Single Layer Reduced Graphene Oxide Research Articles

CdS cubane type clusters encapsulated by rolling of single layer reduced graphene oxide sheets for enhanced mechanical energy harvesting

Composites with Single Layer Graphene Oxide (SLGO) sheets are extremely difficult to achieve, irrespective of the current advancements in graphene composites research. The difficulties in exfoliating the graphite oxide (GO) was associated with a strong interaction among the edge sides of the adjacent layers. This in-turn barricades the foreign intruders to interact with the basal plane, thereby restraining one to form composites with SLGO sheets. In this work, we had successfully exfoliated GO through a spacer [Cd(OAc)2 + polyethylene glycol (PEG)] to result in nano-engineered CdS cubane-type clusters in rolled up SLGO to form graphene oxide complex compound (GOCC), resembling carbon nanotubes (CNTs). The CdS cubane-type clusters were found to interacting with the carbon skeleton of rolled reduced SLGO sheet through a ‘nanogate’ structures, which was supported by density functional theory (DFT) calculations. Our theoretical study reveals that the obtained complex compound (GOCC) is thermodynamically more favourable than its ancestor materials (CdS cubane and empty CNT). Flexible piezoelectric nanogenerators (PENGs) fabricated from GOCC and thermoplastic polyurethane (TPU) resulted in output voltage (Voc) of 4.5 V and output current of 0.4 µA at applied force of 13 N. The nanoengineering helps to achieve superior mechanical energy harvesting performance for GOCC compared to pristine CdS, which demonstrate the potential of nanogate structures to enhance the intrinsic properties of materials.

Ultrahigh concentration, single-layer of graphene paste as conductive additive for lithium-ion battery

Graphene is a superior active material in energy storages due to its exceptional properties, such as high specific area, high electrical conductivity, and excellent chemical stability. Currently, the large-scale preparation of graphene powder constitutes a research hotspot. Usually, the as-prepared graphene powders was used directly leading to poor dispersion which greatly affects the electrode's properties. Thus, one crucial application problem which needs to be solved urgently is how to obtain ultrahigh concentration and stable dispersion of single-layer graphene. Therefore, in this work, we prepared successfully a single-layer reduced graphene oxide (RGO) powder by expansion-oxidation-expansion process. The RGO paste was obtained through high-speed ball-milling technology, offering ultrahigh concentration (27 mg/mL) and high stability. Meanwhile, the above-mentioned paste be combined with LiFePO4 (LFP) towards obtaining cathode materials for Li-ion batteries. [email protected] demonstrated an excellent discharge capacity of 168.3 mA h g−1 at 0.1 C, and maintained 99.9% of capacity after 100 cycles at 0.5 C. Herein, we demonstrated an effective way to prepare the ultrahigh concentration, and stable dispersion of single-layer graphene paste in the field of energy storage and conversion.

Controlling Long-Distance Photoactuation with Protein Additives.

Long-distance wireless actuation indicates precise remote control over materials, sensors, and devices that are widely utilized in biomedical, defence, disaster relief, deep ocean, and outer space applications to replace human work. Unlike radio frequency (RF) control, which has low tolerance toward electromagnetic interference (EMI), light control represents a promising method to overcome EMI. Nonetheless, long-distance light-controlled wireless actuation able to compete with RF control has not been achieved until now due to the lack of highly light-sensitive actuator designs. Here, it is demonstrate that amyloid-like protein aggregates can organize photomodule single-layer reduced graphene oxide (rGO) into a well-defined multilayer stack to display long-distance photoactuation. The amyloid-like proteinaceous component docks the rGO layers together to form a hybrid film, which can reliably adhere onto various material surfaces with robust interfacial adhesion. The sensitive photothermal effect and a fast bending in 1 s to switch a circuit are achieved after forming the film on a plastic substrate and irradiating the bilayer film with a blue laser from 100 m away. A photoactuation distance of 50 km can be further extrapolated based on a commercial high-power laser. This study reveals the great potential of amyloid-like aggregates in remote light control of robots and devices.

