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MXenes are a class of two-dimensional materials with potential applications in the fields such as thermal management and high-temperature materials. In this study, the transitions of Ti3C2Tx MXene are investigated during thermal annealing via x-ray photoelectron spectroscopy and two-dimensional correlation spectroscopy. The thermal evolution of MXene samples occurs as two distinct processes in different temperature regions: process I (from 25 to 500 °C) and process II (from 500 to 777 °C). In process I, the terminal groups of MXene are reduced, and fluorine (–F) terminal groups are released. Four different pathways are identified with C–Ti–O and C–C as probable final products. In process II, the reaction resulting in the removal of –F species and decomposition of the Ti3C2 region in the MXene is observed. These results provide insight into the thermal decomposition behavior of Ti3C2Tx MXene, which can assist in the design of MXene-based materials with specific functionalities.

Controlling the microstructures in fibers, such as crystalline structures and microvoids, is a crucial challenge for the development of mechanically strong graphene fibers (GFs). To date, although GFs graphitized at high temperatures have exhibited high tensile strength, GFs still have limited the ultimate mechanical strength owing to the presence due to the structural defects, including the imperfect alignment of graphitic crystallites and the presence of microsized voids. In this study, we significantly enhanced the mechanical strength of GF by controlling microstructures of fibers. GF was hybridized by incorporating polyacrylonitrile (PAN) in the graphene oxide (GO) dope solution. In addition, we controlled the orientation of the inner structure by applying a tensile force at 800 °C. The results suggest that PAN can act as a binder for graphene sheets and can facilitate the rearrangement of the fiber's microstructure. PAN was directionally carbonized between graphene sheets due to the catalytic effect of graphene. The resulting hybrid GFs successfully displayed a high strength of 1.10 GPa without undergoing graphitization at extremely high temperatures. We believe that controlling the alignment of nanoassembled structure is an efficient strategy for achieving the inherent performance characteristics of graphene at the level of multidimensional structures including films and fibers.

Rechargeable sodium-ion batteries (SIBs) have received significant attention as a promising alternative to traditional lithium-ion counterparts for large-scale energy storage applications owing to the low cost and abundance of sodium resources. Herein, we demonstrate the photonic irradiated mesoporous reduced graphene oxide (rGO)-TiO2 nanocomposite architectures using environmentally benign, ultrafast split-second (millisecond) intense pulsed light (IPL) process at room temperature. The photonic IPL irradiation spontaneously triggers the deoxygenation of graphene oxide (GO) and the simultaneous structural engineering of TiO2 nanocomposites. The precisely controlled IPL irradiation (energy density of 10 J cm−2) exhibits excellent conductivity, high surface area, and outstanding electrochemical performance as a green anode material for SIBs. The photonic IPL irradiated rGO-TiO2 nanocomposite delivers a high reversible capacity of 244 mAh g−1 at 0.1 Ag-1, a high rate performance of 112 mAh g−1 at 1 Ag-1, and high cycling stability compared to pristine GO-TiO2 and conventional furnace annealed rGO-TiO2 (FH-rGO-TiO2) nanocomposites. The detailed electrochemical analysis suggests that the improved capacitance contribution results from the fast kinetics of the IPL irradiated rGO-TiO2 nanocomposite anode. This work provides new insight into the fabrication of versatile, cost-effective techniques for developing advanced electrode materials for energy applications.

Self-assembly of two-dimensional MXene sheets is used in various fields to create multiscale structures due to their electrical, mechanical, and chemical properties. In principle, MXene nanosheets are assembled by molecular interactions, including hydrogen bonds, electrostatic interactions, and van der Waals forces. This study describes how MXene colloid nanosheets can form self-supporting MXene hydrogels. Three-dimensional network structures of MXene gels are strengthened by reinforced electrostatic interactions between nanosheets. Stable gel networks are beneficial for fabricating highly aligned fibers because MXene gel can endure structural deformation. During wet spinning of highly concentrated MXene colloids in a coagulation bath, MXene sheets can be transformed into perfectly aligned fibers under a mechanical drawing force. Oriented MXene fibers exhibit a 1.5-fold increase in electrical conductivity (12 504 S cm-1) and Young's modulus (122 GPa) compared with other fibers. The oriented MXene fibers are expected to have widespread applications, including electrical wiring and signal transmission.

