Carbon Monolayer Research Articles

Dispersion of modified fumed silica in elastomeric nanocomposites

In polymer nanocomposites, surface modification of silica aggregates can shield Coulombic interactions that inhibit agglomeration and formation of a network of agglomerates. Surface modification is usually achieved with silane coupling agents although carbon-coating during pyrolytic silica production is also possible. Pyrogenic silica with varying surface carbon contents were dispersed in styrene-butadiene (SBR) rubber to explore the impact on hierarchical dispersion, the emergence of meso-scale structures, and the rheological response. Pristine pyrogenic silica aggregates at concentrations above a critical value (related to the Debye screening length) display correlated meso-scale structures and poor filler network formation in rubber nanocomposites due to the presence of silanol groups on the surface. In the present study, flame synthesized silica with sufficient surface carbon monolayers can mitigate the charge repulsion thereby impacting network structural emergence. The impact of the surface carbon on the van der Waals enthalpic attraction, a∗, is determined. The van der Waals model for polymer nanocomposites is drawn through an analogy between thermal energy, kBT, and the accumulated strain, γ. The rheological response of the emergent meso-scale structures depends on the surface density of both carbon and silanol groups.

Application of transition metal boride nanosheet as sulfur host in high loading Li-S batteries

Two-dimensional (2D) metal boride material (MBene) has aroused concern recently. However, the research and application exploration for MBene materials with more exposure sites are seriously restricted due to lack of suitable preparation methods. Herein, a kind of composites of monolayer MBene nanosheets and carbon nanotube (mono-MBene/CNT) is prepared through ice template method for the first time and applicated as a novel cathode host in high-loading lithium-sulfur (Li-S) batteries. Benefiting from multifunctional advantages of mono-MBene/CNT cathode including anchoring lithium polysulfides (LiPS), multiple functional sites and fast lithium-ion transport, the cells with S@mono-MBene/CNT cathode exhibit superior long-term cycling performance over 1000 cycles. Most notably, even if the sulfur loading is up to 15.28 mg cm−2, the cells with S@mono-MBene/CNT cathode deliver an initial area capacity of 12.73 mAh cm−2 and the capacity can also maintain at 11.07 mAh cm−2 after 120 cycles (86.96 % capacity retention) with current density of 21.80 mA cm−2, which is approximately 3 times higher than the capacity of commercial lithium-ion batteries. This work not only provides a guiding role in preparing monolayer MBene material, but also exhibits the application prospect for MBene material in the fields of energy storage.

Doping at [formula omitted]-site in Me-graphene ([formula omitted]) for new anodes in rechargeable Li-ion battery

In this theoretical study, the monolayer carbon allotrope, Me-graphene (also called C568), was respectively doped with Al, Si, P, and Ge atoms by substituting the sp3-hybridized carbon atom in its unit cell to manipulate its physical properties. Theoretical calculations based on the density functional theory (DFT) confirmed the dynamic stabilities of the related doping systems. Interestingly, the mechanical strengths of the doping systems are even stronger than the pristine one. After doping with Si atom, the band gap of the Me-graphene system narrowed from 1.097 eV to 0.987 eV estimated at HSE06 level. However, the Ge-dopant at the sp3-site has very limited influence on the band gap. In the other two cases with Al and P dopants, the systems changed to be metallic because their Fermi levels cut into the valence bands to a certain extent. Additionally, the adsorption sites of Li atoms and the energy profiles of the Li migrations on the related 2D material systems were also investigated in order to reveal their application potentials as anodes in lithium-ion batteries (LIBs).

