rGO Surface Research Articles

Microwave-assisted preparation of hierarchical CuO@rGO nanostructures and their enhanced low-temperature H2S-sensing performance

Hierarchical CuO@rGO nanostructures, consisting of CuO nanoparticles (NPs) and reduced graphene oxide (rGO) nanosheets, were prepared with a normal-pressure microwave-assisted in-situ growth process. In the CuO@rGO composites, CuO NPs with a size range of 4–11 nm are uniformly anchored on rGO surfaces. In contrast, CuO particles of large and non-uniform distribution in the CuO-doped rGO nanosheets (CuO/rGO) were prepared by a conventional hydrothermal method. The CuO@rGO sensors show high response and selectivity to H2S (1–10 ppm) at low operating temperatures (50–150 °C). The mass ratio of copper acetate to graphene oxide during preparation (6–10) is found to highly influence the gas-sensing properties, and the 8-CuO@rGO sample shows the highest H2S-sensing performance at 100 °C. Compared with pristine CuO nanocrystals, the 8-CuO@rGO composite exhibits considerably enhanced gas-sensing performance, such as good response, high selectivity and low optimal temperature. The improved H2S-sensing performance of the CuO@rGO composites can be attributed to the synergistic effect in components and their hierarchical nanostructure.

Improving Oxygen Reduction Reaction and Selective Hydrodechlorination Performance Based on CoNi on Graphene Using Ionic Liquids as a Binder

As a binder for the stabilization and dispersion of CoNi nanoparticles (NPs), ionic liquids (IL) were designed to connect inorganic anion on IL-functionalized reduced graphene oxide (rGO) and metal cation. The CoNi/IL-rGO described excellent oxygen reduction reaction (ORR) and the selective adsorption of bimetallic CoNi for chlorophene hydrodechlorination (HDC). The prepared electrocatalyst was characterized by SEM, TEM, XPS, Raman spectroscopy, XRD, and UV–vis spectroscopy. Results indicated that ILs could be functionalized by π–π stacking on the rGO surface. The optimal bimetallic CoNi NPs (Co-to-Ni weight ratio of 2.5:2.5) with small particles sizes (3.33 ± 0.03 nm) were uniformly dispersed on the surface of IL-rGO (mass ratio of IL:GO was 2:1) among a series of as-prepared catalysts. The IL on the rGO surface could prevent rGO agglomeration and provide sufficient binding sites to anchor the CoNi NPs via electrostatic interaction. Co(2.5)Ni(2.5)/IL(2)-rGO demonstrated low impedance (7.5 Ω) and diffusion resistance due to the introduction of IL. Co(2.5)Ni(2.5)/IL(2)-rGO exhibited a high peak current (−0.35 mA), preferred two-electron selectivity and high H2O2 productivity (>80%) toward ORR in an alkaline solution. The possible dechlorination mechanism of chlorophene was ascribed to the combination of adsorbed hydrogen on Co and adsorbed chlorophene on Ni.

A rational design of a Pd-based catalyst with a metal–metal oxide interface influencing molecular oxygen in the aerobic oxidation of alcohols

The Pd–PdO interface stabilized on the rGO surface is shown to be the key to achieve enhanced catalytic activity in oxidation of alcohols under O2 as the oxidant.

Decoration and Functionalization of Graphene Oxide Nanocomposites for Sensing Applications

Abstract In the present work, β-cyclodextrin functionalized reduced graphene oxide-silver nanocomposites (GO-β-CD-Ag) are effectively synthesized using wet chemical method. The GO-β-CD nanocomposites are initially produced via hydrazine reduction. The various concentrations (0.002 M, 0.004 M, 0.006 M, 0.008 M and 0.01 M) of silver nanoparticles are decorated on the GO-β-CD surface by the reduction of silver nitrate with sodium borohydrate as a reducing agent. The produced GO-β-CD-Ag nanocomposites are well characterized using XRD, SEM and EDAX analysis. The XRD results firmly established that the β-CD molecules are satisfactorily coated on the rGO surface and also the Ag nanoparticles with an average size of 23 nm are evenly decorated on the GO-β-CD surface. The GO-β-CD-Ag nanocomposites modified glassy carbon electrode is captivated for the selective detection of o-Nitrophenol. Cyclic voltammetry test is employed to determine the presence of o-Nitrophenol compound. The result shows the oxidation and reduction potential for o-Nitrophenol at -0.25 V and -0.5 V respectively, indicating the successful determination of o-Nitrophenol by using the GO-CD-Ag nanocomposite modified electrode.

