Biodegradable polylactic acid emulsion ink based on carbon nanotubes and silver for printed pressure sensors

Investigating biodegradable and biocompatible materials for electronic applications can lead to tangible outcomes such as developing green-electronic devices and reducing the amount of e-waste. The proposed emulsion-based conducting ink formulation takes into consideration circular economy and green principles throughout the entire process, from the selection of materials to the production process. The ink is formulated using the biopolymer polylactic acid dissolved in a sustainable solvent mixed with water, along with conductive carbon nanotubes (CNTs) and silver flakes as fillers. Hybrid conductive fillers can lower the percolation threshold of the ink and the production costs, while maintaining excellent electrical properties. The coating formed after the deposition of the ink, undergoes isothermal treatment at different temperatures and durations to improve its adhesion and electrical properties. The coating's performance was evaluated by creating an eight-finger interdigitated sensor using a Voltera PCB printer. The sensor demonstrates exceptional performance when exposed to various loading and unloading pressures within the 0.2-500.0 kPa range. The results show a consistent correlation between the change in electrical resistance and the stress caused by the applied load. The ink is biodegradable in marine environments, which helps avoiding its accumulation in the ecosystem over time.

Neutron Activation Analysis of Rare Earth Element Extraction from Solution through a Surfactant-Assisted Dispersion of Carbon Nanotubes

We report the preparation of surfactant-assisted carbon nanotube dispersions using gum arabic, Triton X-100, and graphene oxide as dispersing agents for removing rare earth elements in an aqueous solution. The analytical tools, including (a) scanning electron microscopy and (b) neutron activation analysis, were utilized for qualitative and quantitative examinations, respectively. Neutron activation analysis was employed to quantitatively determine the percent of extraction of nuclides onto the carbon structure, while the images produced from the scanning electron microscope allowed the morphological structure of the surfactant-CNT complex to be analyzed. This report tested the effects responsible for nuclide removal onto CNTs, including the adsorbent to target mass ratio, the CNT concentration and manufacturing process, the pH, and the ionic radius. Observable trends in nuclide extraction were found for each parameter change, with the degree of dispersion displaying high dependency.

HRMAS-NMR and simulation study of the self-assembly of surfactants on carbon nanotubes

Polyethoxylated surfactants, such as those of the Tween and Pluronic series, are commonly used to disperse carbon nanotubes (CNTs) and other nanoparticles. However, the current understanding of the nature of interactions between these surfactants and CNTs is limited. The nature of the interactions between surfactants (Tween-80 [T80] and Pluronic F68 [PF68]) and CNTs was investigated using high-resolution magic angle spinning nuclear magnetic resonance (HRMAS-NMR) and coarse-grained molecular dynamics (MD) simulations. HRMAS-NMR revealed that T80 molecules interact with single-walled CNTs (SWCNTs) and multi-walled CNTs (MWCNTs) via the oleyl chain, whereas PF68 molecules interact with the surface of SWCNTs and MWCNTs via the polypropylene oxide residues. The polyethylene oxide chains were oriented towards the external aqueous environment. The HRMAS-NMR results were supported by MD simulations, and the latter provided further insights into the nature of the interactions.

Synthesis of Highly Dispersible Functionalized Carbon Nanotubes as Conductive Material through a Facile Drying Process for High-Power Lithium-ion Batteries

Herein, surface-functionalized carbon nanotubes (CNTs) were successfully synthesized by dry ball milling that facilitates industrial application. The optimal conditions were determined by analyzing the physicochemical characteristics of CNTs, including the content of the carboxyl group (-COOH) induced on the surface of CNTs by co-existing dry ice based on the ball milling time. Among them, 30 s ball milling (CNTs-30s) showed a high dispersibility in N-methyl-2-pyrrolidone (NMP) while retaining most carboxyl groups and maintaining the intrinsic high conductivity. In the evaluation of rate capability and 5 C/5 C cyclability applied to the Li_1+x (Ni_1-y-z Co_y Mn_z )_1-x O₂ with 60 % Ni (NCM622) cathode, CNTs-30s showed excellent performance based on a well-formed conductive network. Regarding improved dispersion properties and electrochemical performance, the optimal surface functionalization conditions, dispersibility, and electrode properties according to the processing time were analyzed; based on these, the correlation with electrochemical performance was confirmed.

Bio-inspired conductive adhesive based on calcium-free alginate hydrogels for bioelectronic interfaces

Electrode impedance is one of the greatest challenges facing neural interfacing medical devices and the use of electrical stimulation-based therapies in the fields of neurology and regenerative medicine. Maximizing contact between electronics and tissue would allow for more accurate recordings of neural activity and to stimulate with less power in implantable devices as electric signals could be more precisely transferred by a stable interfacial area. Neural environments, inherently wet and ion-rich, present a unique challenge for traditional conductive adhesives. As such, we look to marine mussels that use a 3,4-dihydroxyphenyl-L-analine (DOPA)-containing proteinaceous excretion to adhere to a variety of substrates for inspiration. By functionalizing alginate, which is an abundantly available natural polymer, with the catechol residues DOPA contains, we developed a hydrogel-based matrix to which carbon-based nanofiller was added to render it conductive. The synthesized product had adhesive energy within the range of previously reported mussel-based polymers, good electrical properties and was not cytotoxic to brain derived neural precursor cells.

The Use of Electrochemical Impedance Spectroscopy as a Tool for the In-Situ Monitoring and Characterization of Carbon Nanotube Aqueous Dispersions

So far, there is no validated technology for characterizing the dispersion and morphology state of carbon nanotubes (CNTs) aqueous dispersions during sonication. Taking advantage of the conductive nature of CNTs, the main hypothesis of the current study is that Electrochemical Impedance Spectroscopy (EIS) is an appropriate technique for the in-situ monitoring and qualification of the dispersion state of CNTs in aqueous media. To confirm our hypothesis, we monitored the Impedance |Z| during the sonication process as a function of type CNTs/admixtures used for the preparation of the aqueous solutions and of crucial process parameters, such as the applied sonication power and duration (i.e., sonication energy). For dispersions above the percolation threshold, a drop of |Z| by approximately seven orders of magnitude was observed, followed by a linear reduction. The dramatic change in |Z| is regarded as an indication of the formation of a conductive path or destruction of an existing one during sonication and can be used to characterize the dispersion and morphology state of CNTs. The results of the EIS provide, straightforwardly and reliably, the required information to create an optimum dispersion protocol for conductive CNT suspensions. The produced dispersions are part of research focusing on the manufacturing of cement-based composite materials with advanced thermoelectric functionalities for energy harvesting. Such dispersions are not only limited to energy harvesting applications but also to applications where functionalities are introduced through the use of conductive-based suspensions.

