Search

Investigating the surface properties of heteroatom-doped carbon materials is essential because these versatile materials have found use in a variety of energy and environmental applications; an understanding of these properties would also lead to an improved appreciation of the direct interaction between the reactant and the functionalized surface. Herein, we explore the effect of boron (B) doping on the surface properties of activated carbon (AC) materials based on their water adsorption behavior and oxygen reduction reaction. In the high-temperature B doping process, B-doped AC materials at 1400 °C exhibit an open pore structure with B-O bonds, whereas at a temperature of 1600 °C, a nonporous structure containing a large amount of B-C bonds prevails. The B-O species act as active sites for water adsorption on the carbon surface. On the basis of the isothermal adsorption heat, we suggest that B atoms are present at the pore openings and on the surfaces. The B-O moieties at the open edges improve the electrocatalytic activity, whereas the B-C bonds at the closed edges decrease the electrocatalytic activity because of the stable structure of these bonds. Our findings provide new evidence for the electrocatalytic properties associated with the structure of B-doped edges.

Carbon fiber (CNF), prepared by carbonization of electrospun polyacrylonitrile (PAN) fibers, is systematically investigated as a mediator to replace conventional organic matrices for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-MS). CNF exhibits a high salt tolerance, sensitivity, and resolution for organic matrix-free laser desorption/ionization time-of-flight mass spectrometry (LDI-MS) analysis of various analytes under both positive and negative ionization modes. Especially, saccharides, a neutral molecule having low negative ionization efficiency, are successfully detected with CNF. Taken together, this study clearly demonstrates CNF is a promising material to develop an efficient and universal platform for LDI-MS analysis regardless of preferential ionization modes of analytes. Graphical abstract.

Despite significant improvements in the synthesis of nitrogen (N)-doped carbon nanotubes (CNTs) and their versatile applications, there has always been a large difficulty in controlling the bonding configuration of N atoms within CNTs. In the current work, we report an effective chemical strategy to synthesize single-walled carbon nanotubes (SWNTs) with 100% of quaternary N via a chlorosulfonic acid(CSA) treatment. In this process, the pyridinic and pyrrolic groups were selectively and completely removed while retaining the quaternary N atoms. The presence of 2.04 at. % of quaternary N atoms within SWNTs was directly identified from a single sharp peak in the N 1s spectra of XPS, and indirectly supported by the downshift of C 1s peak in XPS, the upshift of G'-band in Raman spectroscopy, and the decrease of the work function from 5.46 to 4.59 eV. The doping effect of the quaternary N atoms on the macroscopic properties of SWNT fibers was verified by a large increase in the electrical conductivity from 0.63 to 2.17 MS/m. In perspective, our chemical approach can now be applied to synthesize carbon materials with controlled N functionalities for different applications.

Nitrogen (N)-doped nanostructured carbons have been actively examined as promising alternatives for precious-metal catalysts in various electrochemical energy generation systems. Herein, an effective approach for synthesizing N-doped single-walled carbon nanohorns (SWNHs) with highly electrocatalytic active sites via controlled oxidation followed by N2 plasma is presented. Nanosized holes were created on the conical tips and sidewalls of SWNHs under mild oxidation, and subsequently, the edges of the holes were easily decorated with N atoms. The N atoms were present preferentially in a pyridinic configuration along the edges of the nanosized holes without significant structural change of the SWNHs. The enriched edges decorated with the pyridinic-N atoms at the atomic scale increased the number of active sites for the oxygen reduction reaction, and the inherent spherical three-dimensional feature of the SWNHs provided good electrical conductivity and excellent mass transport. We demonstrated an effective method for promoting the electrocatalytic active sites within N-doped SWNHs by combining defect engineering with the preferential formation of N atoms having a specific configuration.

In the fabrication of safe, but powerful lithium ion batteries (LIBs), graphene-related materials are being actively examined in order to meet the demand for applications such as electric vehicles and smart grids. However, most of this work has focused on liquid-phase exfoliated graphene and reduced graphene oxide. Herein, we demonstrate a simple, but effective route for significantly improving the electrochemical performance of currently available LIBs by coupling current collector with catalytically grown large-area graphene. When coating current collectors with large-area three-layered graphene, a reduction in the internal resistance (or effective electron transfer) between the current collector and active materials was observed. The graphene also protected the underlying collector from corrosion, greatly improving the power capability and cyclability of LIBs. The three-layered graphene provided the best electrochemical performance and corrosion resistance because of its high electrical conductivity and mechanical stability during the transfer process. We believe that our approach using interfacial graphene coating can be used with all kinds of electrochemical energy-storage systems, in which high corrosion resistance, electrical conductivity, and flexibility are critical.

The low density of porous carbon nanomaterials for supercapacitor electrodes has limited their widespread application, despite their ultra-high gravimetric capacitance. In this work, we successfully prepared highly densified composite electrodes of graphene and single-walled carbon nanohorns (SWCNHs) using a simple spray-drying method that is suitable for mass production. To prepare the high-density composite electrodes, water-based mixtures of oxidized SWCNHs (NHOs) and graphene oxides (GOs) were spray-dried in heated air; after spray-drying, GOs dispersed in water were agglomerated in spherical clusters containing NHO nanoparticles. The reduced spray-dried GO/NHO (rS-GO/NHO) composite electrodes exhibited an extremely high bulk density of 1.23 g·cm−3, which is almost double that of commercial activated carbon (AC) and reduced NHO (r-NHO) electrodes, and three times higher than that of rS-GO electrodes. Of the materials tested, the rS-GO/NHO composite electrode had the highest volumetric capacitance (80 F·cm−3 at 1 mA·cm−2) and a low sheet resistance (0.005 Ω· sq.−1), which are far superior to those of commercial AC (57 F·cm−3 at 1 mA·cm−2 and 0.293 Ω·sq.−1, respectively), without the need for a conductive material, such as carbon black. We expect that these high-density graphene/SWCNH composite electrodes with high volumetric capacitances can be substituted for commercial AC materials in energy storage devices, such as supercapacitors.

