Graphene Oxide Aqueous Suspension Research Articles

Microstructural, durability and colorimetric properties of concrete coated with a controlled application of graphene oxide

The present work analyzes how an aqueous suspension of graphene oxide (GO), as a surface treatment, can influence the properties of conventional concrete. The results show that the application of a GO surface coating on concrete improves its resistance to carbonation and chloride ion penetration, and also increases its electrical resistivity. In the best case, the GO coating can reduce carbonation by 40% and chloride ion diffusion by 75%. An increase of up to 75% in concrete resistivity was also achieved. The application of GO promotes the hydration process and densifies the microstructure of the concrete surface, and this is verified by scanning electron microscopy analysis. In addition, no color modification occurred after application of the treatment.

Performance of graphene oxide as a water-repellent coating nanomaterial to extend the service life of concrete structures

Surface treatments help to protect the built heritage against damage (environmental, accidental, etc.), reducing repair and restitution costs and increasing the useful life of building materials. The use of nanomaterials is currently the most important field of research in surface treatment technology for the preservation of building materials and, more specifically, to improve their durability and prevent their deterioration, extending their useful life. This paper studies the influence of a graphene oxide (GO) suspension as a surface treatment on the properties of concrete. The results indicate that, at best, surface treatment with GO can decrease both the water absorption and capillary absorption of concrete by about 15 %. The increase in the amount of GO deposited as a surface treatment leads to a further reduction in concrete water absorption. It is shown that, at best, GO coating also reduces water penetration at low and high pressures by approximately 20 % and 60 %, respectively. In addition, scanning electron microscopy analysis shows that GO surface treatment facilitates the hydration process and densifies the concrete microstructure. A simple aqueous suspension of GO is revealed as a tool with a high potential to protect concrete surfaces in a fast and cost-effective way, thanks to the easy application by spraying and the small amount of material needed to obtain great results.

Impact of hybrid natural deep eutectic solvent and polyacrylamide flocculant systems on the flocculation of highly stable graphene oxide suspensions

Graphene oxide (GO)-based nanomaterials have garnered significant attentions for various industrial applications due to their remarkable structural and physicochemical properties. Consequently, the impact of the increased discharge of GO into the environment also becomes a matter of significant concern due to the toxicity of GO nanoparticles to human health and the ecosystem. Therefore, efficient removal of GO from wastewaters before discharge into water bodies is crucial and remains a critical challenge in wastewater treatment due to the formation of highly stable GO suspensions in aqueous media. Accordingly, this work investigates the flocculation of aqueous GO suspensions using a range of single and hybrid coagulant/flocculant systems comprising a choline chloride-based natural deep eutectic solvent (NADES) coagulant and commercial high-molecular-weight polyacrylamide (PAM) based flocculants with variable surface charge densities. The effect of variations in the coagulant/flocculant charge type, charge density, and dosage on GO deflocculation was examined using residual turbidity, zeta potential, and floc size measurements. Cationic PAMs demonstrated the best performance among single flocculant systems with GO removal efficiency exceeding 97% and compact settleable flocs (D50 > 20 µm) at optimum doses in the range of 15–20 mg/L. The high charge density of FO 4800 SH further enhanced the GO removal efficiency by 1.1% and reduced the required optimum dose by 5 mg/L compared to FO 4350 SH. Hybrid flocculant systems revealed that anionic PAMs are the best performing flocculants when utilized with a fixed concentration of NADES coagulant. High GO removal efficiencies exceeding 98%, maximum zeta potential reduction, and the formation of large flocs (D50 > 20 µm) were achieved. The low charge density variant AN 923 SH offered better flocculation conditions by reducing the optimum PAM dose required by 5 mg/L compared to AN 956 SH. The NADES/AN 923 SH hybrid system was determined to be the optimal combination for a highly efficient treatment of GO suspensions at a fixed NADES dose of 0.048 M and a low optimum PAM dose of 5 mg/L that resulted in a GO removal efficiency of 98.1%, turbidity of 2.5 NTU, zeta potential of − 3.7 mV, and a mean D50 floc size of 26.1 µm.

