Pristine Multi-walled Carbon Nanotubes Research Articles

A Core-Shell MWCNT-Pt Nanowire Electron Source with Anomalously Long-Term Stable Field Emission.

A hybrid core-shell structured nanowire is proposed for a long-term stable electron source based on an isolated platinum/multi-walled carbon nanotube (Pt/MWCNT). This hybrid nanowire is prepared by growing a Pt shell on a metallic MWCNT through a field-emission-induced deposition (FEID) method. An in situ field emission (FE) platform was constructed inside a scanning electron microscope (SEM) equipped with two nanorobotic manipulators (NRMs) for the preparation and testing of the hybrid nanowire. An in situ fatigue test was conducted with high current intensity (500 nA) to show the influence of the Pt shell. Compared with the pristine bare MWCNT, our hybrid-nanowire-based electron source has a lifetime of hundreds of times longer and can work continuously for up to 48 h under relatively high pressure (3.6×10-3 Pa) without having an apparent change in its structure or emission currents, demonstrating good stability and tolerance to poor working conditions. The anomalous long-term stability is attributed mainly to the shielding of oxygen by Pt from the carbon shells and less heating due to the work function lowering by Pt.

Evaluation of the impact of industrial single-walled and multi-walled carbon nanotubes on human respiratory tract epithelial cells

Introduction. In the present study, a comparative assessment of the toxic effects of industrial single-walled and multi-walled carbon nanotubes (SWCNT and MWCNT) at doses corresponding to industrial exposures on BEAS-2B and A549 cells was carried out. Materials and methods. The size distribution of SWCNT and MWCNT agglomerates in dispersions was estimated by dynamic light scattering and transmission electron microscopy. Cytotoxicity was assessed using a MTS test and LDH assay. The interaction of CNTs with cells was visualized using dark-field and transmission electron microscopy. Results. Cytotoxic effects of pristine SWCNT and MWCNT in concentrations of 50-200 μg/ml and purified SWCNT in the range of 25-200 μg/ml were found in BEAS-2B cells. SWCNT and MWCNT were found to penetrate into the cytoplasm of both BEAS-2B and A549 cells, while MWCNT are more often revealed in the intracellular content as vacuolized clusters, and single SWCNT and agglomerates are visualized in the cytoplasm without a tendency to vacuolization. Limitations. CNT were introduced into cells in the form of dispersions, where both single nanotubes and their agglomerates were found. The calculation of CNT concentrations for introduction into cells was based on computer simulation. Conclusion. Further study of the mechanisms of cytotoxic and genotoxic effects of different types of carbon nanotubes (CNT) may contribute to the identification of MWCNT and SWCNT specific effects on the cells of the respiratory system to develop methodological approaches to the safe use of CNT.

The Influence of the Chemical Composition of Natural Waters about the Triclocarban Sorption on Pristine and Irradiated MWCNTs

The influence of the chemical composition of natural waters on triclocarban (TCC) sorption on pristine and irradiated multi-walled carbon nanotubes (MWCNTs) at different temperatures was studied. Natural waters have been characterized in terms of the concentrations of cations and anions, pH, and electric conductivity. The sorption process of TCC on MWCNTs is influenced by both the chemical composition of natural waters and the variation of the temperature. The adsorption capacity of TCC on pristine and irradiated MWCNTs in the studied natural waters increased by increasing the temperature. The increase of the concentration of monovalent cations (Na+ and K+) in natural waters determined a significant decrease of the adsorption capacity of TCC on both pristine and irradiated MWCNTs while the increase of the bivalent cations (Ca2+ and Mg2+) determined an easy increase adsorption capacity. Freundlich and Langmuir models were selected to describe the steady adsorption of the TCC on the pristine and irradiated MWCNTs.

