Wearable heaters have attracted broad attention due to their applications in personal heating systems and healthcare management, such as heat preservation in textile/clothing and thermotherapy. Protecting heating performance against deterioration under large deformation is is important for the application of wearable heaters. Here, a highly stretchable electrically driven heater based on electrically conductive weft-knitted fabrics is reported, which can be transformed from traditional fabrics through a facile heat treatment process. As an example, a heater made from Modal shows a heating temperature higher than 100 °C at a driving voltage as low as 3 V. The Joule heating performance of the heater does not deteriorate even under a large strain of 70%. Furthermore, according to theoretical analysis and experimental results, the output power and saturated temperature of the heater under a certain voltage can be easily tuned by tailoring the shape and size of the fabric to meet customized demands. The superior performance of the heater originates from the weft-knitted structural configuration. Finally, the application of the ultrastretchable heater in wearable thermal therapy devices is demonstrated, showing its great potential in wearable electronics.

The mechanism for the formation of double-layer vertically aligned carbon nanotube arrays (VACNTs) through single-step CVD growth is investigated. The evolution of the structures and defect concentration of the VACNTs are tracked by scanning electron microscopy (SEM) and Raman spectroscopy. During the growth, the catalyst particles are stayed constantly on the substrate. The precipitation of the second CNT layer happens at around 30 min as proved by SEM. During the growth of the first layer, catalyst nanoparticles are deactivated with the accumulation of amorphous carbon coatings on their surfaces, which leads to the termination of the growth of the first layer CNTs. Then, the catalyst particles are reactivated by the hydrogen in the gas flow, leading to the precipitation of the second CNT layer. The growth of the second CNT layer lifts the amorphous carbon coatings on catalyst particles and substrates. The release of mechanical energy by CNTs provides big enough energy to lift up amorphous carbon flakes on catalyst particles and substrates which finally stay at the interfaces of the two layers simulated by finite element analysis. This study sheds light on the termination mechanism of CNTs during CVD process.

Flexible and wearable sensors have drawn extensive concern due to their wide potential applications in wearable electronics and intelligent robots. Flexible sensors with high sensitivity, good flexibility, and excellent stability are highly desirable for monitoring human biomedical signals, movements and the environment. The active materials and the device structures are the keys to achieve high performance. Carbon nanomaterials, including carbon nanotubes (CNTs), graphene, carbon black and carbon nanofibers, are one of the most commonly used active materials for the fabrication of high-performance flexible sensors due to their superior properties. Especially, CNTs and graphene can be assembled into various multi-scaled macroscopic structures, including one dimensional fibers, two dimensional films and three dimensional architectures, endowing the facile design of flexible sensors for wide practical applications. In addition, the hybrid structured carbon materials derived from natural bio-materials also showed a bright prospect for applications in flexible sensors. This review provides a comprehensive presentation of flexible and wearable sensors based on the above various carbon materials. Following a brief introduction of flexible sensors and carbon materials, the fundamentals of typical flexible sensors, such as strain sensors, pressure sensors, temperature sensors and humidity sensors, are presented. Then, the latest progress of flexible sensors based on carbon materials, including the fabrication processes, performance and applications, are summarized. Finally, the remaining major challenges of carbon-based flexible electronics are discussed and the future research directions are proposed.摘要近年来, 柔性传感器因其在可穿戴电子设备和智能系统中的广阔应用前景而备受关注. 柔性可穿戴传感器具有高灵敏度、 良好的 机械柔性、 优异的稳定性、 人体友好性等特点, 在人体运动与生理信号监测、 环境因素检测等方面具有极大的应用潜力. 一般而言, 柔性 传感器的性能主要取决于敏感材料的选择与器件的结构设计. 得益于其优异的性能和灵活多样的组装结构与形貌>碳材料是目前应用最 广泛的敏感材料之一. 根据需求, 纳米碳材料可组装为各类宏观结枸, 比如一维的纤维, 二维的薄膜和三维的块体结构>从而可用于制备各 种柔性传感器以适应不同的需求.此外, 通过规模化、 低成本的高温碳化工艺可以将天然生物质材料转化为柔性、 导电碳材料, 并用于高 性能柔性传慼器制备. 本文针对碳材料在柔性器件中的应用, 综述了各类碳材料的制备方法与结构特点,并重点介绍了其柔性可穿戴传慼 器的制备与性能. 第一部分简要介绍了柔性传感器与碳材料; 第二部分概述了四类典型柔性传感器的工作原理与性能特点; 第三部分详细 综述了一维、 二维和三维碳材料的制备方法与其在柔性传感器的组装、 性能与应用方面的最新研究进展; 最后, 总结了碳基柔性传感器 领域的发展现状, 讨论了该领域所面临的挑战及其未来前景.

