Water-dispersible Graphene Research Articles

Biocompatible Fluorescent Graphene Oxide Quantum Dots for Imaging of Drosophila melanogaster.

Developing reliable biocompatible bioimaging agents is paramount for diagnosing critical diseases and disorders early through oral ingestion of fluorescent probes to image living organisms. Here, we prepared fluorescent, water-dispersed graphene oxide quantum dots via pyrolysis of a Glycyrrhiza glabra root in the water medium using a cost-effective and environmentally benign method to enable Drosophila melanogaster, an organism analogous to the human genome, to be imaged alive. The prepared graphene oxide quantum dots demonstrated a 2.6 nm diameter and 0.36 nm graphitic spacing with carboxylic acid, carbonyl, and hydroxyl functionalities. The selected area electron diffraction image analysis reveals a series of bright circular patterns that confirm the crystalline nature of the graphene oxide quantum dots. Raman and X-ray diffraction analyses also validate the crystallinity nature of prepared materials. The graphene oxide quantum dots exhibited blue fluorescence under ultraviolet-light irradiation with excitation-dependent emission properties from blue to red emission. The synthesized graphene oxide quantum dots consistently fluoresce in the larva-fed graphene oxide quantum dots without exhibiting toxicity. The current study evaluates the toxic effect of synthesized fluorescent graphene quantum dots by examining several screening and staining methods on D. melanogaster, a fruit fly, as a model.

A Tape-Wrapping Strategy towards Electrochemical Fabrication of Water-Dispersible Graphene.

Graphene has achieved mass production via various preparative routes and demonstrated its uniqueness in many application fields for its intrinsically high electron mobility and thermal conductivity. However, graphene faces limitations in assembling macroscopic structures because of its hydrophobic property. Therefore, balancing high crystal quality and good aqueous dispersibility is of great importance in practical applications. Herein, we propose a tape-wrapping strategy to electrochemically fabricate water-dispersible graphene (w-Gr) with both excellent dispersibility (~4.5 mg/mL, stable over 2 months), and well-preserved crystalline structure. A large production rate (4.5 mg/min, six times faster than previous electrochemical methods), high yield (65.4% ≤5 atomic layers) and good processability are demonstrated. A mechanism investigation indicates that the rational design of anode configuration to ensure proper oxidation, deep exfoliation and unobstructed mass transfer is responsible for the high efficiency of this strategy. This simple yet efficient electrochemical method is expected to promote the scalable preparation and applications of graphene.

Mechanochemical Preparation of Edge-Selectively justify Hydroxylated Graphene Nanosheets Using Persulfate via a Sulfate Radical-Mediated Process.

The production of water-dispersed graphene with low defects remains a challenge. The dry ball milling of graphite with additives produces edge-selectively functionalized graphene. However, the "inert" additives require a long milling time and cause inevitable in-plane defects. Here, the mechanochemical reaction of graphite with persulfate solved the above drawback and produced edge-selectively hydroxylated graphene (EHG) nanosheets through a 2 h ball-milling and a subsequent 0.5 h sonication. The mechanochemical cleavage of persulfate yielded SO4 ⋅- to spontaneously oxidize graphite to form the carbon radical cations selectively at edges, followed by hydroxylation with water of moisture. Because the O-O bond dissociation energy of persulfate is 20 % of the graphitic C-C bond, the rather low milling energy allowed the hydroxylation of graphite at edges with nearly no in-plane defects. The obtained EHG showed high water-dispersibility and excellent photothermal and electrochemical properties, thereby opening up a new door to fabricate graphene-based composites.

Nano-modified feather keratin derived green and sustainable biosorbents for the remediation of heavy metals from synthetic wastewater

In this study, we employed a facile method to synthesize feather keratin derived biosorbents using water dispersed graphene oxide. The successful cross-linking of feather keratin with graphene oxide was investigated through X-ray photoelectrons spectroscopy (XPS), scanning and transmission electron microscopy, and Brunauer–Emmett–Teller (BET) analysis. The modifications resulted in increased surface area of the keratin proteins with substantial morphological changes including the development of cracked and rough patches on the surface. The chicken feather keratin/graphene oxide based biosorbents exhibited excellent performance for the simultaneous removal of metal oxyanions including arsenic (As), selenium (Se), chromium (Cr) and cations including nickel (Ni), cobalt (Co), lead (Pb), cadmium (Cd) and zinc (Zn) up to 99%, from polluted synthetic water containing 600 μgL−1 of each metal concentration in 24 h. The insights into the biosorption mechanism revealed that the electrostatic interaction, chelation and complexation primarily contributed to the removal of multiple heavy metal ions in a single treatment. This study has demonstrated that modification of chicken feather keratin with graphene oxide is an effective way to improve its sorption capacity for removing multiple trace metal ions from contaminated water.

