Size dependence electrocatalytic activity of gold nanoparticles decorated reduced graphene oxide for hydrogen evolution reaction

It is promising for AuNPs/RGO composites to be exploited for hydrogen evolution reaction (HER), due to the collaborative effects between the electrocatalytic Au nanoparticles (AuNPs) and conductive reduced graphene oxide (RGO). In this work, we used a simple way to decorate AuNPs onto the RGO surface by one pot in situ reduction both HAuCl₄ and GO, for which the controlled average size of AuNPs (2.7, 11.5 and 45.7 nm) is adjusting with the mass ratio of HAuCl₄ and GO. The obtained materials, AuNPs/RGO composites, show excellent electrocatalytic activity for the HER that critical dependence on the particle size of AuNPs. The results show that AuNPs/RGO with AuNPs size of 11.5 nm exhibits superior electrochemical activity: low onset potential of 0.029 V versus the reversible hydrogen electrode as well as a small Tafel slope of 86 mV per decade.     

Ultra-small amorphous MoS_2 decorated reduced graphene oxide for supercapacitor application

Amorphous materials have recently gained much attention as electrode materials in supercapacitor application due to the presence of larger amount active sites which can efficiently increase the storage capacity of the materials. Nano engineering is an elegant approach to fully utilize the advantages of the amorphous structure. Moreover, large surface area and high conductivity of reduced graphene oxide(RGO)can efficiently increase the storage capacity of the system. Exploiting this idea, in the present work, we have successfully synthesized amorphous MoS_2 of two different sizes on reduced graphene oxide and thoroughly investigated the supercapacitor behavior of the system. The specific capacitance of the composite structures has been found to be largely increased with decreasing size of the amorphous nano particle. The specific capacitance of amorphous MoS_2-RGO composite containing nearly 50 nm of MoS_2 found to be 270 F/g whereas when the particle size is reduced to 5–7 nm, value of specific capacitance increases to 460 F/g. The large increase in specific capacitance with the tuning of the size of amorphous nano particle has been explained by the presence of a large number of active sulfur edges of ultra-small MoS_2 nano structure along with the better charge transport which can effectively increase the storage capacity of the overall system. The retention in the capacitance of the material has been found to be 90% after 5000 cycles.     

Hg(II) ion detection using thermally reduced graphene oxide decorated with functionalized gold nanoparticles

Fast and accurate detection of aqueous contaminants is of significant importance as these contaminants raise serious risks for human health and the environment. Mercury and its compounds are highly toxic and can cause various illnesses; however, current mercury detectors suffer from several disadvantages, such as slow response, high cost, and lack of portability. Here, we report field-effect transistor (FET) sensors based on thermally reduced graphene oxide (rGO) with thioglycolic acid (TGA) functionalized gold nanoparticles (Au NPs) (or rGO/TGA-AuNP hybrid structures) for detecting mercury(II) ions in aqueous solutions. The lowest mercury(II) ion concentration detected by the sensor is 2.5 × 10(-8) M. The drain current shows rapid response within less than 10 s after the solution containing Hg(2+) ions was added to the active area of the rGO/TGA-AuNP hybrid sensors. Our work suggests that rGO/TGA-AuNP hybrid structures are promising for low-cost, portable, real-time, heavy metal ion detectors.     

Enhanced photo-driven ion pump through silver nanoparticles decorated graphene oxide membranes

Biology systems harvest solar energy to regulate ions and molecules precisely across cell membrane that is essential to maintain their life sustainability.Recently,artificial light-driven directional ion transport through graphene oxide membranes has been established,where the membrane converts light power into a transmembrane motive force.Herein,we report a silver nanoparticles decorated graphene oxide membranes for enhanced photo-driven ionic transport.Asymmetric light stimulated charge carrier dynamics,such as advanced light absorption efficiency,extended lifetime and efficient separation of photo-excited charge carriers,are account for the ion-driven force enhancement.Based on metal nanoparticles decoration,the concept of the guest-interactions of plasmon-enhanced photo-driven ion transport in two-dimentional layered membranes will stimulate broad researches in sensing,energy storage and conversion and water treatment.     

