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A new voltammetry method for the highly sensitive antidepressant drug vortioxetine (VOR) is presented using glassy carbon electrodes modified with hierarchical carbon nanofibers with NiCo nanoparticles (eCNF/CNT/NiCo-GCE). The electrochemical behavior of VOR was investigated by cyclic voltammetry, which indicates that its oxidation is an adsorption-controlled process with the exchange of two electrons and one proton. The effects of various factors on the VOR peak, such as supporting electrolyte type, preconcentration time, and potential, or influence of interferents, were tested using the square wave voltammetry technique (SWV). The linear voltametric response for the analyte was obtained in the concentration range from 0.01·10−6 to 3.0·10−6 mol L−1 with the detection limit of 1.55·10−9 mol L−1 for a preconcentration time of 60 s. The proposed method was successfully applied for highly sensitive VOR determination in complex matrices such as tablets, urine, and plasma with good recovery parameter.

The aim of this study was an extensive analysis of the correlations linking the structure with the electrical properties of hierarchical nanocomposites – electrospun carbon nanofibres/carbon nanotubes (eCNF/CNT). Herein, we focus primarily on the determination and separation of the impact of iron (III) acetylacetonate (Fe(Acac)3) on the structure of core-eCNFs from the overall effect it exerts on the global ordering and electrical properties of nanocomposites. The structure of materials was evaluated using highly local microscopic and diffraction techniques as well as global spectroscopic methods. The charge transport properties were determined through analysis of the temperature-dependent conductivity via Mott's variable-range hopping model. The investigation revealed that increasing concentration of Fe(Acac)3 results in higher surface density of CNTs, which affects the electrical transport in nanocomposites positively (158% increase in σ298K; notable decline in T0). However, it was proved that high catalyst concentrations simultaneously cause amorphisation of core-eCNFs and increase the activation energy of hopping conduction in them. As a consequence of the above, we estimated the concentration of Fe(Acac)3 (~3.0%), ensuring the best electrical properties. Additionally, it was demonstrated that desorption of electrically active guest molecules causes notable changes in the electronic transport in nanocomposites.

The main aim of this study is to investigate the effect of fragmentation of electrospun carbon nanofibers (eCNFs) obtained at different temperatures, i.e., at 750 °C, 1000 °C, 1500 °C, 1750 °C and 2000 °C on the cellular response in vitro. In order to assess the influence of nanofibers on biological response, it was necessary to conduct physicochemical, microstructural and structural studies such as SEM, XPS, Raman spectroscopy, HRTEM and surface wettability of the obtained materials. During the in vitro study, all samples made contact with the human chondrocyte CHON-001 cell lines. The key study was to assess the genotoxicity of eCNFs using the comet test after 1 h or 24 h. Special attention was paid to the degree of crystallinity of the nanofibers, the dimensions of the degradation products and the presence of functional groups on their surface. A detailed analysis showed that the key determinant of the genotoxic effect is the surface chemistry. The presence of nitrogen-containing groups as a product of the decomposition of nitrile groups has an influence on the biological response, leading to mutations in the DNA. This effect was observed only for samples carbonized at lower temperatures, i.e., 750 °C and 1000 °C. These results are important with respect to selecting the temperature of thermal treatment of eCNFs dedicated for medical and environmental functions due to the minimization of the genotoxic effect of these materials.

This work proposes new carbon materials for intermediate layers in solid-contact electrodes sensitive for potassium ions. The group of tested materials includes electrospun carbon nanofibers, electrospun carbon nanofibers with incorporated cobalt nanoparticles and hierarchical nanocomposites composed of carbon nanotubes deposited on nanofibers with different metal nanoparticles (cobalt or nickel) and nanotube density (high or low). Materials were characterized using scanning electron microscopy and contact angle microscopy. Electrical parameters of ready-to-use electrodes were characterized using chronopotentiometry and electrochemical impedance spectroscopy. The best results were obtained for potassium electrodes with carbon nanofibers with nickel-cobalt nanoparticles and high density of nanotubes layer: the highest capacity value (330 µF), the lowest detection limit (10−6.3 M), the widest linear range (10−6–10−1) and the best reproducibility of normal potential (0.9 mV). On the other hand the best potential reversibility, the lowest potential drift (20 μV·h−1) in the long-term test and the best hydrophobicity (contact angle 168°) were obtained for electrode with carbon nanofibers with cobalt nanoparticles and high density of carbon nanotubes. The proposed electrodes can be used successfully in potassium analysis of real samples as shown in the example of tomato juices.

