Nanotube Samples Research Articles

INVESTIGATION OF FLUORINATED DOUBLE-WALL CARBON NANOTUBES

Experimental results of investigation of the original and fluorinated ultra-long double-walled carbon nanotubes (DWCNTs) with a length of at least 1000 μm are presented. The degree of fluoridation did not exceed 27 at.%. It has been shown that the process of fluorination of samples of double-walled carbon nanotubes deforms the outer surface of the nanotube wall although does not destroy its internal concentric structure, while the diameter of the fluorinated nanotube increases by 1.5-2 times. In addition, the fluorinated samples, which were thermochemically purified from iron particles and other forms of carbon before fluorination, demonstrated many split/cut ends of nanotubes. The effect of fluorination on the electrical properties of initial and purified samples of double-walled carbon nanotubes was studied. It was revealed that with an increase in temperature from 80 to 300 K for non-fluorinated and fluorinated purified nanotube samples, the resistivity decreases, which corresponds to the semiconductor nature of the conductivity. It was also revealed that when a sample of initial DWNT is fluorinated, a change in the nature of conductivity from semiconductor to metallic is observed. With an increase in temperature from 80 to 300 K, the resistance of the non-fluorinated sample of the original DWNTs decreased by 45%, while the resistance of the fluorinated sample increased by 11%. Despite the decrease in electrical conductivity as a result of fluorination of the purified samples, all samples remained conductors, which presumably indicates partial fluorination of the outer wall of the DWNTs while maintaining the structure of the inner wall. Thus, fluorination of double-walled carbon nanotubes with a well-aligned and concentric structure leads to the formation of fluorocarbon nanostructures, which can be promising materials for electronic nanodevices. For citation: Karaeva A.R., Khaskov M.A., Kurzhumbaev D.Zh., Kulnitskiy B.A., Mordkovich V.Z. Investigation of fluorinated double-wall carbon nanotubes. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2024. V. 67. N 10. P. 38-48. DOI: 10.6060/ivkkt.20246710.4y.

Mechanism of Co3O4-TiO2 Nanocomposite Formation with Enhanced Photocatalytic Performance

TiO2 nanotubes are tubular structures that have garnered significant attention in materials science and engineering due to their unique properties and diverse applications. In this study, highly ordered and well aligned TiO2 nanotubes were successfully synthesized through anodization of Ti foil in ethylene glycol (C2H6O2) containing ammonium fluoride (NH4F) and hydrogen peroxide (H2O2) at 60 V for 30 minutes. The effectiveness of TiO2 as a photocatalyst under solar light is limited by its wide band gap and high recombination rate of charge carriers. To address these limitations, TiO2 nanotubes were modified with cobalt oxide. The resulting Co3O4-TiO2 nanocomposite was synthesized using a wet impregnation technique, aiming to enhance the photocatalytic performance of TiO2 nanotubes across a broader range of the solar spectrum. The formation of Co3O4-TiO2 nanocomposite is by immersing the TiO2 nanotubes in the metal salt precursor solution of Co(NO3)2 for a certain soaking period. The soaking cycle was repeated a few times to ensure the deposition of cobalt oxide nanostructures on the TiO2 nanotube samples. This diffusion interstitial process via wet impregnation was time dependent, which altered the amount of cobalt loaded on the nanotube's surface. The addition of cobalt significantly improved the photodegradation activity of the nanotubes under visible light, outperforming bare TiO2 nanotubes. This enhancement is likely due to the cobalt acting as shallow traps, which effectively promote the separation of photogenerated charge carriers.

