Few-layer Graphene Oxide Research Articles

2D Materials Decorated with Ultrathin and Porous Graphene Oxide for High Stability and Selective Surface Activity.

2D black phosphorus (BP) and MXenes have triggered enormous research interest in catalysis, energy storage, and chemical sensing. Unfortunately, the low stability of these materials under practical operating conditions remains a critical bottleneck, particularly as they are prone to oxidization under moisture. In this work, the design and application of stable 2D heterostructures obtained from decorating BP and MXene (Ti3 C2 Tx ) with few-layer holey graphene oxide (FHGO) membranes are presented. In the resulting heterostructured systems, FHGO serves as a multifunctional passivation layer that shields BP or MXene from oxidative degradation, while allowing the selective diffusion of target gas molecules through its micropores and toward the underlying 2D material. Through a case study of dilute NO2 sensing, it is demonstrated that these heterostructures show a greatly enhanced sensing performance under humid conditions, where fast sensing speed and response are consistently observed, and high stability is impressively retained upon repetitive sensing cycles for 1000 min. These results corroborate the efficacy of material decoration with porous FHGO membranes and suggest that this is a generalizable strategy for reliable high-performance applications of 2D materials.

Synthesis of a zinc ferrite effectively encapsulated by reduced graphene oxide composite anode material for high-rate lithium ion storage

Effectively immobilizing nano-sized electrochemical active materials with a 3D porous framework constituted by conductive graphene sheets brings in enhanced lithium ion storage properties. Herein, a reduced graphene oxide (RGO) supported zinc ferrite (ZnFe2O4) composite anode material (ZnFe2O4/RGO) is fabricated by a simple and effective method. Firstly, redox reaction takes place between the oxygen-containing functional groups on few-layered graphene oxide (GO) sheets and controlled quantity of metallic Zn atoms. ZnO nanoparticles are in-situ nucleated and directly grow on GO sheets. Secondly, the GO sheets are completely reduced by abundant Fe atoms, and corresponding γ-Fe2O3 nanoparticles are formed neighboring the ZnO nanoparticles. In this step, 3D porous RGO supporting framework are constructed with γ-Fe2O3@ZnO nanoparticles effectively encapsulated between the RGO layers. Finally, the well-designed γ-Fe2O3@ZnO/RGO intermediate product undergoes a thermal treatment to allow a solid-state reaction and obtains the ZnFe2O4/RGO composite. At a high current rate of 1.0 A·g−1, the ZnFe2O4/RGO composite exhibits an inspiring reversible capacity of 1022 mAh·g−1 for 500 consecutive cycles as anode material for lithium ion batteries. And the insight into the attractive lithium storage performance has been studied in this work.

In-situ synthesis of Ta2O5@few-layered rGO core-shell nanosphere with abundant oxygen vacancies for highly stable lithium-ion battery

Metal oxide is a promising anode material in LIBs, which can be further improved by covering with few-layered graphene oxide (FL-rGO). Furthermore, the formation of oxygen vacancies can greatly improve the electrochemical performance; however, the concentration regulation of oxygen defects remains a challenge. In this work, a facile in situ calcination was explored to synthesize Ta2O5@FL-rGO core-shell nanospheres with abundant oxygen vacancies between Ta2O5 and few-layered graphene oxide. And the as-prepared Ta2O5@FL-rGO exhibited highly electrochemical performance, including superior conductivity, high reversible capacity (442.3 mA h g−1 at 0.1 A g−1 after 100 cycles), good cycling performance (288.7 mA h g−1 at 5 A g−1 over 600 cycles), and excellent rate capability, compared with that of bare Ta2O5 and other Ta2O5 based electrode in the literature.

Proficiency of Few-Layered Graphene Oxide Nanosheets as Promising Sorbents for Dye Pollution Management

AbstractGraphene is an evolving class of carbon nanomaterials whose exceptional adsorption features toward organic compounds have not been well understood. In the current research, a modified Humme...

