Continuous efforts have been made to achieve nanostructured carbon materials with highly ordered graphitic structures using facile synthetic methods. 3D graphite nanoballs (GNBs) are synthesized by the low‐temperature pyrolysis of a non‐graphitizable precursor, tannic acid (TA). Abundant phenol groups on TA bind to Ni2+ to form metal‐phenolic coordination, which renders each Ni cation to be atomically distributed by the TA ligands. Even at low temperatures (1000 °C), highly ordered graphitic structure is promoted by the distributed Ni nanoparticles that act as a graphitization catalyzer. The crystallinity of the GNB is fully corroborated by the intense 2D peak observed in Raman spectroscopy. In particular, the graphitic layers have orientations pointing toward multidirections, which are beneficial for the rapid transport of Li‐ions into graphite grains. The resulting materials exhibit outstanding electrochemical performance (120 mAh g−1 at 5 C and 282 mAh g−1 at 0.5 C after 500 cycles) when evaluated as a fast‐chargeable negative electrode for lithium ion batteries.

We produced a graphene oxide (GO) based nitrogen dioxide (NO₂) gas sensor with extremely low limit of detection (LOD), which is far below the WHO and EU annual standards. Based on the derived correlation among the band gap, adsorption energy, and sensing performance, we prepared semiconductive reduced GO (HGO) with simply modified acid washing process of traditional Hummers method. HGO, prepared with dispersed state enables easy fabrication of sensing device by a simple drop casting process and showed great sensing performance when HGO showed band gap of semiconductor. This research is considered that opened a new route to preparing extremely sensitive NO₂ gas sensors through very facile and cost effective processes.

Achieving the high theoretical energy density (~3500 Wh/kg) of Li-O2 batteries involves maximizing the electrochemically active surface area (EASA) of the electrodes. Carbon nanotubes (CNTs) have been widely adopted for Li-O2 electrodes but their EASA is limited by their electrolyte-phobic surface nature and the strong van der Waals interaction between CNTs. To increase the affinity between CNT-based electrodes and the electrolyte without decreasing CNT chemical stability, CNT buckypapers are functionalized with 3,5-bis(trifluoromethyl)phenylmaleimide. The solubility parameters of the electrolyte and CNTs are considered so that the maleimide groups increase the affinity between the electrode and electrolyte and the 3,5-bis(trifluoromethyl)phenyl groups protect the maleimide groups from decomposition. The functionalized CNT cathode exhibits a 58% greater discharge capacity and a 50% increased cyclability compared to pristine CNT cathode using 1:2.5 weight ratio of CNT to electrolyte due to an increased EASA and steric hindrance effect. Finally, a 3D folded Li-O2 cell is fabricated using the functionalized CNT-based cathode and demonstrated 30 cycles at 100 Wh/kgcell cutoff. These results clearly show that high energy density and long cycling performance of Li-O2 batteries can be achieved even with a much reduced amount of electrolyte by increasing the affinity between CNT-based electrodes and the electrolyte.

ABSTRACT 

Boron nitride nanotubes (BNNTs) show exceptional physical properties including high mechanical strength and thermal conductivity; however, their applications have been restricted due to limited dispersibility in processing solvents. Here, a novel BNNT dispersion method with exceptional dispersibility in a wide range of solvents has been demonstrated by surface polarity modulation through short-molecule pyridine attachment. Nitrogen atoms in pyridine are selectively bonded to electron-deficient boron atoms of the BNNT surface through Lewis acid-base reaction, which changes the surface polarity of BNNTs from neutral to negative. Re-dispersing pyridine-attached BNNTs (Py-BNNTs) create a thick and stable electronic double layer (EDL), resulting in uniform dispersion of BNNTs in solvents with an exceptional solubility parameter range of 18.5–48 MPa1/2. The uniform dispersion of BNNTs is maintained even after the mixing with diverse polymers. Finally, composites incorporating uniformly-distributed BNNTs have been realized, and extraordinary property enhancements have been observed. The thermal conductivity of 20 wt.% Py-BNNT/epoxy composite has been significantly improved by 69.6% and the tensile strength of 2 wt.% Py-BNNT/PVA has been dramatically improved by 75.3%. Our work demonstrates a simple and facile route to dispersing BNNTs in diverse solvents, consequently leading to selective utilization of BNNT dispersed solvents in various application fields. 

