Graphene-based Nanostructures Research Articles

Graphene-Based Monolithic Nanostructures for CO2 Capture

Monolithic nanocarbon-based CO2 solid sorbents offer fast mass transport, easy handling, minor pressure drop and cycle operation stability due to the interconnected three-dimensional network of por...

Graphene-based nanostructures for enhanced photocatalytic degradation of industrial dyes

Graphene oxide (GO) is an sp2-bonded single atomic layer of carbon atoms with plenty of oxy-functional groups at its surface. The occurrence of large surface area (~ 2630 m2/g), surface functionalities, electronic, and mechanical properties make graphene-based compounds favorable for remediation applications. We report the synthesis and comparative dye degradation efficiencies of two titania (TiO2)-based composites, GO-TiO2, and reduced GO-TiO2 (rGO-TiO2). Both the composites are characterized using SEM-EDX, TEM, FTIR, and XRD. We study the photocatalysis-mediated degradation of anionic dye Eosin Y and cationic dye Methylene blue (MB) in aqueous dispersions under white light and UV irradiation. Our results demonstrate that rGO(10 wt%)-TiO2 composite shows the maximum degradation (~ 95%) of both 10 ppm Eosin Y and MB dyes in the aqueous dispersion. The enhanced photocatalytic activity of rGO-TiO2 composites as compared to TiO2 and GO-TiO2 can be credited to the presence of efficient electron shuttling from the conduction band of TiO2 into the conductive regions of graphene which eventually restricts further recombination of e−/h+ pairs. Furthermore, the effects of solution pH and TiO2 loading are studied on the degradation process.

Effects of intraperitoneal injection of magnetic graphene oxide on the improvement of acute liver injury induced by CCl4

BackgroundLiver failure is usually associated with the inflammation and oxidation of hepatocytes. Due to their unique properties, graphene and graphene-based nanostructures such as magnetic graphene oxide (MGO) are useful in biomedicine and engineering. In this study, synthesized MGO was used to improve the liver failure induced by carbon tetrachloride (CCl4). The hepatoprotective effects of intraperitoneal injection of MGO on the rat model of CCl4-induced acute liver failure were investigated.Materials and methodsIn order to provide a rat model of acute liver failure, male rats were intraperitoneally injected with 2 ml/kg body weight CCl4. In the experimental groups, rats received 2 ml/kg CCl4 and 300 mg/kg MGO body weight simultaneously. Four days after injection, symptoms of acute liver failure appeared. The control, sham, CCl4, and CCl4 + MGO groups were compared and analyzed both histologically and biochemically.ResultsThe results indicated that the MGO injection reduced all CCl4-induced liver failure such as necrosis, fibrosis, inflammation, aspartate transaminase (AST), alanine aminotransferase (ALT), and alkaline phosphatase (ALP) in the experimental groups of the rat model of acute liver failure.ConclusionThe hepatoprotective effects of MGO might be due to histopathological suppression and inflammation inhibition in the liver.

Importance of Graphene in the Electro-Fenton Process.

Graphene-based nanomaterials have attracted researchers from various fields due to their extraordinary physical, chemical, and electrochemical properties. An emerging class of graphene-based nanostructures and nanocomposites is considered to be a promising solution to various types of environmental pollution. The electro-Fenton process is one of the easy and effective approaches to treating a wide range of organic pollutants in a liquid medium. The usage of graphene-based electrodes in the electro-Fenton process is considered to be a promising and cleaner way to produce reactive oxygen species to mineralize organic contaminants rapidly. Graphene derivatives are used to immobilize various heterogeneous Fenton catalysts for improved catalytic activity, stability, and reusability. In this review, the importance of graphene-based materials in improving the performance efficiency in the electro-Fenton process is presented along with an enhancement mechanism through the following discussions: (i) the significance of oxygen functional groups and nitrogen doping on graphene layers to enhance the two-electron oxygen reduction reactions; (ii) the advantages of iron-loaded graphene-based materials as catalysts and composite electrodes for the enhanced production of reactive oxygen species; (iii) a summary of various forms of graphene-based materials, modifications in their chemical structure, properties, and applications in the electro-Fenton process to remove organic contaminants.

