Few-layer Graphene Research Articles

Improvement of biodegradable polymer film properties by incorporating functionalized few-layer graphene

Functionalized few-layer graphene (FFG) prepared employing an eco-friendly liquid exfoliation method using coffee waste extract was added to three biological and one synthetic polymers. Chitosan/FFG, polyvinyl alcohol (PVA)/FFG, sodium alginate/FFG, and gelatin/FFG composite films were developed using variable concentrations of FFG (0–1 wt% of polymer). The developed films were characterized for water content, swelling degree, thickness, thermal and mechanical properties, water vapor permeability, and indoor soil burial degradation. In comparison to the pure chitosan, PVA, sodium alginate, and gelatin films, the inclusion of FFG significantly increased the tensile strength up to 439%, 247%, 190%, and 195%, respectively. Moreover, the Young’s modulus of the developed composite films was improved up to 515%, 253%, 144%, and 341%, respectively. The elongation at break of chitosan and PVA films declined with FFG concentration, while the maximum elongation at break existed for sodium alginate/FFG and gelatin/FFG films. The water vapor permeability of chitosan, PVA, sodium alginate, and gelatin composite films decreased by 87%, 67%, 50%, and 55%, respectively, with the addition of only 1% FFG. The incorporation of FFG reduced both the water content and swelling degree of all composite films. In addition, the composite films showed similar degradation after addition of FFG in the 60-day soil burial test.

Bubble-Induced Strong Thermal Contraction for Graphene

Abstract The thermal expansion coefficient (TEC) of van der Waals (vdW) layered structures is of crucial importance in governing the dependability and longevity of advanced optoelectronic equipment. Bubbles are commonly found within layered structures, yet their impact on the thermal expansion coefficient of the structure is still not well understood. We derive an analytical formula that describes the influence of bubbles on the variation in length, utilizing both the elastic membrane theory and the improved van der Waals gas state equation. The results demonstrate that as the temperature increases, bubbles can induce significant thermal contraction in few-layer graphene structures. The analytical predictions are validated through molecular dynamic (MD) simulations, confirming the accuracy and reliability of the proposed model. These findings hold significant value in enhancing our understanding of the dependability and durability of functional equipment that relies on van der Waals layered structures.

Large-scale dispersion of the hierarchical (1D, 2D and 3D) carbonaceous nanofillers in thermoplastic polyurethane through supramolecular self-assembly and extrusion

ABSTRACT The hierarchical carbonaceous nanofillers viz. carboxylated multiwalled carbon nanotube (MWCNT-COOH as 1D), hydroxylated few-layer graphene (FLG-OH as 2D), and hybrid 3D i.e., MWCNT-COOH immobilized into FLG-OH were dispersed into segmented thermoplastic polyurethane (TPU) by twin-screw extrusion (TSE). The concentration of nanofillers was varied as 0.25, 0.5, 1.0, 2.0 and 5 wt%. To increase the level of dispersion, hybrid 3D nanofillers were also incorporated into TPU by producing cellular structures through supramolecular self-assembly route (SSAR). The cellular structure in which the nanofillers were found to be uniformly dispersed was then compounded by TSE technique. The large-scale uniform dispersion was observed at higher loading (2 wt%) by SSAR followed by TSE when compared with direct TSE. Uniform dispersion was found at 1 wt% loading by direct TSE. PU nanocomposite film reinforced with 2 wt% hybrid 3D nanofillers showed good gas barrier property with ~63% reduction of helium gas permeability to 472 cm3/m2/day from 1287 cm3/m2/day of neat PU film.