Investigation on radiation shielding potentials of barium calcium aluminosilicate glass material using silicon carbide nanotubes reinforcement

This work investigated the gamma ray attenuation power of barium calcium aluminosilicate glass by using silicon carbide nanotube modifiers. Shielding efficiency of BaO–15CaO–5Al2O3–10B2O3–35SiO2 was investigated by adding different concentrations of silicon carbide nanotubes (10, 15, 20, 25 mol %). Amorphous and fine characteristics of the prepared glass materials were analyzed using XRD and FTIR techniques. In the results obtained, absence of sharp peaks in the XRD pattern revealed that the prepared glass was amorphous. Analysis of the radiation shielding properties was tested against gamma radiation by using PHY-X/PSD software. Various shielding parameters such as linear attenuation coefficient, mass attenuation coefficient, half value layer, tenth value layer, mean free path, and effective atomic number were determined to access the radiation shielding strength of the prepared samples. From the obtained results, composites of barium calcium aluminosilicate and silicon carbide nanotubes (sample 1) with higher values of mass attenuation coefficient (32.92 cm2/g) and effective atomic number (52.02) provided superior gamma ray attenuation. Results also revealed that the density and chemical composition of the prepared glass samples strongly influence photon interactions and weakly influence electronic interactions during the photon attenuation process. The results demonstrated that increasing the weight fractions of silicon carbide nanotubes in the glass samples increases the shielding properties.

(Invited) Analytical Super-Resolution Microscopy Approaches for the Morphological Characterization of Carbon Nanotube Heterogeneity

The ability to determine the shape, size and orientation of fluorescent single-walled carbon nanotubes is critical for a plethora of applications. Yet the heterogeneity of the nanotube samples is often overlooked due to the lack of investigation approaches which may impact the obtained results. Although techniques such as atomic force microscopy (AFM) and transmission electron microscopy (TEM) could be used to this extent, they require heavy instrumentation and analysis, and do not necessarily allow the temporal and in situ characterization of the samples. On the other hand, super resolution microscopy (SRM) approaches can be used to determine the structure of fluorescent nano-objects with high precision while retaining the possibility to perform in situ studies. In particular, analytical SRM approaches are particularly interesting as they rely only on post-processing and do not require any specific optical component.In this context, we study the performances of three analytical SRM approaches for the determination of SWCNT shape, size and orientation. Using correlative microscopy between optical and AFM approaches this study provides an in-depth comparison of the performances of analytical SRM approaches for the morphological characterization of individual SWCNTs.B.P. Lambert et al., in preparation

Self-Calibrating Fluorimetric Analysis of Single-Wall Carbon Nanotube Samples for Electronics Applications

Semiconducting single-wall carbon nanotubes (SWCNTs) are a leading candidate to replace or supplement silicon in future generation chip manufacturing. Because they are produced as structural mixtures with varied electronic properties, SWCNTs must first be carefully sorted and purified. This requires new metrology tools that can reliably measure SWCNT sample compositions to guide sorting processes and confirm product purity. We describe here a novel, self-calibrating optical instrument designed for advanced characterization of SWCNT samples. This desktop system will quickly, sensitively, and non-destructively quantify the concentrations of multiple SWCNT (n,m) species. The key advance is adding variance spectroscopy to rapid excitation-emission fluorimetry. Variance spectroscopy is a recently developed method that can determine absolute concentrations of nanoparticles by analyzing statistical variations in the fluorescence signals from small volumes of dilute samples. Measurements are made by a small accessory module linked to a standard NanoSpectralyzer. It will automatically acquire and analyze variance spectra to find the sensitivity calibration factors needed to convert raw fluorescence intensities into actual concentrations of the different SWCNT species. Those measured calibration factors are valid for subsequent samples with similar processing histories, allowing rapid quantitation from quick excitation-emission scans. We expect that this analytical capability will support advances in basic carbon nanotube science and applications.

UV-Vis quantification of the iron content in iteratively steam and HCl purified single-walled carbon nanotubes.

As-produced carbon nanotubes contain impurities which can dominate the properties of the material and are thus undesired. Herein we present a multi-step purification treatment that combines the use of steam and hydrochloric acid in an iterative manner. This allows the reduction of the iron content down to 0.2 wt. % in samples of single-walled carbon nanotubes (SWCNTs). Remarkably, Raman spectroscopy analysis reveals that this purification strategy does not introduce structural defects into the SWCNTs' backbone. To complete the study, we also report on a simplified approach for the quantitative assessment of iron using UV-Vis spectroscopy. The amount of metal in SWCNTs is assessed by dissolving in HCl the residue obtained after the complete combustion of the sample. This leads to the creation of hexaaquairon(III) chloride which allows the determination of the amount of iron, from the catalyst, by UV-Vis spectroscopy. The main advantage of the proposed strategy is that it does not require the use of additional complexing agents.