Softened sp2−sp3 bonding network leads to strong anharmonicity and weak hydrodynamics in graphene+

Graphene+, a novel carbon monolayer with $s{p}^{2}\text{\ensuremath{-}}s{p}^{3}$ hybridization, was recently reported to exhibit unprecedented out-of-plane half-auxetic behavior and graphenelike Dirac properties [Yu et al., Cell Rep. Phys. Sci. 3, 100790 (2022)]. Herein, based on comprehensive state-of-the-art first-principles calculations, we reveal the significant effect of softened $s{p}^{2}\text{\ensuremath{-}}s{p}^{3}$ bonding on the lattice thermal transport in graphene+. At room temperature, the thermal conductivity (\ensuremath{\kappa}) of graphene+ is obtained as \ensuremath{\sim}170 W/mK, which is much lower than that of graphene (\ensuremath{\sim}3170 W/mK). It is found that the softened $s{p}^{2}\text{\ensuremath{-}}s{p}^{3}$ bonding significantly suppresses the vibrations of acoustic phonons in graphene+, which leads to strong anharmonicity and weak phonon hydrodynamics. Thus, the large reduction in \ensuremath{\kappa} stems from the softened $s{p}^{2}\text{\ensuremath{-}}s{p}^{3}$ bonding network. Our study provides fundamental physical insights into the thermal transport properties of graphene+, which would provide prospective guidance for the promising application in the field of thermal management.

Hydrogenated Carbon Monolayer in Biphenylene Network Offers a Potential Paradigm for Nanoelectronic Devices

Hydrogenated Carbon Monolayer in Biphenylene Network Offers a Potential Paradigm for Nanoelectronic Devices

A pore-scale study for reactive transport processes in double-layer gradient electrode as negative side of a deep eutectic solvent electrolyte-based vanadium-iron redox flow battery

Porous electrodes are critical component of redox flow batteries (RFBs), that decide the fluid, species/charge transport and electrochemical reaction properties during the operation of RFBs. It is a potential way to elevate the performance of RFBs by applying the porous electrodes with gradient pore structures. However, it is still lack of a suitable numerical model to understand the reactive transport processes in the heterogeneous pore structures, thus to design and develop the optimal RFB electrodes. Using a lattice Boltzmann model, this work studies the pore-scale reactive transfer behaviors in a double-layer gradient electrode assembling as the negative side of deep eutectic solvents electrolyte-based vanadium-iron RFB, that consists of a graphite felt near the current collector side and a carbon paper near the membrane side. The numerical results reveal the galvanostatic discharging performance of double-layer electrode under the different electrolyte feeding modes and flow rates. Comparing with full flow-through feeding mode, the interdigitated flow feeding mode would give rise to serious inhomogeneity of electrolyte flowing at the low flow rate condition, thereby resulting in the sluggish convective mass transfer performance near the membrane side. Moreover, the total power loss of double-layer electrode is higher than that of the mono-layer carbon paper electrode within the low flow rate range. Conversely, the double-layer electrode with interdigitated flow mode can achieve the lowest total power loss than mono-layer electrodes at the high inlet flow rate. This work provides a new pathway to investigate the RFB power performance effected by the gradient porous structures of electrodes.

Spontaneous formation of a self-healing carbon nanoskin at the liquid–liquid interface

Biological membranes exhibit the ability to self-repair and dynamically change their shape while remaining impermeable. Yet, these defining features are difficult to reconcile with mechanical robustness. Here, we report on the spontaneous formation of a carbon nanoskin at the oil–water interface that uniquely combines self-healing attributes with high stiffness. Upon the diffusion-controlled self-assembly of a reactive molecular surfactant at the interface, a solid elastic membrane forms within seconds and evolves into a continuous carbon monolayer with a thickness of a few nanometers. This nanoskin has a stiffness typical for a 2D carbon material with an elastic modulus in bending of more than 40–100 GPa; while brittle, it shows the ability to self-heal upon rupture, can be reversibly reshaped, and sustains complex shapes. We anticipate such an unusual 2D carbon nanomaterial to inspire novel approaches towards the formation of synthetic cells with rigid shells, additive manufacturing of composites, and compartmentalization in industrial catalysis.

Structure of Amorphous Two-Dimensional Materials: Elemental Monolayer Amorphous Carbon versus Binary Monolayer Amorphous Boron Nitride.

