Well-dispersed Graphene Research Articles

Fabrication of Self-Assembled Graphene Oxide Film and Its Application in Aqueous Zinc Metal Batteries.

Fabrication of well-dispersed thin graphene oxide (GO) films (GOFs) has always been a challenge. Herein, a quick preparation method for GOFs was developed using our homemade GO with a large lateral size. The film can be prepared in less than 2 h via a metal framework-induced self-assembly process. The thickness of the films can be as thin as ∼15.5 μm, which will be thinner with compression. When it is used as a flexible modification layer on the Zn metal for aqueous Zn-ion batteries, Zn can grow along the [010] direction in plane and stack orderly along the [002] direction even on the Cu substrate with GOF through epitaxial plating owing to negligible lattice mismatch between the (002) plane of Zn and the hexagonal ring [also (002) plane for graphite] of GO. Meanwhile, the rich O groups on the GO film can provide abundant zincophilic points and promote uniform distribution of Zn2+ around the anode. Finally, dendrite-free and dense Zn stripping/plating can be achieved and well remained. The GOF@Zn symmetric cell reveals long cyclic stability of 1300 h at 1 mA cm-2 and 1 mA h cm-2. It still can remain at 350 h even at a very high current density of 10 mA cm-2 accompanied by a high areal capacity of 10 mA h cm-2. With the same plating amount of 5 mA h cm-2, the thickness of the plated Zn is only ∼10 μm with GOF modification, very close to the theoretical value of 8.54 μm, much thinner than that without GOF (∼18 μm), indicating very dense deposition. Full cells assembled with the GOF@Zn anode and the MnO2 cathode exhibit a capacity retention rate of 71% over 1000 cycles at 0.7 A g-1, showing much better cycling performance than that using bare Zn.

Enhancing the fracture toughness of zirconia via highly oriented graphene arrays

Zirconia matrix composites with well-dispersed and highly-oriented two-dimensional graphene arrays were fabricated successfully using tape casting. This significantly improved the fracture toughness (KIC) of zirconia, i.e., an improvement of 64.1 % in KIC, from 4.3 MPa m0.5 to 7.21 MPa m0.5. The interface strengthened by Zr, O and C bonding between zirconia and graphene plays a crucial role in improving the toughness of zirconia. The catastrophic fracture failure mode is transformed into the stable crack propagation behavior with well-oriented graphene arrays. The interface stress transfer behavior analyzed by the shear-lag theory reveals that the graphene layers have little effect on the maximum axial stress and shear stress at graphene/zirconia interface, but the stress distribution are changed. Due to the weak bonding between inner graphene layer, the energy dissipation by graphene pulling-out decreases with increased graphene layers.

Fabrication of FeP2/C/CNTs@3D interconnected graphene aerogel composite for lithium-ion battery anodes and the electrochemical performance evaluation using machine learning

Featuring low cost and high theoretical capacity, phosphorus-rich iron diphosphides (FeP2) have emerged as excellent anode candidates for lithium-ion batteries. However, the typical chemical synthses involving high temperatures and toxic gases have restricted the mass production of FeP2. We now report a FeP2/C/CNTs@3D interconnected graphene aerogel composite synthesized by ball milling and low temperature heat treatment. Because of the unique microstructure and synergistic effect between well-dispersed FeP2 particles and graphene aerogel, the as-prepared FeP2/C/CNTs@GA-2.5% displays excellent lithium storage performance in terms of reversible capacity (886 mA h g−1 at 0.1 A g−1), cycling stability (476 mA h g−1 at 2 A g−1 even after 1000 cycles), and rate capability (685 mA h g−1 at 5 A g−1). Machine learning methods (decision tree and random forest algorithms) prove effective in evaluating and predicting electrochemical performance of the electrode materials.