Sunlight-assisted tailoring of surface nanostructures on single-layer graphene nanosheets for highly efficient cation capture and high-flux desalination

Highly efficient approaches using nanomaterials for ion capture and desalination have been widely explored to address fresh water scarcity worldwide; however, the complex preparation process and the large-scale and high-density perforation of porous graphene layers remain technical challenges. Herein, we found that sunlight-assisted tailoring of surface nanostructures involving controllable morphological and structural alterations of graphene unequivocally improved the ion adsorption and ion filtration performance. Notably, the interlayer spacing of single-layer graphene could be sufficiently tuned via lighting control to promote selective interactions between ions and nanosheets. After 7 d simulated sunlight treatment, the transformed SLG (SLG-S7) exhibited 86.1%, 77.3% and 46.1% increases of adsorption capacity for Na+, Pb2+ and Fe3+ in the complex ion system, respectively. Notably, the adsorption capacity of SLG-S7 for single Pb2+ was even 2.3-fold greater than that of pristine SLG. Further, the layer-stacked SLG-S7 membrane achieved super water fluxes (167.1 L m−2 h−1 bar−1) and a high separation performance without sacrificing salt ion rejection, which was attributed to the sunlight-induced larger water transport channels and defect-free nanosheets in the membrane. This work provides new insight for the design of novel graphene-based nanostructures to address the increasingly serious water contamination issue and the scarcity of fresh water.

Graphene-based metasurface: 4D shape-shift biosensing interface

The flexible functionalized graphene-based auxetic nanostructures are freely adapting the wave fields while their phase and amplitude being entirely controlled by design. Computer modelling can be used to define a biocompatible unit-module, as a GO-composite bilayer able to mimic the relationship between the structural composition of the skin and its response to bio-electro-magnetically stimuli. The selective response of the excited system simulates the functional behaviour of the model unit volume, the skin. Aiming to define a biomimetic interface for personalized medicine use, this model brings a real size-shape relationship between the organic and inorganic nanostructures at this scale, properly considering the size-related phenomena.

Circular dichroism enhancement in grapheme with planar metal nanostructures: A computational study

Circular dichroism (CD) is widely used in bio-sensing, chemical analysis, and negative refraction. However, a concise method is required to enhance CD in planar chiral plasmonic nanostructures. In this work, graphene ribbons (GRs) are introduced in planar h-shaped-metal chiral nanostructures (PHCNs) to enhance CD. Calculated results show that the absorption spectra of PHCNs are differently enhanced because of the plasmonic coupling between PHCNs and GRs under different circularly polarized lights, thereby leading to CD enhancement. The loss distributions of PHCNs@GRs reveal that the loss is transferred from PHCNs to GRs. The current distributions of PHCNs@GRs are regarded as equivalent LC resonant circuits to explain the shift of the CD spectra by tuning the geometrical parameters of PHCNs@GRs. The results help design graphene-based chiral plasmonic nanostructures.

Neutron scattering study of nickel decorated thermally exfoliated graphite oxide

Surface decoration of graphene-based nanostructures with metals has been predicted to be an efficient way towards the development of resistant catalysts and novel materials for energy applications, such as hydrogen production and storage. We report on an extensive neutron scattering study of a defective graphene-based material decorated with nickel nanoparticles, obtained via the chemical decoration of thermally exfoliated graphite oxide. The combination of neutron diffraction and inelastic neutron scattering measurements has been used to characterize the low-dimensional carbon backbone and the presence of the nickel nanoparticles, organized at the nanometer scale on the graphene plane. The structural features of this system, along with the nickel capability of dissociating the hydrogen molecule upon hydrogen treatment, are herein discussed.