Applications, fluid mechanics, and colloidal science of carbon-nanotube-based 3D printable inks

Additive manufacturing, also known as 3D printing (3DP), is a novel and developing technology, which has a wide range of industrial and scientific applications. This technology has continuously progressed over the past several decades, with improvement in productivity, resolution of the printed features, achievement of more and more complex shapes and topographies, scalability of the printed components and devices, and discovery of new printing materials with multi-functional capabilities. Among these newly developed printing materials, carbon-nanotubes (CNT) based inks, with their remarkable mechanical, electrical, and thermal properties, have emerged as an extremely attractive option. Various formulae of CNT-based ink have been developed, including CNT-nano-particle inks, CNT-polymer inks, and CNT-based non-nanocomposite inks (i.e., CNT ink that is not in a form where CNT particles are suspended in a polymer matrix). Various types of sensors as well as soft and smart electronic devices with a multitude of applications have been fabricated with CNT-based inks by employing different 3DP methods including syringe printing (SP), aerosol-jet printing (AJP), fused deposition modeling (FDM), and stereolithography (SLA). Despite such progress, there is inadequate literature on the various fluid mechanics and colloidal science aspects associated with the printability and property-tunability of nanoparticulate inks, specifically CNT-based inks. This review article, therefore, will focus on the formulation, dispersion, and the associated fluid mechanics and the colloidal science of 3D printable CNT-based inks. This article will first focus on the different examples where 3DP has been employed for printing CNT-based inks for a multitude of applications. Following that, we shall highlight the various key fluid mechanics and colloidal science issues that are central and vital to printing with such inks. Finally, the article will point out the open existing challenges and scope of future work on this topic.

Porphyrin nanotubes based on a hydrogen-bonded organic framework

Tubular structures offer a wide variety of applications; therefore, designing such materials with distinct dimensions is highly desirable yet challenging. In the current report, we have demonstrated the synthesis of a one-dimensional (1D) tubular assembly comprising porphyrin nanoring subunits. The porphyrin nanoring (PNR) 2 bearing ester groups was synthesized via Pt-mediated cyclization and then hydrolyzed to obtain PNR 3 with carboxylic groups. Under optimized conditions, porphyrin nanotubes (PNTs) were formed through hydrogen bonding between the carboxylic groups of 3. The morphology investigated by both SEM and TEM displayed well-defined arrays of nanotube bundles up to several micrometers long. Small crystals of PNTs were obtained by heating a solution of 3 in DMSO. High-resolution transmission electron microscopy (HR-TEM) accompanied by selected-area electron diffraction (SAED) exhibited a line of diffractions with d-spacing values of 6.17, 3.08, 2.07, and 1.57 Å. The miller indices of these diffractions could be assigned as 300, 600, 900, and 1200, respectively, suggesting that an ordered structure of 1D PNTs has been formed.

Stabilization of Carbon Nanotubes and Graphene by Tween-80: Mechanistic Insights from Spectroscopic and Simulation Studies

Polyoxyethylene sorbitan monooleate is commonly used to obtain stable dispersions of nanoparticles (NPs) such as carbon nanotubes (CNTs) and graphene. However, the mechanism underlying dispersion is poorly understood. The present study aimed at investigating the mechanism of stabilization of carbon NPs (CNPs), namely, single-walled CNTs (SWCNTs), multi-walled CNTs (MWCNTs), and graphene, by Tween-80 using attenuated total internal reflection-Fourier transform infrared and nuclear magnetic resonance (NMR) spectroscopy. Molecular dynamics (MD) simulations were performed to identify, at the atomic scale, the significant interactions that underlie the adsorption and the stabilizing effect of Tween-80 on CNPs, in this way corroborating the spectroscopy results. Spectroscopic analysis revealed that the alkyl chain tether to SWCNT, MWCNT, and graphene surface, presumably through π-π interactions between the carbon-carbon double bond in the alkyl chain and the aromatic rings of CNPs. The hydrophilic polyethoxylate chains extend into the aqueous environment and stabilize the suspension by steric hindrance. MD simulations also showed that Tween-80 molecules interact with the CNP surface via the alkyl chain, thus corroborating spectroscopy results. MD simulations additionally revealed that Tween-80 aggregates on the CNP surface shifted from planar to micelle-like with increasing Tween-80 ratios, underscoring concentration-dependent changes in the nature of these interactions.

Multiwavelength Photothermal Imaging of Individual Single-Walled Carbon Nanotubes Suspended in a Solvent

Optical imaging of individual single-walled carbon nanotubes (SWCNTs) enables the characterization of heterogeneous SWCNT samples. However, previous measurement methods have targeted SWCNTs fixed on a substrate. In this study, absorption-contrast imaging of individual SWCNTs moving irregularly in a solvent was performed by simultaneous multiwavelength photothermal (PT) microscopy. Using this technique, heterogeneous samples containing semiconducting and metallic SWCNTs were characterized by absorption spectroscopy. The semiconducting and metallic SWCNTs were visualized in different colors in the obtained multiwavelength images due to their different absorption spectra. Statistical analysis of the multiwavelength signals revealed that semiconducting and metallic SWCNTs could be distinguished with more than 90% accuracy. Time-series PT imaging of the nanotube aggregates induced by salt addition was also conducted by performing single-nanotube measurements. Our study demonstrated that PT microscopy is a versatile technique for determining the composition and degree of aggregation of SWCNTs in liquid and polymeric media, which can promote the industrial application of such materials.

