Multiwalled Carbon Nanotubes Samples Research Articles

UV-Irradiation Effects on the Structural, Optical and Electrical Characteristics of Soft Blended Polymeric Materials Loaded with Multi-Walled Carbon Nanotubes (MWCNTs)

Undoped and doped polyvinylpyrrolidone/carboxy-methyl cellulose/zinc sulfide/nickel oxide (PVP/CMC/ZnS/NiO) nanocomposite blends with multi-walled carbon nanotubes (MWCNTs) were prepared using sol-gel and solid-state reactions and casting techniques. Various blends were formed and their composition and morphologies were characterized using X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. The structures of the nano-fillers were examined using the XRD technique. The influence of the concentrations of MWCNTs on the linear and nonlinear optical parameters of PVP/CMC/ZnS/NiO nanocomposite blends was examined. The optical band gap energies were decreased from (direct, indirect: 5.31, 5.06) eV for undoped blends to 4.38 and 3.34 eV for the blends doped with the highest concentration of MWCNTs (0.15 wt%). The refractive indices of the various blends were calculated based on the obtained optical band gap energies using various models. The effect of MWCNTs concentrations on the dielectric constants, energy density, electric modulus and ac conductivity at room temperature of the PVP/CMC/0.5ZnS-0.5NiO/x wt% MWCNTs samples were explored using an Inductance, L, Capacitance, C, and Resistance, R (LCR) meter bridge.

Impact of Atomic Vacancy Defects on Vibrational Characteristics of Chiral MWCNT for Viruses/Bacteria

In this study the authors investigated the vibrations performance of chiral multi-walled carbon nanotubes (MWCNTs). They examined chiral MWCNTs with attached bacteria positioned at both the tip and middle sections of the nanotubes. The main goal of this research was to create a sensor with the ability to detect and distinguish bacteria or viruses that could potentially adhere to the surfaces of chiral MWCNTs. The authors considered two boundary conditions, fixed-fixed and fixed -free for the chiral MWCNT. They utilized a molecular structural mechanics approach. In this approach the vibrational responses of chiral MWCNT-based nano-biosensors with different diameters of the chiral MWCNTs were examined. The study’s objective was to fill research gaps by introducing an innovative approach for detecting defects in chiral MWCNTs through vibrational analysis. They simulated 432 MWCNT samples to investigate the vibrational performance of defective chiral MWCNTs. The results suggested that the first mode of the vibrational frequency of the chiral MWCNT is particularly significant for sensing applications. It was observed that as the percentage of vacancy defects increased, the natural frequency decreased for both boundary conditions.

Chemically doped, purified bulk multi-walled carbon nanotube conductors with enhanced AC conductivity to 40 GHz

Metals used in radio frequency (RF) communications technologies degrade in alternating current (AC) conductivity with frequency due to the skin effect. Bulk carbon nanotube (CNT) materials have demonstrated favorable trends such as constant or increasing AC conductivity, and are emerging as potential alternative conductors. However, the resistive inter-CNT junctions present in these bulk assemblies limit overall conductivity. In this work, a waveguide-based transmission technique is used to measure the AC conductivity from 10 to 40 GHz of a commercial multi-walled CNT (MWCNT) material modified by purification to remove carbon and iron impurities, and by chemical doping with potassium tetrabromoaurate (KAuBr4). Iron impurity removal yields a frequency-independent real AC conductivity. Laser thinning and solvent plying are employed to change transmission by altering the MWCNT sheet thickness, thus enabling accurate measurement of the KAuBr4-doped MWCNT samples. Doping of the purified MWCNTs yields enhanced real AC conductivity of ∼160 kS/m, which remains constant with frequency to 40 GHz and represents a 5–6 × improvement over the as-received material at 40 GHz. KAuBr4 doping is hypothesized to enhance AC conductivity by increasing carrier density, supported by the elevated plasma frequency determined from fitting of a generalized Drude conduction model to the AC conductivity data.