Enhanced thermal conductivity of polyamide nanocomposites involving expanded graphite–carbon nanotube network structure using supercritical CO2

In this study, supercritical carbon dioxide (scCO2) was used to form a network structure of expanded graphite (EG) and multi-walled carbon nanotube (MWCNT) to achieve high thermal conductivity. Continuous processes, such as supercritical drying and rapid expansion of supercritical solutions were applied to pristine graphite and MWCNT. Polyamide 6 (PA6) nanocomposites with scCO2-treated EG and MWCNT were prepared by twin-screw extruder-based melt compounding. In the PA6 nanocomposites, the EG sheets were homogenously dispersed, while the MWCNTs were located between the EG sheets, thereby acting as a bridge for the EG. Subsequently, the 35 wt.% imbedding in PA6 nanocomposite had an effective heat transfer pathway and high thermal conductivity (2.12 W m−1 K−1). It was observed that supercritical fluid processing is a facile and effective strategy to improve the thermal conductivity of polymer nanocomposites.

Pristine, carboxylated, and hybrid multi-walled carbon nanotubes exert potent antioxidant activities in in vitro-cell free systems

Multi-walled carbon nanotubes (MWCNTs) are tubular-shaped carbon allotropes, composed of multiple concentric graphene cylinders. The extended systems of conjugated double bonds, that MWCNTs are constituted by, provide them with high electron affinities, enabling them to act as electron donors or acceptors. Consequently, their potential biomedical applications, as synthetic antioxidant agents, are of particular interest. Based on the above, the purpose of the present study was to evaluate the intrinsic antioxidant properties of pristine and carboxylated MWCNTs, as well as of novel hybrid nanocomposites of MWCNTs and inorganic nanoparticles. To this end, after the synthesis and characterization of MWCNTs, their antiradical, reducing, and antigenotoxic properties were assessed in cell-free assays, using a methodological approach that has been recently proposed by our research group. According to our results, most of the tested MWCNTs exhibited strong antioxidant activities. More elaborately, the hybrid material of MWCNTs and ferrous oxide nanoparticles, i.e., CNTs@Fe3O4, showed robust scavenging capacities in all free-radical scavenging assays examined. As regards reducing properties, the pristine MWCNTs, i.e., CNTs-Ref, exhibited the greater electron donating capacity. Finally, in terms of antigenotoxic properties, the hybrid material of MWCNTs and silicon carbide nanoparticles, i.e., CNTs@SiC, exhibited potent ability to inhibit the formation of peroxyl radicals, thus preventing from the oxidative DNA damage. Conclusively, our findings suggest that the MWCNTs of the study could be considered as promising broad-spectrum antioxidants, however, further investigations are required to evaluate their toxicological profile in cell-based and in vivo systems.

In vitro comparative cytotoxic assessment of pristine and carboxylic functionalized multiwalled carbon nanotubes on LN18 cells.

Multiwalled carbon nanotubes (MWCNTs) have been used in biomedical applications due to their ability to enter the cells. Carboxylic functionalization of MWCNT (MWCNT-COOH) is used to mitigate the toxicity of MWCNTs. Our study focuses on comparing the toxicity of MWCNT and MWCNT-COOH on the neuronal cells, LN18. Concentrations of 5, 10, 20, and 40 µg ml-1 were used for the study, and cytotoxicity was determined at 0, 1, 3, 6, 12, 24, and 48 h of incubation. Cell viability was assessed by Trypan Blue, MTT, and Live dead cell assays, and the oxidative stress produced was determined by reactive oxygen species (ROS) and Lipid peroxidation assays. MWCNT-COOH showed higher cell viability than MWCNT for 20 and 40 µg ml-1 at 24 and 48 h. This was also visually observed in the live dead cell imaging. However, at 48 h, the morphology of the cells appeared more stretched for all the concentrations of MWCNT and MWCNT-COOH in comparison to the control. A significant amount of ROS production can also be observed at the same concentration and time. Viability and oxidative stress results together revealed that MWCNT-COOH is less toxic when compared to MWCNT at longer incubation periods and higher concentrations. However, otherwise, the effect of both are comparable. A concentration of 5-10 µg ml-1 is ideal while using MWCNT and MWCNT-COOH as the toxicity is negligible. These findings can further be extended to various functionalizations of MWCNT for wider applications.