The structure of amorphous materials has been debated since the 1930s as a binary question: amorphous materials are either Zachariasen continuous random networks (Z-CRNs) or Z-CRNs containing crystallites. It was recently demonstrated, however, that amorphous diamond can be synthesized in either form. Here we address the question of the structure of single-atom-thick amorphous monolayers. We reanalyze the results of prior simulations for amorphous graphene and report kinetic Monte Carlo simulations based on alternative algorithms. We find that crystallite-containing Z-CRN is the favored structure of elemental amorphous graphene, as recently fabricated, whereas the most likely structure of binary monolayer amorphous BN is altogether different than either of the two long-debated options: it is a compositionally disordered "pseudo-CRN" comprising a mix of B-N and noncanonical B-B and N-N bonds and containing "pseudocrystallites", namely, honeycomb regions made of noncanonical hexagons. Implications for other nonelemental 2D and bulk amorphous materials are discussed.

Electron-Injection and Atomic-Interface Engineering toward Stabilized Defected 1T-Rich MoS2 as High Rate Anode for Sodium Storage.

1T-phase MoS2 is a promising electrode material for electrochemical energy storage due to its metallic conductivity, abundant active sites, and high theoretical capacity. However, because of the habitual conversion of metastable 1T to stable 2H phase via restacking, the poor rate capacity and cycling stability at high current densities hamper their applications. Herein, a synergetic effect of electron-injection engineering and atomic-interface engineering is employed for the formation and stabilization of defected 1T-rich MoS2 nanoflowers. The 1T-rich MoS2 and carbon monolayers are alternately intercalated with each other in the nanohybrids. The metallic 1T-phase MoS2 and conductive carbon monolayers are favorable for charge transport. The expanded interlayer spacing ensures fast electrolyte diffusion and the decrease of the ion diffusion barrier. The obtained defected 1T-rich MoS2/m-C nanoflowers exhibit high Na-storage capacity (557 mAh g-1 after 80 cycles at 0.1 A g-1), excellent rate capacity (411 mAh g-1 at 10 A g-1), and long-term cycling performance (364 mAh g-1 after 1000 cycles at 2 A g-1). Furthermore, a Na-ion full cell composed of the 1T-rich MoS2/m-C anode and Na3V2(PO4)3/C cathode maintains excellent cycling stability at 0.5 A g-1 during 400 cycles. Theoretical calculations are also performed to evaluate the phase stability, electronic conductivity, and Na+ diffusion behavior of 1T-rich MoS2/m-C. The energy storage performance demonstrates its excellent application prospects.

Graphitization of alumina as a way to stabilize its textural characteristics under hydrothermal conditions

Gamma alumina is a widely used support for catalysts of various processes. However, in the case of aqueous-phase processes, hydrothermal conditions result in transformation of γ-Al 2 O 3 to boehmite, which is accompanied by degradation of the porous structure and leads to rapid catalyst deactivation. Here, we demonstrate a simple approach to stabilize the textural characteristics of γ-Al 2 O 3 under hydrothermal conditions, based on preliminary graphitization of its surface by chemical vapor deposition of ethylene. Different duration (5–240 min) revealed the optimal degree of alumina surface coverage with carbon, ensuring the preservation of its textural characteristics from collapse during hydrothermal treatment (HTT) at 200 °C. Materials characterization was performed by X-ray diffraction, transmission electron microscopy, nitrogen physisorption, and Raman spectroscopy. It is shown that initial γ-Al 2 O 3 during HTT transforms into boehmite with a dramatic decrease in the surface area from 217 to 42 m 2 /g. Whereas the preliminary graphitization of its surface maintains high surface area of the material after HTT, which is achieved by forming a C@boehmite composite (294 m 2 /g). The presented approach makes it possible to modify the surface of alumina supports with a layer of graphite-like carbon and can be used to improve or maintain the catalysts activity. • C@Al 2 O 3 samples were obtained by ethylene CVD for 5–240 min. • Graphitization degree of Al 2 O 3 surface varied from 6 to 100%. • Nanocrystalline graphite with graphene fragment size less than 5 nm is formed in C@Al 2 O 3 . • Monolayer carbon coating prevents Al 2 O 3 texture collapse in hydrothermal conditions. • Mesoporous C@boehmite composite with high surface is formed by hydrothermal treatment of C@Al 2 O 3 .

