Phosphorous-doped graphene nanoflakes (GNFs) were first synthesized by several methods, including pyrolysis of PPh3 solution in toluene, post-treatment of GNFs with H3PO4 and hydrothermal post-treatment of GNFs or oxidized GNFs with PPh3 solution in DMF. The products were characterized by scanning and transmission electron microscopy, low-temperature nitrogen physisorption and X-ray photoelectron spectroscopy. Correlations between composition and structural features were revealed.

This article examines the spark plasma sintering (SPS) of nitrogen-doped carbon nanotubes (N-CNTs), enabling the production of consolidated pellets with nitrogen contents of up to 1.6 at.

In the present study, thin-layered core–shell Gd2O3@SiO1.5R (R is C3H6NH2) structures were synthesized by gas-phase surface modification of a Gd2O3 core with a 3-aminopropyltriethoxysilane (APTES) shell for the first time. The proposed method consists of two consecutive steps carried out in a fixed-bed reactor. The first step involves APTES adsorption on the Gd2O3 surface, followed by APTES hydrolysis by water vapor. The organosyloxane shell formation was confirmed by transmission and scanning electron microscopy, IR spectroscopy, and thermogravimetric data. X-ray attenuation coefficients of Gd2O3 and Gd2O3@SiO1.5R samples were determined by photon-counting computed tomography in a phantom study. The SiO1.5R shells in the synthesized Gd2O3@SiO1.5R samples had minimal thickness and did not affect the attenuation coefficients of Gd2O3.

Synthesized Ln2O3 (Ln = La, Nd or Gd) nanoparticles with sizes of 1–3 nm, 5–6 nm and 10–15 nm were stabilized by carbon nanoflakes (CNFs). The weight content of Ln2O3 in the Ln2O3/CNF composites was 20–50 wt. %, which makes these composites potentially suitable for practical use as computed tomography and magnetic resonance imaging contrast agents. The structure of CNFs and Ln2O3/CNF composites was investigated by X-ray diffraction data, X-ray photoelectron spectroscopy (XPS) and electron paramagnetic resonance (EPR). The EPR spectra of raw CNFs were silent. The oxidation of the CNF surface resulted in the appearance of paramagnetic centers associated with two types of unpaired electrons in the carbon support. After impregnation of the CNFs with the Ln3+ ion solution, the number of unpaired electrons was reduced, presumably due to the formation of C–O–Ln bonds. All Ln3+ ions changed the composites’ EPR spectra by reducing the number of unpaired electrons in the CNF structure.

The synthesis of new carbon nanoflake (CNF)-supported composites with a La2O3/CNFs@C core–shell structure is described. The carbon surface is functionalized by oxidation with nitric acid vapor for 1, 3, or 6 h. The evolutions of the structure and composition are investigated by transmission electron microscopy and X-ray photoelectron spectroscopy.

New contrast agents (CAs) for photon-counting computed tomography (PCCT) were synthesized, including Gd2O3@SiO2 core-shell structures and surface-modified Gd2O3-SiO2-C3H6NH2 nanoparticles. Their composition and structure were assessed by IR spectroscopy, scanning electron microscopy, X-ray phase analysis, and thermogravimetric analysis. The X-ray attenuation of synthesized particles Gd2O3@SiO2 with a size of 150-200 nm and Gd2O3-SiO2-C3H6NH2 with a size of 200-300 nm, as well as the sample of Gd2O3 with a particle size of 300-500 nm in gelatine dispersion, was investigated in phantom studies by PCCT. Energy-specific X-ray attenuation properties of all CA types correlated with their Gd concentrations. Gd2O3 demonstrated higher X-ray attenuation compared to Gd2O3@SiO2 and Gd2O3-SiO2-C3H6NH2 at the same concentrations of Gd, which can be explained by the effect of the SiO2 shells.

