Aligned Carbon Nanofibers Research Articles

3D Printing-Induced Hierarchically Aligned Nanocomposites With Exceptional Multidirectional Strain Sensing Performance.

High-performance sensors capable of detecting multidirectional strains are indispensable to understand the complex motions involved in flexible electronics. Conventional isotropic strain sensors can only measure uniaxial deformations or single stimuli, hindering their practical application fields. The answer to such challenge resides in the construction of engineered anisotropic sensing structures. Herein, a hierarchically aligned carbon nanofiber (CNF)/polydimethylsiloxane nanocomposite strain sensor is developed by one-step 3D printing. The precisely controlled printing path and shear flow bring about highly aligned nanocomposite filaments at macroscale and orientated CNF network within each filament at microscale. The periodically orientated nanocomposite filaments along with the inner aligned CNF network successfully control the strain distribution and the appearance of microcracks, giving rise to anisotropic structural response to external deformations. The synergetic effect of the multiscale structural design leads to distinguishable gauge factors of 164 and 0.5 for applied loadings along and transverse to the alignment direction, leading to an exceptional selectivity of 3.77. The real-world applications of the hierarchically aligned sensors in multiaxial movement detector and posture-correction device are further demonstrated. The above findings propose new ideas for manufacturing nanocomposites with engineered anisotropic structure and properties, verifying promising applications in emerging wearable electronics and soft robotics.

Key role of adsorption site abundance in the direct electrochemical co-detection of estradiol and dopamine

Estradiol (E2) is a hormone that influences various aspects of women’s health. Beyond its reproductive functions, E2 impacts neurotransmitter systems such as dopamine (DA). Vertically aligned carbon nanofibers (VACNFs) have shown good sensitivity, selectivity against ascorbic acid (AA) and uric acid (UA), biocompatibility, and reduced fouling in DA sensing. In this study, we explore the use of Ti-Ni-CNF electrodes with CNFs grown for 5 min and 30 min for the direct electrochemical co-detection of E2 and DA. The longer growth time led to a 142% increase in average CNF length and a 36% larger electroactive surface area. In E2 detection, the electrodes demonstrate a wide linear range of 0.05–10 µM and sensitivity of 0.016 and 0.020 µA/µM for Ti-Ni-CNF-5 min and Ti-Ni-CNF-30 min, respectively. The sensor performance remains largely unaffected even in the presence of other steroid hormones such as progesterone and testosterone. Co-detection of equimolar E2 and DA shows promising peak separation of 0.34 ± 0.01 V and repeatability after 10 measurements. A notable improvement in the E2/DA peak current ratio, from 0.53 ± 0.07 to 0.81 ± 0.16, was achieved with the increased CNF length. Our results demonstrate the influence of adsorption sites in electrochemical detection, especially for analytes such as E2 and DA that both rely on adsorption for oxidation. While detecting small and fluctuating physiological concentrations remains a challenge, these findings can be used in choosing and fabricating electrode materials for more accurate and accessible continuous hormone measurements, including the possibility of multianalyte sensing platforms.Graphic abstract

Enhancing Efficiency and Durability of PEM Water Electrolysis with Low Iridium Loading through Nanofiber-Modified Porous Transport Electrodes

