Self-assembled Graphene Oxide Research Articles

Facile synthesis of N-doped 3D graphene aerogel and its excellent performance in catalytic degradation of antibiotic contaminants in water

3D nitrogen-doped graphene aerogels (NGA) with hierarchically porous architectures and integrated macrostructures were facilely constructed by self-assembly of graphene oxide (GO) nanosheets and melamine. NGA exhibited excellent catalytic activities in peroxymonosulfate (PMS) activation for oxidative degradation of ibuprofen (IBP). NGA attained 44- and 8-fold enhancement in reaction rate over graphene aerogel (GA) and N-doped reduced graphene oxide (NrGO), respectively. Furthermore, the chemical reactivity of NGA could be facilely recovered by thermal annealing. The superior catalysis of NGA can be ascribed to the synergistic effects of 3D porous framework and N-doping in sp2-hybridized NGA. Graphitic N is demonstrated to be the intrinsic active sites in PMS activation. The 3D porous architecture is beneficial for adsorption and diffusion of the pollutant/oxidant and graphitic carbons within the conjugated π system facilitate the electron transfer. Electron paramagnetic resonance and radical quenching tests indicate that NGA/PMS is a radical-based system, where SO4•− and •OH with strong oxidative potentials account for the catalytic degradation of IBP. This study affords an innovative strategy for development of promising metal-free catalysts towards better advanced oxidation processes.

Polymer conjugated graphene-oxide nanoparticles impair nuclear DNA and Topoisomerase I in cancer

Cancer chemotherapy had been dominated by the use of small molecule DNA damaging drugs. Eventually, the emergence of DNA damage repair machinery in cancer cells has led to combination therapy with the DNA topology controlling enzyme, topoisomerase I inhibitor along with DNA impairing agents. However, integrating multiple drugs having diverse water solubility and hence bio-distribution effectively for cancer treatment remains a significant challenge, which can be addressed by using suitable nano-scale materials. Herein, we have chemically conjugated graphene oxide (GO) with biocompatible and hydrophilic polymers [polyethylene glycol (PEG) and ethylene-diamine modified poly-isobutylene-maleic anhydride (PMA-ED)], which can encompass highly hydrophobic topoisomerase I inhibitor, SN38. Interestingly, these sheet structured GO-polymer-SN38 composites self-assembled into spherical nanoparticles in water after complexing with a hydrophilic DNA damaging drug, cisplatin. These nanoparticles showed much improved colloidal stability in water compared to their drug-loaded non-polymeric counterpart. These SN38 and cisplatin laden GO-polymer nanoparticles were taken up by HeLa cancer cells through clathrin-dependent endocytosis to home into lysosomes within 6 h, as confirmed by confocal microscopy. A combination of gel electrophoresis, flow cytometry, and fluorescence microscopy showed that these nanoparticles damaged nuclear DNA and induced topoisomerase I inhibition leading to apoptosis and finally improved HeLa cell death. These self-assembled GO-polymer nanoparticles can be used for strategic impairment of multiple cellular targets involving hydrophobic and hydrophilic drugs for effective combination therapy.

Polyethylenimine Coated Graphene Oxide Nanoparticles for Targeting Mitochondria in Cancer Cells.

Mitochondrion, the powerhouse of the cells, controls bioenergetics, biosynthesis, metabolism, and signaling. Consequently, it has become an unorthodox target for cancer therapeutics. However, specific targeting of mitochondria into subcellular milieu in cancer cells remains a major challenge. To address this, we have engineered polyethylenimine cloaked positively charged self-assembled graphene oxide nanoparticle (PEI-GTC-NP) comprising topotecan and cisplatin concurrently. These PEI-GTC-NPs effectively homed into mitochondria in HeLa cervical cancer cells at 6 h and impaired mitochondria leading to reactive oxygen species generation followed by remarkably improved cancer cell death. This platform can be used for specific subcellular organelle targeting for future cancer therapy.

Mitigating Metal Dendrite Formation in Lithium-Sulfur Batteries via Morphology-Tunable Graphene Oxide Interfaces.

Despite issues related to dendrite formation, research on Li metal anodes has resurged because of their high energy density. In this study, graphene oxide (GO) layers are decorated onto Li metal anodes through a simple process of drop-casting and spray-coating. The self-assembly of GO is exploited to synthesize coatings having compact, mesoporous, and macroporous morphologies. The abilities of the GO coatings to suppress dendrite formation are compared through Li|Li symmetrical cell charging at a current density of 5 mA cm-2 for 2000 cycles-a particularly abusive test. The macroporous structure possesses the lowest impedance, whereas the compact structure excels in terms of stability. Moreover, GO exhibits a low nucleation overpotential and is transformed into reduced GO with enhanced conductivity during the operation of the cells; both factors synergistically mitigate the issue of dendrite formation. Li-S batteries incorporating the GO-decorated Li anodes exhibit an initial capacity of 850 mA h g-1 and maintain their stability for 800 cycles at a C-rate of 1 C (1675 mA h g-1), suggesting the applicability of GO in future rechargeable batteries.

