Wet-spinning of multifunctional graphene fibers using graphene oxide liquid crystals

The recent discovery of liquid crystalline (LC) behavior of graphene oxide (GO) dispersions in various organic, and aqueous media brings added control to the assembly of larger structures using the chemical process approach.[1-3] The LC state can be used to direct the ordered assembly of nanocomponents in macroscopic structures via simple methods like wet-spinning. [3] Here, we developed a scaleable fabrication route to produce graphene fibers via a facile continuoes wetspinning methode. We develop solid understanding in the required criteria to correlate processability with LC behavior, aspect ratio and the dispersion concentration to provide a viable platform for spinning of LC GO. We demonstrate a striking result that highlits the importance of GO sheet size and polydispersity in generating wetspinnable LC GO dispersions from very low spinning dope concentrations (as low as 0.075 wt. %). The new knowledge gained through rheological investigations provides a sound explanation as to why continuous spinning of binder-free GO fibers is enabled by the LC behavior at this very low concentration.

In situ prepared V2O5/graphene hybrid as a superior cathode material for lithium-ion batteries

Developing synthetic methods for graphene based cathode materials, with low cost and in an environmentally friendly way, is necessary for industrial production. Although the precursor of graphene is abundant on the earth, the most common precursor of graphene is graphene oxide (GO), and it needs many steps and reagents for transformation to graphite. The traditional approach for the synthesis of GO needs many chemicals, thus leading to a high cost for production and potentially great amounts of damage to the environment. In this study, we develop a simple wet ball-milling method to construct a V2O5/graphene hybrid structure in which nanometre-sized V2O5 particles/aggregates are well embedded and uniformly dispersed into the crumpled and flexible graphene sheets generated by in situ conversion of bulk graphite. The combination of V2O5 nanoparticles/aggregates and in situ graphene leads the hybrid to exhibit a markedly enhanced discharge capacity, excellent rate capability, and good cycling stability. This study suggests that nanostructured metal oxide electrodes integrated with graphene can address the poor cycling issues of electrode materials that suffer from low electronic and ionic conductivities. This simple wet ball-milling method can potentially be used to prepare various graphene based hybrid electrodes for large scale energy storage applications.

The role of SEBS in tailoring the interface between the polymer matrix and exfoliated graphene nanoplatelets in hybrid composites

Nanocomposites of polypropylene (PP) and polypropylene/styrene-(ethylene-co-butylene)-styrene triblock copolymer (SEBS) blends with exfoliated graphene nanoplatelets (xGnP) were prepared by melt-mixing method. The incorporation of xGnP increased the stiffness and crystallinity of PP at the expense of toughness and the molecular mobility. The effect of addition of SEBS on the mechanical, viscoelastic, thermal degradation and crystallization properties of PP/xGnP composites was studied. The addition of SEBS into PP transformed the phase structure and distribution of xGnP in the PP matrix. SEM micrographs revealed that SEBS polymer chains formed a coating over the graphene nanoplatelets, which strengthened the interface between the filler and the matrix, and improved the dispersion and distribution of the filler throughout the matrix.

Stretchable graphene-based materials of high conductivity

 The application of graphene based materials in the area of stretchable electronics has driven enormous attention, especially in terms of the design of stretchable structures. This thesis has finely tuned the synthesis process of reduced graphene oxide (rGO), focused on the introduction of a thermo-mechanical shrinking process to fabricate wrinkled rGO structure as stretchable conductors and finally presented another potential application of wrinkled rGO structure.