MnO2- and boron-incorporated polyacrylonitrile (PAN)/pitch-based carbon nanofiber (PPBMn) composites for electrochemical supercapacitors are successfully fabricated by one-step electrospinning using a combined solution of MnCl2, B2O3, PAN, and pitch. The surface morphologies, microstructures, surface chemical states, and texture properties of the PPBMn composites are investigated and the effect of the MnCl2 content on the electrochemical performance in aqueous electrolytes is also examined. The PPBMn composites exhibit a high specific surface area with mesoporous structure, and boron and MnO2 functional groups as electroactive sites. Enriched boron and MnO2 functional groups provide low internal resistance of charge diffusion by better wettability of electrolyte ions into the pores and also accommodate more charges, leading to high gravimetric capacitance and energy density, and enhanced cycling stability. Therefore, the PPBMn series exhibits superior electrochemical performance through the combined functions of their double-layer capacitance and pseudo-capacitive character through the high porosity, higher attractive force by the surface chemical activity and the wettability between the electrode and electrolyte.

In this study, the rapid synthesis of graphene via chemical vapor deposition (CVD) using liquefied petroleum gas (LPG), a common and low-cost carbon source majorly composed of butane and propane, as the precursor is investigated. For the synthesis of high-quality graphene, the growth conditions are optimized by controlling CVD parameters such as growth time, temperature, gas amount, and flow rate. Thus, graphene is successfully obtained from LPG in a short time. This synthesis is 10 times faster than that the conventional synthesis using methane as the carbon source. In the X-ray photoelectron spectra, the rapidly grown graphene samples obtained from LPG show small S2p signals due to the presence of few tens ppm ethanethiol in commercial LPG. In addition, graphene is synthesized using a hydrogen and LPG mixture to investigate the quality of graphene. Both samples are characterized by their peak positions and full width at half maximum values of the G and 2D peaks in the Raman spectra and Dirac points in the electrical measurements. In particular, the Dirac points of the graphene sample obtained with a growth time of 1 min sample appear around −22 VG and the sample's mobility is about 1600 cm2/V⋅s.

In this study, we investigated the synergistic effects of thermally conductive hybrid carbonaceous fillers of mesophase pitch-based carbon fibers (MPCFs) and reduced graphene oxides (rGOs) on the thermal conductivity of polymer matrix composites. Micro-sized MPCFs with different lengths (50 &mu, m, 200 &mu, m, and 6 mm) and nano-sized rGOs were used as the thermally conductive fillers used for the preparation of the heat-dissipation polymer composites. For all MPCF fillers with a different length, the thermal conductivity values of the MPCF/epoxy composites were proportional to the MPCF length and loading amount (0&ndash, 50 wt%) of MPCFs. For an MPCF:rGO weight ratio of 49:1 (total loading amount of 50 wt%), the thermal conductivity values of MPCF-rGO/epoxy composites loaded with MPCFs of 50 &mu, m, and 6 mm increased from 5.56 to 7.98 W/mK (approximately 44% increase), from 7.36 to 9.80 W/mK (approximately 33% increase), and from 11.53 to 12.58 W/mK (approximately 9% increase) compared to the MPCF/epoxy composites, respectively, indicating the synergistic effect on the thermal conductivity enhancement. The rGOs in the MPCF-rGO/epoxy composites acted as thermal bridges between neighboring MPCFs, resulting in the formation of effective heat transfer pathways. In contrast, the MPCF-rGO/epoxy composites with MPCF:rGO weight ratios of 48:2 and 47:3 decreased the synergistic effect more significantly compared to rGO content of 1 wt%, which is associated with the agglomeration of rGO nanoparticles. The synergistic effect was inversely proportional to the MPCF length. A theoretical approach, the modified Mori-Tanaka model, was used to estimate the thermal conductivity values of the MPCF-rGO/epoxy composites, which were in agreement with the experimentally measured values for MPCF-rGO/epoxy composites loaded with short MPCF lengths of 50 and 200 &mu, m.

Many studies have been carried out on sensors for detecting hazardous chemicals. In this study, a sensor for detecting the presence of acid was developed and evaluated. The sensor is composed of carbon materials and polyaniline, which is a conductive polymer. Various candidate carbon materials for the sensor were examined, including graphite, reduced graphene oxide (rGO), and graphene nanoplatelets (GNP). From characterization of carbon material-polyaniline and acid reaction test, it was confirmed that the GNP was the best carbon material for the acid sensor. For practical use, the GNP–polyaniline composite was coated on PET to enable a flexible sensor.