Alternative approach for highly sensitive and free-interference electrochemical dopamine sensing

In biological fluids, the concentration of dopamine (DA) provides an important information about neurodegenerative disorders such as Parkinson's disease, schizophrenia and other DA-related ailments like hyperprolactinemia. Therefore, its accurate determination is crucial for the early diagnosis and monitoring of these syndromes. Herein we report a new approach that enables highly sensitive and free-interference of DA electroanalysis. The electrocatalytic properties of silver nanoparticles (AgNPs) towards DA and their ability to limit, in-situ, the uric acid (UA) oxidation were successfully combined with the electron transfer properties of pristine MWCNTs in a nanocomposite (AgNPs@MWCNTs). This nanomaterial showed complete elimination of UA interference and enhanced electron transfer kinetics. Subsequently, AgNPs@MWCNTs properties were successfully synergized with the great ability of graphene oxide (GO) to attract DA while repelling ascorbic acid (AA) and UA via electrostatic interactions, to carry out an electrode material (GO-AgNPs@MWCNTs). AgNPs@MWCNTs were characterized by XRD, Raman spectroscopy, HR-TEM and EDX. The successful GO synthesis was confirmed by XRD, Raman spectroscopy and XPS while its exfoliation and uniform distribution of AgNPs@MWCNTs on its layer surfaces were evidenced by FE-SEM and HR-TEM. The resulting DA sensor showed high sensitivity and complete suppression of UA and AA interferences. Calibration in the concentration range of 0.5–6.5 μM in the presence of 300 μM of AA and 500 μM of UA showed a linear response (R2 = 0.99944) with a detection limit of 2.58 nM (S/N = 3). Moreover, the prepared sensor showed good repeatability, reproducibility, long-term stability and satisfactory recoveries in human serum samples.

Improving reinforcement properties of CNTs in aluminium matrix composites: a case of surface modification through AlN nano-particle grafting

This paper accentuates a newer approach to modify the surfaces of pristine multiwall carbon nanotubes (CNTs) by two-phase acid treatment, followed by silanization and grafting of functionalized AlN nano-particles onto the CNT surfaces, as a preparatory treatment before reinforcing in liquid metallurgy processed aluminium matrix composites (AMCs) without disrupting their structural integrity. Besides, the surface modified CNTs will have the strong potential to improve their dispersion uniformity, wettability and matrix-reinforcement bonding strength in the AMCs. The AlN nano-particle grafted CNTs were characterized through dispersion stability test, UV-Visible spectroscopy, Fourier-transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD) analysis, Raman spectroscopy and Thermogravimetric analysis (TGA). Microstructure and elemental analysis were conducted through Scanning electron microscope (SEM) embedded with Energy dispersive X-ray spectroscope (EDS), Field emission scanning electron microscope (FESEM) and Transmission electron microscope (TEM). The aforementioned characteristics of AlN nano-particle grafted CNTs were compared with those of the pristine CNTs, acid treated CNTs and silanized CNTs to demonstrate the effectiveness of AlN nano-particle grafting on the CNT surfaces. Results revealed improvement of dispersion stability, covalent attachment of AlN nano-particles onto CNT surfaces (FTIR spectroscopy), existence of AlN on the CNT sidewalls (XRD analysis) and peaks corresponding to Al and N (EDS). Evidence of AlN on the CNT surfaces was also established through SEM, FESEM, TEM and EDS. Though there was a paltry degradation of CNT surfaces after the acid treatment, it was recovered substantially during silanization, and there was no evidence of tube shortening or fragmentations in SEM of silanized and AlN grafted CNTs.

Flexural behavior of pMWCNTs filled glass fiber/epoxy nanocomposites: Synthesis and interfacial failure