Impact of biogenic impurities on catalytic synthesis of multi-walled carbon nanotubes and hydrogen from polyolefin resins

Biogenic impurities are common contaminants of plastic waste. This study investigated the effects of biogenic impurities on the conversion of a polyolefin mixture (6 wt% low-density polyethylene, 24 wt% high-density polyethylene, and 70 wt% polypropylene) into multi-walled carbon nanotubes (MWCNTs) and hydrogen via pyrolysis-chemical vapor deposition (CVD). Biogenic components from diverse sources were added to the polyolefin mixture, including lignocellulosic materials (pine sawdust, coconut coir pith), biosolids from wastewater treatment (municipal sewage sludge), animal-based waste (crustaceans), and bio-based plastic (polylactic acid). At contamination levels up to 9.1 wt%, 3 out of 5 impurities (coconut coir pith, sewage sludge and crustaceans) caused a decline in the conversion efficiency of feedstock into MWCNTs (33 ± 7% for polyolefins only compared with 20 ± 6%, 16 ± 1% and 16 ± 2% for polyolefins with 9.1 wt% coconut coir pith, sewage sludge and crustaceans, respectively). According to gas analysis, impurities led to a loss of catalyst activity, resulting in a decreased concentration of H2 and increased concentrations of methane and ethylene in the CVD gas. Furthermore, for polyolefins containing 9.1 wt% coconut coir pith, sewage sludge, crustaceans and polylactic acid, microscopy data revealed changes in the growth of filamentous carbon, leading to the appearance of carbon nanofibers in MWCNT samples. On the contrary, biogenic impurities barely changed outer diameters, ID/IG ratios, interlayer spacing, crystallite sizes of graphite-like sites, and the surface chemistry of MWCNT samples. The results suggest the development of quality management system for contaminated plastic feedstock could be advantageous to ensure consistent outcomes of pyrolysis-CVD process.

Multifunctionality of MWCNT and TiC hybrid filler silicone composite for energy harvesting and strain sensing

AbstractThe flexible silicone elastomer‐conductive composite was developed with enhanced energy harvesting and strain sensing. A hybrid nanofiller system with multi‐walled carbon nanotubes (MWCNTs) and titanium (IV) carbide (TiC) was used as reinforcing agents for the elastomer. The 4 MWCNT +5 TiC composite has 1.34 MPa tensile strength, 136.85% higher than unfilled silicone rubber (SR) matrix. The unfilled sample has a 1.558 MPa compressive modulus, while 4 MWCNT +5 TiC has 3.87 MPa. The machine and finger presses were utilized to test the energy harvesting of the composite. With greater cyclic stability, the 4 MWCNT +5 TiC sample performed exceptionally well in the machine press in the output voltage range of around 120 mV. Among the thumb presses, 2 MWCNT +5 TiC yielded the best results, with a voltage of about 100 mV. The 3 MWCNT +5 TiC sample produced 9044% more energy than the single filler 3 phr MWCNT sample from our previous work. Higher MWCNT content enhanced composite stiffness, making finger pressing harder and decreasing energy output. The strain sensing test on the 4 MWCNT +5 TiC composite showed high gauge factors (GF = 7.532 and 23.944) and good linearity (R2 = 0.909 and 0.939) over a strain range of Δε = 0%–14% and 14%–22%. Silicone composites' mechanical, energy harvesting, and strain sensing performance improved greatly with the MWCNT and TiC hybrid fillers. These composites could be used in self‐powered wearable electronics, machine or structural deformation monitoring, and human motion sensing.Highlights A stretchable device was developed with improved energy harvesting and strain sensing. Rubber composites were fabricated from MWCNTs, TiC hybrid fillers, and SR matrix. The energy harvesting was 9044% higher for hybrid filler compared to MWCNT as the only filler. Robust strain sensing properties with a gauge factor of 23.9, linearity of 0.91, and relaxation time of 0.1 s. The final composites are useful for self‐powered wearable electronics, health monitoring, and human motion sensing.