High torsional strength fibers are of practical interest for applications such as artificial muscles, electric generators, and actuators. Herein, we maximize torsional strength by understanding, measuring, and overcoming rheological thresholds of nanocarbon (nanotube/graphene oxide) dopes. The formed fibers show enhanced structure across multiple length scales, modified hierarchy, and improved mechanical properties. In particular, the torsional properties were examined, with high shear strength (914 MPa) attributed to nanotubes but magnified by their structure, intercalating graphene sheets. This design approach has the potential to realize the hierarchical dimensional hybrids, and may also be useful to build the effective network structure of heterogeneous materials., Fibers with high torsional strength are of practical interest for artificial muscles, electric generators, actuators, etc. Here, the authors optimize torsional strength by overcoming rheological thresholds of nanocarbon (nanotube/graphene oxide) dopes.

The applicability of Na-ion batteries is contingent on breakthroughs in alternative electrode materials that have high capacities and which are economically viable. Unfortunately, conventional graphite anodes for Li-ion battery systems do not allow Na-ion accommodation into their interlayer space owing to the large ionic radius and low stabilizing energy of Na in graphite. Here, we suggest a promising strategy for significantly increasing Na capacity by expanding the axial slab space of graphite. We successfully synthesized reconstructed graphite materials via self-assembly of negative graphite oxide (GO) flakes and Al cation (positive) pillars and by subsequent chemical reaction of the obtained Al-GO materials. Al pillars, atomically distributed in graphite interlayers, can extend the slab space by up to ∼7 Å, which is a 2-fold interlayer distance of pristine graphite. An exceptionally high capacity of 780 mAh/g is demonstrated for reconstructed graphite anodes with Al pillars, compared with rGO materials (210 mAh/g). We investigated the electrochemical reaction mechanism and structural changes associated with discharge and charge to emphasize the benefit of using reconstructed graphite as anodes in Na-ion batteries. Our strategy of modifying the interlayer distance by introducing metallic pillars between the layers can help address the low capacity of carbonaceous anodes.

A highly self-healable polymeric system with enhanced mechanical properties is prepared by blending conventional polyurethane (PU) with functional polyimide (PI). PU and PI synthesized in this stud...

Graphene-based fibers (GFs) have aroused enormous interest in portable, wearable electronics because of their excellent mechanical flexibility, electrical conductivity, and weavability, which make them advantageous for wearable electronic devices. Herein, we report the development of metal binder-free Ti3C2Tx MXene/graphene hybrid fibers by a scalable wet-spinning process. These hybrid fibers exhibit excellent mechanical and electrical properties for applications in flexible wearable gas sensors. The synergistic effects of electronic properties and gas-adsorption capabilities of MXene/graphene allow the created fibers to show high NH3 gas sensitivity at room temperature. The hybrid fibers exhibited significantly improved NH3 sensing response (ΔR/R0 = 6.77%) compared with individual MXene and graphene. The hybrid fibers also showed excellent mechanical flexibility with a minimal fluctuation of resistance of ±0.2% and low noise resistance even after bending over 2000 cycles, enabling gas sensing during deformation. Furthermore, flexible MXene/graphene hybrid fibers were woven into a lab coat, demonstrating their high potential for wearable devices. We envisage that these exciting features of 2D hybrid materials will provide a novel pathway for designing next-generation portable wearable gas sensors.

Inspired by the role of cellular structures, which give three-dimensional robustness to graphene structures, a new type of graphene cantilever with mechanical resilience is introduced. Here, NH4SCN...

Solution-processed nanostructured mesoporous rutile phase titanium dioxides (TiO2) are a fascinating class of materials for energy applications owing to their remarkable properties, including thermal stability. The unique lattice structure of rutile TiO2 (R-TiO2) leads to multifaceted physicochemical properties, which influence its performances. We here report the preparation of mesoporous R-TiO2 via a simple and scalable solution process at a low temperature (

In flexible display technology, the electronic components are constructed on a flexible polymer substrate film and are released from a carrier glass with the detachment of the polymer film. During the debonding process, however, strong polymer-glass bonding often causes the formation of wrinkles and buckles of the polymer film and thereby the damage of electronics. Here, we report on a novel debonding layer (DBL) of graphene/MnO hybrids for scalable and stable detachment of the polymer film. The DBL acted to decrease the polymer-glass bonding strength. The weakly bonded polymer film was safely detached from the glass in ∼170 s by gas-evolution at DBL. The gas-induced debonding (GID) process was functional in H2O2 solution, not in other tested solutions, indicating its good solution selectivity. As proof of concept, flexible thin-film transistors (TFTs) were fabricated using our DBL and exhibited the similar transfer characteristics before and after the GID process. We believe our DBL will also pave the ways for flexible photovoltaic cells, flexible flash memories and flexible sensor arrays as well as flexible displays.