Highly selective and ultra-low power consumption metal oxide based hydrogen gas sensor employing graphene oxide as molecular sieve

The excellent gas sensing performance of metal oxide based nano- and microstructures, including a fast response time and good sensitivity, is typically limited by their low selectivity. Therefore, novel approaches and strategies are required to gain a precise control of the selectivity. Here, we introduce a nanoporous few-layer graphene oxide (GO) membrane with permeability only to specific gas molecules to improve the selectivity of individual zinc oxide microwires (ZnO MWs) toward hydrogen (H2) gas. The fabricated GO-covered ZnO MWs showed ultra-low power consumption (60−200 nW) and an excellent room temperature H2 gas sensing properties with fast response (114 s) and recovery (30 s) times, and a low detection limit of ∼4 ppm, while no gas response was measured to all other tested gases. As proposed, the gas sensing mechanism is based on selective sieving of H2 gas molecules through the GO membrane and further diffusion to the Schottky contacts, resulting in a decreased barrier height. Being based on a bottom-up fabrication approach, the presented results could have great potential for further technological applications such as high-performance and highly selective ultra-low power metal oxide-based gas sensors, opening new opportunities for the design of nanosensors and their integration in wireless and portable devices.

Improved performance of perovskite solar cells using conjugated polymer-graphene oxide as the passivation material

Organic-inorganic hybrid perovskite solar cells (PSCs) have achieved power conversion efficiency (PCE) from 3.8% to 25.2% in recent years. However, the charge transport ability of the transporting layers and the quality of crystalline films limit further development of PSCs. To fabricate highly efficient PSCs, effective charge transport to electrodes through transporting layers is a necessary requirement. Suitable interface engineering is very critical because it can not only benefit the charge extraction and transport, but also effectively passivate the traps on the surface and grain boundary of the perovskite. It has been shown that the passivation layer for the perovskite plays a vital role in the performance of PSCs. The close fit between the charge transport layer and the perovskite layer is required to reduce the interfacial recombination and accelerate the carrier extraction and collection. Besides, the appropriate passivation layer has a potential impact on the crystallization and the morphology of the perovskite film. To achieve high-performance devices, it is crucial to design an effective passivation layer with appropriate nanomaterials. In this work, we synthesized poly[(2-methoxy,5-octoxy)1,4-phenylenevinylene] (MOPPV) on few-layer graphene oxide (GO) by in situ polymerization at room temperature. MOPPV-GO can fully combine the advantages of the two materials. The novel nanocomposite MOPPV-GO is used as the ultra-thin passivation layer of PSCs, of which the structure is ITO/TiO2/(FAPbI3) x (MAPbCl3)1– x /MOPPV-GO/spiro-OMeTAD/Ag. Since the surface morphology of the perovskite layer would affect the performance of devices significantly, the perovskite films with and without the passivation layer by atomic force microscopy is found that the MOPPV-GO can facilitate the growth of perovskite crystal with larger grains and enhance the quality of perovskite films. The root mean square roughness values of the perovskite films with and without MOPPV-GO were evaluated to be 19.87 and 25.85 nm, justifying the improvement of the surface flatness of the perovskite film with the decoration of MOPPV-GO, which would enhance the contact and carrier transport between the hole transport layer and the perovskite layer. As a result, the PSCs with MOPPV-GO exhibited considerably low hysteresis indices (0.02) and showed a short circuit current density of 23.54 mA cm–1, an open circuit voltage of 1.09 V, and a fill factor of 76.46%, corresponding to a high power conversion efficiency of 19.73%. By contrast, the control PSCs without MOPPV-GO showed a high hysteresis index of 0.18, with a poor power conversion efficiency of 16.42%. Meanwhile, it is shown that the EQE curve of MOPPV-GO modified PSC is higher than that of unmodified devices, which is consistent with the experimental results of J-V curve. The steady-state power output of various devices in ambient conditions under continuous AM 1.5G illumination was tested, which shows excellent stability of the PSC with MOPPV-GO during the period of 1000 s, indicating the positive contribution of MOPPV-GO interlayer to the stability. This work could provide a new idea for the synthesis and application of graphene-based materials in solar cells.