A new electrochemical sensor based on hierarchical carbon nanofibers with Ni and Co nanoparticles (eCNF/CNT/NiCo-GCE) was developed. The presented sensor may be characterized by high sensitivity, good electrical conductivity, and electrocatalytic properties. Reproducibility of its preparation expressed as %RSD (relative standard deviation) was equal to 9.7% (n = 5). The repeatability of the signal register on eCNF/CNT/NiCo-GCE was equal to 3.4% (n = 9). The developed sensor was applied in the determination of the antihistamine drug—cetirizine hydrochloride (CTZ). Measurement conditions, such as DPV (differential pulse voltammetry) parameters, supporting electrolyte composition and concentration were optimized. CTZ exhibits a linear response in three concentration ranges: 0.05–6 µM (r = 0.988); 7–32 (r = 0.992); and 42–112 (r = 0.999). Based on the calibration performed, the limit of detection (LOD) and limit of quantification (LOQ) were calculated and were equal to 14 nM and 42 nM, respectively. The applicability of the optimized method for the determination of CTZ was proven by analysis of its concentration in real samples, such as pharmaceutical products and body fluids (urine and plasma). The results were satisfactory and the calculated recoveries (97–115%) suggest that the method may be considered accurate. The obtained results proved that the developed sensor and optimized method may be used in routine laboratory practice.

The goal of this study is to investigate the influence of different types of modifiers, such as sodium hyaluronate (NaH), graphene oxide (GO), silica oxycarbide (SiOC) and oxidation process (ox) on physicochemical, morphological, and biological properties of electrospun carbon nanofibers (eCNFs). Scanning electron microscopy, X-ray photoelectron spectroscopy and infrared spectroscopy (FTIR) were used to evaluate the microstructure and chemistry of as-prepared and modified CNFs. The electrical properties of CNFs scaffolds were examined using a four-point probe method to evaluate the influence of modifiers on the volume conductivity and surface resistivity of the obtained samples. The wettability of the surfaces of modified and unmodified CNFs scaffolds was also tested by contact angle measurement. During the in vitro study all samples were put into direct contact with human chondrocyte CHON-001 cells and human osteosarcoma MG-63 cells. Their viability was analysed after 72 h in culture. Moreover, the cell morphology and cell area in contact with CNFs was observed by means of fluorescence microscopy. The obtained results show great potential for the modification of CNFs with polymer, ceramic and carbon modifiers, which do not change the fiber form of the substrate but significantly affect their surface and volume properties. Preliminary biological studies have shown that the type of modification of CNFs affects either the rate of increase in the number of cells or the degree of spreading in relation to the unmodified sample. More hydrophilic and low electrically conductive samples such as CNF_ox and CNF_NaH significantly increase cell proliferation, while other GO and SiOC modified samples have an effect on cell adhesion and thus cell spreading. From the point of view of further research and the possibility of combining the electrical properties of modified CNF scaffolds with electrical stimulation, where these scaffolds would be able to transport electrical signals to cells and thus affect cell adhesion, spreading, and consequently tissue regeneration, samples CNF_GO and CNF_SiOC would be the most desirable.