Hydrogels have a wide range of medical applications, including use within implantable systems. However, when used in implants, their visibility under conventional medical imaging techniques is limited, creating safety risks for patients. In the current work, we assessed the possibility of enhancing hydrogels using Ln-based contrasting agents to facilitate their visualization in photon-counting computed tomography (PCCT). The contrast enhancement of gelatin, polyacrylamide (PAM), and silicone shells of implants was assessed. A novel synthetic route for producing cross-linked nanosized Ln2O3 with polyacrylamide was proposed and discussed in detail. Several prototypes of silicone implants, including silicone shell and gelatin or PAM filling with different combinations of contrasting agents, were produced and assessed in phantom PCCT studies.

This article describes the one-pot microwave synthesis of silver nanoparticles (AgNPs) assisted with natural polyelectrolytes—humic substances (HS). The humic polyelectrolytes served both as chemical reductants for silver ions and as end-capping agents for AgNPs. Three commercially available sodium humates extracted from lignites and leonardite and one sodium fulvate isolated from natural brown water seeped through peat deposits were used in this study. The dynamics of the growth rate of AgNPs was characterised by UV–VIS spectroscopy by measuring the intensity of surface plasmon resonance at 420 nm. Transmission electron microscopy was used to characterise the size and morphology of AgNPs. Dynamic light scattering was used to determine size distributions of the synthesised AgNPs in the solutions. It was established that both conventional and microwave syntheses assisted with the coal humates produced small-size AgNPs in the range from 4 to 14 nm, with the maximum share of particles with sizes of (6 ± 2) nm by TEM estimates. The peat fulvate yielded much larger NPs with sizes from 10 to 50 nm by TEM estimates. DLS measurements revealed multimodal distributions of AgNPs stabilised with HS, which included both single NPs with the sizes from 5 to 15 nm, as well as their dominating aggregates with sizes from 20 to 200 nm and a smaller portion of extra-large aggregates up to 1000 nm. The given aggregates were loosely bound by humic polyelectrolyte, which prevented the coalescence of AgNPs into larger particles, as can be seen in the TEM images. The significant acceleration in the reaction time—a factor of 60 to 70—was achieved with the use of MW irradiation: from 240 min down to 210–240 s. The coal humate stabilised AgNPs showed antimicrobial properties in relation to S. aureus. A conclusion was made regarding the substantial advantages of microwave synthesis in the context of time and scaling up for the large-scale production of AgNP-HS preparations with antimicrobial properties suitable for external wound-healing applications.

The use of photon-counting detectors (PCD) in X-ray computed tomography (CT) allows for obtaining specific spectral information about the materials present in the studied object. This provides the capability to detect contrast agents (CAs) based on elements with high atomic numbers, which opens up significant prospects for diagnostics and preclinical trials. This work presents a criterion for the extraction of a contrast agent and the determination of its concentration based on the K-edge absorption. The criterion is built on the study of the spectral characteristics of CAs. It considers scenarios where more than two contrast agents are simultaneously used in a wide range of concentrations in the study. The experiment was conducted using a laboratory microtomographic system based on the Medipix3RX detector family. The criterion utilizes five energy thresholds for the identification of a single contrast agent. Lanthanides were used as contrast agents.

2–3 nm Gd 2 O 3 nanoparticles deposited on carbon nanoflakes were prepared. These are new contrast agents for photon-counting computed tomography based on detectors allowing counting of separate photons. Contrast agents of the Gd 2 O 3 @C core–shell structure were prepared by graphitization of the surface of these particles. The Gd 2 O 3 and Gd 2 O 3 @C nanoparticles obtained, aqueous solution of Gd(NO 3 ) 3 ·6H 2 O, and a dispersion of 300–500 nm Gd 2 O 3 particles in gelatin were studied by photon-counting computed tomography. At equal gadolinium concentrations, the highest X-ray absorption was noted for Gd(NO 3 ) 3 ·6H 2 O and Gd 2 O 3 , which is associated with higher density of these samples. Carbon in the contrast agents does not affect the absorption. An algorithm was developed for semiquantitative determination of gadolinium by photon-counting computed tomography.

Covalently cross-linked carbon nanotube network has been synthesized using spark plasma sintering followed by nitric acid treatment. EPR investigation of its electronic structure in comparison with pristine carbon nanotubes has revealed that the covalent cross-linking leads to a decrease in the number of paramagnetic centers, while the oxidation results in an increase in their number. The oxidation affects the cross-linked and pristine materials in a different manner

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.