Surface functionalization of vertical graphene significantly enhances the energy storage capability for symmetric supercapacitors

Vertical graphene (VG) sheets, which consist of few-layer graphene vertically aligned on the substrate with three-dimensionally interconnected porous network, make them become one of the most promising energy storage electrodes, especially for SCs. Nevertheless, the intrinsic hydrophobic nature of pristine VG sheets severely limited its application in aqueous SCs. Here, electrochemical oxidation strategy is adopted to increase the hydrophilicity of VG sheets by introducing oxygen functional groups so that the aqueous electrolyte can fully be in contact with the VG sheets to improve charge storage performance. Our work demonstrated that the introduction of oxygen functional groups not only greatly improved the hydrophilicity but also generated a pseudocapacitance to increase the specific capacitance. The resulting capacitance of electrochemically oxidized VG for 7 min (denoted as EOVG-7) exhibited three orders of magnitude higher (1605 mF/cm2) compared to pristine VG sheets. Through assembled two EOVG-7 electrodes, a symmetric supercapacitor demonstrated high specific capacitance of 307.5 mF/cm2, high energy density of 138.3 μWh/cm2 as well as excellent cyclic stability (84% capacitance retention after 10000 cycles). This strategy provides a promising way for designing and engineering carbon-based aqueous supercapacitors with high performance.

Electronic and Magnetic Properties of FeCl3 Intercalated Bilayer Graphene

Graphene has gained significant attention since its discovery in 2004, and the modification of few-layer graphene provides a platform to tailor its physical and electronic properties. In this study, we employed unrestricted density functional theory (DFT) with the PBE+U functional to investigate the electronic and magnetic properties of FeCl3-intercalated bilayer graphene (BLG). Both in BLG and stage-2 intercalated graphite, a distinct localization of electrons on a specific Fe atom is evident, gaining approximately 0.245 electrons evaluated with Bader analysis, while the holes are delocalized within the graphene layers. This results in p-doped graphene, characterized by a shift of the Dirac cone by 0.74 eV for BLG and 0.70 eV for stage-2 intercalated graphite. Ferromagnetic ordering is observed within the plane of FeCl3-intercalated BLG, whereas the FeCl3 layers exhibit antiferromagnetic coupling in stage-2 intercalated graphite. The ferromagnetic nature and electronic structure of the FeCl3-intercalated BLG is retained under pressure.

Graphenization of graphene oxide films for strongly anisotropic thermal conduction and high electromagnetic interference shielding

A macroscopic carbon film that has a “graphenic” structure (defect-free in-plane graphene lattice yet absence of Bernal type graphitic stacking order), may inherit the exotic properties of rotated/slipped few-layer graphene (e.g., high flexibility and anisotropic transport properties). However, the fabrication of such a film remains challenging and unreported. Here we show that the annealing of reduced electrochemical graphene oxide (REGO), which has fewer in-plane defects than the conventional graphene oxide from Hummers’ method, leads to a nearly intact graphene lattice (Raman ID/IG down to 0.03) without restoring the graphitic stacking order (I2D/IG > 1 and a single Lorentzian 2D peak). Atomic resolution transmission electron microscopy verifies the unique graphenic structure with random interlayer rotations. Density functional theory calculations imply the low defect density of REGO can suppress the interplanar interaction between undercoordinated carbon atoms, therefore inhibiting cross-plane migration of vacancies and the consequent establishment of stacking order. The annealed, graphenic REGO film is highly flexible and has an in-plane to cross-plane thermal conductivity ratio of 835 (among the highest reported for anisotropic thermal conductors). This high anisotropic ratio is attributed to the inhibited through-plane heat transport (0.26 W m−1 K−1) by the interlayer rotations and the high in-plane thermal conductivity (218 W m−1 K−1) enabled by intact graphene lattice. The graphenic films show high electromagnetic interference shielding effectiveness of 80.3 dB at a thickness of 53 μm and 42.4 dB at 5.7 μm, with an absolute effectiveness (>70000 dB cm2 g−1) superior to two-dimensional metal carbides (MXenes) and Al foil.

The Structure Design of a Microstrip Tunable Attenuator Based on Few-Layer Graphene

There are innovative applications for graphene materials in microwave Radio Frequency (RF) due to their unique optoelectronic properties. In this paper, a series of existing tunable microstrip attenuators based on few-layer graphene are compared and studied, and a new microstrip tunable attenuator based on few-layer graphene is proposed on this basis. Firstly, the relationship between the performance of different pair spacing attenuators with 4 pairs of graphene structures is analyzed based on the existing pair spacing studies with 1-3 pairs of structures; after that, the performance characteristics of the existing 1-4 pairs of graphene structures on different substrates are tested and analyzed; finally, a new tunable attenuator structure is proposed based on the above research results. The new attenuator consists of four parts, including a dielectric substrate, a microstrip line, a total of five pairs of graphene flakes on both sides and corresponding metal vias. The resistivity of the graphene flake can be changed by changing the access bias voltage, thus regulating the insertion loss of the attenuator. The experimental results show that the proposed attenuator can operate in the frequency range from 3 GHz to 10 GHz, and the insertion loss can be adjusted from -2 dB to -63 dB, with a high tunable performance of 61 dB.