Cu2O Photocathodes Modified by Graphene Oxide and ZnO Nanoparticles with Improved Photocatalytic Properties.

The modification of photocathodes based on copper(I) oxide (COPC) by coating with ZnO nanoparticles or graphene oxide (GO) with different compositions and morphologies is considered. To cover the catalyst surface with graphene oxide, a technique was proposed via freezing of a sprayed aqueous suspension of graphene oxide followed by sublimation drying under vacuum conditions. This method improves the uniformity of the GO layer in comparison with the traditional drop-casting method and, as a result, improves the photocatalytic properties of the COPC. The influence of the composition and morphology of graphene oxide on the photocatalytic activity and stability of COPC has been established. ZnO nanoparticles and GO particles in contact with copper(I) oxide increase the photocurrent density by the more efficient separation of light-generated charge carriers, providing higher photocathode stability required in photocatalytic water splitting.

Graphene oxide nanosheets immobilised on honeycomb pore structure of pomelo peel for enhanced removal of methylene blue.

Herein, for the first time, a simple, green, direct immersion immobilisation method is reported for graphene oxide (GO) nanosheets using pomelo peel (PL) as a substrate. A GO/PL porous sponge was successfully prepared and used to remove methylene blue (MB) from dye wastewater. Considering the porosity, hydrophilicity and elasticity of the PL, the PL was placed in a GO aqueous suspension through direct immersion immobilisation. The carboxyl and hydroxyl groups in the peel could effectively capture and immobilise the GO nanosheets. GO was adsorbed into the PL pores and dispersed throughout the PL. Finally, the prepared super-hydrophilic and elastic GO/PL exhibited excellent adsorption performance towards MB in dye wastewater. The adsorption results revealed that the adsorption behaviour was consistent with the Langmuir isotherm and quasi-secondary kinetic models. The maximum equilibrium adsorption capacity of GO/PL towards MB was 124.2mg/g, exceeding the values obtained for most of the previously reported adsorbents. Moreover, after five consecutive adsorption-desorption cycles, GO/PL retained 75% of its initial adsorption capacity. Mechanistic analysis revealed that pore filling, electrostatic attraction, ion exchange and hydrogen bonding interactions are the primary driving forces facilitating MB adsorption.

On the Asymmetry in Photo-Induced Motion of Graphene-Oxide Paper

We report on the photo-mobility properties of a free standing large area graphene oxide (GO) paper (GOP). The thickness of the film is ≈20 μm. GOP is made by drop casting an aqueous suspension of GO on a microscope glass slide placed on a hot plate kept at the temperature of 70 °C. The film is peeled-off from the glass substrate and irradiated under different coherent and incoherent light sources. The film bends up to ≈55° when the irradiation is made using a near infra-red (NIR) incoherent incandescent lamp and returns back to the initial position when the NIR lamp is switched-off. The bending mechanism is attributed to the asymmetry of the GOP film obtained during the film formation process. We characterize the film morphology and structure using a Scanning Electron Microscopy (SEM) imaging and X-ray Diffraction (XRD) measurements, respectively. Remarkable differences between the two surfaces of the GOP are evidenced, both on a macroscopic length scale (surface roughness) and on a microscopic one (GO interlayer distance). This asymmetry results in different (negative) thermal expansion coefficients for the two film surfaces and hence in the bending of the film when the film temperature is increased by light absorption.

