 2023, 213, 118270. [Google Scholar] [CrossRef]
  41. Semenikhin, P.V.; Ionov, A.N.; Nikolaeva, M.N. Electron Spin Resonance in a Multilayer Graphene Synthesized with Polystyrene. Tech. Phys. Lett. 2020, 46, 186–188. [Google Scholar] [CrossRef]
  42. Baytimbetova, B.A.; Vermenichev, B.M.; Ryabikin, Y.A.; Mansurov, Z.A.; Abdikasova, A.A. Study of graphene formed in the vapor of aromatic hydrocarbons atmosphere. Izv. Vyss. Uchebnykh Zaved. Fizika 2015, 58, 101–105. [Google Scholar] [CrossRef]
  43. Nikitin, A.P.; Valnyukova, A.S.; Furega, R.I.; Sozinov, S.A.; Ismagilov, Z.R.; Ismagilov, Z.R.; Ismagilov, Z.R. Development of a Recording Method of Coals’s EPR Spectra. Vestn. Kuzbass State Tech. Univ. 2019, 129, 76–82. [Google Scholar] [CrossRef]
  44. Pilawa, B.; Więckowski, A.; Pietrzak, R.; Wachowska, H. Microwave Saturation of EPR Spectra of Oxidised Coal. Open Chem. 2007, 5, 330–340. [Google Scholar] [CrossRef]
  45. Lan, M.; Beghein, N.; Charlier, N.; Gallez, B. Carbon Blacks as EPR Sensors for Localized Measurements of Tissue Oxygenation. Magn. Reson. Med. 2004, 51, 1272–1278. [Google Scholar] [CrossRef]
  46. Mensah, B.; Efavi, J.K.; Konadu, D.S.; Manu, G.P. Graphene-Maleic Anhydride-Grafted-Carboxylated Acrylonitrile Butadiene-Rubber Nanocomposites. Heliyon 2022, 8, e11974. [Google Scholar] [CrossRef]
  47. Osipov, V.Y.; Boukhvalov, D.W.; Takai, K. Structure and Magnetic Properties of Superoxide Radical Anion Complexes with Low Binding Energy at the Graphene Edges. Russ. J. Coord. Chem. 2020, 46, 738–745. [Google Scholar] [CrossRef]
  48. Ulyanov, A.N.; Maslakov, K.I.; Savilov, S.V.; Xia, H.; Aldoshin, S.M. Electronic Structure of Oxidized Nitrogen-Doped Graphene Nanoflakes. Temperature Dependence of Paramagnetic Response, Aging and Thermocycling. Mater. Sci. Eng. B 2023, 287, 116119. [Google Scholar] [CrossRef]
  49. Savilov, S.; Suslova, E.; Epishev, V.; Tveritinova, E.; Zhitnev, Y.; Ulyanov, A.; Maslakov, K.; Isaikina, O. Conversion of Secondary C3-C4 Aliphatic Alcohols on Carbon Nanotubes Consolidated by Spark Plasma Sintering. Nanomaterials 2021, 11, 352. [Google Scholar] [CrossRef]
  50. Ziatdinov, M.; Lim, H.; Fujii, S.; Kusakabe, K.; Kiguchi, M.; Enoki, T.; Kim, Y. Chemically Induced Topological Zero Mode at Graphene Armchair Edges. Phys. Chem. Chem. Phys. 2017, 19, 5145–5154. [Google Scholar] [CrossRef]
  51. Ziatdinov, A.M.; Saenko, N.S.; Skrylnik, P.G. Graphene Oxide and Its Thermally Reduced Nanostructured Derivatives: Synthesis and Comprehensive Study of Properties. Russ. J. Inorg. Chem. 2020, 65, 133–145. [Google Scholar] [CrossRef]
  52. Misochko, E.Y.; Akimov, A.V.; Belov, V.A.; Tyurin, D.A.; Laikov, D.N. High Selectivity of Fluorine Atom Addition to the Asymmetric Chemical Bonds of C70 Fullerene. Mendeleev Commun. 2007, 17, 274–276. [Google Scholar] [CrossRef]
  53. Mikhailova, A.V.; Dedkova, V.P.; Shvoeva, O.P.; Shcherbakova, Y.I.; Efimov, N.N.; Ugolkova, E.A.; Grechnikov, A.A.; Savvin, S.B.; Minin, V.V. Gadolinium(III) Complexation with Modified Polymers According to ESR Data. Russ. J. Inorg. Chem. 2014, 59, 1485–1490. [Google Scholar] [CrossRef]
  54. Lindgren, M.; Laaksonen, A.; Westlund, P.O. A Theoretical Spin Relaxation and Molecular Dynamics Simulation Study of the Gd(H2O)93+ Complex. Phys. Chem. Chem. Phys. 2009, 11, 10368. [Google Scholar] [CrossRef] [PubMed]
  55. Sanivarapu, S.R.; Lawrence, J.B.; Sreedhar, G. Role of Surface Oxygen Vacancies and Lanthanide Contraction Phenomenon of Ln(OH)3 (Ln = La, Pr, and Nd) in Sulfide-Mediated Photoelectrochemical Water Splitting. ACS Omega 2018, 3, 6267–6278. [Google Scholar] [CrossRef] [PubMed]
  56. Vazhenin, V.A.; Potapov, A.P.; Gorlov, A.D.; Chernyshev, V.A.; Kazanskiǐ, S.A.; Ryskin, A.I. Structure of Paramagnetic Defects in Cadmium Fluoride Doped with Yttrium and Gadolinium. Phys. Solid State 2006, 48, 686–692. [Google Scholar] [CrossRef]
  57. Kiselev, Y.M.; Koksharov, Y.A.; Khomutov, G.B.; Tishin, A.M. Effect of the PH of the Medium on the Structure of Gadolinium-Containing Complexes According to EPR Data. Russ. J. Phys. Chem. A 2000, 74, 1284–1289. [Google Scholar]