Effect of Copper Oxide on Structural, Optical and Photocatalytic Activity of Reduced Graphene Oxide for Eosin B

Nowadays incorporation of few oxygen groups between the layers of graphite have shown potential approach for industrialization of graphene oxide for different potential applications. During the strong oxidation process in modified Hummers method, these oxygen based functional groups may increase the distance, weakening the van der Waals forces and facilitation the exfoliation of graphite layers from. The reduced graphene oxide/copper oxide (rGO-CuO) is highly potentially active and selective catalyst for many environmental applications. Different wt. % of Cu(II) and loaded on rGO surface to form a nanocomposite, which were prepared by hydrothermal method. The influence of hydrothermal temperature, rGO sheet and loaded CuO on structure of graphene was systematically investigated. The structure and optical properties of the obtained hybrid composite was evaluated employing scanning electron microscope, X-ray diffraction, UV-visible and infrared spectroscopies. The photocatalytic activities of rGO-CuO nanocomposites for the degradation of Eosin B acid red under sunlight were investigated. The results revealed the decrease in percentage photocatalytic degradation rate occurred on rGO-CuO, because a single sheet of rGO can shield the light from reaching the surface of CuO photocatalyst. It is possible to provide a new way to use the host rGO as prepared by hydrothermal method for water remediation applications.

Biocompatible N-acetyl cysteine reduces graphene oxide and persists at the surface as a green radical scavenger.

We demonstrate that N-acetyl cysteine (NAC) reduces graphene oxide (GO) at room temperature. This represents a new green method to produce reduced GO (rGO). NAC adheres to the rGO surface as demonstrated by several spectroscopy techniques and avoids GO-mediated oxidation of glutathione. This method offers new opportunities for the production of green biocompatible rGO and NAC-based therapies.

Femtomolar Detection of Lipopolysaccharide in Injectables and Serum Samples Using Aptamer-Coupled Reduced Graphene Oxide in a Continuous Injection-Electrostacking Biochip.

A method for microfluidic sample preconcentration to detect femtomolar level of lipopolysaccharide (LPS) is introduced, enabled by 6-carboxyfluorescein (6-FAM) labeled aptamer-LPS binding along with reduced graphene oxide (rGO). The free FAM-aptamers can be adsorbed onto the surface of rGO, resulting in fluorescence quenching of background signals. Conversely, the aptamer-LPS complex cannot be adsorbed by rGO, so the fluorescence is maintained and detected. When an electric field is applied across the microchannel with Nafion membrane in the chip, only the fluorescence of aptamer-LPS complex can be detected and stacked by continuous injection-electrostacking (CI-ES). The method shows a high selectivity (in the presence of pyrophosphate, FAD+, NAD+, AMP, ADP, ATP, phosphatidylcholine, LTA, and β-d-glucans which respond positively to LAL) to LPS and an extreme sensitivity with the limit of detection (LOD) at 7.9 fM (7.9 × 10-4 EU/mL) and 8.3 fM (8.3 × 10-4 EU/mL) for water sample and serum sample, respectively. As a practical application, this method can detect LPS in injections and serum samples of human and sepsis model mouse and quickly distinguish Gram-negative bacteria Escherichia coli ( E. coli) from Gram-positive bacteria Staphylococcus aureus ( S. aureus) and fungus Candida albicans ( C. albicans). More importantly, by changing the aptamers based on different targets, we can detect different analytes. Therefore, aptamer-coupled rGO in a CI-ES biochip is a universal, sensitive, and specific method. For TOC only.