Chemical resistance of synthesized graphene-modified cement paste containing natural pozzolans to acid attack

This research aims to evaluate the impact of pumice and zeolite as natural pozzolans in cement paste prepared by water-dispersed graphene synthesized from graphite and surfactant against an acid attack. Firstly, the optimal amount of dispersed graphene was derived. Then, several tests such as compressive strength, sorptivity, and microstructural examination such as X-ray diffraction (XRD), scanning electron microscope (SEM), and mercury intrusion porosimetry (MIP) were applied to investigate the single and synergic influence of supplementary cementitious materials (SCMs) at various age of curing. Finally, the chemical resistance of different mixtures under H2SO4 and HNO3 attack was evaluated by weight loss and loss of compressive strength, followed by a visual and microstructural examination of the degradation at different immersion times up to 22 weeks. According to the results, in graphene-containing mixtures, pumice and zeolite decreased compressive strength by 15.5% and 20.4% at an early age, respectively. However, based on the MIP and XRD results, this reduction was mitigated by improving pozzolanic reaction in the long term. Regarding weight loss and compressive strength loss from acid attack results, zeolite reduced these characteristics by 251.72 % and 239.4% compared to the reference paste, respectively.

Investigation of two different water-dispersed graphene on the performance of graphene/cement paste: Surfactant and superplasticizer effect

• The compressive strength of graphene-based cement paste with 0.1% SP was increased by 82.05%. • Surfactants did not show better performance in the hydration process due to their hydrophilicity. • The optimized concentration of graphite and dispersing agents is determined. • The graphene produced by the superplasticizer has the lowest level of defects. • The microstructure results are in accordance with compressive resistance results. The excellent performance of graphene-based materials to use in concrete has recently attracted the attention of civil engineering researchers. However, the application of graphene faces obstacles due to the high cost of graphene and agglomeration phenomena in cementitious composites. As a result, research into the production of water-dispersed graphene, a combination of graphite and a dispersing agent, is a particularly cost-effective alternative. In this regard, it is essential to select a dispersing agent capable of effectively separating graphene layers while also improving mechanical properties and impermeability. In this study, the influence of two different dispersive agents, surfactant (S) and superplasticizer (SP), on mechanical properties, permeability, and microstructure of cement paste was investigated. SEM, TEM, and Raman spectroscopic analyses demonstrate that multilayer graphene sheets made using superplasticizer have higher quality and fewer defects than surfactant-based sheets. After 3 days of aging, the compressive strength of graphene-containing cement paste with 0.1 % superplasticizer increased by 82.05 % compared to the control paste. On the other hand, a decrease in sorptivity by 54 % compared to the control paste is observed by graphene-containing cement paste with 0.56 g/l surfactant. The microstructure investigation revealed that graphene accelerates the CH and C-S-H productions due to the nucleation effect in the composite cement matrix; however, the effect of SP is more significant than S in cementitious composites. This research suggests that water-dispersed graphene generated by 0.1 % SP and 0.56 S g/l has the potential to be used as an innovative admixture in cement-based composite materials.

Graphene-Dominated Hybrid Coatings with Highly Compacted Structure on Stainless Steel Bipolar Plates.

Highly conductive corrosion protection coatings are necessary for metallic bipolar plates (BPs) of the proton-exchange membrane fuel cell. Graphene coatings have the potential of protecting metal substrates from corrosion without obscuring their excellent electrical conductivity. The electron transfer in the coatings facilitates the formation of galvanic cells, so the challenge is to block the mass transfer of the corrosion process. Here, we constructed highly compacted hybrid coatings with aligned water-dispersible graphene layers. The water-dispersible graphene (SG) held an electrical conductivity of >270 S cm-1 while providing an unprecedented dispersibility, which can be redispersed from filter cake with a concentration of 120 mg mL-1 or even dry state. The cohesion of the hybrid coatings was attributed to the interaction between highly aligned SG layers and the heterointerface between SG and polydopamine (PDA), as proven by the molecular dynamics simulations. The hybrid coatings presented a corrosion current density of 0.023 μA cm-2 and an interfacial contact resistance of 9.94 mΩ cm2, which meets the requirements of corrosion protection and electron transfer for the coatings on metallic BPs. The water-based fabrication method of the graphene-dominated hybrid coatings was a promising alternative of the vacuum-based deposition method for industrial production.