  58. Panich, A.M.; Shames, A.I.; Sergeev, N.A.; Osipov, V.Y.; Alexenskiy, A.E.; Vul’, A.Y. Magnetic Resonance Study of Gadolinium-Grafted Nanodiamonds. J. Phys. Chem. C 2016, 120, 19804–19811. [Google Scholar] [CrossRef]
  59. Savchenko, D.; Vorlíček, V.; Prokhorov, A.; Kalabukhova, E.; Lančok, J.; Jelínek, M. Raman and EPR Spectroscopic Studies of Chromium-Doped Diamond-like Carbon Films. Diam. Relat. Mater. 2018, 83, 30–37. [Google Scholar] [CrossRef]
  60. Panich, A.M.; Shames, A.I.; Tsindlekht, M.I.; Osipov, V.Y.; Patel, M.; Savaram, K.; He, H. Structure and Magnetic Properties of Pristine and Fe-Doped Micro- and Nanographenes. J. Phys. Chem. C 2016, 120, 3042–3053. [Google Scholar] [CrossRef]
  61. Panich, A.M. Nuclear magnetic resonance studies of nanodiamond surface modification. Diam. Relat. Mater. 2017, 79, 21–31. [Google Scholar] [CrossRef]
  62. Savilov, S.V.; Strokova, N.E.; Ivanov, A.S.; Arkhipova, E.A.; Desyatov, A.V.; Hui, X.; Aldoshin, S.M.; Lunin, V.V. Nanoscale Carbon Materials from Hydrocarbons Pyrolysis: Structure, Chemical Behavior, Utilisation for Non-Aqueous Supercapacitors. Mater. Res. Bull. 2015, 69, 13–19. [Google Scholar] [CrossRef]
  63. Kozlov, A.; Suslova, E.; Maksimov, S.; Isaikina, O.; Maslakov, K.; Shashurin, D.; Savilov, S.; Shelkov, G. The Preparation of Nanocomposite with a Core–Shell Structure Made of Carbon Matrices and Lanthanum Nanoparticles. Phys. Part. Nucl. Lett. 2023, 20, 1254–1258. [Google Scholar] [CrossRef]
  64. Suslova, E.V.; Kozlov, A.P.; Shashurin, D.A.; Maximov, S.V.; Maslakov, K.I.; Savilov, S.V. La2O3-carbon composite with core-shell structure and features of it’s gas-phase oxidation. Mendeleev Commun. 2023; in press. [Google Scholar]
  65. Xia, W.; Jin, C.; Kundu, S.; Muhler, M. A Highly Efficient Gas-Phase Route for the Oxygen Functionalization of Carbon Nanotubes Based on Nitric Acid Vapor. Carbon 2009, 47, 919–922. [Google Scholar] [CrossRef]
  66. Cassani, M.C.; Lappert, M.F.; Laschi, F. First Identification by EPR Spectra of Lanthanum(Ii) Organometallic Intermediates (and E½ for La3+ → La2+) in the C–O Bond Activation of Dimethoxyethane. Chem. Commun. 1997, 16, 1563–1564. [Google Scholar] [CrossRef]
  67. Shames, A.I.; Mogilyansky, D.; Panich, A.M.; Sergeev, N.A.; Olszewski, M.; Boudou, J.P.; Osipov, V.Y. XRD, NMR, and EPR study of polycrystalline micro- and nano-diamonds prepared by a shock wave compression method. Phys. Status Solidi A 2015, 212, 2400–2409. [Google Scholar] [CrossRef]
  68. Osipov, V.Y.; Enoki, T.; Takai, K.; Takahara, K.; Endo, M.; Hayashi, T.; Hishiyama, Y.; Kaburagi, Y.; Vul’, A.Y. Magnetic and High Resolution TEM Studies of Nanographite Derived from Nanodiamond. Carbon 2006, 44, 1225–1234. [Google Scholar] [CrossRef]
  69. Augustyniak-Jabłokow, M.A.; Maćkowiak, M.; Tadyszak, K.; Strzelczyk, R. FMR Evidence of Stable Ferromagnetic Correlations at Zigzag Edge States in Graphene. Acta Phys. Pol. A 2015, 127, 537–539. [Google Scholar] [CrossRef]
  70. Panich, A.M.; Sergeev, N.A.; Goren, S.D. Location of paramagnetic defects in detonation nanodiamond from proton spin-lattice relaxation data. Solid State Nucl. Magn. Reson. 2020, 105, 101624. [Google Scholar] [CrossRef]
  71. Chernyak, S.A.; Podgornova, A.M.; Arkhipova, E.A.; Novotortsev, R.O.; Egorova, T.B.; Ivanov, A.S.; Maslakov, K.I.; Savilov, S.V.; Lunin, V.V. Jellyfish-like Few-Layer Graphene Nanoflakes: Synthesis, Oxidation, and Hydrothermal N-Doping. Appl. Surf. Sci. 2018, 439, 371–373. [Google Scholar] [CrossRef]
  72. Ottaviani, M.F.; Mazzeo, R. EPR Characterization of Graphitized and Activated Micro- and Meso-Porous Carbons. Microporous Mesoporous Mater. 2011, 141, 61–68. [Google Scholar] [CrossRef]
  73. Shames, A.I.; Zegrya, G.G.; Samosvat, D.M.; Osipov, V.Y.; Vul’, A.Y. Size Effect in Electron Paramagnetic Resonance Spectra of Impurity Centers in Diamond Particles. Phys. E Low-Dimens. Syst. Nanostructures 2023, 146, 115523. [Google Scholar] [CrossRef]
  74. Ćirić, L.; Djokić, D.M.; Jaćimović, J.; Sienkiewicz, A.; Magrez, A.; Forró, L.; Šljivančanin, Ž.; Lotya, M.; Coleman, J.N. Magnetism in Nanoscale Graphite Flakes as Seen via Electron Spin Resonance. Phys. Rev. B 2012, 85, 205437. [Google Scholar] [CrossRef]