Mineralization of Few-Layer Graphene Made It Bioavailable in Chlamydomonas reinhardtii.

Numerous studies have emphasized the toxicity of graphene-based nanomaterials to algae, however, the fundamental behavior and processes of graphene in biological hosts, including its transportation, metabolization, and bioavailability, are still not well understood. As photosynthetic organisms, algae are key contributors to carbon fixation and may play an important role in the fate of graphene. This study investigated the biological fate of 14C-labeled few-layer graphene (14C-FLG) in Chlamydomonas reinhardtii (C.reinhardtii). The results showed that 14C-FLG was taken up by C.reinhardtii and then translocated into its chloroplast. Metabolomic analysis revealed that 14C-FLG altered the metabolic profiles (including sugar metabolism, fatty acid, and tricarboxylic acid cycle) of C.reinhardtii, which promoted the photosynthesis of C.reinhardtii and then enhanced their growth. More importantly, the internalized 14C-FLG was metabolized into 14CO2, which was then used to participate in the metabolic processes required for life. Approximately 61.63%, 25.31%, and 13.06% of the total radioactivity (from 14CO2) was detected in carbohydrates, lipids, and proteins of algae, respectively. Overall, these results reveal the role of algae in the fate of graphene and highlight the potential of available graphene in bringing biological effects to algae, which helps to better assess the environmental risks of graphene.

From interface to interphase

A critical brief review of the evolution of the ideas describing the matter, with emphasis on concepts relevant to the journal's goals: surfaces, interfaces, and interphases is presented. The complex relationship between interphase and interface, including the role of the submicron confinement on the physical and chemical properties of matter are analyzed from both theoretical and experimental standpoints. The most important consequences triggered by the recognition of interphases are briefly discussed. Most matter (at a macroscopic scale) is dominated by bulk behavior. The rapid advances in materials and especially the accelerated progress in the synthesis and characterization of submicron materials and associated technologies, labeled as the “nano revolution”, revived the research on interfaces and interphases at atomic and molecular scales. It is suggested that interphase ignites a new kind of material, whose “bulk physical features” have been distorted by the submicron confinement. Such an “interphase surface” (for example a drop of gold with a diameter smaller than a few nanometers, or a few layers of graphene), may exist free standing and be stable. These materials, which no more exhibit the bulk properties will be tentatively referred to as “Sutter” (“Sutter” defines an abbreviation that involves both surface and matter concepts). Sutter is characterized by the fact that its physical and chemical properties are controlled by the interphase. It is concluded that Sutter is essentially a submicron phase of the matter, that exhibits size-dependent features. Sutter materials may be embedded in various materials (such as polymers, metals, and alloys) as nanocomposites, thus projecting specific features at the macroscopic scale. Most free standing interphases may be considered as Sutter materials or phases. The interface does not qualify as a Sutter material.

Optical-fiber-integrated high-speed organic phototransistor with broadband imaging capacity.

Fiber optic communication is becoming the central pillar of modern high-speed communication technology, which involves the abundant fiber components. Currently, most of photodetectors are fabricated on the silicon chip, so mass fiber-to-chip interfaces increase the complexity of advanced optoelectronic system, and also grow the risk of optical information loss. Here, we report an all-fiber organic phototransistor by employing rubrene single crystal and few-layer graphene to realize the "plug-to-play" operation. The device shows a broadband photoresponse from the ultraviolet to visible range, with fast response times of approximately 130/170 µs and reasonable specific detectivity of 6 × 109 Jones, which is close to the level of commercial on-chip device. Finally, several imaging applications are successfully demonstrated by deploying this all-fiber device. Our work provided an efficient strategy for fabricating all-fiber organic devices, and confirmed their significant potential in future optical fiber optoelectronics.

