Reduced Graphene Oxide Nanosheets Research Articles

SnO2 Quantum Dots Decorated Reduced Graphene Oxide Nanosheets Composites for Electrochemical Supercapacitor Applications

SnO2 Quantum Dots Decorated Reduced Graphene Oxide Nanosheets Composites for Electrochemical Supercapacitor Applications

Facile synthesis of Pt-Cu bimetallic catalyst on reduced graphene oxide nanosheets and its application for electrochemical sensing

The fabrication and application of bimetallic catalysts are of significance in enhanced electrocatalytic performance. In this work, sea urchin-like Pt-Cu bimetallic catalyst was synthesized by a one-pot aqueous method. The alloy was reduced and grown directly on the surface of reduced graphene oxide (RGO), which can maximize the contact/interaction between metals and RGO to achieve the enhanced catalytic activity. The transmission electron microscopy images revealed that the Pt-Cu bimetallic particles were uniformly dispersed on RGO in the shape of sea urchin-like with the size about ~ 20 nm. A hydrazine electrochemical sensor was built by modifying glassy carbon electrode with Pt-Cu/RGO nanomaterial. The electrochemical experiments showed that the proposed sensor exhibited an excellent performance for hydrazine analysis with a wide linear range of 0.4 μM-12 mM and a low detection limit of 0.13 μ M (S/N = 3). Additionally, the sensor also demonstrated a long term stability, good selectivity and repeatability.

ZrB2-Based "Brick-and-Mortar" Composites Achieving the Synergy of Superior Damage Tolerance and Ablation Resistance.

The intrinsic brittleness and poor damage tolerance of ultrahigh-temperature ceramics are the key obstacles to their engineering applications as nonablative thermal protection materials. Biomimetic layered or "brick-and-mortar" hybrid composites composed of alternative strong/weak interfaces exhibit excellent strength and high toughness; however, the commonly used interfacial materials are weak and have poor thermal stability and ablation resistance, which strictly limit their use in high-temperature and oxidative environments. In this work, ZrB2-based "brick-and-mortar" hybrid ceramics were constructed with a hierarchical biomimetic design to improve the fracture resistance and damage tolerance. ZrB2-20vol %SiC ceramics containing 30 vol % reduced graphene oxide nanosheets were used as the weak interface to increase crack growth resistance without destroying the excellent ablation resistance. Finally, the ZrB2-based "brick-and-mortar" composites achieve the synergy of superior damage tolerance and ablation resistance.

Fabrication of chlorambucil loaded graphene- oxide nanocarrier and its application for improved antitumor activity

The present study aims at designing a biodegradable and biocompatible nanocarrier using gelatin and reduced graphene oxide nanosheets functionalized with folic acid, for release of chlorambucil drug in controlled manner and achieving high loading efficiency. From scanning electron microscopic studies small pore like structure with rough and thick morphology on the plane of graphene oxide is clearly visible indicating high loading of drug. Further, Drug loading and encapsulation efficiency, in vitro release studies of the drug from the nanocarrier at different concentrations of reduced graphene oxide, different pH were studied. The mean particle size, entrapment efficiency (%) of optimized folic acid functionalized gelatin-graphene oxide formulation was observed to be 300 nm and 56% respectively. From the release studies it is clear that, after 24 h the release rate of the drug was found to be higher at acidic conditions compared to neutral conditions. It was found that 62.1% and 82% of the total bound drug was released from the nanocarrier at pH 5.4 and pH 1.2 respectively. Besides, under neutral conditions (pH 7.4), 43.7% of the total bound drug was released from the nanocarrier in the first 24 h. The % cell viability of free drug, drug loaded nanocomposites against human cervical adenocarcinoma cell line was found to be 11.7% and 28% respectively at the dose of 500 μg mL−1 after 24 h. IC50 values also manifest the significantly lower cytotoxicity of drug loaded nanocarrier (IC50 = 125.9 μg/mL) as compared to free-drug (IC50 = 86 μg/mL). For FAGGO, CLB and CLB-FAGGO the values of mean ± std. deviation were found to be 71.80 ± 6.66; 48.71 ± 23.15; 55.48 ± 19.65 respectively. The unique properties exhibited by biodegradable polymer like gelatin and carbon based materials such as graphene offers an excellent applications in biomedical field.