Graphene-based hierarchical sandwich-type hybrid nanostructures for optical limiters

Graphene-based multi-layer ordered nanostructures have drawn considerable research interest and revealed great potential for various applications. Here, we constructed silver nanoparticle (NP)/graphene-oxide (GO) hierarchical sandwich-type hybrid nanostructures with the use of a highly efficient and convenient chemical self-assembly method, which might be further extended to fabricate other hierarchical graphene-metal NPs hybrid nanostructures. We characterized the morphology, structure, surface chemical states, and linear optical properties of the materials. A hierarchical sandwich-type hybrid nanostructure was obtained through interactions between silver NPs and amino groups on the GO surface. Owing to the protective effect of the multilayer GO, metallic silver was preserved in the sandwich-type nanostructures. Features in the UV/Vis spectrum of the sandwich-type nanostructure were considerably red-shifted and broadened compared with those of silver NPs on a single sheet of GO. We attribute these changes to enhanced coupling of the collective electron excitation within the silver NPs to the graphene oxide. We investigated the nonlinear optical and optical limiting (OL) properties by a nanosecond open-aperture Z-scan technique at 532 nm. These results showed that the hierarchical sandwich-type hybrid nanostructure underwent an intensity-dependent transformation from saturable absorption to reverse saturable absorption. The OL effect of the hierarchical sandwich-type hybrid nanostructure was greater than that of monolayer graphene oxide with silver NPs at the same linear transmittance. We attribute this enhanced OL performance to the unique sandwich structure, which increased interfacial interactions between graphene oxide and the silver NPs and facilitated charge transfer between the two components. The excellent OL performance of hierarchical sandwich-type hybrid nanostructures arises from a combination of photoinduced electron and/or energy transfer, nonlinear absorption, and nonlinear scattering mechanisms. Together, our results indicate that hierarchical sandwich-type hybrid nanostructures might have extensive applications in optoelectronic fields.

Photoelectrochemical response of Ag-graphene heterostructures: insight into the localized surface plasmon enhanced photocurrent generation process

We present Ag-graphene heterostructures by combining few layer graphene (FLG) with plasmonic silver nanoparticle (AgNP) arrays to boost the photoelectrochemical (PEC) efficiency of graphene-based nanostructures. AgNP arrays with controlled coverage and size distribution were fabricated on the graphene surface by means of gas phase cluster beam deposition. The photocurrent generation process in the FLG-based nanostructures was analyzed with a PEC amperometric measurement. A significant photocurrent enhancement was observed in the AgNPs-FLG heterostructures compared with bare FLG. It was found that the PEC performance was strongly related to the wavelength and power of the incident light, as well as the density and size of the AgNPs. The enhancement of the PEC response was attributed to the effect of the surface plasmon local fields of the AgNPs, which induce efficient generation and quick separation of the electron–hole pairs in FLG.

Fabrication of Graphene/Molybdenum Disulfide Composites and Their Usage as Actuators for Electrochemical Sensors and Biosensors.

From the rediscovery of graphene in 2004, the interest in layered graphene analogs has been exponentially growing through various fields of science. Due to their unique properties, novel two-dimensional family of materials and especially transition metal dichalcogenides are promising for development of advanced materials of unprecedented functions. Progress in 2D materials synthesis paved the way for the studies on their hybridization with other materials to create functional composites, whose electronic, physical or chemical properties can be engineered for special applications. In this review we focused on recent progress in graphene-based and MoS2 hybrid nanostructures. We summarized and discussed various fabrication approaches and mentioned different 2D and 3D structures of composite materials with emphasis on their advances for electroanalytical chemistry. The major part of this review provides a comprehensive overview of the application of graphene-based materials and MoS2 composites in the fields of electrochemical sensors and biosensors.

Synthesis of Three-Dimensional Graphene-Based Hybrid Materials for Water Purification: A Review.

Graphene-based nanostructures and nanomaterials have been widely used for the applications in materials science, biomedicine, tissue engineering, sensors, energy, catalysis, and environmental science due to their unique physical, chemical, and electronic properties. Compared to two-dimensional (2D) graphene materials, three-dimensional (3D) graphene-based hybrid materials (GBHMs) exhibited higher surface area and special porous structure, making them excellent candidates for practical applications in water purification. In this work, we present recent advances in the synthesis and water remediation applications of 3D GBHMs. More details on the synthesis strategies of GBHMs, the water treatment techniques, and the adsorption/removal of various pollutants from water systems with GBHMs are demonstrated and discussed. It is expected that this work will attract wide interests on the structural design and facile synthesis of novel 3D GBHMs, and promote the advanced applications of 3D GBHMs in energy and environmental fields.