Selective removal of anionic dyes using poly (N, N -dimethyl amino ethylmethacrylate) functionalized graphene oxide

An in situ polymerization strategy was used to functionalize graphene oxide (GO) with poly(N,N-dimethyl amino ethylmethacrylate) (PDMAEMA) for the selective removal of anionic dyes. Various characterization methods demonstrate that PDMAEMA-grafted GO (GO-PDMAEMA) was successfully synthesized, and the high PDMAEMA content of 68.5% in GO-PDMAEMA changed the zeta potential significantly from -36.5 (GO) to 41.5 (GO-PDMAEMA). This change in the charge of GO-PDMAEMA greatly increased the adsorption capacities for anionic dye orange G (OG) compared to the pristine GO. The maximum adsorption capacity for anionic OG dye based on the Langmuir model is 609.8 mg g-1. The adsorption mechanism is believed to be a consecutive process of intra-particle diffusion and surface adsorption, with electrostatic interactions as the key driving force. The GO-PDMAEMA nanocomposite also showed excellent regeneration capacity and selectivity towards the separation of various anionic dyes (i.e. OG, Eosin yellow and Congo red) from an aqueous dye mixture. In conclusion, our method offers a promising strategy for developing new anionic dye adsorbents.

Fabrication of multifunctional graphene decorated with bromine and nano-Sb₂O₃ towards high-performance polymer nanocomposites

Despite great advances, it remains highly attractive but challenging to create high-performance polymeric materials combining excellent flame-retardancy and outstanding thermal, mechanical and electrical properties. We herein demonstrate a novel strategy for fabricating a multifunctional nano-additive (Br-Sb2O3@RGO) based on graphene decorated with bromine and nano-Sb2O3. Cone calorimetric tests show that incorporating 10 wt% Br-Sb2O3@RGO into thermoplastic polyurethane (TPU) strikingly prolongs the time to ignition and decreases the peak heat release rate by 72%. Besides, tensile strength and Young's modulus are enhanced by 37% and 820%, respectively. Meanwhile, the electric conductibility is increased by eleven orders of magnitude relative to the TPU matrix. This work provides a promising strategy for addressing the critical bottleneck with the existing flame retardants that only enhance flame retardancy at the expense of mechanical properties of polymeric materials. As-prepared high-performance TPU composites are expected to find many applications, especially in aerospace, tissue engineering, and cables and wires.

Strain sensors with adjustable sensitivity by tailoring the microstructure of graphene aerogel/PDMS nanocomposites

Strain sensors with high elastic limit and high sensitivity are required to meet the rising demand for wearable electronics. Here, we present the fabrication of highly sensitive strain sensors based on nanocomposites consisting of graphene aerogel (GA) and polydimethylsiloxane (PDMS), with the primary focus being to tune the sensitivity of the sensors by tailoring the cellular microstructure through controlling the manufacturing processes. The resultant nanocomposite sensors exhibit a high sensitivity with a gauge factor of up to approximately 61.3. Of significant importance is that the sensitivity of the strain sensors can be readily altered by changing the concentration of the precursor (i.e., an aqueous dispersion of graphene oxide) and the freezing temperature used to process the GA. The results reveal that these two parameters control the cell size and cell-wall thickness of the resultant GA, which may be correlated to the observed variations in the sensitivities of the strain sensors. The higher is the concentration of graphene oxide, then the lower is the sensitivity of the resultant nanocomposite strain sensor. Upon increasing the freezing temperature from −196 to −20 °C, the sensitivity increases and reaches a maximum value of 61.3 at −50 °C and then decreases with a further increase in freezing temperature to −20 °C. Furthermore, the strain sensors offer excellent durability and stability, with their piezoresistivities remaining virtually unchanged even after 10 000 cycles of high-strain loading−unloading. These novel findings pave the way to custom design strain sensors with a desirable piezoresistive behavior.

Facile fabrication of supercapacitors with high rate capability using graphene/nickel foam electrode

High-performance reduced graphene oxide/nickel foam (rGO/NF) composite electrodes for high-performance supercapacitors were prepared by flame-induced reduction of dry graphene oxide (GO) coated on nickel foam. Flame reduction of GO is a facile, feasible and cost-effective reduction technique, which is conducted without the need of any reductant. Most importantly, the rGO obtained by flame reduction showed a typical disordered cross-linking network and randomly distributed pores, which provide accessible routes for fast transportation of ions. It was demonstrated that the rGO/NF electrode with embedded current collector (NF) exhibited better electrochemical performance than conventional rGO film counterparts, including a high gravimetric specific capacitance of 228.6 F g-1 at a current density of 1 A g-1, excellent rate capability (over 81% retention at 32 A g-1) and high cycling stability with only 5.3% capacitance decay over 10,000 cycles of cyclic voltammetry at a ultrahigh scan rate of 1000 mV s-1. This facile method for the fabrication of rGO/NF electrodes could envision enormous potential for high performance energy storage devices.