Fabrication of a flexible single-yarn NH3 gas sensor by layer-by-layer self-assembly of graphene oxide

Abstract A novel flexible textile-type NH3 gas sensor was fabricated by the layer-by-layer self-assembly (LBL-SA) of graphene oxide (GO) on a single yarn. A poly(allylamine hydrochloride)(PAH)/poly(4-styrenesulfonic acid) sodium salt (PSS/PAH) bilayer (precursor layer) was deposited LBL on single-yarn substrate. Then, monolayer (GO/PAH) and GO multilayer (GO/PAH)n (n = 2, 3) thin films were self-assembled LBL on a (PSS/PAH)/yarn substrate. The thin films were analyzed by scanning electronic microscopy (SEM). The key step in the operation of the sensor was ion transport, which increased the conductivity of the (GO/PAH)n/PSS/PAH thin films. The electrical properties of the LBL self-assembled GO thin films were studied as functions of the concentration of NH3 gas, to elucidate the effects the number of (GO/PAH)n bilayers on the gas sensing properties (response and linearity). The single-yarn NH3 gas sensor that comprised the (GO/PAH)1 thin film was most sensitive at room temperature. The sensing linearity, response and recovery times, selectivity, bending and humidity effects were also investigated.

Fabrication of Polyamide 6 Nanocomposite with Improved Thermal Conductivity and Mechanical Properties via Incorporation of Low Graphene Content

A 3D graphene network was constructed in polyamide 6 (PA6) monomers through the reduction and self-assembly of graphene oxide (GO), and then PA6 nanocomposites with low graphene content were fabric...

Experimental and DFT investigation of 3D-HBGP/Pt/Co as a superb electrocatalyst for methanol oxidation reaction

Abstract Three-dimensional hollow balls of graphene oxide and polyaniline (3D-HBGP) nanocomposite were constructed by the self-assembly of graphene oxide (GO) and the polymerization of polyaniline (PANI) on poly(methyl methacrylate) (PMMA) particles. The 3D-HBGP was utilized as the support catalyst for platinum–cobalt (Pt–Co) that was electrochemically deposited on its surface for methanol oxidation reaction. Electrochemical measurements illustrates that the peak current density of 3D-HBGP/Pt/Co is 22.53 mA/cm2, which is 2.48 higher than Pt–Co alloy without 3D-HBGP support. According to this observation, the electro-catalytic activity of 3D-HBGP/Pt/Co is higher than that of Pt–Co electrocatalyst for methanol oxidation reaction (MOR). Compared to Pt–Co electrocatalyst, the electrochemical active surface area (ECSA) of 3D-HBGP/Pt/Co increases to 20.38 m2/g during cyclic voltammetry (CV) test. In addition, multi-scan cyclic voltammetry indicates that the 3D-HBGP/Pt/Co electrocatalyst has great catalytic stability for MOR. The density functional theory (DFT) calculation results reveal that utilizing the 3D-HBGP structure alongside Pt and Co leads to decreasing of the energy gap and increasing of the reactivity of catalyst which is in good agreement with experimental findings. The current study results (performance and stability) illustrate that the fabricated 3D-HBGP/Pt/Co electrocatalyst can be a prospective anode catalyst for direct methanol fuel cell (DMFC).

Synergistic water lubrication effect of self-assembled nanofilm and graphene oxide additive

In this study, a pretreatment method was proposed to enhance the lubrication effect of GO as additives. During pretreatment, 3-aminopropyltriethoxysilane (3-APS) nanofilm was successfully fabricated on substrate surface by self-assembled technique. The 3-APS nanofilm with amino groups can chemically adsorb the GO nanosheets in water. Thus the graphene oxide sheets could deposit on 3-APS nanofilm quickly and last longer, forming durable tribofilms on sliding contact areas. Scanning electron microscope (SEM), energy-dispersive spectroscopy (EDS) and water contact angle (WCA) characterizations revealed the successful preparation of 3-APS nanofilm. Importantly, tribological investigations indicated that under the synergistic effect of 3-APS nanofilm and GO additives, the friction coefficient and the wear rate decreased by 43.6% and 79.7%, compared to those of albronze lubricated by deionized water. Control experiments by respectively using GO additive, and 3-APS nanofilm were performed as well. It is found that using 3-APS nanofilm and GO additives together exhibits the best tribological performances among all the samples. Furthermore, GO tribofilms were detected on wear tracks and relative lubricating mechanisms were elucidated.