Nanostructured Polyacrylamide Hydrogels with Improved Mechanical Properties and Antimicrobial Behavior

This work proposes a simple method to obtain nanostructured hydrogels with improved mechanical characteristics and relevant antibacterial behavior for applications in articular cartilage regeneration and repair. Low amounts of silver-decorated carbon-nanotubes (Ag@CNTs) were used as reinforcing agents of the semi-interpenetrating polymer network, consisting of linear polyacrylamide (PAAm) embedded in a PAAm-methylene-bis-acrylamide (MBA) hydrogel. The rational design of the materials considered a specific purpose for each employed species: (1) the classical PAAm-MBA network provides the backbone of the materials; (2) the linear PAAm (i) aids the dispersion of the nanospecies, ensuring the systems' homogeneity and (ii) enhances the mechanical properties of the materials with regard to resilience at repeated compressions and ultimate compression stress, as shown by the specific mechanical tests; and (3) the Ag@CNTs (i) reinforce the materials, making them more robust, and (ii) imprint antimicrobial characteristics on the obtained scaffolds. The tests also showed that the obtained materials are stable, exhibiting little degradation after 4 weeks of incubation in phosphate-buffered saline. Furthermore, as revealed by micro-computed tomography, the morphometric features of the scaffolds are adequate for applications in the field of articular tissue regeneration and repair.

Combining metal nanoclusters and carbon nanomaterials: Opportunities and challenges in advanced nanohybrids

The development of functional materials with uniquely advanced properties lies at the core of nanoscience and nanotechnology. From the myriad possible combinations of organic and/or inorganic blocks, hybrids combining metal nanoclusters and carbon nanomaterials have emerged as highly attractive colloidal materials for imaging, sensing (optical and electrochemical) and catalysis, among other applications. While the metal nanoclusters provide extraordinary luminescent and electronic properties, the carbon nanomaterials (of zero, one or two dimensions) convey versatility, as well as unique interfacial, electronic, thermal, optical, and mechanical properties, which altogether can be put to use for the desired application. Herein, we present an overview of the field, for experts and non-experts, encompassing the basic properties of the building blocks, a systematic view of the chemical preparation routes and physicochemical properties of the hybrids, and a critical analysis of their ongoing and emerging applications. Challenges and opportunities, including directions towards green chemistry approaches, are also discussed.

Functionalization of Pristine, Metallic, and Semiconducting-SWCNTs by ZnO for Efficient Charge Carrier Transfer: Analysis through Critical Coagulation Concentration

Noncovalent functionalization of single-walled carbon nanotubes (SWCNT) by semiconducting oxides is a majorly sought technique to retain individual properties while creating a synergetic effect for an efficient heterostructure charge transfer. Three types of electronically and optically different SWCNTs: metallic (m), semiconducting (s), and pristine (p) are functionalized by ZnO using a facile sonication method. The physicochemical and morphological properties of the ZnO-functionalized SWCNTs, m-SWCNT+ZnO, s-SWCNT+ZnO, and p-SWCNT+ZnO, are analyzed by advanced characterization techniques. Evidence of charge transfer between SWCNT and ZnO is observed with an increase in charge carrier lifetime from 3.31 ns (ZnO) to 4.76 ns (s-SWCNT+ZnO). To investigate the optimum interaction between SWCNTs and ZnO, critical coagulation concentrations (CCC) are determined using UV-vis absorption spectroscopy for m-SWCNT, s-SWCNT, and p-SWCNT using different molar concentrations of ZnO as the coagulant. The interaction and coagulation mechanisms are described by the modified DLVO theory. Due to the variation in dielectric values and electronic properties of SWCNTs, the CCC values obtained have differed: m-SWCNT (1.9 × 10^-4), s-SWCNT (3.4 × 10^-4), and p-SWCNT (2 × 10^-4). An additional analysis of the aggregates and supernatants of the CCC experiments is also shown to give an insight into the interaction and coagulation processes, explaining the absence of influence exerted by sedimentation and centrifugation.

Concentration dependent debundling and single tube dispersions of pristine multiwalled carbon nanotubes functionalized with double tail phospholipids

Multiwalled carbon nanotubes (MWNTs) exist as aggregates of highly entangled tubes due to large aspect ratios and strong Van der Waals interactions among them in their native states. In order to render them suitable for any application, MWNTs need to be separated and dispersed uniformly in a solvent preferably as individual tubes. In the present work, it is demonstrated that a double tail lipid such as 1, 2-dipalmitoyl-sn-glycero-3-phosphoethanolamine (DPPE) is capable of dispersing MWNTs in ethanol. Ultra-stable suspensions were obtained by optimizing two key parameters: DPPE to MWNT weight ratio (ε) and MWNT concentration (c). Stability of the suspensions increased with the increasingεvalue up to an optimum point (ε= 1.8) and then decreased drastically beyond that. CNT dispersions withε= 1.8 were extremely stable (with a Zeta potential of 108.26 ± 2.15 mV) and could be retained in suspended form up to 3 months. Effect of MWNT concentration on disaggregation was very significant and stable suspensions could be formed for MWNT concentrations only below 0.14 mg ml^-1. Above this concentration, no stable dispersions could be obtained even withε= 1.8. Compression isotherms of Langmuir monolayers of the DPPE functionalized MWNTs spread at the air water interface were highly repeatable, suggesting that the MWNTs in dispersion were present as separate tubes coated with phospholipids. SEM micrographs of the Langmuir-Blodgett (LB) films, deposited at high surface pressures on silicon wafers, show that MWNTs remain as single nanotubes with no signs of reaggregation. TEM micrographs of MWNT suspensions indicated random adsorption of DPPE on MWNTs. Our work makes it possible to explore potential applications of LB films of MWNTs (stabilized by DPPE) in the development of conducting thin films for sensor applications or as supports to immobilize catalysts for heterogenous reactions.