Nanoscale infrared identification and mapping of chemical functional groups on graphene

Chemical functionalisation of graphene and other 2-dimensional materials is a key step in realizing their full potential in various applications. There is a need for non-destructive and unambiguous identification of chemical groups and mapping of their distribution on such materials with nanoscale spatial resolution and at monolayer thicknesses. In this work, AFM-coupled infrared spectroscopy is used to analyse single layer reduced graphene oxide flakes that have been non-covalently functionalized with sulfonated pyrenes. We show this technique to be capable of distinguishing between the different pyrene moieties and mapping the sulfonate groups on a 1.7 nm functionalised monolayer of reduced graphene oxide with 32 nm spatial resolution. This technique is also shown to be sensitive to small changes in the sulfonate absorption spectra arising from chemical and surface effects, enough to distinguish between different functionalizing molecules even on materials with anisotropic thermal conductivity.

Synthesis, characterization and application of pH-sensitive CoFe2O4/reduced graphene oxide (RGO) nanocomposite in a circulated photocatalytic reactor for Reactive Red 141 removal of wastewaters

In the present study, CoFe2O4/reduced graphene oxide nanocomposite (CoFe2O4/RGO) has been synthesized, characterized and applied as a photocatalyst for Reactive Red 141 dye removal from colored wastewaters. In order to control the size and reduction of prepared CoFe2O4/RGO, a combination of co-precipitation and hydrothermal methods were employed. NH3 was used as a pH controlling and complexing agent. The nanocomposite was characterized and its properties were evaluated using FTIR, XRD, VSM, FESEM, TEM, TOC, Zeta potential, PL and UV–Vis spectroscopy. The TEM image shows that a well-separated low layer or a single layer reduced graphene oxide and is decorated during nanocomposite synthesis simultaneously with the synthesis, growth and uniform distribution of nanoparticles of 10 nm size. The measurement of magnetic properties of the synthesized nanocomposite shows that the nanocomposites are easily removable from the aqueous medium by applying a magnetic field. The photocatalytic performance was investigated on the degradation of aqueous Reactive Red 141 dye. Results of Zeta potential analysis confirm that photocatalytic performance is independent of surface charge and is related to the position of the valence band of OH−/OH· couples. Therefore, the photocatalyst could be suitable for treatment of basic effluents. A possible mechanism for the formation of the nanocomposite and its photocatalytic performance in various pHs has been proposed based on the results.

THz TDS study of several sp2 carbon materials: Graphite, needle coke and graphene oxides

Terahertz time-domain spectroscopy has been used to probe the properties of four carbon allotropes with a sequenced c-axis stacking order: single-layer reduced graphene oxide, few-layer graphene oxide, disordered needle coke and highly organized graphite. The results obtained demonstrate a very high sensitivity to the structural characteristics of the tested samples. The multi-layer materials show the same type of spectral response with strong variations in the attenuation in the whole terahertz band depending on their constructural organization. The single-layer sample shows a distinct response where conductive effects dominate. The results obtained are consistent with theoretical investigations using semi-empirical quantum chemistry methods.

Heterogeneous Fluorescence Intermittency in Single Layer Reduced Graphene Oxide.

We provide, for the first time, direct experimental evidence for heterogeneous blinking in reduced graphene oxide (rGO) during photolysis. The spatially resolved intermittency originates from regions within individual rGO sheets and shows 1/f-like power spectral density. We describe the evolution of rGO blinking using the multiple recombination center (MRC) model that captures common features of nanoscale blinking. Our results illustrate the universal nature of blinking and suggest a common microscopic origin for the effect.

Synthesis of reduced graphene oxide using indole as a reducing agent and preparation of reduced graphene oxide-Ag nanocomposites

Reduced graphene oxide has been successfully prepared via chemical reduction of graphene oxide by indole as a previously unreported reducing agent. The obtained single layer reduced graphene oxide, with an average thickness of 1.7nm, is dispersible in organic solvents such as ethanol, N,N-dimethylformamide, N-methylpyrrolidone, dimethylsulfoxide, tetrahydrofuran and isopropanol. Several analytical techniques including X-ray diffraction, UV/vis spectroscopy, Raman spectroscopy and X-ray photoelectron spectroscopy have been used to characterize the resulting reduced graphene oxide, which indicates that most of oxygen functionalities are removed and yielding C/O ratio as high as 7.4. We further have demonstrated the subsequent decoration of reduced graphene oxide by direct adsorption of negatively charged Ag nanoparticles. It was found that the average diameter of Ag nanoparticles on the surface of reduced graphene oxide is between 20 and 40nm. Furthermore, the intensity of Raman signals of reduced graphene oxide-Ag nanoparticles is about 21-fold by decorating with Ag nanoparticles, in comparison with reduced graphene oxide showing surface-enhanced Raman scattering activity.