Silkworm silk is gaining significant attention from both the textile industry and research society because of its outstanding mechanical properties and lustrous appearance. The possibility of creating tougher silks attracts particular research interest. Carbon nanotubes and graphene are widely studied for their use as reinforcement. In this work, we report mechanically enhanced silk directly collected by feeding Bombyx mori larval silkworms with single-walled carbon nanotubes (SWNTs) and graphene. We found that parts of the fed carbon nanomaterials were incorporated into the as-spun silk fibers, whereas the others went into the excrement of silkworms. Spectroscopy study indicated that nanocarbon additions hindered the conformation transition of silk fibroin from random coil and α-helix to β-sheet, which may contribute to increased elongation at break and toughness modules. We further investigated the pyrolysis of modified silk, and a highly developed graphitic structure with obviously enhanced electrical conductivity was obtained through the introduction of SWNTs and graphene. The successful generation of these SWNT- or graphene-embedded silks by in vivo feeding is expected to open up possibilities for the large-scale production of high-strength silk fibers.Keywords: carbon nanotubes; carbonization; graphene; mechanical property; Silkworm silk;

The development of nanomaterials has put forward high requirements for characterization techniques. Optical microscopy (OM), with easy accessibility and open operating spaces as compared to scanning electron microscopy, is a good choice to quickly locate materials and to be integrated with other equipment. However, OM is limited by its low resolution. Herein, we present a facile and non-destructive approach for optical observation of nanomaterials under conventional OMs with the aid of volatile nanoparticles (NPs), which can be deposited and removed in a controlled manner. The NPs deposited on the surface of nanomaterials render strong light scattering to enable the nanomaterials to become optically visible. For example, this approach enables the observation of individual carbon nanotubes (CNTs) with OMs at low magnification or even with the naked eye. Both supported CNTs on various substrates and suspended CNTs can be observed with this approach. Most importantly, the NPs can be completely removed through moderate heat treatment or laser irradiation, avoiding potential influence on the properties or subsequent applications of nanomaterials. Furthermore, we systematically investigate the deposition of various volatile NPs (up to 14 kinds) for the optical observation of nanomaterials. We also demonstrated the application of this approach on other nanomaterials, including nanowires and graphene. We showed that this approach is facile, controllable, non-destructive, and contamination-free, indicating wide potential applications.

Recent years have witnessed the explosive development of flexible strain sensors. Nanomaterials have been widely utilized to fabricate flexible strain sensors, because of their high flexibility and electrical conductivity. However, the fabrication processes for nanomaterials and the subsequent strain sensors are generally complicated and are manufactured at high cost. In this work, we developed a facile dry-Meyer-rod-coating process to fabricate sheath–core-structured single-fiber strain sensors using ultrafine graphite flakes as the sheath and silk fibers as the core by virtue of their flexibility, high production, and low cost. The fabricated strain sensor exhibits a high sensitivity with a gauge factor of 14.5 within wide workable strain range up to 15%, and outstanding stability (up to 3000 cycles). The single-fiber-based strain sensors could be attached to a human body to detect joint motions or easily integrated into the multidirectional strain sensor for monitoring multiaxial strain, showing great potential applications as wearable strain sensors.Keywords: dry-Meyer-rod-coating; flexible electronics; graphite flakes; sheath-core structure; silk fiber; strain sensor

This work presents a highly efficient and reliable strategy to grow horizontally aligned carbon nanotube (CNT) arrays on surfaces via preliminarily loading catalysts into the reactor. With the heat treatment before the growth of CNTs, the catalysts would migrate from the inner surface of the reactor to the surface of the targeted substrate to induce the growth of aligned CNTs. With this “in-situ catalyst loading” approach, aligned CNTs could be grown on different bare substrates, such as silicon, quartz and sapphire. The growth of CNTs could be repeated up to 50 times with reliable results via only one-time catalyst preloading process, avoiding the deposition of catalysts before each round of growth and the related randomicity, and thus benefiting the mass production of aligned CNT arrays on surfaces.

