Graphene Nanoscrolls Research Articles

The ultra-low friction mechanism of diamond film by in-situ forming of graphene sheet on sliding interface

In the present study, a novel process of in-situ fabrication of graphene sheets on ultrananocrystalline diamond (UNCD) film with aid of Au layer catalyst was designed. An in-situ ultra strong CC bonds are formed in the graphene-diamond interface under the action of heating, which can decrease the friction coefficient of the film. Besides, the friction-induced formation of graphene nano-scrolls play a pivotal role in achieving an exceptionally low friction coefficient of 0.025 for annealed Au/UNCD film. The potential structural formation mechanisms and frictional mechanisms have been discussed in detail. The achievement in this work provides a novel insight into the in-situ fabrication of graphene-diamond structure in mechanical fields with outstanding low friction coefficient and anti-wear performance.

Energetics and electronic structure of graphene nanoscrolls

Geometric structures and electronic properties of graphene nanoscrolls have been investigated using the density functional theory. A graphene nanoribbon with a width of 21.37 nm, corresponding to a zigzag ribbon with 100 zigzag C chains, prefers scrolled structures until the innermost shell radius of 0.6 nm, because of the competition between the energy gain by the inter-shell van der Waals interaction and the energy cost by the structural strain derived from curvature. The most preferable innermost shell radiuses are 1.3–1.5 nm for the ribbon studied here. The electronic structure of graphene nanoscrolls shows strong position dependence that is sensitive to the shape of nanoscrolls owing to the electrostatic potential modulation by their multi-shell structures.

The Simpler the Better: Ultrafast Air-Plasma Synthesis of 3D Crosslinked Graphene Nanoscroll-Nanosheet Aerogels at Room Temperature for Capacitive Deionization.

Graphene nanoscroll (GNS) is an important 1D tubular form of graphene-derivative materials, which has garnered widely attention. However, conventional fabrication methods commonly suffer from complex processing and time-consuming. Herein, with graphene oxide (GO) as a precursor, the study puts forward a facile air-plasma synthesis strategy to fabricate 3D graphene nanoscroll-nanosheet aerogels (GSSA). It is demonstrated that without using any chemical additives, a highly efficient reduction-exfoliation-scrolling process can be achieved all-in-one at room temperature within 1 s. The GNSs "grew" from 2D graphene sheets and firmly cross-linked them together, and they not only provide a shortcut path for electron transport but also act as intrinsic spacers to prevent restacking of graphene sheets. When using as an electrode material for capacitive deionization (CDI), GSSA exhibits excellent merits of salt-removal performance. These findings open a new pathway to large-scale synthesis of high-quality and high-purity GNS-based materials with promising applications in CDI and beyond.

Calculating and analyzing time delay in zigzag graphene nanoscrolls based complementary metal-oxide-semiconductors

Graphene Nano Scrolls (GNSs) and Zigzag graphene nanoscrolls (ZGNSs) are semi-one-dimensional materials with exceptional electrical and optical properties, making them attractive to be used in nanoelectronics and complementary metal–oxide–semiconductor (CMOS) technology. With in CMOS device technology, time delay is a crucial issue in the design and implementation of CMOS based ZGNSs. Current paper focus is on ZGNSs application in the channel area of metal–oxide–semiconductor field-effect transistors (MOSFETs) in CMOS technology. We studied analytically, the importance of different parameters on time delay reduction, resulting in faster switching and higher frequency in integrated circuits (ICs). The results of this research demonstrates that, the ZGNS-based CMOS proves considerable variations in the current due to the geometrical parameters, such as chirality number, channel length, and nanoscroll length which can be engineered to produce faster ICs.