Construction of novel n-type semiconductor anchor on 2D honey comb like FeNbO4/RGO for visible light drive photocatalytic degradation of norfloxacin

A novel FeNbO4/RGO photocatalyst was prepared via hydrothermal method followed by ultrasonication for the environmental remediation. The obtained samples were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), UV–vis diffuse reflection spectroscopy (UV–vis DRS), photoluminescence (PL) spectroscopy, electrochemical impedance spectra (EIS) and mott-schottky (M–S) plot. It was indicated that the monoclinic FeNbO4 was anchored on reduced graphene oxide nanosheet (RGO) which enhances visible-light absorption. The prepared hybrid samples exhibited the obvious improvement of photocatalytic activity and stability for norfloxacin (NRF) degradation under visible light irradiation 250 W Xe lamp as source with 420 nm UV- cut off filter. A Gas chromatography-mass spectrometry (GC–MS) was used to identify the major intermediates during NRF degradation. The photocatalytic efficiency for FeNbO4/RGO was about 87 % and its rate constant value was greater than bare FeNbO4.

Synthesis of silver nanoparticles decorated on reduced graphene oxide nanosheets and their electrochemical sensing towards hazardous 4-nitrophenol

In this study, an electrochemical sensor for the detection of 4-Nitrophenol (referred to as 4-NP) was developed based on templated silver nanoparticles (AgNPs) on reduced graphene oxide (rGO) nanosheets (Ag-rGO) and utilized as an electrocatalyst. It was found that the resulting composite exhibits enhanced catalytic activity towards the reduction of 4-NP. The cubic shaped AgNPs templated on rGO nanosheets has been successfully fabricated by a chemical reduction method using sodium borohydride (NaBH4), and it was well characterized through morphological and electrochemical techniques: Ultraviolet–Visible spectroscopy (UV -Vis), scanning electron microscopy (SEM) equipped with energy-dispersive spectroscopy (SEM–EDS), transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), cyclic voltammetry (CV), and chronoamperometry. The obtained results revealed that the AgNPs scattered on rGO sheets are spherical in shape, and it’s estimated to be a dimension of ~ 60 nm in size. The prepared crystalline Ag-rGO nano sheets were further applied as an electrode material for the electrochemical examination with three electrode system to sense the hazardous material 4-NP in PBS. The electrochemical studies were conducted through CV under the condition of bare and coated electrode (Ag-rGO/GCE) with influence of concentration (4-NP from 2 to 150 mM), scan rate, reproducibility (RSD-2.87%) and stability test (4-NP-20 µM) were examined. The data reveal that the Ag-rGO/GCE exhibit highly reproducible and sustainable for the reduction of toxic 4-NP. The chronoamperometry study for current and time response was also studied at two different potentials (− 0.3 V & − 0.6 V), respectively.

Bio-reduction of Graphene Oxide: Catalytic Applications of (Reduced) GO in Organic Synthesis.