Silk is a widely available, edible, biocompatible, and environmentally sustainable natural material. Particulate matter (PM) pollution has drawn considerable attention because it is a serious threat to public health. Herein, we report a human-friendly silk nanofiber air filter, which exhibits superior filtration efficiency for both PM2.5 and submicron particles with obviously low pressure drop and low basis weight compared to typical commercial microfiber air filters. Additionally, other functions such as antibacterial activity could be easily integrated into the silk nanofiber air filters, enabling the fabrication of multifunctional air filters. All the above characteristics, combined with the natural abundance and biocompatibility of silk, suggest a great potential for the use of silk nanofibers as air filters, especially as comfortable and personal air purifiers.

Fast and uniform growth of high-quality graphene on conventional glass is of great importance for practical applications of graphene glass. We report herein a confined-flow chemical vapor deposition (CVD) approach for the high-efficiency fabrication of graphene glass. The key feature of our approach is the fabrication of a 2–4 μm wide gap above the glass substrate, with plenty of stumbling blocks; this gap was found to significantly increase the collision probability of the carbon precursors and reactive fragments between one another and with the glass surface. As a result, the growth rate of graphene glass increased remarkably, together with an improvement in the growth quality and uniformity as compared to those in the conventional gas flow CVD technique. These high-quality graphene glasses exhibited an excellent defogging performance with much higher defogging speed and higher stability compared to those previously reported. The graphene sapphire glass was found to be an ideal substrate for growing uniform and ultra-smooth aluminum nitride thin films without the tedious pre-deposition of a buffer layer. The presented confined-flow CVD approach offers a simple and low-cost route for the mass production of graphene glass, which is believed to promote the practical applications of various graphene glasses.

A three-dimensional carbon nanotube (CNT)/graphene hybrid material was synthesized by a two-step chemical vapor deposition (CVD) process. Due to the separated CVD processes for graphene and CNTs, the structures of the hybrid materials could be easily controlled. It is revealed that graphene film was tightly connected with one end of the CNT arrays, forming “jellyfish” structures. Moreover, our results indicate that the presence of graphene influenced the precipitation and growth rate of CNTs. The precipitation of CNTs was postponed due to the existence of graphene. However, the average growth rate of CNTs in the graphene region for the whole process was faster than that in the region without graphene.

We report a facile graphene/graphite sheet assisted CVD process for the synthesis of high-areal-density HACNT arrays. Besides, some metal nanoparticles could eat the graphene/graphite sheets, forming serpentine holes on the sheets in the early stage, and finally leading to the precipitation of CNTs without an additional carbon source.

Fluidized bed filtration is a promising technique to remove particles from gas stream. In this work, a fluidized bed filter with agglomerated carbon nanotubes (CNTs) as bed materials is employed to filtrate aerosol particles and its filtration performance is investigated. The aerosol filtration efficiency of fluidized bed filters is found to highly depend on the fluidization state of the filter media. Agglomerate particulate fluidization brings much higher efficiency than agglomerate bubbling fluidization (ABF). Due to the effect of bubbles and the abrasion of fluidizing media in ABF, there are a growing number of nanoparticles releasing from the bed with the increase of gas velocity. The filtration performance of fluidized bed filters with agglomerated CNTs as the media is compared with that of packed bed filters with the same media. It is found that the former provides much lower resistance and obvious higher quality factor than the latter. The filtration efficiency of fluidized bed filter increases with the increase of the static bed height. Our results show that agglomerated CNTs could be employed as media of the fluidized bed which can be used as the high efficiency particulate air filter.

