Acid-treated Carbon Fiber Research Articles

Construction of all-carbon micro/nanoscale interconnected sulfur host for high-rate and ultra-stable lithium-sulfur batteries: Role of oxygen-containing functional groups

Carbon nanotubes (CNTs) are often used to settle down the sluggish reaction kinetics in lithium–sulfur batteries (LSBs). However, the self-aggregation of CNTs often makes them fail to effectively inhibit the shuttling effect of soluble lithium polysulfide (LiPS) intermediates. Herein, a type of ultra-stable carbon micro/nano-scale interconnected “carbon cages” has been designed by incorporating polar acid-treated carbon fibers (ACF) into three-dimensional (3D) CNT frameworks during vacuum filtration processes. Results show that the ACF-CNT composite frameworks possess a reinforced-concrete-like structure, in which the ACFs can well work as the main mechanical supporting frames for the composite electrodes, and the oxygen-containing functional groups (OFGs) formed on them as cross linker between ACFs and CNTs. Benefitted from this design, the ACF-CNT/S cathodes deliver an excellent rate capability (retain 72.6% at 4C). More impressively, the ACF-CNT/S cathodes also show an ultrahigh cycling stability (capacity decay rate of 0.001% per cycle over 350 cycles at 2C). And further optimization suggests that the suitable treatment on CFs could balance the chemical adsorption (OFGs) and physical confinement (carbon cages), leading to fast and durable electrochemical reaction dynamics. In addition, the assembled soft-pack LSBs further show a high dynamic bending stability.

Improving energy storage ability of acid-treated carbon fibers via simple sonication and heat treatments for flexible supercapacitors

Fiber-type supercapacitor (FSC) is indispensable for soft electronics. Modifying substrate without depositing electroactive material can prevent electroactive material from peeling off and enhance flexibility of FSC. Acid treatment is one of the most effective methods to enhance energy storageability of carbon fiber (CF) via inducing functional groups and creating defects for charge accumulation. In this work, it is firstly to apply sonication and heat treatments on CF electrodes in acid mixture to enhance hydrogen ion diffusion path and acid etching rate. The highest specific capacitance (CL) of 319.0 mF/cm is obtained at 20 mV/s for the CF electrode prepared using full sonication for 45 min and heat treatment at 80 °C at last 25 min, while the untreated CF electrode only shows CL value of 8.3 mF/cm. The FSC with optimized CF electrodes shows maximum energy density of 12 μWh/cm at 250 μW/cm. After 10,000 times repeated charge/discharge process, CL retention of 78% and Coulombic efficiency of 88% are achieved. Excellent flexibility is attained with high CL retentions with bending angle of 180° and bended for 1000 times. Other energy supplying methods are expected to promote the acid treatment on CF and create more efficient FSC in near future.

Fabrication of a High-Energy Flexible All-Solid-State Supercapacitor Using Pseudocapacitive 2D-Ti3C2Tx-MXene and Battery-Type Reduced Graphene Oxide/Nickel-Cobalt Bimetal Oxide Electrode Materials.