The importance of the thermal conductivity of engineering plastics reinforced with nanofillers is increasing in various industries, and the need for a model with which to make reliable predictions continues. We propose a micromechanics-based multiscale model that considers multi-shaped nanofillers to predict the thermal conductivity of composites. The distribution of each phase is assumed to be probabilistically distributed, and the Kapitza resistance at the interface between the filler and matrix was calculated by means of a molecular dynamics simulation. A polybutylene terephthalate (PBT) composite system embedded with multi-walled carbon nanotubes (MWCNTs) was used in a specific simulation. Composites containing MWCNTs of different lengths were also fabricated to obtain appropriate experimental results for the verification of the proposed model. Fourier-transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and field-emission scanning microscopy (FE-SEM) were carried out to confirm that the selected materials could suitably be compared. Finally, the proposed model was applied to the finite element method to examine the heat flux of the composites according to the constitutive properties, and their results were compared to the experimental results.

Hydrothermal liquefaction (HTL) is a thermal depolymerization process used to convert wet biomass such as microalgae into bio-crude oil. Four main products, gas, bio-crude oil, an aqueous phase, and solid residue, are generated through HTL. In this study, various HTL conditions were investigated to enhance the phosphorus content in the aqueous phase as well as the yield of bio-crude oil. Tetraselmis sp. was used as the microalgae feedstock, and the product yields according to catalyst type were explored. The phosphate ion (PO43−) content in the aqueous phase was significantly enhanced when acetic acid was added because of the effect of pH. In addition, it was found that both the bio-crude oil yield and the ammonium ion content could be increased by recycling the post-HTL aqueous phase, while the phosphate content was not.

2-(Trimethylsilyloxy)ethyl methacrylate (SMA)-derived mesoporous carbon nanofiber composite containing MnO 2 (Si-Mn-CNF) is fabricated by electrospinning method and found to be a very promising candidate for supercapacitor electrodes. Si-Mn-CNF possesses a large surface area of 707 m 2 g − 1 , high pore volume of 2.35 cm 3 g − 1 , and high mesopore fraction of 65%. Herein, SMA is used as an activating agent to develop the mesoporous structure by the thermal decomposition of SMA without activation process. As a result, Si-Mn-CNF exhibits a high specific capacitance of 200 Fg − 1 at a discharge current density of 1 mAcm − 2 and energy density of 23.72 Whkg − 1 at a power density of 400 Wkg − 1 in 6 M KOH aqueous electrolyte, due to the pseudocapacitive character associated with the surface redox-type reactions of the MnO 2 nanoparticles (NPs). Furthermore, the Si-Mn-CNF electrode retains a specific capacitance of over 85% of the initial value at a discharge current density of 20 mAcm − 2 compared with only 40% for Mn-CNF without using SMA, due to the rapid diffusion of electrolyte ions and the decrease of resistive characteristics through the developed mesoporous structures. Therefore, Si-Mn-CNF with high mesoporosity induced by SMA exhibits excellent electrochemical performance in terms of high specific capacitance and energy density, and excellent capacitance retention.

A facile fabrication of a porous carbon cryogel from a blend (PAEO) of fluorinated poly(amic acid) and poly(ethylene oxide) (PEO) is demonstrated. The porous carbons are prepared by carbonizing the freeze-dried cyrogels of polymer blend with various contents. The original channel structures of the cryogels with PEO content below 5 wt% are perfectly maintained in the carbon cryogels. In particular, the carbon cyrogel derived from the blend (PEO content: 5 wt%) shows very high specific surface areas, 2646 m 2 /g. From investigation of the carbonization mechanism, it is found that the incorporation of PEO creates mesoporous structure without generating hydrophobic or ambiphilic components, while elimination of fluorine moiety affects the formation of microporous structure in resulting-carbon. In addition, the porous structure in carbon cryogels of high PEO loading is shrunk because PEO component reduces the rigidity of the structure. Lastly, the performance of the carbon cryogels as a capacitor is investigated.

Heteroatoms (B, N, O)-containing porous manganese oxide (MnO 2 )/carbon nanofiber (MnB-CNF) materials are prepared by one-step electrospinning method via polyacrylonitrile (PAN) and manganese(II) chloride (MnCl 2 ) in dimethylformamide (DMF) solution containing different concentrations of B 2 O 3 . The MnB-CNF electrode exhibits optimized electrochemical behavior with a high energy density of 22.6 Whkg − 1 at a power density of 400 Wkg − 1 and a specific capacitance range of 210–160 Fg − 1 in the discharge current density range of 1.0 to 20 mAcm − 2 in aqueous KOH electrolyte. The higher electrochemical performance of MnB-CNF as a result of the electrochemical double-layer capacitor (EDLC), compared to regular Mn-CNF without B-based functional groups, is attributed to well-balanced meso- and micropores affecting the easy adsorption and transport of electrolyte ions, in addition to the pseudocapacitive redox reactions from MnO 2 , N, O, and extra numerous B in alkaline electrolytes. Thus, tailoring the pore structures with proper specific surface area, pore size, and number of heteroatoms is crucial for optimizing their electrochemical properties in the combined efforts to develop EDLCs and pseudocapacitance.

We found that the thermal conductivity of the polycarbonate (PC) composite filled with both 9.9 wt% expanded graphite (EG) and 0.1 wt% multi-walled carbon nanotube (MWCNT) fillers was synergistically improved by 49% compared to that of the PC composite filled with 10 wt% EG alone. In order to induce the optimal internal structure favorable for thermal conduction by enhancing the dispersion of the second MWCNT fillers, we applied a two-step melt-compounding to fabricate composites using a MWCNT masterbatch based on a polymerizable oligomer resin, cyclic butylene terephthalate (CBT), which is characterized by ultra-low viscosity and excellent impregnability during initial melting. Three-dimensional (3D) non-destructive characterization using X-ray micro computed tomography (micro-CT) was utilized to demonstrate the synergistic enhancement and to verify dispersion and 3D thermal network of the fillers in the composites accurately. The synergistic enhancement was significantly affected by the formation of the efficient thermally conductive pathways and dispersion of the second MWCNT fillers.

