Reduced Graphene Oxide Coatings Research Articles

Hydrogen resistance of reduced graphene oxide coatings prepared by electrophoretic deposition on duplex stainless steel

In this study, reduced graphene oxide (rGO) coatings were fabricated on duplex stainless steel (DSS) substrates using the electrophoretic deposition (EPD) method to evaluate their hydrogen resistance performance. The successful fabrication of rGO coatings was confirmed using Fourier Transform Infrared Spectroscopy (FT-IR) and X-ray Photoelectron Spectroscopy (XPS). The structural characteristics were characterized using Raman spectroscopy and X-ray Diffraction (XRD). The results indicate that the EPD voltage is a crucial factor affecting the surface quality of and hydrogen resistance performance of rGO. Lower voltages resulted in lower degrees of rGO reduction and higher surface wrinkle density, while higher voltages caused bubble formation, significantly degrading the coating quality and hydrogen resistance performance. The optimal hydrogen resistance was achieved at an EPD voltage of 7.5V and a deposition time of 6 minutes. Electrochemical hydrogen charging tests and thermal desorption analysis (TDA) demonstrated that rGO coatings prepared under optimal conditions exhibited excellent hydrogen resistance efficiency, significantly reducing hydrogen atom penetration in hydrogen environments. The study further revealed that bubble formation significantly reduces the hydrogen resistance of rGO, which is attributed to increased interlayer spacing and the loss of the “labyrinth effect”.

Revisiting oxidation and reduction reactions for synthesizing a three-dimensional hydrogel of reduced graphene oxide.

An improvement to Hummers' method involving a cascade-design graphite oxidation reaction is reported to optimize safety and efficiency in the production of graphite oxide (GrO) and graphene oxide (GO). Chemical reduction using highly alkaline ammonia solution is a novel approach to synthesizing reduced graphene oxide (RGO). In this original research, we revisit the oxidation and reduction reactions, providing significant findings regarding the synthetic pathway to obtain a bioinspired water-intercalated hydrogel of RGO nanosheets. Influential factors in the graphite oxidation reaction, typically the exothermic reaction temperature and hydrogen peroxide effect, are described. Furthermore, the chemical reaction of GO reduction using highly alkaline ammonia solution (pH 14) was investigated to produce hydrated RGO nanosheets assembled in a hydrogel structure (97% water). Three-dimensional assembly and water intercalation are key to preserve the non-stacking state of RGO nanosheets. Therefore, ultrasound transmission to aqueous channels in the macroscopic RGO hydrogel vibrated and dispersed the RGO nanosheets in water. Analytical results revealed the single-layer nanostructures, functional groups, optical band gaps, optimized C/O ratios, particle sizes and zeta potentials of GO and RGO nanosheets. The reversible self-assembly of RGO hydrogels is essential for many applications, such as RGO coatings and polymer/RGO nanocomposites. In a water purification application, the RGO hydrogel was dispersed in aqueous solution by simple agitation and showed a high capacity for organic dye adsorption. After the adsorption, the RGO/dye particles were easily removed by filtration through ordinary cellulose paper. The process of adsorption and filtration is effective and inexpensive for practical environmental remediation. In summary, a bioinspired structure of RGO hydrogel is conceptualized for prospective nanotechnology.

Enhancing electrical conductivity and mechanical properties of decellularized umbilical cord arteries using graphene coatings.

Traditional decellularized bioscaffolds possessing intact vascular networks and unique architecture have been extensively studied as conduits for repairing nerve damage. However, they are limited by the absence of electrical conductivity, which is crucial for proper functioning of nervous tissue. This study focuses on investigating decellularized umbilical cord arteries by applying coatings of graphene oxide (GO) and reduced graphene oxide (RGO) to their inner surfaces. This resulted in a homogeneous GO coating that fully covered the internal lumen of the arteries. The results of electrical measurements demonstrated that the conductivity of the scaffolds could be significantly enhanced by incorporating RGO and GO conductive sheets. At a low frequency of 0.1 Hz, the electrical resistance level of the coated scaffolds decreased by 99.8% with RGO and 98.21% with GO, compared with uncoated scaffolds. Additionally, the mechanical properties of the arteries improved by 24.69% with GO and 32.9% with RGO after the decellularization process. The GO and RGO coatings did not compromise the adhesion of endothelial cells and promoted cell growth. The cytotoxicity tests revealed that cell survival rate increased over time with RGO, while it decreased with GO, indicating the time-dependent effect on the cytotoxicity of GO and RGO. Blood compatibility evaluations showed that graphene nanomaterials did not induce hemolysis but exhibited some tendency toward blood coagulation.

