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Structure and chemical evolution during N-dopant-specific unzipping of NCNTs. (a) Aberration-corrected TEM images of 2-, 8- and 16-h-unzipped nanostructures (in 1 M H2SO4 at 0.8 V). (b) Np and O contents versus unzipping time. (c) Capacitive current in cyclic voltammogram versus unzipping time. Scale bar, 2 nm.
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Atomic level engineering of graphene-based materials is in high demand to enable customize structures and properties for different applications. Unzipping of the graphene plane is a potential means to this end, but uncontrollable damage of the two-dimensional crystalline framework during harsh unzipping reaction has remained a key challenge. Here w...
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... configuration of edges developed during unzipping reaction is characterized with the angle between in-plane hexagonal carbon lattice and edge direction 29,30 (Fig. 1d). Zigzag edge configuration (green line) predominates in the unzipped structures ( Supplementary Fig. 2). Figure 1e shows an atomic-force microscopy (AFM) image of 1.7-nm-thick tri-layer graphene sheet produced from 5.9-nm-diameter triple-walled NCNTs ( Supplementary Fig. 3). The lateral width of unzipped structures is slightly larger than the diameter of parent NCNTs as expected ( Supplementary Fig. 4). ...
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... of the unzipping time (at 0.8 V) enables the fine controllability of unzipping propagation. Figure 3a shows TEM images of 2-, 8-and 16-h-unzipped structures. Although the outermost walls are selectively peeled off after 2 h, fully unzipped structures are predominantly formed after 8 h. ...
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... hexagonal crystallinity of graphitic domains remains intact in basal plane even after 16 h. Figure 3b presents the evolution of O and N p contents along with unzipping process. The drastic N p content reduction at the initial stage of unzipping substantiates the selective and concurrent commencement of unzipping initiation at multiple N p -dopant sites, which are subsequently transformed into oxygen functional groups. ...
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... unzipping rate. High unzipping rate rapidly diminishes for the first 8 h and gradually reaches to near-zero in the next 16 h. The final structure obtained by prolonged 24-h-unzipping exhibits the O content of 11.9 % along with the dramatic improvement in the dispersibility of unzipped structures in polar solvents 39 (inset optical image in Fig. 3b and Supplementary Fig. ...
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... evolution of capacitive current (I c ) is another measure to monitor the unzipping progress, particularly in terms of surface area enhancement 19 . I c rapidly increases in the early stage because of the enlargement of surface area by gradual exposure of the inner surface of NCNTs, and the rate enhancement of I c slowdowns after 4 h (Fig. 3c). The sudden reduction of I c at 8 h reflects the serious damage of inmost wall of NCNTs that causes a loss of electrical connectivity 40 . Such a deterioration of the electrical integrity eventually leads to the self-termination of unzipping ...
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Changes in wettability based on the dispersion properties of carbon nanotubes are generally achieved by chemical functionalization methods using acid treatments. Compared to a highly crystalline carbon structures (i.e., single-walled carbon nanotube and fullerene), low crystalline carbon structures (i.e., multi-wall carbon nanotubes and graphene) a...
Citations
... Overall, the choice of nanoribbon depends on the specific heavy metal ion being detected, as well as the sensitivity, selectivity, and cost of the detection method as shown in Table 1, which thoroughly comprises the details and parameters of different studies conducted on detection of HMs. The researchers functionalized the graphene nanoribbons with a fluorescent chemical that only binds to lead ions in order to produce a fluorescence quenching effect that may be utilized to identify the presence of lead ions (Lim et al. 2016). As indicated in Table 2, single-walled carbon nanotube (SWCNT) ribbons were also used to detect mercury ions. ...
Worldwide, heavy metal pollution is a major problem that has an impact on human health and the environment. The identification and removal of heavy metals from the environment is necessary to safeguard both human health and the ecology. An emerging family of nanomaterials called nanoribbons has shown significant promise in the monitoring and eradication of heavy metals (HMs) in various industries. We first go over how nanoribbons are made and their structural characteristics before talking about how their special surface chemistry and reactivity make it possible for them to highly efficiently and specifically adsorb and collect heavy metals. Recently, progress has been made in the use of nanoribbons as heavy metal sensors, and these sensors have shown great promise for real-time heavy metal contamination monitoring due to their hyper sensitivity, rapid reaction times, and inexpensive production. They are a feasible alternative to traditional remediation procedures because of their greater adsorption capacity and quick separation. In this study, the current state of the art and possible uses of nanoribbons for the removal and detection of heavy metals are briefly discussed. Additionally, it highlights their significant potential for alleviating the global issue of heavy metal contamination on a worldwide scale.