This work is based on various bio-reduction of graphene oxide into reduced graphene oxide and their applications in organic synthesis and group transformations. Graphene oxide, with abundant oxygencontaining functional groups on its basal plane, provides potential advantages, including excellent dispersibility in solvents and the good heterogeneous catalyst. This manuscript reviews various methods of synthesis of graphene and graphene oxide and a comparative study on their advantages and disadvantages, how to overcome disadvantages and covers extensive relevant literature review. In the last few years, investigation based on replacing the chemical reduction methods by some bio-compatible, chemical/impurity-free rGO including flash photo reductions, hydrothermal dehydration, solvothermal reduction, electrochemical approach, microwave-assisted reductions, light and radiation-induced reductions has been reported. Particularly, plant extracts have been applied significantly as an efficient reducing agent due to their huge bioavailability and low cost for bio-reduction of graphene oxide. These plant extracts mainly contain polyphenolic compounds, which readily get oxidized to the corresponding unreactive quinone form, which are the driving force for choosing them as bio-compatible catalyst. Currently, efforts are being made to develop biocompatible methods for the reduction of graphene oxide. The reduction abilities of such phytochemicals have been reported in the synthesis and stabilization of various nanoparticles viz. Ag, Au, Fe and Pd. Various part of plant extract has been applied for the green reduction of graphene oxide. Furthermore, the manuscript describes the catalytic applications of graphene oxide and reduced graphene oxide nanosheets as efficient carbo-catalysts for valuable organic transformations. Herein, important works dedicated to exploring graphene-based materials as carbocatalysts, including GO and rGO for organic synthesis including various functional group transformations, oxidation, reduction, coupling reaction and a wide number of multicomponent reactions have been highlighted. Finally, the aim of this study is to provide an outlook on future trends and perspectives for graphene-based materials in metal-free carbo-catalysis in green synthesis of various pharmaceutically important moieties.

How the fluorographene replaced graphene as nanoadditive for improving tribological performances of GTL-8 based lubricant oil

Fluorographene, a new alternative to graphene, it not only inherits the 2-dimensional (2D) layered structure and outstanding mechanical properties, but also possesses controllable C–F bonds. It is meaningful to reveal the evolution processes of the tribological behaviors from graphene to fluorographene. In this work, fluorinated reduced graphene oxide nanosheets (F–rGO) with different degree of fluorination were prepared using direct gas-fluorination and they were added into gas to liquid-8 (GTL-8) base oil as lubricant additive to improve the tribological performance. According to the results, the coefficient of friction (COF) reduced by 21%, notably, the wear rate reduced by 87% with the addition of highly fluorinated reduced graphene oxide (HF–rGO) compared with rGO. It was confirmed that more covalent C–F bonds which improved the chemical stability of HF–rGO resisted the detachment of fluorine so the HF–rGO nanosheets showed less damage, as demonstrated via X-ray photoelectron spectroscopy (XPS), Raman spectra, and transmission electron microscopy (TEM). Meanwhile, the ionic liquid (IL) adsorbed on HF–rGO successfully improved the dispersibility of F–rGO in GTL-8 base oil. The investigation of tribofilm by TEM and focused ion beam (FIB) illustrated that IL displayed a synergy to participate in the tribochemical reaction and increased the thickness of tribofilm during the friction process.

Colorimetric biosensing of nopaline synthase terminator using Fe3O4@Au and hemin-functionalized reduced graphene oxide.

In this paper, we present a simple and label-free colorimetric biosensor for detection of the nopaline synthase (NOS) terminator in genetically modified (GM) plants. The "signal on" colorimetric biosensor was developed using a nanocomposite consisted of gold nanoparticles doped magnetic Fe3O4 nanoparticles (Fe3O4@Au NP), capture probe DNA (cDNA), and hemin-functionalized reduced graphene oxide nanosheets (H-GN). The nanocomposite was successfully prepared by means of Au-S bonds and the strong π interactions between cDNA and H-GN. The sensing approach is based on the excellent peroxidase-mimicking activity of H-GN and its different electrostatic interactions with single-stranded DNA (ssDNA) and double-stranded DNA (dsDNA). In presence of the target NOS, the cDNA in the nanocomposite will hybridize with its complementary sequence, and form dsDNA structure. Due to the weak π interactions between dsDNA and H-GN, a portion of H-GN will be released from the surface of Fe3O4@Au NPs and transferred into solution. After magnetic separation was performed, the supernatant was incubated with 3,3',5,5'-tetramethylbenzidine (TMB) in the presence of H2O2. The released H-GN can catalyze the oxidation reaction of TMB and turn the colorless solution blue. This "signal-on" colorimetric biosensor shows a broad linear range of 0.5-100nM for the target NOS, with a 0.19nM detection limit. The application of the biosensor for determination of NOS segments in samples of GM and non-GM tomatoes shows that it can discriminate between GM and non-GM plants. The reliability of the method for samples of NOS-spiked GM tomato suggests satisfactory recoveries in the range of 93.6%-94.2%.