Sulfur nanoparticles encapsulated in reduced graphene oxide nanotubes for flexible lithium-sulfur batteries

Rapid development of flexible electronic devices is promoting the design of flexible energy-storage devices. Lithium-sulfur (Li-S) batteries are considered as promising candidates for high energy density energy-storage devices. Therefore, flexible Li-S batteries are desired. In this study, we fabricated composite films of freestanding reduced graphene oxide nanotubes wrapped sulfur nanoparticles (RGONTs@S) by pressing RGONTs@S composite foams, which were synthesized by combining cold quenching with freeze-drying and a subsequent reduction process. These RGONTs@S composite films can serve as self-supporting cathodes for Li-S batteries without additional binders and conductive agents. Their interconnected tubular structure allows easy electron transport throughout the network and helps to confine the polysulfides produced during the charge/discharge process. As a result, the RGONTs@S composite films exhibited a high initial specific capacity, remarkable cycling stability, and excellent rate capability. More importantly, the RGONTs@S composite films can serve as electrodes in flexible Li-S batteries. As a proof of concept, soft-packaged Li-S batteries were assembled using these electrodes and they displayed stable electrochemical performance at different bending states.

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An electrochemically reduced graphene oxide-based electrochemical immunosensing platform for ultrasensitive antigen detection

We present an electrochemically reduced graphene oxide (ERGO)-based electrochemical immunosensing platform for the ultrasensitive detection of an antigen by the sandwich enzyme-linked immunosorbent assay (ELISA) protocol. Graphene oxide (GO) sheets were initially deposited on the amine-terminated benzenediazonium-modified indiun tin oxide (ITO) surfaces through both electrostatic and π-π interactions between the modified surfaces and GO. This deposition was followed by the electrochemical reduction of graphene oxide (GO) for preparing ERGO-modified ITO surfaces. These surfaces were then coated with an N-acryloxysuccinimide-activated amphiphilic polymer, poly(BMA-r-PEGMA-r-NAS), through π-π stacking interactions between the benzene ring tethered to the polymer and ERGO. After covalent immobilization of a primary antibody on the polymer-modified surfaces, sandwich ELISA was carried out for the detection of an antigen by use of a horseradish peroxidase (HRP)-labeled secondary antibody. Under the optimized experimental conditions, the developed electrochemical immunosensor exhibited a linear response over a wide range of antigen concentrations with a very low limit of detection (ca. 100 fg/mL, which corresponds to ca. 700 aM). The high sensitivity of the electrochemical immunosensor may be attributed not only to the enhanced electrocatalytic activity owing to ERGO but also to the minimized background current owing to the reduced nonspecific binding of proteins.     

Appropriate conditions for preparing few-layered graphene oxide and reduced graphene oxide

Oxidation time and exfoliated conditions of graphite oxides (GOs) were investigated to prepare few–layer graphene oxide and reduced graphene oxide via a modified Hummers approach. Different oxidative degree of GOs was prepared by changing oxidation time, and the effects of oxidative degree of GOs in different oxidation time were studied by XRD, FT-IR. Afterwards, highly oxidized GOs were used as precursor to prepare graphene oxide and reduced graphene oxide by ultrasonic dispersion method and thermal expansion method. The exfoliated conditions (ultrasonic power and ultrasonic time, thermal exfoliated temperature) were investigated to prepare few-layered graphene oxide and reduced graphene oxide.     

High-performance ammonia gas sensor based on bimetallic oxide Zn2SnO4 decorated with reduced graphene oxide

The coupling effect and synergistic effect between the two metal elements of the bimetallic oxide make it has unique electrical characteristics and gas-sensitive properties, but it has the limitation of low conductivity. In this paper, the bimetallic oxide Zn₂SnO₄ was decorated with reduced graphene oxide (rGO) to increase its electrical conductivity and promote charge transfer during gas adsorption, which enhances the response and shortens the response time of the bimetallic oxide gas sensor. The high-performance ammonia sensor based on Zn₂SnO₄/rGO nanocomposite material was prepared by environmentally friendly hydrothermal method and spin coating technology. The structure and properties of composite materials were analyzed by X-ray diffraction (XRD), field emission scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). The ammonia sensing performance of Zn₂SnO₄/rGO nanocomposite sensor was tested at room temperature, including the dynamic response, response/recovery time, selectivity, repeatability, long-term stability. It showed a good sensing response to ammonia (22.94 for 100 ppm), and a fast response/recovery time (20 s/27 s). Finally, the response mechanism of Zn₂SnO₄/rGO nanocomposite sensor is explained. The enhanced ammonia sensing properties of Zn₂SnO₄/rGO nanocomposite sensor were ascribed to the synergistic effect and p–n heterojunction between Zn₂SnO₄ and rGO.