A cost-effective disposable graphene-based sensor for sensitive and selective detection of uric acid in human urine

A rapid and facile method has been developed for uric acid (UA) sensing in human urine. The graphite pencil electrode's (GPE) sensitivity and electrochemical activity for sensing uric acid in human urine were enhanced by the electrochemically reduced graphene oxide on GPE in acetate buffer (ac-dERGO-GPE). Acetate, medium-supported graphene oxide reduction, is more facile, fast, and sensitive than water-dispersed graphene oxide. The surface of the modified and bare electrode was thoroughly investigated using the Fourier transform-infrared (FTIR), Field emission-scanning electron microscopy (FE-SEM), cyclic voltammetry (CV), square wave voltammetry (SWV), and electrochemical impedance spectroscopy (EIS). The electroactive surface area of the modified electrode was significantly improved from 0.0686 cm2 to 0.3615 cm2. The graphene layers greatly enhanced the electroactive surface area and the sensitivity of the ac-dERGO/GPE. A linear response was observed for UA in the range of 0.200 μM–22.0 μM with a 0.996 regression coefficient and a low detection limit of 0.037 μM. The modified electrode retained its response intact in the presence of the potential interferences and successfully applied for UA sensing in human urine. The ac-dERGO/GPE sensor, due to its facile fabrication, low cost, excellent sensitivity, and high selectivity could be a potential candidate for trace level quantification of uric acid in human urine.

Hydrothermal Unzipping of Multiwalled Carbon Nanotubes and Cutting of Graphene by Potassium Superoxide.

The dual use of potassium superoxide (KO2) to unzip multiwalled carbon nanotubes (MWCNTs) and cut graphene under hydrothermal conditions is described in this work. The KO2-assisted hydrothermal treatment was proven to be a high-yield method for forming graphene nanoribbons and dots or sub-micro-sized graphene nanosheets. Starting with functionalized MWCNTs, the method produces water-dispersible graphene nanoribbons with characteristic photoluminescence depending on their width. Using pristine graphene, the hydrothermal treatment with KO2 produces nanosized graphene sheets and graphene quantum dots with diameters of less than 10 nm. The latter showed a bright white photoluminescence. The effective hydrothermal unzipping of MWNTs and the cutting of large graphene nanosheets is a valuable top-down approach for the preparation of graphene nanoribbons and small nanographenes. Both products with limited dimensions have interesting applications in nanoelectronics and bionanotechnology.

Investigation of Two Different Water-Dispersed Graphene on the Performance of Graphene/Cement Paste: Surfactant and Superplasticizer Effect

Investigation of Two Different Water-Dispersed Graphene on the Performance of Graphene/Cement Paste: Surfactant and Superplasticizer Effect

Evaluation of Inkjet-Printed Reduced and Functionalized Water-Dispersible Graphene Oxide and Graphene on Polymer Substrate-Application to Printed Temperature Sensors.

The present work reports on the detailed electro-thermal evaluation of a highly water dispersible, functionalized reduced graphene oxide (f-rGO) using inkjet printing technology. Aiming in the development of printed electronic devices, a flexible polyimide substrate was used for the structures’ formation. A direct comparison between the f-rGO ink dispersion and a commercial graphene inkjet ink is also presented. Extensive droplet formation analysis was performed in order to evaluate the repeatable and reliable jetting from an inkjet printer under study. Electrical characterization was conducted and the electrical characteristics were assessed under different temperatures, showing that the water dispersion of the f-rGO is an excellent candidate for application in printed thermal sensors and microheaters. It was observed that the proposed f-rGO ink presents a tenfold increased temperature coefficient of resistance compared to the commercial graphene ink (G). A successful direct interconnection implementation of both materials with commercial Ag-nanoparticle ink lines was also demonstrated, thus allowing the efficient electrical interfacing of the printed structures. The investigated ink can be complementary utilized for developing fully printed devices with various characteristics, all on flexible substrates with cost-effective, few-step processes.

Highly Water-Dispersible Graphene Nanosheets From Electrochemical Exfoliation of Graphite.

