Graphene Oxide Heterostructure Research Articles

Layered Assembly of Reduced Graphene Oxide and Vanadium Oxide Heterostructure Supercapacitor Electrodes with Larger Surface Area for Efficient Energy-Storage Performance

The architecture of a supercapacitor (SC) electrode plays a crucial role in defining the overall energy-storage performance of the SC. Layer-by-layer assembly of a reduced graphene oxide (rGO) and vanadium oxide (V2O5) (rGO/V2O5)-based heterostructure is patterned in interdigitated electrodes (IDEs) deposited directly on a flexible conducting current collector for the SC. The IDE pattern offers efficient accessibility to the electrolyte ions and a synergistic contribution for energy storage. An as-fabricated solid-state flexible sandwich-type SC with IDEs displays a more efficient energy-storage performance than a conventional solid-state flexible sandwich-type SC composed of rGO/V2O5 electrodes. Moreover, a solid-state flexible in-plane microsupercapacitor (MSC) is fabricated, which offers much higher capacitance (24 mF/cm2 and 34.28 F/cm3) and energy density (3.3 μWh/cm2 and 4.7 mWh/cm3). The as-fabricated flexible in-plane MSC displays a negligible capacitance loss of about 6.3% after 10 000 charge–dis...

Synthesis of Nb doped TiO2 nanotube/reduced graphene oxide heterostructure photocatalyst with high visible light photocatalytic activity

Limited by the narrowed photoresponse range and unsatisfactory recombination of photoinduced electron-hole pairs, the photocatalytic efficiency of TiO2 is still far below what is expected. Here, we initially doped TiO2 nanotubes (TNTS) by transition metal ion Nb, then it is coupled with reduced graphene oxide (rGO) to construct a heterostructure photocatalyst. The defect state presented in TiO2 leading to the formation of localized midgap states (MS) in the bandgap, which regulating the band structure of TiO2 and extending the optical absorption to visible light region. The internal charge transport and transfer behavior analyzed by electrochemical impedance spectroscopy (EIS) reveal that the coupling of rGO with TNTS results in the formation of electron transport channel in the heterostructure, which makes a great contribution to the photoinduced charge separation. As expected, the Nb-TNTS/rGO exhibits a stable and remarkably enhanced photocatalytic activity in the visible-light irradiation degradation of methylene blue (MB), up to ∼5 times with respect to TNTS, which is attributed to the effective inhibition of charge recombination, the reduction of bandgap and higher redox potential, as well as the great adsorptivity.

Enhanced visible light driven photocatalytic activity of CdO–graphene oxide heterostructures for the degradation of organic pollutants

Synthesis of efficient CdO based photocatalysts for enhanced visible light driven photocatalytic degradation of organic pollutants mostly emphasize on (1) increase of surface area of the photocatalyst and (2) high charge separation and suppressed recombination of photogenerated electron–hole pairs.

Development of defects in ZnO/RGO composites under wet chemical synthesis

ZnO/reduced graphene oxide (RGO) heterostructures were fabricated using a simple two-step wet chemical technique and post-annealing treatment. ZnO nanoparticles with different sizes (20–200 nm) and shapes were randomly distributed on mono- and/or multi-layered RGO sheets. The microstructures of the ZnO/RGO composites examined using transmission electron microscopy indicated that the heterostructures are polycrystalline in nature, implying the possibilities of diverse defects present in the samples. The photoluminescence spectra examinations revealed the enhancement of defect-level emission peaks observed at a relatively long wavelength ranges (i.e., 779 nm, 666 nm, and 574 nm) as compared with the band to band transition observed at relatively short wavelengths (i.e., 378 nm).

Transfiguring UV light active “metal oxides” to visible light active photocatayst by reduced graphene oxide hypostatization

This work explains about the visible light photocatalytic activities of wide band gap metal oxides (TiO2, ZnO, CeO2, Eg>3.0eV) after the overture of reduced graphene oxide. The reduced graphene oxide and metal oxide heterostructures (RGO-MO) Ca. RGO-TiO2, RGO-ZnO, RGO-CeO2 were synthesized through microwave, template assisted, and hydrothermal methods respectively. This explains about the activity of the photocatalysts towards hydrogen production via water splitting, water treatment towards inorganic contaminants with or without dye sensitization activity as well. RGO-MO having particle size 5–10nm which shows great activity towards various photocatalytic activities. Pure TiO2, CeO2 and ZnO are UV active semiconductors having wide band gap 3.2eV. However, when these semiconductors are modified with RGO they are showing better visible light activity towards photoreduction of Chromium (VI) and hydrogen production by half reaction of water.