Rheological study of highly concentrated aqueous graphene oxide suspensions: the effects of concentration, particle lateral dimensions and number of layers per particle

Aqueous graphene oxide (GO) suspensions have attracted considerable attention due to their unique properties, which can find numerous applications in various fields, from industry to biomedicine. When designing a GO hydrogel for a specific application, a thorough understanding of the effects of appropriate starting material properties and its concentration range on the suspension stability, structural and rheological properties is of essential importance. The present work is concerned with high solids content (from 1.00 to 2.00 w/v%) GO aqueous suspensions exhibiting marked elastic properties. The effects of the GO particles lateral dimensions and the number of GO layers per particle on the flow and viscoelastic properties are investigated. Rheological parameters useful for quantitative interpretation of the results were obtained by fitting the experimental data using Cross, Herschel-Bulkley, and generalized Maxwell models. All GO suspensions showed a marked shear thinning and thixotropic behaviour with a significant yield stress. Their mechanical spectra confirmed viscoelastic behaviour typical for a suspension in an arrested state. Observed differences in values of rheological parameters and their variations with concentration are explained by particle properties and corresponding rotational restrictions, electrostatic attraction/repulsion, nematic phase formation, and particle agglomeration. The research presents fundamental insights into the rheological properties of GO suspensions, which can be manipulated by varying particle geometry and concentration.

Tribocorrosion behavior of graphene-based solid lubricants biofunctionalized with hyaluronic acid on CoCr surfaces

In this work graphene-based solid lubricants biofunctionalized with hyaluronic acid were deposited on CoCr surfaces to decrease wear-corrosion phenomena. Graphene oxide was electrochemically reduced on CoCr in an aqueous suspension of graphene oxide 4 g/L by cyclic voltammetry. Biofunctionalization in phosphate buffer solution with HA 3 g/L (PBS-HA) for 24 h was performed. A pin-on-disk tribometer with an integrated cell was used for tribocorrosion tests. Wear-corrosion tests were performed against AISI316 steel balls applying normal load 1 N, 120 rpm for 500 m, in PBS and PBS-HA. Coefficients of friction in PBS were higher than in PBS-HA. ErGO and HA-ErGO increased wear rate in AISI316 balls, i.e., ErGO hardens the CoCr surface. Biofunctionalization reduces abrasive properties of ErGO deposits.

Directly loading graphene oxide into melamine sponge for fast and high-efficiency adsorption of methylene blue

Graphene oxide (GO) is considered as a promising adsorbent for removal of dye pollutants. Herein, to improve the adsorption ability, GO was directly loaded and immobilized in a commercial melamine sponge with a three-dimensional skeleton. Based on the porous, hydrophilic and elastic characteristics of the sponge, GO sheets were sucked into the pores and dispersed throughout the sponge by a facile squeezing-sucking method in GO aqueous suspension. The sucked GO sheets are stably bound to the skeleton by non-covalent bonds, forming a three-dimensional structure and exposing as many functional groups as possible. Such adsorbent showed high competitiveness in adsorption rate and adsorption capacity for methylene blue (MB). The adsorption efficiency for a MB solution could reach ∼95% in 30 s. By optimizing the loading amount of GO and pH of MB solution, the adsorption reached equilibrium within 90 min and the adsorption capacity could reach 260.9 mg·g−1. The adsorption behavior follows a Pseudo-second-order kinetic model and the Langmuir isotherm model. The main adsorption mechanism is a monolayer adsorption process based on electrostatic interactions. The facile loading method and the high adsorption efficiency of the adsorbent will promote the application of GO in low-cost, fast, and highly efficient treatment of dye pollutants.

Synthesis of Graphene Quantum Dots by a Simple Hydrothermal Route Using Graphite Recycled from Spent Li-Ion Batteries

Graphene quantum dots (GQDs) are nanosized systems that combine beneficial properties typical of graphenic materials (such as chemical stability, biocompatibility and ease of preparation from low-cost precursors) with remarkable photoluminescent features. GQDs are well-known for their low cytotoxicity and for being promising candidates in applications, such as bioimaging, optoelectronics, electrochemical energy storage, sensing and catalysis, among others. This work describes a simple and low-cost synthesis of GQDs, starting from an alcoholic aqueous suspension of graphene oxide (GO) and using a hydrothermal route. GO was prepared using graphite recycled from spent Li-ion batteries, via a modified Hummers method. The GO suspension was submitted to hydrothermal treatments at different temperatures using a homemade hydrothermal reactor that allows the control of the heating program and the assessment of the internal pressure generated in the reaction. The synthesized GQDs exhibited bright blue/green luminescence under UV light; showing the success of the chosen route and opening the way for future applications of these materials in the field of optoelectronic devices.