Low-temperature green synthesis of few-layered graphene sheets from pomegranate peels for supercapacitor applications

Graphene presents practical applications in energy storage devices, especially supercapacitors. However, mainstream synthesis of graphene includes toxic chemical usage, which threatens the environment. With the recent attention shift to synthesizing nanomaterials from agro-waste due to their easy availability, cost-effectiveness, and, most importantly, their environmental friendliness, we present, in this work for the first time, a novel and green synthesis of few-layered graphene sheets using pomegranate peels as a precursor at a low temperature of 80 °C. The surface morphology and microstructural properties are determined by Transmission Electron Microscopy (TEM), Energy Dispersive X-Ray spectroscopy (EDX), X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), UV–visible spectroscopy (UV–vis), and the electrical properties determined by Hall Effect Measurement. The application as a supercapacitor is also examined using Cyclic Voltammetry (CV), Charge–Discharge Cycling (GCD), and Electrochemical Impedance Spectroscopy (EIS). The resulting supercapacitor delivers an areal capacitance of 3.39 mF{cm}^{-2} at a current density of 15.6 μA {cm}^{-2}, making our synthesized graphene a good choice for electrochemical storage devices.

Ab Initio Molecular Dynamics of the Initial Growth of Few-Layer Graphene on a Cu–Ni(111) Catalyst

Ab Initio Molecular Dynamics of the Initial Growth of Few-Layer Graphene on a Cu–Ni(111) Catalyst

Characterization of graphene films formed using radical plasma species

Previously the authors of this paper have reported the synthesis of highly tethered, planarized graphene films on 6H-SiC(0001) using a two-step CF4-based plasma assisted synthesis (PAS) process. In the first step, silicon was selectively etched from the SiC surface to form a carbon-rich overlayer, and in the second step, a rapid thermal anneal was used to form the graphene film from this carbon-rich layer. The etch process was performed in an inductively coupled plasma-reactive ion etching system and utilized both physical etching due to ions and chemical etching due to radicals. This paper reports the plasma assisted synthesis of few-layer graphene films using only the radical species produced in a CF4-based plasma. That is, only chemical etching was involved in the selective etching process. This was achieved by placing a physical mask over the substrate to block the ion flux and allowing the microplasma formed from the ambient radical species to etch the SiC surface. This process followed by the rapid thermal anneal is referred to as microplasma assisted synthesis (MPAS) of graphene. The resulting graphene films were characterized using x-ray photoelectron spectroscopy, Raman spectroscopy and atomic force microscopy. These analyses reveal that the MPAS films are less tethered than those produced by the PAS process, and they reflect the step and terrace structure of the initial SiC substrate. Consequently, the few layer graphene films formed using MPAS show marked progress toward the quasi-freestanding graphene films formed by high temperature sublimation. Overall, these results suggest that a radical based etching process may provide a chemical route to the synthesis of quasi-freestanding graphene on SiC. Additionally, these results provide insight into the roles of radicals and ions in the etching process.

Direct etching of nano/microscale patterns with both few-layer graphene and high-depth graphite structures by the raster STM electric lithography in the ambient conditions.

The development of raster STM electric lithography has enabled the etching of nano/microscale patterns on both few-layer graphene (FLG) and high-depth graphite structures on the bulk HOPG substrates under ambient conditions. This approach utilises a nanoscale probe tip as a machining tool to directly fabricate conductive sample surfaces without the need for resists or masks. Compared to conventional nano/micro machining methods, the capability of ultraaccurate fabrication of nanoscale patterns using this technique is unmatched. The resulting FLG structures exhibit ultrasmooth flat bottoms and uniformly controlled depths ranging from 0.34 to 3.0nm (less than 10 layers). This work represents a significant advancement as it demonstrates the perfect etching of FLG structures in designated nano/microscale regions using raster STM electric lithography in the constant current mode, which reaches the limitation of top-down manufacturing techniques. Additionally, raster STM electric lithography in the constant height mode can directly etch high-depth structures (up to ∼100nm). The geometric shape and number of layers of the etched graphene structures determined by either local anodic oxidation (LAO) or the electric discharge (ED) mechanism. The LAO mechanism results in less debris and smoother edges compared to the ED mechanism, which is caused by the random electrical discharge between the tip and the sample. The well-controlled raster STM electric lithography technique is believed to be a promising and facile approach for constructing nano/microscale graphene-based devices.