Fiber nanomaterials can become fundamental devices that can be woven into smart textiles, for example, miniaturized fiber-based supercapacitors (FSCs). They can be utilized for portable, wearable electronics and energy storage devices, which are highly prospective areas of research in the future. Herein, we developed porous carbon nanotube–graphene hybrid fibers (CNT–GFs) for all-solid-state symmetric FSCs, which were assembled through wet-spinning followed by a hydrothermal activation process using environmentally benign chemicals (i.e., H2O2 and NH4OH in deionized water). The barriers that limited effective ion accessibility in GFs were overcome by the intercalation of CNTs in the GFs which enhanced their electrical conductivity and mechanical properties as well. The all-solid-state symmetric FSCs of a precisely controlled activated hybrid fiber (a-CNT–GF) electrode exhibited an enhanced volumetric capacitance of 60.75 F cm–3 compared with those of a pristine CNT–GF electrode (19.80 F cm–3). They also s...

Over the past few years, several nanofluidic channels have been constructed using ion-conductive materials. However, the design and fabrication of surface-charge-controllable nanochannels remain a scientific as well as a technological challenge. This study investigated the feasibility of graphene oxide (GO)-based fiber-type nanochannels for generating electrical energy by converting the salinity gradient. Owing to their large lateral size and the localized charged species on the edge, the low charge density of the GO fibers remains a critical bottleneck in their wider investigation. To address this critical issue, highly negatively charged and extremely small (2.42 ± 0.38 nm) graphene quantum dots (GQDs) were synthesized and intercalated through the interstitial network of GO sheets in fibers. With the application of GQDs, the charge density was significantly increased to 1.12 mC m−2 so that the ion conductance was enhanced to an average of 21 nS and the electrical energy generation was 0.25 W m−2. This study presents a facile and novel approach of enhancing ion selectivity and ion conductivity of graphene-fiber based miniaturized nanofluidic channels, proving their potential for osmotic energy generation and efficiency.

The conversion of the electrokinetic energy arising from evaporation-induced water flow through nanoporous materials has great potential for renewable energy production. In this study, we prepare a nanocapillary membrane containing both nanopores and nanochannels based on an assembly of holey graphene oxide (HGO) nanosheets, which enables water molecules to permeate and simultaneously evaporate from the nanostructure. In particular, we find that the performance of our HGO membrane-based water evaporation-induced energy harvester (WEEH) can be significantly improved by ensuring (1) a high capillary flow of water through low-friction nanochannels and (2) a high rate of evaporation, which is achieved by the presence of large nanoscale pores with a broad size distribution. Our WEEH yields a maximum voltage of 0.44 V, current of 200 nA, and output energy density of 2.2 μWh cm−2. Furthermore, the use of multiple WEEHs allows for the generation of sufficient energy to charge a 1-F supercapacitor and power a light-emitting diode (2 V × 20 mA). Thus, our proposed nanocapillary, thin-membrane-based WEEH has great practical potential for energy generation, as well as other membrane-based technologies such as water purification.

Noble metal/metal-oxide-based hybrid gas sensors exhibit a low operating temperature, remarkable sensitivity, and fast recovery. As additives, noble metals induce a catalytic sensitization effect, which promotes charge transfer from the metal oxide to the analyte molecules, the so-called spillover mechanism. This suggests that metal catalysts can improve gas sensing performance. Herein, for the first time, non-noble metals are introduced on hybrid metal oxide/graphene fibers as sensitizers to fabricate high-performance chemiresistive sensors. The formation of metal components can be effectively controlled by annealing the metal oxide on graphene. Remarkably, compared with the corresponding metal oxide/graphene fiber sensors without metal components, the metal/metal oxide/graphene fiber sensors exhibit over a 16-fold higher response to NO2 gas as well as effective recovery characteristics. Specifically, the Cu/Cu2O/graphene and Ni/NiO/graphene fiber sensors operating at 150 °C exhibit sensitivities of 18.90 % and 0.82 %, respectively, for 5 ppm NO2 gas. The proposed strategy to achieve flexible graphene fiber chemiresistors by decorating them with non-noble metal and metal oxide nanoparticles opens a new avenue for realizing high-performance devices, such as photovoltaic devices, photocatalysts, and chemical catalysts.