Compact stacking of building blocks is essential in order to utilize the impermeable nature of reduced graphene oxide (rGO) for encapsulating barriers in organic electronics. To obtain the desired accumulation characteristic, rGO films were fabricated via spraying process using phase-controlled graphene oxide (GO) dispersion. The rGO laminate prepared from the isotropic-phase dispersion exhibits a morefavorable face-on orientation of rGO building blocks than that from the nematic-phase GO, which implies effective stacking of building blocks. As a result, the resulting gas barrier performance of the low-temperature annealed rGO film is superior to previously reported low-temperature solution-processed materials. Fabricated gas barriers are adopted to seal the polymer solar cell with 57.2 times longer lifetime than that of the unsealed device. A device covered by an optimized rGO/polyethylene naphthalate gas barrier maintains photovoltaic performance as high as 88% of the initial efficiency after 28 days.

A facile synthetic strategy based on a water-based process is developed for the preparation of MOF-derived materials by revisiting the hydrolyzed non-porous metal-organic frameworks (h-MOF). The poor water stability of metal-organic frameworks (MOF) has been recognized as key limitations for its commercialization and large-scale applications because the hydrolysis resulted in the complete loss of their functionalities. However, we found that the negative effect of hydrolysis on MOF can be nullified during the heat treatment. As similar to the intact MOF, h-MOF can be used as a precursor for the preparation of MOF-derived materials from porous MOF-derived carbons (MDCs) to MDC@ZnO composites. The property of h-MOF-derived materials is almost equivalent to that of MOF-derived materials. In addition, h-MOF turned the weakness of water instability to the strength of facile water-based process for hybridization. With the demonstration of the hybrid composite between h-MDC@ZnO and reduced graphene oxide (rGO) as a prototype example, it exhibited superior electrochemical performance when evaluated as an electrode material for lithium-ion batteries.

N-doped hierarchical porous carbon with uniaxially packed carbon nanotubes (CNTs) was prepared by copolymer single-nozzle electrospinning, carbonization, and KOH activation. Densely and uniaxially aligned CNTs improve the electrical conductivity and act as a structural scaffold, enhancing the electrochemical performance of the anode. A partially graphitized N-doped carbon shell, which has a rapid ion accessible pore network and abundant redox sites, was designed to expand the redox sites from the surface of the material to the whole material, including the inner part. As an anode, this material exhibited a superior reversible capacity of 1814.3 mA h g–1 at 50 mA g–1 and of 850.1 mA h g–1 at 1000 mA g–1. Furthermore, the reversible capacity decreased by only 36% after 400 cycles and showed superior rate capability to that of the same material without CNTs, indicating that the CNT acted successfully as a structural scaffold and enhanced the electrical conductivity. This study not only allowed the rational design of the ideal structure of CNT-based carbonaceous anode material, which has both a rapid ion accessible structure and fast electron-transfer path, but also shed light on a potential strategy by which to use CNTs to modify the nitrogen bonding configuration in N-doped carbon for better electrochemical performance.

There has been remarkable progress with regard to the fabrication of yarns based on high-performance carbon nanotubes (CNTs). However, the theoretically predicted tensile strength of CNTs has yet to be realized in practical CNT yarns or CNT-reinforced composites. Having considered that there are few systematic guidelines for preparing high-strength CNT yarns, we attempted to revisit the-state-of-the-art progress in the theories and yarn formation processes of CNT yarns and then draw possible correlations between the intrinsic and extrinsic structural parameters of elementary CNTs, yarn formation processes and the tensile strength of the resulting CNT yarns. On the basis of these considerations and discussions of advanced technologies and theoretical approaches, possible routes to improve the strength of CNT yarns further are suggested.

The lithium-sulfur (Li-S) battery has been considered as a promising future energy storage device owing to its high theoretical energy density, low cost of the raw active material (sulfur), and its environmental friendliness. On the other hand, there are still challenging issues for the practical applications of Li-S batteries, including low-sulfur utilization, poor cyclability, and rate capability. Although considerable efforts have been made to overcome the current obstacles in Li-S batteries, it is still far from meeting the requirements for the commercialization of Li-S batteries. This review outlines the recent progress in Li-S batteries based on novel configurations, such as incorporating functional interlayers/separators beyond the approach for preparing novel cathodes, and discusses the role of the configuration in Li-S batteries. The functions of the newly introduced functional interlayer/separator are highlighted to address the problems of Li-S batteries. From classification of the functions, the perspectives and outlook are presented to rationally design a novel functional interlayer/separator for high performance Li-S batteries.