Structural transformation of Cu-coated multi-walled carbon nanotubes subjected to high-energy laser irradiation

The Cu coating on carbon nanotubes (CNTs) with low infrared laser absorptivity was applied to provide a protective layer against the structural damage caused by laser irradiation in this paper. The effect of Cu coating on the structural evolution of multi-walled carbon nanotubes (MWCNTs) under a ring-shaped high-energy laser beam was studied. As the laser power increases, the morphology of 35 wt.% Cu-coated MWCNTs (35Cu-CNTs) samples transforms from discrete fine powder particles to caking structure with a roughened surface. A 45 wt.% Cu coating effectively provides structural protection for MWCNTs against laser-induced damage at a laser power of 600 W. During laser irradiation, the Cu coating melts, detaches from the surface of MWCNTs, and subsequently solidifies into a mixture of nearly spherical particles. Without the protection of Cu coating, the MWCNTs bundles are fragmented into nanoscale segments in varying sizes. These segments undergo a transformation into amorphous carbon particles as a result of the rapid heating and cooling process induced by the high-energy laser irradiation. The thermal impact of the high-energy laser beam plays a crucial role in determining the structural transformation of MWCNTs. The coalescence and spheroidization of amorphous carbon particles can be induced by the reduction of surface energy.

Differential multi-probe thermal transport measurements of multi-walled carbon nanotubes grown by chemical vapor deposition

Carbon nanotubes (CNTs) are quasi-one dimensional nanostructures that display both high thermal conductivity for potential thermal management applications and intriguing low-dimensional phonon transport phenomena. In comparison to the advances made in the theoretical calculation of the lattice thermal conductivity of CNTs, thermal transport measurements of CNTs have been limited by either the poor temperature sensitivity of Raman thermometry technique or the presence of contact thermal resistance errors in sensitive two-probe resistance thermometry measurements. Here we report advances in a multi-probe measurement of the intrinsic thermal conductivity of individual multi-walled CNT samples that are transferred from the growth substrate onto the measurement device. The sample-thermometer thermal interface resistance is directly measured by this multi-probe method and used to model the temperature distribution along the contacted sample segment. The detailed temperature profile helps to eliminate the contact thermal resistance error in the obtained thermal conductivity of the suspended sample segment. A differential electro-thermal bridge measurement method is established to enhance the signal-to-noise ratio and reduce the measurement uncertainty by over 40%. The obtained thermal resistances of multiple suspended segments of the same MWCNT samples increase nearly linearly with increasing length, revealing diffusive phonon transport as a result of phonon-defect scattering in these MWCNT samples. The measured thermal conductivity increases with temperature and reaches up to 390 ± 20 W m−1 K−1 at room temperature for a 9-walled MWCNT. Theoretical analysis of the measurement results suggests submicron phonon mean free paths due to extrinsic phonon scattering by extended defects such as grain boundaries. The obtained thermal conductivity is decreased by a factor of 3 upon electron beam damage and surface contamination of the CNT sample.

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.

The influence of water absorption on reinforced polymers (FRP) using MWCNT and HGB

In the current paper, different MWCNTs filler amounts, containing PA6 and HGBs were prepared by injection moulded. The water uptake at saturation, normalized to the polyamide mass, decreases; hence the diffusion rate in both MWCNTs is slower, respectively HGBs which is faster. Injected moulded polymer samples can take less (6%) water uptake than neat polymer granules (11%). The addition of 15 wt% of multi-walled carbon nanotubes (sample 3) led to a minimum water absorption rate of 5%; this value is 15% less than the majority of the polymer composite mixtures and 1% less than pure PA6, mainly because other polymer composites which contained the HGB filler, absorbed more water. The best results highlight the improved water resistance of polyamide composite (sample 3), which reduces the impact of water on the component and expresses better applicability in the water environment than other polymer composites or even pure PA6.