Synthesis of MXene-based nanocomposite electrode supported by PEDOT:PSS-modified cotton fabric for high-performance wearable supercapacitor

The rapid development of wearable and portable electronic devices prompts the ever-growing demand for wearable, flexible, and light-weight power sources. In this work, a MXene/GNS/PPy@PEDOT/Cotton nanocomposite electrode with excellent electrochemical performances was fabricated using cotton fabric as a substrate. Poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) was coated on the cotton fabric to obtain a conductive substrate through a controllable dip-drying coating process, while a nanocomposite consisting of MXene, Graphene nanoscroll (GNS), and polypyrrole (PPy) was directly synthesized and deposited on the PEDOT:PSS-modified cotton fabric via a one-step in situ polymerization method. The resultant MXene/GNS/PPy@PEDOT/Cotton electrode delivers excellent electrochemical performances including an ultra-high areal capacitance of 4877.2 mF·cm−2 and stable cycling stability with 90 % capacitance retention after 3000 cycles. Moreover, the flexible symmetrical supercapacitor (FSC) assembled with the MXene/GNS/PPy@PEDOT/Cotton electrodes demonstrates a prominent areal capacitance (2685.28 mF·cm−2 at a current density of 1 mA·cm−2) and a high energy density (322.15 μWh·cm−2 at a power density of 0.46 mW·cm−2). In addition, the application of the FSC for wearable electronic devices was demonstrated.

Scalable Generation of Hybrid Graphene Nanoscrolls for High-Performance Solid Lubricants

Graphene and other 2D materials have been extensively studied as solid lubricants in recent years. Low friction can sometimes be observed in those 2D lubricants, and one possible mechanism is that scroll-shaped nanostructures are formed during friction, which decreases the contact area and energy barrier, thus substantially reducing friction. The integration of graphene with metal or metal oxide nanostructures can further enhance its lubrication properties by increasing film formation ability and easy shearing of the nanosheets. However, it is not possible to reliably promote the formation of such nanoscroll-shaped low friction wear products, which limits the reproducibility and application of such nanostructures as solid lubricants. In this study, we address this issue by creating a scalable method for the synthesis of hybrid graphene-titanium oxide (G–TiO2) nanoscrolls and demonstrating their potential as solid lubricants with macroscopic coefficient of friction as low as 0.02 in ambient conditions. Our approach to generate the nanoscrolls is based on the in situ sol–gel synthesis of TiO2 on graphene followed by spray-freeze-drying–induced shape transformation. The solid lubrication performance of such G–TiO2 nanoscrolls can be further enhanced by applying a thin graphene oxide primer layer, which provides high affinity to both the substrate and the active materials. These hybrid nanoscrolls hold promising potential for applications in aerospace, automotive, and precision manufacturing fields as effective solid lubricants.Graphical

Effects of Humidity on Tribological Properties of 8YSZ/C Coating Designed by the Combination of Thermal Spraying and Hydrothermal Reaction

Thermal spraying ceramic coatings have been widely used to prevent wear damage. However, the poor lubricating ability seriously restricted their application. In this article, zirconia stabilized by 8 wt% yttria (8YSZ)‐C composite coating is prepared with the combination of in‐situ synthesis carbon microspheres in the pores of as‐sprayed 8YSZ coating by hydrothermal reaction. The chemical constituents and morphologies of the synthesized powders and the composite coatings are analyzed by scanning electron microscope (SEM) and X‐ray diffraction (XRD). The microstructure and tribological behaviors of the composite coating are studied by SEM, TEM. and Raman analysis. The influence of humidity on the structural evolution of carbon microspheres during sliding wear process is discussed. The results show that the synthetic C powders exhibit a typical spherical structure. Meanwhile, carbon microspheres adhere to the pores of the 8YSZ coating. The friction and wear experiments in different humidity show that the re‐graphitization of amorphous carbon becomes extremely obvious with the increase of humidity. Under the 80% humidity, an ordered graphene nanoscroll structure is formed, resulting in the optimization of the tribological properties. Furthermore, the friction coefficient of composite coating is reduced to 0.18, and its wear rate is about 1 times lower than that of under the 10% humidity.