Preparation and comparison of Fe3O4@graphene oxide nanoclusters for analysis of glimepiride in urine by surface-assisted laser desorption/ionization time-of-flight mass spectrometry.

Graphene oxide (GO) has the ability to absorb certain compounds, and it can be modified with functional groups for different purposes; for instance, iron oxide (IO) nanoparticles can be used to concentrate analyte by a magnet. Recently, many kinds of GO have been developed, such as single-layer GO (SLGO), two-to-four layers of GO (i.e., few-layer GO, FLGO2-4), and four-to-eight layers of GO (i.e., multi-layer GO, MLGO4-8). However, the abilities of these layered GO coated with IO nanoparticles have not been investigated. In this study, we conducted a novel analysis of glimepiride by using layered GO-coated magnetic clusters of IO nanoparticles that were synthesized through a simple and facile emulsion-solvent evaporation method. The methodology is based on (i) enrichment of glimepiride using the layered GO-coated magnetic clusters of IO nanoparticles (IO@SLGO, IO@FLGO2-4, and IO@MLGO4-8), and (ii) rapid determination using magnetic cluster-based surface-assisted laser desorption/ionization time-of-flight mass spectrometry (SALDI-TOFMS). We found that IO@MLGO4-8, the magnetic cluster with the greatest number of GO layers, had the best limit of detection (28.6pmol/μL for glimepiride). The number of GO layers played a significant role in increasing the sensitivity of the SALDI-MS, indicating that the size of GO in the magnetic clusters contributed to the desorption/ionization efficiency. To the best of our knowledge, this is the first study to enrich glimepiride using magnetic clusters of different GO types and to show that the glimepiride in HLB purified urine adsorbed by magnetic clusters can be analyzed by SALDI-TOFMS.

Nanolitre solution drop-casting for selective area graphene oxide coating on planar surfaces

Selective area coating of graphene and graphene oxide thin films provides a cost-effective approach for the integration of functional materials in electronics and photonics devices, such as transparent conductive electrodes, humidity sensors and optical modulators. For solution dispersed graphene oxides, solution drop-casting technique is commonly used. To produce coatings with precise thickness and coating area control, the dispensing volume and solution concentration in turn needs to be precisely controlled. Herein, we report a nanolitre solution drop-casting technique for selective area graphene oxide (GO) thin film coatings. A motorized actuator was used to control the micro-syringe to dispense precise volume of GO solution down to the nanolitres level. GO coatings using the proposed method were performed on two surfaces with different surface characteristics: thermal oxide (TOx) layer and photoactive UV curable resin (ZPU13-RI polymer) layer. We found that the difference in surface characteristics of both substrate surfaces greatly affects the diameter and thickness of GO coatings produced. The minimum diameter of GO coating obtained on TOx surface was 52 ± 5 μm, while the minimum GO coating diameter obtained on ZPU13-RI surface was 340 ± 17 μm. By controlling both the solution volume and solution concentration, single- and few-layer GO coatings can be produced on both TOx and ZPU13-RI surfaces using this technique. When integrated with 2-axis automated movement system, this technique can be used for selective area coating of GO thin film with controlled thickness on large planar surfaces such as in the production of sensors and other functional devices.

Graphene Surfaces Interaction with Proteins, Bacteria, Mammalian Cells, and Blood Constituents: The Impact of Graphene Platelet Oxidation and Thickness.

