Self-assembled Reduced Graphene Oxide Research Articles

Conductive polymer-coated red phosphorus encapsulated in 3D graphene oxide aerogel for high-performance sodium-ion batteries anode

Relying on the high theoretical capacity for sodium storage, red phosphorus (RP) has attracted tremendous attention. However, its utilization is confronted with numerous limitations, such as substantial volume expansion and inferior conductivity. Herein, a RP anode (P/PPy@rGO) coated by conductive polypyrrole (PPy) was encapsulated in a spatially self-assembled reduced graphene oxide (rGO) aerogel by electrostatic interaction. The coating of PPy can not only enhance the conductivity of RP effectively, but also facilitate the connection between RP and rGO. Moreover, the rGO aerogel can accommodate the volume expansion of RP. Benefited from this unique structure, the P/PPy@rGO electrode can exhibit an enhanced rate performance (619 mAh/g at 5.2A g−1) and excellent cycling stability with a capacity retention of 89.5 % after 100 cycles. This work would contribute to the suitable design of phosphorus-based anode for sodium storage.

Three-dimensional self-assembled reduced graphene oxide composite as a promising adsorbent for the collection of palladium (II) and platinum (IV) in a low concentration

Three-dimensional self-assembled reduced graphene oxide composite as a promising adsorbent for the collection of palladium (II) and platinum (IV) in a low concentration

Highly stretchable strain sensors based on Marangoni self-assemblies of graphene and its hybrids with other 2D materials

Graphene and other two-dimensional materials (2DMs) have been shown to be promising candidates for the development of flexible and highly-sensitive strain sensors. However, the successful implementation of 2DMs in practical applications is slowed down by complex processing and still low sensitivity. Here, we report on a novel development of strain sensors based on Marangoni self-assemblies of graphene and of its hybrids with other 2DMs that can both withstand very large deformation and exhibit highly sensitive piezoresistive behaviour. By exploiting the Marangoni effect, reference films of self-assembled reduced graphene oxide (RGO) are first optimized, and the electromechanical behaviour has been assessed after deposition onto different elastomers demonstrating the potential of producing strain sensors suitable for different fields of application. Hybrid networks have been then prepared by adding hexagonal boron nitride (hBN) and fluorinated graphene (FGr) to the RGO dispersion. The hybrid integration of 2D materials is demonstrated to become a potential solution to increase substantially the sensitivity of the produced resistive strain sensors without compromising the mechanical integrity of the film. In fact, for large quasi-static deformations, a range of gauge factor values up to 2000 were demonstrated, while retaining a stable performance under cyclic deformations.

Synergistic Interfacial Bonding in Reduced Graphene Oxide Fiber Cathodes Containing Polypyrrole@sulfur Nanospheres for Flexible Energy Storage

Flexible lithium sulfur batteries with high energy density and good mechanical flexibility are highly desirable. Here, we report a synergistic interface bonding enhancement strategy to construct flexible fiber-shaped composite cathodes, in which polypyrrole@sulfur (PPy@S) nanospheres are homogeneously implanted into the built-in cavity of self-assembled reduced graphene oxide fibers (rGOFs) by a facile microfluidic assembly method. In this architecture, sulfur nanospheres and lithium polysulfides are synergistically hosted by carbon and polymer interface, which work together to provide enhanced interface chemical bonding to endow the cathode with good adsorption ability, fast reaction kinetics, and excellent mechanical flexibility. Consequently, the PPy@S/rGOFs cathode shows enhanced electrochemical performance and high-rate capability. COMSOL Multiphysics simulations and density functional theory (DFT) calculations are conducted to elucidate the enhanced electrochemical performance. In addition, a flexible Li-S pouch cell is assembled and delivers a high areal capacity of 5.8 mAh cm-2 at 0.2 A g-1 . Our work offers a new strategy for preparation of advanced cathodes for flexible batteries.

Multi-porous NiAg-doped Pd alloy nanoparticles immobilized on reduced graphene oxide/CoMoO4 composites as a highly active electrocatalyst for direct alcohol fuel cell