A multidimensional and nitrogen-doped graphene/hierarchical porous carbon as a sulfur scaffold for high performance lithium sulfur batteries

Constructing 3D heteroatom-doped carbon framework from sp2-hybridized nanocarbon (graphene) and sp3-hybridized porous carbon (activated carbon) has been considered as an effective method to achieve excellent performance in energy conversion and storage due to the synergistic effect between building blocks. Herein, a facile assembly of graphene oxide and porous carbon is reported to fabricate the inherent nitrogen-doped porous carbon and graphene composited nanostructures. When used as the sulfur scaffold for lithium sulfur batteries, the materials suggest outstanding electrochemical properties, including a high reversible capacity (1372 mAh g−1 at 0.1C), excellent rate performance (451 mAh g−1 at 3C) and cycling stability (579 mAh g−1 at 1C after 500 cycles). The enhancement in electrochemical properties can be ascribed to the 3D hierarchical porous structure of the carbon hybrid, in which, besides, the inherent doping of nitrogen can generate homogeneous active sites and defects that can effectively improve the interfacial adsorption. Thus, the simple strategy of pyrolysis and self assembly of graphene oxide and porous carbon provided in this work opens a new avenue for combining different dimensional nanocarbons to construct nitrogen-doped, multi-dimensional carbon architecture for high performance lithium sulfur batteries.

Synthesis of ZnO nanoparticles-decorated spindle-shaped graphene oxide for application in synergistic antibacterial activity

A novel spindle-shaped graphene oxide (GO) was performed by the self-assembly of graphene oxide in the DMF. Loading uniform ZnO nanoparticles on spindle-shaped GO is used to study antibacterial property. In the ZnO/GO composites, spindle-shaped GO possessed special structure that was crumpled together with a length of ~1.0 μm and a mean diameter of 100 nm, and spherical ZnO particles with a diameter of 50 nm were fully characterized by field-emission scanning electron microscope (FE-SEM), a high-resolution transmission electron microscope (HR-TEM) and X-ray diffraction (XRD). Due to the antibacterial advantages of ZnO and GO, the mechanism underlying the interaction between composites and bacteria is elucidated in this work. The results showed that the composites could prevent bacterial proliferation and could destroy bacterial integrated membrane by the release of Zn2+ and generation of abundant reactive oxygen species (ROS). The typical gram-negative (Escherichia coli and Salmonella typhimurium) and gram-positive (Bacillus subtilis and Enterococcus faecalis) bacteria were used to investigate the significant antibacterial activity of ZnO/GO composites. The minimum inhibit concentration (MIC) value of ZnO/GO composites for the gram-positive bacteria was 31.25 ± 0.25 μg/mL, however, that for the gram-negative bacteria was 15.625 ± 0.5 μg/mL. Based on our study, this new structure composites with good antibacterial activity is regarded as a promising material for application in the medical field.

Fabrication of graphene-fullerene hybrid by self-assembly and its application as support material for methanol electrocatalytic oxidation reaction

Graphene-fullerene hybrids were facilely fabricated by self-assembly of graphene oxide (GO) and multi-substituted fulleropyrrolidines (PyrC60). The hybrids (GO-PyrC60) were applied as support materials to deposit Pd nanoparticle catalyst by a simple hydrothermal co-reduction approach. The as-prepared electrocatalysts (Pd/RGO-PyrC60) were characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS), respectively. The RGO-PyrC60 hybrid supported Pd catalyst with the optimal ratio of RGO to PyrC60, exhibited much enhanced electrocatalytic activity and stability toward methanol oxidation reaction (MOR) compared to the RGO alone supported Pd as well as commercial Pd/C. The introduction of fulleropyrrolidine as spacer between graphene layers could increase the electrocatalytic activity and improve the long-term stability. This strategy may contribute to developing graphene-fullerene hydrids as effective support materials for advanced electrocatalysts.