We investigated the heat transfer behavior of thermally conductive networks with one-dimensional carbon materials to design effective heat transfer pathways for hybrid filler systems of polymer matrix composites. Nano-sized few-walled carbon nanotubes (FWCNTs) and micro-sized mesophase pitch-based carbon fibers (MPCFs) were used as the thermally conductive materials. The bulk density and thermal conductivity of the FWCNT films increased proportionally with the ultrasonication time due to the enhanced dispersibility of the FWCNTs in an ethanol solvent. The ultrasonication-induced densification of the FWCNT films led to the effective formation of filler-to-filler connections, resulting in improved thermal conductivity. The thermal conductivity of the FWCNT-MPCF hybrid films was proportional to the MPCF content (maximum thermal conductivity at an MPCF content of 60 wt %), indicating the synergistic effect on the thermal conductivity enhancement. Moreover, the MPCF-to-MPCF heat transfer pathways in the FWCNT-MPCF hybrid films were the most effective in achieving high thermal conductivity due to the smaller interfacial area and shorter heat transfer pathway of the MPCFs. The FWCNTs could act as thermal bridges between neighboring MPCFs for effective heat transfer. Furthermore, the incorporation of Ag nanoparticles of approximately 300 nm into the FWCNT-MPCF hybrid film dramatically enhanced the thermal conductivity, which was closely related to a decreased thermal interfacial resistance at the intersection points between the materials. Epoxy-based composites loaded with the FWCNTs, MPCFs, FWCNT-MPCF hybrids, and FWCNT-MPCF-Ag hybrid fillers were also fabricated. A similar trend in thermal conductivity was observed in the polymer matrix composite with carbon-based hybrid films.

The exfoliated MXene (e-MXene) is systematically investigated as a mediator for laser desorption/ionization time-of-flight mass spectrometry (LDI-MS) analysis. Whereas un-exfoliated MXene has no activity for LDI-MS analysis, the e-MXene presents a high resolution, salt-tolerance and efficiency for LDI-MS analysis of various small molecules regardless of their polarity, aromaticity and molecular weight owing to its physicochemical properties such as high laser energy absorption, electrical conductivity and photothermal conversion. Based on our findings, it is clearly confirmed that e-MXene is a promising material for the development of an efficient platform for LDI-MS analysis of small molecules.

Recently, some studies have utilized silicon (Si) as an anode material of lithium ion battery by recycling Si from the slurry of wafer slicing dust. The filtration of Si particles condensed from Si vapors that were exhausted from the ingot growing furnace could propose another method of Si recycling. In this study, we investigated the possibility of using such collected silicon oxides (SiOx) particles as an anode material. After collecting SiOx particles, FE-SEM, TEM, EDS, XRD, XPS analysis, and charge/discharge test were carried out to investigate characteristics and usability of these particles. FE-SEM and FE-TEM images showed that these particles mainly consisted of spherical primary particles with a diameter of 10 nm or less. Agglomerates of these primary particles were larger than 300 nm in diameter. In TEM image and EDS analysis, crystalline particles were observed along with amorphous particles. As a result of XRD analysis, amorphous silica (SiO2) and crystalline Si were observed. Charge/discharge tests were carried out to determine the feasibility of using these particles as an anode material for lithium ion batteries. A cycle efficiency of 40.6% was obtained in the test in which the total number of charge/discharge cycle was 100 under the condition of C-rate 0.2 for the first three times and C-rate 1.0 for the remaining 97 times. Results showed that these collected particles could be used as an anode material for lithium ion batteries.

Si-based composites wrapped in multiple graphene shells were successfully fabricated as binder-free anodes for Li-ion batteries (LIBs). Reduced graphene oxide (rGO) and Si nanoparticles were prepared as spherical composite structures using a facile spray-drying process. The microspheres were homogeneously incorporated into a 3D porous graphene aerogel (GA) structure using an aerogel synthesis process. The inner rGO shell surrounding the Si nanoparticles promoted an effective electron transfer from the surface of the Si nanoparticles to electrolytes and suppressed the continuous formation of an unstable solid–electrolyte interface layer. Moreover, the 3D, porous GA framework, which demonstrated high electrical conductivity and mechanical stability, promoted the homogeneous dispersion of the Si nanoparticles, an effective and fast Li+ ion diffusion, and the suppression of volume expansion during lithiation. The rGO/Si/GA composite anode constructed by multiple graphene shells had an extremely high initial discharge capacity (1217 mAh g−1), excellent cyclic stability (462 mAh g−1 at 1.0 C after 200 cycles), and superior rate capability (819 mAh g−1 at 10 C) owing to its multilayered structure. We expect that our simple and scalable approach for fabricating Si-based anodes wrapped in multiple graphene shells can contribute to the development of high-performance LIBs for use in electric vehicles.