Electrostatic modulation of excitonic fluid in GaN/AlGaN quantum wells by deposition of few-layer graphene and nickel/gold films

Electrostatic modulation of excitonic fluid in GaN/AlGaN quantum wells by deposition of few-layer graphene and nickel/gold films

Boosting Copper Biocidal Activity by Silver Decoration and Few-Layer Graphene in Coatings on Textile Fibers.

The outbreak of the Coronavirus disease 2019 (COVID-19) pandemic has highlighted the importance of developing antiviral surface coatings that are capable of repelling pathogens and neutralizing them through self-sanitizing properties. In this study, a novel coating design based on few-layer graphene (FLG) is proposed and silver-decorated micro copper flakes (CuMF) that exhibit both antibacterial and antiviral properties. The role of sacrificial anode surfaces and intrinsic graphene defects in enhancing the release of metal ions from CuMF embedded in water-based binders is investigated. In silico analysis is conducted to better understand the molecular interactions of pathogen-repelling species with bacterial or bacteriophage proteins. The results show that the optimal amount of CuMF/FLG in the coating leads to a significant reduction in bacterial growth, with reductions of 3.17 and 9.81 log for Staphylococcus aureus and Escherichia coli, respectively. The same coating also showed high antiviral efficacy, reducing bacteriophage phi6 by 5.53 log. The antiviral efficiency of the coating is find to be doubled compared to either micro copper flakes or few-layer graphene alone. This novel coating design is versatile and can be applied to various substrates, such as personal protective clothing and face masks, to provide biocidal activity against both bacterial and viral pathogens.

Rational engineering of a carbon skeleton supported tin dioxide nanocomposite from MOF on graphene precursor for superior lithium and sodium ion storage

Tin dioxide (SnO2) is being investigated as a promising anode material for both lithium-ion batteries (LIBs) and sodium-ion batteries (SIBs). Effectively dispersing small sized SnO2 crystals in well-designed carbonaceous matrices using eco-friendly materials and simplified methods is an urgent task. Herein, gallic acid (GA) molecules, abundant in plant kingdom, are firstly selected to react with few-layered graphene oxide (GO) in mild hydrothermal condition, and the GA modulated reduced graphene oxide (GA@RGO) supporting skeleton can be obtained. Then Sn-GA metal–organic framework (MOF) domains can be directly engineered on the surface of the GA@RGO sheets with controlled size and improved dispersion. Finally, the well-designed Sn-GA@RGO precursor is converted to the SnO2/C/RGO nanocomposite with significantly optimized microstructure. The SnO2/C/RGO sample delivers an excellent specific capacity of 823.6 mAh·g−1 after 700 cycles at 1000 mA·g−1 in half-cells and 741.3 mAh·g−1 after 50 cycles at 200 mA·g−1 in full-cells for LIBs, a specific capacity of 370.3 mAh·g−1 after 600 cycles at 200 mA·g−1 in half-cells for SIBs. The sample preparation strategy is rationally established by comprehensively understanding the interactions between GO sheets, Sn2+ ions and GA molecules, and the engineered SnO2/C/RGO nanocomposite has good prospects in wider fields.