Information on the possible correlations between the characteristics of graphene itself or the performance of graphene-based devices and the conditions of its preparation or fabrication is scarce. This study examined how the characteristics and performance of graphene in applications, such as batteries and supercapacitors, conductive electrodes, and gas barrier films, change according to the conditions of the adopted process focusing mainly on graphene derived from GO. The overall aim was to determine the possible relationships between the characteristics and the conditions of the oxidation and reduction processes and the performance of devices based on the graphene prepared. Through a deeper understanding of the chemistry involved in the oxidation and reduction processes, possible routes along which the characteristics of graphene from GO can be tuned to a specific application were suggested. These guidelines will provide insights to those wanting to extend their exploration of graphene to new areas, such as catalysts, semiconductors, and biomedical materials.

Displaying information on transparent screens offers new opportunities in next-generation electronics, such as augmented reality devices, smart surgical glasses, and smart windows. Outstanding luminance and transparency are essential for such “see-through” displays to show vivid images over clear background view. Here transparent quantum dot light-emitting diodes (Tr-QLEDs) are reported with high brightness (bottom: ≈43 000 cd m−2, top: ≈30 000 cd m−2, total: ≈73 000 cd m−2 at 9 V), excellent transmittance (90% at 550 nm, 84% over visible range), and an ultrathin form factor (≈2.7 µm thickness). These superb characteristics are accomplished by novel electron transport layers (ETLs) and engineered quantum dots (QDs). The ETLs, ZnO nanoparticle assemblies with ultrathin alumina overlayers, dramatically enhance durability of active layers, and balance electron/hole injection into QDs, which prevents nonradiative recombination processes. In addition, the QD structure is further optimized to fully exploit the device architecture. The ultrathin nature of Tr-QLEDs allows their conformal integration on various shaped objects. Finally, the high resolution patterning of red, green, and blue Tr-QLEDs (513 pixels in.−1) shows the potential of the full-color transparent display.

This study reports on a simple and efficient strategy to prepare macroscopically assembled nanostructured porous carbon (MNPC) based on metal-phenolic interactions. The abundant coordination sites contained in tannic acid enable to form a stable, interconnected hydrogel dough. The porosity evolution mechanism during carbonization process is studied by temperature programmed desorption-mass spectroscopy. Hierarchical pore structure of the MNPC can be developed by modulating the zinc chloride content. The resulting material provides versatile adsorption behaviors for various ranging from small gas molecules to larger molecules such as dye, oil and organic solvents.

A novel dual imprinting method is suggested to synthesize pyridinic N‐enriched, hierarchically porous carbon. Rose‐like melamine cyanurate (MCA) mesocrystal is prepared by simple self‐assembly and utilized as a sacrificial template. The unique morphological and chemical features of the MCA are imprinted into the carbon source during carbonization. Curled graphene‐like layers with a high nitrogen content (19.9 at%, especially 8.9 at% of pyridinic N) are interconnected to form a unique red blood cell‐shaped morphology with a hierarchical pore structure. The resulting material exhibits outstanding electrochemical performance (2019 mAh g‐1 at 100 mA g‐1 and 643 mAh g‐1 at 2000 mA g‐1 after 250 cycles) when evaluated as an anode material for lithium ion batteries. Furthermore, this novel imprinting strategy can provide a simple and efficient methodology to produce pyridinic N‐enriched, hierarchically porous carbonaceous materials for extensive applications.

Graphene oxide liquid crystals (GO LC) prove their potential usefulness in a new design of carbon scaffold composites with ordered structures from nano to macro scale. This paper highlights the degree of GO functionalization as a notable influencing factor on GO LC formation. The large amount of oxygen functional groups, which cause secondary interactions between GOs, decrease the critical concentration for the phase transitions from isotropic to biphasic to nematic phases. In the biphasic state where isotropic and anisotropic phases coexist, highly oxidized GO sheets spontaneously develop LC phases among themselves. Furthermore, the strong hydrogen bonding networks between GO sheets govern the stabilization of the GO aqueous dispersion for a long period. This unique behavior can be used to design GO based architecture with controllable density and ordering.