Nonlinear Optical Properties and Temperature Dependent Photoluminescence in hBN-GO Heterostructure 2D Material

Recently, there has been a renaissance in theoretical and experimental studies on 2D heterostructures of two 2D wonder materials, namely graphene and hexagonal boron nitride (hBN) having plethora of application potentials in fundamental research as well as in developments of new technological devices. However, the nonlinear optical (NLO) property of hexagonal boron nitride nanosheets–graphene oxide (BNNS–GO) heterostructure has hitherto remained unexplored. Here, in this work NLO properties of BNNS–GO have been reported, for the first time, in the visible region by Z-scan technique in nanosecond regime. Nonlinear absorption coefficient (β2PA) and third order nonlinear susceptibility (χ3) of BNNS–GO have been found to be enhanced significantly by 13.4% and 21.7%, respectively in compared to those of bare BNNS. The synthesized heterostructure is showing a superior optical limiting property as compared to that of bare BNNS. The change in polarizabilities of GO sheets with the insertion of hBN in its framewor...

Cu2ZnSnS4/MoS2-Reduced Graphene Oxide Heterostructure: Nanoscale Interfacial Contact and Enhanced Photocatalytic Hydrogen Generation

Hydrogen generation from water using noble metal-free photocatalysts presents a promising platform for renewable and sustainable energy. Copper-based chalcogenides of earth-abundant elements, especially Cu2ZnSnS4 (CZTS), have recently arisen as a low-cost and environment-friendly material for photovoltaics and photocatalysis. Herein, we report a new heterostructure consisting of CZTS nanoparticles anchored onto a MoS2-reduced graphene oxide (rGO) hybrid. Using a facile two-step method, CZTS nanoparticles were in situ grown on the surface of MoS2-rGO hybrid, which generated high density of nanoscale interfacial contact between CZTS and MoS2-rGO hybrid. The photoexcited electrons of CZTS can be readily transported to MoS2 through rGO backbone, reducing the electron-hole pair recombination. In photocatalytic hydrogen generation under visible light irradiation, the presence of MoS2-rGO hybrids enhanced the hydrogen production rate of CZTS by 320%, which can be attributed to the synergetic effect of increased charge separation by rGO and more catalytically active sites from MoS2. Furthermore, this CZTS/MoS2-rGO heterostructure showed much higher photocatalytic activity than both Au and Pt nanoparticle-decorated CZTS (Au/CZTS and Pt/CZTS) photocatalysts, indicating the MoS2-rGO hybrid is a better co-catalyst for photocatalytic hydrogen generation than the precious metal. The CZTS/MoS2-rGO system also demonstrated stable photocatalytic activity for a continuous 20 h reaction.

Controlling of the electronic properties of WS2 and graphene oxide heterostructures from first-principles calculations

We investigated the structural stability and electronic properties of WS2 and graphene oxide (GO) heterostructures via first-principles calculations. It is found that the band gap and the work function of the WS2/GO heterostructures can be efficiently tuned by changing the oxygen functionals and its concentrations.

1D Cu@Ni nanorods anchored on 2D reduced graphene oxide with interfacial engineering to enhance microwave absorption properties

In this work, one-dimensional core–shell Cu@Ni nanorods which were anchored on two dimensional reduced graphene oxide (rGO) heterostructures were successfully prepared by a simple co-reduction method.

Porous copper–graphene heterostructures for cooling of electronic devices

Recently, research on micro-electronic and optoelectronic devices has been rapidly increasing. Parts and products related to these devices are becoming smaller and more integrated within circuits. As a result, the heat generated in devices has increased greatly. When excess heat is generated, important properties are affected such as efficiency and lifetime and, in severe cases, this can result in the failure of devices. Therefore, efficient cooling is required and it becomes necessary to study the heat dissipation properties of device materials. Research on heat-dissipating materials with high thermal conductivities and large surface areas, and which can transfer heat rapidly to facilitate progressive heat-release, is being actively pursued. In this study, a porous copper with reduced graphene oxide (pCu-rGO) heterostructure was fabricated by thermal annealing using Cu powder and GO. The thermal properties were then investigated and the results indicated that the pCu-rGO heterostructure exhibits a higher thermal conductivity than porous Cu. In addition, the thermal resistance of the sample was measured by applying it as a heat sink of a light emitting diode (LED). The result was 18.33% lower than that of bulk Cu. Also, when an overcurrent of 750 mA was applied for 144 hours, the luminance of bulk Cu decreased from 100% to 86.07%. On the other hand, the pCu-rGO showed that the luminance was maintained at 95.64%. Therefore, it is expected to resolve the existing problem of heat generation in electronic and optical devices.