... Electrochemical capacitors are expected to replace conventional electrolytic capacitors in line filtering for integrated circuits and portable electronics [1][2][3][4][5][6][7][8] . However, practical implementation of electrochemical capacitors into line-filtering circuits has not yet been achieved owing to the difficulty in synergistic accomplishment of fast responses, high specific capacitance, miniaturization and circuit-compatible integration 1,4,5,[9][10][11][12] . ...
... Line filtering is crucial for precision power supply to integrated circuits such as central processing units (CPUs) and memory devices 15,16 . For circuit miniaturization and device portability, electrochemical capacitors can be used as an alternative to conventional electrolytic capacitors (ELCs) because of their high specific capacitance [1][2][3][4][5][6][7][8] . However, the practical application of the electrochemical capacitors in line-filtering circuits remains a huge challenge because of the difficulty in achieving fast responses, high specific capacitance, miniaturization and circuit-compatible integration simultaneously 1,4,5,[9][10][11][12] . ...
... Electrochemical performance calculations. Based on the data from electrochemical and EIS measurements, the performance parameters were derived according to other reports on line-filtering electrochemical capacitors [1][2][3][4][5][6][7][8] . ...
Electrochemical capacitors are expected to replace conventional electrolytic capacitors in line filtering for integrated circuits and portable electronics1–8. However, practical implementation of electrochemical capacitors into line-filtering circuits has not yet been achieved owing to the difficulty in synergistic accomplishment of fast responses, high specific capacitance, miniaturization and circuit-compatible integration1,4,5,9–12. Here we propose an electric-field enhancement strategy to promote frequency characteristics and capacitance simultaneously. By downscaling the channel width with femtosecond-laser scribing, a miniaturized narrow-channel in-plane electrochemical capacitor shows drastically reduced ionic resistances within both the electrode material and the electrolyte, leading to an ultralow series resistance of 39 mΩ cm² at 120 Hz. As a consequence, an ultrahigh areal capacitance of up to 5.2 mF cm⁻² is achieved with a phase angle of −80° at 120 Hz, twice as large as one of the highest reported previously4,13,14, and little degradation is observed over 1,000,000 cycles. Scalable integration of this electrochemical capacitor into microcircuitry shows a high integration density of 80 cells cm⁻² and on-demand customization of capacitance and voltage. In light of excellent filtering performances and circuit compatibility, this work presents an important step of line-filtering electrochemical capacitors towards practical applications in integrated circuits and flexible electronics.
... The capacitance at 100 Hz, in this case, was improved to 1145 μF (Fig. 6c). A comparison between the ESR values vs. capacitance in the high-frequency region reported for values in carbon-based electrode structures is presented in Fig. 6d [6,15,16,18,19,[41][42][43][44][45]. ...
... The high-frequency region of the Nyquist plot evidenced a low ESR of 5.8 mΩ, demonstrating one of the lowest resistance values in carbonbased electrode structures [6,15,16,18,19,[41][42][43][44][45]. The ESR value is lower than the one determined for the two electrode cells, where the ESR value is 30 mΩ. ...
Portable electronic devices require high-performance miniaturised electronic components, preferably produced at low cost. In most line-powered applications, alternating current line filters are used to filter AC lines to direct current signals, making filtering capacitors a key necessity in modern electronic devices. Currently, aluminium electrolytic capacitors (AECs) are commonly used, which are bulky and have narrow electrochemical performance. Thus, replacing AECs with a compact capacitor design is highly desirable for future portable electronic devices but simultaneously very demanding. Here, we report the fabrication of an electrochemical capacitor with an electrode based on vertically aligned carbon nanostructures produced by a green plasma-enabled deposition technique. These capacitors delivered a high capacity of 1145 μF with a phase angle close to −80 ° at 100 Hz in a lab-scale two-electrode set-up. A prismatic prototype capacitor fabricated by stacking 10 pairs of electrodes (2.5 × 3.5 cm²) showed one of the lowest equivalent series resistance values, about 5.8 mΩ, with a high capacitance of ∼12 mF at 100 Hz. This performance delivered at the lab scale and in industrial-relevant environments suggests such electrochemical capacitors represent a suitable alternative to conventional AECs for high-frequency filtering applications.