Magnetic iron oxide nanoparticles decorated graphene for chemoresistive gas sensing: The particle size effects

We report a synthesis of magnetic nanoparticles chemically immobilized onto reduced graphene oxide sheets (referred to as rGO-Fe3O4 NPs) as a gas and vapor sensing platform with precisely designed particle size of 5, 10 and 20 nm to explore their influence of particle size on sensing performance. The rGO-Fe3O4 NP sensors have been investigated their responses to different gases and volatile organic compounds (VOCs) at part-per-million (ppm) levels. Results show that the Fe3O4 NPs with smaller size (5 and 10 nm) on the rGO surface led to a lower sensitivity, while particles of a size of 20 nm have a significant enhancement of sensitivity compared to the bare rGO sensor. The rGO-Fe3O4 NP20 sensor can detect trace amounts of NO2 gas and ethanol vapor at the 1 ppm and is highly selective to the NO2 and ethanol among other tested gases and VOCs, respectively. The particle size causes different distribution behaviour of NPs over rGO surface and interspaced between them, which results in deceased or increased the surface interactions between gas and graphene. The NPs themselves contained different defects level and the charge depletion layer that affect their adsorption gas/vapor molecules, which are explained for different sensing responses.

Synthesis of RGO/BiOI/ZnO composites with efficient photocatalytic reduction of aqueous Cr(VI) under visible-light irradiation

The photocatalytic performance of BiOI was limited by slow electron transfer and fast charge recombination. In this study, RGO/BiOI/ZnO (RBZ) composites were successfully synthesized by two-step hydrothermal method. The phase structure, morphology, and optical property of the as-synthesized samples were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, ultraviolet-visible diffuse reflectance spectroscopy and photoluminescence. The results revealed that BiOI appears as a flower-like microspheres assembled by nanosheets which are anchored over RGO surface, while ZnO nanoparticles attached on the BiOI nanosheets. The photocatalytic activity of RBZ composites with different ZnO contents was investigated by the photocatalytic reduction of aqueous Cr(VI) under visible-light irradiation. The highest photocatalytic activity was observed in samples of RBZ composite with 8% ZnO. This can be attributed to the significantly enhanced efficient separation and transfer of photoinduced electron-hole pairs in RBZ composite. Therefore, the RGO/BiOI/ZnO composite photocatalyst can be a favorable alternative for practical use in environmental photocatalysis.

Magnetically Separable Ag/CuFe2O4 /Reduced Graphene Oxide Ternary Nanocomposite with High Performance for the Removal of Nitrophenols and Dye Pollutants from Aqueous Media

In this work, a novel ternary magnetic nanocomposite namely Ag/CuFe2O4/rGO was produced by a facile solvothermal route. The reduction of graphene oxide (GO) to reduced form (rGO) and the in-situ deposition of CuFe2O4 and Ag nanoparticles on rGO occurred simultaneously in a one-pot reaction. The structure, composition and morphology of the as-prepared nanocomposite were characterized by FT-IR, XRD, VSM, FESEM, EDX, TEM, and BET analyses. The results indicated that the Ag and CuFe2O4 nanoparticles were successfully loaded on the surface of rGO. The catalytic performance of the Ag/CuFe2O4/rGO nanocomposite was evaluated for the reduction of nitroarenes to corresponding amines in the presence of sodium borohydride (NaBH4) as a reducing agent. The nanocomposite exhibited the high performance in the reduction of the reduction of nitroarenes with 100% conversion within 10-30 min. The catalytic activity of the Ag/CuFe2O4/rGO was enhanced compared with Ag/CuFe2O4, Ag/rGO and CuFe2O4/rGO samples due to easier electron transfer process. Furthermore, the adsorption data revealed that cationic methylene blue (MB) dye could be removed almost completely on the Ag/CuFe2O4/rGO composite within 2 min and the composite could also selectively adsorb MB from the mixed solution with anionic methyl orange (MO). Due to the existence of magnetic CuFe2O4 nanoparticles, the Ag/CuFe2O4/rGO nanocomposite can be magnetically separated and reused without any change in structure and performance.