Functionalized carbon nanotubes: synthesis, properties and applications in water purification, drug delivery, and material and biomedical sciences

Carbon nanotubes (CNTs) are considered as one of the ideal materials due to their high surface area, high aspect ratio, and impressive material properties, such as mechanical strength, and thermal and electrical conductivity, for the manufacture of next generation composite materials. In spite of the mentioned attractive features, they tend to agglomerate due to their inherent chemical structure which limits their application. Surface modification is required to overcome the agglomeration and increase their dispersability leading to enhanced interactions of the functionalized CNTs with matrix materials/polymer matrices. Recent developments concerning reliable methods for the functionalization of carbon nanotubes offer an additional thrust towards extending their application areas. By chemical functionalization, organic functional groups are generated/attached to the surfaces as well as the tip of CNTs which opens up the possibilities for tailoring the properties of nanotubes and extending their application areas. Different research efforts have been devoted towards both covalent and non-covalent functionalization for different applications. Functionalized CNTs have been used successfully for the development of high quality nanocomposites, finding wide application as chemical and biological sensors, in optoelectronics and catalysis. Non covalently functionalized carbon nanotubes have been used as a substrate for the immobilization of a large variety of biomolecules to impart specific recognition properties for the development of miniaturized biosensors as well as designing of novel bioactive nanomaterials. Functionalized CNTs have also been demonstrated as one of the promising nanomaterials for the decontamination of water due to their high adsorption capacity and specificity for various contaminants. Specifically modified CNTs have been utilized for bone tissue engineering and as a novel and versatile drug delivery vehicle. This review article discusses in short the synthesis, properties and applications of CNTs. This includes the need for functionalization of CNTs, methods and types of functionalization, and properties of functionalized CNTs and their applications especially with respect to material and biomedical sciences, water purification, and drug delivery systems.

Recent Advances in High-Throughput Nanomaterial Manufacturing for Hybrid Flexible Bioelectronics

Hybrid flexible bioelectronic systems refer to integrated soft biosensing platforms with tremendous clinical impact. In this new paradigm, electrical systems can stretch and deform with the skin while previously hidden physiological signals can be continuously recorded. However, hybrid flexible bioelectronics will not receive wide clinical adoption until these systems can be manufactured at industrial scales cost-effectively. Therefore, new manufacturing approaches must be discovered and studied under the same innovative spirit that led to the adoption of novel materials and soft structures. Recent works have taken mature manufacturing approaches from the graphics industry, such as gravure, flexography, screen, and inkjet printing, and applied them to fully printed bioelectronics. These applications require the cohesive study of many disparate parts. For instance, nanomaterials with optimal properties for each specific application must be dispersed in printable inks with rheology suited to each printing method. This review summarizes recent advances in printing technologies, key nanomaterials, and applications of the manufactured hybrid bioelectronics. We also discuss the existing challenges of the available nanomanufacturing methods and the areas that need immediate technological improvements.

A New Method for Dispersing Pristine Carbon Nanotubes Using Regularly Arranged S-Layer Proteins

Homogeneous and stable dispersions of functionalized carbon nanotubes (CNTs) in aqueous solutions are imperative for a wide range of applications, especially in life and medical sciences. Various covalent and non-covalent approaches were published to separate the bundles into individual tubes. In this context, this work demonstrates the non-covalent modification and dispersion of pristine multi-walled carbon nanotubes (MWNTs) using two S-layer proteins, namely, SbpA from Lysinibacillus sphaericus CCM2177 and SbsB from Geobacillus stearothermophilus PV72/p2. Both the S-layer proteins coated the MWNTs completely. Furthermore, it was shown that SbpA can form caps at the ends of MWNTs. Reassembly experiments involving a mixture of both S-layer proteins in the same solution showed that the MWNTs were primarily coated with SbsB, whereas SbpA formed self-assembled layers. The dispersibility of the pristine nanotubes coated with SbpA was determined by zeta potential measurements (−24.4 +/− 0.6 mV, pH = 7). Finally, the SbpA-coated MWNTs were silicified with tetramethoxysilane (TMOS) using a mild biogenic approach. As expected, the thickness of the silica layer could be controlled by the reaction time and was 6.3 +/− 1.25 nm after 5 min and 25.0 +/− 5.9 nm after 15 min. Since S-layer proteins have already demonstrated their capability to bind (bio)molecules in dense packing or to act as catalytic sites in biomineralization processes, the successful coating of pristine MWNTs has great potential in the development of new materials, such as biosensor architectures.

Multifunctional Additives for High-Energy-Density Lithium-Ion Batteries: Improved Conductive Additive/Binder Networks and Enhanced Electrochemical Properties

Cylindrical-type cells have been widely adopted by major battery and electric vehicle manufacturers owing to their price competitiveness, safety, and easy expandability. However, placement of electrodes at the core of cylindrical cells is currently restricted because of high electrode curvature and the lack of specialized electrodes and electrode materials. Here, we report the realization of highly flexible high-energy-density electrodes (active material loading of >98.4%) that can be used at the cores of cylindrical cells. The improved properties result from the introduction of a multifunctional poly(melamine-co-formaldehyde) (MF copolymer) additive, which yields a relatively more fluidic and well-dispersed slurry using only 0.08 wt %. MF copolymer-mediated formation of completely wrapped CNT/PVDF networks on LiCoO₂ (LCO) and accompanying contact enhancement between LCO and carbon nanotubes (CNTs) resulted in an increase of electrical and mechanical properties of the two types (composites with or without collectors) of electrodes compared with those of additive-free electrodes. Flexibility tests were carried out by rolling electrodes onto cylinder substrates (diameters of ca. 1 and 10 mm); this process resulted in relatively lower resistance changes of the MF copolymer-containing electrodes than for the reference electrodes. In addition, capacity retention after 100 cycles for cells with and without MF copolymers was approximately 10-20% better for the samples with the MF copolymer than for those without. CNT/PVDF networks with MF copolymers were proven to induce a relatively thin and stable cathode electrolyte interface layer accompanying the chemical bond formation during cycling.

Carbon nanotube columns for flow systems: influence of synthesis parameters

Flow reactors are expected to play an increasingly important role in the production of chemicals. A simple carbon-based scaffold to easily develop flow systems is here detailed. Using a chemical vapour deposition technique, the controlled in situ growth of vertically aligned (VA) multi-wall carbon nanotubes (MWCNTs) into quartz columns with 2 mm inner diameter is achieved. Several of the described MWCNT columns (CNCs) can be produced at a time. The influence of synthesis parameters on the formation of these VA-MWCNT scaffolds is reported and discussed (e.g. injection time of the precursor, carrier gas flow rate, inner diameter and length of the quartz column, position in the furnace during synthesis). Raman spectroscopy, optical microscopy, scanning and transmission electron microscopy are used to assess the coverage of the inner channel of the quartz column with VA-MWCNTs and their overall quality. The length of the CNCs together with the carrier gas flow rate are found to be key parameters to control the MWCNT length profile within the CNCs. Fluoresceinamine molecules and platinum nanoparticles are successfully immobilised within these MWCNT scaffolds. The benefits of the CNCs for flow system design are summarised as the controlled filling with MWCNTs makes the detailed CNCs versatile scaffolds for flow catalysis and filtration.