     

PdCu alloy nanoparticles supported on reduced graphene oxide for electrocatalytic oxidation of methanol

PdCu nanoparticles supported on reduced graphene oxide nanosheets (PdCu/rGO) with uniform size distribution and dispersion are fabricated by a facile two-step reduction method. During the whole synthesis procedure, no capping agent or surfactant has been used. By varying the Pd/Cu molar ratio, electrocatalysts with different size distribution and dispersion of nanoparticles on graphene are prepared, and their electrocatalytic performance toward methanol oxidation reaction has been studied. It is concluded that the as-prepared electrocatalyst of Pd₂Cu₂/rGO, of which the Pd/Cu molar ratio is 1:1, exhibits the highest mass activity and most stable electroactivity. Compared to commercial Pd/C, the as-prepared Pd₂Cu₂/rGO also demonstrates 2.49 times higher mass activity and much more stable electroactivity. The excellent performance of the Pd₂Cu₂/rGO electrocatalyts is mainly due to the advantages of bimetallic synergistic effects and the supporting material of graphene. Owing to the advantages of high electroactivity, long stability, and cost-effectiveness, the as-prepared Pd₂Cu₂/rGO nanocomposites are promising anode electrocatalysts for direct methanol fuel cells.     

Gold nanoparticles/graphene oxide composite for electrochemical sensing of hydroxylamine and hydrogen peroxide

It has been discovered that the complex formed by cetyltrimethyl ammonium bromide (CTAB) and graphene oxide (GO) is highly stable in aqueous solution and adhesive to the glassy carbon electrode (GCE) surface in our previous research. In this work, the film of CTAB/GO complex was directly formed on GCE and gold nanoparticles were facilely incorporated into the matrix of CTAB/GO complex at the same time. Scanning electron microscopic (SEM) investigation shows that gold nanoparticles were distributed uniformly on the sheets of graphene. Cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and amperometry were used to investigate the electrochemical behaviors of AuNP/CTAB/GO. The obtained AuNP/CTAB/GO presents excellent catalytic capabilities towards the oxidation of hydroxylamine (HA) and the reduction of H₂O₂. The oxidation current of HA and the reduction current of H₂O₂ are linear with their concentrations in the range of 10～1000 μM and 1.0～5000 μM, respectively. The detection limits for HA and H₂O₂ are 3.5 μM and 0.67 μM, respectively. The mechanism of the oxidation of HA on AuNP/CTAB/GO modified GCE was also studied.     

Iron oxide/gold nanoparticles‐decorated reduced graphene oxide nanohybrid as the thermo‐radiotherapy agent

The main focus of the current study is the fabrication of a multifunctional nanohybrid based on graphene oxide (GO)/iron oxide/gold nanoparticles (NPs) as the combinatorial cancer treatment agent. Gold and iron oxide NPs formed on the GONPs via the in situ synthesis approach. The characterisations showed that gold and iron oxide NPs formed onto the GO. Cell toxicity assessment revealed that the fabricated nanohybrid exhibited negligible toxicity against MCF‐7 cells in low doses (<50 ppm). Temperature measurement showed a time and dose‐dependent heat elevation under the interaction of the nanohybrid with the radio frequency (RF) wave. The highest temperature was recorded using 200 ppm concentration nanohybrid during 40 min exposure. The combinatorial treatments demonstrated that the maximum cell death (average of 53%) was induced with the combination of the nanohybrid with RF waves and radiotherapy (RT). The mechanistic study using the flow cytometry technique illustrated that early apoptosis was the main underlying cell death. Moreover, the dose enhancement factor of 1.63 and 2.63 were obtained from RT and RF, respectively. To sum up, the authors’ findings indicated that the prepared nanohybrid could be considered as multifunctional and combinatorial cancer therapy agents.Inspec keywords: radiation therapy, toxicology, gold, biomedical materials, nanofabrication, nanoparticles, iron compounds, cancer, nanomedicine, cellular biophysics, tumours, graphene compounds, biothermicsOther keywords: graphene oxide nanohybrid, combinatorial cancer treatment agent, cell toxicity assessment, MCF‐7 cells, dose‐dependent heat elevation, multifunctional cancer therapy agents, thermoradiotherapy agent, graphene oxide‐iron oxide‐gold nanoparticles, temperature measurement, radiofrequency wave, flow cytometry, time 40.0 min, CO‐FeO‐Au     