Long-Term Aging of Concentrated Aqueous Graphene Oxide Suspensions Seen by Rheology and Raman Spectroscopy.

Today, graphene oxide (GO) has gained well-deserved recognition, with its applications continuing to increase. Much of the processing of GO-based devices occurs in a dispersed form, which explains the commercialization of GO suspensions. Aging of these suspensions can, however, affect the shelf life and thus their application potential. Aging of GO preparations is often acknowledged, but no longer-term systematic study has been reported on the alteration of GO suspensions. This paper investigates high-concentration (10 mg/mL) aqueous GO suspensions over a 2-year time scale. In addition to steady shear tests, the dynamic behavior of the suspensions was studied in more detail by transient shear and frequency sweep measurements. Both the viscosity and the dynamic moduli increased with age, particularly within the first year. The results of the complementary Raman spectroscopic studies indicate that the change in the rheological behavior with aging results from a slow oxidation process occurring in the highly acidic aqueous medium during the relatively long-term storage. The (over)oxidized layers peel off spontaneously or are removed by high shear stress, resulting in increased viscosity, as it was corroborated by XRD and XPS.

Simulations of Graphene Oxide Dispersions as Discotic Nematic Liquid Crystals in Couette Flow Using Ericksen-Leslie (EL) Theory

The objective of this study was to simulate the flow of graphene oxide (GO) dispersions, a discotic nematic liquid crystal (DNLC), using the Ericksen-Leslie (EL) theory. GO aqueous suspension, as a lubricant, effectively reduces the friction between solid surfaces. The geometry considered in this study was two cylinders with a small gap size, which is the preliminary geometry for journal bearings. The Leslie viscosity coefficients calculated in our previous study were used to calculate the stress tensor in the EL theory. The behavior of GO dispersions in the concentration range of 15 mg/mL to 30 mg/mL, shown in our recent experiments to be in the nematic phase, was investigated to obtain the orientation and the viscosity profile. The viscosities of GO dispersions obtained from numerical simulations were compared with those from our recent experimental study, and we observed that the values are within the range of experimental uncertainty. In addition, the alignment angles of GO dispersions at different concentrations were calculated numerically using EL theory and compared with the respective theoretical values, which were within 1% error. The anchoring angles corresponding to viscosity values closest to the experimental results were between 114 and 118 degrees. Moreover, a sensitivity analysis was performed to determine the effects of different ratios of the elasticity coefficients in EL theory. Using this procedure, the same study could be extended for other DNLCs in different geometries.

Extraordinary Protective Efficacy of Graphene Oxide over the Stone‐Based Cultural Heritage (Adv. Mater. Interfaces 23/2021)

Protecting Monumental Stones with Graphene Oxide The coating of carbonated stones from our historical heritage with an aqueous graphene oxide suspension is an efficient and cost-effective method to shield them from climatic erosion, as presented in article number 2101012 by María Fernández-Raga, Jose Miguel González-Domínguez, and co-workers. By simply spraying such additive-free aqueous colloids on surface, an outstanding protective effect against rainfall and temperature is revealed, without altering the stones' original aesthetics.