  75. Vitiello, G.; De Falco, G.; Picca, F.; Commodo, M.; D’Errico, G.; Minutolo, P.; D’Anna, A. Role of Radicals in Carbon Clustering and Soot Inception: A Combined EPR and Raman Spectroscopic Study. Combust. Flame 2019, 205, 286–294. [Google Scholar] [CrossRef]
  76. Ohta, T.; Bostwick, A.; McChesney, J.L.; Seyller, T.; Horn, K.; Rotenberg, E. Interlayer Interaction and Electronic Screening in Multilayer Graphene Investigated with Angle-Resolved Photoemission Spectroscopy. Phys. Rev. Lett. 2007, 98, 206802. [Google Scholar] [CrossRef] [PubMed]
Nanomaterials 13 02945 g001
Figure 1. TEM image of raw CNFs.
Figure 1. TEM image of raw CNFs.
Nanomaterials 13 02945 g001
Nanomaterials 13 02945 g002
Figure 2. The scheme of synthesis processes.
Figure 2. The scheme of synthesis processes.
Nanomaterials 13 02945 g002
Nanomaterials 13 02945 g003
Figure 3. TG curves of La2O3/CNFs@C and La2O3/CNFs@C_x (x = 1, 3, 6) samples.
Figure 3. TG curves of La2O3/CNFs@C and La2O3/CNFs@C_x (x = 1, 3, 6) samples.
Nanomaterials 13 02945 g003
Nanomaterials 13 02945 g004
Figure 4. TG and XPS data correspond to bulk and surface La2O3 content (a). Carbon and oxygen content according to XPS (b). The ratio between different carbon (c) and oxygen (d) atom types according to XPS.
Figure 4. TG and XPS data correspond to bulk and surface La2O3 content (a). Carbon and oxygen content according to XPS (b). The ratio between different carbon (c) and oxygen (d) atom types according to XPS.
Nanomaterials 13 02945 g004
Nanomaterials 13 02945 g005
Figure 5. Survey C1s (a) and O1s (b) XPS spectra of La2O3/CNFs@C and La2O3/CNFs@C_x samples.
Figure 5. Survey C1s (a) and O1s (b) XPS spectra of La2O3/CNFs@C and La2O3/CNFs@C_x samples.
Nanomaterials 13 02945 g005
Nanomaterials 13 02945 g006
Figure 6. EPR spectra of La2O3/CNFs@C (a), La2O3/CNFs@C_1 (c), La2O3/CNFs@C_3 (e) and La2O3/CNFs@C_6 (g). Absorption EPR spectra of La2O3/CNFs@C (b), La2O3/CNFs@C_1 (d), La2O3/CNFs@C_3 (f) and La2O3/CNFs@C_6 (h). Background signal was subtracted using the Bruker WinEPR System Version 2.11b software. Absorption spectra were fitted with two Lorentzian lines.
Figure 6. EPR spectra of La2O3/CNFs@C (a), La2O3/CNFs@C_1 (c), La2O3/CNFs@C_3 (e) and La2O3/CNFs@C_6 (g). Absorption EPR spectra of La2O3/CNFs@C (b), La2O3/CNFs@C_1 (d), La2O3/CNFs@C_3 (f) and La2O3/CNFs@C_6 (h). Background signal was subtracted using the Bruker WinEPR System Version 2.11b software. Absorption spectra were fitted with two Lorentzian lines.
Nanomaterials 13 02945 g006
Nanomaterials 13 02945 g007
Figure 7. The changes of g-factors (a), linewidths (ΔH) (b), numbers of spins (N) (c) and normalized to carbon-oxygen frame (d) of EPR spectrum lines of samples. Subscripts l and h denote the lines attributed to the peaks, located at low and high applied field. The error in the ΔH determination is about 3%. The error of g-factor is about 0.0000(5). Uncertainty of the spin numbers is less than 15%.
Figure 7. The changes of g-factors (a), linewidths (ΔH) (b), numbers of spins (N) (c) and normalized to carbon-oxygen frame (d) of EPR spectrum lines of samples. Subscripts l and h denote the lines attributed to the peaks, located at low and high applied field. The error in the ΔH determination is about 3%. The error of g-factor is about 0.0000(5). Uncertainty of the spin numbers is less than 15%.
Nanomaterials 13 02945 g007
Nanomaterials 13 02945 g008
Figure 8. The ratio of sp2/sp3-hybridized carbon atoms and Nh/Nl according to XPS and EPR data.
Figure 8. The ratio of sp2/sp3-hybridized carbon atoms and Nh/Nl according to XPS and EPR data.
Nanomaterials 13 02945 g008
Disclaimer/Publisher’s Note: The statements, opinions and data contained in all publications are solely those of the individual author(s) and contributor(s) and not of MDPI and/or the editor(s). MDPI and/or the editor(s) disclaim responsibility for any injury to people or property resulting from any ideas, methods, instructions or products referred to in the content.