Free-standing arrays of BaTiO3 nanotubes for non-enzymatic glucose sensing & hydrophobic coating applications

BaTiO3 nanostructures have been considered as a promising candidates in recent past for energy and biomedical sectors owing to their excellent physiochemical properties, such as high dielectric constant, excellent piezoelectric property, good biocompatibility, non-linear optical characteristics etc. Present study reveals on free-standing arrays of BaTiO3 nanostructures, were fabricated by hydrothermal conversion of anodic TiO2 nanotubes. Morphological and structural information of the BaTiO3 nanotubes were done using FESEM and XRD studies. FESEM analysis revealed that the fabricated samples were having tubular morphology of average length and pore diameter of 4.63 μm and 290 nm respectively. Cubical perovskite crystalline phase of BaTiO3 was confirmed through XRD analysis. The BaTiO3 nanotube samples had shown a higher sensitivity of 44.43 μA mM−1 cm−2 and a faster response of 0.1 s for glucose detection. The fabricated BaTiO3 nanotubes film also showed a higher contact angle of 122.70°. Therefore, our present fabrication on Titanium foil study emphasizes on arrays of BaTiO3 nanotubes which will open up a new window in the development of various types of sensing and hydrophobic coating applications.

Review of: "bulk samples of single-walled carbon nanotubes as well as for multi-walled single nanotubes"

Review of: "bulk samples of single-walled carbon nanotubes as well as for multi-walled single nanotubes"

Электрохимические сенсоры на основе сеток из однослойных углеродных нанотрубок для вольтамперометрического определения аскорбиновой кислоты

Modern highly sensitive and selective sensors are able to determine biologically active substances, which makes this direction one of the most popular areas of analytical chemistry. The study featured the electrochemical properties of new fiber materials based on single-wall carbon nanotubes with prospects of using them in the voltammetry of ascorbic acid. 
 The authors developed a new technology to synthesize films from disordered single-wall carbon nanotubes by chemical vapor deposition. Fibers were produced from a solvent by wet-pulling of single-wall carbon nanotubes networks. Thin films of randomly oriented single-wall carbon nanotube bundles were deposited downstream of a floating aerosol CVD reactor, which included a high temperature furnace with a quartz tube. The synthesis of the single-wall carbon nanotube samples was performed at 825°C. Ethanol served as carbon source while ferrocene was used as catalyst precursor. The single-wall carbon nanotubes were collected on a nitrocellulose filter in the form of films with transmittances of 10% in the middle of the visible wavelength (550 nm). The method was optimized to involve air annealing at 300–320°C and a treatment with strong inorganic acids, i.e., HCl, HNO3 + H2SO4. The voltammetric curves recording included background electrolyte, scan rate, and preconditioning. These parameters were selected experimentally to obtain the maximal sensor response to ascorbic acid content. The anodic peak of ascorbic acid in the phosphate buffer electrolyte (pH 6.86) was observed at a potential of +0.2 V. The current and peak area of ascorbic acid oxidation depended neither on the time nor on the conditioning potential of the sensor. The linear dependences of these parameters on the concentration of ascorbic acid stayed within 50–500 μmol/L (8.8–90 mg/L) at a scan rate of 0.1 mV/s. The single-wall carbon nanotube microsensor had a length of 0.5 cm and an average width of 400 μm. Its sensitivity was two times as high as that of a disk glassy carbon electrode with a diameter of 5 mm. 
 The experimental sensors proved effective in determining ascorbic acid in food products, pharmaceuticals, and biological fluids.

