Self-assembled Graphene Research Articles

Development of 3D Urchin-Shaped Coaxial Manganese Dioxide@Polyaniline (MnO2@PANI) Composite and Self-Assembled 3D Pillared Graphene Foam for Asymmetric All-Solid-State Flexible Supercapacitor Application.

We have fabricated high-energy-density all-solid-state flexible asymmetric supercapacitor by using a facile novel 3D hollow urchin-shaped coaxial manganese dioxide@polyaniline (MnO2@PANI) composite as positive electrode and 3D graphene foam (GF) as negative electrode materials with polyvinyl alcohol (PVA)/KOH gel electrolyte. The coaxial MnO2@PANI composite was fabricated by hydrothermal route followed by oxidation without use of an external oxidant. The formation mechanism of the 3D hollow MnO2@PANI composite occurs first by nucleation and growth of the MnO2 crystal species via dissolution-recrystallization and oriented attachment mechanisms followed by the oxidation of aniline monomers on the MnO2 crystalline template. The self-assembled 3D graphene block was synthesized by hydrothermal route using vitamin C as a reducing agent. The microstructures of the composites are analyzed by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. The morphology is characterized by field-emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM), which clearly showed the formation of urchin-shaped coaxial MnO2@PANI composite. The electrochemical studies are explored by cyclic voltammetry, electrochemical impedance spectrometry, and cyclic charge-discharge tests. The symmetric all-solid-state flexible MnO2@PANI//MnO2@PANI and GF//GF supercapacitors exhibit the specific capacitance of 129.2 and 82.1 F g-1 at 0.5 A/g current density, respectively. The solid-state asymmetric supercapacitor shows higher energy density (37 Wh kg-1) with respect to the solid-state symmetric supercapacitors MnO2@PANI//MnO2@PANI and GF//GF, where the obtained energy density are found to be 17.9 and 11.4 Wh kg-1, respectively, at 0.5 A/g current density. Surprisingly, the asymmetric supercapacitor shows a high energy density of 22.3 Wh kg-1 at a high current density of 5 A g-1. The solid-state asymmetric supercapacitor shows a good cyclic stability in which ∼11% capacitance loss was observed after 5000 cycles.

Self-assembled high-performance graphene oxide fibers using ionic liquid as coagulating agent

An efficient strategy for fabricating high-performance GO fibers (GFs) by using ionic liquids as coagulating agent via wet-spinning technique was reported for the first time. The interactions between the functional groups of the GO sheets and the ionic liquids cations could be tuned by choosing ionic liquids cations with designed structure, yielding GFs with varied mechanical properties. No organic solvent or postdrawing processes involved makes this process green and facile.

Self-assembled graphene film to enable highly conductive and corrosion resistant aluminum bipolar plates in fuel cells

We report in this paper a novel method to form protective graphene film on aluminum substrate, which is particularly applicable to bipolar plates in proton exchange membrane (PEM) fuel cells. By simply immersing an aluminum sheet in an aqueous solution of graphene oxide (GO), a layer of cross-linked GO gel forms on the aluminum sheet, taking advantage of dissociated aluminum ions as a cross-linker. Then the cross-linked GO is converted to graphene at 400 °C in hydrogen atmosphere. The chemistry of the self-assembled GO layer and its conversion to graphene film is revealed by FTIR and XPS. Under simulated fuel cell environment the graphene coated aluminum sheet shows a corrosion current density of <1 × 10−6 A/cm2, which is around four orders of magnitude lower than a bare aluminum sheet. Meanwhile, the graphene film on aluminum results in a much lower and more stable interfacial contact resistance (ICR) of <5 mΩ cm2. These enable the graphene coated aluminum sheet to meet the U.S. DOE targets of 2020 for bipolar plates in terms of both the corrosion and electrical resistance. Thus the proposed method is very promising for protecting aluminum bipolar plates in PEM fuel cells.