The presented work reports the application of the electrospun carbon nanofibers decorated with cobalt nanoparticles (CNF-Co) in the fabrication of a new, highly sensitive electrochemical sensor (GCE-CNF-Co). Morphology, phase composition and structure as well as the chemical state of the surface of used material were evaluated using the following methods: scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS). The proposed sensor might be characterized by a simple and fast process of preparation and low cost but in the same time exhibits excellent electrical conductivity and electrocatalytic properties. Reproducibility of its preparation expressed as relative standard deviation (%RSD) was estimated to be 9.0% (n = 5 electrodes). A single sensor might perform at least 700 measurements without compromising metrological parameters. The developed sensor was used in the determination of atorvastatin (ATOR)—substance used for the prevention of cardiovascular incidents. ATOR exhibits linear response in the range 0.08–1.04 μM (r = 0.998) and 1.2–9.1 μM (r = 0.999). Limit of detection (LOD) was equal to 3.4 nM (1.9 μg l−1) (tacc = 50 s). The applicability of the method was proved by analysis of urine and pharmaceutical products containing ATOR. Recoveries were in the range 102%–110%, what proves the accuracy of the method.

In this work, we present a comparative study of the impact of secondary carbon nanofillers on the electrical and thermal conductivity, thermal stability, and mechanical properties of hybrid conductive polymer composites (CPC) based on high loadings of synthetic graphite and epoxy resin. Two different carbon nanofillers were chosen for the investigation—low-cost multi-layered graphene nanoplatelets (GN) and carbon black (CB), which were aimed at improving the overall performance of composites. The samples were obtained by a simple, inexpensive, and effective compression molding technique, and were investigated by the means of, i.a., scanning electron microscopy, Raman spectroscopy, electrical conductivity measurements, laser flash analysis, and thermogravimetry. The tests performed revealed that, due to the exceptional electronic transport properties of GN, its relatively low specific surface area, good aspect ratio, and nanometric sizes of particles, a notable improvement in the overall characteristics of the composites (best results for 4 wt % of GN, σ = 266.7 S cm−1, λ = 40.6 W mK−1, fl. strength = 40.1 MPa). In turn, the addition of CB resulted in a limited improvement in mechanical properties, and a deterioration in electrical and thermal properties, mainly due to the too high specific surface area of this nanofiller. The results obtained were compared with US Department of Energy recommendations regarding properties of materials for bipolar plates in fuel cells. As shown, the materials developed significantly exceed the recommended values of the majority of the most important parameters, indicating high potential application of the composites obtained.

In the following study, the electrical and mechanical properties of granular-fibrous carbon-carbon composites with short recycled carbon fibres have been investigated. The examined composites contained from 0 to 12 wt% of three types of recycled carbon fibres that differ in length. The conducted study has proven that it is not the type of applied fibre, but rather the resultant porosity of composites that exerts the predominant influence on the electrical resistivity and mechanical properties of the tested materials. The curve fitting revealed mathematical formulas correlating the studied properties with the apparent density of the composite samples. Owing to the addition of the shortest carbon fibres, the mechanical and electrical properties were significantly improved (50.14% and 24.06% increase in modulus of elasticity and flexural strength respectively for the sample with 12 wt% of the shortest fibres). A 21.39% decline in the resistivity ( ϱ = 161.26 µ Ω ⋅ m ) of the composite containing 4% of shortest fibres was noted in comparison with the reference sample. Unlike powdered fibres, the addition of longer fibres caused an increase in porosity and deterioration of microstructure, which resulted in a significant decline in the key properties of the investigated composites.

The aim of this study was to investigate potential applications of milled secondary carbon fibres as a primary filler in conductive polymer composites. The examined composites were based on epoxy resin, milled secondary carbon fibres and selected carbon nanoadditive used as a secondary conductive filler. Three kinds of nanopowders were tested: multiwalled carbon nanotubes, graphene nanoplatelets and graphitized carbon black. In the first stage of the experiment, composites with different percentages of carbon fibres were examined in order to determine the electrical conductivity and percolation threshold. Subsequently, the most conductive composition (70% of carbon fibres, σ = 9.05 S cm−1) was modified by adding nanofillers. The addition of carbon nanotubes caused more than twofold increase in in-plane conductivity to 20.18 S cm−1. The composites with graphene nanoplatelets showed deterioration of properties due to strongly increased viscosity of a binder with graphene. Small loadings of graphitized carbon black had a minor positive impact on the electrical conductivity and mechanical properties of composites.