Extraordinary Protective Efficacy of Graphene Oxide over the Stone‐Based Cultural Heritage

AbstractThe deterioration of monumental stones is a common event occurring to our historical and cultural heritage, threatening the preservation of our social identity and its legacy to future generations. The prolonged effect of inclement weather is very harmful for particular stone materials such as limestone and dolomite, to which a truly effective and durable protective agent has not yet been found. Herein, an unprecedented performance of graphene oxide (GO) for the shielding of carbonated ornamental stones against environmental aggressions, namely intense rainfall and extreme temperatures, is demonstrated. A simple additive‐free aqueous suspension of GO serves as the perfect coating, exceedingly preventing from any kind of wear or erosion after different climatic simulations. Additionally, the stones’ original aesthetics is not altered (a critical issue in monuments), together with an improvement in their mechanical properties, reasserting the unique potential of GO for conserving exposed stone‐based monuments in an affordable, accessible, and revolutionary way.

Fabrication and simulation of a layered ultrahigh thermal conductive material made of self-assembled graphene and polydopamine on a copper substrate.

A composite material of graphene (G) and polydopamine (PDA) on a copper (Cu) substrate (G/PDA@Cu) was fabricated successfully by sequential immersion deposition in a dopamine solution and an aqueous graphene oxide suspension before annealing. Optimum preparation conditions were explored by the orthogonal experimental method. The morphology and chemical composition of G/PDA@Cu were studied systematically by a series of characterization techniques. The thermal-conductive performance was evaluated by a laser flash thermal analyser. The thermal conductivity of G/PDA@Cu was 519.43 W m−1 K−1, which is ultrahigh and 30.50% higher than that of the Cu substrate. The adhesion force between G/PDA and the Cu substrate was 4.18 mN, which means that G bonds to the Cu substrate tightly. The model simulation also showed that G/PDA@Cu exhibits excellent thermal conductivity, allowing it to play a significant role in the thermal management of advanced electronic chips. The thermal-conductive devices using this material were prepared for practical applications.

Anodic Aqueous Electrophoretic Deposition of Graphene Oxide on Copper Using Different Cathode Materials

The effect of four different cathode materials on the anodic deposition of graphene oxide (GO) nanosheets was studied experimentally. First, synthesis of graphite oxide from graphite powder was done by modified Hummers' method. Ultrasonic technique was adopted for the preparation of the stable aqueous suspension of GO by using liquid exfoliation of graphite oxide. Deposition of GO coating on copper sheets (the anode) was done via electrophoretic deposition (EPD) at the same operating condition (5V, 2 min, concentration of 0.5 mg/ml of GO per deionized water) with different cathode materials (copper, stainless steel, aluminum and graphite). The coatings’ morphological and microstructure were investigated using scanning electron microscope (SEM) and the effect of the current density in the EPD process was obtained. The change in the deposition weight was also measured. It was ascertained that the cathode’s material is a major factor can affect the GO’s EPD process and the characteristics of the final coating.

Facile fabrication of GO/Al composites with improved dispersion of graphene and enhanced mechanical properties by Cu doping and powder metallurgy

In recent years, graphene has attracted a lot of attention as a reinforcement to enhance aluminum (Al) matrix composites due to its two dimensional structure and excellent mechanical properties. However, there are still some obstacles that limit the performance of the composites, such as uniform distribution of graphene oxide (GO) and the interfacial bonding between GO and Al matrix. In this work, Cu2+ ions acting as a bonding bridge were added into GO/Al powder suspension to improve the distribution of GO sheets on Al powder via a simple electrostatic adsorption method. Then, vacuum hot-pressing sintering was applied to fabricate bulk composites, and their mechanical properties were investigated. The results showed that doping 3 wt% Cu2+ ions illustrated the best dispersion of GO on the surface of Al powder, meanwhile GO was maximally reduced. Compared with unreinforced Al, the hardness, compressive strength and flexural strength of the 3 wt% Cu-doped bulk composite were increased by 121%, 120% and 28%, respectively. However, the mechanical properties were deteriorated after doping 5 wt% Cu2+ ions, due to the aggregation of GO on the surface of Al powder. This was attributed that Cu2+ ions had a critical coagulation concentration in aqueous GO suspensions. It was expected this work could offer some useful information for preparing graphene reinforced metal composites.