Vinyl-ester nanocomposites based on a binary-solvent system for well-exfoliated graphene and enhanced performance

This paper introduces a green approach for preparing well-dispersed graphene nanoplates (GNPs) in vinyl-ester (VE) resin. The GNPs were exfoliated in a novel binary-solvent system comprised of a water and ethanol mixture (S nanocomposites). Water and ethanol were considered poor solvents for graphene, but a combination of them could be an ideal solvent mixture. TEM images of the S nanocomposites revealed well-exfoliated graphene sheets with a few wrinkles. Hence, the effective surface areas of the GNPs considerably increased, playing a vital role in enhancing the performance of the nanocomposites. With the incorporation of just 0.4 wt% of exfoliated GNPs (S2 nanocomposite) in the VE, the tensile strength, and toughness enhanced by 51%, and 63%, respectively. Fractography analysis indicated smooth fracture surfaces of pure resin changed to very rough surface structures for the S2 nanocomposite. The viscoelastic properties of the specimens indicated that directly loading GNPs into the resin decreased the glass transition temperature (Tg) of the VE resin. In contrast, the samples prepared by liquid-phase exfoliation enhanced the Tg of the VE. Lastly, the barrier properties of the S2 nanocomposite revealed that its water absorption decreased by 26% compared to the pure resin.

Preparation and anticorrosion performance of graphene-reinforced epoxy powder coating

Existing studies have reported that graphene can enhance the corrosion resistance of solvent-based organic coatings. However, the role of graphene in organic powder coatings remains to be obscure. In the present study, the graphene powder was prepared through liquid-phase exfoliation of graphite followed by freeze drying and the effects of graphene on structures, anticorrosion performance and adhesion strength of epoxy powder coatings were investigated. Scanning electron microscopy (SEM) demonstrated that graphene reduced surface micropores and enhanced structural compactness of the epoxy powder coatings. Electrochemical impedance spectra, Tafel polarization measurement and salt spray test indicated that a small amount (0.0125, 0.025 and 0.05 wt%) of well-dispersed graphene powder would be sufficient to effectively reinforce the anticorrosion performance of the epoxy powder coatings, especially for the coating with 0.025 wt% graphene, of which the impedance modulus maintained the highest values of nearly 107 and 105.8 Ω cm2 after immersion in 3.5 % NaCl solution for 21 and 30 days. Pull-off test confirmed that graphene enhanced the adhesion strength of coatings after salt spray test for 240 h, while the coating with 0.025 wt% graphene exhibited the highest adhesion strength up to 3.88 MPa. In addition, differential scanning calorimetry (DSC) indicated that graphene sheets could improve the thermal conductivity and promote curing reactions of epoxy powder. The mechanism for the reinforcement of epoxy powder coating by graphene has also been proposed.

Fabrication of the superhydrophobic and oleophilic graphene-based sponge for the treatment of oil- and organic solvent-contaminated wastewater

Graphene, a 2D nanomaterial, has been extensively studied and applied in many applications including, but not limited to, energy storage, environmental treatment, additives for paints, rubber, and composite, sensors, and electronic devices. In this work, graphene-based sponge was facilely fabricated by simply immersing melamine sponge into well-dispersed graphene nanoplaletes solution. The prepared graphene sponge revealed superhydrophobic and oleophillic properties in nature. The graphene-based sponge showed remarkable adsorption performance toward oils and organic solvents with the adsorption capacity ranging from 40 to 70 folds of sponge’s weight. The sponge also exhibited high recyclability, which is considered as a promising material for the practical application.

Preparation of well-dispersed graphene oxide-silica nanohybrids/ poly(lactic acid) composites by melt mixing