Review of: "The results of laboratory experiments also indicate the presence of this feature in mass samples of single-walled carbon nanotubes"

Review of: "The results of laboratory experiments also indicate the presence of this feature in mass samples of single-walled carbon nanotubes"

Influence of Anodizing Parameters on the Morphological Characteristics of TNTAs

TiO2 nanotubes arrays (TNTAs) were synthesized using the anodization method in ethylene glycol (EG)-based electrolyte with different percentages of ammonium fluoride (0.3, 0.4, and 0.5 wt.%) and water content (2.5, 5, and 7.5% vol%). All the samples were ultrasonically cleaned in acetone, ethanol, and deionized water, then dried in air and kept in an etching solution for a while before anodization. The two-step anodization was carried out, followed by thermal treatment at 450°C for the crystallization. The nanotube samples were characterized using FE-SEM analysis. The FE-SEM results showed that the largest tube diameter was 87.74±1.89 nm of the TNTAs prepared in the EG electrolyte with a composition of 7.5% water content and 0.5% ammonium fluoride. The longest tube length analyzed was around 5.3 µm of the TNTAs prepared in the ethylene glycol electrolyte with the composition of 2.5% water content and 0.4% ammonium fluoride percentage, exhibiting a highly ordered, compact honeycomb structure and thick single-walled structure.

Micro-DRIFTS for small area hyper-black spectroscopy.

We have developed a low-cost micro-diffuse reflectance infrared Fourier transform spectroscopic (micro-DRIFTS) setup for measuring the reflectance of small area diffuse samples. The system performance is characterized and then demonstrated on small area vertically aligned carbon nanotube (VACNT) samples. We find that our system can measure samples with a spatial resolution of approximately 140 µm with sensitivities of 10s of ppm in the 2 µm - 18 µm spectral window. Our uncertainty budget is presented along with how our measured reflectance can be equated to directional-hemispherical reflectance.

The computational study of external heat flux and silicon doping effect on displacement of C20 molecule in a carbon nanotube (CNT): A molecular dynamics method

This study focuses on the behavior of the Carbon Nanotube (CNT)-C20 system as a nano-pumping configuration for drug delivery processes. The system was modeled using a molecular dynamics (MD) method, and the effects of external heat flux and silicon doping were investigated. The predicted MD outputs showed high stability throughout the nanopumping process, even when different ratios of external heat flux were applied. The entropy value of the CNT-C20 system decreases from 412.91 to 403.394 eV/K as the heat flux increases to 0.03 W/m2. Also, the kinetic energy of the target atomic sample increased from 3.50 to 5.42 eV as heat flux increased. This kinetic energy enlarging occurred for the translational component of the target molecule’s kinetic energy, and the rotational component didn’t change effectively. Additionally, the results show that increasing atomic doping of silicon particles from 1 to 3 % decreased the displacement time of C20 molecule (7.22 ps for a 3 % doping ratio), indicating that atomic doping may also improve the nano-pumping process. By increasing Si doping to 3 %, the potential energy decreased, and the stability of the defined compound was reduced. This procedure caused the target molecule to not stabilize inside the nanotube sample, and this molecule displaced inside the deliverer system in less time. However, the negative ratio of potential energy showed physical stability of the total system wasn’t disrupted. With further doping increase to 5 %, the defined compound’s potential energy increased and stability enlarged. This process can be delayed nano-pumping procedure. Overall, the outcomes of this simulation provide insights into the optimal method for pumping fluids at the nanoscale and for drug delivery systems. These findings have practical implications for developing more efficient and effective drug delivery technologies that can help improve patient outcomes.