Graphene/PVA buckypaper for strain sensing application

Strain sensors in the form of buckypaper (BP) infiltrated with various polymers are considered a viable option for strain sensor applications such as structural health monitoring and human motion detection. Graphene has outstanding properties in terms of strength, heat and current conduction, optics, and many more. However, graphene in the form of BP has not been considered earlier for strain sensing applications. In this work, graphene-based BP infiltrated with polyvinyl alcohol (PVA) was synthesized by vacuum filtration technique and polymer intercalation. First, Graphene oxide (GO) was prepared via treatment with sulphuric acid and nitric acid. Whereas, to obtain high-quality BP, GO was sonicated in ethanol for 20 min with sonication intensity of 60%. FTIR studies confirmed the oxygenated groups on the surface of GO while the dispersion characteristics were validated using zeta potential analysis. The nanocomposite was synthesized by varying BP and PVA concentrations. Mechanical and electrical properties were measured using a computerized tensile testing machine, two probe method, and hall effect, respectively. The electrical conducting properties of the nanocomposites decreased with increasing PVA content; likewise, electron mobility also decreased while electrical resistance increased. The optimization study reports the highest mechanical properties such as tensile strength, Young’s Modulus, and elongation at break of 200.55 MPa, 6.59 GPa, and 6.79%, respectively. Finally, electrochemical testing in a strain range of ε ~ 4% also testifies superior strain sensing properties of 60 wt% graphene BP/PVA with a demonstration of repeatability, accuracy, and preciseness for five loading and unloading cycles with a gauge factor of 1.33. Thus, results prove the usefulness of the nanocomposite for commercial and industrial applications.

Study of Dispersions of Carbon Nanotubes Modified by the Method of Rapid Expansion of Supercritical Suspensions

The effectiveness of carbon nanotubes (CNT) deagglomeration by rapid expansion of supercritical suspensions (RESS) in nitrogen and carbon dioxide fluids was studied in this work. Two different mechanisms of deagglomeration were proposed for these two fluids at various temperature and pressure conditions. Ultrasound attenuation spectroscopy was applied as an express method of determining median diameter and aspect ratio of CNTs. At least twofold reduction of the diameter was shown for CNT bundles processed by RESS technique. Aspect ratio of processed CNTs, calculated from acoustic attenuation spectra, increased to 340. These results were in a good agreement with atomic force microscopy data.

3D-printed scaffolds with carbon nanotubes for bone tissue engineering: Fast and homogeneous one-step functionalization

Three-dimensional (3D) printing is a promising technology for tissue engineering. However, 3D-printing methods are limited in their ability to produce desired microscale features or electrochemical properties in support of robust cell adhesion, proliferation, and differentiation. This study addresses this deficiency by proposing an integrated, one-step, method to increase the cytocompatibility of 3D-printed scaffolds through functionalization leveraging conductive carbon nanotubes (CNTs). To this end, CNTs were first sonicated with water-soluble single-stranded deoxyribonucleic acid (ssDNA) to generate a negatively charged ssDNA@CNT nano-complex. Concomitantly, 3D-printed poly(propylene fumarate) (PPF) scaffolds were ammonolyzed to introduce free amine groups, which can take on a positive surface charge in water. The ssDNA@CNT nano-complex was then applied to 3D-printed scaffolds through a simple one-step coating utilizing electric-static force. This fast and facile functionalization step resulted in a homogenous and non-toxic coating of CNTs to the surface, which significantly improved the adhesion, proliferation, and differentiation of pre-osteoblast cells. In addition, the CNT based conductive coating layer enabled modulation of cell behavior through electrical stimuli (ES) leading to cellular proliferation and osteogenic gene marker expression, including alkaline phosphatase (ALP), osteocalcin (OCN), and osteopontin (OPN). Collectively, these data provide the foundation for a one-step functionalization method for simple, fast, and effective functionalization of 3D printed scaffolds that support enhanced cell adhesion, proliferation, and differentiation, especially when employed in conjunction with ES. STATEMENT OF SIGNIFICANCE: Three-dimensional (3D) printing is a promising technology for tissue engineering. However, 3D-printing methods have limited ability to produce desired features or electrochemical properties in support of robust cell behavior. To address this deficiency, the current study proposed an integrated, one-step method to increase the cytocompatibility of 3D-printed scaffolds through functionalization leveraging conductive carbon nanotubes (CNTs). This fast and facile functionalization resulted in a homogenous and non-toxic coating of CNTs to the surface, which significantly improved the adhesion, proliferation, and differentiation of cells on the 3D-printed scaffolds.

CNT-sorbents for heavy metals: Electrochemical regeneration and closed-loop recycling

Heavy metal contamination of aquatic environments is a major concern. Carbon nanotubes (CNTs) are among the most effective adsorbents for heavy metal removal due. However, their high cost and their uncertain environmental impact necessitates a closed-loop process through sorbent regeneration and recycling for practical application. Our work demonstrates heavy metal adsorption by carboxylic acid-functionalized single-walled/double-walled carbon nanotubes (f-SW/DWCNTs) and their regeneration using electric fields. We follow a multi-step process: 1) copper in an aqueous solution is adsorbed onto the surface of f-SW/DWCNTs, 2) the copper-saturated f-SW/DWCNTs are filtered onto a microfiltration (MF) membrane, 3) the f-SW/DWCNT coated membrane is used as an anode in an electrochemical cell, 4) an applied electric field desorbs the metals from the CNTs into a concentrated waste, and 5) the CNTs are separated from the membrane, re-dispersed and reused in copper-contaminated water for successive adsorption. With an applied positive electric potential, we achieved ∼90 % desorption of Cu from f-SW/DWCNTs. We hypothesize that the electric field generated at the anode causes electrostatic repulsion between the anode and the electrostatically adsorbed heavy metal ions. The effect of applied voltages, electrode spacing and electrolyte conductivity on the desorption of Cu from CNTs was also investigated.