Multi-component nanocomposite infrared flare with superior infrared signature via synergism of nanothermite and reduced graphene oxide

Infrared-guided missiles caused 90% aircraft damage. Infrared decoy flares are effective counter measure against infrared missiles. Decoy flare thermal signature depends mainly on black body emission of carbonaceous combustion products. Thermite particles can offer substantial heat output to promote black body emission. Reduced graphene oxide (RGO) is a promising material for advanced infrared decoy flares. RGO could act as ideal black-body emitter with superior thermal properties and high interfacial surface area. This study is dedicated to investigate novel synergism between Fe2O3 and RGO; Fe2O3 NPs of 3.56 nm were fabricated using hydrothermal synthesis technique. RGO nano-sheets of 10 µm dimensions and 10 nm thickness were developed via the reduction of graphene oxide, developed by Hummer method. Complete reduction of GO to RGO was confirmed by Raman spectroscopy. Amorphous nano-sheets structure was observed using TEM; XRD diffractogram demonstrated tiny characteristic broad peak for amorphous RGO. Decoy flare formulation based on Fe2O3, RGO, reactive metal fuel (Mg), and fluorocarbon polymer (teflon) were developed. Thermal signature was evaluated using Arc-Optics IR spectrometer (1–6 µm). Multi-component MTV nanocomposite flare based on 6 wt % RGO and 2 wt % Fe2O3 demonstrated superior spectral and radiometric performance. It offered an increase in average intensity by 130% to reference MTV formulation; additionally it offered superior relative intensity Ɵ value of 0.76. While RGO could act as novel black body emitter; thermite reaction between Fe2O3 NPs and surplus magnesium fuel could provide substantial heat output; that could promote RGO black body emission.

Honeycomb-like open-edged reduced-graphene-oxide-enclosed transition metal oxides (NiO/Co3O4) as improved electrode materials for high-performance supercapacitor

• Honeycomb reduced graphene oxide (HOrGO) serves as an efficient conductive network. • The HOrGO/TMOs (NiO/Co 3 O 4 ) hybrids were synthesized via microwave-assisted method. • The micron-sized (~100 μm) open edges of HOrGO NSs hold the NiO/Co 3 O 4 nanoparticles. • The HOrGO/TMOs hybrids deliver specific capacitance 910 F/g at scan rate 20 mV/s. • The HOrGO/TMOs hybrids exhibited high retention with stabile performance. Honeycomb-like open edges reduced graphene oxide nanosheets (HOrGO NSs) filled with transition metal oxides (TMOs) as NiO/Co 3 O 4 nanoparticles (NPs) has been synthesized by a simple and cost-effective microwave irradiation method. The microwave irradiation assisted synthesized HOrGO filled with NiO/Co 3 O 4 NPs (HOrGO/TMOs) hybrids exhibits high specific capacitance with improved cycling stability as excellent electrode materials for supercapacitors (SCs). The HOrGO NSs contains high surface area (~570 m 2 g −1 ) due to highly exfoliated nanostructure comprising open edges enriched morphology. In HOrGO/TMOs hybrids, the several micron-sized (~100 μm) open edges of HOrGO NSs holds the NiO/Co 3 O 4 NPs with finely separated thin few-layer graphene NSs. The structural/ morphological analysis of synthesized HOrGO NSs and HOrGO/TMOs hybrids were extensively characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDS), X-ray photoelectron spectroscopy (XPS), Raman spectra, thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) surface area. The HOrGO/TMOs hybrids deliver high specific capacitance of 910 F g −1 and high robust cycling stability with capacitance retention as 89.9% after continuous 2000 cycles. The proposed mechanism explain the microwave irradiation assisted formation of HOrGO/TMOs hybrids and provides a general and low-cost approach to synthesized high quality graphene hybrids materials for SCs application.