Graphene oxide has a strong tendency to agglomerate in polymers that are only hydrogen bonded acceptors due to the strong hydrogen bonding and van der Waals forces between its lamellae, which greatly limits its application. In this work, Silica (SiO2) was introduced on the surface of graphene oxide (GO) by hydrolysis of tetraethoxysilane (TEOS). Graphene oxide-silica/polylactic acid (PLA) composites with different grafting ratios were prepared by melt blending. The results by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), and X-ray photoelectron spectrometry (XPS) show that the silica is grafted on the GO surface in the form of covalent bonds. Other test results show that regulating the amount of TEOS addition could effectively control the grafting rate. The performance test shows that grafting SiO2 on the GO surface can increase the layer spacing of graphene oxide flakes and thus improve its melt dispersion. It also slows down or improves the performance degradation caused by the severe agglomeration of graphene oxide. At the grafting rate of 45.65%, GO is well exfoliated and well dispersed in PLA in the form of monolayers resulting in a substantial improvement in crystalline properties, mechanical properties, and barrier properties. This work solves the problem of severe agglomeration of GO in polymers that are only hydrogen bond acceptors by modifying GO, and provides guidance for the melt processing of graphene oxide and polymers that are only hydrogen bond acceptors.

Well-dispersed graphene toward robust lubrication via reorganization of sliding interface

Excellent lubrication performance of graphene lubricant is mostly attributed to the dispersion of graphene and forming of tribo-film. Herein, diethylene glycol dodecyl ether (E2C12) functionalized graphene oxide (E2C12-GO) was successfully prepared by simple esterification. The physicochemical properties of as-prepared samples were characterized by a series of characterization methods. E2C12-GO with flat edge and high-level spacing possesses high dispersion stability in PAO 20 base oil. Compared with base oil, 0.08 wt% E2C12-GO could achieve the reduction of average friction coefficient and wear rate by 30 % and 57 % at 150 N, respectively. Even with each long-term friction, E2C12-GO could still maintain the state of robust low friction coefficient. Meanwhile, the addition of E2C12-GO can significantly improve the load-bearing capacity (PB value and PD value) of base oil. The excellent tribological properties of E2C12-GO were attributed to high dispersion and high layer spacing, as well as the reorganization of sliding interface. Prospectively, the E2C12-GO shows promising potential as a multi-functional oil-based lubricating additive in industrial applications.

Ultrasonic photoacoustic emitter of graphene-nanocomposites film on a flexible substrate

Photoacoustic devices generating high-amplitude and high-frequency ultrasounds are attractive candidates for medical therapies and on-chip bio-applications. Here, we report the photoacoustic response of graphene nanoflakes – Polydimethylsiloxane composite. A protocol was developed to obtain well-dispersed graphene into the polymer, without the need for surface functionalization, at different weight percentages successively spin-coated onto a Polydimethylsiloxane substrate. We found that the photoacoustic amplitude scales up with optical absorption reaching 11 MPa at ∼ 228 mJ/cm2 laser fluence. We observed a deviation of the pressure amplitude from the linearity increasing the laser fluence, which indicates a decrease of the Grüneisen parameter. Spatial confinement of high amplitude (> 40 MPa, laser fluence > 55 mJ/cm2) and high frequency (Bw-6db ∼ 21.5 MHz) ultrasound was achieved by embedding the freestanding film in an optical lens. The acoustic gain promotes the formation of cavitation microbubbles for moderate fluence in water and in tissue-mimicking material. Our results pave the way for novel photoacoustic medical devices and integrated components.

Improvement of anticorrosion properties of waterborne coatings by designing a new type of modified graphene with high dispersion and low conductivity

Gallic acid modified and reduced graphene coated by polydopamine (DM-GO) is synthesized. The results show that gallic acid can reduce graphene oxide and promote the stable dispersion of graphene in solution, and repair some defects of graphene surface through π-π interactions. Polydopamine can effectively mitigate serious corrosion caused by graphene due to its high electrical conductivity. Because of the barrier effect of well-dispersed graphene and the presence of polydopamine, the addition of DM-GO into waterborne coating leads to the significant improvement of the adhesion and long-term corrosion resistance of coatings.