Annealing effect on the thermoelectric properties of multiwall carbon nanotubes

In this article, it is demonstrated that transport properties and thus thermoelectric performance of multiwall carbon nanotubes (MWCNTs) can be enhanced significantly by annealing. Two different samples of MWCNTs with small and large diameters were investigated. The as-prepared MWCNT samples were treated at different conditions of annealing. The pristine and annealed MWCNTs were investigated using x-ray diffraction, Raman spectroscopy and scanning electron microscope in order to investigate the microstructure, defect content and morphology before and after the annealing process. The electrical conductivity, Seebeck coefficient and thermal conductivity were measured over the temperature range of (300–450 K) and were found to correlate with the tube diameter and the annealing conditions. The electrical conductivity and Seebeck coefficient measurements show that the conduction mechanism in MWCNTs is thermal activation as the samples have degenerate semiconductor-like behavior. Upon annealing, the Seebeck coefficient increases, followed by a reduction in the thermal conductivity. The thermoelectric power factor was enhanced by annealing to realize the highest value of 1.06 μW m −1 K −2 at 475 K for the sample with the larger diameter. The thermoelectric figure of merit ZT was calculated to determine the performance of the materials. ZT of the sample of the larger tube's diameter was enhanced by about 247% at 450 K. • Pristine and annealed MWCNTs were investigated using x-ray diffraction, Raman spectroscopy and scanning electron microscope. • Thermoelectric performance of multiwall carbon nanotubes (MWNTs) is significantly enhanced by annealing. • The thermoelectric figure of merit ZT was enhanced by about 247% at 450 K.

Effect of Multi-Walled Carbon Nanotubes (MWCNTs) in Reducing the Corrosion Rate in Cr-MWCNTs Composite Coatings

Carbon steel was coated with Cr-multi-walled carbon nanotube (MWCNTs) coatings via electrodeposition. In this article, the impact of a combination of MWCNTs into the chromium coating on the morphology of the coating surface and corrosion characteristics was inspected. The MWCNTs seem to be evenly distributed across the chromium layer, according to scanning electron microscopy (SEM). Electrochemical measurements were used to conduct corrosion tests on samples of MWCNTs– chromium composite coated and pure chromium coated samples in aqueous NaCl (3.5 wt.%). The outcomes demonstrated a considerable increase in the resistance of corrosion due to the inclusion of MWCNTs during the chromium deposition procedure. In addition, the mechanism of anti-corrosion of the composite coating is also presented. Using an electrolyte bath containing various concentrations of dispersed MWCNTs (0.5, 1, and 1.5 g/L), crack-free and compact coating of Cr-MWCNT composite were electrodeposited on the substrates of the mild steel. The potentiodynamic polarization technique was used to examine the coatings corrosion performance subjected to a 3.5 weight percent of NaCl medium. When compared to chromium coating, the Cr-MWCNT composite coating showed the lowest corrosion rate (1.045x108 mpy) compared to chromium coating (4.891x108 mpy).

Physical, mechanical, and biological characterization of robocasted carbon nanotube reinforced microwave sintered calcium phosphate scaffolds for bone tissue engineering

This study analyses the influence of the addition of Multi Walled Carbon Nanotubes (MWCNT) on the physical, mechanical, and biological behaviour of Calcium Phosphate (CP) bone scaffolds developed using the robocasting technique for bone regeneration. Three different mass percentages (0.5, 1, and 2 wt%) of MWCNT are added to the CP powder and a slurry is prepared using a CMC binder for printing the scaffolds. The scaffolds were printed in 2 infill ratios, 50 and 100%, and were sintered under an inert atmosphere in a microwave furnace which was then taken for various characterization studies. Physical characterisation studies revealed that the shrinkage rate of scaffolds is very low compared to other additive manufacturing techniques. The incorporation of 0.5 wt% of MWCNT produced the best results in mechanical characterization studies with a compressive strength of 10.38 MPa and 11.89 MPa for 50% and 100% infill ratios respectively. In Vitro Biocompatibility studies also proved that 0.5 wt% MWCNT samples are the most suitable for cell growth while the hemocompatibility tests showed that the samples are blood compatible. . The 100% infill samples fared better than the 50% samples in physical and mechanical properties. The results suggest that the MWCNT incorporated CP scaffolds can be used to treat critical size bone defects.