TGA and DSC analyses were performed at the Electronics and Telecommunications Research Institute (ETRI). The SEM and FTIR were analyzed at Hanyang LINC Analytical Equipment Center (Seoul). This work was supported by "Civil research projects for solving social problems" through the National Research Foundation of Korea (NRF) funded by the Ministry of Science, ICT & Future Planning (2015M3C8A6A06014792).

Ti3C2Tx MXene is an emerging class of two-dimensional nanomaterials with exceptional electroconductivity and electrochemical properties, and is promising in the manufacturing of multifunctional macroscopic materials and nanomaterials. Herein, we develop a straightforward, continuously controlled, additive/binder-free method to fabricate pure MXene fibers via a large-scale wet-spinning assembly. Our MXene sheets (with an average lateral size of 5.11 μm2) are highly concentrated in water and do not form aggregates or undergo phase separation. Introducing ammonium ions during the coagulation process successfully assembles MXene sheets into flexible, meter-long fibers with very high electrical conductivity (7,713 S cm−1). The fabricated MXene fibers are comprehensively integrated by using them in electrical wires to switch on a light-emitting diode light and transmit electrical signals to earphones to demonstrate their application in electrical devices. Our wet-spinning strategy provides an approach for continuous mass production of MXene fibers for high-performance, next-generation, and wearable electronic devices., Large-scale production of fibers from two dimensional materials opens a pathway to promising applications. Here the authors report meter-long MXene fibers with high electrical conductivity that are fabricated via continuous wet spinning and demonstrated in electrical wires.

2D nanoscale oxides have attracted a large amount of research interest due to their unique properties. Here, a facile synthetic approach to prepare graphene-mimicking, porous 2D Co3O4 nanofoils using graphene oxide (GO) as a sacrificial template is reported. The thermal instability of graphene, as well as the catalytic ability of Co3O4 particles to degrade carbon backbones, allow the fabrication of porous 2D Co3O4 nanofoils without the loss of the 2D nature of GO. Based on these results, a graphene mimicking as a route for large-area 2D transition metal oxides for applications in electrochemical energy storage devices is proposed. As a proof of concept, it is demonstrated that graphene-like, porous 2D Co3O4 nanofoils exhibit a high reversible capacity (1279.2 mAh g−1), even after 50 cycles. This capacity is far beyond the theoretical capacity of Co3O4 based on the conversion mechanism from Co3O4 to Li2O and metallic Co.

A facile strategy to control the interfacial energy at graphite-water interface is introduced by coating the hydrophobic graphite powder with a hydrophilic manganese oxide layer. This modification not only improves the aqueous dispersion stability of graphite particles, but also supplements the low lithium ion storage capacity of graphite due to the high lithium ion uptake capability of manganese oxide. A catalytic reaction between graphite particles and permanganate ions leads to the formation of MnO2 layer on the surface of graphite particles. Successively, annealing the resulting composite powder in a reducing atmosphere transforms surface MnO2 to MnO. The electrode prepared with MnO-coated graphite powder showed the specific capacitance of 402 mAh g−1 at a current density of 25 mA g−1, which is higher than that of the pristine graphite electrode (338 mAh g−1 at 25 mA g−1). In addition, the electrode exhibited outstanding charge–discharge cycling stability for 100 cycles at a current density of 100 mA g−1 without any fluctuation or abnormal increase in the capacity that is often observed in transition metal oxide-based electrodes. It also showed excellent rate capability comparable to the pristine graphite electrode.