Electrical Stimulated Polyvinyl Alcohol-Borax-Graphene Hydrogel for Drug Releasing and Delivery

Polyvinyl Alcohol hydrogel has promising applications in numerous biomedical, biomaterial, and tissue engineering. However, it has poor conductive properties, restraining its development within huge fields such as bio-signals acquisition systems, thermal stability, and drug delivery. Adding Graphene as a nanofiller will produce PVA/Borax/Graphene nanocomposite hydrogel, which is an excellent procedure to significantly improve the conductive properties of PVA. The toxicity will not affect the nanocomposite while very well-dispersed graphene will significantly improve the thermal and conductivity stability of the nanocomposite. In this study, we investigated the performance of a newly prepared conductive hydrogel gel using the freezing/thawing method

Optimization of Spray-Drying Process with Response Surface Methodology (RSM) for Preparing High Quality Graphene Oxide Slurry

The “Drying-redissolution” method is promising for the industrial production of high-concentration well-dispersed graphene oxide slurry (GOS). As the potential key step in this method, the spray drying process requires a statistical investigation which guides the large-scale preparation of graphene oxide powder (GOP). This work systematically studies the effects of operating parameters, including nozzle airflow rate (439–895 L·h−1), atomization pressure (0.5–0.7 MPa), and liquid feed rate (3.0–9.0 mL·min−1), by using the response surface methodology integrated Box–Behnken design (RSM–BBD), aiming to produce GOP with high yield and easy re-dispersion. The optimized spray drying condition is predicted to be 439 L·h−1, 0.59 MPa, and 9.0 mL·min−1, at which a powder yield of 70.45% can be achieved. The experimentally obtained GOP has an average particle size of 11.65 μm and the low crumpling degree of the particle morphology results in the good re-dispersibility (97.95%) and excellent adsorption performance (244.1 mg·g−1) of GOP. The GOS prepared by the spray-dried GOP possess low viscosity and high exfoliation efficiency with a single-layer fraction up to 90.8%, exhibiting good prospects for application. This work first applied the RSM–BBD model on the spray drying process of GO, and evidenced the possibility of producing high-quality GO slurry with the “drying-redissolution” method.

Characterization of PVDF/Graphene Nanocomposite Membranes for Water Desalination with Enhanced Antifungal Activity

Seawater desalination is a worldwide concern for the sustainable production of drinking water. In this regard, membrane distillation (MD) has shown the potential for effective brine treatment. However, the lack of appropriate MD membranes limits its industrial expansion since they experience fouling and wetting issues. Therefore, hydrophobic membranes are promising candidates to successfully deal with such phenomena that are typical for commercially available membranes. Here, several graphene/polyvinylidene (PVDF_G) membranes with different graphene loading (0–10 wt%) were prepared through a phase inversion method. After full characterization of the resulting membranes, the surface revealed that the well-dispersed graphene in the polymer matrix (0.33 and 0.5 wt% graphene loading) led to excellent water repellence together with a rough structure, and a large effective surface area. Importantly, antifungal activity tests of films indicated an increase in the inhibition percentage for PVDF_G membranes against the Curvularia sp. fungal strain. However, the antifungal surface properties were found to be the synergistic result of graphene toxicity and surface topography.

A graphene oxide-copper nanocomposite for the regeneration of the dentin-pulp complex: An odontogenic and neurovascularization-inducing material

