The incorporation of electrothermal films into smart windows has been of intense research interest in developing highly conductive transparent films. However, achieving a high optical transparency and exceptional electrothermal performance simultaneously remains a great challenge. We reported a transparent conductive single-wall carbon nanotube (SWCNT) film comprised of highly-crystalline and long SWCNTs in small bundles. The SWCNT film with an average bundle diameter of 7.1 nm had a low sheet resistance of 26 Ω/□ at a transmittance of 82%, and had a constant temperature of 102 °C at a low applied voltage of 20 V. Integrating this transparent heating film with thermochromic materials enabled the fabrication of a flexible smart window with thermally triggered dynamic transparency. The device has a broad reversible visible light transparency range (~ 78%) and excellent cycling stability.
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Carbon nanotube fibers (CNTFs) are regarded as a promising candidate material for use in high frequency AC transmission line, electromagnetic shielding cable, antenna, lightweight high-strength composites due to their advantages in low-density, high conductivity and high-strength. Recent advances are made in the fabrication of CNTFs, especially those spun by a wet-spinning technology. However, CNTFs fabricated by a conventional wet spinning method generally have irregular cross-section and non-uniform radial structure, resulting in a rapid double diffusion between chlorosulfonic acid (CSA) in the spinning solution and acetone coagulation bath and a significant radial stiffness gradient in the fiber, thus easily leading to core-shell and wrinkled structures. In this work, we selected N-Methylpyrrolidone (NMP) as a coagulation bath to decrease the diffusion rate between CSA and coagulation bath. Single-wall carbon nanotube fibers (SWCNTFs) with a circular cross section could be continuously spun in NMP. We further introduced ethanol into NMP coagulation bath to control the double diffusion rate and viscosity to improve the draw ratio of SWCNTFs. As a result, SWCNTFs with circular cross-section, high orientation, and desirable electrical and mechanical properties were fabricated.
Single-wall carbon nanotubes (SWCNTFs) with a high crystallinity and a high purity were synthesized by a floating catalyst chemical vapor deposition method. The SWCNTs were put into a beaker, and transferred to a glove box in Ar atmosphere. CSA was then added to the glass bottle, and agitated for 30 min to obtain a liquid crystal (LC) phase. The LC spinning solution was transferred into a stainless steel syringe in Ar atmosphere and extruded through a spinneret into coagulation bath by an injection pump to form macroscopic fibers. An appropriate draw ratio was applied to the SWCNTFs through a drawing device, and fibers were then wound on a PTFE roll and dried under 30 ℃ for 12 h. In this work, all the fibers were spun at a maximum draw ratio that they could endure.
The SWCNTFs spun from NMP coagulation bath have a higher circularity of 0.80, while their alignment and packing density is relatively low due to the smaller draw ratio. We therefore introduces ethanol into the NMP coagulation bath to tune the double diffusion rate to increase the applied draw ratio. The results show that the maximum draw ratio applied to SWCNTFs increases with the increase of ethanol content and reaches to the maximum value of 169% at the ethanol content of 75%. The obtained SWCNTFs have a high circularity of 0.87 and a high orientation Herman factor of 0.987. We analyzes the mechanical behavior of the nascent fiber in the coagulation bath, clarifying how the coagulation bath affects the formation of wet-spun fibers. The results show that optimizing the coagulation bath viscosity effectively reduces a frictional resistance during fiber formation, while an optimized double diffusion rate promotes a denser packing within the surface solidification layer. These synergistic effects collectively enable higher fiber draw ratios and facilitate the development of a highly oriented microstructure with a circular cross-section.
This study investigated the radial structural heterogeneity and surface wrinkling in conventional wet-spun CNTFs via developing a novel NMP-based coagulation bath. The NMP coagulation bath significantly reduced the double-diffusion rate of CSA, enabling the fabrication of SWCNTFs without a core-shell structure, while improving radial structural uniformity. Ethanol was then introduced into the NMP coagulation bath to improve the draw ratio and orientation of the fibers. The optimized SWCNTFs showed a high circular cross-section of 0.87, which was twice more than that of previously reported SWCNTFs (i.e., 0.37). The fibers simultaneously had high orientation Herman factor of 0.987, high mechanical properties with tensile strength of (1047±44) MPa and Young's modulus of (24.0±3.26) GPa, as well as high electrical characteristics with conductivity of (5.74±0.28)×106 S/m and ampacity of (3.99±0.07)×108 A/m2. The developed SWCNTFs with a homogeneous structure and a regular morphology could have a promising potential for applications in high-frequency transmission wires and fiber reinforced composite materials.