The electrochemical exfoliation of graphite has been considered to be an effective approach for the mass production of high-quality graphene due to its easy, simple, and eco-friendly synthetic features. However, water dispersion of graphene produced in the electrochemical exfoliation method has also been a challenging issue because of the hydrophobic properties of the resulting graphene. In this study, we report the electrochemical exfoliation method of producing water-dispersible graphene that importantly contains the relatively low oxygen content of <10% without any assistant dispersing agents. Through the mild in situ sulfate functionalization of graphite under alkaline electrochemical conditions using a pH buffer, the highly water-dispersible graphene could be produced without any additional separation processes of sedimentation and/or centrifugation. We found the resulting graphene sheets to have high crystalline basal planes, lateral sizes of several μm, and a thickness of <5 nm. Furthermore, the high aqueous dispersion stability of as-prepared graphene could be demonstrated using a multi-light scattering technique, showing very little change in the optical transmittance and the terbiscan stability index over time.

A novel preparation of water-dispersed graphene and their application to electrochemical detection of dopamine

In the paper, water-dispersed graphene-GQDs composites were prepared by electrochemical exfoliation under alternating voltage combining ultrasonic treatment. The effects of alternating voltage, alternating frequency and the distance between electrodes were carefully explored. The results showed that the quality of composites prepared by alternating voltage was higher than that by direct voltage. The existence of graphene quantum dots (GQDs) hindered the agglomeration of graphene and facilitated dispersion of graphene in water. The sensor based on the obtained graphene-GQDs composites was used to detect dopamine (DA). The electrochemical investigation showed that the sensor had good selectivity and wide linear ranges for the detection of DA (0.1–100 µM). The detection limit could be down to 3 × 10−8 M (S/N = 3) with a sensitivity of 14.25 µA µM−1 cm−2.

Graphene quantum dots doped conducting polymer nanocomposite for high performance supercapacitor application

Water-dispersible graphene quantum dots are synthesised by the hydrothermal method. Graphene quantum dots polypyrrole nanocomposites (PGQDs) are prepared by the chemical oxidation polymerisation method. The properties of the composite were characterised by UV-Visible absorption spectra, transmission electron microscopy, and impedance spectroscopy (temperature from 300 K to 393 K, frequency 20 Hz−1 MHz). The dielectric and modulus parameters were studied and high conductivity of 1.62 S/Cm was observed. A solid-state supercapacitor with a simple structure is designed based on polymer quantum dots composite film using stainless steel electrodes with PVA/KOH gel electrolyte. The performance of the supercapacitor was analysed by using cyclic voltammetry (CV), galvanostatic charge-discharge curves (GCD), and electrochemical impedance spectra (EIS) and Nyquist plot. It was observed that PPY-GQDs supercapacitors exhibited a maximum specific capacitance of 790.3 F/g. The electrochemical properties of the supercapacitor with high flexibility and stability are enhanced by optimising the concentration of electrically conductive substances like polymer gel and an increase in the concentration of GQDs.

Toxicological evaluation of highly water dispersible few-layer graphene in vivo

In the last decade, graphene-based materials have received increasing attention for both academic research and industrial uses. However, products containing graphene must meet the same standards for quality, safety and efficacy as products not containing nanomaterials. Our aim is to shed light on the toxicological characterization of few-layer graphene (FLG) dispersions. In the present study, graphene was easily dispersed in water using biocompatible riboflavin-5′-phosphate sodium salt (Rib). A highly concentrated FLG dispersion (G-Rib) was stable for months. G-Rib sheets presented an average lateral size of about 840 nm and an average thickness of 5 layers. Our results showed that even at high concentration of G-Rib, cell survival was always above 85%. Then, we investigated the tissue distribution and toxic effects of G-Rib in mice up to 30 days after intravenous injections. Histological analysis of the tissues revealed hepatic accumulation and excretion through the kidneys. The biochemical and hematological parameters remained within the reference range showing no hematotoxicity. Finally, no signs of inflammation were detected in the cells isolated from the lymph nodes and spleen. The results of the study show that highly water dispersed FLG is a material with a very low toxic profile, which is one of the first requirements for the future development of biomedical applications.