• Well-dispersed water soluble graphene oxide-copper nanocomposites is synthesized. • The GO-Cu can promote odontogenesis of DPSCs. • Odontogenesis and neurovascularization was observed in regenerated dentin-pulp-like tissues. Dentin–pulp complex tissue engineering is a promising novel therapy in endodontics. Materials currently used in regenerative endodontics, e.g., calcium hydroxide and mineral trioxide aggregate, do not ensure full regeneration of the dentin–pulp complex, especially in terms of neurovascular induction. In this study, we fabricated a water-soluble graphene oxide–copper nanocomposite (GO-Cu) and investigated its odontogenic and neurovascularization-inducing abilities by means of dental pulp stem cells (DPSCs). Low-dose (≤10 µg/mL) GO-Cu had no effect on DPSC viability and promoted proliferation and adhesion. DPSCs treated with GO-Cu differentiated into odontoblasts and secreted larger amounts of vascular endothelial growth factor (VEGF) and glia-derived neurotrophic factor (GDNF) just as when they were cultured on a GO-Cu–coated calcium phosphate cement (CPC/GO-Cu) scaffold. Human umbilical vein endothelial cells treated with GO-Cu showed more tube formation, higher VEGF expression, and a stronger migratory ability. In addition, immunomodulatory genes, including indoleamine 2,3-dioxygenase (IDO), human leukocyte antigen G (HLA-G), and hepatocyte growth factor (HGF), were upregulated in DPSCs by the GO-Cu treatment. When CPC/GO-Cu was transplanted subcutaneously into nude mice, dentin–pulp complex–like structures formed expressing dentin sialophosphoprotein (DSPP), CD31, and GAP43, and the mineralized area and blood vessel numbers were greater in the CPC/GO-Cu group than CPC-alone group. These results show odontogenic and neurovascularization-inducing abilities of GO-Cu and suggest its promising application in regenerative endodontics.

A novel titania/graphene composite applied in reinforcing microstructural and mechanical properties of alkali-activated slag

Alkali-activated slag (AAS) binder with low carbon footprint is a promising alternative to high energy-embodied ordinary Portland cement binders. However, wider applications are hindered by their ceramic-type fractural behaviours. This study involves improving the microstructure and mechanical properties of alkali-activated slag pastes by using an in-situ fabricated titania/graphene composite assisted with a novel titania intercalating method. The result indicates that titania located in between the layers of graphene could make graphene homogeneously dispersed in an aqueous solution, which is conducive to obtaining well-dispersed graphene nanoparticles in AAS pastes. Besides, the highly dispersed titania/graphene composites lead to a less disordered microstructure of AAS paste compared to the normal counterpart. Moreover, both the compressive strength, flexural strength, Young's modulus were improved as the content of titania/graphene composites (0%-0.03 wt%) increased. In addition, the fractural behaviours were also improved remarkably evidenced by a 89.7% increase of flexural toughness for AAS pastes with 0.03% titania/graphene composite. Scanning electron microscopy observations confirmed that the microstructure of the AAS pastes with titania/graphene composites was denser compared to normal AAS which is probably due to the effects of crack bridging and branching. Overall, the developed new intercalating method could be used to improve the dispersibility of graphene which is then employed effectively for reinforcing microstructure and mechanical properties of AAS binders.

In-situ grafted graphene oxide-based waterborne epoxy curing agent for reinforcement corrosion protection of waterborne epoxy coating

Abstract Well-dispersed graphene oxide (GO) in resin matrix has been found for improving corrosion protection performance of the coatings. In this paper, a new strategy relying on waterborne epoxy curing agent contained GO (GO-WCA) was developed, which was prepared via endcapping, modifying and in-situ grafting process. Wherein, endcapping includes blocking the high-activity hydrogen which is used to modulate curing activity. And the modifying process introduces homologous epoxy segment so as to improve compatibility between curing agent, resin matrix and GO. Attributing to this evolvement of WCA and superior barrier effects of GO, the epoxy coatings cured by GO-WCA exhibit desirable corrosion protection capacity. Besides, the failure mode is discovered as bubbling. This environmentally-friendly waterborne curing agent, only with 4.2 g/L VOC content, is anticipated to become available in diverse waterborne epoxy coatings system with excellent barrier property.

Fluid-like graphene oxide organic hybrid materials as efficient anti-wear and friction-reducing additive of polyethylene glycol

Achieving graphene-based lubricants with simultaneous excellent dispersibility and tribological performance remains challenging as graphene tends to agglomerate in lubricating oils. Herein, a fluid-like graphene oxide (FL-GO) was developed based on covalent grafting and epoxide ring-opening reactions, which exhibited obviously improved dispersion ability and tribological behaviors in polyethylene glycol (PEG). The dispersion stability of FL-GO was demonstrated by sedimentation experiment and the 0.5% of FL-GO reduced wear volume of 91.1% and friction coefficient of 43.7%. This well-dispersed graphene helps continue to generate an uneven lubricating film on the rubbing surface, thereby improving the friction and wear performance of the lubricating oils.