AbstractGlass fiber reinforced polymer composite (GFRP) encounter many practical situations during its application, exposed to different temperature fluctuation. Absorption of moisture and the fluctuated thermal environment cause mechanical degradation of GFRP. The current plan is to explore the mechanical and chemical behavior of pristine multiwall carbon nanotubes(pMWCNTs)‐glass fiber strengthens epoxy composites during thermal shock (TS). The laminates were prepared by the hand‐lay‐up process followed by compression molding. The thermal shock was performed at the temperature for the required samples was 135°C for 24 h, followed by −135°C for 24 h. A flexural test has been carried out at 1 mm/min loading speed. 0.2 wt% pMWCNTs filled nanocomposite appeared to have the highest flexural strength and modulus compared to ambient samples. The thermomechanical behavior of nanocomposites has been accomplished by analyzing the dynamic mechanical thermal analysis graph (DMTA). Field emission scanning electron microscope (FESEM) analyzed the fracture surface of in‐situ mechanical failure samples to find out the primary failure modes for strengthening and weakening mechanisms. The glass transition temperature (Tg) of the nanocomposite observed decreased due to homogeneous dispersion of pMWCNTs, imparting some effect on crosslink density and reinforcement up to 0.2 wt%. This study reveals that the uniform distribution of pMWCNTs and thermal shock treatment enhances the matrix stiffness and improves the mechanical properties.

A Study on the Effects of Potassium Permanganate on the Functionalization of Multi-Walled Carbon Nanotubes

In this work, multi-walled carbon nanotubes (MWCNTs) are functionalized by a wet chemical oxidation method using a mixture of potassium permanganate (KMnO4) and sulfuric acid (H2SO4) at 70 °C, for 12 h. The effects of various KMnO4 amounts on the functionalization of MWCNTs are studied and reported. The surface morphologies, structural properties, dispersion and thermal stability of the MWCNTs are characterized using a field emission scanning electron microscope (FE-SEM), Raman spectroscopy, UV-visible spectroscopy (UV–vis), thermal gravimetric analysis (TGA). The FE-SEM images display some surface roughness, cutting and open ends of functionalized MWCNTs (f-MWCNTs). The TGA curves of f-MWCNTs indicate a weight loss between 150 °C and 350 °C, which is attributed to the loss of carboxyl groups on the MWCNTs surface and the weight loss is increased when KMnO4 mass is increased. The highest weight loss value of 22.23% is recorded for the oxidation treatment with a mixture of 5 M H2SO4 and 200 mg KMnO4. UV–vis measurements indicate that the f-MWCNTs are highly dispersed in the aquoues solution in comparision to the pristine MWCNTs (p-MWCNTs). And f-MWCNTs with higher functionalization degree show better dispersibility. This study provides a great prospect of effective method to cut, end-open, functionalize and disperse MWCNTs.

Strength Evaluation of Functionalized MWCNT-Reinforced Polymer Nanocomposites Synthesized Using a 3D Mixing Approach.

The incorporation of carboxyl functionalized multi-walled carbon nanotube (MWCNT- COOH) into a polymethyl methacrylate (PMMA) has been investigated. The resultant tensile and flexural mechanical properties have been determined. In this paper, a novel synthesis process for a MWCNT-reinforced polymer nanocomposite is proposed. The proposed method significantly eliminates the most challenging issues of the nano-dispersed phase, including agglomeration and non-homogeneous mixing within a given matrix material, and also resolves the issues occurring in conventional mixing processes. The results of scanning electron microscopy support these claims. This 3D-mixing process is followed by an extrusion process, using a twin-screw extruder for pristine MWCNT, and a compression molding process for COOH-MWCNT, to prepare test specimens for experimentally determining the mechanical properties. The test specimens are fabricated using 0.1, 0.5, and 1.0 wt.% MWCNT, with a remaining PMMA phase. The testing is conducted according to ASTM D3039 and ASTM D7264 standards. Significant improvements of 25.41%, 35.85%, and 31.75% in tensile properties and 18.27%, 48%, and 33.33% in flexural properties for 0.1, 0.5, and 1.0 wt.% COOH-MWCNT in PMMA, respectively, compared to non-functionalized MWCNTs, were demonstrated. The highest strength was recorded for the nanocomposite with 0.5 wt.% f-MWCNT content, indicating the best doping effect at a lower concentration of f-MWCNT. The proposed CNT-PMMA nanocomposite may be found suitable for use as a scaffold material in the domain of bone tissue engineering research. This type of research possesses a high strength requirement, which may be fulfilled using MWCNT. Furthermore, this analysis also shows a significant amount of enhancement in flexural strength, which is clinically required for fabricating denture bases.

