Graphene-based Hybrid Nanostructures Research Articles

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.

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.

Increasing the biocompatibility of graphene-based hybrid nanostructures with glycopolymer

Hybrid nanostructures decorated with glycopolymers are appropriate for biomedical applications. In this paper, the results are obtained from nanographene (NG) decorated with glycoblock copolymer to increase their potential in use in therapies and in examining lectin interactions. A pyren-1-ylmethyl 4-cyano-4-((phenylcarbonothioyl)thio)pentanoate (CPADB-py) chain transfer agent was used in the synthesis of methyl methacrylate glycoblock copolymers (P2 and P3) by reversible addition-fragmentation chain transfer (RAFT) polymerization to adhere the polymer to the nanographene surface. Hybrid nanographenes (NG-1 and NG-2) were obtained by the non-covalent interaction of deprotected P2 and P3 with different fructopyranose groups (3-O-methacryloyl-1,2:4,5- di-O-isopropylidene-β-D-fructopyranose and 1-O-methacryloyl-2,3:4,5-di-O-isopropylidene-β-D-fructopyranose) in their backbones. Images obtained from transmission electron microscopy (TEM) of NG-1 and NG-2 show that glycoblock copolymer coating was performed homogeneously. Moreover, thermal gravimetric analysis (TGA) also confirmed a glycoblock copolymer coating of NG-1 and NG-2 by weight loss of 41% and 31%, respectively. In the last step of the study, the binding ability of glycoblock copolymers (P2-hyd and P3-hyd) with concanavalin A (ConA) lectin was investigated by a turbidimetric assay. Promising results were obtained from P3-hyd for the ConA interactions. Hence, this study may open a new avenue in the design of new multifunctional glyconanomaterials that show favorable binding properties with lectins.

Metal/Metal Oxide Modified Graphene Nanostructures for Electrical Biosensing Applications: A Review

Tremendous accomplishments have been made in the field of metal/metal oxide modified graphene nanostructures to overcome the problems of agglomeration and restacking in graphene biosensors. Some review articles are available on electrochemical biosensing applications of graphene based composites and hybrids. However, none of them have made significant contributions in their applications in the domain of field effect transistor (FET) and impedance biosensors. In this manuscript, the authors analytically summarize not only the state-of-the art electrochemical biosensors using metal/metal oxide modified graphene but also a detailed discussion on FET and impedance-based biosensors has been presented along with the comprehensive physics behind enhanced sensing performance of such devices. It has been observed that sub-femtomolar detection limits are achievable using FET and impedance based label free sensing which has been attributed to the metal nanoparticle induced modulation in band gap. Moreover, the technological advancements in the synthesis techniques based on encapsulation of various metal nanoforms onto electrochemically activated graphene to initiate more reactive sites on the graphene surface have been thoroughly compiled. Despite these advances, the use of graphene-based hybrid nanostructures for biosensors is still in its early stages and we have highlighted the existing challenges and indicated the future research direction.

Electric Directional Steering of Cathodoluminescence From Graphene-Based Hybrid Nanostructures

Controlling directional emission of nanophotonic radiation sources is fundamental to tailor radiation-matter interaction and to conceive highly efficient nanophotonic devices for on-chip wireless communication and information processing. Nanoantennas coupled to quantum emitters have proven to be very efficient radiation routers, while electrical control of unidirectional emission has been achieved through inelastic tunneling of electrons. Here we prove that the radiation emitted from the interaction of a high-energy electron beam with a graphene-nanoparticle composite has beaming directions which can be made to continuously span the full circle even through small variations of the graphene Fermi energy. Emission directionality stems from the interference between the double cone shaped electron transition radiation and the nanoparticle dipolar diffraction radiation. Tunability is enabled since the interference is ruled by the nanoparticle dipole moment whose amplitude and phase are driven by the hybrid plasmonic resonances of the composite and the absolute phase of the graphene plasmonic polariton launched by the electron, respectively. The flexibility of our method provides a way to exploit graphene plasmon physics to conceive improved nanosources with ultrafast reconfigurable radiation patterns.

Increasing the biocompatibility of graphene-based hybrid nanostructures with glycopolymer.