A self-assembled reduced graphene oxide (rGO)/CoMoO4 supported Pd, PdNi, PdAg and PdNiAg electrocatalysts were synthesized via hydrothermal and in situ impregnation-reduction method to investigate their performance for methanol, ethanol and ethylene glycol (EG) electrooxidation in alkaline media. XRD, TEM, SEM, EDS, XPS and BET were used to characterize the structure, surface features, and porosity of the catalysts, respectively. Electrochemical measurement revealed that tri-metallic PdNiAg@rGO/CoMoO4 catalyst displays outstanding electrocatalytic activity, toxicity resistance, and durability comparing to mono-metallic Pd and bi-metallic PdNi, PdAg counterparts and commercial Pd/C. The excellent electrocatalytic activity has been successfully achieved thanks to NiAg-doped Pd alloy nanoparticles (NPs) owning more surface-active centers and strong synergistic effects, and the host of GO/CoMoO4 providing superior electron transfer performance and multi-porous for the ternary catalyst. Further electrocatalysis mechanism of three kinds of alcohol oxidation drew up a detailed analysis. The design, preparation, and prominent performance of these novel composites offer a conception and promising potential for application of electrocatalyst in direct alcohol fuel cells.

Self-assembled reduced graphene oxide films with different thicknesses as high performance supercapacitor electrodes

Graphene-based materials have attracted considerable attention as the electrochemical energy storage and conversion material due to their high electronic conductivity and large ion-accessible surface area. Herein, a series of self-assembled reduced graphene oxide (rGO) films are facilely prepared via a scalable vacuum filtration method, whose thickness is regulated by changing the concentration of the filtering rGO solution. The effect of the mass loading (thickness) of rGO film electrodes on its electrochemical performance is investigated. These rGO film electrodes with mass loading of 6.7 mg cm−2 exhibit a high specific capacitance of 173.4 F g − 1 (1.16 F cm−2) at 1 A g − 1 and show high utilization of the active material due to their large specific surface area and uniform pore distribution. Moreover, a quasi-solid supercapacitor fabricated with the as-prepared rGO film electrode shows a high area capacitance of 1.03 F cm−2 and large specific energy of 0.073 mWh cm−2 at the specific power of 3.3 mW cm−2, as well as excellent cycling stability of 85.6% retention after 10,000 cycles. Such remarkable performance suggests that this rGO film is promising electrode material for supercapacitor application.

Synthesis of silver nanoparticles/porphyrin/reduced graphene oxide hydrogel as dye adsorbent for wastewater treatment

Facile and versatile strategies for the preparation of reduced graphene oxide hydrogel (rGH) are of great interest due to its various applications in pollution adsorption, catalysis, gas sensors and tissue engineering. In this study, the preparation of a novel self-assembled reduced graphene oxide hydrogel modified with silver nanoparticles (AgNPs) and various porphyrin complexes using the green hydrothermal approach were reported. The AgNPs were successfully decorated on the reduced graphene sheets via electrostatic interactions. On the other hand, the interaction of porphyrin complex with the Ag/rGH is via esterification and π-π interactions. Based on thermogravimetric analysis and BET analysis, the intercalation of porphyrin complex improved the thermal stability and specific surface area (SSA) of the modified hydrogels. Further characterizations of the modified hydrogel were accomplished using Raman spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectrometer (FT-IR), scanning electron microscope-energy dispersive spectroscopy (SEM/EDS), and UV–Vis spectrophotometry. The adsorption capacity of the modified hydrogels increased with the integration of AgNPs and porphyrin complexes due to the increase of the number of adsorption sites. The Ag/TPP/rGH exhibited the highest adsorption capacity (130.37 mg/g) towards the cationic dye, methylene blue (MB) which is attributed to the additional binding sites from the available unoccupied aromatic structures of the TPP. All prepared hydrogels kinetic reaction conformed to the pseudo second-order model with good stability for removing MB with efficiency above 90%.

Self-assembled reduced graphene oxide nanoflakes assisted by post-sonication boosted electrical performance in gold interdigitated microelectrodes

Reduced graphene oxide (rGO) is widely utilised to develop various types of biosensors; however, producing self-assembled rGO nanoflake networks through single-droplet drop-casting remains inconsistent. In the present work, we systematically used three different methods to prepare rGO suspensions in order to produce large scale self-assembled rGO nanoflake networks through single-droplet drop-casting. The rGO suspensions were prepared using only deionised water with no added any chemicals/organic solvents, which we considered to be a low-cost method. Subsequently, the most effective preparation method was used to deposit rGO nanoflakes onto commercial gold interdigitated microelectrodes (Au-IDE) to examine their electrical performance. Assessment of the yields, developed methods, surface morphologies, spectroscopy and structural analyses of the as-prepared rGO nanoflakes were conducted. The results revealed that method-3 (involving sonication, centrifugation and post-sonication) produced large self-assembled rGO nanoflake networks with strong adhesion to glass substrates. Furthermore, the as-prepared rGO/Au-IDE modified sensors showed excellent electron mobility where the electrical conductivity was enhanced approximately ~ 1000 fold compared to the bare devices. The present work provided new insights for depositing large self-assembled interconnected rGO nanoflake networks through single-droplet drop-casting which will be beneficial for biosensor development and other downstream applications.