Owing to excellent metallic conductivity, hydrophilic surfaces, and surface redox properties, a two-dimensional (2D) metal carbide of Ti3C2Tx-MXene could serve as a promising pseudocapacitive electrode material for energy storage devices. Meanwhile, the 2D reduced graphene oxide (rGO) combining with the hierarchical cubic spinel nickel-cobalt bimetal oxide (NiCo2O4) nanospikes could control ion diffusion for charge storage, thereby facilitating the improvement of the energy density of a supercapacitor. As per the strategy, the pseudocapacitive 2D Ti3C2Tx was loaded on a flexible acid-treated carbon fiber (ACF) backbone to prepare a Ti3C2Tx/ACF negative electrode by a convenient drop-casting method. Meanwhile, 2D rGO was deposited on ACF by a simple dip-dry process, which was further decorated by the spinel NiCo2O4 nanospikes using a hydrothermal method to obtain a NiCo2O4@rGO/ACF positive electrode. The fabricated Ti3C2Tx/ACF electrode exhibited an excellent specific capacitance of 246.9 F/g (197.5 mF/cm2) at 4 mA/cm2 along with 96.7% capacity retention over 5000 charge/discharge cycles, whereas the NiCo2O4@rGO/ACF electrode showed a specific capacitance of 1487 F/g (458.3 mA h/g) at 3 mA/cm2 with a cycling stability of 88.2% over 10 000 charge/discharge cycles. As a result, a flexible all-solid-state hybrid supercapacitor (FHSC) device using the pseudocapacitive Ti3C2Tx/ACF on the negative side with a widespread voltage window and the battery-type NiCo2O4@rGO/ACF on the positive side with high electrochemical activity delivered an excellent volumetric capacitance of 2.32 F/cm3 (141.9 F/g) at a current density of 5 mA/cm2 with a high-energy density of 44.36 Wh/kg (0.72 mWh/cm3) at a power density of 985 W/kg (16.13 mW/cm3) along with a cycling stability of 90.48% over 4500 charge/discharge cycles. Therefore, the pseudocapacitive 2D Ti3C2Tx/ACF negative electrode could replace carbon-based electrodes and a combination of it with the battery-type NiCo2O4@rGO/ACF positive electrode should be a promising way to step up the energy density of a supercapacitor.

Influence of chemically treated carbon fibers on the electromagnetic shielding of ultra-high-performance fiber-reinforced concrete

The effects of carbon fiber and its surface treatment through chemical solutions on the mechanical properties and electromagnetic (EM) shielding of ultra-high-performance fiber-reinforced concrete (UHPFRC) were analyzed. Three types of carbon fibers chemically treated with sodium hydroxide, nitric acid, and ammonia solutions were evaluated, along with a plain carbon fiber control sample, at two different concentrations of 0.1% and 0.3% by weight. The surface of carbon fiber was oxidized by chemical solutions. The conductivity of UHPFRC increased with increasing the carbon fiber content, and slightly better conductivity was obtained using the chemically treated carbon fibers than plain fibers at the lower content of 0.1 wt%. Both steel and carbon fibers were effective at improving the shielding effectiveness of ultra-high-performance concrete, and a higher shielding effectiveness was achieved for higher carbon fiber content. Surface treatment using the nitric acid solution was the most effective at enhancing the tensile performance and EM shielding effectiveness, and the best shielding effectiveness (49.0 dB at 1 GHz) was achieved for UHPFRC with 0.1 wt% nitric acid treated carbon fibers. The shielding effectiveness was found to be generally proportional to the electrical conductivity, although its increase was minor relative to that of the conductivity.

Enhanced Surface Area, Graphene Quantum Dots, and Functional Groups for the Simple Acid-Treated Carbon Fiber Electrode of Flexible Fiber-Type Solid-State Supercapacitors without Active Materials

Flexible fiber-type solid-state supercapacitors (FSCs) are demanded for energy storage of wearable soft electronics. A flexible carbon fiber (CF) with high electrical conductivity and good energy s...

Grafting carbon nanotubes densely on carbon fibers by poly(propylene imine) for interfacial enhancement of carbon fiber composites

Due to the weak interfacial bonding caused by the poor wettability and adsorption between carbon fibers (CFs) and matrix, CFs cannot fully exert their excellent mechanical properties in carbon fiber reinforced polymer composites. To settle this problem and bring a significant increase of interfacial strength in the composites, chemical grafting method was applied to fabricate the hierarchical reinforcement structure containing carbon nanotubes (CNTs) and CFs using poly(propylene imine) (PPI) molecules as bridges, which had a giant amount of amino groups at the periphery of molecules. CNTs were grafted on the surface of CF homogeneously and firmly with an extremely high grafting density. The surface free energy increased about 66% compared to the acid-treated carbon fiber, due to the obvious change of surface morphology and the increase of polar functional groups. The interfacial shear strength (IFSS) of the CNTs-grafted CF composite greatly increased by as much as 109% compared with that of CF composite without functionalization. The mechanism of this tremendous enhancement was also illustrated in details.

