Graphene-based Nanostructures Research Articles

Expression of Concern: Adsorptions of phenol molecules by graphene-based nanostructures, modified with nitrogen and bromine, from petroleum wastewater using molecular dynamics simulation

Expression of Concern: Adsorptions of phenol molecules by graphene-based nanostructures, modified with nitrogen and bromine, from petroleum wastewater using molecular dynamics simulation

Analogous electronic states in graphene and planer metallic quantum dots

Graphene nanostructures offer wide range of applications due to their distinguished and tunable electronic properties. Recently, atomic and molecular graphene were modeled following simple free-electron scattering by periodic muffin tin potential leading to remarkable agreement with density functional theory. Here we extend the analogy of the π\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\pi$$\\end{document}-electronic structures and quantum effects between atomic graphene quantum dots (QDs) and homogeneous planer metallic counterparts of similar size and shape. Specifically, we show that at high binding energies, below the M¯\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\overline{M}$$\\end{document}-point gap, graphene QDs enclose confined states and standing wave quasiparticle interference patterns analogous to those reported on coinage metal surfaces for nanoscale confining structures such as vacancy islands and quantum corrals. These confined and quantum corral-like states in graphene QDs can be resolved in tomography experiments using angle-resolved photoemission spectroscopy. Likewise, the shape of near-Fermi frontier orbitals in graphene quantum dots can be reproduced from electron confinement within homogeneous metal QDs of identical size and shape. Furthermore, confined states analogous to those found in metallic quantum stadiums can be realized in coupled QDs of graphene for reduced separation. The present study offer a simple fundamental understanding of graphene electronic structures and also open the way towards efficient modeling of novel graphene-based nanostructures.

Unveiling the potential of graphene and S-doped graphene nanostructures for toxic gas sensing and solar sensitizer cell devices: insights from DFT calculations.

In this work, we explore the potential of 2D materials, particularly graphene and its derivatives, for eco-friendly electricity generation and air pollution reduction. Leveraging the significant surface area of graphene nanomaterials, the susceptibility of these graphene-based nanostructures to hazardous substances and their applicability in clean solar cell (SSC) devices were systematically investigated using density functional theory (DFT), as implemented within Gaussian 5.0 code. Time-dependent DFT (TD-DFT) was employed to characterize the UV-visible spectrum of unstrained nanostructures. Herein, we considered three potentially harmful gases-CO, NH3, and Br2. Adsorption calculations revealed a notable interaction between the pure graphene nanostructure and Br2 gas, while the S-doped counterpart exhibited reduced interaction. Saturated S-doped nanostructures demonstrated an enhanced affinity for NH3 and CO gases compared to their pure S-doped counterparts, attributed to the sulfur (S) atom facilitating gas molecule binding to the nanostructure's surface. Furthermore, simulations of the SSC device architecture indicated the superior performance of the pure graphene nanostructure in terms of light-harvesting efficiency, injection energy, and electron injection into the lower conduction band of CBM titanium dioxide (TiO2). These findings suggest a potential avenue for developing nanostructures tailored for SSC devices and gas sensors, offering a dual solution to address air pollution concerns. Density function theory was used to compute the ground and excited state properties for pure and sulfur-doped graphene nanostructures. The hybrid function B3LYP with a 6-31G* basis set was utilized to describe the exchange correlation. Gauss Sum 2.2 software is used to estimate the density of state (DOS) for all structures under investigation.

Processing and Functionalization of Vertical Graphene Nanowalls by Laser Irradiation.

The processing of vertical graphene nanowalls (VGNWs) via laser irradiation is proposed as a means to modulate their physicochemical properties. The effects of the number of applied pulses and fluence of each pulse are examined. Raman spectroscopy studies the effect of irradiation on the chemical structure of the VGNWs. Results show a decrease in density of defects and number of layers, which points toward a mechanism including evaporation of amorphous or loosely bonded C from defective points and recrystallization of graphene. Moreover, the effect of laser irradiation parameters on the morphology of Mo thin films deposited on VGNWs is investigated. The received thermal dosage results in the formation of particles. In this case, the number of pulses and pulse fluence are found to affect the size and distribution of these particles. The study provides a novel approach for the functionalization of VGNWs via laser irradiation, which can be extended to other graphene-based nanostructures.