... These groups come either from precursor organic compounds such as citric acid (widely used for bottom-up fabrication of CQDs [16]) or appear due to oxidation during the unzipping and top-down cutting of larger nanoscale carbon bodies (nanotubes, graphite, etc.). [17] Additionally, it is assumed (although widely explored, this has not yet been confirmed by the data available in the literature) that carbon dots may contain other molecular fragments on the surface (e.g., planar molecules or embedded sp 2 -hybridised carbon domains consisting of up to 18 conjugated aromatic rings) which can fluoresce in the range from 400 to 700 nm [18]. ...
We propose and demonstrate a novel range of models to accurately determine the optical properties of nitrogen-free carbon quantum dots (CQDs) with ordered graphene layered structures. We confirm the results of our models against the full range of experimental results for CQDs available from an extensive review of the literature. The models can be equally applied to CQDs with varied sizes and with different oxygen content in the basal planes of the constituent graphenic sheets. We demonstrate that the experimentally observed blue fluorescent emission of nitrogen-free CQDs can be associated with either small oxidised areas on the periphery of the graphenic sheets, or with sub-nanometre non-functionalised islands of sp2-hybridised carbon with high symmetry confined in the centres of oxidised graphene sheets. Larger and/or less symmetric non-functionalised regions in the centre of functionalised graphene sheet are found to be sources of green and even red fluorescent emission from nitrogen-free CQDs. We also demonstrate an approach to simplify the modelling of the discussed sp2-islands by substitution with equivalent strained polycyclic aromatic hydrocarbons. Additionally, we show that the bandgaps (and photoluminescence) of CQDs are not dependent on either out-of-plane corrugation of the graphene sheet or the spacing between sp2-islands. Advantageously, our proposed models show that there is no need to involve light-emitting polycyclic aromatic molecules (nanographenes) with arbitrary structures grafted to the particle periphery to explain the plethora of optical phenomena observed for CQDs across the full range of experimental works.
... As shown in Fig. 1(c), Lim et al. further expanded the concept to nitrogen-doped CNTs, wherein the pyridinic nitrogen sites selectively initiate the unzipping process under reduced voltage. 28 The analysis of the nitrogen groups reveals the disappearance of pyridinic nitrogen while the quaternary nitrogen remains unchanged. This feature is a key indicator of the selective unzipping mechanism at dopant sites. ...
... Furthermore, in the studies on electrochemically unzipping MWNTs and nitrogen-doped CNTs by Shinde et al. and Lim et al., the measured oxygen content was ∼23% and ∼12%, respectively. 28,32 The unzipping process initiated by KMnO 4 leads to higher levels of oxygen functional groups. Further mechanistic studies may reveal pathways to facilitate the unzipping process while minimizing or avoiding the use of strong oxidizers, thereby enabling the production of GONRs with fewer oxygen groups. ...
... Lim et al. reported dopantselective unzipping of nitrogen CNTs for use in supercapacitors. 28 The fabricated supercapacitors exhibited ideal capacitive behavior at rates up to 400 V/s, indicating fast charge transfer [ Fig. 6(f)]. Lin et al. prepared MWNT/GONR heterostructures with remaining CNT cores. ...
Graphene oxide nanoribbons (GONR) are prepared by the top-down oxidative unzipping of carbon nanotubes. The unique one-dimensional morphology and the abundant functional groups of GONR distinguish it from other graphene-based carbon materials with increased solvent dispersibility and self-assembly behavior. These features have been exploited throughout the literature for various applications, including energy storage materials, sensors, catalysts, fillers for composites, and separation membranes. However, despite its drastically different chemical and physical properties, GONRs are often only discussed in the sub-context of graphene nanoribbons. This Perspective highlights GONRs specifically, focusing on their chemical properties and structuring behaviors, which can be manipulated to yield appealing structures for target applications. These characteristics constitute significant importance in scalable applications. The final section of this Perspective catalogs a comprehensive summary of recent GONR developments and additional perspectives for future research.