Highly aligned GO gel fibers are fabricated under high extensional flow for efficient nanofluidic transport of ion species., Colloidal dispersions with liquid crystallinity hold great promise for fabricating their superstructures. As an example, when graphene oxide (GO) sheets are assembled in the liquid crystalline state, they can turn into ordered macroscopic forms of GO such as fibers via the wet spinning process. Here, we report that by reinforcing intersheet interactions, GO liquid crystals (LCs) turn into mechanically robust hydrogels that can be readily drawn into highly aligned fibrillar structures. GO hydrogel fibers with highly aligned sheets (orientation factor, f = 0.71) exhibit more than twice the ionic conductivity compared to those with partially aligned structures (f = 0.01). The hierarchically interconnected two-dimensional nanochannels within these neatly aligned GOLC hydrogel fibers may facilitate controlled transport of charge carriers and could be potentially explored as cables for interconnecting biosystems and/or human-made devices.

The effective removal technique is necessary for the real world treatment of a hazardous pollutant (e.g., gaseous benzene). In an effort to develop such technique, the adsorption efficiency of benzene in a nitrogen stream (5 Pa (50 ppm) at 50 mL atm min−1 flow rate and 298 K) was assessed against 10 different metal oxide/GO composite materials (i.e., 1: graphene oxide Co (GO-Co (OH)2), 2: graphene oxide Cu (GO-Cu(OH)2), 3: graphene oxide Mn (GO-MnO), 4: graphene oxide Ni (GO-Ni(OH)2), 5: graphene oxide Sn (GO-SnO2), 6: reduced graphene oxide Co (rGO-Co(OH)2), 7: reduced graphene oxide Cu (rGO-Cu(OH)2), 8: reduced graphene oxide Mn (rGO-MnO), 9: reduced graphene oxide Ni (rGO-Ni(OH)2), and 10: reduced graphene oxide Sn (rGO-SnO2)) in reference to their pristine forms of graphene oxide (GO) and reduced graphene oxide (rGO). The highest adsorption capacities (at 100% breakthrough) were observed as ~23 mg g−1 for both GO-Ni(OH)2 and rGO-SnO2, followed by GO (~19.1 mg g−1) and GO-Co(OH)2 (~18.8 mg g−1). Therefore, the GO-Ni(OH)2 and rGO-SnO2 composites exhibited considerably high capacities to treat streams containing >5 Pa of benzene. However, the lowest adsorption capacity was found for GO-MnO (0.05 mg g−1). Alternately, if expressed in terms of the 10% breakthrough volume (BTV), the five aforementioned materials showed values of 0.50, 0.46, 0.40, 0.44, and 0.39 L g−1, respectively. The experimental data of target sorbents were fitted to linearized Langmuir, Freundlich, Elovich, and Dubinin-Radushkevich isotherm models. Accordingly, the non-linear Langmuir isotherm model revealed the presence of two or more distinct sorption profiles for several of the tested sorbents. Most of the sorbents showed type-III isotherm profiles where the sorption capacity proportional to the loaded volume.

Control of the crystal structure of electrochemically active materials is an important approach to fabricating high-performance electrodes for lithium-ion batteries (LIBs). Here, we report a methodology for controlling the crystal structure of TiO2 nanofibers by adding aluminum isopropoxide to a common sol–gel precursor solution utilized to create TiO2 nanofibers. The introduction of aluminum cations impedes the phase transformation of electrospun TiO2 nanofibers from the anatase to the rutile phase, which inevitably occurs in the typical annealing process utilized for the formation of TiO2 crystals. As a result, high-temperature stable anatase TiO2 nanofibers were created in which the crystal structure was well-maintained even at high annealing temperatures of up to 700 °C. Finally, the resulting anatase TiO2 nanofibers were utilized to prepare LIB anodes, and their electrochemical performance was compared to pristine TiO2 nanofibers that contain both anatase and rutile phases. Compared to the electrode ...

The chemical stability of basalt filament fiber in acidic condition was investigated by weight retention and tensile strength tests. It was found that the dissociation constant of acids was closely related to the weight retention. Furthermore, the tensile strength drastically decreased in the early immersion period even though weight retention was still high.

The authors are grateful to Dr. Hannah S. Leese for her helpful discussion. The morphology of fiber (SEM) was analyzed on NOVA Nano SEM 450 installed at the Hanyang LINC Analytical Equipment Center (Seoul). This research was mainly supported by the Basic Science Research Program (NRF 2014R1A1A1008196) and the Nano Material Technology Development Program (NRF 2016M3A7B4905609) through the National Research Foundation of Korea funded by the Ministry of Science, ICT and Future. Also, it was partially supported by the MOTIE (Ministry of Trade, Industry a Energy) (10052027) and the KDRC (Korea Display Research Corp.).