High‐Harmonic Generation Enhancement with Graphene Heterostructures

AbstractHigh‐harmonic generation (HHG) in graphene heterostructures, consisting of metallic nanoribbons separated from a graphene sheet by either a few‐nanometer layer of aluminum oxide or an atomic monolayer of hexagonal boron nitride, is investigated. The nanoribbons amplify the near‐field at the graphene layer relative to the externally applied pumping, thus allowing the observation of third‐ and fifth‐harmonic generation in the carbon monolayer at modest pump powers in the mid‐infrared. The dependence of the nonlinear signals on the ribbon width and spacer thickness, as well as pump power and polarization are studied, and enhancement factors (EF) relative to bare graphene reaching 1600 and 4100 for third‐ and fifth‐harmonic generation, respectively, are demonstrated. The work supports the use of graphene heterostructures to selectively enhance specific nonlinear processes of interest, an essential capability for the design of nanoscale nonlinear devices.

Localization of the Optical Phonon Modes in Boron Nitride Nanotubes: Mixing Effect of 10B Isotopes and Vacancies.

We explored the mixing effect of 10B isotopes and boron (B) or nitrogen (N) vacancies on the atomic vibrational properties of (10,0) single-wall boron nitride nanotubes (BNNTs). The forced oscillation technique was employed to evaluate the phonon modes for the entire range (0–100%) of 10B isotopes and atomic vacancy densities ranging from 0 to 30%. With increasing isotope densities, we noticed a blue shift of the Raman-active A1 phonon peak, whereas an increased density of mixed or independent B and N vacancies resulted in the emergence of a new low-frequency peak and the annihilation of the A1 peak in the phonon density of states. High-energy optical phonons were localized as a result of both 10B isotopes and the presence of mixing defects. We found an asymmetrical nature of the localization length with increasing 10B isotope content, which corresponds well to the isotope-inherited localization length of carbon nanotubes and monolayer graphene. The localization length falls abruptly with the increase in concentration of both atomic vacancies (B or N) and mixing defects (10B isotope and vacancies). These findings are critical for understanding heat conduction and nanoscopic vibrational investigations such as tip-enhanced Raman spectra in BNNTs, which can map local phonon energies.

(Invited) Two-Dimensional Amorphous Carbon Prepared from Solution Precursor As Novel Dielectrics for Nanoelectronics

Low-dimensional electronic materials such as carbon nanotubes, graphene, and transition-metal chalcogenides have drawn a lot of interest from the aspects of both fundamental studies and practical applications. Their atomic-scale thickness and unique electrical properties make them become promising candidates as the drop-in replacement of conventional bulk electronic materials in future electronic devices to enable better performance and enhanced functionality. Research on low-dimensional electronic materials so far has predominantly focused on crystalline semimetals and semiconductors. However, advanced electronic devices also require suitable low-dimensional insulators, which are ideally in the highly disordered amorphous form, similar as SiO2 for silicon, to avoid the nonuniformity and defects related with grain boundaries, in order to fulfill their potentials. Here we present a new strategy for the solution-based preparation of atomically thin amorphous carbon as a novel 2D insulator. Our unique process can precisely control the film thickness at atomic level and has excellent scalability toward wafer-scale deposition. The obtained 2D amorphous carbon monolayer exhibits mechanical robustness comparable to graphene and can be suspended as a free-standing membrane on transmission-electron-microscopy grid, allowing the structural characterization down to atomic resolution. The structure-property relationship for such amorphous materials at 2D limit was then established based on a combination of experiment and density-functional theory simulation. The unique physical properties of 2D amorphous carbon suggest it as a promising candidate to accompany crystalline low-dimensional semiconductors and semimetals in future nanoelectronic devices, and its performance advantages over conventional 3D metal oxides and polycrystalline 2D insulators were verified in experiment : Serving as the gate dielectric in graphene transistors, the absence of grain boundaries in 2D amorphous carbon allows us to aggressively reduce the gate-dielectric thickness down to merely three-atomic layers to enhance the capacitance coupling between the gate and the channel, while still maintaining a low leakage current density below 10-4 A/cm2, which is many orders of magnitude lower compared to the leakage current across the polycrystalline hexagonal boron nitride with the same thickness. Meanwhile, the perfectly clean van der Waals interface it forms with the graphene channel leads to the sharply reduction of the device hysteresis and thus average effective mobility twice as high as that of devices built with bulk SiO2 as gate dielectric. Serving as the switching medium in resistive random access memory cells, the atomic-level thinness of the 2D amorphous carbon enables low operating voltage below 0.4 V, fast switching time <20 ns, and low energy consumption per write operation below 20 fJ, together with excellent endurance (>104) and data retention (>10 years @ 85oC). Moreover, its atomic structural heterogeneity provides well defined ion-transport pathways as suggested in ab initio simulations, leading to the drastically improved device-to-device and cycle-to-cycle uniformity with the standard deviation of Set/Reset voltages below 50 mV in experiment, which is among the lowest values ever reported for memristors. The concurrent achievement of all these performance metrics has not been accomplished with memristors built on either bulk oxides or polycrystalline 2D materials.