Hybrid nanostructures decorated with glycopolymers are appropriate for biomedical applications. In this paper, the results are obtained from nanographene (NG) decorated with glycoblock copolymer to increase their potential in use in therapies and in examining lectin interactions. A pyren-1-ylmethyl 4-cyano-4-((phenylcarbonothioyl)thio)pentanoate (CPADB-py) chain transfer agent was used in the synthesis of methyl methacrylate glycoblock copolymers (P2 and P3) by reversible addition-fragmentation chain transfer (RAFT) polymerization to adhere the polymer to the nanographene surface. Hybrid nanographenes (NG-1 and NG-2) were obtained by the non-covalent interaction of deprotected P2 and P3 with different fructopyranose groups (3-O-methacryloyl-1,2:4,5-di-O-isopropylidene-β-D-fructopyranose and 1-O-methacryloyl-2,3:4,5-di-O-isopropylidene-β-D-fructopyranose) in their backbones. Images obtained from transmission electron microscopy (TEM) of NG-1 and NG-2 show that glycoblock copolymer coating was performed homogeneously. Moreover, thermal gravimetric analysis (TGA) also confirmed a glycoblock copolymer coating of NG-1 and NG-2 by weight loss of 41% and 31%, respectively. In the last step of the study, the binding ability of glycoblock copolymers (P2-hyd and P3-hyd) with concanavalin A (ConA) lectin was investigated by a turbidimetric assay. Promising results were obtained from P3-hyd for the ConA interactions. Hence, this study may open a new avenue in the design of new multifunctional glyconanomaterials that show favorable binding properties with lectins.

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.

Plasmonic metamaterial-based chemical converted graphene/TiO2/Ag thin films by a simple spray pyrolysis technique

Graphene based hybrid nanostructures have received special attention in both the scientific and technological development due to their unique physicochemical behavior, which make them attractive in various applications such as, batteries, supercapacitors, fuel cells, solar cells, photovoltaic devices and bio-sensors. In the present study, the role of plasmonic metamaterials in light trapping photovoltaics for inorganic semiconducting materials by a simple and low cost spray pyrolysis technique has been studied. The plasmonic metamaterials thin film has been fabricated by depositing chemically converted graphene (CCG) onto TiO2-Ag nanoparticles which has a low resistivity and a low electron–hole recombination probability. The localized surface plasmon resonance at the metal-dielectric interface for the Ag nanoparticles has been observed at 403nm after depositing chemical converted graphene (CCG) on the TiO2-Ag thin film. The results suggest that the stacking order of the CCG/TiO2/Ag plasmonic metamaterials samples did not change the band gap of TiO2 while it changed the conductivity of the film. Thus the diffusion of the noble metals in the glass and TiO2 matrices based thin films can trap the light of a particular wavelength by mean of plasmonic resonance and may be useful for superior photovoltaic and optoelectronic applications.

Hydrothermal Synthesis of a rGO Nanosheet Enwrapped NiFe Nanoalloy for Superior Electrocatalytic Oxygen Evolution Reactions.

Graphene-based hybrid nanostructures possess many advantages in the field of electrochemical energy applications. In this work, a facile and efficient hydrothermal approach has been developed for the preparation of NiFe alloy nanoparticles/rGO hybrid nanostructures, in which the nanoparticles are well combined with rGO nanosheets and the size of the nanoparticles is about 100 nm. Moreover, the electrochemical oxygen evolution reaction (OER) tests confirmed that the obtained NiFe/rGO hybrid nanostructures possess notably higher activity than both the rGO-free NiFe nanoparticles and pure Ni/rGO hybrids, and the optimal NiFe ratio is 2:1. The OER overpotential at 20 mA cm(-1-2) with Ni2 Fe/rGO is as low as 0.285 V, which is 96 mV lower than that of pure Ni/rGO hybrids. Meanwhile, the Ni2 Fe/rGO catalyst has excellent stability. Therefore, this work contributes a facile and efficient method to prepare a NiFe alloy nanoparticles/rGO hybrid structure for potential applications in the field of electrochemical energy devices, such as electrochemical water splitting cells, rechargeable metal/air batteries, etc.

Recent advances in graphene-based hybrid nanostructures for electrochemical energy storage.

In recent years, graphene has emerged as a promising candidate for electrochemical energy storage applications due to its large specific surface area, high electrical conductivity, good chemical stability, and strong mechanical flexibility. Moreover, its unique two-dimensional (2D) nanostructure can be used as an ideal building block for controllable functionalization with other active components and the resulting graphene-based hybrids exhibit desirable properties for improved energy storage capability. This review summarizes the most recent progress on graphene and graphene-based hybrid nanostructures for three frontier electrochemical energy storage device applications, i.e., lithium-ion batteries, lithium-sulfur batteries and supercapacitors. Finally, we outline the future perspectives and trends in this research field including several challenges and opportunities.