(Invited, Digital Presentation) In-Situ Prussian Blue Formation on Intrinsic Iron-Containing MWCNT As a Template and Its Scanning Electrochemical Microscopic Interrogation and Hydrogen Peroxide Electrocatalysis

Prussian blue (PB; iron (III) hexacyanoferrate), is a mixed-valent polynuclear complex widely used in electrochromic display, biosensors, ion-selective electrodes, electrocatalysis and energy storage systems like batteries and fuel cells [1,2]. For the PB preparation, an electrochemical deposition using an equimolar concentration of Fe2+ and Fe(CN)6 3- in 0.1 M KCl-electrolyte condition was reported. In another case, a template approach, wherein either Fe2+ (or ironic species) or Fe[(CN)6]3- immobilized on the electrode surface followed by interaction with counter ion were reported [3]. For instance, a deliberately added ironic species (>20 wt.%) into a multiwalled carbon nanotube (MWCNT) modified electrode has been utilized as a template for the PB functionalized MWCNT preparation by potential cycling of the precursor electrode with Fe[(CN)6]3- [3]. Meanwhile, an intrinsic iron species that originated from its catalytic source has been referred an influencing parameter in altering the electronic conductivity of the MWCNT (MWCNT-Fe*, Fe*-Instrinsic iron) [4]. Our group has utilized the pristine MWCNT as a template for in-situ preparation MWCNT@Fe*(bpy)3 2+ and as an electro-Fenton catalyst for electroanalytical applications [5]. However, the in-situ derivation of iron impurity (2-4 wt.%) into the Prussian blue complex has not been explored yet. The inaccessibility of the iron and its low concentrations are the likely reason for the limitation. This report demonstrates an in-situ electrochemical PB formation using MWCNT-Fe* modified glassy carbon electrode as a template and Fe(CN)6 3- as a counter ionic species. This modified electrode (GCE/MWCNT-Fe@PB) showed a characteristic redox peak for the high-spin ironic state of PB at about 0.2 V vs Ag/AgCl in addition with a post-peak at 0.3 V vs Ag/AgCl [Figure 1A]. The nickel impurity in the pristine MWCNT is suspected to be involved in the complexation with Fe(CN)6 3- ion along with the ironic species.In-situ formation of PB on MWCNT-Fe* was probed using the scanning electrochemical microscope technique (SECM). In a typical experiment, MWCNT-Fe* modified GCE was taken as a base-electrode along with 5 mM Fe(CN)6 3- in pH 2 KCl-HCl electrolyte and the potentials were set as 0.1 V and 0.5 V vs Ag/AgCl accordingly to reduce FeIII(CN)6 3- + e-® FeII(CN)6 4- and parallely reoxidize it as FeII(CN)6 4- ® FeIII(CN)6 3- + e- on the Pt-tip surface (Figure 1B). The FeII(CN)6 4- ion formed as an intermediate species interacts chemically with Fe2+ ion that might be stripped out from the MWCNT-Fe* on the interface for the in-situ PB formation [Figure 1C]. An island-like morphology with average particle size, few micrometers of PB crystallites on the MWCNT-Fe* surface was noticed. Typical SECM surface imaging of a controlled carbon, carbon nanofiber (CNF), which doesn’t have any metal impurity, was displayed in Figure 1D. A feature-less surface morphology was noticed under the identical imaging condition. Physico-electrochemical characterization of GCE/MWCNT-PB modified electrode using Raman, FT-IR, UV visible spectroscopy and Field emission scanning electron microscopy (FESEM) supported the formation of a hybrid complex on MWCNT-Fe* electrode surface. It has been confirmed that intrinsic iron content was responsible for the PB-formation. As an independent electroanalytical study, the selective electrocatalytic reduction of H2O2 was carried out using a newly developed MWCNT-PB system [Figure 1B]. As an electroanalytical application, amperometric i-t sensing of H2O2 was carried out, which showed a calibration plot wth linearity upto ~5mM of H2O2 at an operating potential, 0.1 V vs Ag/AgCl in pH 2 solution. There is no interference by common biochemical such as ascorbic acid (AA), uric acid (UA), dopamine (DA), cysteine (CySH), nitrite, nitrate and glucose etc.In conclusion, we have prepared a Prussian blue functionalized MWCNT modified glassy carbon electrode using an intrinsic iron-containing MWCNT as a template in an acidic solution. The in-situ formation of PB on the MWCNT-Fe* has been probed and imaged using the scanning electrochemical microscope technique. The selective electrocatalytic and electroanalytical applications of the GCE/MWCNT-Fe@PB towards H2O2 have been demonstrated. This study will provide unique info about the intrinsic iron in the MWCNT and its in-situ derivatization process. Acknowledgement The authors acknowledge the Department of Science and Technology – Science and Engineering Research Board and Technology Development Program, DST-SERB-EMR/2016/002818, IDP/MED/04/2017 and CRG/2021/001048 Schemes for the funding. References A.A. Karyakin, Electroanalysis, 13, 813 (2001).J. Chen, L. Wei, A. Mahmood, Z. Pei, Z. Zhou, X. Chen and Y. Chen, Energy Storage Mater., 25, 585 (2020).R. Shanmugam, P. Barathi and A.S. Kumar, Colloids Surf. A: Physicochem. Eng. Aspects, 452, 129 (2014).C.E.Banks, A.Crossley, C.Salter, S.J.Wilkins, R.G.Compton, R. Angew. Chem., Int. Ed. 45, 2533 (2006)P. Mayuri and A.S. Kumar, Langmuir, 31, 5945 (2015). Figure 1