Superstable copper nanowire network electrodes by single-crystal graphene covering and their applications in flexible nanogenerator and light-emitting diode

Copper nanowires (CuNWs), with excellent electronic properties and high cost-effectiveness, have tremendous potential in the field of transparent conductive electrodes for flexible electronics, large touch screen display and triboelectric energy harvesters, while their vulnerability to oxidation in air has impeded possible practical applications. Fortunately, it has been recognized that graphene encapsulation of CuNWs is capable of protecting CuNWs. However, neither self-assembled reduced graphene oxide nor chemical vapor deposition-grown polycrystalline graphene coatings can guarantee full protection to CuNWs, due to their ubiquitous voids, grain boundaries and wrinkles that allow water and oxygen molecules to pass through and result in the accelerated electrochemical corrosion at the graphene-copper interface, especially under folding conditions. Herein, we demonstrate a sandwich-structured single-crystal graphene/copper nanowire network/UV-curable resin (SCG/CuNW/UVR) composite film with ultrahigh electronic performance stability. The SCG/CuNW/UVR electrode exhibits a good optical and electrical performance (~19 Ω sq−1 under 84.3% transmittance), excellent mechanical robust and remarkably high oxidation resistance (ΔR/R0 < 0.2 within 180 days), in sharp contrast with the bare CuNWs (ΔR/R0 > 1 after 1 day) and polycrystalline graphene-covered CuNWs counterparts (ΔR/R0 > 1 after 7 days). Furthermore, the SCG/CuNW/UVR electrodes can replace indium tin oxide (ITO) electrodes to construct the triboelectric nanogenerators (TENG) and quantum dot light emitting diodes (QLED), comparable to the flexible commercial ITO counterparts. The fabrication of such high-performance SCG/CuNW/UVR electrode is facile to be scaled-up with low cost, providing the feasibility for industrial applications of flexible ITO-free electronic and optoelectronic devices.

A supercapacitor with ultrahigh volumetric capacitance produced by self-assembly of reduced graphene oxide through phosphoric acid treatment

Self-assembled reduced graphene oxide was prepared by a phosphoric acid heat-treatment method and exhibited an ultra-high volumetric capacitance.

Electricity generation by sliding an ionic solution droplet on a self-assembled reduced graphene oxide film

A voltage at the millivolt level could be generated by moving ionic droplets on a partially reduced, smooth graphene oxide film.

Self-assembled reduced graphene oxide–cerium oxide nanocomposite@cytochromechydrogel as a solid electrochemical reactive oxygen species detection platform

A new dimension for the selective detection of short-lived ROS by an electroactive reduced graphene oxide–cerium oxide nanocomposite@cytochromechydrogel.

Reduced-Graphene-Oxide-Guided Directional Growth of Planar Lithium Layers.

Rechargeable lithium (Li) metal batteries hold great promise for revolutionizing current energy-storage technologies. However, the uncontrollable growth of lithium dendrites impedes the service of Li anodes in high energy and safety batteries. There are numerous studies on Li anodes, yet little attention has been paid to the intrinsic electrocrystallization characteristics of Li metal and their underlying mechanisms. Herein, a guided growth of planar Li layers, instead of random Li dendrites, is achieved on self-assembled reduced graphene oxide (rGO). In situ optical observation is performed to monitor the morphology evolution of such a planar Li layer. Moreover, the underlying mechanism during electrodeposition/stripping is revealed using ab initio molecular dynamics simulations. The combined experiment and simulation results show that when Li atoms are deposited on rGO, each layer of Li atoms grows along (110) crystallographic plane of the Li crystals because of the fine in-plane lattice matching between Li and the rGO substrate, resulting in planar Li deposition. With this specific topographic characteristic, a highly flexible lithium-sulfur (Li-S) full cell with rGO-guided planar Li layers as the anode exhibits stable cycling performance and high specific energy and power densities. This work enriches the fundamental understanding of Li electrocrystallization without dendrites and provides guidance for practical applications.

Rational design of reduced graphene oxide film for solar thermal desalination

Abstract Solar water evaporation assisted by photothermal membranes is considered to be one of the sustainable and cost-effective strategies for pure water generation and wastewater treatment. In this work, a self-assembled reduced graphene oxide (rGO) film has been prepared and proposed for direct solar thermal desalination. The morphology, structure, absorbance and desalination performance of the rGO film are explored. It is found that rGO film with optimized microstructure delivers an evaporation rate of 0.87 kg m−2 h−1 with solar thermal conversion efficiency of 46% under 1 sun illumination. Moreover, the evaporation rate of rGO film remains at 0.86 kg/m2·h−1 after ten times recycling, demonstrating the superior reusability.