Fabrication of hierarchical nanohybrids with assistance of supercritical CO<sub>2</sub> for high-performance supercapacitor applications

Graphene,a novel one-atom-thick two-dimensional(2D) nanomaterial,has attracted much attention,owing to its outstanding chemical and physical properties. In order to expand the application of graphene-based materials in environment,energy,biological and sensing fields,it is necessary to assemble 2D graphene sheets into three-dimensional(3D) architectures. It may furnish graphene materials with higher specific surface areas,stronger mechanically strengths and faster mass and electron transport kinetics because of the combination of 3D porous structure and the outstanding intrinsic properties of graphene. Building 3D graphene-based hybrid nanostructures with anticipated function has become one of the most active research fields. Considering the single-phased nanomaterials always have their intrinsic defects,scientists are inclined to combine unique properties of individual nanostructures and explore their synergistic effect. Considering its low viscosity,high diffusivity,zero surface tension,and plasticization to polymer,supercritical CO2(sc CO2)has been applied in the fabrication of nanomaterials. In view of the soft matter theory and the great tunabililty of sc CO2,it is anticipated that nanocomposites of tailored structure and controlled assembly of nanoparticles can be achieved with the help of sc CO2. Graphene-pyrrole(G-Py) aerogel was prepared by a green hydrothermal route,while carbon nanotube/polyaniline(CNT/PANI) composite dispersion was obtained via in-situ polymerization method. Then a series of nanohybrids were successfully prepared with the assistance of sc CO2. The obtained nanohybrids were characterized by FTIR,X-ray diffraction,Raman,and their electrochemical performance were further evaluated. It was fascinating to observe that the nanohybrid prepared through one step method with the assistance of sc CO2 had superior performance. Such hybrid materials exhibit significant specific capacitance of up to 373 F g–1,which is 1.4 times that of the nanocomposite without the assistance of sc CO2 electrode. The experimental results are a proof of concept that sc CO2 is an efficient method to help achieve hierarchical multi-component nanohybrids and as well as it may guide the way for designing new functional materials that can be used as electrode materials for lightweight and flexible energy storage device in the near future.

Cl-Doped ZnO Nanowire Arrays on 3D Graphene Foam with Highly Efficient Field Emission and Photocatalytic Properties.

An environmentally friendly, low-cost, and large-scale method is developed for fabrication of Cl-doped ZnO nanowire arrays (NWAs) on 3D graphene foam (Cl-ZnO NWAs/GF), and investigates its applications as a highly efficient field emitter and photocatalyst. The introduction of Cl-dopant in ZnO increases free electrons in the conduction band of ZnO and also leads to the rough surface of ZnO NWAs, which greatly improves the field emission properties of the Cl-ZnO NWAs/GF. The Cl-ZnO NWAs/GF demonstrates a low turn-on field (≈1.6 V μm(-1)), a high field enhancement factor (≈12844), and excellent field emission stability. Also, the Cl-ZnO NWAs/GF shows high photocatalytic efficiency under UV irradiation, enabling photodegradation of organic dyes such as RhB within ≈75 min, with excellent recyclability. The excellent photocatalytic performance of the Cl-ZnO NWAs/GF originates from the highly efficient charge separation efficiency at the heterointerface of Cl-ZnO and GF, as well as improved electron transport efficiency due to the doping of Cl. These results open up new possibilities of using Cl-ZnO and graphene-based hybrid nanostructures for various functional devices.

Atomistic simulation study of mechanical properties of periodic graphene nanobuds

Among the graphene-based hybrid nanostructures, graphene nanobuds (GNBs); a hybrid of graphene/fullerene architecture, are one of the most interesting nanostructured materials. In this study we have investigated the mechanical properties of graphene nanobud through molecular dynamic simulations. The effects of temperature, size of graphene sheet and also neck’s length on the mechanical properties of this novel material were investigated, for the first time. The calculated Young’s modulus ranges from 440 to 760GPa and the failure stress changes from 100 to 200GPa. The results show that the Young’s modulus changes a little with temperature increment while, with increasing the neck’s length the Young’s modulus decreases. We found that with both temperature and neck’s length increment, the failure stress decreases. Furthermore, when the size of graphene sheet was increased all the respected mechanical properties were increased too. These findings will augment the current understanding of the mechanical performance of GNBs, which will conduct the design of GNBs and shed lights on its various applications.

2D Hybrid Nanostructure of Reduced Graphene Oxide-CdS Nanosheet for Enhanced Photocatalysis.