Enhanced electricity generation for biocathode microbial fuel cell by in situ microbial-induced reduction of graphene oxide and polarity reversion

A simple effective and environmentally friendly pathway to form graphene modified biocathode was induced by polarity reversion of graphene modified bioanode, which was made by in situ microbial-induced reduction of graphene oxide (GO). Graphene assembled by microbes showed that D/G intensity increased from 0.84 to 0.91 and C/O atomic ratio added from 2.13 to 4.45, indicating GO was reduced largely. The graphene modified biocathode exhibited crumples that grown on the lamellar and glossy surface and was capable of improving catalytic reduction of oxygen. Microbial fuel cell (MFC) fabricated with graphene modified biocathode obtained 1.22 times in maximum power density, 0.21 times in interfacial charge transfer resistance, and recorded an obvious redox peaks at −0.50 V (vs. SCE) than control biocathode MFC. Geobacter, Clostridium, Pseudomonas, Geothrix and Hydrogenophaga belonged to exoelectrogens occupied 17.53% in graphene modified biocathode, 2.07% in control biocathode in genus level. This study provided a new insight into the feasibility to make microbes self-assembled graphene to improve electrochemical performance of biocathode MFC.

High-performance sulfur dioxide sensing properties of layer-by-layer self-assembled titania-modified graphene hybrid nanocomposite

This paper demonstrates layer-by-layer (LbL) self-assembled titania (TiO2)/graphene film device towards ultralow sulfur dioxide (SO2) gas sensing at room temperature. The as-prepared film was realized through the layer-by-layer alternative deposition of TiO2 nanospheres and graphene oxide (GO) to form a nanostructure, and followed by thermally reducing GO into reduced graphene oxide (rGO). The nanostructural, morphological and compositional properties of TiO2/rGO sample was examined by SEM, TEM, XRD, EDS and Raman spectroscopy. The gas-sensing properties of TiO2/rGO hybrid were investigated at room temperature against low concentration SO2 gas. The sensor in our work exhibited ppb-level detection, rapid response and recovery, good reversibility, selectivity and repeatability for SO2 gas sensing. The possible sensing mechanism for the presented sensor was attributed to the synergistic effect of TiO2 and rGO, as well as special interaction at TiO2/rGO interfaces. This work shows that the fabricated TiO2/rGO film sensor possesses potential applications for SO2 detection with advantages of cost-effective, low power consumption and distinguished sensing abilities.

Synthesis of Cobalt Phosphide Nanoparticles Supported on Pristine Graphene by Dynamically Self‐Assembled Graphene Quantum Dots for Hydrogen Evolution

A highly active, durable, and low-cost hydrogen evolution reaction (HER) catalyst is desirable for energy storage through water splitting but its fabrication presents great challenges. Herein, mediated by dynamically self-assembled graphene quantum dots (GQDs), small, uniform, high-density, and well-dispersed CoP nanoparticles were grown in situ on pristine graphene for the first time. This hybrid nanostructure was then employed as HER electrocatalyst, showing an onset potential of 7 mV, an overpotential of 91.3 mV to achieve 10 mA cm-2 , a Tafel slope of 42.6 mV dec-1 , and an exchange current density of 0.1225 mA cm-2 , all of which compare favorably to those of most reported non-noble-metal catalysts. The developed catalyst also exhibits excellent durability with negligible current loss after 2000 cyclic voltammetry cycles (+0.01 to -0.17 V vs. RHE) or 34 h of chronoamperometric measurement at an overpotential of 91.3 mV. This work not only develops a new strategy for the fabrication of high-performance and inexpensive electrocatalysts for HER but also provides scientific insight into the mechanism of the dynamically self-assembled GQDsmediated synthesis process.

Self-Assembled Biofunctionalized Graphene Oxide Models for Nanomedicine

Self-assembly is one of the most favorable nanofabrication solutions but above all it is an intrinsic attribute of living biostructures. In order to become bio-functional any fabricated nanostructure should be firstly biomimetic, answering to the environmental stimuli alike a living structure. On the last decade graphene (G), graphene oxide (GO) and reactive graphene oxide (RGO) become the promising solutions in a wide range of research areas from aeronautics to medicine, and from material science to mathematics. Based on their outstanding chemical, mechanical, optical and electrical properties graphene and other emerging 2D materials are seen as the key solution and a paradigm shift approach on bioscience and nanomedicine.In this paper are presented some self-assembled bio-functionalized graphene oxide models aiming to be biomimetic through their entire modeling and simulation pathway.