Influence of graphene-based nanostructures processing routes and aspect ratio in flexural strength and fracture mechanisms of 3Y-TZP-matrix composites

In this work, the influence of the aspect ratio of graphene-based nanostructures (GBNs) and content on the mechanical properties of 3 mol% yttria tetragonal zirconia polycrystalline 3Y-TZP matrix composites was analysed. The influence of the dispersion method and sintering parameters on the flexural strength and elastic modulus of the composites was studied, and the fracture surfaces were characterized to determine the fracture mechanisms that occur. The results showed that small amounts of exfoliated graphene nanoplatelets, with reduced lateral size, and few layer graphene, up to 1.0 and 2.5 vol%, respectively, slightly increase the 3Y-TZP flexural strength. This has been attributed to the tortuosity of the crack propagation pathways and strengthening mechanisms. Higher contents cause a decrease in flexural strength and stiffness because of overlapped GBNs, which can promote the crack propagation. The pull-out of GBN was more significant in composites with non-exfoliated graphene nanoplatelets, where no increase on the flexural or biaxial strength was measured.

Nonlinear wave propagation in graphene incorporating second strain gradient theory

The exploration of graphene has attracted extensive interest owing to its significant structural and mechanical properties. In this research, we numerically investigate wave propagation in defect-free single-layer graphene, considering its geometrically nonlinear behavior through second-strain gradient elasticity. To capture the geometric nonlinearity, firstly, the nonlinear strain–displacement relations are introduced. The governing equation and associated boundary conditions are derived using Hamilton’s principle. Then, the weak form, including the element matrices, is established. The eigenvalue problem is solved for 2D wave propagation through periodic structures theory. Finally, the dynamical properties such as band structures, mode shapes, energy flow, and wave beaming effects are analyzed. The numerical results reveal that the geometric nonlinearity through the second strain gradient influences the wave propagation characteristics in graphene. The findings are significant and contribute to the understanding of graphene’s dynamic response, with implications for the engineering applications of graphene-based nanostructures.

On the plasmonic properties of a graphene nanoribbon and noble metal composite array

Graphene, composed of sp2 hybrid orbitals, is a hexagonal nanomaterial with a two-dimensional honeycomb lattice structure. Nowadays, thanks to its great electronic, optical, and thermal properties, there have been many promising applications based on graphene nanostructures. Under irradiations of external electromagnetic fields, the free electrons on graphene surfaces can be excited to oscillate collectively, resulting in highly localized surface plasmons. This phenomenon may provide foundations for designs of tunable plasmonic devices, therefore, graphene-based nanostructures have been widely studied so far. Besides, investigations on noble metals is another hot topic in the plasmonic community. With irradiations of incident lights, collective oscillations of free electrons on noble metals’ surfaces can also be induced, forming surface plasmons. The plasmonic characteristics can be adjusted by varying the parameters of the metals, including the geometries, thicknesses, as well as dimensions, etc. In this paper, a composite array consisting of graphene nanoribbons and noble metals is proposed, and its plasmonic properties are studied at mid-infrared wavelengths. In the structure, graphene nanoribbons are placed in between two SiO2 layers, and gold semi-cylinders and silver nanofilms are placed above the upper SiO2 layer, respectively. Using the finite difference time domain method, the light transmittance and electric field of the array are investigated, by varying the graphene’s Fermi energy and layer number, the noble metals’ sizes, as well as the period of the array, respectively. The results show that a plasmonic resonance feature is revealed in the 4–18 μm wavelength range, and the resonance characteristics can be tuned by adjusting the above parameters. The composite array structure proposed in this work may provide us with a new platform for the design of plasmonic devices in the mid-infrared regime.