Simultaneous reduction and surface functionalization of graphene oxide for highly conductive and water dispersible graphene derivatives

A simple and effective preparation method for the simultaneous reduction and functionalization of graphene oxide (rGO) by 2,4-diamino benzene sulfonic acid has been developed. The derivatives exhibit excellent conductivity and high dispersibility in various solvents. The successful preparation of rGO and the presence of the sulfonated aromatic diamine on rGO surface has been confirmed by infrared and X-ray photoelectron spectroscopy, while, the analysis by micro-Raman spectroscopy indicated that the reduction/functionalization alters the lattice structure of GO by the increment the defect density when the 2,4-diamino benzene sulfonic acid is used. Moreover, the study of the dried products by X-ray diffraction spectroscopy suggested the turbostratic restacking of the exfoliated rGO into graphite-like nanostructures. The obtained derivative of simultaneous reduction and functionalization of GO was used for the preparation of highly conductive water-based gravure ink, which in turn, was successfully applied in printing on various flexible substrates, demonstrating its great potentiality in graphene-based flexible and printed electronics applications.

In-situ growing D-A polymer from the surface of reduced graphene oxide: Synthesis and nonvolatile ternary memory effect

As the cornerstone of the modern information technology, the development of memory devices with high speed, large capacity, long life time, low power consumption and ease of operation characteristics is beneficial for the fast revolution of the digital world. Using soluble 4-bromobenzene functionalized reduced graphene oxide (RGBr) as two dimensional template, in-situ growing of a novel donor-accept type conjugated polymer “poly[(1,4-diethynyl- benzene)-alt-(4,4′-(quinoxaline-2,3-diyl)bis(N,N-diphenylaniline))](PDQ)” from the RGO surface has been successfully realized via the palladium-catalyzed Sonogashira-Hagihara polymerization. The resultant material called as RGO-PDQ is highly soluble in some common organic solvents. The nonvolatile ternary rewritable memory performance has been observed in an electronic device with the RGO-PDQ film sandwiched between the Al and ITO electrodes. The switching threshold voltages on the ON-1 and ON-2 states are −0.74 and −1.44 V, respectively. The achieved current ratio of OFF: ON-1: ON-2 is about 1: 10: 104. The memory effect of the Al/RGO-PDQ/ITO device on the ON-1state can be assigned to the contribution of the PDQ moieties in the structure of RGO-PDQ. By using conductive atomic force microscopy (C-AFM) technique, the conductive nature of the RGO-PDQ film-based device was in-situ observed.

Engineering of ZnO/rGO nanocomposite photocatalyst towards rapid degradation of toxic dyes

Abstract ZnO quantum dot (QD) is prepared in a soft chemical route by ageing process and successfully embedded on reduced graphene oxide (rGO) surface using solvothermal method as confirmed by XRD, TEM and Raman studies. Due to charge transfer from the lowest unoccupied molecular orbital of the rGO layer to the conduction band of ZnO, the luminescence of rGO is also found to be quenched in ZnO/rGO composites. A brief systematic study of photocatalytic behavior towards degradation of various toxic medical and textile dyes, like Safranin O, Methylene blue and Rhodamine 6G by ZnO QD and ZnO/rGO composites are showcased in this work. As a result of high surface to volume ratio, ZnO QD showed good photocatalytic activity towards degradation of different dyes under ultraviolet (UV) irradiation. A composite with ZnO and rGO in 3:1 wt ratio degraded almost 100% of dyes under UV irradiation within 15, 25 and 30 min, showing good efficacy in dye degradation. Photoluminescence lifetime measurement revealed the charge transfer process from rGO to ZnO resulting a Prompt recombination of the UV light induced electron-hole pair in ZnO/rGO composite.