Self-assembled nanoporous graphene quantum dot-Mn3O4 nanocomposites for surface-enhanced Raman scattering based identification of cancer cells

A nanoporous graphene quantum dot-Mn3O4 nano-composite was synthesized, and used as a new platform for surface-enhanced Raman scattering-based identification of cancer cells.

Versatile self-assembled graphene oxide membranes obtained under ambient conditions by using a water–ethanol suspension

The study reports a low cost and scalable pathway for preparing free-standing GO membranes by a self-assembly process under ambient conditions at an air–liquid interface of an isopycnic sorted GO water–ethanol fraction.

Three-dimensional graphene hollow spheres with high sulfur loading for high-performance lithium-sulfur batteries

Lithium-sulfur batteries have currently attracted wide interest due to their high theoretical capacity, but the practical applications are being hampered by capacity decay, mainly attributed to the polysulfide shuttle. Here, we have designed a novel three-dimensional (3D) nanostructure of graphene hollow spheres (HGs) as the sulfur host. The 3D HGs were successfully prepared via a self-assembly method of wrapping graphene oxide (GO) on SiO2 spheres, and then followed by carbonization and etching of the SiO2. The impregnation of sulfur into the hollow graphene spheres lead to obtaining the HGs/S cathode, which reaches up a high sulfur loading of 90wt% in the composite (72wt % in the whole cathode). The HGs/S cathode material remains a high discharge capacity of 810mAhg−1 after 200 cycles at 0.5C rate. Furthermore, it demonstrates a low capacity-decay rate of 0.083% per cycle after 600 cycles at 1C rate. Compared with pristine reduced graphene oxide/sulfur composites (RGO/S), the as-prepared 3D self-assembled graphene hollow spheres HGs/S exhibit significantly improved electrochemical performances in terms of high specific capacity, remarkable rate capability and excellent cycling stability. These synergistic effects are achieved by more effective 3D ion/electron transport pathways, and efficient confinement of polysulfide dissolution and shuttling.

Detection of chemicals in water using a three-dimensional graphene porous structure as liquid-vapor separation filter

In this study, we report the utilization of a three-dimensional (3D) porous graphene structure as liquid–vapor separation filter, which allows the passage of chemical vapors while blocking liquid chemicals and water. The blockage of liquid chemicals and water from semiconducting sensing regions is required to avoid abnormal transistor characteristics. In order to impart omniphobic characteristics, a (heptadecafluoro-1,1,2,2-tetrahydrodecyl)trichlorosilane (HDF-S) self-assembled monolayer was coated on the surface of the 3D porous graphene structure. The concentration of chemical agents in water could be consistently detected by observing the shift in the threshold voltage in the oxide nanowire transistor covered by the HDF-S self-assembled 3D graphene structure. The proposed monitoring method is expected to offer means for application in different environments by providing a stable sensing performance.

Supramolecular assembled three-dimensional graphene hybrids: Synthesis and applications in supercapacitors

Graphene-based materials have received worldwide attention in the focus of forefront energy storage investigations. Currently, the design of novel three-dimensional (3D) graphene structures with high energy capability, superior electron and ion conductivity, and robust mechanical flexibility is still a great challenge. Herein, we have successfully demonstrated a novel approach to fabricate 3D assembled graphene through the supramolecular interactions of β-cyclodextrin polymers (β-CDP) with an adamantine end-capped poly(ethylene oxide) polymer linker (PEG-AD). The incorporation of PEG-AD linker into rGO sheets increased the interlayer spacing of rGO sheets to form 3D graphene materials, which can provide efficient 3D electron transfer pathways and ion diffusion channels, and facilitate the infiltration of gel electrolyte. The as-prepared 3D self-assembled graphene materials exhibit significantly improved electrochemical performances of supercapacitor in terms of high specific capacitance, remarkable rate capability, and excellent cycling stability compared to pristine reduced graphene oxide. This study shed new lights to the construction of three dimensional self-assembled graphene materials and their urgent applications in energy storage.