Thermal transport in a defective pillared graphene network: insights from equilibrium molecular dynamics simulation.

Graphene-based hybrid nanostructures have great potential to be ideal candidates for developing tailored thermal transport materials. In this study, we perform equilibrium molecular dynamics simulations employing the Green-Kubo method to investigate the influence of topological defects in three-dimensional pillared graphene networks. Similar to single-layer graphene and carbon nanotubes, the thermal conductivity (k) of pillared graphene systems exhibits a strong correlation with the system size (L), following a power-law relation k ∼ Lα, where α ranges from 0.12 to 0.15. Our results indicate that the vacancy defects significantly reduce thermal conductivity in pillared graphene systems compared to Stone-Wales defects. We observe that, beyond defect concentration, the location of the defects also plays a crucial role in determining thermal conductivity. We further analyze the phonon vibrational spectrum and the phonon participation ratio to obtain more insight into the thermal transport in the defective pillared graphene network. In most scenarios, longitudinal and flexural acoustic phonons experience significant localization within the 15-45 THz frequency range in the defective pillared graphene system.

Recent Progress of Vertical Graphene: Preparation, Structure Engineering, and Emerging Energy Applications.

Vertical graphene (VG) nanosheets have garnered significant attention in the field of electrochemical energy applications, such as supercapacitors, electro-catalysis, and metal-ion batteries. The distinctive structures of VG, including vertically oriented morphology, exposed, and extended edges, and separated few-layer graphene nanosheets, have endowed VG with superior electrode reaction kinetics and mass/electron transportation compared to other graphene-based nanostructures. Therefore, gaining insight into the structure-activity relationship of VG and VG-based materials is crucial for enhancing device performance and expanding their applications in the energy field. In this review, the authors first summarize the fabrication methods of VG structures, including solution-based, and vacuum-based techniques. The study then focuses on structural modulations through plasma-enhanced chemical vapor deposition (PECVD) to tailor defects and morphology, aiming to obtain desirable architectures. Additionally, a comprehensive overview of the applications of VG and VG-based hybrids d in the energy field is provided, considering the arrangement and optimization of their structures. Finally, the challenges and future prospects of VG-based energy-related applications are discussed.

Graphene-Based Engineered Living Materials.

With the rise of engineered living materials (ELMs) as innovative, sustainable and smart systems for diverse engineering and biological applications, global interest in advancing ELMs is on the rise. Graphene-based nanostructures can serve as effective tools to fabricate ELMs. By using graphene-based materials as building units and microorganisms as the designers of the endmaterials, next-generation ELMs can be engineered with the structural properties of graphene-based materials and the inherent properties of the microorganisms. However, some challenges need to be addressed to fully take advantage of graphene-based nanostructures for the design of next-generation ELMs. This work covers the latest advances in the fabrication and application of graphene-based ELMs. Fabrication strategies of graphene-based ELMs are first categorized, followed by a systematic investigation of the advantages and disadvantages within each category. Next, the potential applications of graphene-based ELMs are covered. Moreover, the challenges associated with fabrication of next-generation graphene-based ELMs are identified and discussed. Based on a comprehensive overview of the literature, the primary challenge limiting the integration of graphene-based nanostructures in ELMs is nanotoxicity arising from synthetic and structural parameters. Finally, we present possible design principles to potentially address these challenges.

Electron cooling in graphene enhanced by plasmon-hydron resonance.