Tailored CNTs Buckypaper Membranes for the Removal of Humic Acid and Separation of Oil-in-Water Emulsions

Carbon nanotubes (CNTs) are a robust material and proven as a promising candidate for a wide range of electronic, optoelectronic and environmental applications. In this work, two different methods were utilized for the preparation of CNTs exhibiting different aspect ratios via chemical vapor deposition (CVD). The as-prepared CNTs were analyzed using scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂adsorption isotherms, thermogravimetric analysis and Raman spectroscopy in order to investigate their morphological and structural properties. Free-standing CNTs "buckypaper" membranes were fabricated, characterized and tailored to meet the requirements of two applications, i.e., (1) the removal of humic acid (HA) from water and (2) separation of oil-in-water emulsions. It was revealed that the hydrophobic buckypapers showed high separation performance for Shell oil-in-water emulsions filtration, with up to 98% through the accumulation of oil droplets onto the membrane surface. The absorption capacity of buckypaper membranes for various organic liquids (oil, chloroform and toluene) was evaluated over 10 absorption cycles to investigate their recyclability and robustness. Moreover, surface modification was introduced to the pristine CNTs to increase their surface hydrophilicity and improve the pure water permeability of buckypapers. These modified buckypapers showed high flux for HA solutions and excellent HA rejection efficiency up to 95%via size exclusion and electrostatic repulsion mechanisms.

Transparent Conductive Flexible Trilayer Films for a Deicing Window and Self-Recover Bending Sensor Based on a Single-Walled Carbon Nanotube/Polyvinyl Butyral Interlayer

A flexible transparent conductive film (TCF) is an important component in many modern smart devices. Recent TCF is always fabricated based on indium tin oxide (ITO). However, the drawbacks of ITO (e.g., brittle nature, high cost, and resource scarcity) and the complex preparation process of TCF limit the massive production and further application of TCF. Herein, a facile and low-cost method is proposed to prepare flexible TCF. Rolls of single-walled carbon nanotubes (SWCNTs)/polyvinyl butyral (PVB) interlayer film were first fabricated by the roll-to-roll (R2R) spraying method. Then, the interlayer film was laminated between polycarbonate (PC) films (0.1 mm in thickness) to fabricate a transparent (80% optical transmittance) but flexible trilayer film. Such a prepared trilayer film shows multifunctional applications. For example, on the one hand, high conductivity and uniform distribution of resistance ensure that it can work as a deicing window with good performance at a low voltage. On the other hand, its flexibility, rapid self-recovery, and stable response enable it to be used as a bending sensor, which shows remarkable stability, repeatability, and durability. This study provides a facile method to fabricate TCF based on commercial but low-cost materials, which is suitable for industrial production and wide practical applications.

Ag nanoparticle-decorated carbon nanotube sponges for removal of methylene blue from aqueous solution

Fabrication of AgNP-Pdop-CNTS for MB adsorption and regeneration.

Nanoscale Patterning of Carbon Nanotubes: Techniques, Applications, and Future

Carbon nanotube (CNT) devices and electronics are achieving maturity and directly competing or surpassing devices that use conventional materials. CNTs have demonstrated ballistic conduction, minimal scaling effects, high current capacity, low power requirements, and excellent optical/photonic properties; making them the ideal candidate for a new material to replace conventional materials in next-generation electronic and photonic systems. CNTs also demonstrate high stability and flexibility, allowing them to be used in flexible, printable, and/or biocompatible electronics. However, a major challenge to fully commercialize these devices is the scalable placement of CNTs into desired micro/nanopatterns and architectures to translate the superior properties of CNTs into macroscale devices. Precise and high throughput patterning becomes increasingly difficult at nanoscale resolution, but it is essential to fully realize the benefits of CNTs. The relatively long, high aspect ratio structures of CNTs must be preserved to maintain their functionalities, consequently making them more difficult to pattern than conventional materials like metals and polymers. This review comprehensively explores the recent development of innovative CNT patterning techniques with nanoscale lateral resolution. Each technique is critically analyzed and applications for the nanoscale-resolution approaches are demonstrated. Promising techniques and the challenges ahead for future devices and applications are discussed.

Carboxymethyl-botryosphaeran stabilized carbon nanotubes aqueous dispersion: A new platform design for electrochemical sensing of desloratadine

The polysaccharide carboxymethyl-botryosphaeran (CMB) was used to improve the dispersion of multi-walled carbon nanotubes (MWCNTs) in water. This feature was applied in modifying a glassy carbon electrode (GCE) to construct a sensitive voltammetric sensor for the determination of desloratadine (DESL), a tricyclic antihistamine. The morphology and spectroscopic behavior of the sensor were evaluated. The modified sensor was characterized as homogeneous, and presented a higher electroactive area and a lower charge transfer resistance compared to the unmodified GCE. Using linear sweep voltammetry at 25 mV s^-1, the developed sensor presented a sensitivity of 1.018 μA L μmol^-1 in the linear working range of 1.99-32.9 μmol L^-1, with a detection limit of 0.88 μmol L^-1 of DESL in 0.10 mol L^-1 potassium hydrogen-phosphate solution (pH 8.0). In addition, the sensor showed excellent repeatability with a relative standard deviation of only 1.02% for a sequence of 10 measurements. The sensor was successfully applied in the analysis of pharmaceutical preparations containing DESL, with equivalent results compared to a validated spectrophotometric method at the 95% confidence level. The sensor was also employed in the analysis of a spiked sample of DESL in rat serum.

The Role of Functionalization in the Applications of Carbon Materials: An Overview

The carbon-based materials (CbMs) refer to a class of substances in which the carbon atoms can assume different hybridization states (sp1, sp2, sp3) leading to different allotropic structures -. In these substances, the carbon atoms can form robust covalent bonds with other carbon atoms or with a vast class of metallic and non-metallic elements, giving rise to an enormous number of compounds from small molecules to long chains to solids. This is one of the reasons why the carbon chemistry is at the basis of the organic chemistry and the biochemistry from which life on earth was born. In this context, the surface chemistry assumes a substantial role dictating the physical and chemical properties of the carbon-based materials. Different functionalities are obtained by bonding carbon atoms with heteroatoms (mainly oxygen, nitrogen, sulfur) determining a certain reactivity of the compound which otherwise is rather weak. This holds for classic materials such as the diamond, the graphite, the carbon black and the porous carbon but functionalization is widely applied also to the carbon nanostructures which came at play mainly in the last two decades. As a matter of fact, nowadays, in addition to fabrication of nano and porous structures, the functionalization of CbMs is at the basis of a number of applications as catalysis, energy conversion, sensing, biomedicine, adsorption etc. This work is dedicated to the modification of the surface chemistry reviewing the different approaches also considering the different macro and nano allotropic forms of carbon.