Single wall carbon nanotube (SWCNT)/Si heterojunction photodetectors have the advantages of high photoresponse ability and simple structure, however, their detection wavelength range are usually lower than 1100 nm, which limits their application in the infrared band. We report a SWCNT/Cu/Si photodetector with both a high photoresponse and a detection range up to the infrared band by depositing a Cu nanoparticles (NPs) layer between a SWCNT film and a n-Si substrate. It was found that the Cu NPs produce strong surface plasmon resonance (SPR) under laser irradiation, which breaks through the limitation of Si band gap and greatly improves the photoresponse of the SWCNT/Cu/Si photodetector in the near infrared band. The responsivity (R) of the photodetector in the wavelength range of 1850–1200 nm reached 2.2–14.15 mA/W, which is the highest value in the reported plasmon enhanced n-Si based photodetectors, and about 20,000 times higher than that of a SWCNT/Si photodetector. Its R value for 1550 nm wavelength used in optical communications reached ~ 8.2 mA/W, which is 64% higher than the previously reported values of commonly used photodetectors. We attribute the significant increase to the strong SPR and low Schottky barrier of Cu with n-Si, which facilitates the generation and transfer of the carriers.
Carbon nanotube (CNT) fibers have great promise for constructing multifunctional fabrics with high electrical conductivity, good electro-heating ability, excellent flexibility, and a low density. However, the inter-fiber contacts in the fabric greatly reduce these advantages and limit their application. Herein, a simple pressure-fusing method to fabricate single-wall CNT (SWCNT) fiber non-woven fabrics (NWFs) that are composed of interconnected SWCNT fibers with fused joints is reported, which have good flexibility, a low density of 0.46 g/cm3, a high electrical conductivity of 3.7 × 105 S/m, and a record high specific electrical conductivity of 803 (S·m2)/kg. They also showed excellent electrical heating ability, so that a temperature of ~ 160 °C was rapidly reached at a low voltage of 2 V. Combined with their low density, the SWCNT fiber NWFs are promising for use as a heating unit for low temperature battery protection and de-icing applications.
Rate-controlled growth of carbon nanotubes (CNTs) and catalyst design are considered efficient ways for the preparation of CNTs with specific structures and properties. However, due to the difficulties in capturing the growth process of the CNTs with tiny size under a complex growth environment, the growth kinetics of CNTs and their correlation with the catalyst seed have been seldom revealed. Here, we investigated the growth process of CNTs from Ni nanoparticles (NPs) in real-time under atmospheric pressure using transmission electron microscopy equipped with a closed gas cell. It was found that the growth rates of CNTs fluctuated, and a phase transition from Ni3C to Ni, and a reshaping of the catalyst NPs occurred during the growth process. We demonstrated that CNTs dynamically interacted with the connected catalyst NPs and the fluctuated growth rates of CNTs were correlated with the structure change of catalyst NPs. The origin of the growth rate fluctuation is attributed to the change of carbon concentration gradient in catalyst NPs.
The efficient recovery of gold from industrial sewage is important for saving precious metals and remains a big challenge. We report the extraction of gold ions from a trace-level aqueous solution using a tannic acid (TA) coated single-wall carbon nanotube (SWCNT) film. The TA has many redox ligands that efficiently adsorb Au(III) from the solution and reduce them to Au particles. The interwoven SWCNTs not only act as a framework to improve the mechanical stability of the hybrid membrane, but also provide abundant paths for H2O transport, and facilitate the full exposure of the TA. As a result, the hybrid membrane has an excellent ability to capture gold ions from solution with a high flux of 157 L/(m2·h·bar), and an ultra-high adsorption capacity of 2095 mg/g from solutions with an extremely low gold concentration of 20 ppm. The adsorbed gold ions are reduced to Au particles, which can be easily collected by oxidation. The recovered Au nanoparticles on the TA–SWCNT hybrid film had a remarkable surface-enhanced Raman scattering effect that enabled the sensitive detection of rhodamine 6G.
It has been a great challenge to optimize the growth conditions toward structure-controlled growth of single-wall carbon nanotubes (SWCNTs). Here, a high-throughput method combined with machine learning is reported that efficiently screens the growth conditions for the synthesis of high-quality SWCNTs. Patterned cobalt (Co) nanoparticles were deposited on a numerically marked silicon wafer as catalysts, and parameters of temperature, reduction time and carbon precursor were optimized. The crystallinity of the SWCNTs was characterized by Raman spectroscopy where the featured G/D peak intensity (IG/ID) was extracted automatically and mapped to the growth parameters to build a database. 1, 280 data were collected to train machine learning models. Random forest regression (RFR) showed high precision in predicting the growth conditions for high-quality SWCNTs, as validated by further chemical vapor deposition (CVD) growth. This method shows great potential in structure-controlled growth of SWCNTs.
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