Shear-induced assembly of graphene oxide particles into stripes near surface

ABSTRACTWe report the shear-induced assembly of graphene oxide (GO) particles into periodic stripe-like patterns near the surface. These stripe-like patterns, which have an average periodic length of 100–250 μm, are aligned in a wavy manner along the normal to the flow direction. The self-assembled GO structures are investigated at different depths using three different analysis methods, namely, reflective microscopy observations of the photonic-crystalline GO dispersion, polarized optical microscopy, and fluorescence confocal laser scanning microscopy. The surface microstructures observed in reflection mode are different from the shear-induced band structures formed in bulk thermotropic liquid crystals and liquid crystal polymers, in terms of the shape and scale of the stripes. Further, there is also a difference in terms of the dependence of the stripe width on the shear rate. The observations suggest that the stripes are formed because of a competition between the stable surface-field-induced planar alignment of the GO particles near the surface and their relatively unstable shear-induced vertical alignment in the bulk. The findings of this study should advance our understanding of GO assembly under shear stress. Further, the proposed method is a novel one for inducing the assembly of GO particles into microstructures shaped as thread-like stripes.

Self-assembly of graphene aerogel on carbon fiber for improvement of interfacial properties with epoxy resin

The three-dimensional multiscale reinforcement of graphene aerogel-carbon fibers (GA-CF) was prepared by one-step reduction and self-assembly of graphene oxide with L-ascorbic acid followed by freeze-drying. The interconnected GA networks serving as bridges guaranteed efficient stress transfer from epoxy to CF. GA-CF exhibited improvement of the interfacial shear strength from 38.8 MPa to 71.1 MPa, and the interfacial failure mode was transformed from adhesive failure to cohesive failure. The enhancement of interfacial properties could be attributed to enhanced surface roughness, increased surface area of the GA assembled CF and strengthened mechanical interlocking between GA and epoxy.

Self-Assembled AgNP-Containing Nanocomposites Constructed by Electrospinning as Efficient Dye Photocatalyst Materials for Wastewater Treatment.

The design and self-assembly of graphene oxide (GO)-based composite membranes have attracted enormous attention due to their wide application in nanomaterial and environmental fields. In this work, we have successfully developed a strategy to fabricate new composite membranes based on poly(vinyl alcohol)/poly(acrylic acid)/carboxyl-functionalized graphene oxide modified with silver nanoparticles (PVA/PAA/GO-COOH@AgNPs), which were prepared via thermal treatment and the electrospinning technique. Due to the strong π-π forces and strong electrostatic interactions of GO–COOH sheets, the prepared composite membranes and their lager surface areas were modified by scores of AgNPs, which demonstrated that a high-efficiency photocatalyst removed the organic dyes from the aqueous solutions. The prepared PVA/PAA/GO-COOH@AgNPs nanocomposite membranes showed a remarkable photocatalytic capacity in the catalytic degradation of the methylene blue dye solutions. Most importantly, the whole process was easy, mild, and eco-friendly. Additionally, the as-prepared membranes could be repeatedly used after the catalytic reaction.

Hierarchically porous, ultra-strong reduced graphene oxide-cellulose nanocrystal sponges for exceptional adsorption of water contaminants.

Self-assembly of graphene oxide (GO) nanosheets into porous 3D sponges is a promising approach to exploit their capacity to adsorb contaminants while facilitating the recovery of the nanosheets from treated water. Yet, forming mechanically robust sponges with suitable adsorption properties presents a significant challenge. Ultra-strong and highly porous 3D sponges are formed using GO, vitamin C (VC), and cellulose nanocrystals (CNCs) - natural nanorods isolated from wood pulp. CNCs provide a robust scaffold for the partially reduced GO (rGO) nanosheets resulting in an exceptionally stiff nanohybrid. The concentration of VC as a reducing agent plays a critical role in tailoring the pore architecture of the sponges. By using excess amounts of VC, a unique hierarchical pore structure is achieved, where VC grains act as soft templates for forming millimeter-sized pores, the walls of which are also porous and comprised of micron-sized pores. The unique hierarchical pore structure ensures the interconnectivity of pores even at the core of large sponges as evidenced by micro and nano X-ray computed tomography. The unique pore architecture translates into an exceptional specific surface area for adsorption of a wide range of contaminants, such as dyes, heavy metals, pharmaceuticals and cyanotoxin from water.

PLGA-based nanofibers with a biomimetic polynoradrenaline sheath for rapid in vivo sampling of tetrodotoxin and sulfonamides in pufferfish.

