Sulfonitric Treatment of Multiwalled Carbon Nanotubes and Their Dispersibility in Water

Wireless Alerts and Data Monitoring from BNNO-MWCNTs/PDMS Composite Film-Based TENG Integrated Inhaler for Smart Healthcare Application

In recent years, the implementation of energy-harvesting technology in medical equipment has attracted significant interest owing to its potential for self-powered and smart healthcare systems. Herein, the integration of a triboelectric nanogenerator (TENG) is proposed into an inhaler for energy-harvesting and smart inhalation monitoring. For this initially, barium sodium niobium oxide (Ba2NaNb5O15) microparticles (BNNO MPs) are synthesized via a facile solid-state synthesis process. The BNNO MPs with ferroelectricity and high dielectric constant are incorporated into polydimethylsiloxane (PDMS) polymer to make BNNO/PDMS composite films (CFs) for TENG fabrication. The fabricated TENG is operated in a contact-separation mode, and its electrical output performance is compared to establish the optimal BNNO MPs concentration. Furthermore, multi-wall carbon nanotubes (MWCNTs), a conductive filler material, are used to enhance the electrical conductivity of the CFs, thereby improving the electrical output performance of the TENG. The robustness/durability of the proposed BNNO-MWCNTs/PDMS CF-based TENG are investigated. The proposed TENG device is demonstrated to harvest electrical energy from mechanical motions via regular human activities and power portable electronics. The TENG is integrated into the inhaler casing to count the number of sprays remaining in the canister, send the notification to a smartphone via Bluetooth, and harvest energy.

Promoting Effect of Ball Milling on the Functionalization and Catalytic Performance of Carbon Nanotubes in Glycerol Etherification

A facile and eco-friendly approach using in situ-generated 4-benzenediazonium sulfonate (BDS) was applied to prepare highly functionalized carbon nanotubes (CNTs). The effectiveness of this functionalization was additionally enhanced by a green and short-time ball milling process applied beforehand. The obtained BDS-modified CNTs presented significant activity in glycerol etherification, producing tert-butyl glycerol ethers, which are considered promising fuel additives. Excellent results of ~56% glycerol conversion and ~10% yield of higher-substituted tert-butyl glycerol ethers were obtained within just 1 h of reaction at 120 °C using a low catalyst loading of only 2.5 wt.%. Furthermore, the sulfonated CNTs were reusable over several reaction cycles, with only a minor decrease in activity. Additionally, the sample activity could be restored by a simple regeneration approach. Finally, a clear correlation was found between the content of -SO3H groups on the surface of CNTs and the catalytic performances of these materials in glycerol etherification. Improved interaction between functionalized ball-milled CNTs and the reactants was also suggested to positively affect the activity of these catalysts in the tested process.

Treatment of Multi-Walled Carbon Nanotubes with Dichromic Acid: Oxidation and Appearance of Intercalation

This work is dedicated to the study of the treatment of multi-walled carbon nanotubes (MWCNTs) with dichromic acid. The dichromic acid was formed by dissolving different concentrations of CrO3 in water. The effect of the concentration of dichromic acid on the change in texture characteristics, elemental composition, defectiveness, graphitization degree, and surface chemistry of MWCNTs was investigated using various analytical techniques, such as transmission electron microscopy, energy-dispersive X-ray spectroscopy (EDX), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction, and X-ray photoelectron spectroscopy (XPS). Testing of MWCNTs as electrodes for supercapacitors in 3.5 M H2SO4 solution was carried out using cyclic voltammetry. A decrease in the average diameter of CNTs after treatment was found. The EDX and XPS showed that the oxygen content on the surface of MWCNTs increased after treatment with dichromic acid. The formation of Cr2O3 after treatment with dichromic acid was detected by XPS. High angle annular dark field scanning transmission electron microscopy was used to confirm the intercalation of the chromium-containing compound between graphene layers of MWCNTs after treatment with dichromic acid. It was found that two different types of MWCNTs showed diverse behavior after treatment. The highest specific capacitance of the MWCNTs after treatment was 141 F g-1 (at 2 mV s-1) compared to 0.3 F g-1 for the untreated sample.