Iron oxide induced preparation of nanoscrolls of reduced graphene oxide for electrochemical charge storage applications

Fe3O4 - reduced graphene oxide nanoscrolls (FRGNS) are tailored for fabricating electrode material for supercapacitor applications. The scrolling of reduced graphene oxide is initiated by the magnetic field produced by the superparamagnetic iron oxide NPs. The formation mechanism and critical concentration of nanoparticles required for scroll formation is investigated by varying the weight ratio of iron oxide NPs. The nanoscroll formation is completely reversible and reproducible. The unique end open morphology of nanoscrolls facilitates the electrolytic accessibility and the Fe3O4 NPs favor the redox reactions as well. At a current density of 1Ag-1, FRGNS12 (rGO: Fe3O4 1:12) achieve a noteworthy specific capacitance value of 1498 Fg-1 within a potential ranging from 0 to −0.73 V in 1 M Na2S2O3 with exceptional energy density of 110.9 Wh Kg−1 and power density of 405 Wkg-1. A prominent cycling stability of 88% capacitance retention after 4000 cycles is also obtained. The electrochemical performance of opened as well as regenerated scrolls (RFRGNS12) are also evaluated. The specific capacitance increases to 1514 Fg-1 for RFRGNS12 due to the further exfoliation of rGO sheets take place during the unscrolling and scroll regeneration process. The unique fabrication methodology for the synthesis of graphene nanoscrolls and their utilization as electrode material for supercapacitors paves a new pathway for the advancement of novel electrode materials for supercapacitors.

Tailoring d-band center over electron traversing effect of NiM@C-CoP (M=Zn, Mo, Ni, Co) for high-performance electrocatalysis hydrogen evolution

Attaining a highly efficient and inexpensive electrocatalyst is significant for the hydrogen evolution reaction (HER) but still challenging nowadays. The transition-metal phosphides (TMPs) catalysts with platinum-like electronic structures are a potential candidate for the HER, but those are prone to be strongly bound with hydrogen intermediates (H*), resulting in sluggish HER kinetics. Herein we report a unique hybrid structure of CoP anchored on graphene nanoscrolls@carbon nano tubes (CNTs) scaffold (NiM@C-CoP) encapsulating various NiM (M=Zn, Mo, Ni, Co) bimetal nanoalloy via chemical vapor deposition (CVD) growth of CNT on graphene nanoscrolls followed by the impregnation of cobalt precursors and phosphorization for efficiently electrocatalytic hydrogen evolution. CoP nanoparticles mainly scattered at the tip of CNT branches which exhibited the analogical ``Three-layer core-shell'' structures. Experiments and density functional theory(DFT) calculations consistently disclose that the encapsulated various NiMs can offer different numbers of electrons to weaken the interactions of outmost CoP with H* and push the downshift of the d-band center to different degrees as well as stabilize the outmost CoP nanoparticles to gain catalytic stability via the electron traversing effect. The electrocatalytic HER activity can be maximumly enhanced with low overpotentials of 78 mV (alkaline) and 89 mV (acidic) at a current density of 10 mA/cm2 and sustained at least 24 h especially for NiZn@C-CoP catalyst. This novel system is distinct from conventional three-layer heterostructure, providing a specially thought of d-band center control engineering strategy for the design of heterogeneous catalysts and expanding to other electrocatalysts, energy storage, sensing, and other applications.

Tribological behavior of graphene/DLC coatings after AO and UV irradiation in vacuum environment

Friction and wear remain as the primary modes of energy dissipation in transmission system. Here, the uniform coating of graphene on the diamond like carbon (DLC) surface is achieved with the effect of argon protection and low-temperature heating of the substrate. The generation of graphene nanoscrolls is induced by the dual function of high-contact stress at the friction interface and frictional heat. The results show that the Graphene/DLC coatings maintain a stable low friction coefficient (average friction coefficient < 0.03) for a long time in atmospheric, vacuum (Before and after AO and UV irradiation) environments.