Genotoxicity of graphene nanoribbons in human mesenchymal stem cells

Single-layer reduced graphene oxide nanoribbons (rGONRs) were obtained through an oxidative unzipping of multi-walled carbon nanotubes and a subsequent deoxygenation by hydrazine and bovine serum albumin. Human mesenchymal stem cells (hMSCs) were isolated from umbilical cord blood and used for checking the concentration- and time-dependent cyto- and geno-toxic effects of the rGONRs and reduced graphene oxide sheets (rGOSs). The cell viability assay indicated significant cytotoxic effects of 10μg/mL rGONRs after 1h exposure time, while the rGOSs exhibited the same cytotoxicity at concentration of 100μg/mL after 96h. The oxidative stress was found as the main mechanism involved in the cytotoxicity of the rGOSs which induced a slight cell membrane damage, while RNA efflux of the hMSCs indicated that neither generation of reactive oxygen species nor the significant membrane damage of the cells could explain the cell destructions induced by the rGONRs. Our results demonstrated that, the rGONRs could penetrate into the cells and cause DNA fragmentations as well as chromosomal aberrations, even at low concentration of 1.0μg/mL after short exposure time of 1h.

Comparative studies on single-layer reduced graphene oxide films obtained by electrochemical reduction and hydrazine vapor reduction

The comparison between two kinds of single-layer reduced graphene oxide (rGO) sheets, obtained by reduction of graphene oxide (GO) with the electrochemical method and hydrazine vapor reduction, referred to as E-rGO and C-rGO, respectively, is systematically studied. Although there is no morphology difference between the E-rGO and C-rGO films adsorbed on solid substrates observed by AFM, the reduction process to obtain the E-rGO and C-rGO films is quite different. In the hydrazine vapor reduction, the nitrogen element is incorporated into the obtained C-rGO film, while no additional element is introduced to the E-rGO film during the electrochemical reduction. Moreover, Raman spectra show that the electrochemical method is more effective than the hydrazine vapor reduction method to reduce the GO films. In addition, E-rGO shows better electrocatalysis towards dopamine than does C-rGO. This study is helpful for researchers to understand these two different reduction methods and choose a suitable one to reduce GO based on their experimental requirements.

FEMTOSECOND PHOTOEXCITED CARRIER DYNAMICS IN REDUCED GRAPHENE OXIDE SUSPENSIONS AND FILMS

We report ultrafast response of femtosecond photoexcited carriers in single layer reduced graphene oxide flakes suspended in water as well as few layer thick film deposited on indium tin oxide coated glass plate using pump–probe differential transmission spectroscopy at 790 nm. The carrier relaxation dynamics has three components: ~200 fs, 1 to 2 ps, and ~25 ps, all of them independent of pump fluence. It is seen that the second component (1 to 2 ps) assigned to the lifetime of hot optical phonons is larger for graphene in suspensions whereas other two time constants are the same for both the suspension and the film. The value of third order nonlinear susceptibility estimated from the pump–probe experiments is compared with that obtained from the open aperture23 Z-scan results for the suspension.

A new reducing agent to prepare single-layer, high-quality reduced graphene oxide for device applications

We report on a novel, efficient, and one-step approach to prepare single-layer reduced graphene oxide (RGO) suspensions and films using hydroxylamine hydrochloride. The effective chemical reduction of GO was evidenced by a significant increase in the C/O ratio and five orders of magnitude decrease in the GO resistance. Field-effect transistor gas sensors were fabricated using as-produced RGO sheets and the resulting sensor exhibited a fast response and a high sensitivity to low-concentration target gases at room temperature.