Hydrogen plays a significant role in the transition of the global energy system towards achieving net-zero emissions. According to the “Hydrogen for Net-Zero” report by Hydrogen Council and McKinsey & Company, the demand for clean hydrogen could reach 140 metric tons (MT) by 2030, with a further increase to 660 MT by 2050. For future high-volume production of green hydrogen, Proton Exchange Membrane Water Electrolysis (PEMWE) is a crucial technology due to its advantages of high-purity hydrogen, large operational current densities, and great energy conversion efficiency [1]. However, the use of precious metal-based catalysts for the sluggish oxygen evolution reaction (OER) on the anode side hinders the high-volume manufacturability of PEMWE. To ensure cost-effectiveness in large-scale PEMWE deployment for hydrogen production, developing strategies to reduce Iridium loading to 0.1 - 0.2 mg Ir/cm2 without compromising overall performance is essential. The challenge of reducing Ir loading also involves improving or maintaining the electrical contact between the catalyst layers and the substrate [2-3].Smoltek Hydrogen has made significant strides in achieving low iridium loading through our innovative Porous Transport Electrode (PTE) concept. This approach involves modifying a Porous Transport Layer (PTL) by growing vertically aligned Carbon Nanofibers (CNFs) using our in-house patented technology, efficiently increasing surface area [4]. Following this modification, a protective layer of corrosion-resistant and conductive material (e.g., Platinum) is applied to the CNFs. Subsequently, an OER catalyst layer is deposited utilizing a three-electrode cathodic electrodeposition method (Fig. 1a and 1b). The electrodeposited Ir catalyst exhibits strong adhesion to the CNF PTEs, resulting in a high electrical conductivity [5].In this work, we successfully reduced Ir loadings to 0.1 mg/cm2 in the PTE, demonstrating excellent mass activity in the half-cell tests (Fig. 1c). In the PEMWE tests, the polarization curves of electrodes with low Ir loading exhibited superior performance compared to cells with significantly higher Ir loading (Fig. 1d). The next step of our research involves conducting constant current durability tests for over 600 hours on PEMWE operation using low Ir loaded PTEs. The aim is to minimize degradation and overcome mass transport limitations, particularly at higher current densities.These unique PTEs developed by Smoltek Hydrogen, with CNF technology, maximize the electrode surface area and pave a new way to increase the utilization ratio of catalyst surface at a low loading amount, which makes it a competitive anode material in today’s PEMWE market. References https://www.iea.org/reports/hydrogen-2156#dashboardMöckl et al. J. Electrochem. Soc., 2022, 169, 064505.Bernt et al. Chem. Ing. Tech., 2020, 92, 31-39.https://www.smoltek.com/applications/electrolyzers/Krivina et al. Adv.Mater., 2022, 34, 2203033.https://publications.jrc.ec.europa.eu/repository/handle/JRC104045 Figure 1

Ultrasensitive Monolithic Dopamine Microsensors Employing Vertically Aligned Carbon Nanofibers.

Brain-on-Chip devices, which facilitate on-chip cultures of neurons to simulate brain functions, are receiving tremendous attention from both fundamental and clinical research. Consequently, microsensors are being developed to accomplish real-time monitoring of neurotransmitters, which are the benchmarks for neuron network operation. Among these, electrochemical sensors have emerged as promising candidates for detecting a critical neurotransmitter, dopamine. However, current state-of-the-art electrochemical dopamine sensors are suffering from issues like limited sensitivity and cumbersome fabrication. Here, a novel route in monolithically microfabricating vertically aligned carbon nanofiber electrochemical dopamine microsensors is reported with an anti-blistering slow cooling process. Thanks to the microfabrication process, microsensors is created with complete insulation and large surface areas. The champion device shows extremely high sensitivity of 4.52× 104 µAµM-1·cm-2, which is two-orders-of-magnitude higher than current devices, and a highly competitive limit of detection of 0.243 nM. These remarkable figures-of-merit will open new windows for applications such as electrochemical recording from a singleneuron.

Deciphering the effect of nucleation/growth kinetics on the morphology of Li plating/stripping on vertically aligned carbon nanofibers - A low-tortuosity 3-D nanostructured carbon host

Reversible lithium metal anodes (LMAs) are the holy grail for future rechargeable lithium metal batteries. Three-dimensional (3-D) conductive hosts have been extensively explored as an effective approach to suppressing dendrite formation and enabling reversible Li plating/stripping. However, the microscopic morphologies of Li plating and their correlation with the cell performance are not clear. Herein we unravel these issues using the vertically aligned carbon nanofiber (VACNF) array as a model 3-D conductive carbon host which has a well-defined vertical low-tortuosity structure allowing observation of the intrinsic Li morphologies infiltrated into the 3-D host. The VACNF array indeed provides much higher stability and reversibility for Li plating/stripping due to its high surface area and lithiophilic properties. We found that Li plating on both VACNF array and planar Cu electrodes follows the classical nucleation and growth model. Though the low plating current density (≤0.10 mA/cm2) provides better cycling stability consistent with the Sand’s equation, it forms sparse irregular grains stacked with dendrite-like long Li fibers. In contrast, the moderate to high plating current densities (1.0 − 5.0 mA/cm2) produce more uniform Li morphologies consisting of smaller micro-columns or micro-spheres. By decoupling the plating and stripping current densities, we unravel that the more uniform micro-columnar Li infiltrated in the VACNF array obtained at the moderate plating current density (∼1.0 mA/cm2) indeed exhibits the highest cycling performance. This provides new insights into the relationship between macroscopic electrochemical tests and microscopic Li morphologies, aiding in optimizing the performance of LMAs based on 3-D conductive hosts.