Construction of core-shell heterostructure containing sandwich-like nanoarray for high-performance supercapacitors

Designing and constructing an ideal architecture is an effective approach to realize high-performance energy storage system. Core-shell heterostructure materials have attracted much attention due to their excellent performance in energy storage applications. Whereas, core-shell heterostructure containing sandwich-like nanoarray materials have rarely been reported by far. Herein, sandwich-like NiCo-PPy-layered double hydroxide (NiCo-PPy-LDH) nanosheets with polypyrrole (PPy) as the intercalation agent were vertically anchored on 3D cross-linked graphene nanoscroll (GNS) skeleton via a hydrothermal method and subsequent in situ polymerization process. Impressively, the as-prepared NiCo-PPy-LDH@GNS composite delivers a prominent specific capacitance of 2561 F·g−1 (equivalent conversion to 1024.4C·g−1) at 1 A·g−1 with 82 % capacitance retention at 10 A·g−1. The superior electrochemical properties of the NiCo-PPy-LDH@GNS is mainly attributed to its novel heterostructure which enhances the synergistic effect between NiCo-LDHs, GNSs, and PPy. The intercalation of PPy enriches hetero-interface and active sites for the redox reaction, while the GNSs skeleton provides a 3D rigid conductive network for further enhancing charge transportation and preventing the aggregation of LDH nanosheets.

Heterophase interfacial hybrid//graphene nanoscrolls based high performance lithium-ion hybrid supercapacitor

Heterophase interfacial hybrid//graphene nanoscrolls based high performance lithium-ion hybrid supercapacitor

Colossal enhancement of electrical and mechanical properties of graphene nanoscrolls

One of the most important characteristics of two-dimensional (2D) electrolytes [1] is their ability to reversibly transform into one-dimensional (1D) structures, such as nanoscrolls. However, when formed, these 1D structures are soft and unstable (because of the weak internal chemical bonds) and poorly electrically conducting (since chemical functionalization introduces a large degree of disorder in the 2D material basal plane). Using PeakForce™ quantitative nano-mechanics (PF-QNM™) mode in atomic force microscopy (AFM) and electrical transport measurements, we demonstrate that a one-step, catalyst-free, graphitization of 1D graphene nanoscrolls leads to an enhanced structural stability (an increase of 6 times in the Young's modulus) and a dramatic reduction of structural disorder (observed by a resulting 5 orders of magnitude reduction of the electrical resistance) These large changes in physical properties open up the doors for the use of 1D graphene nanoscrolls in the study of exotic materials in 1D as well as a plethora of possible industrial applications, such as hydrogen and energy storage, akin to carbon nanotubes but with a much bigger flexibility in terms of morphologies and functionalities.

Caterpillar-like 3D graphene nanoscrolls@CNTs hybrids decorated with Co-doped MoSe2 nanosheets for electrocatalytic hydrogen evolution