Fischer-Tropsch synthesis by reduced graphene oxide nanosheets supported cobalt catalysts: Role of support and metal nanoparticle size on catalyst activity and products selectivity

In this paper, a series of cobalt catalysts supported on reduced graphene oxide (rGO) nanosheets with the loading of 5, 15 and 30 wt-% were provided by the impregnation method. The activity of the prepared catalysts is evaluated in the Fischer-Tropsch synthesis (FTS). The prepared catalysts were carefully characterized by nitrogen adsorption-desorption, hydrogen chemisorption, X-ray diffraction, Fourier transform infrared spectro-scopy, Raman spectroscopy, temperature programmed reduction, transmission electron microscopy, and field emission scanning electron microscopy techniques to confirm that cobalt particles were greatly dispersed on the rGO nanosheets. The results showed that with increasing the cobalt loading on the rGO support, the carbon defects are increased and as a consequence, the reduction of cobalt is decreased. The FTS activity results showed that the cobalt-time yield and turnover frequency passed from a maximum for catalyst with the Co0 average particle size of 15 nm due to the synergetic effect of cobalt reducibility and particle size. The products selectivity results indicated that the methane selectivity decreases, whereas the C5+ selectivity raises with the increasing of the cobalt particle size, which can be explained by chain propagation in the primary chain growth reactions.

Effect of Water in Fabricating Copper Nanoparticles onto Reduced Graphene Oxide Nanosheets: Application in Catalytic Ullmann-Coupling Reactions

Abstract Copper nanoparticles fabricated onto reduced graphene oxide (Cu NPs/rGO) were successfully synthesized via a one-pot dimethylformamide (DMF) reduction approach with an addition of nominal water. This small amount of water can significantly decrease the degree of GO reduction by DMF. As a result, the remaining oxygen-containing functionality on rGO can still interact with the copper cation precursor leading to the high Cu content fabricated onto the support material, which was evidenced by X-ray photoelectron spectroscopy (XPS). Moreover, small particle sizes and high dispersion of Cu NPs on rGO were confirmed by scanning transmission electron microscopy (STEM). In addition, our Cu NPs/rGO was competent to catalyze the Ullmann-coupling reaction (i.e., arylation of 3,5-dimethylphenol with 86% yield and turnover number of 2,642).

Reduced graphene oxide: a novel black body emitter for advanced infrared decoy flares

ABSTRACT Reduced graphene oxide (RGO) possesses unique thermal and optical properties. It could act as black body emitter with high-infrared emissivity. RGO could meet wide applications in advanced infrared decoy flares. In this study, RGO nano-sheets were synthesized through the reduction of GO after applying Hummers’ method using graphite powder as a precursor. The synthesized RGO owns 10 µm dimensions and 10 nm thicknesses. TEM analysis revealed the amorphous structure of the prepared nano-sheets. XRD diffractogram demonstrated the amorphous RGO structure. Moreover, Raman spectroscopy confirmed the complete reduction of GO into RGO. In addition, decoy flare formulations based on RGO, reactive metal fuels, and fluorocarbon polymer were developed. Additionally, thermal signature was evaluated using Arc-Optics IR spectrometer (1–6 µm) to reference formulation. Our results revealed that nanocomposite flare based on 6 wt % RGO demonstrated superior spectral intensity with an increase in average intensity by 147%. Moreover, advanced radiometric performance with superior relative intensity value (Ɵ) of 0.7 was recorded. To sum up, RGO can act as an excellent source of carbonaceous materials that can strengthen incandescence emission. Surplus magnesium could vaporize and combust with substantial heat output that could promote black body emission.