(Invited) Flexible and Self-Healing Aqueous Supercapacitors By Polyampholyte Gel Electrolytes with Biochar Electrodes and Their Unique Low Temperature Properties

Quenched polyampholytes provide a novel class of tough hydrogel that has self-healing ability, strong adhesion, and mechanical flexibility. Understanding the structure of polymer chains in the hydrogel and the phase behavior of water therein has broad impact on various applications, such as lubrication, adhesion, and electrical conductivity, as well as the hydrogel’s low temperature properties. In this paper, the structure of polymer chains of hydrogels made of a model charge-balanced polyampholyte, a random copolymer of poly(4-vinylbenzenesulfonate-co-[3-(methacryloylamino) propyl] trimethylammonium chloride), was investigated by small- and wide-angle x-ray scattering (SAXS and WAXS). The SAXS results suggested a networked globule structure in the charge-balanced polyampholyte hydrogels prevented freezing of water in the hydrogel, while the evidence of non-frozen water at low temperatures, such as –45 °C was monitored by solid-state 2H NMR. Correspondingly, we observed high ionic conductivity at low temperatures using electrochemical impedance spectroscopy (EIS). Interestingly, multiple freezing-thawing cycles did not impact the phase behavior of water in the hydrogel. We also found evidence that the crosslinked network structure of the polyampholyte chains disrupts the crystalline growth of ice, resulting in ‘slush-like’ ice formation. Utilizing the scientific investigations, a flexible and self-healing supercapacitor with high energy density in low temperature operation was fabricated using a polyampholyte hydrogel electrolyte. The electrode material was a biochar (produced from the low-temperature pyrolysis of biological wastes) bound by self-assembled reduced graphene oxide. Our novel sample preparation technique to enable the self-reinforcing wrapping of reduced graphene oxide sheets is turned out to have universal efficacy. The procedures of this technique will be introduced in the presentation. At the room temperature, the fabricated supercapacitor showed high energy density of 30 Wh/kg with 90% capacitance retention after 5000 charge-discharge cycles at room temperature at a power density of 50 W/kg. At –30 °C, the supercapacitor exhibited an energy density of 10.5 Wh/kg at a power density of 500 W/kg, which is threefold increase compared to control sample that do not incorporate polyampholyte hydrogel electrolyte. We also harnessed the tunable optical property of the polyampholyte hydrogel to fabricate a smart window. Specifically, we modulated the overall hydrophilicity/phobicity of polyampholyte chains when synthesizing the random copolymer and adjusted the upper critical solution temperature (UCST) at high precision, thus achieved a fine-tuning of UCST between 15 and 65 °C. Finally, we developed a stretchable, high-contrast, optically tunable stretchable window which consists of the PA hydrogel and a printed stretchable electric heater by our own ink recipe. In summary, we performed fundamental studies on the phase behavior of polymer chains and water molecules in quenched polyampholyte hydrogels by using synchrotron SAXS/WAXS, solid-state NMR, EIS, and DSC. We utilized the understanding in energy storage and smart window applications, both of which are unconventional for the application of tough hydrogels. In addition, we utilized renewable resource of biochar to fabricate low-cost, high-performance electrode material.

Graphene/Ruthenium Active Species Aerogel as Electrode for Supercapacitor Applications.

Ruthenium active species containing Ruthenium Sulphide (RuS2) is synthesized together with a self-assembled reduced graphene oxide (RGO) aerogel by a one-pot hydrothermal synthesis. Ruthenium Chloride and L-Cysteine are used as reactants. The hydrothermal synthesis of the innovative hybrid material occurs at 180 °C for 12 h, by using water as solvent. The structure and morphology of the hybrid material are fully characterized by Raman, XRD, XPS, FESEM and TEM. The XRD and diffraction pattern obtained by TEM display an amorphous nanostructure of RuS2 on RGO crystallized flakes. The specific capacitance measured in planar configuration in 1 M NaCl electrolyte at 5 mV s−1 is 238 F g−1. This supercapacitor electrode also exhibits perfect cyclic stability without loss of the specific capacitance after 15,000 cycles. In summary, the RGO/Ruthenium active species hybrid material demonstrates remarkable properties for use as active material for supercapacitor applications.