Functionalized graphene oxide: Carrier for corrosion inhibitor and barrier in waterborne epoxy coatings

The physical barrier network in polymer matrix composites can be formed by well-dispersed graphene layers, which efficiently inhibited the diffusion of corrosive molecules and improved the corrosion protection properties of the composite coatings. In this work, hydroxyethylidene-1, 1-diphosphonic acid (HEDP) was carried by graphene oxide (GO) layers through covalent bonding and dispersed in waterborne epoxy matrix, aiming for the combined effects of chemical inhibition and physical barrier. Epoxy monomer, ethylene glycol diglycidyl ether (EGDE), was grafted on GO surfaces before the reaction between GO and HEDP in order to prevent the multiple-linkage of graphene layers by HEDP, while improving the compatibility between graphene fillers and the epoxy matrix. The interlayer spacing between GO layers was enlarged from 0.79 nm to 1.03 nm by the reaction with EGDE. The impedance modulus of the composite coatings was kept above 1.5 × 109 Ω cm2 for five months by adding 0.5 wt% graphene derivatives.

Epoxy/graphene nanocomposites prepared by in-situ microwaving

Many preparation methods reported for polymer/graphene nanocomposites are associated with graphene surface modification and consumption of organic solvents. A facile, green and novel approach has been developed in this study for preparation of epoxy/graphene nanocomposites. The approach involves microwaving a commercial graphene precursor and mechanically stirring to produce graphene platelets in a hot, liquid-state epoxy resin, eliminating the need for organic solvents and surfactants. The process created both single-layer graphene and graphene platelets of 4.17 ± 0.63 nm in thickness and 1.00–4.77 μm in lateral dimension. Most of the surface oxygenated groups survived in this process, and more importantly, the process grafted epoxy molecules with graphene platelets. A thin film of platelets displayed an electrical conductivity of 889 ± 141 S/cm. The platelets caused large improvements to the mechanical and functional properties of the epoxy, i.e. 175% increase in critical strain energy release rate at 1.03 vol% of graphene, 14.9% increase in Young’s modulus at 1.55 vol%, a percolation threshold of electrical conductivity at 0.85 vol%, and a glass transition temperature increment from 85.4 to 100.0 °C at 1.03 vol%. The research clearly demonstrates the use of microwave radiation as an environmentally sustainable, low-cost and simple method for the development of polymer nanocomposites containing exfoliated and well-dispersed graphene platelets.

Advanced G-MPS-PMMA Bone Cements: Influence of Graphene Silanisation on Fatigue Performance, Thermal Properties and Biocompatibility.

The incorporation of well-dispersed graphene (G) powder to polymethyl methacrylate (PMMA) bone cement has been demonstrated as a promising solution to improving its mechanical performance. However, two crucial aspects limit the effectiveness of G as a reinforcing agent: (1) the poor dispersion and (2) the lack of strong interfacial bonds between G and the matrix of the bone cement. This work reports a successful functionalisation route to promote the homogenous dispersion of G via silanisation using 3-methacryloxypropyltrimethoxy silane (MPS). Furthermore, the effects of the silanisation on the mechanical, thermal and biocompatibility properties of bone cements are presented. In comparison with unsilanised G, the incorporation of silanised G (G_MPS1 and G_MPS2) increased the bending strength by 17%, bending modulus by 15% and deflection at failure by 17%. The most impressive results were obtained for the mechanical properties under fatigue loading, where the incorporation of G_MPS doubled the Fatigue Performance Index (I) value of unsilanised G-bone cement—meaning a 900% increase over the I value of the cement without G. Additionally, to ensure that the silanisation did not have a negative influence on other fundamental properties of bone cement, it was demonstrated that the thermal properties and biocompatibility were not negatively impacted—allowing its potential clinical progression.