Discrimination of individual semiconducting and metallic single-walled carbon nanotubes by multi-wavelength photothermal microscopy

The coexistence of semiconducting and metallic single-walled carbon nanotubes (SWCNTs) after synthesis is one of the factors preventing their practical applications. A method for quantifying the purity of a nanotube sample with high accuracy is essential because each type has different applications. In this study, we investigated the accuracy in distinguishing between semiconducting and metallic SWCNTs using multi-wavelength photothermal microscopy. Linear discrimination analysis of the multi-wavelength signals of individual nanotubes was performed to show that the two types of SWCNTs could be distinguished with more than ∼95% accuracy when the SWCNTs were embedded in a dry polymer film. In contrast, the discrimination rate decreased to about 80% when the SWCNTs were dispersed in aqueous media. The optimal wavelength combinations, number of lasers required for discrimination, and relationship between the signal-to-noise ratio and discrimination rate are also discussed.

Length reduction kinetics of multiwalled carbon nanotubes correlated to planetary ball mill impact energy

Four commercial multiwalled carbon nanotubes with distinct lengths and diameters were subject to planetary ball milling to induce length reduction. The Burgio-Rojac energy model was employed to calculate the single impact energy and cumulative energy dissipated to the carbon nanotubes during milling. The ratio of sample mass to bead mass and the nanotube bulk density did not affect length reduction during grinding. The minimum impact energy barrier for carbon nanotube length reduction appeared directly proportional to nanotube diameter for parallel wall morphologies, although a nanotube sample with a cup-stacked wall morphology showed a much lower energy barrier. A normalized exponential equation relating carbon nanotube length and cumulative impact energy collapsed all data to a single exponential master curve described by the same scaling parameters, namely a pre-exponential term that includes the initial nanotube length and a scaling energy in the exponent.

Rapid scan white light pump–probe spectroscopy with 100 kHz shot-to-shot detection

We demonstrate a femtosecond pump–probe spectrometer that utilizes a white light supercontinuum as input and relies on mutual synchronization of the laser repetition rate, acousto-optical chopper, pump–probe delay stage, and the CCD camera to record shot-to-shot pump–probe spectra while the pump–probe delay is scanned synchronously with the laser repetition rate. The unique combination of technologies implemented here allows for electronically controllable and repetition-rate scalable detection throughput that is only limited by the camera frame rate. Despite high probe RMS fluctuations due to sample scatter (from ∼1.8% with solvent to 7.9% with sample scatter), a combination of fast and slow averaging with a fine sampling of pump–probe delay leads to reduction of RMS noise without multichannel referencing down to ∼0.4 mOD for a scattering nanotube sample. Throughput and limitations of the rapid versus stepwise scanning approaches are analyzed. Experimental comparison with stepwise scan shows ∼1.9x noise reduction in a significantly faster experiment, suggesting an additional suppression of 1/f noise enabled by rapid scan data collection. The particular combination of technologies implemented here makes our approach especially suitable for high throughput impulsive pump–probe micro-spectroscopy of highly scattering samples, without added cost and complexity of light sources, multichannel detection, or long sample exposure.

Kinetics of Single-Wall Carbon Nanotube Coating Displacement by Single-Stranded DNA Depends on Nanotube Structure.

Time-resolved fluorescence spectroscopy has been used to study the displacement of adsorbed sodium dodecyl sulfate (SDS) from the surface of single-wall carbon nanotubes (SWCNTs) by short strands of single-stranded DNA. Intensity changes in near-infrared emission peaks of various SWCNT structures were analyzed following the addition of six different (GT)n oligomers (n from 3 to 20) to SDS-coated nanotube samples. There is a strong kinetic dependence on the oligomer length, with (GT)3 giving an initial rate more than 300 times greater than that of (GT)20. For shorter oligos in the (GT)n series, we observe an inverse dependence of the displacement rate on the SWCNT diameter, with SDS displaced from (6,5) more than twice as fast as from (8,7). However, this diameter dependence is reversed for oligos with more than six (GT) units. There is also a systematic dependence of the displacement rate on the nanotube chiral angle that is strongest for (GT)5, leading to a factor of ∼3 initial rate difference between (9,1) and (6,5) despite their identical diameters. To account for these findings, we propose a simple two-step kinetic model in which disruption of the original SDS coating is followed by conformational relaxation of ssDNA on the nanotube surface. The relaxation is relatively fast for ssDNA oligos shorter than 12 bp, making the first step rate-determining. Conversely, relaxation of the longer oligomers is slow enough that the second step becomes rate-determining.