We report a tremendous structural evolution of carbon nanosheets (CNSs) through the graphenization of isotropic pitches prepared by reforming commercially available naphtha cracking bottom oil. CNSs with thicknesses of 2–13 nm were prepared by spin-coating on quartz substrates directly without a catalytic material, followed by two successive thermal treatments consisting of stabilization at 270 °C in air and carbonization at up to 1200 °C in H₂/Ar. The development of well-ordered graphene layers around pebble-like structures with increasing carbonization temperature was observed in only the 13-nm thick CNSs by transmission electron microscopy, whereas thin CNSs did not reveal well-developed fringe growth. In addition, Raman, UV–vis, and X-ray photoelectron spectroscopies along with mass spectrometry unanimously showed clear evidence indicating that unusually well-developed crystalline structure was formed in the thick CNSs. It should be noted that isotropic pitches, which are intrinsically non-graphitizable carbon sources, evolved into highly ordered structures at a relatively low carbonization temperature (1200 °C). We believe that the graphenization of spin-coated films of pitch molecules resulted from the condensation of small pitch molecules and their self-assembled structure during carbonization under the anisotropic pressure induced by significant shrinkage in the vertical axis.

The gas permeability of reduced graphene oxide (rGO) films is influenced by controlling the lateral size and void generation. The low gas permeability was achieved by the controlled parent graphene oxide (GO) synthesis. The organic device lifetime using rGO-coated barriers was prolonged by 65.9 times when compared to bare samples.

This paper introduces poly(ethylene oxide) (PEO)-based modification of graphene oxide (GO) layers through the grafting onto the surface of GO as one of the excellent tools to improve the solubility and the processing ability of graphene. Methylene blue (MB)-mediated intercalation of graphite (flake) was first performed at 25 o C in aqueous media, followed by the Hummers’ process for oxidation, leading to an efficient production of GO. Direct oxidation of graphite (powder) also yielded the corresponding GO. The reaction of neutralized GO with “living” PEOs synthesized from alkyllithium- or sodium azide-initiated polymerization of ethylene oxide (EO) in polar solvents led to the production of the corresponding graphene oxide-gPEOs soluble in different solvents such as tetrahydrofuran (THF), methanol, dimethyl sulfoxide (DMSO), and H2O, etc. The resulting products were characterized by the combination of size exclusion chromatographic, 1 H nuclear magnetic resonance (1 H NMR), Raman, thermogravimetric anlysis (TGA), transmission electron microscopy (TEM), and atomic force microscopy (AFM) analyses.

Future electronic applications such as wearable electronics depend on the successful construction of energy storage devices with superior flexibility and high electrochemical performance. However, these prerequisites are challenging to combine: external forces often cause performance degradation while the trade-off between the required nanostructures for strength and electrochemical performance results only in energy storage. In this paper, we present a flexible supercapacitor design based on tannic acid (TA) and carbon nanotubes (CNTs) with a unique nanostructure. Here, TA is self-assembled on the surface of the CNTs by metal-phenolic coordination bonds which provides the hybrid film with both, high strength and high pseudocapacitance. Besides a 17 times increased mechanical strength of the final composite, the hybrid film simultaneously exhibits excellent flexibility and volumetric capacitance.

We prepared liquid phase exfoliated edge-selectively oxidized graphene (LPEOG) with a high concentration in water (∼14.7 mg ml⁻¹) and a high ratio of a single layer (70%). The edge of graphite was selectively oxidized by step II oxidation of the modified Hummers method, and we subsequently exfoliated the edge-selectively oxidized graphite (EOG) into LPEOG. The edge selective oxidation of the LPEOG was confirmed by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), zeta-potentiometry, Raman spectroscopy, Fourier-transform infrared spectroscopy (FT-IR), atomic force microscopy (AFM), and transmission electron microscopy (TEM). The highly concentrated LPEOG ink can be used in solution processing such as simple drawing or spin casting. Reduced LPEOG showed a higher conductivity (120000 S m⁻¹) than that of reduced graphene oxide (68800 S m⁻¹) despite the small lateral size. A transparent conducting film prepared from the LPEOG ink showed a lower surface resistance (∼2.97 kΩ sq⁻¹) at a higher transmittance (>83.0 %T) compared to those of the graphene oxide based film. These results indicate that preservation of π-conjugation of the basal plane of graphene is critical for electrical performance of graphene. Our method facilitates solution processing of graphene for a wide range of applications.