Graphene-based materials (GBMs) have been increasingly explored for biomedical applications. However, interaction between GBMs-integrating surfaces and bacteria, mammalian cells, and blood components, that is, the major biological systems in our body, is still poorly understood. In this study, we systematically explore the features of GBMs that most strongly impact the interactions of GBMs films with plasma proteins and biological systems. Films produced by vacuum filtration of GBMs with different oxidation degree and thickness depict different surface features: graphene oxide (GO) and few-layer GO (FLGO) films are more oxidized, smoother, and hydrophilic, while reduced GO (rGO) and few-layer graphene (FLG) are less or nonoxidized, rougher, and more hydrophobic. All films promote glutathione oxidation, although in a lower extent by rGO, indicating their potential to induce oxidative stress in biological systems. Human plasma proteins, which mediate most of the biological interactions, adsorb less to oxidized films than to rGO and FLG. Similarly, clinically relevant bacteria, Staphylococcus epidermidis, Staphylococcus aureus, Pseudomonas aeruginosa, and Escherichia coli, adhere less to GO and FLGO films, while rGO and FLG favor bacterial adhesion and viability. Surface features caused by the oxidation degree and thickness of the GBMs powders within the films have less influence toward human foreskin fibroblasts; all materials allow cell adhesion, proliferation and viability up to 14 days, despite less on rGO surfaces. Blood cells adhere to all films, with higher numbers in less or nonoxidized surfaces, despite none having caused hemolysis (<5%). Unlike thickness, oxidation degree of GBMs platelets strongly impact surface morphology/topography/chemistry of the films, consequently affecting protein adsorption and thus bacteria, fibroblasts and blood cells response. Overall, this study provides useful guidelines regarding the choice of the GBMs to use in the development of surfaces for an envisioned application. Oxidized materials appear as the most promising for biomedical applications that require low bacterial adhesion without being cytotoxic to mammalian cells.

Lipase immobilized on functionalized superparamagnetic few-layer graphene oxide as an efficient nanobiocatalyst for biodiesel production from Chlorella vulgaris bio-oil

BackgroundMicroalgae, due to its well-recognized advantages have gained renewed interest as potentially good feedstock for biodiesel. Production of fatty acid methyl esters (FAMEs) as a type of biodiesel was carried out from Chlorella vulgaris bio-oil. Biodiesel was produced in the presence of nano-biocatalysts composed of immobilized lipase on functionalized superparamagnetic few-layer graphene oxide via a transesterification reaction. A hybrid of few-layer graphene oxide and Fe3O4 (MGO) was prepared and characterized. The MGO was functionalized with 3-aminopropyl triethoxysilane (MGO–AP) as well as with a couple of AP and glutaraldehyde (MGO–AP–GA). The Rhizopus oryzae lipase (ROL) was immobilized on MGO and MGO–AP using electrostatic interactions as well as on MGO–AP–GA using covalent bonding. The supports, MGO, MGO–AP, and MGO–AP–GA, as well as nano-biocatalyst, ROL/MGO, ROL/MGO–AP, and ROL/MGO–AP–GA, were characterized using FESEM, VSM, FTIR, and XRD. The few-layer graphene oxide was characterized using AFM and the surface charge of supports was evaluated with the zeta potential technique. The nano-biocatalysts assay was performed with an evaluation of kinetic parameters, loading capacity, relative activity, time-course thermal stability, and storage stability. Biodiesel production was carried out in the presence of nano-biocatalysts and their reusability was evaluated in 5 cycles of transesterification reaction.ResultsThe AFM analysis confirmed the few-layer structure of graphene oxide and VSM also confirmed that all supports were superparamagnetic. The maximum loading of ROL (70.2%) was related to MGO–AP–GA. The highest biodiesel conversion of 71.19% achieved in the presence of ROL/MGO–AP–GA. Furthermore, this nano-biocatalyst could maintain 58.77% of its catalytic performance after 5 cycles of the transesterification reaction and was the best catalyst in the case of reusability.ConclusionsIn this study, the synthesized nano-biocatalyst based on bare and functionalized magnetic graphene oxide was applied and optimized in the process of converting microalgae bio-oil to biodiesel for the first time and compared with bare lipase immobilized on magnetic nanoparticles. Results showed that the loading capacity, kinetic parameters, thermal stability, and storage stability improved by the functionalization of MGO. The biocatalysts, which were prepared via covalent bonding immobilization of enzyme generally, showed better characteristics.