To store more energy in limited spaces, the volumetric performance of energy storage devices used in electric vehicles and portable electronics has attracted more research attention than their gravimetric performance. Herein, we describe the preparation of N/O co-doped single-walled carbon nanohorns (SWCNH) using chemical vapor deposition with pyridine followed by acid treatment to obtain a supercapacitor electrode material with high specific volumetric capacitance. The synthesized N/O co-doped SWCNH (N and O contents of 6.1 and 9.1 at%, respectively) electrode had a higher bulk density (1.05 g cm−3) than that of the pristine SWCNH electrode (0.86 g cm−3). Moreover, the N/O co-doped SWCNH supercapacitor electrode exhibited drastically increased specific volumetric, gravimetric, and areal capacitances (123 F cm−3, 117 F g−1, and 91.4 μF cm−2, respectively) in 1 M H2SO4 electrolyte, compared with those of a pristine SWCNH electrode (36 F cm−3, 42 F g−1, and 11.4 μF cm−2, respectively). The superior electrochemical performances are associated with enhanced pseudocapacitive contribution and high bulk density of electrode upon N/O co-doping. The simple method described herein for producing SWCNH electrodes with high bulk density and high specific volumetric capacitance should contribute to the development of supercapacitors with high volumetric performance.

The design and development of an economic and highly active non-precious electro-catalyst for ethanol electro-oxidation is challenging due to expensiveness of the precursors as well as processes and non-Eco friendliness. In this study, a novel preparation of mesoporous NiCo2O4-MWCNT nanocomposite aerogels based on sol–gel technique is proposed. Multiwall carbon nanotube (MWCNT)-supported NiCo2O4 nanocomposite aerogels as an efficient catalyst for the ethanol electro-oxidation is reported. The MWCNTs exhibit an interconnected fibrous network with uniform dispersion of NiCo2O4 nanoparticles. The effects of MWCNT concentration on the ethanol electro-oxidation of MWCNT/NiCo2O4 aerogels are studied. We found that using a proper loading of MWCNTs allowed us to reach higher current densities for the oxidation of ethanol in an alkaline media. The highly porous and fibrous MWCNT/NiCo2O4 aerogels are the promising electro-catalysts for the oxidation of a direct ethanol fuel cell.

In this study, an effective and novel method was developed to improve the thermal conductivity of epoxy composites by functionalization of graphene. The functionalization of graphene was carried out with a simple refluxing method using a double N-precursor with O-phenylenediamine (OPD), in which the graphene was first treated with acid (2 : 6 molar H2SO4 : HNO3) to form oxygen containing groups on the graphene surface (O-graphene). Amidation and nucleophilic addition reactions through amine groups in OPD contributed significantly to the doping of nitrogen into the graphene layers. The OPD functionalized graphene (OPD-f-graphene) was highly effective and compatible with an epoxy matrix, resulting in homogenous dispersion of a filler in the matrix. The in-plane and through-plane thermal conductivity of the functionalized graphene filled epoxy composite (fG–epoxy) was significantly increased ∼13 fold and ∼4.8 fold, respectively, in comparison to the neat epoxy composite (G–epoxy) with the addition of 6 wt% of the filler. This improvement in thermal conductivity was attributed to better dispersion of the filler into fG–epoxy which generated phonon conduction pathways.

The low energy density of commercially available activated carbon-based supercapacitors has limited their widespread applications. In the current work, we demonstrated fabrication of carbon nanofiber-based supercapacitors that exhibited ultra-high energy density by rationally tailoring their pore structure in an ionic liquid system. To gain control on the pore structure, three different methods were employed for the synthesis of an electrospinning-derived freestanding carbon nanofiber web. They are incorporation of a pore generator (i.e., tetraethyl orthosilicate) in the electrospinning step, physical activation (e.g., H2O or CO2), and hydrogen treatment. We observed finely tuned pore sizes ranging from 0.734 to 0.831 nm and accompanying changes in BET surface areas ranging from 1160 to 1624 m2 g−1. The entrapped TEOS within the electrospun organic nanofiber web provided high tuning ability of the pore structure in the following carbonization step, and decreased the activation energy of the pore formation. Both high specific capacitance (161 F g−1) and ultra-high energy density (246 W h kg−1) were achieved when the pore size on the surface of carbon nanofibers matched with the ionic size of the electrolyte. Our results demonstrate the importance of a finely tuned pore structure to secure high-temperature operable carbon nanofiber-based supercapacitors with ultrahigh energy density using ionic liquids as electrolytes.

In the current work, a high performance NO2 gas sensors has been fabricated from activated carbon fibers containing enriched boron moieties. The porous carbon fibers decorated with boron moieties exhibited rapid, repetitive and selective NO2 sensing performance at room temperature. The shallow, narrow and uniform micropores on the surface of the carbon fiber allowed target gases to be adsorbed and desorbed very easily whereas boron moieties induced high selectivity toward NO2 over NH3 via the strong binding energy. The excellent NO2 gas sensing performance of boron doped porous carbon fibers is attributed to synergetic effect of intrinsic pore structure of the carbon fibers and the boron moieties decorated on their surface.

This manuscript describes an efficient and cost-effective method to remove heavy metals of Hg and Cd in aqueous solutions via adsorption on activated carbon fibers after modification with NaOH solution (NaACF). The Hg and Cd metals in the aqueous solution exist as Hg(OH)2 and Cd2+ in the experimental condition of pH 6–8. Surface characterization of the NaACF reveals uniform and narrower micropores with an increase in oxygen functional groups of phenol and lactone compared with the original ACF (pACF). The NaACF demonstrates a superior adsorption rate to both aqueous samples of heavy metal compounds. The granular activated carbon (GAC) with diverse pore structures consisting of micropores, mesopores, and macropores adsorbed the heavy metals at a relatively slow rate. The adsorption mechanisms of the heavy metals into NaACF pores are proposed as pore-filling with non-ionic Hg(OH)2 and electron sharing of oxygens in phenolic, lactone, and carboxylic acid groups with ionic Cd2+. The results from continuous feeding are also reported for the sample blend of 10 wt% NaACF and 90 wt% GAC in increasing the cost performance ratio.