Nanomaterials have shown great potential for application in microextraction due to their distinguishing nanoscale architectures and superior physicochemical properties. Herein, novel poly(lactic-co-glycolic acid) (PLGA) solid-phase microextraction (SPME) fibers, which were incorporated with a self-assembled graphene oxide (GO)-coated γ-Al2O3 composite (Al2O3@GO), were fabricated on stainless steel wires via an electrospinning method. The as-spun nanofibers were further sheathed through the self-polymerization of noradrenaline (NA), an agonist found in oysters, to provide a compatible biointerface and antifouling capacity. Acting as the coating substrate of the as-prepared fibers, PLGA is known for its prominent biocompatibility and biodegradability, while the adsorptive Al2O3@GO particles helped to increase their loading capacity. The modified PLGA-based electrospun nanofibers exhibited much higher extraction efficiency compared with the thicker polydimethylsiloxane (PDMS) coatings (165 μm) and polyacrylate (PA) coatings (85 μm). Due to the fine biointerface of the PLGA-based nanofibers, a rapid extraction equilibrium was observed and sampling with the custom-made Al2O3@GO-PLGA@PNA fibers could be accomplished within 15 min. The fibers were then successfully employed for simultaneous in vivo sampling of tetrodotoxin (TTX) and sulfonamides (SAs) in the dorsal-epaxial muscle of living pufferfish (Takifugu obscurus), and satisfactory sensitivities with limits of detection (LODs) in the range of 0.52-2.30 ng g-1 and comparable accuracies to the conventional liquid extraction (LE) method were achieved. In vivo sampling of target pharmaceuticals with the modified nanofibers showed their feasibility for further metabolomics and pharmacokinetics studies in biotissues.

Graphene-based cellular materials with extremely low density and high pressure sensitivity based on self-assembled graphene oxide liquid crystals

A flexible strain sensor based on an ultralow density cellular material exhibits extremely high sensitivity.

Visible light induced degradation of pollutant dyes using a self-assembled graphene oxide–molybdenum oxo-bis(dithiolene) composite

An easily separable graphene oxide–molybdenum oxo-bis(dithiolene) ([Ph4P]2[MoO(S2C2(CN)2)2]) composite degraded Rhodamine B and Rose Bengal dye upon visible light exposure.

Self-assembling porous 3D titanium dioxide-reduced graphene oxide aerogel for the tunable absorption of oleic acid and RhodamineB dye

In this study, 3D titanium dioxide-reduced graphene oxide aerogels (TiO2-rGA) was synthesized by a modified hydrothermal treatment. Graphene is self-assembled into the 3D interconnected networks aerogel while TiO2 nanoparticles are uniformly and densely dispersed onto the graphene nanosheets. The as-obtained composite aerogels show a change of surface wettability from hydrophobic to hydrophilic depending on addition of incorporated TiO2. Absorption abilities of TiO2-rGA with different ratios of TiO2 for Oleic acid and RhodamineB (RhB) dye were tested. The result demonstrates that the composite aerogel with addition ratio of TiO2 can selectively absorb oleic acid floating on the water and RhB in aqueous systems. The resulting TiO2-rGA can be potentially applied in organic waste recovery.

Pulse-Driven Capacitive Lead Ion Detection with Reduced Graphene Oxide Field-Effect Transistor Integrated with an Analyzing Device for Rapid Water Quality Monitoring.

Rapid and real-time detection of heavy metals in water with a portable microsystem is a growing demand in the field of environmental monitoring, food safety, and future cyber-physical infrastructure. Here, we report a novel ultrasensitive pulse-driven capacitance-based lead ion sensor using self-assembled graphene oxide (GO) monolayer deposition strategy to recognize the heavy metal ions in water. The overall field-effect transistor (FET) structure consists of a thermally reduced graphene oxide (rGO) channel with a thin layer of Al2O3 passivation as a top gate combined with sputtered gold nanoparticles that link with the glutathione (GSH) probe to attract Pb2+ ions in water. Using a preprogrammed microcontroller, chemo-capacitance based detection of lead ions has been demonstrated with this FET sensor. With a rapid response (∼1-2 s) and negligible signal drift, a limit of detection (LOD) < 1 ppb and excellent selectivity (with a sensitivity to lead ions 1 order of magnitude higher than that of interfering ions) can be achieved for Pb2+ measurements. The overall assay time (∼10 s) for background water stabilization followed by lead ion testing and calculation is much shorter than common FET resistance/current measurements (∼minutes) and other conventional methods, such as optical and inductively coupled plasma methods (∼hours). An approximate linear operational range (5-20 ppb) around 15 ppb (the maximum contaminant limit by US Environmental Protection Agency (EPA) for lead in drinking water) makes it especially suitable for drinking water quality monitoring. The validity of the pulse method is confirmed by quantifying Pb2+ in various real water samples such as tap, lake, and river water with an accuracy ∼75%. This capacitance measurement strategy is promising and can be readily extended to various FET-based sensor devices for other targets.