A facile immobilization of polyphenol oxidase enzyme on graphene oxide and reduced graphene oxide thin films: An insight into in-vitro activity measurements and characterization

Graphene oxide (GO) and reduced graphene oxide (rGO) Langmuir-Blodgett (LB) films with specific surface properties and functional groups were prepared as negative ideal substrates. Immobilization of the polyphenol oxidase (PPO) enzyme on these films was easily accomplished by electrostatic interaction without the need for any chemical bonding or surface modification. The PPO binding regions to GO and rGO surfaces were shown by an electrostatic surface potential map for pH: 5.0 value. The catalytic performances of the enzyme immobilized on GO and rGO substrates were found to be higher in GO-PPO LB films compared to RGO-PPO LB films in-vitro media. The reason why in-vitro enzyme activity is higher in GO-PPO LB films than in rGO-PPO LB films was also proved by SEM studies. The immobilization onto both the GO and rGO thin films as the GO-PPO and rGO-PPO complexes were further demonstrated by FT-IR measurement. This study revealed that the immobilized PPO enzyme on biodegradable GO is superior to the inorganic materials in terms of its use in biological systems. In addition, the fact that regular film structures with a single molecule thickness were prepared by LB film technique, contributed to the stability and recycling of immobilization of PPO enzyme on GO and rGO. In this respect, the in-vitro storage stability of immobilization on both film structures was determined to be one month at +4 °C.

Microwave absorption enhancement and loss mechanism of lamellar MnO2 nanosheets decorated reduced graphene oxide hybrid

Manganese oxide/reduced graphene oxide (MnO2/rGO) hybrid with layered MnO2 nanosheets grow on rGO surfaces have been prepared for microwave absorbing. The hybrid exhibits significantly enhanced microwave absorption properties compared with rGO and MnO2. A maximum reflection loss value can reach − 26.7 dB at 11.04 GHz with the matching thickness of 2.6 mm, and the effective absorption bandwidths exceeding − 10 dB and − 20 dB are 3.6 GHz and 1.06 GHz, respectively. The enhancement in microwave absorption efficiency of MnO2/rGO hybrid is arose from the synergistic effects between lamellar MnO2 and rGO in its unique three-dimensional (3D) architecture, which leads to strong conduction loss and multiple reflections, and further in favour of appropriate impedance matching ratio and good attenuation ability. These fundamental understandings on the property–structure relationship of as-synthesized MnO2/rGO hybrid will prove an efficient approach to the designing and construction of MnO2-based 3D nanostructures for advanced electromagnetic wave absorbing applications.

Nickel induced in situ growth of nickel hydroxide nanoflakes on reduced graphite oxide with high energy and power density

Layered hexagonal Ni(OH)2 nanoflakes have been successfully fabricated on the surface of reduce graphite oxide (rGO) via nickel induced in situ growth in this study. The layers number and size of Ni(OH)2 nanoflakes could be controlled by adjusting the concentration of Ni2+ precursors with nickel as active site on rGO surface. In the three electrode systems, the composite showed a relatively high specific capacitance achieved 1012.2 F∙g−1 at current density of 1 A∙g−1 with coulombic efficiency of 98.3%. As assembled in asymmetric devices (Ni(OH)2 nanoflakes loaded on rGO as positive electrode and active carbon as negative electrode), the maximum specific capacitance reaches to 260.9 F∙g−1 at current density of 0.5 A∙g−1 and the energy density can be maintained at 71.1 Wh∙kg−1 at power density of 26.95 kW∙kg−1 with good rate capability and acceptable cycling stability.

Effect of graphene oxide loading on TiO2: Morphological, optical, interfacial charge dynamics-A combined experimental and theoretical study