In Situ Decoration of Gold Nanoparticles on Graphene Oxide via Nanosecond Laser Ablation for Remarkable Chemical Sensing and Catalysis.

Gold decorated graphene-based nano-hybrids find extensive research interest due to their enhanced chemical catalytic performance and biochemical sensing. The unique physicochemical properties and the very large surface area makes them propitious platform for the rapid buildouts of science and technology. Graphene serves as an outstanding matrix for anchoring numerous nanomaterials because of its atomically thin 2D morphological features. Herein, we have designed a metal-graphene nano-hybrid through pulsed laser ablation. Commercially available graphite powder was employed for the preparation of graphene oxide (GO) using modified Hummers’ method. A solid, thin gold (Au) foil was ablated in an aqueous suspension of GO using second harmonic wavelength (532 nm) of the Nd:YAG laser for immediate generation of the Au-GO nano-hybrid. The synthesis strategy employed here does not entail any detrimental chemical reagents and hence avoids the inclusion of reagent byproducts to the reaction mixture, toxicity, and environmental or chemical contamination. Optical and morphological characterizations were performed to substantiate the successful anchoring of Au nanoparticles (Au NPs) on the GO sheets. Remarkably, these photon-generated nano-hybrids can act as an excellent surface enhanced Raman spectroscopy (SERS) platform for the sensing/detection of the 4-mercaptobenzoic acid (4-MBA) with a very low detection limit of 1 × 10−12 M and preserves better reproducibility also. In addition, these hybrid materials were found to act as an effective catalyst for the reduction of 4-nitrophenol (4-NP). Thus, this is a rapid, mild, efficient and green synthesis approach for the fabrication of active organometallic sensors and catalysts.

Enhancing the Hydrophobicity of a Copper Pipe by Electrophoretic Deposition of Graphene Oxide

Thin film coatings of graphene oxide (GO) onto copper pipe was investigating using electrophoretic deposition (EPD) technique. Graphite oxide was produced from graphite powder by chemical oxidation using modified Hummers' method. An aqueous colloidal suspension of graphene oxide was prepared by exfoliation of the graphite oxide via ultrasonic treatment. GO coatings were deposited on copper pipes through EPD from GO aqueous suspension. The EPD parameters such as voltage, time and particle concentration were optimized to obtain uniform GO coatings. The optimal EPD conditions for well-formed deposits were observed when the operating voltage was equal to 30 V and 90 s deposition time. The thin film coated copper pipe was characterized using various techniques such as SEM, XRD and contact angle. XRD confirmed that GO was reduced during the EPD process itself due to the removal of oxygen containing functional groups. SEM images elucidated the formation of GO thin layer onto copper pipe with thickness 5 μm. The contact angle improved from 70° for bare copper to 102.4° for GO coating.

Electrophoretic Deposition of Graphene Oxide Nanosheets on Copper Pipe for Corrosion Protection

This work is ultimately aimed to deposit graphene oxide (GO) nanosheets onto the surface of copper (Cu) pipe by electrophoretic deposition (EPD) technique for enhancing the corrosion resistance. A stable aqueous GO suspension was prepared by liquid exfoliation of graphite oxide in deionized water which acted as an EPD electrolyte solution. Anodic deposition on Cu pipe was carried out under different operating parameters such as applied voltage, running time and GO nanosheets concentration. The GO-deposited film onto Cu pipe was investigated using scanning electron microscope, X-ray diffraction and Fourier transform infrared spectroscopy. The results showed that 20 V and 60 s deposition time with 0.5 mg/ml concentration induced a uniform continuous coating film on Cu pipe. The corrosion resistance of Cu pipe treated with GO which was tested in 3.5% sodium chloride corrosive media was twofold higher than that of untreated Cu pipe. Collectively, the Cu pipe treated with GO using EPD deposition technique would have a potential in the application of harsh corrosive industrial environments.