... Meanwhile, the increased O 1s peak is attributed to the electrochemical etching in Ti 3 C 2 T x nanoflakes and CNTs, which has been proved in many other reports. 29,31 In the high-resolution Ti 2p spectra (Figure 3b), both Ti 3 C 2 T x and Ti 3 C 2 T x @CNT revealed the same four doublet peaks. The Ti−C 2p doublet peak (455.0 and 461.0 eV) in Ti 3 C 2 T x @ CNT indicates the stable chemical state of the deposited Ti 3 C 2 T x nanoflakes. ...
Two-dimensional (2D) MXene nanosheets are attractive for electrochemical energy storage applications due to their superior surface-controlled charge storage capacity. However, the slow ion transport in the closely packed electrode limits their electrochemical performances. Meanwhile, the restricted surface-controlled pseudocapacitance of MXene nanosheets requires to be enhanced. Herein, a well-controlled electrophoretic deposition strategy is developed to disperse Ti3C2Tx nanosheets into a freestanding, porous carbon nanotube (CNT) sponge. The constructed Ti3C2Tx@CNT hybrid sponge can provide high-speed ion-transport pathways for the charge-discharge process. Furthermore, by tuning the deposition potential, the inserted MXene nanosheets can be partially oxidized, boosting the pseudocapacitance performance. A large gravimetric capacitance of 468 F g-1 at 10 mV s-1 and a retention of 79.8% at 100 mV s-1 can be achieved in the Ti3C2Tx@CNT electrode. Meanwhile, the highest areal capacitance of 661 mF cm-2 at 1 mA cm-2 was obtained in the sample with high-loading Ti3C2Tx. For the assembled symmetric supercapacitor, 92.8% of the capacitance is retained after 10 000 cycles of the charge-discharge process at 10 mA cm-2. Thus, this study develops a promising electrophoretic deposition strategy for dispersing 2D MXene nanosheets and boosting their pseudocapacitive performance, resulting in a high-capacitive electrochemical energy storage electrode.
... The recent method based on the simple mechanism of unzipping or unrolling of single walled carbon nanotubes or multiwalled carbon nanotubes for the synthesis of graphene is used extensively these days. The cylindrical structures of carbon nanotubes are opened either longitudinally or axially to flat carbon sheets using various methods such as intercalation, chemical attack, metal-catalysed cutting, and plasma etching (Lim et al. 2016;Zheng et al. 2020). The unzipping process can be induced easily by the inter-tube intercalation of carbon nanotubes using suitable ions which results Fig. 1 Methods for the synthesis of graphene using different carbon-based precursors. ...
Biosensors are gaining interest in biomedical and environmental sciences. In particular, graphene-based biosensors are promising due to the unique properties of graphene. Here we review the synthesis, characterization, and applications of graphene in enzymatic sensors, immunosensors, DNA sensors, and wearable sensors. Graphene displays advantages such as biocompatibility and oxygenated functional groups that enable chemical functionalization to form composites with metals. We discuss sensor reproducibility, detection limits, sensitivity, multi-targets, and portability.
... This work provides a solid development platform for flexible electronics in monitoring sector. The proposed configurations are within the current experimental scope in three manners: CNT irradiated by energetic particles [26], selective chemical etching [27][28][29][30][31], and deriving carbon atomic chains in graphene [32,33]. ...
Multifunctionality, interference-free signal readout, and quantum effect are important considerations for flexible sensors equipped within a single unit towards further miniaturization. To address these criteria, we present the slotted carbon nanotube (CNT) junction features tunable Fano resonance driven by flexoelectricity, which could serve as an ideal multimodal sensory receptor. Based on extensive ab initio calculations, we find that the effective Fano factor can be used as a temperature-insensitive extrinsic variable for sensing the bending strain, and the Seebeck coefficient can be used as a strain-insensitive intrinsic variable for detecting temperature. Thus, this dual-parameter permits simultaneous sensing of temperature and strain without signal interference. We further demonstrate the applicability of this slotted junction to ultrasensitive chemical sensing which enables precise determination of donor-type, acceptor-type, and inert molecules. This is due to the enhancement or counterbalance between flexoelectric and chemical gating. Flexoelectric gating would preserve the electron–hole symmetry of the slotted junction whereas chemical gating would break it. As a proof-of-concept demonstration, the slotted CNT junction provides an excellent quantum platform for the development of multistimuli sensation in artificial intelligence at the molecular scale.