• The CNTs are CVD grown on the surface and inner space of graphene nanoscrolls to form unique caterpillar-like structure. • The caterpillar-like carbon materials as scaffold greatly improve the catalytic activity of active materials (MoSe 2 ). • The encapsulated Ni nanoparticles of unique caterpillar-like structure can optimize the electron structure of the outmost loading (MoSe 2 ) by electron traversing effect. • Electron traversing effect and doping effect can be synergistically applied in elevating catalytic performance. Hydrogen is a clean and flexible energy carrier that has the promising to satisfy urgent demands of the energy crisis and environmental protection. Electrochemical hydrogen evolution reaction (HER), a critical half-reaction in water splitting, is one of the greenest and most common methods to obtain high-purity hydrogen. Designing preeminent activity and stability electrocatalysts for hydrogen precipitation reaction (HER) to reduce energy consumption is of great essential. 3D carbon-based materials have attracted widespread concern as the potential scaffolds of highly active and durable electrocatalysts for HER. To boost the HER activity and prolong the lifespan of electrocatalysts, multifarious 3D carbon architectures make an appearance to be engineered for accelerating electronic/mass transfer and maximizing the exposure of active sites. Herein, we designed and fabricated high-performance electrocatalysts based on a special caterpillar-like 3D graphene nanoscrolls@CNTs (GNS@CNTs) scaffold decorated with Co-doped MoSe 2 nanosheets for HER. In the caterpillar-like hierarchical structure, CNTs were seamlessly co-bonded and dilated the interlayer and outer spacing of GNS through CVD growth technology, and nickel nanoparticles were covered by the CNTs tips. Taking advantage of the plentiful hierarchical pore, larger specific surface area, and higher chemical stability of the caterpillar-like structure, the catalysts exhibited enhanced electrocatalytic properties than some existing data reported. Density functional theory calculations showed that the encapsulated nickel nanoparticle could tune the electronic structure of the outer anchored Co-doped MoSe 2 and optimize its ∆ G of H* adsorption by electron traversing effect and doping effect. These indicate that caterpillar-like GNS@CNT is an ideal scaffold for anchoring actives substance and is suitable for high-efficient HER. This study provides new insights for designing hierarchical carbon composite nanostructures for catalysts, sensors, energy materials, and other applications.

A Phenomenological Model for Electrical Transport Characteristics of MSM Contacts Based on GNS.

Graphene nanoscroll, because of attractive electronic, mechanical, thermoelectric and optoelectronics properties, is a suitable candidate for transistor and sensor applications. In this research, the electrical transport characteristics of high-performance field effect transistors based on graphene nanoscroll are studied in the framework of analytical modeling. To this end, the characterization of the proposed device is investigated by applying the analytical models of carrier concentration, quantum capacitance, surface potential, threshold voltage, subthreshold slope and drain induced barrier lowering. The analytical modeling starts with deriving carrier concentration and surface potential is modeled by adopting the model of quantum capacitance. The effects of quantum capacitance, oxide thickness, channel length, doping concentration, temperature and voltage are also taken into account in the proposed analytical models. To investigate the performance of the device, the current-voltage characteristics are also determined with respect to the carrier density and its kinetic energy. According to the obtained results, the surface potential value of front gate is higher than that of back side. It is noteworthy that channel length affects the position of minimum surface potential. The surface potential increases by increasing the drain-source voltage. The minimum potential increases as the value of quantum capacitance increases. Additionally, the minimum potential is symmetric for the symmetric structure (Vfg = Vbg). In addition, the threshold voltage increases by increasing the carrier concentration, temperature and oxide thickness. It is observable that the subthreshold slope gets closer to the ideal value of 60 mV/dec as the channel length increases. As oxide thickness increases the subthreshold slope also increases. For thinner gate oxide, the gate capacitance is larger while the gate has better control over the channel. The analytical results demonstrate a rational agreement with existing data in terms of trends and values.

Fabrication and Characterization of Free-Standing and Flexible Polyaniline Membranes: Role of Graphene Nanoscrolls

Wearable technologies can contribute to the early and accurate detection of chronic diseases which can be achieved by the integration of biosensors into wearable technologies. However, the challenges associated with the performance of current electrode materials—i.e., flexibility, conductivity, and mechanical stability, made from conducting polymers are preventing their widespread usage. Herein, we report a freestanding and flexible electrode synthesized from polyaniline (PANI) and graphene nanoscrolls (GNS). The PANI-GNS nanohybrid membranes were synthesized via chemical oxidative polymerization and characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), nanoindentation (NI), and four-point probe techniques. FTIR results showed an increase in conjugation length of the PANI after the addition of GNS into the mixture which can be indicative of an enhancement of electrical properties. Nanoindentation studies showed an elastic modulus and hardness of 2.6 GPa and 0.17 GPa, respectively, for PANI-GNS-5 nanocomposite, compared to 1.9 GPa and 0.08 GPa, for pure PANI. This was later confirmed by the four-point probe technique as the addition of GNS increased the conductivity of electrodes up to 9 S/cm at a 5% weight ratio. Moreover, SEM results of the PANI-GNS showed an open porous morphology of the polymer matrix in comparison with pure PANI samples which would readily translate into higher amounts of enzyme immobilization on the surface.