A triatomic carbon and derived pentacarbides with superstrong mechanical properties

SummaryDiamond has the largest hardness of any natural material with an experimental Vickers hardness value of 90–150 GPa. Here, we reported the stable triatomic carbon allotrope with giant hardness closing that of diamond and a family of pentacarbides with superstrong mechanical properties from the state-of-the-art theoretical calculations. The triatomic carbon allotrope can be transformed into a two-dimensional carbon monolayer at a high temperature. We predicted that the triatomic carbon allotrope holds a hardness of 113.3 GPa, showing the potential capability of cracking diamond. Substitution with Al, Fe, Ir, Os, B, N, Si, W, and O element resulted in strong pentacarbides with Young’s modulus of 400–800 GPa. SiC5, BC5, IrC5, and WC5 are superhard materials with Vickers hardness over 40 GPa, of which BC5 was successfully synthesized in previous experimental reports. Our results demonstrated the potential of the present strong triatomic carbon and pentacarbides as future high-performance materials.

Functional Carbon and Silicon Monolayers in Biphenylene Network

Functional Carbon and Silicon Monolayers in Biphenylene Network

Synthesis of monolayer carbon-coated TiO2 as visible-light-responsive photocatalysts

Increasing visible light absorption and constructing an active surface for TiO2 have long been pursued to obtain high photocatalytic activities. Modifying TiO2 at an atomic scale is desirable to optimize its surface state and band structure but remains a huge challenge. Herein, we developed an ultrasmall (∼5 nm) visible-light-responsive TiO2 photocatalyst with a novel hybrid structure (TiO2/C) through a chemical vapor deposition process on large scale. Environmental in-situ transmission electron microscope studies confirmed the anatase TiO2 with a monolayer carbon shell in a hybrid structure. The resulted structure possesses narrowed bandgap 2.83 eV, favoring the enhanced visible-light-responsive photocatalytic activity. Density functional theory (DFT) simulations confirm the tunable mechanism of carbon-induced localized energy band within the bandgap of TiO2. As a physical barrier without turning TiO2 black, the monolayer carbon shell stabilizes Ti3+ inside TiO2, facilitates the separation of photo-induced carriers and enriches abundant absorbing sites of target pollutants. Consequently, the TiO2/C exhibits outstanding photocatalytic performance in both photoelectrochemical water oxidation and dye degradation under visible light besides superior activity for hydrogen evolution under simulated sunlight irradiation. This design proved a meaningful strategy in obtaining visible-light-responsive photocatalysts with a stable active surface for industrial application.

In-situ one-step synthesis of porous monolayer carbon nitride nanosheets doped with carbon quantum dots for photocatalytic degradation of Meloxicam

The energy storage and upconversion effect of carbon quantum dots (CQDs) could improve the photocatalytic efficiency of materials. In this study, a visible-light-driven photocatalyst, CQDs-doped carbon nitride nanosheets composite (CNS/CQDs) was in-situ synthesized by the thermal stripping of carbon nitride bulk (CNB). The as-prepared CNS/CQDs photocatalyst was systematically characterized and applied to the removal of Meloxicam (Mel) in water. The results showed that the introduction of CQDs could improve the visible light utilization of the carbon nitride. Mel (50 mL, 10 mg L−1) was degraded by 99.60% in 45 min with CNS/CQDs (20 mg). The stability and recycling experiments showed that CNS/CQDs could maintain high photocatalytic activity under complex matrix and multiple cycles. This work will provide a new attempt to synthesize the CQDs doped photocatalytic materials for the effective removal of organic pollutants in water under visible light.