... 4−7 However, their performance is impeded because of the slow kinetics and high overpotentials of oxygen reduction reaction/oxygen evolution reaction (ORR/OER) during discharge/recharge processes on the air-cathode, resulting in low round-trip efficiency and short-cycle life. 8,9 As well known, Ir and RuO 2 exhibit superior OER activity but inferior ORR performance, 10,11 whereas Pt and its alloys deliver excellent ORR performance but are not efficient for catalyzing OER. 12 Some studies reported that mixing of nonprecious materials into Pt and RuO 2 is an effective way to improve bifunctional catalytic performance and reduce costs. 13,14 On the other hand, transition metal-based compounds, such as CoNi and CoMn metal oxides, Co hydroxides and Co oxides, are another promising alternatives to be used as a bifunctional OER/ORR catalyst because of their low costs and abundance. ...
Two-dimensional (2D) transition metal oxides are promising bifunctional electrocatalysts for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR). Herein, atomically-thin nickel-doped spinel cobalt oxide (NCO) was prepared as OER/ORR catalyst through a simple hydrothermal method. Electrochemical test results show that the NCO nanosheets exhibit bifunctional catalytic performances with the overpotential of 275 mV for OER and the onset-potential of 0.92 V for ORR. Moreover, the assembled Zn−air battery based on the material exhibit excellent performance among transition metal oxides based oxygen electrocatalysts, such as a power density of 222.3 mW cm⁻² and a specific capacity of 968.8 mA h gZn⁻¹. Characterization results demonstrate that the Ni dopants contribute to creating the oxygen vacancies and promoting the electron transfer from cobalt to nickel. More importantly, the ratio of Co²⁺ and Ni³⁺ in the octahedral oxygen gap are significantly increased, which serve as the active sites for ORR and OER, respectively. In addition, the 2D nanostructure and Ni dopants help to facilitate the charge transfer during the reaction and the real active species of OER process is more biased towards Ni ions which were proven by in-situ Raman. This work offers a strategy for preparing highly active and durable spinel transition metal oxides materials for bifunctional oxygen catalysts.
... The rising need for advanced electrochemical technologies has continued to increase along with the ever-increasing demands for future electrochemical applications including high performance electrochemical energy conversion/storage devices and synthesis of well-ordered nanomaterial arrays for optical/sensing devices [1][2][3][4][5]. Electrodeposition is basically a useful and expandable electrochemical synthetic route due to its controllability, scalability, expandability and simplicity, enabling facile and diverse shape control, such as well-ordered nano-objects, uniform thin films and micro-thick foils [6][7][8]. ...
Electrochemical synthetic routes to sophisticated nanoobjects have been considered promising and reliable strategies for diverse purposes in a wide range of applications. In particular, electrodeposition using nanoporous templates has attracted intensive research interest due to the potential for realizing diverse nanostructures and delicate composition control of the resulting fabricated materials. Unfortunately, the electrochemical filling of nanomaterials into nanoporous templates still suffers from unexpected nonuniform formation of nanoobjects, originating from random nucleation in each nanopore and overgrowth from only a few nanopores. Here, we present a highly uniform, straightforward and controllable fabrication of Cu nanoobjects via an artificial nucleation-assisted electrodeposition principle using nanoporous AAO templates. Pre-electrodeposited Ni nanoparticles at the bottom of the nanopores of AAO successfully acted as nuclei at the early stage of the Cu electrodeposition process. The artificial nuclei enable highly uniform and stable Cu electrodeposition inside the nanopores of AAO templates by effectively suppressing the random overgrowth of Cu. By taking advantage of the stable electrodeposition behaviour, we demonstrate precise control of the geometry of Cu nanoobjects, uniformly dispersed over whole surfaces of substrates.