Graphene oxide (GO) has been synthesized by the Hummers method with modification of experimental condition by different research groups, but there is no guideline to prepare tailored GO for targeted applications. In this research, we suggest a guideline for tailor-fittable functionalization of graphene on the basis of the scope of our previous report on the two-step oxidation of GO. We describe a detailed procedure for synthesis of GO, effects of degree of step I oxidation on characteristics of GO and comparing them with effects of degree of step II oxidation. Characteristic changes of GO occurring during step I oxidation and those occurring during step II oxidation are different in species of oxygen functional groups, interlayer spacing, thermal stability, size distribution, and yield of GO. Based on the results, three types of tailor-fitted GO for a fiber, transparent conducting film, and hydrogen storage material are synthesized by controlling the degree of step I and step II oxidation. Compared to the reference GO synthesized by conventional modified Hummers method, the tailor-fitted GO showed 33.5 %, 117 %, and 104 % enhanced performance in strength of the fiber, figure of merits of transparent conducting film, and hydrogen storage, respectively. Our results show that the performance of GO based application is significantly influenced by the synthesis condition of GO, and optimized performance of the applications can be obtained by the tailor-fitted functionalization of GO. We anticipate that this study would be helpful for a variety of researches, both synthesis and application of GO.

The thermal decomposition behavior of multi-walled carbon nanotubes (MWCNTs) was revisited to prepare partially opened MWCNTs by a simple air oxidation method which allows massproductivity. As a promising matrix for sulfur cathodes, the partially opened MWCNTs can incorporate sulfur in hidden internal areas in the carbon nanotubes, leading to a homogeneous distribution through the MWCNT matrix. The resulting materials enable Li-S batteries to exhibit greatly enhanced electrochemical performance.  

The air plasma spraying method has a problem in the formation of many splat boundaries throughout the plasma sprayed layer, which seriously degrades mechanical properties of the metal layer. In order to improve the mechanical properties of air plasma sprayed tungsten (APS-W) by reducing the splat boundaries, a pulsed electric current is applied on as-sprayed specimens. Through microstructure observations and microhardness measurements, it was confirmed that the reduction of splat boundaries and the increase of hardness were obtained. The results are compared with those of APS-W annealed using induction heating under the same temperature, time and pressure.

Flexible lithium ion batteries (LIBs) are promising energy storage devices that can facilitate the advancement of wearable and flexible electronics. The main drawbacks of flexible LIB development are their low energy densities, poor mechanical strengths, and lack of flexibility. In this paper, we developed a facile method to prepare flexible and freestanding LIBs by modifying the CNT yarn (CNTY) synthesis. Iron catalysts in CNTYs were directly converted to electrochemically-active Fe₂O₃ nanoparticles featuring homogeneous distribution without agglomeration, monodisperse, and tight adhesion to CNT. This unique microstructure in the electrochemically activated CNTY (A-CNTY) electrode contributed to a good electrochemical performance (capacity, cyclability, and rate capability) of the resulting CNTY when evaluated as an anode material for LIB. We also fabricated a flexible fiber battery prototype composed of A-CNTY anode and commercially available lithium iron phosphate coated CNTY cathode with a gel electrolyte. The fabricated batteries are 30 cm-long with a diameter of a few hundred micrometers. In addition, our CNTY-based flexible LIBs are able to endure deformation without any substrates due to the good mechanical properties of CNTY. Our fiber type LIBs were able to successfully power various LED lights even during deformation.