Sonochemical fabrication of a hybrid electrode material based on pristine carbon nanotubes and bentonite clay for fast and highly sensitive determination of dopamine in the presence of ascorbic and uric acid

This work focuses on the attachment of bentonite clay to external surface of individual pristine multiwalled carbon nanotubes (MWCNTs) and the use of the resulting hybrid material for the fast and highly sensitive electrochemical determination of dopamine (DA) in the presence of ascorbic acid (AA) and uric acid (UA). XRD, FE-SEM and EDX highlighted the pristine state of MWCNTs and bentonite clay. HR-TEM confirmed the adsorption of clay on the external surfaces of individual pristine MWCNTs. Electrochemical characterization showed that the fabricated sensor possesses a large electrochemical surface area with excellent electron transfer properties. The influence of parameters likely to affect sensor performance was studied; 40 s, 10 μL suspension, and pH 7.4 were found to be the optimal accumulation time, optimal suspension volume, and optimal electrolyte pH, respectively. Under these optimal conditions, DPV peak currents were linearly related to DA concentrations in the range of 0.4–14 μM, and the detection limit was found to be 6 nM (S/N = 3). The Interference study revealed that the sensor eliminates AA and UA interference up to concentrations above their blood levels. Furthermore, the developed sensor exhibited good repeatability, satisfactory long-term stability, and was successfully applied to the detection and quantification of DA in human serum sample with satisfactory recoveries.

Influence of functional carbon nanotube and multi‐cyclic shape memory performance on thermally triggered polyurethane nanocomposites

AbstractIn this study, thermally triggered shape memory thermoplastic polyurethane‐multiwall carbon nanotube (TPU/MWCNTs) nanocomposites with varying nanofiller content (0–5 wt%) were prepared. Melt flow, morphology, and shape memory properties of TPU/MWCNTs nanocomposites were investigated. We attempt to clarify the reinforcement effect of CNTs on the shape memory behavior of TPU/MWCNTs nanocomposites. Moreover, the influence of acid treatment on surface morphology, thermal stability, and dispersion state of MWCNTs has been evaluated. Pristine MWCNTs were treated with highly concentrated nitric acid (68%) and introduced by solution mixing to TPU as an efficient reinforcement phase. The thermogravimetric analysis revealed thermal stability improvement of acid treatment MWCNTs. Field emission‐scanning electron microscopy images confirmed the homogenous distribution of oxidized MWCNTs in the matrix and some aggregated structures at 5 wt% nanofiller. Higher melt flow rate values were observed for composites loaded with 0.5–1 wt% ox‐MWCNTs compared with 2–5 wt% because of their better dispersion in TPU. The experimental results show a higher shape recovery ratio of TPU/ox‐MWCNTs nanocomposites than pure polyurethane (over 20%). A good shape recovery in the 90%–100% range could be obtained during a shape recovery test when ox‐MWCNTs content of 0.5–2 wt% is proposed to synthesize TPU/ox‐MWCNTs nanocomposites.