Modified Carbon Fiber Paper-Based Electrodes Wrapped by Conducting Polymers with Enhanced Electrochemical Performance for Supercapacitors.

An easy approach to fabricating carbon fiber paper (CFP) based electrodes has been developed. This method can be mainly divided into two steps, for which the mixture of cellulose nanofibers (CNFs) and carbon nanotubes (CNTs) was first deposited on the surface of carbon fiber paper through a vacuum filtration device followed by immersing the hybrid paper into concentrated aniline solution to polymerize polyaniline (PANI). Compared to carbon fiber paper, the acid-treated carbon fiber paper (A-CFP)-based electrode provides more active sites, which are beneficial for the polymerization of polyaniline. The mixture of CNFs and CNTs could coat on the A-CFP by vacuum-filtration due to the high hydrophilicity of A-CFP improved by acid-treatment. PANI with different polymerization time was in-situ synthesized on the surface of the hybrid paper to form a three-dimensional cross-linked structure that greatly enhanced the electrochemical performance of the electrode by improving high capacitance, high rate-capability, and long cycle-life. Moreover, the assembled symmetrical supercapacitor showed a high area capacitance of 626 mF·cm−2 and an energy density of 87 µWh·cm−2. This facile, easy performed, and low-cost strategy may provide a feasible method for the production of supercapacitor electrodes.

Preparation of titanium dioxide immobilized on carbon fibers annealed in steam ambient and their photocatalytic properties

Composites of titanium dioxide (TiO2) immobilized on carbon fibers (CFs) were synthesized by a two-step process. Acid-treated CFs were dip-coated in a TiO2 sol and then annealed under superheated steam ambient to form TiO2/CF composites. The effects of titanium sol concentration and annealing temperature on the micromorphology and phase structure of the TiO2/CF were investigated by field emission scanning electron microscopy and X-ray diffraction, respectively. The photocatalytic properties of the as-prepared TiO2/CFs were evaluated by photocatalytic degradation of acid orange II under ultraviolet light irradiation. The TiO2/CF composites prepared by superheated steam annealing exhibited a uniform surface morphology and high loading degree. The photocatalytic degradation of acid orange indicated that the TiO2/CF composites exhibited excellent photocatalytic performance and reached up to 98.7% degradation rate after 2.5 h of irradiation.

Nitric Acid-Treated Carbon Fibers with Enhanced Hydrophilicity for Candida tropicalis Immobilization in Xylitol Fermentation.

Nitric acid (HNO3)-treated carbon fiber (CF) rich in hydrophilic groups was applied as a cell-immobilized carrier for xylitol fermentation. Using scanning electron microscopy, we characterized the morphology of the HNO3-treated CF. Additionally, we evaluated the immobilized efficiency (IE) of Candida tropicalis and xylitol fermentation yield by investigating the surface properties of nitric acid treated CF, specifically, the acidic group content, zero charge point, degree of moisture and contact angle. We found that adhesion is the major mechanism for cell immobilization and that it is greatly affected by the hydrophilic–hydrophilic surface properties. In our experiments, we found 3 hto be the optimal time for treating CF with nitric acid, resulting in an improved IE of Candida tropicalis of 0.98 g∙g−1 and the highest xylitol yield and volumetric productivity (70.13% and 1.22 g∙L−1∙h−1, respectively). The HNO3-treated CF represents a promising method for preparing biocompatible biocarriers for multi-batch fermentation.