The catalytic activity of K10 montmorillonite (K10 Mt) as a substrate during the chemical vapor deposition (CVD) of carbon nanotubes (CNT) was investigated. The influence of free iron present in the structure of K10 Mt during CNT synthesis was investigated. The synthesis was carried out both on samples containing free iron and after its chemical extraction. The structural and microstructural parameters of the samples were characterized by scanning electron microscopy with X-ray dispersion spectroscopy (SEM/EDS), energy dispersive transmission electron microscopy (TEM/EDS), X-ray fluorescence spectroscopy, X-ray diffraction (XRD), infrared spectroscopy (FTIR), and Raman spectroscopy, and X-ray photoelectron spectroscopy. It was found that K10 Mt, before Fe removal, was covered with coarser forms of carbon with rounded shapes characteristic for pyrolytic carbon deposits, while after chemical purification the K10 Mt particles were covered with regular forms of CNT. During the CVD process at 850 °C, multi-walled carbon nanotubes about 1 μm in length were formed on the surface of pure K10 Mt. Under the conditions of synthesis, the K10-Mt/CNT nanocomposites were formed. After extraction of free iron from K10 Mt, the most likely nucleation sites for CNT growth were Mg- and Fe-containing compounds structurally integrated with the K10 Mt substrate, such as iron phosphides, magnesia, and magnesium aluminate.

The work presents a new carbon nanostructure in the form of stacked toroidal carbon nanotubes (STCNT) crystallized from the gas phase through a catalyst-free deposition process. Vapor-grown STCNT were obtained on a graphite substrate using methane as a source of carbon. The carbon structure was analyzed using Transmission Electron Microscopy (TEM), Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/EDX), Raman spectroscopy, X-ray Diffraction and X-ray photoelectron spectroscopy. The TEM images revealed that the nanostructured carbon phase consisted of a single toroidal element (toroid) that was composed of rolled multi-walled carbon nanotubes. The SEM/EDX study of different substrate sites showed the presence of the pure carbon structure. The average external diameter of a single toroid was 1000 nm, and the average distance between neighboring toroids was 100 nm. The space inside the toroids contained carbon spheres made of turbostratic crystallites.

Polysiloxane resins-derived ceramic precursors were used as a binder to manufacture polygranular carbon and graphite-based composite materials. Two types of poly[methyl(phenyl)siloxane]-based resins differing in the structure and O/Si and C/Si ratios were used. During controlled annealing the composite samples up to 2000 °C, the ceramic polymer precursors were transformed into amorphous silicon oxycarbide (SiOC) or nanocrystalline β-SiC (nc-3C) phase. Resins-derived ceramic residues obtained at 2000 °C formed a nanocrystalline layer surrounding graphite grains, whereas in the anthracite material the ceramic phase precipitated between the grains forming separated, single crystallites. The differences in morphology of the carbide compounds formed in the presence of anthracite and graphite grains resulted from the difference in their structural stability and from the nature of interfacial bonding formed at the early stage of composites preparation. Strong interfacial adhesion between the anthracite grains and the polysiloxane resin caused the formation of large cracks in the composite samples during their heating to 1000 °C. The oxidation resistance was higher for graphite-based composites compared to anthracite-containing samples.

In this work polyurethane/graphene nanocomposites containing segments of poly(ethylene glycol) with defined molecular weight were obtained as new phase change materials for thermal energy storage. The prepared materials were investigated by means of DSC, TG, SEM and ultrasonic non-destructive methods. Enhancements in the thermal stability and thermal conductivity in polyurethane systems modified with graphene were found which is important for thermal energy storage applications. Additionally materials modified with graphene showed lower supercooling in comparison to samples without graphene.