Graphene-based hybrid nanostructures have recently emerged as a new class of functional materials for light-energy conversion and storage. Here, we have synthesized reduced graphene oxide (RGO)-semiconductor composites to improve the efficiency of photocatalysis. Zero-dimensional CdS nanoparticles (0D), one-dimensional CdS nanorods (1D), and two-dimensional CdS nanosheets (2D) are grafted on the RGO sheet (2D) by a surface modification method using 4-aminothiophenol (4-ATP). Structural analysis confirms the attachment of CdS nanocrystals with RGO, and the strong electronic interaction is found in the case of a CdS nanosheet and RGO, which has an influence on photocatalytic properties. The degradation of dye under visible light varies with changing the dimension of nanocrystals, and the catalytic activity of the CdS NS/RGO composite is ∼4 times higher than that of CdS nanoparticle/RGO and 3.4 times higher than that of CdS nanorod/RGO composite samples. The catalytic activity of the CdS nanosheet/RGO composite is also found to be ∼2.5 times than that of pure CdS nanosheet samples. The unique 2D-2D nanoarchitecture would be effective to harvest photons from solar light and transport electrons to reaction sites with respect to other 0D-2D and 1D-2D hybrid systems. This observation can be extended to other graphene-based inorganic semiconductor composites, which can provide a valuable opportunity to explore novel hybrid materials with superior visible-light-induced catalytic activity.

Mesoporous cobalt monoxide nanorods grown on reduced graphene oxide nanosheets with high lithium storage performance

Graphene-based hybrid nanostructures could offer many opportunities for improved lithium storage performance. Herein, we report a facile synthesis of mesoporous CoO nanorods (CoO NRs) on a reduced graphene oxide (rGO) substrate by hydrothermal and calcination treatment. Transmission electron microscopy (TEM) investigation reveals that the CoO NRs with a diameter of 20–60nm are tightly anchored on the surface of rGO sheets. Compared to pure CoO NRs, the CoO NRs/rGO composite shows higher lithium storage capacity and superior rate capability as anode materials for Li-ion batteries. The CoO NRs/rGO composite delivers an initial discharge capacity of 1452 mAh g−1, and it can still remains 960 mAh g−1 after 50 cycles at 0.1 A g−1. After each 10 cycles at 0.1, 0.2, 0.5, and 1 A g−1, the specific capacities of the composite are about 1096, 1049, 934 and 513 mAh g−1, respectively. The enhanced electrochemical performance of the composite is closely related to its unique structure, such as 1D mesoporous morphology of CoO NRs and its tightly-contacting with rGO nanosheets, which could shorten the transport pathway for both electrons and ions, enhance the electrical conductivity and accommodate the volume expansion during prolonged cycling.

Recent progress on graphene-based hybrid electrocatalysts

Graphene-based hybrid nanostructures have attracted increasing interest worldwide. Benefiting from their remarkable electrochemical catalytic properties derived from chemical compositions and synergetic effects of multi-functionalities, these graphene-based hybrid nanomaterials will play a significant role in cutting-edge innovation for novel electrocatalysts. In this review, we summarize recent progress in the design and synthesis of graphene-based hybrid nanomaterials with controlled shape, size, composition and structure, and their application as efficient electrocatalysts for energy related systems. We conclude this article with some future trends and prospects which are highlighted for further investigations on graphene-based nanomaterials as advanced electrocatalysts.

Graphene/Fe3O4 hollow sphere nanocomposites as superior anode material for lithium ion batteries

Graphene wrapped Fe3O4 hollow nanospheres are synthesized via a simple self-assembly process driven by electrostatic interaction. The nanocomposites are characterized by XRD, SEM, TEM, HRTEM, FTIR, cyclic voltammogram and galvanostatic charge/discharge tests. The results demonstrate that the graphene-wrapped Fe3O4 hollow nanospheres present excellent cycling stability and high discharge capacity of 1148mAhg−1 until 50 cycles at 0.2C. Both the graphene wrapped around the surfaces of Fe3O4 hollow nanospheres and the porosity resulting from the void in nanoparticle packing in the overall assembled structure contribute to remarkable electrochemical performance of this material. The developed strategy can be readily generalized to fabricate other graphene-based hybrid nanostructures, which will be promising materials for high-performance electrochemical devices.

Optical properties of functionalized graphene

Hybrid nanostructures are an emerging field in current research. The goal is to tailor material systems with desired electronic or optical properties by functionalization with molecules. Based on the density matrix formalism, we present a theoretical study on the optical properties of graphene functionalized with photoactive spiropyran molecules. Our calculations reveal the impact of the functionalization conditions on the absorption spectrum of graphene-based hybrid nanostructures. In particular, we find that the molecular coverage has a significant effect on the optical transition energy and shape, while the molecular dipole orientation plays a minor role. The external molecular dipole field induces changes in the optical properties of graphene. Inset: The photoactive spiropyran molecules can be optically switched into the merocyanine configuration that is characterized by a pronounced dipole moment [after Guo et al., J. Am. Chem. Soc. 127(43), 15045 (2005)].