K and Au bicatalyst assisted growth of carbon nanocoils from acetylene: effect of deposition parameters on field emission properties

Recent Advances in Conductive Polymers-Based Electrochemical Sensors for Biomedical and Environmental Applications

Electrochemical sensors play a pivotal role in various fields, such as biomedicine and environmental detection, due to their exceptional sensitivity, selectivity, stability, rapid response time, user-friendly operation, and ease of miniaturization and integration. In addition to the research conducted in the application field, significant focus is placed on the selection and optimization of electrode interface materials for electrochemical sensors. The detection performance of these sensors can be significantly enhanced by modifying the interface of either inorganic metal electrodes or printed electrodes. Among numerous available modification materials, conductive polymers (CPs) possess not only excellent conductivity exhibited by inorganic conductors but also unique three-dimensional structural characteristics inherent to polymers. This distinctive combination allows CPs to increase active sites during the detection process while providing channels for rapid ion transmission and facilitating efficient electron transfer during reaction processes. This review article primarily highlights recent research progress concerning CPs as an ideal choice for modifying electrochemical sensors owing to their remarkable features that make them well-suited for biomedical and environmental applications.

Recent Developments and Implementations of Conductive Polymer-Based Flexible Devices in Sensing Applications

Flexible sensing devices have attracted significant attention for various applications, such as medical devices, environmental monitoring, and healthcare. Numerous materials have been used to fabricate flexible sensing devices and improve their sensing performance in terms of their electrical and mechanical properties. Among the studied materials, conductive polymers are promising candidates for next-generation flexible, stretchable, and wearable electronic devices because of their outstanding characteristics, such as flexibility, light weight, and non-toxicity. Understanding the interesting properties of conductive polymers and the solution-based deposition processes and patterning technologies used for conductive polymer device fabrication is necessary to develop appropriate and highly effective flexible sensors. The present review provides scientific evidence for promising strategies for fabricating conductive polymer-based flexible sensors. Specifically, the outstanding nature of the structures, conductivity, and synthesis methods of some of the main conductive polymers are discussed. Furthermore, conventional and innovative technologies for preparing conductive polymer thin films in flexible sensors are identified and evaluated, as are the potential applications of these sensors in environmental and human health monitoring.

Synthesis of Diamond-Like Carbon Nanofiber Films

A film formed of densely packed amorphous carbon nanofibers is synthesized by chemical vapor deposition using acetylene and hydrogen gases as precursors and copper nanoparticles (<25 nm in diameter) as the catalyst at low temperatures (220-300 °C). This film has a high concentration of sp³ carbon (sp³/sp² carbon ratio of ∼1-1.9) with a hydrogen concentration of 25-44 atom %, which qualifies it as hydrogenated diamond-like carbon. This hydrogenated diamond-like carbon nanofiber film has properties akin to those of diamond-like carbon films. It has a high electrical resistivity (1.2 ± 0.1 × 10⁶ Ω cm), a density of 2.5 ± 0.2 g cm^-3, and is chemically inert. Because of its morphology, different from diamond-like carbon films on the nanometer scale, it has a higher surface area of 28 ± 0.7 m² g^-1 and has differences in mechanical properties, such as Young's modulus, hardness, and coefficient of friction. The hydrophobicity of this film is comparable to the best diamond-like carbon films, and it is wettable by oil and organic solvents. The nanofibers can also be separated from the substrate and each other and be used in a powder form.

Controllable Synthesis of Co@CoOx/Helical Nitrogen-Doped Carbon Nanotubes toward Oxygen Reduction Reaction as Binder-free Cathodes for Al-Air Batteries

Efficient and stable electrocatalysts for oxygen reduction reaction and freestanding electrode structure were developed to reduce the use of polymer binders in the cathode of metal-air batteries. Considering the unique geometrical configurations of helical carbon nanotubes (CNTs) and improved properties compared with straight CNTs, we prepared high-purity Co@CoO_x/helical nitrogen-doped carbon nanotubes (Co@CoO_x/HNCNTs) on a carbon fiber paper by hydrothermal and single-step in situ chemical vapor deposition strategies. Under an optimized growth time (1 h), the synthesized Co@CoO_x/HNCNTs provide richer edge defects and active sites and show prominent electrocatalytic performance toward oxygen reduction reaction (ORR) under alkaline media compared with Co@CoO_x/HNCNTs-0.5 h and Co@CoO_x/HNCNTs-2 h. The soft X-ray absorption spectroscopy technique is used to investigate the influences of different growth times on the electronic structure and local chemical configuration of Co@CoO_x/HNCNTs. Furthermore, the Al-air coin cell employing Co@CoO_x/HNCNTs-1 h as the binder-free cathode exhibits an open-circuit voltage of 1.48 V, a specific capacity of 367.31 mA h g^-1 at the discharge current density of 1.0 mA cm^-2, and a maximum power density (P_max) of 3.86 mW cm^-2, which are superior to those of Co@CoO_x/HNCNTs-0.5 h and Co@CoO_x/HNCNTs-2 h electrodes. This work provides valuable insights into the development of scalable binder-free cathodes, exploiting HNCNT composite materials with an outstanding electrocatalytic performance for ORR in Al-air systems.