Fe-CONTAINING CARBON NANOTUBES AS CATALYSTS IN THE AEROBIC OXIDATION REACTIONS OF DECALIN AND TETRADECANE

This article studies the catalytic activity of multi-walled carbon nanotubes (MWCNTs) in the oxidation reactions of aliphatic and polycyclic hydrocarbons is studied. In order to determine the catalytic activity, MWCNTs catalysts containing 22.8% Fe each were used. Catalyst samples were synthesized from propane gas under optimal conditions determined by CVD method. The experiments were performed at 5 different temperatures (60, 80, 100, 120, 1400C) for 2 hours. No significant change in the oxidation reaction of both hydrocarbons was observed at relatively low temperatures. In the oxidation of decalin, when the reaction temperature rises to 1200C and 1400C, oxidation has already taken place, and the rate of the reaction is directly proportional to the increase in temperature. The same trend can be seen in the oxidation reaction of tetradecane at MWCNTs with temperatures of 120 and 1400C. However, unlike decalin, the MWCNTs sample in tetradecane oxidation showed optimal catalytic performance at 1200C. However, at these temperatures, where oxidation occurs, the oxidation of decalin and tetradecane in an environment without a catalyst is almost non-existent

Tuning surface composition of multiwalled carbon nanotubes supported Pt-Co bimetallic nanoparticles for boosting methanol oxidation catalysis

Developing catalysts with high performance and low cost for methanol oxidation reaction (MOR) is the key to promoting the industrialization of direct methanol fuel cells (DMFCs). In this work, multiwalled carbon nanotubes (MWCNTs) supported PtCo alloys catalysts with improved MOR properties and anti-CO poisoning ability are successfully prepared by integrating low temperature adsorption and high temperature reduction method. The Pt1Co3@NC/MWCNTs sample with moderate Co2+ feeding content (0.81 mA/ugPt) achieves a factor of 1.93 enhancement in MOR mass activity compared to the commercial Pt/C catalyst (0.42 mA/ugPt). In addition, the Pt1Co3@NC/MWCNTs sample displays a lower CO oxidation onset potential respect to pristine Pt/C catalyst (0.74 V vs. 0.82 V). Scuh improvement of MOR activity, durability and anti-CO poisoning ability of the Pt1Co3@NC/MWCNTs catalyst is ascribed to the moderate surface compositions, optimal electronic interaction between PtCo alloys and MWCNTs, and the protection of N-doped carbon (NC) shells. This study provides a new direction to decrease the utilization of platinum and improve the MOR activity, stability and anti-CO poisoning ability of electrocatalysts which will be potential in design and fabrication of the highly efficient electrocatalysts for DMFCs applications.

Flexible Electromagnetic Shielding Material Using Multi-Walled Carbon Nanotube Coated Cotton Fabric

The present work focuses on the development of cotton fabric with multi-walled carbon nanotube coating (CMC) through a dip and dry process. The influence of multi-walled carbon nanotubes (MWCNTs) concentration on transmission, reflection, and absorption properties, which leads to an estimation of electromagnetic interference (EMI) shielding, was also studied. The merits of MWCNTs coating on the cotton fabric were evaluated using field-emission scanning electron microscopy (FESEM), thermogravimetric analysis (TGA), and surface resistivity. The Fourier transform infrared (FTIR) spectroscopy result supports the bonding between MWCNTs and cotton fabric. The significant increase of 98.9% of EMI shielding for the highest MWCNTs weight percentage (22.23 wt%) was attributed due to the well-interconnected network of MWCNTs. The shielding mechanism in the high wt% MWCNTs samples is dominated by both reflection and absorption properties.

Mori-Tanaka-based statistical methodology to compute the effective Young modulus of polymer matrix nano-composites considering the experimental quantification of nanotubes dispersion and alignment degree