Current approaches in use of water-insoluble photosensitizers for photodynamic therapy (PDT) of cancer often demand a nano-delivery system. Here, we report a photosensitizer-loaded biocompatible nano-delivery formulation (PPaN-20) whose size was engineered to ca. 20 nm to offer improved cell/tissue penetration and efficient generation of cytotoxic singlet oxygen. PPaN-20 was fabricated through the physical assembly of all biocompatible constituents: pyropheophorbide-a (PPa, waterinsoluble photosensitizer), polycaprolactone (PCL, hydrophobic/biodegradable polymer), and Pluronic F-68 (clinically approved polymeric surfactant). Repeated microemulsification/evaporation method resulted in a fine colloidal dispersion of PPaN-20 in water, where the particulate PCL matrix containing well-dispersed PPa molecules inside was stabilized by the Pluronic corona. Compared to a control sample of large-sized nanoparticles (PPaN-200) prepared by a conventional solvent displacement method, PPaN-20 revealed optimal singlet oxygen generation and efficient cellular uptake by virtue of the suitably engineered size and constitution, leading to high in vitro phototoxicity against cancer cells. Upon administration to tumor-bearing mice by peritumoral route, PPaN-20 showed efficient tumor accumulation by the enhanced cell/tissue penetration evidenced by in vivo near-infrared fluorescence imaging. The in vivo PDT treatment with peritumorally administrated PPaN-20 showed significantly enhanced suppression of tumor growth compared to the control group, demonstrating great potential as a biocompatible photosensitizing agent for locoregional PDT treatment of cancer.

A bioinspired hydrogen storage medium uses polydopamine (PD) which acts as a reducing agent, functionalizer, and strong metal binder. By controlling the degree of functionalized PD on graphene, the specific surface area of three-dimensionally interconnected graphene foam can be controlled. In addition, the functionalization degree of PD affects the size, distribution, and amount of platinum (Pt) nanoparticles decorated on the foam. By combining a high surface area and a uniform distribution of small sized Pt nanoparticles, the Pt-decorated PD-functionalized graphene (rGO/PD_Pt) exhibits a high hydrogen storage capacity of 3.19 wt.% at room temperature and 100 bar, which is the best hydrogen storage medium exhibiting the highest hydrogen uptake per unit specific surface area.

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The self-assembled nanostructures of carbon nanomaterials possess a damagetolerable architecture crucial for the inherent mechanical properties at both micro- and macroscopic levels. Bone, or “natural composite,” has been known to have superior energy dissipation and fracture resistance abilities due to its unique load-bearing hybrid structure. However, few approaches have emulated the desirable structure using carbon nanomaterials. In this paper, we present an approach in fabricating a hybrid composite paper based on graphene oxide (GO) and carbon nanotube (CNT), mimicking the natural bone structure. The size-tuning strategy enables smaller GO sheets to have more cross-linking reactions with CNTs and be homogeneously incorporated into CNT-assembled paper, which is advantageous for effective stress transfer. The resultant hybrid composite film has enhanced mechanical strength, modulus, toughness, and even electrical conductivity compared to previously reported CNT-GO based composites. We further demonstrate the usefulness of the size-tuned GOs as the “stress transfer medium” by performing in-situ Raman spectroscopy during the tensile test.

Hummers method has been used for fifty years to prepare graphene oxide (GO) by oxidizing graphite using Mn₂O₇. In this work, a new angle on Hummers method is described. The oxidation procedure before the addition of water, which has been respected as the main oxidation step of Hummers method, is named step I oxidation and the widely ignored further oxidation step after the addition of water is named step II oxidation. The chemical and structural evolutions during step II oxidation was demonstrated for the first time using various techniques including AFM, DLS, XPS, UV-Vis, FT-IR, 13C NMR and zeta-potentiometry. Step II oxidation influences the size of GO, defects within the layers, and functional groups on the surface, which affect the thermal stability of GO and the properties of resultant thermally reduced GO. This work provides new chemical insights into GO and guidelines for preparation of tailor-fitted GO.

Functionalization is one of the key procedures for real applications of carbon nanotube (CNT) as it involves the generation of the acidic functional groups on their surfaces. In these procedures, precise elucidation of these surface acidic groups is significant for the proper utilization of the functionalized CNT. For easy characterization of the practical acidic groups on CNT, one-pot titration methodology is developed, breaking the boundary between the conventional indirect and direct titration methods. The practical acidic functional groups including carboxylic, lactonic, and phenolic groups were successfully computed from the acid ionization constant (pK_a) distribution from the direct titration of nitric acid-oxidized multi-walled CNT by means of a one-pot titration methodology. These results were fairly identical to the results of the popular indirect titration method, showing that the developed methodology is essentially applicable for the surface characterization of acidic groups on CNT and potentially extended to the other carbon nanomaterials.