Carbon cycle using the CO2 conversion to methane as environmental feasibility on Ni/TiO2-Na nanotubes catalysts

xNi/TiO2-Na nanotubes catalysts were evaluated in CO2-methanation. The catalysts were characterized by FE-SEM, TEM, XRD, MS, CO2-TPD, DRIFTS and TPR. 50Ni/TiO2-Na catalyst showed better CO2 conversion and high CH4 selectivity while, the 5Ni/TiO2-Na catalyst that showed high CO selectivity, low CO2 methanation and Ni species in intimate contact with the support. In this latter, the difficulty of CO2 hydrogenation can be associated with the strength of the catalyst basic sites, which is influenced by the Ni species in intimate contact with the support, promoting the SMSI effect. According with TPD results, the CO2 is retained on the surface of the catalysts with 5 and 20 wt% Ni, and needs higher temperature than in the 50Ni/TiO2-Na nanotube sample to desorb it and liberate the active sites blocked for the reaction to proceed. Although, a high amount of the Ti0.75Ni0.23O cubic phase was observed on the 50Ni/TiO2-Na sample, a large number of metallic Ni particles remained supported on the TiO2-Na which could reduce the SMSI effect on this catalyst. DRIFTs studies showed that Ni impregnation to TiO2-Na nanotubes generated new sites for CO2 adsorption and H2 is necessary to produce carbonates, bicarbonates, formate and carboxilates as intermediaries of the reaction during CO2-hydrogenation.

XPS Characterization of TiO2 Nanotubes Growth on the Surface of the Ti15Zr15Mo Alloy for Biomedical Applications.

Ti15Zr15Mo (TMZ alloy) has been studied in recent years for biomedical applications, mainly due to phase beta formation. From the surface modification, it is possible to associate the volume and surface properties with a better biomedical response. This study aimed to evaluate the possibility of using anodization to obtain TiO2 nanotubes due to the presence of valve-type metal (Zr) in their composition. X-ray photoelectron spectroscopy (XPS) was performed to determine the surface chemical composition in both after-processing conditions (passive layer) and after-processing plus anodization (TiO2 nanotube growth). The anodization resulted in nanotubes with diameters and thicknesses of 126 ± 35 and 1294 ± 193 nm, respectively, and predominated anatase phase. Compared to the passive layer of titanium, which is less than ~10 nm, the oxide layer formed was continuous and thicker. High-resolution spectra revealed that the oxide layer of the element alloys contained different oxidation states. The major phase in all depths for the nanotube samples was TiO2. While the stable form of each oxide was found to predominate on the surface, the inner part of the oxide layer consisted of suboxides and metallic forms. This composition included different oxidation states of the substrate elements Ti, Zr, and Mo.

Investigation of Amorphous Carbon in Nanostructured Carbon Materials (A Comparative Study by TEM, XPS, Raman Spectroscopy and XRD).

Amorphous carbon (AC) is present in the bulk and on the surface of nanostructured carbon materials (NCMs) and exerts a significant effect on the physical, chemical and mechanical properties of NCMs. Thus, the determination of AC in NCMs is extremely important for controlling the properties of a wide range of materials. In this work, a comparative study of the effect of heat treatment on the structure and content of amorphous carbon in deposited AC film, nanodiamonds, carbon black and multiwalled carbon nanotube samples was carried out by TEM, XPS, XRD and Raman spectroscopy. It has been established that the use of the 7-peak model for fitting the Raman spectra makes it possible not only to isolate the contribution of the modes of amorphous carbon but also to improve the accuracy of fitting the fundamental G and D2 (D) modes and obtain a satisfactory convergence between XPS and Raman spectroscopy. The use of this model for fitting the Raman spectra of deposited AC film, ND, CB and MWCNT films demonstrated its validity and effectiveness for investigating the amorphous carbon in various carbon systems and its applicability in comparative studies of other NCMs.