Synthesis of Single-Crystalline Hexagonal Graphene Quantum Dots from Solution Chemistry.

Graphene-based carbon nanostructures with nanometer dimensions have been of great interest due to the existence of a bandgap. So far, well-ordered edge structure and uniformly synthesized graphene quantum dots (GQDs) with a hexagonal single-crystalline structure have not been directly observed owing to the limited precision of current synthesis approaches. Herein, we report on a novel approach not just for the synthesis of the size-controlled single-crystalline GQDs with hexagonal shape but also for a new discovery on constructing 2D and 3D graphene single crystal structures from d-glucose via catalytic solution chemistry. With size-controlled single-crystalline GQDs, we elucidated the crucial role of edge states on luminescence from the correlation between their crystalline size and exciton lifetime. Furthermore, blue-emissive single-crystalline GQDs were used as an emitter on light-emitting diodes and exhibit stable deep-blue emission regardless of the voltage and doping level.

High-performance microwave absorption of hierarchical graphene-based and MWCNT-based full-carbon nanostructures

A creative fabrication strategy is proposed for synthesizing two kinds of hierarchical graphene-based and MWCNT-based full-carbon nanostructures (FCNS), both of which are excellent microwave absorption (MA) fillers. Through using precursor graphite and MWCNTs, the FCNSs are prepared by simple ultrasonic exfoliation/dispersion and exothermal erosion methods. The hierarchical carbon nanostructures (carbon nanoparticles, carbon nanofilms and carbon hollow hemispheres) and abundant interfaces in FCNSs generate strong dielectric loss. Consequently, the FCNSs present ideal microwave impedance match, attenuation characteristics and excellent MA properties. Results show that the MWCNT-based FCNS and graphene-based FCNS composites achieve extremely strong absorption with minimum microwave reflection loss (RL) values of −58 dB with a thickness of 2.6 mm and −54 dB with a thickness of only 1.2 mm, respectively. And the effective absorption bandwidth (RL < −10 dB) can be reached to 3.44 GHz at 1.4 mm and 4.3 GHz at 1.1 mm, respectively. Moreover, we also elaborate on the fundamental MA mechanism and correlation between the nanostructures and MA properties. The ultrathin MAM can be used as predominant candidate with strong MA properties and wide bandwidth.

Revealing the trap emission in graphene-based nanostructures

Enhancing the photoconversion efficiency of graphene-based nanomaterials, especially graphene quantum dots (GQDs) and graphene nanoribbons (GNRs), has been a long pursued interest in diverse optical applications. Though chemical modification has shown its effectiveness to enhance the photoluminescence efficiencies of these materials, an accurate, comprehensive fundamental understanding of this enhancement is demanded for further development. Herein, density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations reveal that chemical species on the graphene nanostructure surface perturb the intrinsic electronic structures of the graphene moiety, with the perturbation manner and extent crucially depending on the binding positions of the species. In several configurations studied, the surface species lead to significantly enlarged oscillator strengths for the lowest optical transition (S1→S0) and localized excitons (bounded electron and hole) compared to those of the pristine nanographene structures, indicative of their role in enhancing the photoluminescence as emission centers. By contrast, the surface species in the other configurations show trivial influence on the emission efficiency, as indicated by the only slightly altered electronic/excitonic structures and oscillator strengths. These results provide a fundamental understanding of the trap emission mechanism and also the tuning/engineering of photoluminescence efficiencies in relevant materials.

Coexistence of two graphene-induced modulation effects on surface plasmons in hybrid graphene plasmonic nanostructures.