Reduced graphene oxide (rGO)TiO2 composites are prepared using photo-reduction method by varying GO to TiO2 weight ratio from low (rGOT-0.001, 0.01, & 0.1) to high (rGOT-1, 3 & 10) range and its effect on morphological, optical and mechanism of fast charge dynamics at the interface are investigated. Experimental analysis confirm that reduction process improves as TiO2 amount increases in rGO-TiO2 but leads to aggregation of TiO2 nanoparticles. rGOT-3 composite displayed the highest photocatalytic activity for degradation of phenols compared to TiO2, GO and other composites. This was achieved due to uniform dispersion of TiO2 nanoparticles over rGO surface, which enables distinct formation of TiOC bond between each TiO2 nanoparticle and rGO surface, and results in slight red shift in the band edge. This TiOC bond facilitates fast electron transfer from TiO2 to rGO and reduces recombination rate as revealed by photoluminescence and time resolved photoluminescence spectroscopy. The experimental findings were further investigated using density functional theory simulations. Band structure calculation confirms high mobility states induced within the band gap due to formation of TiOC bond in rGO-TiO2 model which assists in fast electron transfer from TiO2 to rGO during the photocatalytic process and hence reduces recombination rate.

Au-aided reduced graphene oxide-based nanohybrids for photo-chemotherapy

Graphene-based nanomaterials show great potential in photo-chemotherapy, but their photo-thermal effect is not very satisfactory. Herein, we presented a facile and low-cost strategy to grow Au clusters on the reduced graphene oxide (rGO) sheets aiming to improve photothermal effect. Au clusters with low-concentration was directly conjugated on the surface of rGO by electrostatic forces. To improve its biocompatibility, 3‑(3‑phenylureido) propanoic acid (PPA)-PEG (PPEG) had been introduced as biodegradable backbone to form rGO/Au/PPEG nanohybrids via π-π accumulation. The obtained rGO-based nanohybrids showed excellent biocompatibility, stability, low cytotoxicity, and enhanced photo-thermal conversion efficiency. To verify the synergistic photo-chemotherapy, doxorubicin (DOX) as a drug model had been loaded in rGO/Au/PPEG nanohybrids. The results indicated that rGO/Au/PPEG/DOX exhibited synergistic therapeutic efficacy compared with single chemotherapy or photothermal therapy, endowing this designed rGO-based nanohybrids with great potential for cancer treatments.

Mesoporous Mn3O4 coated reduced graphene oxide for high-performance supercapacitor applications

We report the facile synthesis of mesoporous Mn3O4 coated reduced graphene oxide (rGO) nanocomposite using a simple low temperature wet chemical process and demonstrated the nanocomposite material as high-performance electrodes for electrochemical supercapacitor. The nanocomposite structure is unique as it consists of an ultra-thin, mesoporous (pore size ∼1.9–2.6 nm) with oriented pore size of Mn3O4 layer deposited on the surface of rGO. The structure and the orientation of nanopores in the Mn3O4 layer were further confirmed using HRTEM, while structural and morphological analysis were carried out using XRD, Raman spectroscopy, SEM, TEM, and SAED. The pore size and the pore distributions were verified using BET surface area technique, which demonstrated the nanocomposite exhibits uniform distribution of pores of dimension ∼1.9–2.6 nm throughout. The electrocatalytic behavior of the nanocomposite was found to be ideal for their use as supercapacitor electrodes as high-performance charge storage devices. Finally, we demonstrate the supercapacitor electrode using Mn3O4-rGO nanocomposite followed by their electrochemical characterizations for electrocatalytic activity for charge storage. The hybrid material shows best capacitance value of 221 F g−1 at current density 0.15 A g−1 with good cycling stability. We believe that our investigations will pave a pathway towards various new applications, including, electrochemical catalysis, sensing, energy harvesting and storage and many more.

Preparation of Graphene Oxide and Its Application as Substrates for SERS

Graphene oxide (GO) was synthesized by a modified Hummer’s method and was then reduced by the hydrothermal process. Both GO and reduced GO (rGO) were employed as surface-enhanced Raman scattering (SERS) substrates to detect rhodamine 6G (R6G). After adsorbed on the surface of GO, the fluorescence background of R6G was highly quenched, and its Raman scatterings were enhanced. When adsorbed on the surface of rGO, the fluorescence background was further quenched at the price of lower SERS intensity. The results displayed that oxygen groups on the surface of GO had positive effect on the SERS effect of GO. The amount of oxygen groups on the surface of GO should be one key parameter to adjust the SERS activity of GO.