Tunable Optical Transparency in Self-Assembled Three-Dimensional Polyhedral Graphene Oxide.

The origami-like self-folding process is an intellectually stimulating technique for realizing three-dimensional (3D) polyhedral free-standing graphene oxide (GO) structures. This technique allows for easy control of size, shape, and thickness of GO membranes, which in turn permits fabrication of free-standing 3D microscale polyhedral GO structures. Unlike 2D GO sheets, the 3D polyhedral free-standing GO shows a distinct optical switching behavior, resulting from a combination of the geometrical effect of the 3D hollow structure and the water-permeable multilayered GO membrane that affects the optical paths.

Facile self-assembly N-doped graphene quantum dots/graphene for oxygen reduction reaction

Nitrogen doping carbon nanomaterial has become an important metal-free electrocatalyst for oxygen reduction reaction (ORR) in fue cells. N-doped graphene quantum dots (N-GQDs) are one of the most promising nanomaterials due to abundant electrocatalytic edging and N doping active sites, but low yield, high dispersity and no forming efficient percolative conductive network hinder their direct application as the electrocatalyst. Hydrothermal method is an effective route for preparing high-quality N-GQDs and meanwhile, overcomes the drawbacks of complicated preparing progress and low yield. We further hydrothermally prepare the hybrid material of N-GQDs/Graphene (G) to immobilize N-GQDs on graphene and construct 3D conductive network. Therefore, the inexpensive N-GQDs/G integrates the advantages of rich edges, N doping active sites, high conductivity, and large specific surface area. As confirmed by a series of characterizations and tests, the N-GQDs/G performs high electocatalytic performance (dominating four-electron pathway), long-term stability and resistance to methanol crossover. Moreover, we demonstrate that the type of N specie plays an important role in ORR, especially, the pyridinic-N.

Fabrication and characterization of self-assembled graphene oxide/silane coatings for corrosion resistance

Abstract Flexible barrier films preventing corrosion are important for many industries ranging from engineering to medical to electronic materials. In order to improve the corrosion resistance ability of GO-based composite films, the Bis[3-(triethoxysilyl)propyl]tetrasulfide (BTESPT)/GO multi-layered films were layer by layer self-assembled on the surface of 2024 aluminum alloy (AA 2024). The results showed that the designed composite films obviously improved the corrosion resistance ability of AA2024 substrate. The composite films, especially for the middle GO layer, effectively hinders the corrosion reaction by reducing the rate of both the cathodic and the anodic reactions. Furthermore, the formation of Si–O–C covalent bonds based on the XPS analysis implies the improved binding force between silane film and the fabricated middle GO layer. After 40 days immersion in 3.5% NaCl solution, the composite films still had better corrosion resistance ability, which implied the fabricated composite films had better resistance to penetration ability for corrosive ions, and the corrosion mechanism was also analyzed for the long-term immersion process based on the EIS results.

Recent Progress in Multifunctional Graphene Aerogels

Two dimensional (2D) graphene has become one of the most intensively explored carbon allotropes in materials science owing to attractive features like its outstanding physicochemical properties. In order to further realize practical applications, the fabrication of self-assembled 2D individual graphene sheets into 3D graphene aerogels (GAs) with special structures and novel functions, is now becoming essential. Moreover, GAs are ideal as supports for the introduction of nanoparticles, polymers, and functional materials to further enhance their applications in broad areas. GAs have light weight, large surface area, good compressibility, extensibility, and high electrical conductivity. They have been used as efficient electrodes for batteries, in supercapacitors, and in sensors and actuators. This critical review mainly addresses recent progress in the methods used for their syntheses, their properties, and applications for energy storage, and in sensors and actuators. Furthermore, to assist advanced research for practical applications of these emerging materials, the technical challenges are discussed, and future research directions are proposed.