Carbon Nanotube Assembly and Integration for Applications

Carbon nanotubes (CNTs) have attracted significant interest due to their unique combination of properties including high mechanical strength, large aspect ratios, high surface area, distinct optical characteristics, high thermal and electrical conductivity, which make them suitable for a wide range of applications in areas from electronics (transistors, energy production and storage) to biotechnology (imaging, sensors, actuators and drug delivery) and other applications (displays, photonics, composites and multi-functional coatings/films). Controlled growth, assembly and integration of CNTs is essential for the practical realization of current and future nanotube applications. This review focuses on progress to date in the field of CNT assembly and integration for various applications. CNT synthesis based on arc-discharge, laser ablation and chemical vapor deposition (CVD) including details of tip-growth and base-growth models are first introduced. Advances in CNT structural control (chirality, diameter and junctions) using methods such as catalyst conditioning, cloning, seed-, and template-based growth are then explored in detail, followed by post-growth CNT purification techniques using selective surface chemistry, gel chromatography and density gradient centrifugation. Various assembly and integration techniques for multiple CNTs based on catalyst patterning, forest growth and composites are considered along with their alignment/placement onto different substrates using photolithography, transfer printing and different solution-based techniques such as inkjet printing, dielectrophoresis (DEP) and spin coating. Finally, some of the challenges in current and emerging applications of CNTs in fields such as energy storage, transistors, tissue engineering, drug delivery, electronic cryptographic keys and sensors are considered.

Multi-walled Carbon Nanotubes Reinforced into Hollow Fiber by Chitosan Sol-gel for Solid/Liquid Phase Microextraction of NSAIDs from Urine Prior to HPLC-DAD Analysis

Background:

The efficient analytical method for the analysis of nonsteroidal antiinflammatory drugs (NSAIDs) in a biological fluid is important for determining the toxicological aspects of such long-term used therapies.

Methods:

In the present work, multi-walled carbon nanotubes reinforced into a hollow fiber by chitosan sol-gel assisted-solid/ liquid phase microextraction (MWCNTs-HF-CA-SPME) method followed by the high-performance liquid chromatography-diode array detection (HPLC–DAD) was developed for the determination of three NSAIDs, ketoprofen, diclofenac, and ibuprofen in human urine samples. MWCNTs with various dimensions were characterized by various analytical techniques. The extraction device was prepared by immobilizing the MWCNTs in the pores of 2.5 cm microtube via chitosan sol-gel assisted technology while the lumen of the microtube was filled with few microliters of 1-octanol with two ends sealed. The extraction device was operated by direct immersion in the sample solution.

Results:

The main factors influencing the extraction efficiency of the selected NSAIDs have been examined. The method showed good linearity R2 ≥ 0.997 with RSDs from 1.1 to 12.3%. The limits of detection (LODs) were 2.633, 2.035 and 2.386 µg L-1, for ketoprofen, diclofenac, and ibuprofen, respectively. The developed method demonstrated a satisfactory result for the determination of selected drugs in patient urine samples and comparable results against reference methods.

Conclusion:

The method is simple, sensitive and can be considered as an alternative for clinical laboratory analysis of selected drugs.

Flexible Graphene/Carbon Nanotube Electrochemical Double-Layer Capacitors with Ultrahigh Areal Performance

The fabrication of electrochemical double-layer capacitors (EDLCs) with high areal capacitance relies on the use of elevated mass loadings of highly porous active materials. Herein, we demonstrate a high-throughput manufacturing of graphene/carbon nanotubes hybrid EDLCs. The wet-jet milling (WJM) method is exploited to exfoliate the graphite into single-few-layer graphene flakes (WJM-G) in industrial volumes (production rate ca. 0.5 kg/day). Commercial single-/double-walled carbon nanotubes (SDWCNTs) are mixed with graphene flakes in order to act as spacers between the flakes during their film formation. The WJM-G/SDWCNTs films are obtained by one-step vacuum filtration of the material dispersions, resulting in self-standing, metal- and binder-free flexible EDLC electrodes with high active material mass loadings up to around 30 mg cm^-2 . The corresponding symmetric WJM-G/SDWCNTs EDLCs exhibit electrode energy densities of 539 μWh cm^-2 at 1.3 mW cm^-2 and operating power densities up to 532 mW cm^-2 (outperforming most of the reported EDLC technologies). The EDCLs show excellent cycling stability and outstanding flexibility even in highly folded states (up to 180°).

Diameter of Carbon Nanotube-Directed Self-Assembly of Amphiphilic Block Copolymers

The cooperative self-assembly of nanoparticles and amphiphilic block copolymers has attracted increasing interests as it offers effective routes to achieve nanocomposite supramolecular structures with desired structure and properties. The incorporation of nanoparticles usually tunes the self-assembly structure of block copolymers, as the copolymer-nanoparticle interactions may change the relative volume ratio of hydrophobic block/hydrophilic block copolymers. It should be noted that the micro-size length and the strong nonpolar feature of carbon nanotubes (CNTs) may cause the block copolymer-CNT interactions to differ from the the block copolymer-nanoparticle interactions. Herein, we show that the diameter of CNTs and the copolymer/CNT ratio have a profound effect on the self-assembly behavior of amphiphilic block copolymers. Upon the addition of carboxylated multi-walled carbon nanotubes (c-MWCNTs, diameter <8 nm,) to the methoxy polyethylene glycol-poly (D,L-lactic acid) (MPEG-PDLLA) solution, it is difficult to observe the c-MWCNTs directly in TEM images. However, it has been found that they form supramolecular nanocomposite structures with MPEG-PDLLA. Moreover, these supramolecular structures transform from core-shell spherical micelles into rod-like micelles and then into large composite aggregates with the increase of the c-MWCNT addition. However, in the case of the addition of c-MWCNTs with a diameter of 30-50 nm, the dispersed c-MWCNTs and spherical core-shell micelles could be observed simultaneously in the TEM images at a low c-MWCNT addition, and then the micelle structure disappeared and only well-dispersed c-MWNTs were observed in TEM images at a high c-MWCNT addition. A possible model was proposed to explain the rule of CNTs participating in the formation of copolymer/CNT nanocomposite structures. It was also shown that as-prepared copolymer/CNT supramolecular nanocomposites could be used as drug carriers, enabling the adjustment of the drug loading and release time.