Hierarchical and gradient nanostructures are important to exploit the full potential of nanofibers in filtration applications. The introduction of a gradient into carbon nanotube (CNT)/fiber hierarchical structures could result in a change of the particle capturing properties. Here, we show the fabrication of hierarchical carbon nanotube (CNT)/quartz-fiber (QF) filters with gradient nanostructures where the content of CNTs decreases exponentially along the thickness direction of the filters. The loading of catalysts for the growth of CNTs in the QF filter has been achieved using an aerosol technique, which can be carried out on a large-scale. With only 1.17 wt% CNT, the penetration of the CNT/QF filter at the most penetrating particle size (MPPS) has been reduced by one order of magnitude, while the pressure drop only increases about 6% with respect to that of the pristine QF filter, leading to an obvious higher quality factor (Qf) for the CNT/QF filter. More importantly, the service life of the CNT/QF filter with the CNT-rich side downstream has increased by 64% when compared with the pristine QF filter. In contrast, when the CNT-rich side is placed upstream, the service life of CNT/QF filter is only 41.7% of that observed when placing the CNT-rich side downstream. Scanning electron microscopy (SEM) images reveal that the gradient nanostructure of the CNT/QF filter, together with the CNT/QF hierarchical structure play very important roles in the simultaneous enhancement of the filtration efficiency and the service life of the air filters.

The reason why few carbon nanotubes (CNTs) nucleated in the catalyst region on substrates grow into ultralong ones during gas flow directed chemical vapor deposition (CVD) of horizontally aligned CNT arrays was explored. Small catalyst nanoparticles tend to merge into large ones due to the high processing temperature, which accordingly produces multi-wall CNTs (MWCNTs). These MWCNTs usually follow a base-growth mechanism and cannot be guided by the gas flow during growth. These MWCNTs are often shorter than 20 μm. Only the CNTs that follow the tip-growth mechanism, which are catalyzed by smaller nanoparticles and have fewer walls than most of the CNTs, tend to grow into longer ones. Besides, other factors influencing the areal density of ultralong CNTs, such as the entanglement of CNTs and the falling down of the growing tip of floating CNTs to the substrate, were also discussed.

High-density parallel arrays of ultralong carbon nanotubes (CNTs) were prepared by utilizing catalyst nanoparticles anchored by silica nanospheres through chemical vapor deposition (CVD). Silica nanospheres and catalyst solution were sequentially spin-coated onto the substrates for the growth of ultralong CNTs, followed by annealing to remove the polymer residues. Catalyst nanoparticles can be anchored on the top of or around the silica nanospheres. Then, ultralong CNTs were synthesized with methane as the carbon source at 1010 °C under ambient pressure. Our results show that the areal density of the ultralong CNTs produced by this nanosphere-assisted process was obviously improved compared with that by the typical process without nanospheres.

The Schulz–Flory distribution is a mathematical function that describes the relative ratios of polymers of different length after a polymerization process, based on their relative probabilities of occurrence. Carbon nanotubes (CNTs) are big carbon molecules which have a very high length-to-diameter ratio, somewhat similar to polymer molecules. Large amounts of ultralong CNTs have not been obtained although they are highly desired. Here, we report that the Schulz–Flory distribution can be applied to describe the relative ratios of CNTs of different lengths produced with a floating chemical vapor deposition process, based on catalyst activity/deactivation probability. With the optimized processing parameters, we successfully synthesized 550-mm-long CNTs, for which the catalyst deactivation probability of a single growth step was ultralow. Our finding bridges the Schulz–Flory distribution and the synthesis of one-dimensional nanomaterials for the first time, and sheds new light on the rational design of process toward controlled production of nanotubes/nanowires.Keywords: carbon nanotubes; catalyst activity; chemical vapor deposition; Schulz−Flory distribution; ultralong

The synthesis of pure δ-MoN with desired superconducting properties usually requires extreme conditions, such as high temperature and high pressure, which hinders its fundamental studies and applications. Herein, by using a chemical solution method, epitaxial δ-MoN thin films have been grown on c-cut Al2O3 substrates at a temperature lower than 900 °C and an ambient pressure. The films are phase pure and show a Tc of 13.0 K with a sharp transition. In addition, the films show a high critical field and excellent current carrying capabilities, which further prove the superior quality of these chemically prepared epitaxial thin films.

We report a facile graphene/graphite sheet assisted CVD process for the synthesis of high-areal-density HACNT arrays. Besides, some metal nanoparticles could eat the graphene/graphite sheets, forming serpentine holes on the sheets in the early stage, and finally leading to the precipitation of CNTs without an additional carbon source.