Synthesis of integrated graphene films with self-assembled single-layer channels and multi-layer electrodes via a single process

Integrated graphene films (IGFs) with self-assembled single-layer graphene as a channel and multi-layer graphene as an electrode material were synthesized simultaneously using a one-step process by thermal chemical vapor deposition. The prominent difference in graphene growth rate between Ni and Cu catalytic substrates made enable to synthesize the IGFs with self-assembled single-layer and multi-layer graphene on a Cu foil with pre-patterned Ni films. The thickness of multi-layer graphene for IGFs was precisely controlled by optimizing conditions including the injection temperature of carbon feedstock and the surface concentration of Ni atoms affected by the inter-diffusion related to the growth temperature and time. The thickness and crystallinity of synthesized IGFs were evaluated by resonant Raman spectroscopy. We fabricated the IGFs-based field effect transistors (FETs) to examine electrical transport properties of the films. These results suggest that the synthesis technique for IGFs could lead to mass fabrication of wearable graphene-based FETs in the near future.

A self-assembling RNA aptamer-based graphene oxide sensor for the turn-on detection of theophylline in serum

To date, few effective fluorescent biosensors based on RNA aptamers have been developed because the intrinsic instability of RNA in the presence of nucleases precludes the application of RNA aptamers for the analysis of biological fluids. In this study, we developed a simple, sensitive, selective turn-on fluorescent aptasensor for theophylline detection in serum, utilizing ligand-induced self-assembling RNA aptamers and two different interaction stages of the aptamer fragments with graphene oxide (GO). A single strand of the theophylline RNA aptamer (33-mer) was split at the end loop region into two shorter fragments, one of which was labeled with a fluorophore (FAM). In the absence of theophylline, the adsorption of the two individual fragments on GO brought the fluorophore in close proximity to the GO surface, resulting in highly efficient quenching of fluorescence. The system showed very low background fluorescence. Conversely, the fragments self-assembled into an RNA aptamer/theophylline complex and were dissociated from GO. The quenched fluorescence was significantly recovered, and theophylline could be detected at a wide range of concentrations from 1 to 100μM, with a detection limit of 0.155μM and good selectivity in serum. Moreover, because of the shorter RNA fragments and the effective protection ability of GO from nuclease cleavage, the RNA sequences remained stable during the experiments. This design may serve as an example for the application of RNA aptasensors in the clinical setting.

Graphene/biofilm composites for enhancement of hexavalent chromium reduction and electricity production in a biocathode microbial fuel cell

In this study, a simple method of biocathode fabrication in a Cr(VI)-reducing microbial fuel cell (MFC) is demonstrated. A self-assembling graphene was decorated onto the biocathode microbially, constructing a graphene/biofilm, in situ. The maximum power density of the MFC with a graphene biocathode is 5.7 times that of the MFC with a graphite felt biocathode. Cr(VI) reduction was also enhanced, resulting in 100% removal of Cr(VI) within 48h, at 40mg/L Cr(VI), compared with only 58.3% removal of Cr(VI) in the MFC with a graphite felt biocathode. Cyclic voltammogram analyses showed that the graphene biocathode had faster electron transfer kinetics than the graphite felt version. Energy dispersive spectrometer (EDS) and X-ray photoelectron spectra (XPS) analysis revealed a possible adsorption-reduction mechanism for Cr(VI) reduction via the graphene biocathode. This study attempts to improve the efficiency of the biocathode in the Cr(VI)-reducing MFC, and provides a useful candidate method for the treatment of Cr(VI) contaminated wastewater, under neutral conditions.

Nitrogen-doped activated graphene/SWCNT hybrid for oxygen reduction reaction

Pt-free catalyst towards oxygen reduction reaction (ORR) that is highly active, stable, and low-cost is highly desirable for commercialization of fuel cells but still remains unresolved. Here, we report a hybrid material of nitrogen-doped activated graphene/carbon nanotubes via a simple self-assembly of graphene and carbon nanotubes followed by KOH activation and high temperature annealing in NH3 for an efficient metal-free catalyst for ORR. The single-walled carbon nanotubes are well intercalated into nanoporous graphene layers, which lead to a high surface area and electrical conductivity of the hybrid. The nitrogen doping provides more reactive sites for ORR and significantly enhances the reaction properties. The hybrid structure exhibits excellent catalytic behavior with a four-electron pathway in alkaline media and better stability than the commercial Pt/C catalyst. This study opens a new direction for developing low-cost and highly efficient carbon-based ORR electrocatalysts.