RGO-templated lignin-derived porous carbon materials for renewable high-performance supercapacitors

Porous carbon materials are considered as one of the most promising electrode materials of supercapacitors. However, it is inevitable to use an expensive and high-polluting activation treatment for obtaining porous structure. Herein, we reported a scalable and sustainable approach to fabricate lignin-derived porous carbon materials by combining hydrothermal reaction and high-temperature carbonization without using any chemical or physical activating reagents. During the hydrothermal reaction, industrial waste lignin as a green reducing agent deoxidized graphene oxide (GO) effectively, while reduced GO (RGO) hydrogels as 3D templates transitioned lignin molecules from ellipsoidal to disk-like conformation via non-covalent interactions and orderly aligned them on the surface of RGO nanosheets. Through this way, the intermediate products, lignin reduced GO aerogels (LRGOs), delivered superior pseudocapacitive performance caused by the reversible phenol-quinone structural transition of lignin molecules. Results indicated a highly positive correlation between the pseudocapacitance of LRGOs and the reduction degree of RGO. After carbonization, the carbonized LRGOs (C-LRGOs) presented a hierarchical porous structure and the resulted high specific surface area rendered the material an ideal electrical double layer capacitive behavior showing high specific capacitance (330 F g−1 at 1 A g−1), high energy density (11.3 Wh kg−1) at a power density of 254 W kg−1, as well as reliable cycle performance.

Green Synthesis of Reduced Graphene oxide Nanosheets Using Leaf Extract of Lantana camara and Its In-Vitro Biological Activities

In recent years, sustainable green chemistry sets eco-efficiency approaches to synthesis next generation nanomaterials using plant sources as reducing agents. Among them, reduced Graphene oxide (rGO) has been developing as biocompatible nanomaterials in biomedicine. The present work deals with facile synthesis of rGO using leaf extract of Lantana camara (LC). The bioreduction of graphene oxide (GO) to reduced Graphene oxide by L. camara (LCrGO) was confirmed by spectroscopic techniques such as UV–visible, XRD, FTIR, Raman spectrometer, Zeta potential and DLS. SEM and TEM microscopic revealed the presence of thin nano sheets of LCrGO. EDX detected intense signals of Carbon (86%) and Oxygen (13%) present in LCrGO. The bioreduced LCrGO showed potential in vitro biological effects. DPPH assay showed 79% radical inhibition at 500 µg/ml. The LCrGO exhibited enhanced bactericidal effects against B. subtilis (16 mm) and E. coli (12 mm) at 500 µg/ml. MTT assay showed concentration dependent cytotoxic effects against lung cancer cell lines (A549) with decrease in cell viability (44%) at maximum concentration of LCrGO (500 µg/ml). From the observations, it is concluded that rGO nanosheets synthesized using L. camara could be used for formulation of nanomedicine.

Superior performance of Ni(OH)2-ErGO@ NF electrode materials as pseudocapacitance using electrochemical deposition via two simple successive steps

Abstract In this work we report the synthesis of electrochemically deposited Ni(OH)2 nanoparticles on the surface of in-situ electrochemically reduced graphene oxide nanosheets (ErGO NSs) supported on 3D networked nickel foam (NF) to form Ni(OH)2-ErGO@NF as electrode materials for supercapacitor (SCs) application. The adopted three-electrode electrochemical system via a two-step process for the synthesis of Ni(OH)2-ErGO@NF was fast and cost effective. First, 2D nanosheets of ErGO were deposited on NF by potential square wave technique. Second, Ni(OH)2 nanoparticles were deposited on the surface of 2D nanosheets ErGO by potentiostat. The electrochemical behavior of the Ni(OH)2-ErGO@NF electrode was measured in 1 M KOH and revealed an impressive supercapacitive performance, with high specific capacitance of 3138 F/g at scan rate 20 mV/s. The synthesized Ni(OH)2-ErGO@NF exhibited excellent cyclic stability, with capacitance retention of 88.6% after 3000 cycles at a scan rate 50 mV/s. The enhanced electrochemical performance of SCs was attributed to the superior conductivity of ErGO NSs, which facilitated the transfer of charges and the diffusion of KOH electrolyte, making it is a promising candidate for SCs electrodes. This synthesis provides an appropriate approach for preparing other kinds of metal hydroxides with rGO for improved SCs electrode performance.