Graphene electronic tattoos 2.0 with enhanced performance, breathability and robustness

Graphene electronic tattoos (GETs) have recently emerged as unique tools for personalized healthcare. The monolayer GETs have been used to monitor human electrophysiological signals, including brain, heart, and muscle activities, skin temperature, and hydration level. However, a few drawbacks of the earlier GETs hindered their perception by clinical and biomedical experts: they were not permeable to sweat, and the tattoo performance varied greatly. In this work, we introduce GETs 2.0: the skin wearable tattoo sensors with superior electrical properties, permeability to sweat, and robustness. We report on the categorical analysis of the graphene tattoos of different layer constitutions. When stacking the graphene monolayers within a single tattoo, we see a drastic enhancement in their electronic properties. The older monolayer GETs were susceptive to minor growth- or transfer-related discrepancies, resulting in highly scattered electrical properties. In this work, the GETs 2.0 with the addition of graphene nanoscrolls (GNS) or multilayer (2 L and 3 L) graphene structures exhibit 3.5-fold decreased sheet resistance, 2.5-fold lower skin impedance, and 5-fold reduced standard deviations of these values. In addition, we introduced holes into the tattoo, enabling healthy sweat evaporation without a substantial decrease in electrical properties. Furthermore, we show that microholes allow for advanced biplanar contact with graphene tattoos. Finally, we show that multilayer GETs 2.0 can be used as efficient skin-wearable electronic heaters, exhibiting heating efficiency of ~6 mW/°C.

Graphene, Dirac equation and analogue gravity

We provide an updated study of some electronic properties of graphene nanoscrolls, exploiting a related curved space Dirac equation for the charge carriers. To this end, we consider an explicit parametrization in cylindrical coordinates, together with analytical solutions for the pseudoparticle modes living on the two–dimensional background. These results are then used to obtain a compact expression for the sample optical conductivity, deriving from a Kubo formula adapted to the 1 + 2 dimensional curved space. The latter formulation is then adopted to perform some simulations for a cylindrical nanoscroll geometry.

Observation of Interfacial Instability of an Ultrathin Water Film

We observed the instability of a few-nanometer-thick water film encapsulated inside a graphene nanoscroll using transmission electron microscopy. The film, that was left after recession of a meniscus, formed ripples along the length of the nanoscroll with a distance only 20%-44% of that predicted by the classical Plateau-Rayleigh instability theory. The results were explained by a theoretical analysis that incorporates the effect of the van der Waals interactions between the water film and the graphene layers. We derived important insights into the behavior of liquid under nanoscale confinement and in nanofluidic systems.

Formation of Graphene Nanoscrolls and Their Electronic Structures Based on Ab Initio Calculations.

Rolling up two-dimensional (2D) materials can form quasi-one-dimensional nanoscrolls, which are expected to have novel properties due to their larger space of structural parameters. In this Letter, the structural dependence of formation energy was investigated based on more than 90 different graphene nanoscrolls (GNSs) through ab initio calculations. A quantified relationship between formation energy and structural parameters is discovered, which could provide universal description of rolling up 2D materials beyond graphene. Further calculations on electronic structures show the opening of bandgap in GNSs with ultrahigh carrier mobilities up to 107 cm2 V-1 s-1. The structural stability under room temperature was also testified by using molecular dynamic simulations. This work provides general insights into the rolling-up strategy and demonstrates the tunable properties of GNSs, thus extending the scope of the research field for 2D materials.