Electrochemical exfoliation of water-dispersible graphene from graphite towards reinforcing the mechanical and flame-retardant properties of poly (vinyl alcohol) composites

Functional graphene is a very efficient support material to improve the performance of polymer composites, but the commercial application of functional graphene is hindered by its complex preparation procedure and high pollution. Herein, the water-dispersible graphene nanosheets (DGNS) were prepared by a simple and eco-friendly electrochemical method assisted with an anionic surfactant DNS86, and then DGNS were mixed into poly (vinyl alcohol) (PVA) matrix to fabricate PVA composite films. DGNS could be well dispersed in PVA matrix and form strong interfacial interaction with PVA molecular chains. The tensile strength, tensile modulus and storage modulus of PVA composite film containing 0.3 wt% DGNS were increased by 50.1%, 50.4% and 154.5%, respectively, compared to those of pure PVA. Moreover, the addition of DGNS also improved the flame retardancy of PVA composite films, achieving an obvious reduction (60.9%) in the peak heat release rate with the load of 2.0 wt% DGNS. The analysis revealed that the addition of DGNS could facilitate the formation of the compact and highly graphitic char residues, retarding the heat and mass transfer to protect underlying matrix during combustion process. This paper will supply a promising strategy to industrially produce functionalized graphene nanosheets for graphene-based reinforced composites.

Electrochemical exfoliation for few-layer graphene in molybdate aqueous solution and its application for fast electrothermal film

There are still serious barriers from laboratory exploration to large-scale production of commercializing high-quality graphene, especially by environmental-friendly methods. In this study, a simple and efficient electrochemical method for the preparation of high-quality water-dispersible graphene has been developed using molybdate aqueous solutions as the electrolyte. The exfoliation of graphite paper could be achieved in the electrolyte with a high yield of a few layers graphene (1–5 layers, 76%) and uniform lateral size (1–6 μm, 90%). The as-obtained few layers graphene well dispersed in aqueous solution with a solubility of ~4 mg mL−1 and stability for at least 2 months. It provides a new green method to prepare high-quality graphene. The as-prepared water-dispersible graphene films exhibit significant electrothermal performance, with a steady-state temperature of 147 °C under voltage of 10 V and a maximum heating rate achieved of 11.8 °C s-1.

Effects of Size and Oxidation on the Nonlinear Optical Response and Optical Limiting of Graphene Oxide Sheets

In the present work we report on the effect of the size and the degree of oxidation on the third-order nonlinear optical response and the optical limiting action of water dispersed graphene oxide (...

Room-temperature synthesis of water-dispersible sulfur-doped reduced graphene oxide without stabilizers.

Sulfur-Doped graphene has attracted significant attention because of its potential uses in sensors, catalysts, and energy storage applications. In conventional approaches, the sulfur-doped graphene is fabricated with graphene oxide and sulfur-containing compounds through thermal annealing or hydrothermal process, which generally involves special equipment and heat treatment, and requires additional stabilizers to make it solution-processable. In this work, we report a facile one-step approach to synthesize water-dispersible sulfur-doped reduced graphene oxide (S-rGO). Graphene oxide (GO) could be readily reduced and converted to S-rGO simultaneously by directly mixing GO dispersion with hydrosulfide hydrate (NaSH·xH2O) at room temperature. The sulfur doping is confirmed by high resolution S 2p XPS spectrum and element mapping. The colloidal dispersion state of S-rGO is confirmed by the investigation of Tyndall effect, the zeta potential and particle size distribution measurement. Compared with previously reported strategies, NaSH can initiate the reduction and sulfur doping at room temperature, demand no heat treatment, require no equipment and form stable aqueous S-rGO dispersion without using any stabilizer. These advantages will facilitate large-scale production of water-dispersible (sulfur doped) graphene and further boost their applications in sensors, catalysts and energy storage devices.

Electrochemically Exfoliated Graphene for Nanosensor Applications.

Water dispersible graphene layer are the excellent nano materials used for wide range of electronic applications. High quality graphene was synthesized by an eco-friendly, easy and cost effective electrochemical exfoliation method. In this work, graphite rod was used both as an anode and cathode for the production of graphene. Potassium sulphate (K₂SO₄) was used as an intercalating agent. Electrochemically exfoliated graphene (EEG) was coated on glassy carbon electrode (GCE) and evaluated towards the electrochemical oxidation of vanillin and L-phenylalanine. The fabricated electrode was able to detect vanillin and L-Phenylalanine as low as 0.2 μM with signal to noise ratio of 3. A significant increase in the current was observed for the graphene coated electrode for both vanillin and L-phenylalanine when compared to bare Glassy electrode. The finding clearly demonstrated the higher detection capability, selectivity and reproducibility of EEG.