Enhanced electrocatalytic degradation of tetracycline by ZIF-67@CNT coupled with a self-standing aligned carbon nanofiber anodic membrane

Due to the misuse and overuse of the antibiotic tetracycline (TC), as well as its refractory degradability, it has become a stubborn environmental contaminant. In this study, a self-standing polyacrylonitrile-based ZIF-67@CNT/ACF aligned anodic membrane was fabricated by innovatively incorporating ZIF-67@CNT nanoparticles into an aligned carbon nanofiber (ACF) membrane to treat the TC. The flow-through nanoporous construction of the ZIF-67@CNT/ACF membrane reactor can compress the diffusion boundary layer on the electrode surface to enhance mass transfer under microscopic laminar flow, which can further enhance the degradation rate. In addition, the enhanced degradation performance also benefited from the significant electrooxidation capacity of the ZIF-67@CNT/ACF membrane. At the optimal electrocatalytic condition of 3.0 V applied potential and pH 6, the degradation rate reached 81% in 1 h for an initial TC concentration of 10 mg l−1. The refractory and highly toxic TC was electrochemically degraded into small non-toxic molecules. Our results indicate that electrocatalytic TC degradation can be enhanced by ZIF-67@CNT/ACF membrane.

Rational design of conductive metal-organic frameworks and aligned carbon nanofibers for enhancing the performance of flexible supercapacitors.

Carbonaceous materials are attractive active materials for the manufacture of flexible electrochemical double-layer capacitors (EDLCs) because of their high electrical conductivity, large surface area, and inherent resilience against deformation. However, compared to pseudocapacitors, which store electrochemical energy via faradaic redox reactions, EDLCs generally exhibit inferior energy density. One potential approach to addressing this issue is to incorporate highly porous and electrically conductive materials into carbonaceous material-based EDLCs. In this paper, we present a hybrid electrode consisting of a conductive metal-organic framework (c-MOF) with high electrical conductivity and unique porous structure combined with a mat of aligned carbon nanofibers (ACNFs). Its highly ordered structure facilitates electronic/ionic transport, increasing the areal capacitance by up to 3.9 times compared to randomly-oriented carbon nanofibers (RCNFs). An additional increase in areal capacitance (+64%) is achieved by introducing c-MOF (RCNFs: 25.4 mF cm-2; ACNFs: 98.7 mF cm-2; c-MOF/ACNF: 161.8 mF cm-2). Additionally, an ACNF mat exhibits excellent mechanical flexibility and electrochemical reliability, making it highly suitable for the assembly of freestanding flexible supercapacitors. By optimizing the electrochemical performance of c-MOF/ACNF and its suitability for utilization in flexible energy storage systems, this study presents a promising avenue for the practical implementation of c-MOF-based supercapacitors.

Using Vertically Aligned Carbon Nanofiber Arrays on Rigid or Flexible Substrates for Delivery of Biomolecules and Dyes to Plants.

The delivery of biomolecules and impermeable dyes to intact plants is a major challenge. Nanomaterials are up-and-coming tools for the delivery of DNA to plants. As exciting as these new tools are, they have yet to be widely applied. Nanomaterials fabricated on rigid substrate (backing) are particularly difficult to successfully apply to curved plant structures. This study describes the process for microfabricating vertically aligned carbon nanofiber arrays and transferring them from a rigid to a flexible substrate. We detail and demonstrate how these fibers (on either rigid or flexible substrates) can be used for transient transformation or dye (e.g., fluorescein) delivery to plants. We show how VACNFs can be transferred from rigid silicon substrate to a flexible SU-8 epoxy substrate to form flexible VACNF arrays. To overcome the hydrophobic nature of SU-8, fibers in the flexible film were coated with a thin silicon oxide layer (2-3 nm). To use these fibers for delivery to curved plant organs, we deposit a 1 µL droplet of dye or DNA solution on the fiber side of VACNF films, wait 10 min, place the films on the plant organ and employ a swab with a rolling motion to drive fibers into plant cells. With this method, we have achieved dye and DNA delivery in plant organs with curved surfaces.