Langmuir-Blodgett assembly of visible light responsive TiO2 nanotube arrays/graphene oxide heterostructure

The hybrid nanocomposites of titanium dioxide (TiO2) with graphene oxide (GO) have recently garnered much attention as electronic devices, energy conversion devices, photocatalysts and other applications. In this study, Langmuir-Blodgett (LB) assembly method was firstly reported to prepare a TiO2 nanotube arrays (TNA)-GO heterostructure. The as-prepared TNA-GO sample was characterized by X-ray diffraction, Raman spectra, scanning electron microscopy, transmission electron microscopy, energy dispersive X-ray spectroscopy and X-ray photoelectron spectroscopy. The promising characteristics of this TNA-GO material, the inexpensive, nontoxic and highly visible-light responsiveness, may raise the potential uses in many, various photocatalytic applications.

Microwave heating time dependent synthesis of various dimensional graphene oxide supported hierarchical ZnO nanostructures and its photoluminescence studies

Microwave heating reaction time dependent various graphene oxide based zinc oxide (G-ZnO) heterostructures such as graphene oxide-ZnO microcubes (GZMC), graphene oxide-ZnO nanoflakes (GZNF) and graphene oxide-ZnO nanoneedles (GZNN) are synthesized by simple and cost effective microwave assisted exfoliation method. These heterostructures supported on graphene oxide nanosheets (GNSs) represent three dimensional (3D) ZnO microcubes and various confined two dimensional (2D) nanoflakes and one dimensional (1D) ZnO nanoneedles like structures. The recorded PL intensity variations show the strong evidence of the interfaces interaction between graphene oxide and ZnO heterostructures. However the differences in the PL intensities are also caused by the 3D and various confined G-ZnO heterostructures. The photoluminescence characterization of GZMC, GZNF and GZNN nanostructures exhibit a decrement in the PL intensity. The PL intensity of the GZNN is lowered by 67.50% and 39.7%to the GZMC and GZNF nanostructures respectively. The results show that ZnO heterostructures grown on GNSs with different morphologies and dimensionalities exhibit the variation in PL intensity due to preventing a direct recombination of the electrons and holes in ZnO. A tentative growth mechanism has been given for the growth of various graphene based zinc oxide heterostructures.

Facile Synthesis of Hierarchical Cu2MoS4 Hollow Sphere/Reduced Graphene Oxide Composites with Enhanced Photocatalytic Performance

We present a controllable synthesis of ternary hierarchical hollow sphere, assembling by numerous particle-like Cu2MoS4, via a facile hydrothermal method. By adding graphene oxides (GO) in the reaction process, Cu2MoS4/reduced graphene oxide (RGO) heterostructures were obtained with enhanced photocurrent and photocatalytic performance. As demonstrated by electron microscopy observations and X-ray characterizations, considerable interfacial contact was achieved between hierarchical Cu2MoS4 hollow sphere and RGO, which could facilitate the separation of photoinduced electrons and holes within the hybrid structure. In comparison with the pure Cu2MoS4 hollow sphere, the obtained hybrid structures exhibited significantly enhanced light absorption property and the ability of suppressing the photoinduced electron–holes recombination, which led to significant enhancement in both photocurrent and efficiency of photocatalytic methyl orange (MO) degradation under visible light (λ > 420 nm) irradiation.

Strong interlayer coupling mediated giant two-photon absorption inMoSe2/graphene oxide heterostructure: Quenching of exciton bands

A complex few-layer $\mathrm{MoS}{\mathrm{e}}_{2}$/graphene oxide (GO) heterostructure with strong interlayer coupling was prepared by a facile hydrothermal method. In this strongly coupled heterostructure, we demonstrate a giant enhancement of two-photon absorption that is in stark contrast to the reverse saturable absorption of a weakly coupled $\mathrm{MoS}{\mathrm{e}}_{2}$/GO heterostructure and saturable absorption of isolated $\mathrm{MoS}{\mathrm{e}}_{2}$. Spectroscopic evidence of our study indicates that the optical signatures of isolated $\mathrm{MoS}{\mathrm{e}}_{2}$ and GO domains are significantly modified in the heterostructure, displaying a direct coupling of both domains. Furthermore, our first-principles calculations indicate that strong interlayer coupling between the layers dramatically suppresses the $\mathrm{MoS}{\mathrm{e}}_{2}$ excitonic bands. We envision that our findings provide a powerful tool to explore different optical functionalities as a function of interlayer coupling, which may be essential for the development of device technologies.