Disposable stochastic sensors for fast analysis of ibuprofen, ketoprofen, and flurbiprofen in their topical pharmaceutical formulations

Three disposable stochastic sensors based on maltodextrin (dextrose equivalent = 4–7) and nanostructures (copper monolayer, carbon monolayer and carbon-copper composite layer) deposited using cold plasma on copy paper were proposed for the fast analysis of ibuprofen, ketoprofen and flurbiprofen in pharmaceutical formulation samples. The widest linear concentration ranges recorded were: for ibuprofen 1 fmol/L – 1 mmol/L when the disposable stochastic sensor based on carbon monolayer was used, for ketoprofen 1 fmol/L – 1 mmol/L when the disposable stochastic sensors based on copper monolayer and carbon-copper composite layer were used, and for flurbiprofen 1 fmol/L – 10 mmol/L when the disposable stochastic sensor based on carbon-copper composite layer was used. The lowest limit of detection recorded for each non-steroidal anti-inflammatory drug was 1 fmol/L.

Coupling of N-Doped Mesoporous Carbon and N-Ti3 C2 in 2D Sandwiched Heterostructure for Enhanced Oxygen Electroreduction.

2D heterostructures provide a competitive platform to tailor electrical property through control of layer structure and constituents. However, despite the diverse integration of 2D materials and their application flexibility, tailoring synergistic interlayer interactions between 2D materials that form electronically coupled heterostructures remains a grand challenge. Here, the rational design and optimized synthesis of electronically coupled N-doped mesoporous defective carbon and nitrogen modified titanium carbide (Ti3 C2 ) in a 2D sandwiched heterostructure, is reported. First, a F127-polydopamine single-micelle-directed interfacial assembly strategy guarantees the construction of two surrounding mesoporous N-doped carbon monolayers assembled on both sides of Ti3 C2 nanosheets. Second, the followed ammonia post-treatment successfully introduces N elements into Ti3 C2 structure and more defective sites in N-doped mesoporous carbon. Finally, the oxygen reduction reaction (ORR) and theoretical calculation prove the synergistic coupled electronic effect between N-Ti3 C2 and defective N-doped carbon active sites in the 2D sandwiched heterostructure. Compared with the control 2D samples (0.87-0.88V, 4.90-5.15 mA cm-2 ), the coupled 2D heterostructure possesses the best onset potential of 0.90V and limited density current of 5.50 mA cm-2 . Meanwhile, this catalyst exhibits superior methanol tolerance and cyclic durability. This design philosophy opens up a new thought for tailoring synergistic interlayer interactions between 2D materials.

High-Throughput Screening of Efficient Biatom Catalysts Based on Monolayer Carbon Nitride for the Nitric Oxide Reduction Reaction.

Exploring efficient catalysts for the nitric oxide reduction reaction (NORR) toward NH3 synthesis is becoming increasingly important for tackling both NH3 synthesis and NO removal problems. Currently, only a few NORR catalysts have been proposed, which are exclusively concentrated on bulk metals or single-atom catalysts. Here, taking monolayer C2N as an example, we explore the potential of biatom catalysts (BACs) for direct NO-to-NH3 conversion by means of high-throughput first-principles calculations. According to a rational five-step screening strategy, a promising BAC of Cr2-C2N is successfully screened out, exhibiting high stability, activity, and selectivity and a low kinetic barrier for the NORR toward NH3 synthesis. Importantly, the adsorption energy of N atoms (ΔE*N) and the Gibbs free energy of NO adsorption (ΔG*NO) are identified as effective descriptors for efficient NORR catalysts. In addition, through tuning the NO coverage, the NORR on Cr2-C2N could produce different products of NH3 and N2O, providing the possibility to realize controllable multiproduct BACs. These findings not only suggest the great potential of BACs for direct NO-to-NH3 conversion but also help in rationally designing high-performance BACs.