Immobilization of zinc oxide nanoparticles on graphene sheets for lithium ion storage and electromagnetic microwave absorption

A simple one-step method to immobilize zinc oxide nanoparticles (ZnO NPs) in reduced graphene oxide (RGO) supporting framework is reported in this work. Under mild hydrothermal condition, ZnO NPs function as an effective catalyzer for few-layered graphene oxide (GO) deoxygenation to construct an RGO protecting framework and in the meantime ZnO NPs are immobilized between the RGO sheets. The synthesized ZnO/RGO composite not only delivered good lithium ion storage capability with a reversible capacity of 560 mA h·g−1 for 250 cycles under a current density of 500 mA g−1, but also exhibited good electromagnetic microwave absorption performance with the maximum reflection loss value of −67.13 dB when the thickness is 3.2 mm while the effective absorption bandwidth is 7.44 GHz with the thickness of 2.8 mm. The improved performances of the ZnO/RGO composite compared with bare ZnO NPs are ascribed to the synergistic effect from well-dispersed ZnO NPs and RGO framework, particularly, the formation of Zn–O–C bond between the two components brings in good immobilization between the two components, which was verified by both theoretical calculation and XPS characterization techniques. The method to prepared ZnO/RGO composite is facile, eco-friendly and effective, which has great potential to find wider applications for massive production.

Gas Barrier Polymer Nanocomposite Films Prepared by Graphene Oxide Encapsulated Polystyrene Microparticles

The dispersion and orientation of two-dimensional (2D) inorganic nanoplatelets in polymers are technical challenges faced in polymer nanocomposite manufacturing. This work demonstrates an effective way to facilitate the dispersion and orientation of graphene oxide (GO) nanoplatelets in a polymer matrix through encapsulating the polymer within a nanoplatelet shell. Briefly, few-layered GO nanoplatelets encapsulated polystyrene (PS) microparticles were synthesized by a Pickering suspension polymerization method. The synthesis conditions, morphologies, and barrier properties of the GO encapsulated PS spheres and the melt-compressed films are characterized. The addition of salt induces flocculation of GO onto the surface of the styrene monomer droplet, resulting in the formation of a multilayered GO shell as well as the sedimenting of the PS/GO particles during polymerization. The obtained GO encapsulated PS microspheres were purified, dried, and melt-compressed to form composite films. The oxygen permeabilit...

Understanding Gas Transport Behavior through Few-Layer Graphene Oxide Membranes Controlled by Tortuosity and Interlayer Spacing.

Here, we elucidate the gas transport behavior through few-layer graphene oxide membranes (FGOMs) that have a systematically controlled diffusion pathway, including tortuosity and channel width. The obtained unusual gas permeation order (especially, CH4 > O2 > N2) of the FGOM provides strong evidence that gas molecules can indeed penetrate through the empty voids created by horizontally assembled GO, which allows selective gas transport features. These unique transport features of the FGOM originate from its continuously connected channel structure, which is an analogue of an ultrapermeable glassy polymer with extremely large free volumes in dense films. Furthermore, variation of the channel width in the range of 0.50-0.55 nm leads to notable changes in the gas permeance orders related to CH4, indicating that there is a transition region for switching the gas transport mechanism between a molecular sieving character and the solution-diffusion model.

Polyvinylamine Membranes Containing Graphene-Based Nanofillers for Carbon Capture Applications.