Gemini surfactants as efficient dispersants of multiwalled carbon nanotubes: Interplay of molecular parameters on nanotube dispersibility and debundling

Surfactants have been widely employed to debundle, disperse and stabilize carbon nanotubes in aqueous solvents. Yet, a thorough understanding of the dispersing mechanisms at molecular level is still warranted. Herein, we investigated the influence of the molecular structure of gemini surfactants on the dispersibility of multiwalled carbon nanotubes (MWNTs). We used dicationic n-s-n gemini surfactants, varying n and s, the number of alkyl tail and alkyl spacer carbons, respectively; for comparisons, single-tailed surfactant homologues were also studied. Detailed curves of dispersed MWNT concentration vs. surfactant concentration were obtained through a stringently controlled experimental procedure, allowing for molecular insight. The gemini are found to be much more efficient dispersants than their single-tailed homologues, i.e. lower surfactant concentration is needed to attain the maximum dispersed MWNT concentration. In general, the spacer length has a comparatively higher influence on the dispersing efficiency than the tail length. Further, scanning electron microscopy imaging shows a sizeable degree of MWNT debundling by the gemini surfactants in the obtained dispersions. Our observations also point to an adsorption process that does not entail the formation of micelle-like aggregates on the nanotube surface, but rather coverage by individual molecules, among which the ones that seem to be able to adapt best to the nanotube surface provide the highest efficiency. These studies are relevant for the rational design and choice of optimal dispersants for carbon nanomaterials and other similarly water-insoluble materials.

Adsorption of bisphenol A on dispersed carbon nanotubes: Role of different dispersing agents

Although the adsorption of organic contaminants on carbon nanotubes (CNTs) and the dispersion of CNTs have been extensively investigated separately, the adsorption behavior of organic contaminants on dispersed CNTs, which may be a missing link to understanding their environmental behavior and risks, remain unclear yet rarely studied. In this study, the effect of the dispersing agent structure on the adsorption characteristics of BPA (a representative organic contaminant) on dispersed CNTs were investigated using tannic acid (TA), sodium dodecylbenzenesulfonate (SDBS), and gallic acid (GA) as model dispersing agents. Our results showed that at low dispersing agent concentrations, adsorption of TA could lead to higher CNT suspension than adsorption of SDBS and GA due to greater steric hindrance. However, the presence of TA reduced the adsorption of BPA due to strong competitive adsorption on dispersed CNTs. At high concentrations of TA, the suspension of CNTs was reduced by the "bridging effect," in which adjacent dispersed CNTs form hydrogen bonds and re-aggregate. However, the adsorption of BPA dramatically increased due to the enhanced partition of BPA into pseudomicelles of TA on dispersed CNTs, as indicated by the significantly increased index of heterogeneity at high TA concentration. Transmission electron microscopy images confirmed the formation of TA pseudomicelles. This study highlights the key role of the dispersing agent structure on CNT dispersion and adsorption of organic contaminants. The high mobility and transport of CNT-adsorbed contaminants may lead to higher environmental risks compared with aggregated CNTs.

An Overview of the Recent Progress in the Synthesis and Applications of Carbon Nanotubes

Carbon nanotubes (CNTs) are known as nano-architectured allotropes of carbon, having graphene sheets that are wrapped forming a cylindrical shape. Rolling of graphene sheets in different ways makes CNTs either metals or narrow-band semiconductors. Over the years, researchers have devoted much attention to understanding the intriguing properties CNTs. They exhibit some unusual properties like a high degree of stiffness, a large length-to-diameter ratio, and exceptional resilience, and for this reason, they are used in a variety of applications. These properties can be manipulated by controlling the diameter, chirality, wall nature, and length of CNTs which are in turn, synthesis procedure-dependent. In this review article, various synthesis methods for the production of CNTs are thoroughly elaborated. Several characterization methods are also described in the paper. The applications of CNTs in various technologically important fields are discussed in detail. Finally, future prospects of CNTs are outlined in view of their commercial applications.

Toxicity testing of MWCNTs to aquatic organisms

The increase in global production of carbon nanotubes (CNTs), as well as their use in polymer nanocomposites has raised concerns as to their possible effects on the marine environment that could ultimately affect human populations. Specifically, CNTs have already been tested in antifouling formulations for the prevention of biofouling, mainly to protect ships' hulls, as well as in composite materials that come in contact with seawater. At this point, it seems crucial to assess the possible effects of CNTs on aquatic organisms and assess their toxicity. Thus, in this study, three different model organisms were selected for toxicity testing: Daphnia magna water flea, Artemia salina nauplii and Danio rerio zebrafish. The CNTs that were tested have been produced in house via the chemical vapour deposition method and were fully characterised in order to understand the effect of their properties on the aquatic organisms. In this study pristine multiwalled carbon nanotubes (MWCNTs) as well as functionalised with carboxyl groups were used. Dispersion issues were evident in all tests, both for the pristine and functionalised carbon nanotubes, thus their toxicity could not be determined in relation to their concentration. To overcome this issue, optical observation of the organisms took place. MWCNT black aggregates were clearly observed in the intestine of A. salina. Following an additional 24 h in seawater the intestine appeared clean and restored to its normal appearance. This observation leads to the conclusion that MWCNTs did not prove to be fatal to D. magna and A. salina despite their presence in the digestive track of both non-target organisms. These results show that MWCNTs do not affect the non-target organisms in the short term, thus their use in antifouling coatings and composite materials for maritime applications can be further investigated.

Optical observation of Artemia salina′s intestine after 100 mg L⁻¹ MWCNT-COOH exposure: the intestine appeared clean and restored to its normal appearance.