Hydration kinetics and products of MgO-activated slag are investigated by employing multiple analytical characterization techniques and thermodynamic modelling. The main hydration products of this cement are a calcium-aluminosilicate hydrate type gel, ettringite, monosulfate, hydrotalcite, brucite, and a third aluminate hydrate, while the extent of reaction and formation of reaction products significantly varied by MgO dosages. Higher dosage of MgO increased the degree of reaction of slag, and led to a higher population of Al in the octahedral region, which can be attributed to greater competition for Al required for the formation of hydrotalcite. The experimental and simulated volume of the solid binder increased as the MgO dosage increased, showing a good correlation with the strength increase of the samples with higher MgO dosage.

Recently, two-dimensional tungsten disulfide (WS2) has attracted attention as a next generation thermoelectric material due to a favorable Seebeck coefficient. However, its thermoelectric efficiency still needs to be improved due to the intrinsically low electrical conductivity of WS2. In the present study, thermoelectric properties of WS2 hybridized with highly conductive single-walled carbon nanohorns (SWCNHs) were investigated. The WS2/SWCNH nanocomposites were fabricated by annealing the mixture of WS2 and SWCNHs using a high-frequency induction heated sintering (HFIHS) system. By adding SWCNHs to WS2, the nanocomposites exhibited increased electrical conductivity and a slightly decreased Seebeck coefficient with the content of SWCNHs. Hence, the maximum power factor of 128.41 &mu, W/mK2 was achieved for WS2/SWCNHs with 0.1 wt.% SWCNHs at 780 K, resulting in a significantly improved thermoelectric figure of merit (zT) value of 0.027 compared to that of pristine WS2 with zT 0.017.

Environmentally benign natural amino acids, especially histidine-derived nitrogen-doped carbon materials were readily synthesized from polycondensation reaction and subsequent carbonization via the stepwise thermolysis process with high yields of ~40% even at a high temperature of 1000 °C and the nitrogen-atom contents of around 5 wt%. These materials possessed rolled planar structures as well as thick 2D-like planar structures with specific surface area of 455 m2/g, exhibiting a notable specific capacitance of 58 F/g at current densities of 0.1 A/g and superior stability without deterioration of performance values up to 2000 cycles.

In the last decades, carbon fibers with light weight and high strength have experienced the largely increased uses in various industrial applications. However, their expected uses in the automotive industry and building are largely limited because of their high production cost. Herein, we have demonstrated an effective method of making low cost carbon fibers via the melt spinning of petroleum-processing residue (pyrolyzed fuel oil, PFO)/lignin blends. Careful selection of tetrahydrofuran as the solvent to dissolve both PFO and lignin was made to optimize the miscible blend. The melt spinnable blend with a softening point of 260–280 °C exhibited good spinning ability at 280 °C. The plasticizing function of PFO allowed the highly cross linked lignin-based pitch to have high fluidity in the melt spinning process. Based on detailed TEM observations, the thermally treated fiber prepared at 2800 °C exhibited a shell–core structure, consisting of a highly crystalline surface from PFO and an amorphous disordered core from lignin. Such a crystalline surface structure gave rise to a high modulus value (up to 100 GPa) to the prepared carbon fibers.

We explore the importance of the size and position of nanoholes on the electrochemical performance of single-walled carbon nanohorn (SWCNH)-based supercapacitors using an ionic liquid electrolyte. The oxidized sample at 673 K showed a low specific capacitance per unit of internal specific surface area (4.0 μF cm–2), as the nanoholes created on the tips of SWCNHs via a selective chemical attack are too small to introduce electrolyte ions. For a sample oxidized at 723 K, the enlarged diameter of the nanoholes on the tips allows electrolyte ions to penetrate into the internal spaces of the SWCNHs, thereby resulting in a 2-fold capacitance improvement (8.6 μF cm–2). However, the abrupt decrease in the capacitance of the oxidized SWCNHs at 823 K (3.8 μF cm–2) can be explained by the selective formation of nanoholes on the sidewalls of the SWCNHs, where the small interstitial pores restrict ion diffusion to deeply positioned nanoholes on the sidewalls of the SWCNHs. Our study clearly reveals that the size and p...

It has become critically important to develop reliable method to transfer chemical vapor deposited (CVD) graphene from its growth substrate to the target substrate without leaving undesired polymer residues on the graphene surface. Here, we have found that for the two different transfer method – wet transfer using poly(methyl methacrylate) (PMMA) and dry transfer using polydimethylsiloxane (PDMS) as support layer, the amount of polymer residues and other impurities left on the graphene surface varies depending on the solvent used to remove those polymers. The exposure of the graphenes to different organic solvents such as acetone and chloroform resulted in different amount of polymer residues and impurities present on the graphene surface, which impact the electronic structure of the transferred graphene. It was found that the graphene obtained using the dry transfer method and acetone as solvent with a 2D to G (I2D/IG) intensity ratio of 4.58 and a 2D peak full width-half maximum (FWHM) of 24.66, which was higher than that using the wet transfer method and chloroform as solvent. These results showed that graphene was less affected by the polymer residues and impurities or the dry transfer method rather than the wet transfer method. In addition, using acetone rather than chloroform as solvent in the dry transfer method led to less contaminated graphene.