Reduced TiO2-Graphene Oxide Heterostructure As Broad Spectrum-Driven Efficient Water-Splitting Photocatalysts.

The reduced TiO2-graphene oxide heterostructure as an alternative broad spectrum-driven efficient water splitting photocatalyst has become a really interesting topic, however, its syntheses has many flaws, e.g., tedious experimental steps, time-consuming, small scale production, and requirement of various additives, for example, hydrazine hydrate is widely used as reductant to the reduction of graphene oxide, which is high toxicity and easy to cause the second pollution. For these issues, herein, we reported the synthesis of the reduced TiO2-graphene oxide heterostructure by a facile chemical reduction agent-free one-step laser ablation in liquid (LAL) method, which achieves extended optical response range from ultraviolet to visible and composites TiO(2-x) (reduced TiO2) nanoparticle and graphene oxide for promoting charge conducting. 30.64% Ti(3+) content in the reduced TiO2 nanoparticles induces the electronic reconstruction of TiO2, which results in 0.87 eV decrease of the band gap for the visible light absorption. TiO(2-x)-graphene oxide heterostructure achieved drastically increased photocatalytic H2 production rate, up to 23 times with respect to the blank experiment. Furthermore, a maximum H2 production rate was measured to be 16 mmol/h/g using Pt as a cocatalyst under the simulated sunlight irradiation (AM 1.5G, 135 mW/cm(2)), the quantum efficiencies were measured to be 5.15% for wavelength λ = 365 ± 10 nm and 1.84% for λ = 405 ± 10 nm, and overall solar energy conversion efficiency was measured to be 14.3%. These findings provided new insights into the broad applicability of this methodology for accessing fascinate photocatalysts.

A selector device based on graphene–oxide heterostructures for memristor crossbar applications

Most of the potential applications of memristive devices adopt crossbar architecture for ultra-high density. One of the biggest challenges of the crossbar architecture is severe residue leakage current (sneak path) issue. A possible solution is introducing a selector device with strong nonlinear current–voltage (I–V) characteristics in series with each memristor in crossbar arrays. Here, we demonstrate a novel selector device based on graphene–oxide heterostructures, which successfully converts a typical linear TaO x memristor into a nonlinear device. The origin of the nonlinearity in the heterostructures is studied in detail, which highlights an important role of the graphene–oxide interfaces.

Photocatalytic hydrogen generation of ZnO rod–CdS/reduced graphene oxide heterostructure prepared by Pt-induced oxidation and light irradiation-assisted methods

A synthesis method including Pt-induced oxidation and light irradiation-assisted routes has been developed to prepare a ZnO rod–CdS/reduced graphene oxide (RGO) heterostructure. Here, graphene oxide nanosheets are reduced and loaded onto the surface of Zn spheres using a redox process. ZnO rods are generated from Zn spheres by a Pt-induced oxidation method, and CdS nanoparticles are then loaded onto the surface of RGO via a light irradiation-assisted method. The ZnO rod–CdS/RGO heterostructure exhibits 3.8 times higher photocatalytic hydrogen generation rate from an aqueous solution containing Na2S/Na2SO3 than the reference ZnO rod–CdS heterostructure under simulated solar light irradiation. The optimal contents of RGO nanosheets and CdS nanoparticles are 2wt% and 20at.%, respectively.

High efficiency electron field emission from protruded graphene oxide nanosheets supported on sharp silicon nanowires

Graphene oxide (GO) potentially has applications in vacuum microelectronic devices for realization of field emission displays. Graphene and its derivatives are expected to be efficient field emitters due to their unique electrical properties. However, the flat sheet structure of graphene or GO allows electron field emission only from the edges of graphene and GO nanosheets. In order to extract maximum field emission current density at lower applied voltage from the GO nanosheets, we supported and stretched them on sharp tips of silicon nanowires (SiNWs). Highly efficient and stable field emission with low turn-on field was observed for these SiNW–GO heterostructures. The sharp protrusions created by stretching of the GO nanosheets on SiNWs locally enhance the electric field and thus enhance the field emission characteristics. The dominant use of silicon in electronic devices makes this approach robust for the development of field emission devices using graphene based field emitters.