In the present study, the separation performance of new self-standing polyvinylamine (PVAm) membranes loaded with few-layer graphene (G) and graphene oxide (GO) was evaluated, in view of their use in carbon capture applications. PVAm, provided by BASF as commercial product named LupaminTM, was purified obtaining PVAm films with two degrees of purification: Low Grade (PVAm-LG) and High Grade (PVAm-HG). These two-grade purified PVAm were loaded with 3 wt% of graphene and graphene oxide to improve mechanical stability: indeed, pristine tested materials proved to be brittle when dry, while highly susceptible to swelling in humid conditions. Purification performances were assessed through FTIR-ATR spectroscopy, DSC and TGA analysis, which were carried out to characterize the pristine polymer and its nanocomposites. In addition, the membranes′ fracture surfaces were observed through SEM analysis to evaluate the degree of dispersion. Water sorption and gas permeation tests were performed at 35 °C at different relative humidity (RH), ranging from 50% to 95%. Overall, composite membranes showed improved mechanical stability at high humidity, and higher glass transition temperature (Tg) with respect to neat PVAm. Ideal CO2/N2 selectivity up to 80 was measured, paired with a CO2 permeability of 70 Barrer. The membranes’ increased mechanical stability against swelling, even at high RH, without the need of any crosslinking, represents an interesting result in view of possible further development of new types of facilitated transport composite membranes.

Few-layer graphene oxide with high yield via efficient surfactant-assisted exfoliation of mildly-oxidized graphite

A surfactant-assisted ultrasonic exfoliation of mildly oxidized graphite has been successfully demonstrated. Four typical surfactants including three cationic surfactants and one anionic surfactant are explored and the exfoliation mechanism of these surfactants has been studied. The surfactant charge was found to be an important factor in affecting the exfoliation efficiency. The anionic surfactant was more favorable than the cationic ones as the influence of its concentration on the exfoliation efficiency was weak while the cationic surfactants with high concentration may obstruct the exfoliation. The thickness of graphene oxide sheets prepared with surfactants was mainly distributed at 1–1.5 nm. The X-Ray diffraction results showed that the intercalation capacity of cationic surfactant was higher than that of anionic surfactant. The results of X-ray photoelectron spectra and Fourier-transform infrared spectra measurement showed that the polar parts of cationic surfactants should be bonded with O− on mildly oxidized graphite by electrostatic attractive force to form hydrophobic force in the interlamination of mildly oxidized graphite. The anionic surfactant was intercalated into the interlayers of mildly oxidized graphite by hydrophobic force and hydrogen bond, leading to the formation of weak electrostatic repulsion force to facilitate the exfoliation slightly.

The role of graphene oxide precursor morphology in magnetic and microwave absorption properties of nitrogen-doped graphene

Morphological features, reduction and doping degree of graphene could pose varied effects on its electronic configuration, polarization states, and further trigger of magnetic moments. Herein, three different kinds of graphene oxide (GO) with different corrugations: rippled, folded and flower-like GO in combination with urea were used as precursors to synthesize nitrogen doped graphene (NG) via a facile one-step thermal annealing method to simultaneously achieve nitrogen doping and GO reduction. The magnetic and microwave absorption properties of the three kinds of GO and their corresponding NG were evaluated in terms of structure, C/O ratio (GO reduction degree) and nitrogen doping. The overall results revealed that the reduction is more efficient in the few-layered GO but may be hindered by a folded structure which tends to trap the doped nitrogen atoms. In terms of magnetic properties, flower-like GO and NG with a crumpled structure exhibited the highest magnetization. The NG with a flower-like structure and highest C/O showed the best microwave absorption performance with filling content as low as 10 wt.%, reflected in a reflection loss (RL) of −21.7 dB at 16.8 GHz (d = 2 mm) and 2.3 GHz of bandwidth. While at the same filling content and absorber thickness, the rippled and folded NGs with lower C/O ratio did not exhibit absorption values of practical application. Thus, higher C/O, proper doping degree and low filler content are required to achieve optimized permittivity and consequently favorable microwave absorbing performance.