Carbon fibers are considered as one of the promising heating elements in various industrial applications because of their excellent thermal stability and electrical conductivity. In order to achieve controllability of the power output, gas-phase carbon deposition was carried out on the surface of carbon fibers by flowing a mixture of liquefied petroleum gas and hydrogen via electro-conduction chemical vapor deposition. We confirmed the tuning ability of the temperature ranging from 800 to 1330 °C. The microtexture of the deposited carbon was sequentially changed; the initial layer with small-sized domains, the intermediate layer with medium crystallinity, and the top layer with large-sized domains and high crystallinity. However, the linear decrease in the electrical conductivity of the heating elements was ascribed to the change in the growing direction of the crystallites from a longitudinal to a perpendicular direction with respect to the fibers. The wide range of power output for our carbon fiber composites from 270 to 448 W at 50 V will be useful for various industrial electric heating applications.

A series of multi-walled carbon nanotube (MWCNT) coated carbon fabrics was fabricated using a facile dip coating process, and their performance in electrical conductivity, thermal stability, tensile strength, electromagnetic interference (EMI) and shielding effectiveness (SE) was investigated. A solution of MWCNT oxide and sodium dodecyl sulfate (SDS) in water was used in the coating process. MWCNTs were observed to coat the surfaces of carbon fibers and to fill the pores in the carbon fabric. Electrical conductivity of the composites was 16.42 S cm−1. An EMI shielding effectiveness of 37 dB at 2 GHz was achieved with a single layer of C/C composites, whereas the double layers resulted in 68 dB EMI SE at 2.7 GHz. Fabricated composites had a specific SE of 486.54 dB cm3 g−1 and an absolute SE of approximately 35,000 dB cm2 g−1. According to the above results, MWCNT coated C/C composites have the potential to be used in advanced shielding applications such as aerospace and auto mobile electronic devices.

Here, we show that chemical vapor deposition growth of graphene on copper foil is strongly affected by the cooling conditions. Variation of cooling conditions such as cooling rate and hydrocarbon concentration in the cooling step has yielded graphene islands with different sizes, density of nuclei, and growth rates. The nucleation site density on Cu substrate is greatly reduced when the fast cooling condition was applied, while continuing methane flow during the cooling step also influences the nucleation and growth rate. Raman spectra indicate that the graphene synthesized under fast cooling condition and methane flow on cool-down exhibit superior quality of graphene. Further studies suggest that careful control of the cooling rate and CH4 gas flow on the cooling step yield a high quality of graphene.

Nanoscale defects in the outer tube to preserve the electrical and optical features of the inner tube can be engineered to exploit the intrinsic properties of double walled carbon nanotubes (DWCNTs) for various promising applications. We demonstrated a selective way to make defects in the outer tube by the fluorination of DWCNTs followed by the thermal detachment of the F atoms at 1000 °C in argon. Fluorinated DWCNTs with different amounts of F atoms were prepared by reacting with fluorine gas at 25, 200, and 400 °C that gave the stoichiometry of CF 0.20 , CF 0.30 , and CF 0.43 , respectively. At the three different temperatures used, we observed preservation of the coaxial morphology in the fluorinated DWCNTs. For the DWCNTs fluorinated at 25 and 200 °C, the strong radial breathing modes (RBMs) of the inner tube and weakened RBMs of the outer tube indicated selective fluorine attachment onto the outer tube. However, the disappearance of the RBMs in the Raman spectrum of the DWCNTs fluorinated at 400 °C showed the introduction of F atoms onto both inner and outer tubes. There was no significant change in the morphology and optical properties when the DWCNTs fluorinated at 25 and 200 °C were thermally treated at 1000 °C in argon. However, in the case of the DWCNTs fluorinated at 400 °C, the recovery of strong RBMs from the inner tube and weakened RBMs from the outer tube indicated the selective introduction of substantial defects on the outer tube while preserving the original tubular shape. The thermal detachment of F atoms from fluorinated DWCNTs is an efficient way to make highly defective outer tubes for preserving the electrical conduction and optical activity of the inner tubes.

Carbon nanotubes have shown great potential as conductive fillers in various composites, macro-assembled fibers, and transparent conductive films due to their superior electrical conductivity. Here, we present an effective defect engineering strategy for improving the intrinsic electrical conductivity of nanotube assemblies by thermally incorporating a large number of boron atoms into substitutional positions within the hexagonal framework of the tubes. It was confirmed that the defects introduced after vacuum ultraviolet and nitrogen plasma treatments facilitate the incorporation of a large number of boron atoms (ca. 0.496 atomic %) occupying the trigonal sites on the tube sidewalls during the boron doping process, thus eventually increasing the electrical conductivity of the carbon nanotube film. Our approach provides a potential solution for the industrial use of macro-structured nanotube assemblies, where properties, such as high electrical conductance, high transparency, and lightweight, are extremel...

We have experimentally and theoretically clarified the effect of oxygen functional groups on the capacitive performance of a photochemically treated activated carbon electrode. A high density of CO groups at the mouth of the micropores, where the chemically active edge sites are predominantly available, increases the energy barrier for ions to enter the pores, thereby resulting in a large decrease in the specific capacitance.