Growth of Carbon Nanocoils by Porous α-Fe2O3/SnO2 Catalyst and Its Buckypaper for High Efficient Adsorption

High-purity (99%) carbon nanocoils (CNCs) have been synthesized by using porous α-Fe2O3/SnO2 catalyst. The yield of CNCs reaches 9,098% after a 6 h growth. This value is much higher than the previously reported data, indicating that this method is promising to synthesize high-purity CNCs on a large scale. It is considered that an appropriate proportion of Fe and Sn, proper particle size distribution, and a loose-porous aggregate structure of the catalyst are the key points to the high-purity growth of CNCs. Benefiting from the high-purity preparation, a CNC Buckypaper was successfully prepared and the electrical, mechanical, and electrochemical properties were investigated comprehensively. Furthermore, as one of the practical applications, the CNC Buckypaper was successfully utilized as an efficient adsorbent for the removal of methylene blue dye from wastewater with an adsorption efficiency of 90.9%. This study provides a facile and economical route for preparing high-purity CNCs, which is suitable for large-quantity production. Furthermore, the fabrication of macroscopic CNC Buckypaper provides promising alternative of adsorbent or other practical applications.

Chemical Vapor Deposition of Carbon Nanocoils Three-Dimensionally in Carbon Fiber Cloth for All-Carbon Supercapacitors

An Au/K bicatalyst-assisted chemical vapor deposition process using C₂H_2(g) to grow high-density carbon nanocoils (CNCs) uniformly on the fibers in carbon fiber cloth substrates three-dimensionally was developed. An as-deposited substrate (2.5 × 1.0 cm²) showed a high electrochemical active surface area (16.53 cm²), suggesting its potential usefulness as the electrode in electrochemical devices. The unique one-dimensional (1D) helical structure of the CNCs shortened the diffusion pathways of the ions in the electrolyte and generated efficient electron conduction routes so that the observed serial resistance R _s was low (3.7 Ω). By employing two-electrode systems, a liquid-state supercapacitor (SC) in H₂SO_4(aq) (1.0 M) and a solid-state SC with a polypropylene (PP) separator immersed in H₂SO_4(aq) (1.0 M)/polyvinylalcohol were assembled and investigated by using CNC-based electrodes. Both devices exhibited approximate rectangular shape profiles in the cyclic voltammetry measurements at various scan rates. The observations indicated their electric double-layer capacitive behaviors. From their galvanostatic charge/discharge curves, the specific capacitances of the liquid SC and the solid SC were measured to be approximately 137 and 163 F/g, respectively. In addition, the solid-state CNC-based SC possessed excellent energy density (15.3 W h/kg) and power density (510 W/kg). The light weight solid SC (0.1965 g, 2.5 × 1.0 cm²) was bendable up to 150° with most of the properties retained.

Synthesis of Helical Carbon Fibers and Related Materials: A Review on the Past and Recent Developments

Helical carbon fibers (HCFs) have been widely studied due to their unique helical morphology and superior properties, which make them efficient materials for several potential applications. This review summarizes the past and current advancement on the synthesis of HCFs. The review focuses and discusses synthesis strategies and effect of experimental parameters on the growth of HCFs. The effect of preparation method of catalyst, catalyst nature, catalyst composition, catalyst size, catalyst initial and final shape, reaction temperature, reaction time, carbon source, impurities, and electromagnetic field on the growth of HCFs is reviewed. We also discuss the growth mechanism for HCFs and the synthesis of HCFs related materials. Finally, we conclude with a brief summary and an outlook on the challenges and future prospects of HCFs.

Size-selective catalytic growth of nearly 100% pure carbon nanocoils with copper nanoparticles produced by atomic layer deposition

In this paper, Cu nanoparticles with narrow size distribution are synthesized by reduction of CuO films produced by atomic layer deposition (ALD), which are used as catalysts for the catalytic growth of carbon nanostructures. By properly adjusting the ALD cycle numbers, the size of produced Cu nanoparticles can be well controlled. Uniform carbon nanocoils with near 100% purity can be obtained by using 50-80 nm Cu nanoparticles, while thin straight fibers and thick straight fibers are produced by applying 5-35 and 100-200 nm Cu nanoparticles, respectively. The mechanism of the particle size-dependent growth of the carbon nanostructure was analyzed based on the experimental results and theoretical simulation. Our results can provide important information for the preparation of helical carbon nanostructures with high purity. Moreover, this work also demonstrates that ALD is a viable technique for synthesizing nanoparticles with highly controllable size and narrow size distribution suitable for studying particle size-dependent catalytic behavior and other applications.