The data on spark plasma sintering (SPS) of carbon nanomaterials (CNMs) are summarized for the first time in this review. An information about the properties and possible applications of the prepared consolidates depending on the SPS temperature and pressure is presented. Probable sintering processes and mechanisms are considered. A special section is devoted to CNM consolidates with metals or oxides. Application of such composites in the hydrogenation of carbon oxides is considered.

Few-layer graphene nanoflakes (GNFs) containing 8–10 graphene layers were treated at temperatures of 600–1800°C and pressures of 10–50 MPa by spark plasma sintering. At 600°С, the GNF powders did not consolidate; sintering with formation of pellets occurred at 1200–1800°С. As the temperature and pressure of sintering increased, the graphite structure became improved, and the number of carbon layers increased to 15–20; all the sintered samples were mesoporous.

Electron paramagnetic resonance (EPR) spectroscopy was used to study an electronic structure of carbon nanotubes (CNTs) consolidated by spark plasma sintering and additionally oxidized in vapor of boiling nitric acid. Two components were distinguished in the EPR absorption spectra: narrow and broad lines with different g-factors. This testified to the different surrounding of paramagnetic centers associated with the lines. Temperature dependence of spin numbers, associated with the narrow line, transfers from Curie-Weiss law to Curie law with increasing temperature. EPR susceptibility, associated with the broad line, can be attributed to a paramagnetic matrix with superparamagnetic inclusions.

The subject of the current research study is aimed at the development of novel types of contrast agents (CAs) for multi-energy computed tomography (CT) based on Ln–graphene composites, which include Ln (Ln = La, Nd, and Gd) nanoparticles with a size of 2–3 nm, acting as key contrasting elements, and graphene nanoflakes (GNFs) acting as the matrix. The synthesis and surface modifications of the GNFs and the properties of the new CAs are presented herein. The samples have had their characteristics determined using X-ray photoelectron spectroscopy, X-Ray diffraction, transmission electron microscopy, thermogravimetric analysis, and Raman spectroscopy. Multi-energy CT images of the La-, Nd-, and Gd-based CAs demonstrating their visualization and discriminative properties, as well as the possibility of a quantitative analysis, are presented.

Local electronic structure of carbon nanotubes (CNTs) consolidated by spark plasma sintering and further oxidized by nitric acid was studied by electron paramagnetic resonance (EPR), transmission electron microscopy, X-ray photoelectron and Raman spectroscopy. It was found that long time oxidation perforated and fragmented sintered CNTs and increased the oxygen content in the material causing an increase in the number of paramagnetic centers. Two components in the absorption EPR spectra were distinguished: A narrow and a broad line with different [Formula: see text]-factors, which testifies the different surrounding of paramagnetic centers associated with the lines. The results are of great importance for understanding the mechanism of nanotubes oxidation and development new types of catalysts, electromagnetic shielding materials and absorbents.

Electron paramagnetic resonance (EPR) at different temperatures is used to study samples of multi-walled carbon nanotubes (CNTs) for the first time. The tubes are obtained via the pyrolytic decomposition of hexane and consolidated by spark plasma sintering with subsequent oxidation. The CNTs are characterized via X-ray photoelectron spectroscopy and high-resolution transmission electron microscopy. It is established that the intensity of the lines in the EPR spectra, their width, and the g -factor depend on temperature. Two components can be distinguished in the composition of the lines: narrow and wide. Different g -factors of narrow and wide lines reflect the environments of paramagnetic centers attributed to these lines. Intensity and the g -factor fall with temperature, and the linewidth varies nonmonotonically. The spin density associated with both broad and narrow lines diminishes with temperature, and the attribution of these lines to localized or mobile electrons is discussed in connection with the conduction mechanism.

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.

The mixtures of template carbon foams and carbon spheres were synthesized by pyrolysis of hexane over Ni foam, followed by graphitization. All samples were analyzed by scanning and transmission electron microscopy, the BET method, thermogravimetry, Raman spectroscopy and X-ray diffraction. The standard enthalpy of formation of the presented material (ΔfH2980=1.29±0.35kJg−1) was determined for the first time.