Highly dispersed Co-Mo sulfide nanoparticles on reduced graphene oxide for lithium and sodium ion storage

Nano Research - A novel hybrid, highly dispersed spinel Co-Mo sulfide nanoparticles on reduced graphene oxide (Co3S4/CoMo2S4@rGO), is reported as anode for lithium and sodium ion storage. The...     

Chemical sensitivity of graphene edges decorated with metal nanoparticles

Graphene is a novel two-dimensional nanomaterial that holds great potential in electronic and sensor applications. By etching the edges to form nanoribbons or introducing defects on the basal plane, it has been demonstrated that the physical and chemical properties of graphene can be drastically altered. However, the lithographic or chemical techniques required to reliably produce such nanoribbons remain challenging. Here, we report the fabrication of nanosensors based on holey reduced graphene oxide (hRGO), which can be visualized as interconnected graphene nanoribbons. In our method, enzymatic oxidation generated holes within the basal plane of graphene oxide, and after reduction with hydrazine, hRGO was formed. When decorated with Pt nanoparticles, hRGO exhibited a large and selective electronic response toward hydrogen gas. By combining experimental results and theoretical modeling, we propose that the increased edge-to-plane ratio, oxygen moieties, and Pt nanoparticle decoration were responsible for the observed gas sensing with hRGO nanostructures.     

Wafer-scale reduced graphene oxide films for nanomechanical devices

We report a process to form large-area, few-monolayer graphene oxide films and then recover the outstanding mechanical properties found in graphene to fabricate high Young's modulus ( =185 GPa), low-density nanomechanical resonators. Wafer-scale films as thin as 4 nm are sufficiently robust that they can be delaminated intact and resuspended on a bed of pillars or field of holes. From these films, we demonstrate radio frequency resonators with quality factors (up to 4000) and figures of merit ( f x Q>10(11)) well exceeding those of pure graphene resonators reported to date. These films' ability to withstand high in-plane tension (up to 5 N/m) as well as their high Q-values reveals that film integrity is enhanced by platelet-platelet bonding unavailable in pure graphite.     

Ambient flash sintering of reduced graphene oxide/zirconia composites:Role of reduced graphene oxide

Fabrication of graphene/ceramic composites commonly requires a high-temperature sintering step with long times as well as a vacuum or inert atmosphere,which not only results in property degradation but also significant equipment complexity and manufacturing costs.In this work,the ambient flash sintering behavior of reduced graphene oxide/3 mol% yttria-stabilized ZrO₂(rGO/3 YSZ) composites utilizing rGO as both a composite component and a conductive additive is reported.When the sintering condition is carefully optimized,a dense and conductive composite can be achieved at room temperature and in the air within 20 s.The role of the rGO in the FS of the rGO/3 YSZ composites is elucidated,especially with the assistance of a separate investigation on the thermal runaway behavior of the rGO.The work suggests a promising fabrication route for rGO/ceramic composites where the vacuum and furnace are not needed,which is of interest in terms of simplifying the fabrication equipment for energy and cost savings.     

Fibers of reduced graphene oxide nanoribbons

Reduced graphene oxide nanoribbon fibers were fabricated by using an electrophoretic self-assembly method without the use of any polymer or surfactant. We report electrical and field emission properties of the fibers as a function of reduction degree. In particular, the thermally annealed fiber showed superior field emission performance with a low potential for field emission (0.7?V?μm(-1)) and a giant field emission current density (400?A?cm(-2)). Moreover, the fiber maintains a high current level of 300?A?cm(-2) corresponding to 1?mA during long-term operation.