Consecutive engineering of anodic graphene supported cobalt monoxide composite and cathodic nanosized lithium cobalt oxide materials with improved lithium-ion storage performances

Downsizing the electrochemically active materials in both cathodic and anodic electrodes commonly brings about enhanced lithium-ion storage performances. It is particularly meaningful to explore simplified and effective strategies for exploiting nanosized electrode materials in the advanced lithium-ion batteries. In this work, the spontaneous reaction between few-layered graphene oxide (GO) and metallic cobalt (Co) foils in mild hydrothermal condition is for the first time employed to synthesize a reduced graphene oxide (RGO) supported nanosized cobalt monoxide (CoO) anode material (CoO@RGO). Furthermore, the CoO@RGO sample is converted to nanosized lithium cobalt oxide cathode material (LiCoO2, LCO) by taking the advantages of the self-templated effect. As a result, both the CoO@RGO anode and the LCO cathode exhibit inspiring lithium-ion storage properties. In half-cells, the CoO@RGO sample maintains a reversible capacity of 740.6 mAh·g−1 after 300 cycles at the current density of 1000 mA·g−1 while the LCO sample delivers a reversible capacity of 109.1 mAh·g−1 after 100 cycles at the current density of 100 mA·g−1. In the CoO@RGO//LCO full-cells, the CoO@RGO sample delivers a reversible capacity of 553.9 mAh·g−1 after 50 cycles at the current density of 200 mA·g−1. The reasons for superior electrochemical behaviors of the samples have been revealed, and the strategy in this work can be considered to be straightforward and effective for engineering both anode and cathode materials for lithium-ion batteries.

Photo‐stabilization mechanisms of High‐Density Polyethylene (HDPE) by a commercial few‐layer graphene

AbstractThis work studied few‐layer graphene (FLG) dominant action mechanisms as a photo‐stabilizer. High‐density polyethylene (HDPE) containing 0–0.5 wt% FLG were exposed to UVA radiation in a QUV chamber, according to ASTM G154 for different exposure times, ranging from 0 to 672 h. The chemical, rheological, and mechanical properties were tracked using attenuated total reflection‐Fourier transform infrared (ATR‐FTIR), rheological measurements, and tensile tests. The experimental results showed that the addition of only 0.25 wt% FLG fully stabilized 1‐ to 3‐mm thick HDPE for an exposure time of 672 h. Electron paramagnetic resonance (EPR) test was performed on the UV‐exposed mixture of hydrogen peroxide (H2O2) and the FLG aqueous suspensions (0, 0.2, 1, and 5 mg/mL), to study the FLG performance and mechanisms as a photo‐stabilizer. The results showed that FLG effectively decreased the characteristic EPR signal intensity due to both UV absorption/reflection and free radical scavenging. Fifty‐seven percent of the reduction was found to be due to UV absorption/reflection and 43% due to free radical scavenging. It is demonstrated that UV absorption/reflection and free radical scavenging are the dominant ones among the three FLG photo‐stabilizing mechanisms (UV absorption/reflection, free radical scavenging, and physical barrier to oxygen).Highlights FLG showed potential as a photo‐stabilizer for HDPE. Addition of 0.25 wt% FLG fully stabilized HDPE for 672 h of UVA exposure. FLG demonstrated UV absorption/reflection and free radical scavenging effects.

Novel Aerosol‐Based Approach toward Mesoporous Silica Nanoparticles

This study introduces a novel gas‐phase method for the synthesis of mesoporous silica nanoparticles (MSNs). The method is a two‐step templating approach by first forming silicon‐coated carbon structures in a hybrid microwave‐plasma/hot‐wall reactor followed by an annealing step to produce mesoporous silica with distinct nanostructure and porosity. Two different (sacrificial) carbonaceous templates have been prepared (plasma reactor) and coated (hot‐wall reactor), 2D few‐layer graphene (FLG) flakes and soot‐like fractal aggregates. Results show that the wall thickness of the porous silica structures can be adjusted by changing the concentration of the silicon precursor (monosilane). High monosilane concentrations, however, result in solid silica particles after annealing. Using soot‐like particle templates permitted to control of the shell thickness of the hollow porous particles, while the FLG template results in ultrathin silica sheets after heat treatment. The pore volume and specific surface area increase up to 263 m2 g−1 and 0.6 cm3 g−1, respectively, by the formation of hollow porous particles. An adsorption study on carbamazepine reveals up to ≈86% removal. The gas‐phase aerosol‐based template method presented here offers scalability and versatility, and it is capable of producing MSNs with a controlled structure and porosity by modifying the carbonaceous templates.