Evidence is accumulating for the crucial role of a solid's free electrons in the dynamics of solid-liquid interfaces. Liquids induce electronic polarization and drive electric currents as they flow; electronic excitations, in turn, participate in hydrodynamic friction. Yet, the underlying solid-liquid interactions have been lacking a direct experimental probe. Here we study the energy transfer across liquid-graphene interfaces using ultrafast spectroscopy. The graphene electrons are heated up quasi-instantaneously by a visible excitation pulse, and the time evolution of the electronic temperature is then monitored with a terahertz pulse. We observe that water accelerates the cooling of the graphene electrons, whereas other polar liquids leave the cooling dynamics largely unaffected. A quantum theory of solid-liquid heat transfer accounts for the water-specific cooling enhancement through a resonance between the graphene surface plasmon mode and the so-called hydrons-water charge fluctuations-particularly the water libration modes, which allows for efficient energy transfer. Our results provide direct experimental evidence of a solid-liquid interaction mediated by collective modes and support the theoretically proposed mechanism for quantum friction. They further reveal a particularly large thermal boundary conductance for the water-graphene interface and suggest strategies for enhancing the thermal conductivity in graphene-based nanostructures.

Giant and broadband THz and IR emission in drift-biased graphene-based hyperbolic nanostructures

We demonstrate that Cherenkov radiation can be manipulated in terms of operation frequency, bandwidth, and efficiency by simultaneously controlling the properties of drifting electrons and the photonic states supported by their surrounding media. We analytically show that the radiation rate strongly depends on the momentum of the excited photonic state, in terms of magnitude, frequency dispersion, and its variation vs the properties of the drifting carriers. This approach is applied to design and realize miniaturized, broadband, tunable, and efficient terahertz and far-infrared sources by manipulating and boosting the coupling between drifting electrons and engineered hyperbolic modes in graphene-based nanostructures. The broadband, dispersive, and confined nature of hyperbolic modes relax momentum matching issues, avoid using electron beams, and drastically enhance the radiation rate—allowing that over 90% of drifting electrons emit photons. Our findings open an exciting paradigm for the development of solid-state terahertz and infrared sources.

Dynamic Observation of the Coulomb Explosion and Field Evaporation of a Few-Layer Graphene Nanoribbon.

The Coulomb explosion and field evaporation are frequently observed physical phenomena for a metallic tip under an external electric field, which can modify the structures of the tip and have broad applications, such as in the atomic-probe tomography and field ion microscopy. However, the mechanistic comprehending of how they change the structures of the tip and the differences between them are not clear. Here, dynamic observations of Coulomb explosions and field evaporations on the positively biased and charged few-layer graphene (FLG) nanoribbon inside a transmission electron microscope are reported. By combining the atomic-scale molecular dynamic simulations, it is shown that the FLG is split into several sheets under Coulomb explosion. It is also observed to break by emitting the carbon ions/segments under the field evaporation. It is further demonstrated that the split and breaking of FLG can be tuned by the shape of the nanoribbon. FLG ribbons with sharp tips have splitting and breaking occur in sequence. FLG with blunt tips break without a split. These results provide a fundamental understanding of Coulomb explosion and field evaporation in graphene nanomaterials and suggest potential methods to engineer graphene-based nanostructures.

3D porous nanostructured reduced graphene oxide and nafion composite as an ultrasensitive interface for rapid and nanomolar determination of a flavonoid, galangin

Graphene-based nanostructures are considered ideal modifiers for electrochemical sensors owing to their unique structural, conductive, and catalytic properties. Given this, herein we have developed a three-dimensional reduced porous graphene oxide-nafion nanocomposite film modified glassy carbon electrode (p-rGO/NAF/GCE) for electrochemical determination of a flavonoid, galangin (GAL) for the first time. A simple, almost instantaneous, and environmentally benign “low-temperature solution combustion” method was used for the preparation of p-rGO using glycine as a fuel and green reducing agent simultaneously, followed by compositing it with nafion and coating on GCE to form an electrochemical sensor. The p-rGO/NAF/GCE promoted the mass transfer of GAL to the electrode surface and exhibited excellent electrocatalytic activity towards the oxidation of GAL with a significant enhancement (∼70-fold) in the peak current. The enhanced electrocatalytic activity was attributed to the synergistic contribution from p-rGO and nafion, which provided higher active surface area, porous network structure, feasible cation exchangeability, and strong adsorption capacity. The two anodic peaks exhibited by GAL at p-rGO/NAF/GCE involved an equal number of protons and electrons via diffusion-controlled (peak a1) and adsorption-controlled (peak a2) processes. Linear response over concentration range of 1.99 × 10−8 – 4.5 × 10−5 mol L−1 of GAL was established with the lowest limit of detection value of 1.11 nM by square wave voltammetric (SWV) method. Importantly, the fabricated sensor demonstrated repeatability, high stability, and potential anti-interference properties with practical utility for the analysis of analyte-fortified biological samples and pharmaceutical formulations with good recoveries.