This paper presents a Mori-Tanaka-based statistical methodology to predict the effective Young modulus of carbon nanotubes (CNTs)-reinforced composites considering three variables: weight content, reinforcement dispersion and orientation. Last two variables are quantified by two parameters, namely, free-path distance between nano-reinforcements and orientation angle regarding the loading direction. To validate the present methodology, samples of multi-walled CNTs (MWCNTs)-reinforced polyvinyl alcohol (PVA)-matrix composite were manufactured by mixing solution. The MWCNT/PVA Young modulus was measured by nano-indentation, while the MWCNTs Young modulus was quantified by micro-Raman spectroscopy. Both stretched and unstretched composite specimens were fabricated. Transmission electron microscopy (TEM) and in-plane image analysis were used to obtain fitting coefficients of log-normal frequency distribution functions for the free-path distance and orientation angle. It was evidenced that numerical results fit well to measured values of effective Young modulus of MWCNTs and MWCNT/PVA, with exception of some particular cases where significant differences were found. Microstructural heterogeneities, cluster formation, polymer chains alignment, errors associated with the dispersion, orientation and mechanical characterization procedures, as well as idealization and statistical errors, were identified as possible causes of these differences. Finally, using the proposed methodology and the dispersion and orientation distribution functions experimentally obtained, the effective Young modulus is estimated for three kinds of thermoplastic matrices (polyvinyl alcohol, polyethylene ketone, and ultra-high molecular weight polyethylene) with different kinds of nanotubes (single wall, double wall, and multi-walled), at different weight contents, finding the superior mechanical performance for double-walled CNTs-reinforced composites and the lower one for multi-walled CNTs-reinforced ones.

Synthesis and characterization of catalytic CVD growth pristine and functionalized MWCNT

The catalyzed CVD method is considered significant for the production of low cost and high yield carbon nanostructures. In this study, multiwall carbon nanotubes (MWCNTs) were synthesized using a facile and efficient way with the modified CVD method, using Co nanoparticles as the metallic catalysis for MWCNT growth, in a distinct temperature range of 650–750 °C. The structural and magnetic properties of pristine and functionalized MWCNT (p-MWCNT and f-MWCNT) are investigated in the temperature range of 10–300 K. The phase structure of all MWCNT samples was analyzed using various characterization techniques, namely, x-ray diffraction, Raman, and x-ray photoelectron spectroscopy. Scanning electron microscopy and particle size analysis suggested that the diameter of MWCNTs increases with a rise in the growth temperature, but the nanotube density decreases at 750 °C. Temperature-dependent magnetization studies of the p-MWCNT and f-MWCNT samples were investigated using a quantum design physical property measurement system-vibrating sample magnetometer mode. The magnetic properties and the effect of the growth temperature and acid functionalization on the morphology of MWCNT were also investigated. The results revealed that the diamagnetism effect of the graphitic nanotubes is dominating for p-MWCNT, and it reduces for f-MWCNT. A possible explanation for this feature is discussed in detail in the later part of this article. It may be considered that this study, which emerged with different growth temperatures of MWCNTs using a facile method for gaining control over magnetic properties, can be fundamental for further consideration of magnetic MWCNTs for various potential applications.

Synthesis and study of polyaniline/MWCNT composite for optoelectronic application

In this study, the effect of multi-walled carbon nanotubes (MWCNTs) addition on optical bandgap of polyaniline (PANI) was reported. Pure PANI and 5 mg MWCNTs/PANI, 10 mg MWCNTs/PANI and 15 mg MWCNTs/PANI composite samples were synthesized by in-situ polymerization process. Synthesized composite sample and pure PANI sample were characterized by X-ray diffraction, scanning electron microscopy, Fourier transform-infrared and UV–visible spectroscopy. Optical bandgap, molar absorptivity coefficient are estimated for pristine MWCNTs sample, pure PANI sample and composite samples using UV–visible spectroscopy data and Tauc plot. It is observed that optical bandgap of PANI decreases on increasing the concentration of MWCNTs, while keeping the concentration of PANI constant. Lowest bandgap of 3.55 eV is obtained for 15 mg MWCNTs/PANI composite sample. Strong interaction between π-bonded surface of MWCNTs and quinoid rings of PANI is found, as indicated by the obtained results of FTIR and UV–visible spectroscopy. The information on the optical bandgap of the composite samples is of great importance for the development of optical antenna and other optoelectronic devices.