Effect of Surface Modification on Structural and Thermal Properties of Nanocarbons of Different Dimensionalities

Multi-walled carbon nanotubes and graphite nanoplatelets were functionalized via acid treatment to overcome the problem of agglomeration. Fourier transform infrared spectroscopy showed the chemical modification of the nanocarbons while the general relationship between the chemical treatment and the defects population was analyzed by Raman spectroscopy. The information regarding the mass loss and impurities is obtained from the thermogravimetric analysis. X-ray diffraction showed the effect of acid treatment on the physical states of the nanocarbons including the crystalline texture. The comparative high interlayer distance in graphite suggested that graphite particles are exfoliated into sheets of graphene by this technique with smaller particle sizes. The thermogravimetric analysis confirmed the complete removal of impurities in the case of multi-walled carbon nanotubes (MWCNTs) and about 20 % of impurities as seen in oxidized graphite attributable to the presence of residual manganese that might have been introduced during the functionalization process. Moreover, the thermal stability was also observed well in the case of MWCNTs with lesser impurities left. Overall, two different nanocarbons with well-structured chemical modifications were obtained with a variation in the feasibility of functionalization.

Surface-Oxidised Carbon Nanofibre-Based Nanofluids: Structural, Morphological, Stability and Thermal Properties

The reputation of nanofluids as a convenient heat transfer media has grown in recent years. The synthesis of nanofluids is often challenging, particularly carbon-based nanofluids, due to the rapid agglomeration of the nanoparticles and the instability of the nanofluids. In this regard, surface modification and surfactant addition are potential approaches to improve the physical and thermal properties of carbon-based nanofluids that have been studied and the structural, morphological, and thermal characteristics of surface-oxidised carbon nanofibre (CNF)-based nanofluids has been characterised. Commercial CNF was first subjected to three different acid treatments to introduce surface oxygen functional groups on the CNF surface. Following the physical and thermal characterisation of the three surface-oxidised CNFs (CNF-MA, CNF-MB, and CNF-MC), including Raman spectroscopy, Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and field emission scanning electron microscopy (FESEM), the CNF-MB was selected as the best method to synthesise the surface-oxidised CNF-based nanofluid. A total of 40 mL of ultrapure water was used as a pure base fluid and mixed with the surface-oxidised CNF at a concentration range of 0.1-1.0 wt.%, with a fixed of 10 wt.% amount of polyvinylpyrrolidone (PVP). The thermal conductivity of CNF-based nanofluid was then characterised at different temperatures (6, 25, and 40 °C). Based on the results, surface oxidation via Method B significantly affected the extent of surface defects and effectively enhanced the group functionality on the CNF surface. Aside from the partially defective and rough surface of CNF-MB surfaces from the FESEM analysis, the presence of surface oxygen functional groups on the CNF wall was confirmed via the Raman analysis, TGA curve, and FTIR analysis. The visual sedimentation observation also showed that the surface-oxidised CNF particles remained dispersed in the nanofluid due to the weakened van der Waals interaction. The dispersion of CNF particles was improved by the presence of PVP, which further stabilised the CNF-based nanofluids. Ultimately, the thermal conductivity of the surface-oxidised CNF-based nanofluid with PVP was significantly improved with the highest enhancement percentage of 18.50, 16.84, and 19.83% at 6, 25, and 40 °C, respectively, at an optimum CNF concentration of 0.7 wt.%.

Plasma Functionalization of Multi-Walled Carbon Nanotubes for Ammonia Gas Sensors

The role of plasma functionalization of multi-walled carbon nanotubes (MWCNTs) for room-temperature ammonia gas sensors was investigated. Plasma functionalization of MWCNTs with maleic anhydride was carried out at various durations. The active material of the gas sensor was investigated by scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, and X-ray photoelectron spectroscopy. It was shown that the formation of functional groups on the surface of carbon nanotubes led to an increase in the ammonia sensor response by two to four times. The increase in functionalization duration induced the rise of O/C from 0.28 to 0.335, an increase in sensor resistance, and the distortion of the shape of the I-V curves.

Mechanical Properties and Characterization of Epoxy Composites Containing Highly Entangled As-Received and Acid Treated Carbon Nanotubes

Huntsman–Merrimack MIRALON^® carbon nanotubes (CNTs) are a novel, highly entangled, commercially available, and scalable format of nanotubes. As-received and acid-treated CNTs were added to aerospace grade epoxy (CYCOM^® 977-3), and the composites were characterized. The epoxy resin is expected to infiltrate the network of the CNTs and could improve mechanical properties. Epoxy composites were tested for flexural and viscoelastic properties and the as-received and acid treated CNTs were characterized using Field-Emission Scanning and Transmission Electron Microscopy, X-Ray Photoelectron Spectroscopy, and Thermogravimetric Analysis. Composites containing 0.4 wt% as-received CNTs showed an increase in flexural strength, from 136.9 MPa for neat epoxy to 147.5 MPa. In addition, the flexural modulus increased from 3.88 GPa for the neat epoxy to 4.24 GPa and 4.49 GPa for the 2.0 wt% and 3.0 wt% as-received CNT/epoxy composites, respectively. FE-SEM micrographs indicated good dispersion of the CNTs in the as-received CNT/epoxy composites and the 10 M nitric acid 6 h treatment at 120 °C CNT/epoxy composites. CNTs treated with 10 M nitric acid for 6 h at 120 °C added oxygen containing functional groups (C–O, C=O, and O=C–O) and removed iron catalyst present on the as-received CNTs, but the flexural properties were not improved compared to the as-received CNT/epoxy composites.