Synthesis of SnO2/graphene composite anode materials for lithium-ion batteries

A tin dioxide/reduced graphene oxide composite (SnO2/RGO) is synthesized using combined methods, including in-situ metal tin reduction, spray drying and thermal treatment. Under mild hydrothermal condition, metal tin works as both reducing agent for few-layered graphene oxide (GO) to prepare restacked 2-dimensional (2D) reduced graphene oxide (RGO) sheets and metal source for homogeneously distributed nanostructured Sn and Sn oxides (Sn/SnO/SnO2). The 2D precursors are shrunk to a micro-sized dried blueberry shape via a spray drying process. After further thermal treatment, SnO2/RGO composite is obtained, in which Sn and SnO species are converted to SnO2 and the nano-sized SnO2 is well stabilized by the micro-sized 3D porous RGO supporting framework. The 3D SnO2/RGO composite exhibits not only a higher reversible capacity of 708 mAh·g−1 under a current density of 500 mA·g−1 over 150 cycles compared with 2D counterpart, but also a long and stable cycling life under a high current density of 1000 mA·g−1. This synthesis route can be considered as simple, economic and environmental-friendly, and it has great potential to find applications in other fields.

Hierarchical zinc oxide/reduced graphene oxide composite: Preparation route, mechanism study and lithium ion storage

A novel and simple approach to preparing hierarchical zinc oxide/reduced graphene oxide (ZnO/RGO@RGO) composite is demonstrated using few-layered graphene oxide (GO) and metal zinc as starting materials following combined processes, including in-situ metal zinc reduction and catalyzed GO deoxygenation. Metal zinc can directly reduce GO sheets in aqueous GO suspension at room temperature to obtain a porous composite precursor (ZnO/RGO) with ZnO nanoparticles anchored on the RGO sheets. Then another RGO protecting layer is directly coated on the ZnO/RGO precursor to obtain the hierarchical ZnO/RGO@RGO composite. In this step, the exposed ZnO nanoparticles on the surface of ZnO/RGO play the role of catalyst to accelerate the deoxygenation of GO from the extra added GO aqueous suspension under mild hydrothermal condition. The reaction mechanism of metal zinc with GO aqueous suspension has been explored and the catalyst role of ZnO has been verified in this work. The prepared ZnO/RGO@RGO composite exhibited both stable cycling performance and good rate capability as anode for lithium-ion batteries. The method to prepare ZnO/RGO composite is economic and eco-friendly, and the ZnO catalyzing GO reduction opens a new approach to prepare graphene derivates.

Facile Synthesis of ZnO Nanorods/GO Composite and Its Optical Performance.

The ZnO nanorods/GO composite was fabricated by facilely covering monolayer or few-layer graphene oxide (GO) film on the uniformly distributed ZnO nanorods, which was synthesized on Si substrate using a solution method. The as-synthesized products were characterized by scanning electron microscopy (SEM), transmission electron microscope (TEM), as well as X-ray diffraction (XRD). The photoluminescence (PL) measurement indicates that the ZnO nanorods have a strong ultraviolet (UV) emission centered at ~391 nm attributed to the recombination of free excitons and a defect-related visible emission centered at ~530 nm. After the nanorods were covered with GO film, the PL intensity of the composite is quenched compared to that of the bare one at the same excitation condition. The fluorescence quenching mechanism suggests that there is an interfacial charge-transfer process between the excited ZnO and the GO film, and the composite fabricated in this experiment be possible to improve the photocatalysis performance.

Performance and stability of counter electrodes based on reduced few-layer graphene oxide sheets and reduced graphene oxide quantum dots for dye-sensitized solar cells

Graphene-based materials represent an attractive alternative to platinum in dye-sensitized solar cells (DSSC) counter electrodes to contribute to an efficient conversion of solar energy into electricity. Despite the slower kinetics of carbon for the reduction of triiodide compared to platinum, they are characterized by low cost and promising stability. In this work, two different materials are investigated: reduced few-layer graphene oxide (rFLGO) and reduced graphene oxide quantum dots (rGOQD). The electrochemical performance of DSSC assembled with either rFLGO or rGOQD at the counter electrode is correlated to their most important physico-chemical features. The domain size of graphene sheets had an important effect on the performance at the counter electrode, with quantum dots performing 13% higher efficiency than rFLGO, correlated with a higher density of active sites. Both graphene nanostructures exhibited a better stability behavior upon electrochemical cycling and seasoning of the cells as compared to Pt counter electrode.