Binder-free Li-O 2battery cathodes using Ni- and PtRu-coated vertically aligned carbon nanofibers as electrocatalysts for enhanced stability

The development of an ideal cathode for Li-O₂ battery (LOB) has been a great challenge in achieving high discharge capacity, enhanced stability, and longevity. The formation of undesired and irreversible discharge products on the surface of current cathode materials limit the life span of the LOB. In this study, we report the systematic electrochemical study to compare the performance of LOB employing a unique graphitic nanostructured carbon architecture, i.e., vertically aligned carbon nanofiber (VACNF) arrays, as the cathode materials. Transition metal (Ni) and noble metal alloy (PtRu) are further deposited on the VACNF array as electrocatalysts to improve the discharge/charge processes at the cathode. The structure of as-prepared electrodes was examined with the field emission scanning electron microscopy, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy (XPS). The LOB with VACNF-Ni electrode delivered the highest specific and areal discharge capacities (14.92 Ah·g⁻¹, 4.32 mAh·cm⁻²) at 0.1 mA·cm⁻² current density as compared with VACNF-PtRu (9.07 Ah·g⁻¹, 2.62 mAh·cm⁻²), bare VACNF (5.55 Ah·g⁻¹, 1.60 mAh·cm⁻²) and commercial Vulcan XC (3.83 Ah·g⁻¹, 1.91 mAh·cm⁻²). Cycling stability tests revealed the superior performance of VACNF-PtRu with 27 cycles as compared with VACNF-Ni (13 cycles), VACNF (8 cycles), and Vulcan XC (3 cycles). The superior cycling stability of VACNF-PtRu can be attributed to its ability to suppress the formation of Li₂CO₃ during the discharge cycle, as elucidated by XPS analysis of discharged samples. We also investigated the impact of carbon cloth and carbon fiber as cathode electrode substrate on the performance of LOB.

Mechanistic understanding of Li metal anode processes in a model 3D conductive host based on vertically aligned carbon nanofibers

The use of three dimensional (3D) conductive hosts is a promising strategy to alleviate dendrite formation in lithium metal anodes. However, the fundamental issues associated with the 3D hosts, such as formation of excessive solid electrolyte interphase (SEI) and complicated Li deposition morphologies, have not been well studied. This study focuses on understanding these critical issues using vertically aligned carbon nanofiber (VACNF) array as a model 3D host. Various characterization tools are employed to elucidate the morphology and composition of electrodeposited Li (e-Li) and its associated SEI. The e-Li on VACNFs exhibits two different morphologies – a dominant micron-scale columnar infiltrative Li and a small amount of nanoscale coaxial Li sheath on VACNFs in the unfilled interstitial area between infiltrative grains. During Li intercalation, an organic-rich loose SEI film forms on the top of VACNF array and an inorganic-rich SEI sheath forms around individual VACNFs. Li plating transforms them into inorganic dominant SEIs directly in contact with the e-Li surface. The SEI skins on the infiltrative Li remain loosely attached to the VACNF array after stripping Li and irreversibly accumulate during Li plating/stripping cycling, while the coaxial SEI on the nanoscale Li remains as a stable elastic sheath. The loose SEI skins cause electrolyte consumption and increased heterogeneity, eventually leading to cell failure.

Bundled carbon nanofiber arrays grown on Cu-Ni tube textile boosting superior sodium-ion storage kinetics

Achieving high energy and power density in micro sodium-ion storage device is imperative and challenging due to the large radius of sodium ions and induced sluggish sodiation kinetics. Herein, we develop a vertically aligned carbon nanofiber arrays with a graphite dome (G-CNFAs/Textile) using the unique Cu-Ni solid solution textile as catalyst and thin substrate. As a flexible electrode with a maximum thickness of 4.0 µm, the G-CNFAs/Textile combines the merits of the thinner intertwined/ interconnected carbon nanofiber bundles, high porosity and abundant defects, thereby deriving enhanced sodium-ion storage kinetics. As a result, the flexible micrometer-scale G-CNFAs/Textile not only delivers an impressive gravimetric performance of 332.6 mA h g−1 at 1000 mA g−1 after 500 cycle numbers, but also exhibits outstanding volumetric capacity of ca. 1387.6 mA h cm−3 in half-type SIBs. Meanwhile, as the submicron-scale self-supporting symmetric electrode of SICs, the G-CNFAs//G-CNFAs capacitor also presents an impressive gravimetric capacitance of 66.5 F g−1 at 0.1 A g−1, superior energy-power density (80.9 W h kg−1 and 7771.8 W kg−1), as well as outstanding cyclic stability. Thus, we hope that this flexible micro-submicron-scale electrode structures could provide inspirations for thin, light-weight and miniaturized sodium-ion storage devices.