Removal of Pb (II) ions using polymer based graphene oxide magnetic nano-sorbent

Graphene oxide (GO) based magnetic nano-sorbent was synthesized by assembling the Fe3O4 and GO on the surface of polystyrene (denoted as PS@Fe3O4@GO). The morphology of the nano-sorbent was studied using scanning electron microscopy (SEM), while their individual nano-components were characterized using UV-visible spectroscopy, atomic force microscopy (AFM), zeta potential, transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The assembled nano-sorbent was further investigated for Pb (II) ions removal by optimizing the parameters including pH, temperature and contact time. The obtained data was modelled for adsorption kinetics, adsorption isotherms and thermodynamics. Kinetic experiments indicated the Pb (II) adsorption followed first order kinetics. The adsorption equilibrium data fits Langmuir isotherm model well and the adsorption process was found to be spontaneous. The adsorption capacity of the prepared nano-sorbent was estimated to be 73.52mgg-1, with a maximum removal of 93.78% at pH 6. The nano-sorbent can be regenerated by nitric acid (HNO3) for reuse. FT-IR and X-ray photoelectron spectroscopy (XPS) studies confirmed the interactions between the Pb (II) ions and the nano-sorbent.

Controllable graphene oxide mediated efficient electron transfer pathways across self-assembly monolayers: a new class of graphene based electrodes

In this paper, the influence of chemically reduced graphene oxide sheets (CRGOs) on the electrochemical performance through methyl or carboxylic acid terminated self-assembled monolayers (SAMs) is reported. The gold electrode was initially modified with methyl or carboxylic acid terminated alkanethiols with various carbon chain lengths (n = 4, 6, 8 and 11) and subsequently immobilization of the CRGOs on a SAM surface was achieved via a hydrophobic and electrostatic interaction. By using the potassium ferricyanide as a redox probe, it was observed that CRGOs could effectively enhance the heterogeneous electron transfer (ET) of the SAM due to a tunneling effect. The assemblies based on thiol end groups with methyl head groups were observed to afford more hydrophobic interaction binding with CRGOs with a higher reduction time than the assemblies developed with thiol end groups and a -COOH group which were shown to bind more electrostatically with CRGOs, a lowering reduction time. The Nyquist plots developed show a gradual decrease of the charge transfer resistance (Rct) of [Fe(CN)6]3-/4- redox couple at the CRGOs-SAMs electrode with the controllable adsorption of different CRGO's onto the SAM. Depending on the chain length and terminal functional group the electron transfer rate kinetics were observed to differ considerably.

Graphene NanoPlatelets Reinforced Tantalum Carbide consolidated by Spark Plasma Sintering

Hypersonic aerospace vehicles are severely limited by the lack of adequate high temperature materials that can withstand the harsh hypersonic environment. Tantalum carbide (TaC), with a melting point of 3880°C, is an ultrahigh temperature ceramic (UHTC) with potential applications such as scramjet engines, leading edges, and zero erosion nozzles. However, consolidation of TaC to a dense structure and its low fracture toughness are major challenges that make it currently unviable for hypersonic applications. In this study, Graphene NanoPlatelets (GNP) reinforced TaC composites are synthesized by spark plasma sintering (SPS) at extreme conditions of 1850˚C and 80-100 MPa. The addition of GNP improves densification and enhances fracture toughness of TaC by up to ~100% through mechanisms such as GNP bending, sliding, pull-out, grain wrapping, crack bridging, and crack deflection. Also, TaC-GNP composites display improved oxidation behavior over TaC when exposed to a high temperature plasma flow exceeding 2500 ˚C.