Femtosecond pulsed laser microscopy: a new tool to assess the in vitro delivered dose of carbon nanotubes in cell culture experiments

BackgroundIn vitro models are widely used in nanotoxicology. In these assays, a careful documentation of the fraction of nanomaterials that reaches the cells, i.e. the in vitro delivered dose, is a critical element for the interpretation of the data. The in vitro delivered dose can be measured by quantifying the amount of material in contact with the cells, or can be estimated by applying particokinetic models. For carbon nanotubes (CNTs), the determination of the in vitro delivered dose is not evident because their quantification in biological matrices is difficult, and particokinetic models are not adapted to high aspect ratio materials. Here, we applied a rapid and direct approach, based on femtosecond pulsed laser microscopy (FPLM), to assess the in vitro delivered dose of multi-walled CNTs (MWCNTs).Methods and resultsWe incubated mouse lung fibroblasts (MLg) and differentiated human monocytic cells (THP-1) in 96-well plates for 24 h with a set of different MWCNTs. The cytotoxic response to the MWCNTs was evaluated using the WST-1 assay in both cell lines, and the pro-inflammatory response was determined by measuring the release of IL-1β by THP-1 cells. Contrasting cell responses were observed across the MWCNTs. The sedimentation rate of the different MWCNTs was assessed by monitoring turbidity decay with time in cell culture medium. These turbidity measurements revealed some differences among the MWCNT samples which, however, did not parallel the contrasting cell responses. FPLM measurements in cell culture wells revealed that the in vitro delivered MWCNT dose did not parallel sedimentation data, and suggested that cultured cells contributed to set up the delivered dose. The FPLM data allowed, for each MWCNT sample, an adjustment of the measured cytotoxicity and IL-1β responses to the delivered doses. This adjusted in vitro activity led to another toxicity ranking of the MWCNT samples as compared to the unadjusted activities. In macrophages, this adjusted ranking was consistent with existing knowledge on the impact of surface MWCNT functionalization on cytotoxicity, and might better reflect the intrinsic activity of the MWCNT samples.ConclusionThe present study further highlights the need to estimate the in vitro delivered dose in cell culture experiments with nanomaterials. The FPLM measurement of the in vitro delivered dose of MWCNTs can enrich experimental results, and may refine our understanding of their interactions with cells.

Improved CO2 adsorption properties through amine functionalization of multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNT) with different functionalities (standard–; OH–; and COOH– functionalized) are chemically modified with N1-(3-trimethoxysilylpropyl)diethylenetriamine (DETASi) aiming to enhance their CO2 adsorption/separation properties. The grafting of the DETASi groups to the surface of the MWCNT samples is studied by X-ray photoelectron spectroscopy (XPS), operando thermogravimetric analysis - infrared spectroscopy (TGA-IR), –196 °C N2-sorption isotherms, and scanning electron microscopy (SEM). A comprehensive overview of the reaction mechanism and samples structure/composition is provided. It was found that the aforementioned functionalities highly influence the physical–chemical and the textural properties of the DETASi modified-MWCNT materials, impacting in the DETASi functionalization degree and its distribution on the sample. Amount (by TGA-IR) and homogeneity (by SEM) of the organosilicon group in the functionalized samples increases with the increase of the functionalities in the parent MWCNT materials. Standard-MWCNT and OH– functionalized MWCNT showed to be unable to adsorb CO2, while COOH– modified MWCNT adsorbed just 0.1% at 1 bar and 30 °C. At the same adsorption conditions, DETASi modification of the MWCNT materials enhanced the CO2 adsorption capacity, with the maximum CO2 uptake (2.11%) for COOH-MWCNT functionalized with DETASi. The selectivity for CO2/N2 separation was also improved after DETASi grafting reaction, with the highest value (1.89%) observed for the standard-MWCNT material modified with DETASi. In general, the increase of the DETASi amount and of the microporosity in the functionalized MWCNT sorbents is accompanied by an improvement of the CO2 adsorption-separation properties. The water vapor adsorption indicated that the standard-MWCNT sample modified with DETASi is resistant to the presence of water and its presence (water vapor of ~3.2 kPa) can improve the CO2 uptake.