An efficient strategy for the enhancement of mechanical properties of carbon nanotube (CNT) fibers is developed using functionalized graphene oxide with a quaternary ammonium (QA) group (QA-FGO). QA-FGO is designed to induce the π-cation interaction, one of the strongest interactions in living systems, with CNT fibers. Based on the strategy, the tensile strength (58 MPa), specific strength (0.49 N/tex), modulus (2.5 GPa) and toughness (1.1 MJ/m3) of CNT fibers are enhanced to 409 MPa, 0.65 N/tex, 13.4 GPa, and 10.1 MJ/m3, respectively. The reinforcement mechanism is systematically demonstrated with experimental and theoretical approaches.

We investigated the importance of the specific effective surface area through a detailed study on the relationship between electrical conductivity of single-walled carbon nanohorns (SWCNHs) and accessibility of the electrolyte ions in the SWCNH-based supercapacitor. After heat treatment of the SWCNHs, the ratio of sp2/sp3 carbons dramatically increased, suggesting an enhanced electrical conductivity of the SWCNHs. Even though the specific surface area (SSA) slightly decreased by 16% as a result of heat treatment, the specific capacitance per SSA of the SWCNH electrode remarkably increased from 22 to 47 μF cm–2. Such a result indicates an explicit increase in accessible effective surface area by electrolyte ions. Our result clearly showed that a higher degree of utilization for the interstitial pore of SWCNHs by solvated ions is a key factor in achieving a high volumetric capacitance of SWCNH-based supercapacitors.

Flexible transparent conducting films (TCFs) were fabricated by dip-coating single-wall car- bon nanotubes (SWCNTs) onto a flexible polyethylene terephthalate (PET) film. The amount of coated SWCNTs was controlled simply by dipping number. Because the performance of SWCNT-based TCFs is influenced by both electrical conductance and optical transmittance, we evaluated the film performance by introducing a film property factor using both the number of interconnected SWCNT bundles at intersection points, and the coverage of SWCNTs on the PET substrate, in field emission scanning electron microscopic images . The microscopic film property factor was in an excellent agreement with the macroscopic one determined from electrical conductance and optical transmittance measurements, especially for a small number of dippings. Therefore, the most crucial factor governing the performance of the SWCNT-based TCFs is a SWCNT-network structure with a large number of intersection points for a minimum amount of deposited SWCNTs.

The hydrothermal synthesis behavior of ZnO nanowire (NW) on carbon nanotubes (CNTs) with respect to molar concentrations of zinc nitrate hexahydrate and hexamethylenetetramine and temperature was investigated. The ZnO NWs could be synthesized with a single-crystalline wurtzite structure and a diameter in the range of tens of nanometers. Their size does not strongly depend on the temperature, while it increases with increasing molar concentration. The NWs tend to have pyramidal shape at a growth front with increasing temperature and molar concentration probably due to enriched Zn2+ ion concentration. This demonstrates the morphological dependence of ZnO NWs on the relative rates between the decomposition of Zn precursor and subsequent oxidation of Zn to ZnO in hydrothermal synthesis.

Poly(vinylidene chloride) (PVDC)-derived nanoporous carbons were prepared by various activation methods: heat-treatment under an inert atmosphere, steam activation, and potassium hydroxide (KOH) activation at 873, 1073, and 1273 K. The pore structures of PVDC-derived nanoporous carbons were characterized by the N 2 adsorption technique at 77 K. Heat treatment in an inert atmosphere increased the specific surface area and micropore volume with elevating temperature, while the average micropore width near 0.65 nm was not significantly changed, reflecting the characteristic pore structure of ultramicroporous carbon. Steam activation for PVDC at 873 and 1073 K also yielded ultramicroporosity. On the other hand, the steam activated sample at 1273 K had a wider average micropore width of 1.48 nm, correlating with a supermicropore. The KOH activation increased the micropore volume with elevating temperature, which is accompanied by enlargement of the average micropore width from 0.67 to 1.12 nm. The average pore widths of KOH-activated samples were strongly governed by the activation temperature. We expect that these approaches can be utilized to simply control the porosity of PVDC-derived nanoporous carbons.

The importance of nanopore structures of carbons is shown in terms of interaction potential for various molecules including supercritical gases such as and . The key factors for adsorption of supercritical and are shown for single wall carbon nanohorn, single wall carbon nanotube, and double wall carbon nanotube. The cluster formation of molecules is a key process for water adsorption on hydrophobic carbon nanopores. The X-ray absorption spectroscopic examination elucidates an explicit dehydration structure of ions confined in carbon nanopores.

Single wall carbon nanotubes (SWCNTs) were treated with a HNO3/H2SO4 mixed solution to increase the number of narrow micropores. The mixed acid treatment increased the micropore volume from 0.13 to 0.35 mL g−1 as measured by N2 adsorption at 77 K. The micropore volume evaluated with CO2 adsorption at 273 K increased from 0.06 to 0.27 mL g−1. This remarkable micropore volume increase was ascribed to the formation of a highly packed and ordered SWCNT assembly with the acid treatment, which was confirmed by field emission scanning electron microscopy. The adsorption amount of supercritical H2 at 77 K under 5 MPa pressure increased twofold as a result of the acid treatment, while the supercritical CH4 adsorption amount at 303 K and 5 MPa pressure increased by 40%. These remarkable increases were caused by increased amount of narrow micropores as a result of the acid treatment.