A stretchable and highly sensitive chemical sensor using multilayered network of polyurethane nanofibres with self-assembled reduced graphene oxide

sStretchable chemical sensors for detection of gases/vapours are of great interest for wearable applications in healthcare and environmental safety. Here, we demonstrate a simple but effective approach based on layering electro-spun elastomeric polyurethane (PU) nanofibres to produce stretchable chemically responsive nanohybrids of PU nanofibres with self-assembled reduced-graphene oxide (R-GO). The study using a chemiresistive structure reveals the positive effects of layering the elastomeric fibres of R-GO/PU nanohybrids on both stretching and sensing capabilities. The R-GO/PU devices layered four and five times own excellent sensitivity towards NO2 (50 ppb‒5 ppm at room temperature) as well as mechanical sustainability under static and cyclic stretching tests up to 50% of strain. These stretchable chemiresistors based on multilayering of hybrid fibre network of an elastomer and 2D sensing nanomaterials provides a good premise for wearable chemical sensing applications.

In situ self-assembled reduced graphene oxide aerogel embedded with nickel oxide nanoparticles for the high-efficiency separation of ovalbumin.

A three-dimensional reduced graphene oxide aerogel with embedded nickel oxide nanoparticles was prepared by a one-step self-assembly reaction in a short time. The nanoparticles could be captured into the interior of reduced graphene oxide network during the formation of the three-dimensional architecture. The composite exhibited porosity, good biocompatibility, and abundant metal affinity binding sites. The aerogel was used to isolate ovalbumin selectively from egg white, and favorable adsorption was achieved at pH 3. An adsorption efficiency of 90.6% was obtained by using 1 mg of the composite for adsorbing 70μg/mL of ovalbumin in 1.0mL of sample solution, and afterwards a recovery of 90.7% was achieved by using an eluent of 1.0mL Britton-Robinson buffer solution at pH 5. After the adsorption/desorption, ovalbumin showed no change in the conformation. The adsorption behavior of ovalbumin on the reduced graphene oxide composite well fitted to the Langmuir adsorption model, and a corresponding theoretical maximum adsorption capacity was 1695.2mg/g. A sodium dodecyl sulfate polyacrylamide gel electrophoresis assay demonstrated that the aerogel could selectively isolate ovalbumin from chicken egg white.

Au nanoparticle decorated graphene nanosheets for electrochemical immunosensing of p53 antibodies for cancer prognosis.

The accurate quantification of the level of p53 antibodies in serum is crucial for cancer prognosis. We report a novel and sensitive label-free immunosensor based on gold nanoparticles (Au NPs) self-assembled onto electrochemically reduced graphene oxide (ERGO) for the detection of p53 antibodies. An electrografted p-aminophenol organic layer was used to immobilize graphene oxide (GO) onto the surface of screen printed carbon electrodes (SPCE). The Au NP/ERGO hybrid interface provides a large surface area for the effective immobilization of p53 antigens, as well as it ascertains the bioactivity and stability of immobilized p53 antigens. Scanning electron microscope, Raman and X-ray photoelectron spectroscopies were used to monitor the sensor fabrication and cyclic voltammetry was used to quantify the extent of Au NPs' surface coverage by p53 antigens. Square wave voltammetry (SWV) of a [Fe(CN)6](3-/4-) couple was employed to investigate the immunosensor fabrication and to monitor the binding events between p53 antigens and p53 antibodies. Under optimized experimental conditions, the biosensor displayed good sensitivity and specificity. The p53 antibodies were detected in a concentration as low as 0.088 pg mL(-1) with a linear range from 0.1 pg mL(-1) to 10 ng mL(-1). The high sensitivity of the immunosensor may derive from the high loading of p53 antibodies on Au NPs which increases the number of binding events.

Reduced graphene oxide/hierarchical flower-like zinc oxide hybrid films for room temperature formaldehyde detection

We report a potential method to improve the room temperature formaldehyde (HCHO) gas-sensing properties of the layer-by-layer self-assembled reduced graphene oxide (rGO) film by introducing a special hierarchical flower-like zinc oxide (ZnO) structure. Hierarchical flower-like ZnO structures are developed by one step hydrothermal synthesis methods. Both rGO and rGO/ZnO sensitive films respond at once when exposed to HCHO at room temperature. The gas-sensing responses to 2–10ppm formaldehyde are enhanced in rGO/ZnO hybrid films compared with pure rGO films. The enhanced formaldehyde gas-sensing responses are attributed to the more adsorption sites on the surface of the rGO/ZnO hybrid films and the reduced barrier height for the electron transfer during the gas sensing process.