Adsorptions of phenol molecules by graphene-based nanostructures, modified with nitrogen and bromine, from petroleum wastewater using molecular dynamics simulation

Today, industrial wastewater treatment has attracted the attention of many governments and environmental experts. Basically, the pollution of these wastewaters is due to the presence of organic pollutants such as dyes, halogenated hydrocarbons, phenolic compounds, etc. Meanwhile, phenol is widely used in oil, petrochemical, coal production, and pharmaceutical industries. Several methods such as surface adsorption are used to remove phenol from water. In this work, the adsorption of phenol molecules by carbon nanostructures and carbon nanostructures modified with nitrogen and bromine has been investigated using Molecular Dynamics simulation. According to the obtained results, BCN-graphene has been introduced as the best nanostructure for the removal of phenol molecules from the aqueous environment, having the highest adsorption energy and greater adsorption stability. This work paves the way for the development of the use of bromine nitride structures in the treatment of petroleum wastewater.

Ag@Fe3O4 nanoparticles decorated NrGO nanocomposite for supercapacitor application

There is still a great need for production and design of electrode materials with superior electrochemical properties for supercapacitor application. Nanocomposites containing graphene-based metal-metal oxide nanostructures are promising electrode materials because of their high conductivity, excellent surface properties, and effective charge storage with both EDLC and pseudocapacitance mechanisms. In this study, Ag@Fe3O4 core@shell nanoparticles decorated nitrogen doped reduced graphene oxide (NrGO) was obtained with a facile and simple method. On the surface of NrGO nanosheets, Ag nanoparticles were found to be coated with Fe3O4 nanoparticles with a particle size of 5–12 nm. The electrochemical measurements of NrGO-Ag@Fe3O4 nanocomposite were carried out in a two-electrode cell. The ternary nanocomposite exhibited 212.2 F/g specific capacitance at a current density of 1 A/g, as well as high cyclic stability, the NrGO-Ag@Fe3O4 nanocomposite retained 77 % of its specific capacitance after 10,000 cycles. The Ag@Fe3O4 decorated NrGO nanocomposite indicates great potential as an electrode material for supercapacitor applications.

Graphene/Al2O3/InGaAs-based nanostructures for near-infrared photodetectors passivated by InP layer

In the past decade, graphene-based near infrared photodetectors (NIR PDs) have attracted attention for their high response speed and high responsivity. As a promising graphene-based nanostructure, the InGaAs/Al2O3/graphene device has been proven to have important applications in the detection of the near infrared light. The monolayer graphene and a thin Al2O3 layer could improve the device performance. However, the device degraded the current-voltage (I–V) characteristics. To enhance the resistance of this Schottky nanostructure NIR PD to the irreversible degradation, a layer of p-InP under the SiNx is expected to reduce the defects and enhance the absorption of NIR light. In this work, the Schottky nanostructure NIR PD with the InP layer has a high detectivity of 2.3⨯1013 cm Hz1/2 W−1, a high response speed of 557 ns/3.22 μs, and a high responsivity of 11.23 A/W at −1.5 V and 1.32 A/W at 0 V to 1550 nm infrared light, which is even larger than that of the metal-oxidation-semiconductor (MOS) structure. The wavelength-responsivity (λ-R) characteristics measured by different infrared lasers ranging from 808 nm to 1870 nm indicated a wide response spectrum. Moreover, the phenomenon of the reverse photocurrent was observed and analyzed.