Share and Cite

MDPI and ACS Style

Suslova, E.V.; Ulyanov, A.N.; Kozlov, A.P.; Shashurin, D.A.; Savilov, S.V.; Chelkov, G.A. Composition and Electronic Structure of La2O3/CNFs@C Core-Shell Nanoparticles with Variable Oxygen Content. Nanomaterials 2023, 13, 2945. https://doi.org/10.3390/nano13222945

AMA Style

Suslova EV, Ulyanov AN, Kozlov AP, Shashurin DA, Savilov SV, Chelkov GA. Composition and Electronic Structure of La2O3/CNFs@C Core-Shell Nanoparticles with Variable Oxygen Content. Nanomaterials. 2023; 13(22):2945. https://doi.org/10.3390/nano13222945

Chicago/Turabian Style

Suslova, Evgeniya V., Alexander N. Ulyanov, Alexey P. Kozlov, Denis A. Shashurin, Serguei V. Savilov, and Georgy A. Chelkov. 2023. "Composition and Electronic Structure of La2O3/CNFs@C Core-Shell Nanoparticles with Variable Oxygen Content" Nanomaterials 13, no. 22: 2945. https://doi.org/10.3390/nano13222945

Note that from the first issue of 2016, this journal uses article numbers instead of page numbers. See further details here.

Article Metrics

Back to TopTop