Surface modification of MWCNT to improve the mechanical and thermal properties of natural rubber nanocomposites

AbstractIn this study, we focused on the synergistic effect between carbon black (CB) and multiwall carbon nanotube (MWCNT) hybrid fillers. In particular, the surface modification of pristine MWCNT (P‐MWCNT) via an acid (oxidation) treatment was used to improve their dispersion, as well as the mechanical and thermal properties of their corresponding natural rubber (NR)‐based nanocomposites. Fourier‐transform infrared spectroscopy (FTIR), X‐ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM) were carried out to determine the presence of functional groups on the oxidized MWCNT (O‐MWCNT). After vulcanization, dynamic mechanical analysis (DMA), tensile properties, hardness, thermal conductivity, swelling behaviour in toluene and SEM characterizations were performed on both NR/CB/P‐MWCNT‐ and NR/CB/O‐MWCNT‐based nanocomposites. The results showed the positive effect of MWCNT surface oxidation on the fillers' dispersion and nanocomposites' properties.

Overturning photoreduction product of CO2 by defect- and COOH-functionalized multi-wall carbon nanotubes

We functionalize MWCNTs with defects and COOH groups to form MWCNTs30 through a novel discharge process. In the photoreduction of CO2 with pure H2O in the absence of sacrificial reagent, with CdS as light absorber, MWCNTs30 triggers a selective CH3OH production, with a CH3OH selectivity of 100% and an internal quantum efficiency of 3.9%, but CO is the only C-based product by using pristine MWCNTs without functionalization. The defects on MWCNTs30 are active sites for enhancing CO2 adsorption, H2O dissociation to produce H and H transfer to CO2, thus boosting CO2 hydrogenation to CH3OH. The COOH groups on MWCNTs30 provide H for promoting CO2 hydrogenation to CH3OH. The multiple roles of defects and COOH groups overturn the photoreduction product from CO to CH3OH. The results open a new way to achieve more efficient photoreduction of CO2 in the absence of noble metal and sacrificial reagent.

Features of carbon-based reinforcements influencing the electrochemical behaviour of bi-phase Na-titanate based anode materials for Na-ion batteries

Na-titanate is a class of potentially ‘safe’ anode material for Na-ion batteries, with the combination of Na2Ti3O7 and Na2Ti6O13, as ‘Bi-phase NTO’, often performing better than the single-phase counterparts. Nevertheless, good coverage and intimate contact of the Na-titanate particles with conducting reinforcements is needed for achieving superior electrochemical performance by suppressing deleterious reactions with electrolyte and providing connectivity across particles. Against this backdrop, the present manuscript reports on the effects of dimensionality, functional groups and conductivity of carbon-based reinforcements [viz., pristine and functionalized multi-walled carbon nanotubes (MWCNTs), reduced graphene oxide, carbon black] towards the performances of ‘Bi-phase NTO’/carbon-based electrodes. High aspect ratio, along with the presence of functional groups, of functionalized MWCNTs results in complete coverage/‘wrapping’ of Na-titanate surface; thus, leading to the best improvements of Na-storage capacity and cyclic stability of ‘Bi-phase NTO’, along with negligible increment in impedance over electrochemical sodiation/desodiation cycles. Nevertheless, higher overall electronic conductivity bestowed by the less defected and less functional group containing pristine MWCNT leads to the best rate-capability. However, carbon black, lacking in terms of both aspect ratio and presence of functional groups, and leading to a very poor coverage of the Na-titanate surface, does not improve the electrochemical performances of ‘Bi-phase NTO’.