The Importance of Evaluating the Lot-to-Lot Batch Consistency of Commercial Multi-Walled Carbon Nanotube Products

The biological response of multi-walled carbon nanotubes (MWNTs) is related to their physicochemical properties and a thorough MWNT characterization should accompany an assessment of their biological activity, including their potential toxicity. Beyond characterizing the physicochemical properties of MWNTs from different sources or manufacturers, it is also important to characterize different production lots of the same MWNT product from the same vendor (i.e., lot-to-lot batch consistency). Herein, we present a comprehensive physicochemical characterization of two lots of commercial pristine MWNTs (pMWNTs) and carboxylated MWNTs (cMWNTs) used to study the response of mammalian macrophages to MWNTs. There were many similarities between the physicochemical properties of the two lots of cMWNTs and neither significantly diminished the 24-h proliferation of RAW 264.7 macrophages up to the highest concentration tested (200 μg cMWNTs/mL). Conversely, several physicochemical properties of the two lots of pMWNTs were different; notably, the newer lot of pMWNTs displayed less oxidative stability, a higher defect density, and a smaller amount of surface oxygen species relative to the original lot. Furthermore, a 72-h half maximal inhibitory concentration (IC-50) of ~90 µg pMWNTs/mL was determined for RAW 264.7 cells with the new lot of pMWNTs. These results demonstrate that subtle physicochemical differences can lead to significantly dissimilar cellular responses, and that production-lot consistency must be considered when assessing the toxicity of MWNTs.

Synthesis of oxygen functionalized carbon nanotubes and their application for selective catalytic reduction of NO x with NH3

Oxygen functionalized carbon nanotubes synthesized by surface acid treatment were used to improve the dispersion properties of active materials for catalysis. Carbon nanotubes have gained attention as a support for active materials due to their high specific surface areas (400-700 m2 g-1) and chemical stability. However, the lack of surface functionality causes poor dispersion of active materials on carbon nanotube supports. In this study, oxygen functional groups were prepared on the surface of carbon nanotubes as anchoring sites for decoration with catalytic nanoparticles. The oxygen functional groups were prepared through a chemical acid treatment using sulfuric acid and nitric acid, and the amount of functional groups was controlled by the reaction time. Vanadium, tungsten, and titanium oxides as catalytic materials were dispersed using an impregnation method on the synthesized carbon nanotube surfaces. Due to the high density of oxygen functional groups, the catalytic nanoparticles were well dispersed and reduced in size on the surface of the carbon nanotube supports. The selective catalytic reduction catalyst with the oxygen functionalized carbon nanotube support exhibited enhanced NO x removal efficiency of over 90% at 350-380 °C which is the general operating temperature range of catalysis in power plants.

Compressive Strength Prediction of PVA Fiber-Reinforced Cementitious Composites Containing Nano-SiO2 Using BP Neural Network

In this study, a method to optimize the mixing proportion of polyvinyl alcohol (PVA) fiber-reinforced cementitious composites and improve its compressive strength based on the Levenberg-Marquardt backpropagation (BP) neural network algorithm and genetic algorithm is proposed by adopting a three-layer neural network (TLNN) as a model and the genetic algorithm as an optimization tool. A TLNN was established to implement the complicated nonlinear relationship between the input (factors affecting the compressive strength of cementitious composite) and output (compressive strength). An orthogonal experiment was conducted to optimize the parameters of the BP neural network. Subsequently, the optimal BP neural network model was obtained. The genetic algorithm was used to obtain the optimum mix proportion of the cementitious composite. The optimization results were predicted by the trained neural network and verified. Mathematical calculations indicated that the BP neural network can precisely and practically demonstrate the nonlinear relationship between the cementitious composite and its mixture proportion and predict the compressive strength. The optimal mixing proportion of the PVA fiber-reinforced cementitious composites containing nano-SiO₂ was obtained. The results indicate that the method used in this study can effectively predict and optimize the compressive strength of PVA fiber-reinforced cementitious composites containing nano-SiO₂.