Fabrication of dye-sensitized solar cells based on push-pull asymmetrical substituted zinc and copper phthalocyanines and reduced graphene oxide nanosheets

Dye sensitized solar cells (DSSCs) were fabricated by using 2(3,5-biscarboxyphenoxy), 9(10), 16(17), 23(24)-tri(tertbutyl) phthalocyaninato Cu (4) and Zn (5) complexes as dyes on the ITO-TiO2 photoanodes containing reduced graphene oxide nanosheets (rGONS) or nitrogen-doped rGONS (NrGONS). The evaluation of the assembled DSSCs revealed that using ITO-TiO2-NrGONS-CuPc photoanode had the highest fill factor (FF) and power conversion efficiency (ɳ) of 69% and 4.36% respectively. These results show that the asymmetrical phthalocyanine complexes (4) and (5) exhibit significant improvement on the performance of the DSSC compared to our previous work on symmetrical carboxylated phthalocyanines with ɳ = 3.19%.

Sonochemical assisted synthesis of manganese–nickel molybdate/reduced graphene oxide nanohybrid for energy storage

Abstract In the present study, manganese-nickel molybdate was synthesized using an ultrasonic assisted method for the first time. The hybrid of reduced graphene oxide (RGO) with manganese-nickel molybdate was also prepared. The structure of nanohybrid was characterized by Raman spectroscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, and inductively coupled plasma optical emission spectrometry (ICP-OES). Field emission scanning electron microscopy images showed that the manganese-nickel molybdate has the nanorod morphology. In addition, transmission electron microscopy images confirmed the presence of reduced RGO nanosheets in the nanohybrid. From ICP-OES, the nanohybrid formula was obtained as Mn0.63Ni0.37MoO4-RGO. Some electrodes with different RGO weight ratios were also prepared on nickel foam (NF) plates. Cyclic voltammetry studies showed that nanohybrid has typical faradaic redox behavior in 2 M KOH. Additionally, galvanostatic investigations showed that Mn0.67Ni0.37MoO4- RGO (60 wt %) nanohybrid can provide the high specific capacity of 161.1 mA h g−1 at 2 A g−1, which is higher than that for MnMoO4-RGO and NiMoO4-RGO nanohybrids. Furthermore, the electrode based on Mn0.67Ni0.37MoO4 provided higher specific capacity than that for MnMoO4 or NiMoO4. Owing to the synergistic effect of both Mn and Ni elements with RGO in nanohybrid, the Mn0.67Ni0.37MoO4-RGO showed the high energy density of 87 W h kg−1 at 1080 W kg−1 and the power density of 8640 W kg−1 at 9.6 W h kg−1. The electrode provided the cyclic stability about 92% of its initial capacity after 2000 cycles at 50 mV s−1. Our results showed the successful synthesis of manganese-nickel molybdate/RGO nanohybrid for the potential use in energy storage systems.

Reduced graphene oxide nanosheets doped by Cu with highly efficient visible light photocatalytic behavior

Abstract Graphene oxide (GO) and reduced graphene oxide (RGO) exhibit good electrochemical properties due to their semiconducting nature, large surface area, high concentration of functional groups and unique layered structure. They have been used widely for the removal of heavy metal ions, dyes and other organic contaminants from water. In the present study, a modified Hummer’s method was used to prepare GO while Cu-doped RGO which was obtained by employing a simple hydrothermal process. X-ray diffraction analysis confirmed the presence of GO sheets and Cu-doped RGO in the synthesized product. Examination with field emission scanning and high resolution transmission electron microscopes revealed an ultrathin, porous and layered structure of GO nanosheets while RGO sheets appeared as a well-defined, layered and non-agglomerated sponge. Dispersion of Cu within RGO sheets was also confirmed during microstructural study. Optical properties, such as absorption of light and bandgap width, were studied using UV–visible spectroscopy. Photoluminescence characterization showed maximum emission between 300 and 350 nm (UV region) caused by the presence of vacancies and surface defects in synthesized sheets. In aqueous media, methylene blue (MB) pollutant was photodegraded up to 91% within 80 min when Cu-doped RGO photocatalyst was employed under visible light irradiation. The present work shows the ability of Cu-doped RGO to degrade aqueous pollutants in an efficient manner. In conclusion, this product can find potential application in the removal of organic pollutants from wastewater.