Hydrophobic metal-organic framework@graphene oxide membrane with enhanced water transport for desalination

As a new generation of high-performance alternative, graphene-based membranes have shown great prospect in water purification. Among them, numerous efforts are concentrated on designing hydrophilic membranes while less attention is paid to hydrophobic membranes, which limit the potential application of graphene-based membranes, such as desalination via membrane distillation (MD) process. Anisotropic heat transfer and easy hydrophobic modification of graphene oxide (GO) make it suitable for MD membrane fabrication. Herein, we developed a novel porous and hydrophobic MOF-801@GO-PDMS membrane with enhanced water vapor transport for water desalination via direct contact membrane distillation (DCMD). MOF-801 nanoparticles were in-situ grown within GO interlayer followed with vacuum filtration to fabricate MOF-801@GO membrane which was subsequently modified with polydimethylsiloxane (PDMS) to fabricate the MOF-801@GO-PDMS membrane. The water-stable porous MOF-801 nanoparticle was introduced to increase the porosity of GO laminate and provide extra water vapor transport channels. PDMS was employed to ensure the membrane hydrophobic stability by utilizing its intrinsic hydrophobicity and segment entanglement. The optimum MOF-801@GO membrane exhibited water flux of 29.24 kg m−2 h−1 and NaCl rejection of over 99.99%, as well as robust stability during continuous DCMD desalination test. This work not only gives a promising candidate for water desalination, but also provides a method to design hydrophobic and porous graphene-based nanostructures for other potential applications.

Single-band to multi-band perfect absorption in monolayer-graphene-based dielectric metasurfaces

Perfect absorption in graphene-based nanostructures has attracted much attention due to its potential applications in novel photodectors and light modulators with high integrability. Based on critical coupling theory, we propose a graphene-based dielectric metasurface, demonstrating graphene-assisted single-band to multi-band perfect absorption with independent band selectivity in the near-infrared range. The proposed graphene-metasurface absorber can support a delocalized guided mode resonance and a series of localized cavity modes with different order, which can be selectively excited at will by simply tuning the geometry of the system, thus realizing an independent control of single-band to multi-band perfect absorption at critical coupling condition. The proposed hybrid structure possesses simple structural configuration and is easily accessible by standard nano-fabrication technique. Our results may find potential applications in the design of novel photoelectronic devices such as graphene-based photodectors or light modulators with flexible multi-band selectivity for desired wavelength.

Mesoporous graphene-based hybrid nanostructures for capacitive energy storage and photocatalytic applications

The development of multi-functional nanomaterials is nowadays more than a necessity to address both energy and environmental needs of our society. In this perspective, the hybridization of graphene (Gr) with TiO2 nanotubes (TiNT) is very promising to meet these issues. In the present work, bi-functional graphene-modified TiO2 nanotubes electrodes (Gr/TiNT) were successfully prepared. A simple and effective approach for graphene production, by electrochemical exfoliation of pure graphite foil in inorganic salt (Na2SO4) is used. Graphene sheets were formed on the surface of TiO2 nanotube arrays through electrodeposition process by chronoamperometry. Mesoporous graphene of high surface area is promising material for photocatalytic applications. Gr/TiNT electrode displays significantly improved photodegradation efficiency to MB, achieving a degradation percentage of 60% in 2 hours, which is about 50% higher than that of TiNT. Moreover, Gr/TiNT with high conductivity demonstrated good capability to deliver extremely high energy and power in a very short period of time, the relaxation time constant was only about 48 ms, which is far lower than that of most conventional activated carbon-based electrochemical capacitors. Capacitance retention of 98% was also demonstrated after 1000 cycles.