An efficient and broadly applicable method for transient transformation of plants using vertically aligned carbon nanofiber arrays.

Transient transformation in plants is a useful process for evaluating gene function. However, there is a scarcity of minimally perturbing methods for gene delivery that can be used on multiple organs, plant species, and non-excised tissues. We pioneered and demonstrated the use of vertically aligned carbon nanofiber (VACNF) arrays to efficiently perform transient transformation of different tissues with DNA constructs in multiple plant species. The VACNFs permeabilize plant tissue transiently to allow molecules into cells without causing a detectable stress response. We successfully delivered DNA into leaves, roots and fruit of five plant species (Arabidopsis, poplar, lettuce, Nicotiana benthamiana, and tomato) and confirmed accumulation of the encoded fluorescent proteins by confocal microscopy. Using this system, it is possible to transiently transform plant cells with both small and large plasmids. The method is successful for species recalcitrant to Agrobacterium-mediated transformation. VACNFs provide simple, reliable means of DNA delivery into a variety of plant organs and species.

Dual-Aligned carbon nanofiber scaffolds as heat conduction path to enhance thermal conductivity of polymer composites

To improve the thermal conductivity of thermal interface materials (TIM), we constructed a dual-aligned scaffold, i.e., both aligned carbon nanofiber (CNFs) in the microscopic structures and directional microporous channels, serving as the heat conduction paths of TIMs. The dual-aligned scaffold was firstly fabricated by combining magnetic alignment and conventional freeze-casting, and the composites of the dual-aligned scaffold and silicone rubber (D-AS/SR) were then obtained by immersing the dual-aligned scaffold into the silicone rubber with vacuum assistance. Through this method, not only the high axial thermal conductivity of CNFs can be fully utilized, but also a long-range continuous and parallel structure can be fabricated as the heat conduction paths of TIMs. The results show that the thermal conductivity of the D-AS/SR composites reached 4.66 W/(m·K) at 7.73 vol% CNFs, which is 1.5 times higher than that of the composites constructed by conventional freezing casting and 25 times higher than that of pure silicone rubber. Additionally, the compressive strength of the D-AS/SR composites was greatly improved, whereas the electrical insulation of the composites was significantly reduced, which limited the use of D-AS/SR composites in conditions requiring good electrical insulation.

Theoretical Investigation of the Oxygen Reduction Reaction over Platinum Catalysts Supported by Multi‐Edged Vertically Aligned Carbon Nanofiber for Electrocatalyst Preparation

AbstractVertically aligned carbon nanofibers (VACNFs) are promising supports for oxygen reduction reaction (ORR) electrocatalysts in fuel cells. Although experimentally these catalytic systems have shown great potential, there is lack of molecular understanding of the catalytic sites and reaction mechanisms. This work investigated the origin of the ORR reactivities of the platinum catalysts on multi‐edged VACNFs (Pt/VACNF) using a multiscale modeling approach combining Density Functional Theory (DFT) and classical Molecular Dynamics (MD) simulations. Based on the ReaxFF potential, all nanoscale Pt particles (Pt55, P100, and Pt147) are stabilized by the open edges located axially along the VACNF walls. The calculated first‐shell coordination numbers, , of surface Pt atoms are 6.63, 7.27, and 7.85, respectively, suggesting that the percentage of low coordination sites increases as the particle size decreases. The adsorption energies of OOH, O, and OH on Pt55 were systematically probed using DFT calculations. These adsorption energies retain a linear correlation against the generalized coordination numbers ( ). For Pt nanoparticles supported on VACNF, we found that the OOH and OH bind stronger than on Pt (111) by 0.14 and 0.17 eV, respectively, which can hinder the ORR activity with lower limiting potential than Pt (111). Our theoretical prediction is in good agreement with the linear sweeping voltammetry that revealed a left shift of the half‐wave potential.