Integrating gate-tunable graphene with plasmonic nanostructures or metamaterials offers a great potential in achieving dynamic control of plasmonic response. While remarkable progress has been made in realizing efficient graphene-induced modulations of plasmon resonances, a full picture of graphene-plasmon interactions and the consequent deep understanding on graphene-enabled tuning mechanism remain largely unexplored. Here, we theoretically identify, for the first time, two distinct modulation effects that can coexist in graphene-based plasmonic nanostructure: graphene can influence the plasmon resonances by either acting as equivalent nanocircuit elements or effectively altering their excitation environment, leading to totally different tuning behaviors. A general dependency of tuning features on the graphene-induced impedance, irrespective of structure geometries, is established when graphene serves as nanocircuit elements. We demonstrate that these two modulation effects can be dynamically controlled by appropriately integrating graphene with plasmonic nanostructures, which provide an active window for efficient modulation of surface plasmons. Our findings may pave the way towards realizing dynamic control of plasmonic response, which holds great potential applications in graphene-based active nanoplasmonic devices.

Universal Method for Producing Reduced Graphene Oxide/Gold Nanoparticles Composites with Controlled Density of Grafting and Long-Term Stability.

In this study, we report a universal approach allowing the non-covalent deposition of gold nanoparticles on reduced graphene oxide surface in a controlled fashion. We used a modified Hummers method to obtain graphene oxide, which then underwent surficial functionalization with carboxyl moieties coupled with simultaneous reduction. Nanoparticles were synthesized ex-situ and capped with a thiolated poly-ethylene glycol (PEG) ligand. The interactions between the surface of modified graphene oxide and nanoparticle ligands enabled the formation of stable hybrid graphene-nanoparticles materials in the aqueous phase. Using this technique, we were able to cover the surface of graphene with gold nanoparticles of different shapes (spheres, rods, triangles, stars, and bipyramids), broad range of sizes (from 5 nm to 100 nm) and controlled grafting densities. Moreover, materials obtained with this strategy exhibited long-term stability, which coupled with the versatility and facility of preparation, makes our technique appealing in the light of increasing demand for new graphene-based hybrid nanostructures.

Model of Field Electron Emission from the Edge of Flat Graphene into Vacuum

Graphene-based nanostructures are the promising materials for applications as electron emitters.The aim of the work is to study the field electron emission from the edge of a single graphene plane.In the semi-classical approximation, a model of field electron emission from the edge of a rectangular graphene sheet has been developed.The current density of field electron emission into vacuum from the edge of a flat graphene sheet was calculated depending on the magnitude of the pulling electric field strength.The analysis and comparison of limiting emission currents from graphene and from bulk systems have been carried out.The results of the work can be used in the development of graphene-based field effect cathodes.

Terahertz plasmon-induced transparency and absorption in compact graphene-based coupled nanoribbons

We investigate theoretically and numerically the possibility of realizing plasmon-induced transparency (PIT) and plasmon-induced absorption (PIA) in a novel compact graphene-based nanostructure. The main graphene bus waveguide is coupled to two graphene nanoribbons (GNRs). The PIT effect is obtained by setting the two GNRs in an inverted L-shape aside of the main waveguide, giving rise to lambda-like configuration in analogy with three atomic-level systems. The possibility of improving the quality factors of PIT-like resonances is shown and the associated slow light effects are showcased. The mechanism behind the observed transparency windows is related to mode splitting also known as Autler–Townes splitting phenomenon. Two PIA resonances are also demonstrated by the same system. This is achieved by inserting the two GNRs, forming an inverted T-shape, inside the main waveguide. Here the two GNRs are also set in a lambda-like configuration. We indicate the possibility of improving the Q-factor of the PIA resonances and showcase their fast light features. The PIA absorption bands are shown to be essentially caused by interference phenomena between three states as in electromagnetic-induced transparency. The proposed system may help the design of tunable integrated optical devices such as sensors, filters or high speed switches.

Deciphering the Impact of Surface Defects and Functionalization on the Binding Strength and Electronic Properties of Graphene–Polypyrrole Nanocomposites: A First-Principles Approach

The distinct effectiveness of graphene-based nanostructures, including pristine graphene, graphene with Stone–Wales defects, graphene oxides, and multilayered graphene materials, toward the develop...