High Microwave Absorption of Nano-Fe3O4 Deposited Electrophoretically on Carbon Fiber

Production of magnetite (nano-Fe3O4)-coated carbon fibers (MCCFs) composites using the electrophoretic deposition (EPD) technique has been investigated in the present research. Fe3O4 nano-powder was synthesized by the reduction of Fe (III)-tri-ethanolamine (TEA) in an aqueous alkaline solution. By the deposition of nano-Fe3O4 particles distributed stably in a suspension on the surface, a uniform and compact Fe3O4 thin-film was fabricated on nitric acid-treated carbon fiber. According to the results, the strongest reflection loss (RL) of MCCFs was recognized to be −11 dB at 10.37 and 11.4 GHz for a layer of 1.7 mm in thickness. EPD was introduced as a suitable method for the production of MCCFs due to its low cost, easy productivity and time efficiency as well as the high absorption properties of the resulting MCCFs compared with the previous reported works.

Study on the Magnetic and Microwave Properties of Electrophoretically Deposited Nano-Fe3O4 on Carbon Fiber

Microwave absorbing paints made of magnetite (nano-Fe3O4) coated carbon fibers (MCCFs) play an important role in wireless data communication, local area network, satellite television, heating system, vehicles stealthing and so on. In this study production of MCCFs composites using electrophoretic deposition (EPD) technique has been investigated. For this purpose, the Fe3O4 nanoparticles with an average size of 50nm were synthesized by reduction of Fe (III)-tri-ethanolamine in an aqueous alkaline solution and then a uniform and compact Fe3O4 thin-film was coated on the surface of nitric acid treated carbon fiber by EPD method. The crystal structure, morphology and particle size distribution of the powders and composites were examined using the X-ray diffraction (XRD), scanning electron microscopy (SEM) and dynamic light scattering (DLS) techniques, respectively. The magnetic properties and the microwave absorption behaviors of the MCCFs were determined in the form of epoxy matrix composites using a J-H hysteresis loop tracer and a vector network analyzer (VNA, at the X-band frequency range), respectively. According to the results, the XRD patterns of composites and nano powders showed that in temperature of 80 0C Fe3O4 phases have been formed. Moreover, the strongest reflection loss (RL) of MCCFs was recognized to be −7.8dB (i.e. absorbing 83%) at 9.3GHz for a layer containing 50%wt MCCFs with 2mm in thickness. Electrophoretic deposition was introduced as a suitable method for production of MCCFs due to its low cost, easy productivity and time efficiency.

Effect of surface treatment on surface characteristics of carbon fibers and interfacial bonding of epoxy resin composites

This paper aims to study the effect of aqueous ammonia etching, nitric acid oxidation and aqueous ammonia/nitric acid combined treatment on surface characteristics of carbon fibers (CFs) and interfacial bonding properties of CF/epoxy resin composites. The morphologies and chemical compositions of pristine CFs and treated CFs were characterized using a Scanning Electron Microscope (SEM), Atomic Force Microscopy (AFM), and X-ray Photoelectron Spectroscopy (XPS). It was found that the surface of treated CFs has greater roughness compared with the surface of pristine CFs; moreover, the surface roughness is at maximum with the aqueous ammonia/nitric acid combined treatment. No obvious change in chemical composition takes place with aqueous ammonia etching of CFs. On the other hand, the oxygen content on the surface of CFs increases with nitric acid oxidation and aqueous ammonia/nitric acid combined treatments. The effect of surface treatment on the wettability, single filament tension strength, and interfacial shear strength (IFSS) of CF/epoxy resin composites was measured. Results show that the wettability of CFs against distilled water improves with the surface treatment. The wettability optimum with the aqueous ammonia/nitric acid combined treatment. Compared with pristine CFs, there is only a slight loss in tension strength with the treated CFs. In addition, the IFSS value of composites increased greatly. The IFSS of aqueous ammonia/nitric acid treated carbon fibers reinforced with epoxy resin composites increases by 46.36 % compared with pristine ones, This resulted from the combined action of the increase in the carbon fiber surface roughness and surface oxygen containing functional groups.