Enhanced performance of microbial fuel cells with a bacteria/shape-controllable aligned carbon nanofibers hybrid biofilm

Improving the bacterial loading contents and extracellular electron transfer (EET) efficiency are promising strategies to enhance the overall performance of microbial fuel cells (MFCs). Herein, an aligned carbon nanofiber-bacteria (ACNF-bacteria) hybrid is prepared and used as an efficient anode employing the electrospinning and co-filtration method. The ACNF matrix reveals rich porous structure, large specific surface area, and obviously improved electrocatalytic performance compared to the pristine carbon cloth (CC) anode. Specifically, MFC with the ACNF-bacteria anode achieves a maximum power density of 704 mW m−2, which is 1.7, 2.1 times higher than that of ACNF, CNF and CC anode. Impressively, the coulombic efficiency and chemical oxygen demand (COD) removal rate for ACNF-bacteria anode reach 47.4% and 87.9%, respectively, far exceeding the CC anode (29.3% and 47.6%). Considering all the factors of low cost, facial fabrication, and high-power output, this novel ACNF-bacteria anode provides great potential for high-performance and cost-effective MFCs in a large scale.

Mechanistic Understanding of Lithium Plating/Stripping Processes on the 3D Conductive Host Based on Vertically Aligned Carbon Nanofibers for Li Metal Anode

The highest theoretical capacity (3860 mAh/g) and lowest redox potential (-3.04 V vs standard hydrogen electrode) makes lithium metal as a promising anode for next generation high energy density batteries.1 Despite theoretical advantages, there are challenges in commercializing Li metal anodes such as low coulombic efficiency, dendrite formation and poor cycling life. Dendrite formation can cause short circuit and thermal runaway, which is a safety concern. Among the various ways to mitigate the Li dendrite formation, using three-dimensional (3D) current collectors with lithiophilic properties and low tortuous pore architecture is an effective way. It would decrease the local current density owing to high active surface area while accommodating the large volume change during prolonged charge/discharge cycles.Vertically aligned carbon nanofibers (VACNF) have been demonstrated as a promising candidate as a lithiophilic 3D host for lithium metal anodes as they possess unique conically stacked lithiophilic graphitic edges with O containing functional groups and high N doping (~6.5 at%).2 However, a fundamental, deeper understanding of the Li plating/stripping processes on such 3D electrodes has not been developed yet. Here in, we investigate the lithium nucleation and growth processes and its morphological changes using ex-situ structural characterization techniques such as SEM and cryo-TEM. The composition of the solid electrolyte interface is investigated using XPS. In-situ Raman spectroscopic studies provided further information about the changes that occur in the VACNFs during Li plating/stripping processes and Li intercalation/deintercalation processes. Ion-beam sputtering of an ultrathin gold layer onto the VACNFs was found to further improve the lithiophilicity of the 3D electrode and lead to more reversible Li metal plating/stripping. The new insights on the electrodeposition of lithium in 3D electrodes and its relationship with the enhanced cycle life acquired using various analytical tools will be discussed.Reference:(1) Manthiram, A.; Chung, S.-H.; Zu, C. Lithium–Sulfur Batteries: Progress and Prospects. Advanced Materials 2015, 27 (12), 1980–2006.(2) Chen, Y.; Elangovan, A.; Zeng, D.; Zhang, Y.; Ke, H.; Li, J.; Sun, Y.; Cheng, H. Vertically Aligned Carbon Nanofibers on Cu Foil as a 3D Current Collector for Reversible Li Plating/Stripping toward High-Performance Li–S Batteries. Advanced Functional Materials 2020, 30 (4), 1906444.

Thermal conductivity and compressive strength of silicone rubber composites enhanced by aligned carbon nanofiber scaffold

AbstractPolymer composites with high enough thermal conductivity, known as thermal interface materials (TIMs), are continuously pursued in the thermal management of high‐power density electronic and energy devices. In this article, to improve the heat transfer performance of TIMs, we constructed an aligned carbon nanofiber (CNFs) scaffold via the freeze‐casting method to serve as heat conduction paths in the TIMs. The composites of aligned CNF scaffold and silicone rubber were obtained by immersing the aligned scaffold into the silicone rubber with vacuum assist. We studied the influences of different CNFs diameters on the thermal conductivity of the composites, the pore sizes of the aligned CNF scaffold and the thermal conductivity of the composites fabricated under different freezing temperatures, and also the mechanical properties of the composites. Owing to the aligned scaffold, providing directional and continuous heat conduction paths, the thermal conductivity of the composites reached 3.17 W/(m·K) at 7.73 vol% CNFs. Additionally, the compressive strength and fracture strain of the composites were also greatly improved.