Thermally induced all-optical inverter and dynamic hysteresis loops in graphene oxide dispersions

We experimentally study the temporal dynamics of amplitude-modulated laser beams propagating through a water dispersion of graphene oxide sheets in a fiber-to-fiber U-bench. Nonlinear refraction induced in the sample by thermal effects leads to both phase reversing of the transmitted signals and dynamic hysteresis in the input- output power curves. A theoretical model including beam propagation and thermal lensing dynamics reproduces the experimental findings. © 2015 Optical Society of America.

Aligned nanofibers from polypyrrole/graphene as electrodes for regeneration of optic nerve via electrical stimulation

The damage of optic nerve will cause permanent visual field loss and irreversible ocular diseases, such as glaucoma. The damage of optic nerve is mainly derived from the atrophy, apoptosis or death of retinal ganglion cells (RGCs). Though some progress has been achieved on electronic retinal implants that can electrically stimulate undamaged parts of RGCs or retina to transfer signals, stimulated self-repair/regeneration of RGCs has not been realized yet. The key challenge for development of electrically stimulated regeneration of RGCs is the selection of stimulation electrodes with a sufficient safe charge injection limit (Q(inj), i.e., electrochemical capacitance). Most traditional electrodes tend to have low Q(inj) values. Herein, we synthesized polypyrrole functionalized graphene (PPy-G) via a facile but efficient polymerization-enhanced ball milling method for the first time. This technique could not only efficiently introduce electron-acceptor nitrogen to enhance capacitance, but also remain a conductive platform-the π-π conjugated carbon plane for charge transportation. PPy-G based aligned nanofibers were subsequently fabricated for guided growth and electrical stimulation (ES) of RGCs. Significantly enhanced viability, neurite outgrowth and antiaging ability of RGCs were observed after ES, suggesting possibilities for regeneration of optic nerve via ES on the suitable nanoelectrodes.

Modulated deformation of lipid membrane to vesicles and tubes due to reduction of graphene oxide substrate under laser irradiation

Biomembrane transformations are closely related to many biological processes including endo/exocytosis and the cellular response to the local physical environment. In this work, we investigated the transformation between lipid membranes and lipid vesicles/tubes modulated by the solid substrate of graphene oxide (GO) aggregates under laser irradiation. We firstly fabricate a novel type of lipid@GO composite consisting of micrometer-sized GO aggregates surrounded by lamellar lipid membranes. Upon laser irradiation, lipid protrusion occurs and leads to the formation of vesicles adsorbed on the GO aggregate surface, with an average size as 0.43 times of the radius of GO aggregate. Both the location and the dynamic formation process of vesicles can be modulated. The arising of vesicles prefers to occur at edges of the GO planes rather than on surface of individual GO sheets within the GO aggregate. Furthermore, at a reduced laser power density, the lipid protrusion mainly grows to tubes instead of vesicles. Such transformations from lipid membrane to vesicles and tubes is ascribed to the reduction of GO to reduced-GO (rGO) under laser irradiation, probably along with the release of gases leading to the deformation of lipid membrane surrounding the GO surface.

Opening lids: modulation of lipase immobilization by graphene oxides

Lipases, which can be immobilized and reused for many reaction cycles, are important enzymes with many industrial applications. A key challenge in lipase immobilization for catalysis is to open the lipase lid and maintain it in an open conformation in order to expose its active site. Here we have designed "tailor-made" graphene-based nanosupports for effective lipase (QLM) immobilization through molecular engineering, which is in general a grand challenge to control biophysicochemical interactions at the nano-bio interface. It was observed that increasing hydrophobic surface increased lipase activity due to opening of the helical lid present on lipase. The molecular mechanism of lid opening revealed in molecular dynamics simulations highlights the role of hydrophobic interactions at the interface. We demonstrated that the open and active form of lipase can be achieved and tuned with an optimized activity through chemical reduction of graphene oxide. This research is a major step toward designing nanomaterials as a platform for enhancing enzyme immobilization/activity.