Interfacial enhancement of carbon fiber composites by poly(amido amine) functionalization

Abstract Carbon fiber reinforced composites have stimulated increasing attention due to their excellent mechanical properties. However, the interface tends to be weak because carbon fiber does not naturally have a good wettability and adsorption with most polymers matrix, which could not effectively transfer the load from the matrix to the fibers. Here we proposed to chemically functionalize carbon fiber (CF) by poly (amido amine) (PAMAM), which has more concentration of amino groups than traditional coupling agents. The chemical bond formation between acid-treated CF and PAMAM was confirmed. The PAMAM functionalization did not change the surface morphology while significantly increased the wettability of CF surface. The interfacial shear strength has an increase of 85% compared to that without functionalization. The interfacial enhancement mechanism was also explored in details.

Adsorption of precious metal ions onto electrochemically oxidized carbon fibers

Electrochemically oxidized carbon fibers (ECF) adsorbed a prodigious amount of Ag+ in contrast to oxygen plasma and nitric acid treated carbon fibers. The amount of adsorbed Ag+ reached 3700 μmol/g after 5652 C/g of electrochemical oxidation. This value approaches the 4050 μmol/g of Ag+ which adsorbed onto steam-activated Kenaf-based carbon (with a surface area of 1284 m2/g determined by N2/BET) under the same adsorption conditions. ECF oxidized to 9540 C/g adsorbed more than its own weight of Ag+ (12 608 μmol/g). These fibers exhibited a surface area of 115 m2/g (CO2–DR). Two different reactions occurred during Ag+ adsorption. These reactions were ion exchange adsorption between Ag+ and acidic functions (carboxyl) and redox adsorption between Ag+ and reducing functions such as catechol groups on these electrochemically oxidized fibers (ECF). The redox capability was expressed by the reaction electric potential (E) using the Nernst equation. High resolution XPS C 1s spectra of ECFs (level of oxidation 5300 C/g), before and after Ag+ adsorption, showed that the carbon atoms present in phenolic, alcohol or ether groups and those present in carbonyl or quinone groups increased after Ag+ adsorption. X-ray diffraction and X-ray photoelectron spectroscopy (XPS) Ag 3d spectra of the ECF showed that adsorbed Ag+ was reduced to Ag0 after both Ag+ adsorption and subsequent post-heat treatment of the fibers under N2 at 550°C for 30 min. Only about one-third as much Au3+ adsorption occurred versus the extent of electrochemical oxidation as was observed for Ag+. This ratio matches the requirement that three electrons are required to convert Au3+ to Au0 versus one to convert Ag+ to Ag. High resolution angle resolved XPS (ARXPS) Pd 3d and Pt 4f spectra show that there are two different Pd oxidation states and three different Pt oxidation states present after adsorption of Pd2+ and Pt2+ onto ECF. The peak areas as a function of take off angle showed that substantial amounts of Pd0 and Pt0 are present in addition to Pd2+ and Pt2+ and Pt4+ on the outermost surface regions of oxidized fibers.

Radical grafting from carbon fiber surface: graft polymerization of vinyl monomers initiated by azo groups introduced onto the surface

This paper describes the radical graft polymerizations of vinyl monomers from carbon fiber surface initiated by azo groups introduced onto the fiber surface. The carbon fiber used in this experiment was the polyacrylonitrile type. The introduction of azo groups onto the carbon fiber surface was achieved by the reaction of 4,4'-azobis (4-cyanopentanoic acid) with isocyanate groups which were previously attached onto the surface by the treatment of the fiber with tolylene 2,4-diisocyanate. The amount of surface azo groups introduced onto nitric acid-treated carbon fiber was determined to be 0.60 x 10-5 mol 9-1 by nitrogen analysis. The radical graft polymerization of methyl methacrylate (MMA) was tried. Though the thermal polymerization of MMA proceeded slightly in the absence or in the presence of untreated carbon fiber, the rate of the polymerization was considerably low. In contrast, the graft polymerization of MMA was initiated in the presence of the carbon fiber having surface azo groups, and part of r...