To allow for the use of graphene in various nanoelectronic applications, the methods for the large-scale production of graphene with controllable electrical properties need to be developed. Here, we report the results of a fundamental study on the remarkable conversion between n- and p-type reduced graphene oxide (rGO) with changes in the thermal annealing temperature. It was found that the charge carriers in rGO for temperatures of 300–450 °C and 800–1000 °C are electrons (n-type), whereas for temperatures of 450–800 °C, they are holes (p-type). This is because the individual oxygen functional groups present on rGO are determined by the annealing temperature. We found that the predominance of electron-withdrawing groups (i.e., carboxyl, carbonyl, and sp3-bonded hydroxyl, ether, and epoxide groups) resulted in p-type rGO, while that of electron-donating groups (sp2-bonded hydroxyl, ether and epoxide groups) lead to n-type rGO. In addition, as a proof of concept, a flexible thermoelectric device consisting of GO-700 and GO-1000 as p-type and n-type components, respectively, was fabricated. This device, which contained eight pairs of the two components, exhibited an output voltage of 4.1 mV and an output power of 41 nW for ΔT = 80 K. These results demonstrate that the carrier characteristics of rGO can be altered significantly by changing the functional groups present on it, thus allowing it to be used in various applications including flexible thermoelectrics.

As commercial interest in flexible power-conversion devices increases, the demand is growing for high-performance alternatives to brittle inorganic thermoelectric materials. As an alternative, we propose a flexible single-walled carbon nanotube (SWCNT)-doped tellurium nanowire (TeNW) hybrid film and, for the first time, rationally engineer the work function of the SWCNTs to effectively filter charge carriers in an energy-dependent manner at the interfaces between the carbon and the inorganic semiconductor. The acid treatment used to control the SWCNT work function allows the interfacial barrier between the SWCNT and the TeNW to be raised and lowered. While the hybrid film with a large barrier of 0.82 eV has a low power factor due to poor carrier transfer, the power factor (3.40 μW·m⁻¹·K⁻²) in the film with a lower barrier of 0.23 eV is several times higher than that of either pure TeNW or hybrid film with 0.82 eV due to effective energy filtering effect. The transport characteristics of the hybrid film are explored to quantitatively elucidate the carrier filtering at the SWCNT-TeNW interfaces. These demonstrate the effectiveness of optimizing SWCNT work functions to improve the thermoelectric properties of SWCNT/TeNW hybrid films, thus indicating that this strategy can be applied to flexible/or wearable thermoelectrics.

Continuous efforts have been made to attain high performance Li-S batteries by preventing loss of soluble polysulfides, whereas issues related to insoluble discharge products, Li₂S₂ and Li₂S, have been underestimated. In this paper, we demonstrate that facile and mild method, diazotization, enables uniform functionalization on the surface of ordered mesoporous carbon (CMK-3) with aniline functional groups while it does not deteriorate the original CMK-3 microstructure. The aniline groups possess favorable interactions with insoluble discharge products. Thus, they homogeneously distribute the insoluble discharge products during cycling. The proposed materials exhibit outstanding electrochemical properties with regards to stability (920 mAh g^-1 at 0.2 C after 100 cycles) and rate capability (814 mAh g^-1 at 1 C) when evaluated as a cathode material for lithium sulfur batteries.

Length of multi-walled carbon nanotube (MWCNT) has strong impact on mechanical strength of MWCNT/polymer composite. In this paper, MWCNT/polyamide 6, 6 (PA 66) composites using ten different MWCNTs were prepared by melt processing. The harsh mixing process used to achieve a fine dispersion of MWCNTs in the polymer matrix broke and severely reduced the lengths of the MWCNTs. The characteristics of MWCNTs that influence the breakage and length reduction were systematically and experimentally explored. Insights into designing the microstructures and morphological properties of pristine MWCNTs were provided, based on the correlation data and statistical evaluation results, in an effort to preserve the high aspect ratio of the MWCNTs during the melt mixing process, thereby expecting the enhanced mechanical properties of the composite.