Novel electrochemical sensor based on molecularly imprinted polymer combined with L-His-MWCNTs@PDMS-5 nanocomposite for selective and sensitive assay of tetracycline

Herein, we designed a novel electrochemical sensor by modifying L-histidine functionalized multi-walled carbon nanotubes (L-His-MWCNT)-molecularly imprinted polymer for the selective, rapid, and simple detection of tetracycline (TET). Firstly, PDMS-1000 was decorated with pristine multi-walled carbon nanotubes (P-MWCNTs) by physical adsorption and then functionalized with L-histidine (L-His-MWCNTs@PDMS-5). The MIP-based electrochemical sensor was constructed on a glassy carbon electrode (GCE) via sol-gel consisting of tetraethoxysilane (TEOS) and cetyltrimethylammonium bromide (CTAB) with L-His-MWCNTs@PDMS-5 in the presence of TET. The structural characterization of P-MWCNTs and polymer nanocomposite were examined by Fourier transform infrared spectroscopy-attenuated total reflectance (FTIR-ATR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and particle size distribution techniques. The performance of the newly developed sensor was evaluated using cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) methods. The limit of detection (LOD) was found to be 2.642 × 10−12 M, while a linear operating range of 1 × 10−11 M–1 × 10−10 M was found. The validity of the developed sensor was checked by TET detection in capsule dosage form, human serum, and tap water samples, and the recovery results were found to be 99.69%, 98.92%, and 100.60%, respectively. The developed L-His-MWCNTs@PDMS-5/MIP sensor demonstrated an excellent electrochemical response for TET.

Synthesis and Application of Heteroatom-Doped Graphite as the Electrode Material: Influences of Defect Density and Heteroatom on Heterogeneous Electron Transfer Rate

Thermal method was applied for the synthesis of O-doped and N-doped graphite materials using melamine and glucose as the sources of O and N, respectively. Graphite paste electrodes were prepared with the synthesized O-doped and N-doped graphite materials. The route of synthesis was explored by cyclic voltammetry using the fabricated paste electrodes and [Fe(CN)6]3–/4– as a simple outer-sphere redox probe. The results of structural and electrochemical investigations clearly showed that doping of O and N as heteroatom in the synthesized materials not only increased the defect density, the ratio of edge to basal plane sites, of graphite materials but also enhanced the rate of heterogeneous electron transfer at their corresponding paste electrodes. The heterogeneous electron transfer rate constant (k0) for [Fe(CN)6]3–/4– at the fabricated O-doped and N-doped graphite paste electrodes were about 51 and 46 times that observed for graphite paste electrode, respectively. The values of electroactive surface area calculated for both O-doped and N-doped graphite materials were about 5 times that obtained for graphite paste electrode. Thereafter, electrochemical behaviors of isoniazid, ascorbic acid, dopamine, and uric acid as the models of biologically relevant molecules were investigated at the prepared heteroatom-doped graphite paste electrodes, and the obtained results were compared with those obtained using paste electrodes prepared by pristine graphite, pristine multiwalled carbon nanotubes, and oxidized multiwalled carbon nanotubes and also by glassy carbon electrode.

Impact of γ-irradiation on the structural and electrical characteristics of functionalized multiwalled carbon nanotubes

In the present study, modifications induced in the functionalized multiwalled carbon nanotubes (FMWCNTs) by gamma (γ) irradiation are explored. Functionalization of pristine MWCNTs is performed by acid treatment and their films are deposited via doctor-blading technique on the glass substrate. As-deposited films are exposed with the γ–ray irradiation at various doses of 60 kGy, 120 kGy, 180 kGy, and 240 kGy to examine the alteration in structural, morphological and electrical characteristics. XRD analysis of pre and post gamma irradiated FMWCNTs films revealed that there is no phase variation in the post irradiated samples. The crystalline nature of films is enhanced after gamma exposure up to 180 kGy and decreased at a dose of 240 kGy. Raman spectral analysis identifies the structural ordering/disordering developed in the nanotubes after gamma irradiation of different doses. XPS analysis is exploited to expose the chemical composition in pre and post irradiated FMWCNTs. FTIR spectra exhibited the presence of different functional groups like O–H, O–CO and CO, etc. in pristine and gamma irradiated nanotubes. The significant variation in the electrical properties of gamma irradiated nanotubes is also noticed. The fluctuation in the properties of irradiated nanotubes may be due to defects generation, annihilation, and ionization process.