Flexible strain sensors fabricated using aligned carbon nanofiber membranes with cross-stacked structure for extensive applications

ABSTRACT Carbon nanofibers (CNFs) with excellent conductivity and stability have become a promising material to design the strain sensing network. To date, however, the effect of the stacked structure of CNF membrane on the sensing performance has rarely been studied. In this work, we reported a high-performance sensor based on the cross-stacked aligned CNF membrane. The effects of cross-stacked structures on the sensing characteristics were systematically investigated. The flexible strain sensor could capture low detection limit (<0.1%) with a gauge factor (GF) of 4.24 and wide strain range up to 130%. The uniform GF value reached 2050 when the strain was in the range of 100–130%. In addition, the high linearity under 40% strain (>0.998), excellent durability and quick response time (<200 ms) were demonstrated. The excellent comprehensive performances were simultaneously obtained. The sensor could be used in extensive applications, such as monitoring body movements and distinguishing the track of writing.

Nanoscale geometry determines mechanical biocompatibility of vertically aligned nanofibers

Vertically aligned carbon nanofibers (VACNFs) are promising material candidates for neural biosensors due to their ability to detect neurotransmitters in physiological concentrations. However, the expected high rigidity of CNFs could induce mechanical mismatch with the brain tissue, eliciting formation of a glial scar around the electrode and thus loss of functionality. We have evaluated mechanical biocompatibility of VACNFs by growing nickel-catalyzed carbon nanofibers of different lengths and inter-fiber distances. Long nanofibers with large inter-fiber distance prevented maturation of focal adhesions, thus constraining cells from obtaining a highly spread morphology that is observed when astrocytes are being contacted with stiff materials commonly used in neural implants. A silicon nanopillar array with 500 nm inter-pillar distance was used to reveal that this inhibition of focal adhesion maturation occurs due to the surface nanoscale geometry, more precisely the inter-fiber distance. Live cell atomic force microscopy was used to confirm astrocytes being significantly softer on the long Ni-CNFs compared to other surfaces, including a soft gelatin hydrogel. We also observed hippocampal neurons to mature and form synaptic contacts when being cultured on both long and short carbon nanofibers, without having to use any adhesive proteins or a glial monoculture, indicating high cytocompatibility of the material also with neuronal population. In contrast, neurons cultured on a planar tetrahedral amorphous carbon sample showed immature neurites and indications of early-stage apoptosis. Our results demonstrate that mechanical biocompatibility of biomaterials is greatly affected by their nanoscale surface geometry, which provides means for controlling how the materials and their mechanical properties are perceived by the cells. Statement of significanceOur research article shows, how nanoscale surface geometry determines mechanical biocompatibility of apparently stiff materials. Specifically, astrocytes were prevented from obtaining highly spread morphology when their adhesion site maturation was inhibited, showing similar morphology on nominally stiff vertically aligned carbon fiber (VACNF) substrates as when being cultured on ultrasoft surfaces. Furthermore, hippocampal neurons matured well and formed synapses on these carbon nanofibers, indicating high biocompatibility of the materials. Interestingly, the same VACNF materials that were used in this study have earlier also been proven to be capable for electrophysiological recordings and sensing neurotransmitters at physiological concentrations with ultra-high sensitivity and selectivity, thus providing a platform for future neural probes or smart culturing surfaces with superior sensing performance and biocompatibility.

Fabrication of aligned carbon nanofiber doped with SnO2-Sb for efficient electrochemical removal of tetracycline

In recent years, tetracycline (TC) has become an emerging refractory antibiotic pollutant due to excessive use and abuse. The aim of this work is to prepare aligned carbon nanofibrous (ACFs) membrane by electrospinning technology and then dope with SnO2-Sb to electrocatalytic degrade TC. The in-situ growth of SnO2-Sb on the carbon nanofiber surface to fabricate SnO2-Sb/ACFs membrane can increase the oxygen evolution reaction potential and improve conductivity. And the SnO2-Sb/ACFs membrane was used as the anodic membrane of a flow-through mode electrochemical membrane reactor to remove TC in aqueous solutions. The outstanding degradation performance of SnO2-Sb/ACFs membrane on TC was investigated systematically. The results show that the 3-layer SnO2-Sb/ACFs-3 membranes can effectively degrade 20 mg/L TC at an applied potential of 2.5 V. Moreover, SnO2-Sb/ACFs-3 membrane shows excellent degradation stability after 10 cycles of degradation experiments. For exploring the possible TC degradation pathways, HPLC-MS was used to identify the main intermediates during the electrochemical oxidation process. The anodic membrane electrode prepared in this work puts forward a new idea for the safe and efficient degradation of TC.