Naproxen electrooxidation using carbon paper electrodes modified with reduced graphene oxide and platinum nanoparticles

This research study investigates the electrooxidation of naproxen (NPX), an anti-inflammatory pharmaceutical, on modified carbon paper (CP) electrodes. Electrochemical modification of CP electrodes was accomplished with Pt or reduced graphene oxide (RGO)-Pt coatings, resulting in the production of electroactive electrodes. RGO coatings synthesized by cyclic voltammetry (CV) for 10 scans provided the optimal coverage for the CP electrode surface. The deposition of Pt nanoparticles (Pt NPs) on the electrodes (CP or CP-RGO) by CV produced a good electrode surface coverage with 20 synthesis scans. The voltammetric analysis of the electrodes in 230 mg/L NPX solution showed oxidation peaks around 1.0 to 1.2 V. Moreover, the inclusion of RGO in the coating led to an increase in the current density of these oxidation peaks and a decrease of the electrode electron transfer resistance as measured by electrochemical impedance spectroscopy.The electrolysis of NPX in different electrolytes (Na2SO4 and Na2SO4/NaCl) was conducted at 1.4 V, and the removal of NPX was analyzed using high-performance liquid chromatography. The CP-RGO-Pt electrode in Na2SO4/NaCl media showed the fastest NPX degradation kinetics, resulting in a 90 % degradation in only 90 min with low charge consumption (0.07 A·h·L-1). The smaller size of Pt NPs deposited on CP-RGO, as observed by field emission scanning electron microscopy and transmission electron microscopy, contributed to the higher electrochemical response in CV and a faster kinetic degradation of NPX.

Reduced Graphene Oxide Coating LiFePO4 Composite Cathodes for Advanced Lithium-Ion Battery Applications.

Recently, the application of LiFePO4 (LFP) batteries in electric vehicles has attracted extensive attention from researchers. This work presents a composite of LFP particles trapped in reduced graphene oxide (rGO) nanosheets obtained through the high-temperature reduction strategy. The obtained LiFePO4/rGO composites indicate spherical morphology and uniform particles. As to the structure mode of the composite, LFP distributes in the interlayer structure of rGO, and the rGO evenly covers the surface of the particles. The LFP/rGO cathodes demonstrate a reversible specific capacity of 165 mA h g-1 and high coulombic efficiency at 0.2 C, excellent rate capacity (up to 10 C), outstanding long-term cycling stability (98%) after 1000 cycles at 5 C. The combined high electron conductivity of the layered rGO coating and uniform LFP particles contribute to the remarkable electrochemical performance of the LFP/rGO composite. The unique LFP/rGO cathode provides a potential application in high-power lithium-ion batteries.

Study on the Influence of the Reduced Graphene Oxide Coating on the Hydrophobicity of PU Sponge for Oil Recovery

In order to produce a hydrophobic material for oil removal from surface waters, in this study, the reduced graphene oxide coated PU sponges (rGO@PU) were prepared by ultrasonication of PU sponges with suspension of rGO in ethanol. The chemical structure of the rGO coatings was investigated by X-ray diffraction and FT-IR spectroscopy methods. The surface morphology of the obtained materials was also examined by SEM. The influence of the rGO loadings and the number of coatings on the hydrophobicity of the materials was investigated. The testing on the surface hydrophobicity indicated that the water drops were remained on the surface of rGO@PU for 4.5 - 5 hours. The results indicated that the best hydrophobic sponge was obtained at the rGO loading of 3 mg/mL and after three times of coatings. The water contact angle (WCA) of the optimal rGO@PU was up to 119°. The kerosene oil absorption capacity of the rGO@PU in 5 minutes is 32.34 g/g. Besides, the oil-water separation ability of the material was also investigated by passing the kerosene-water mixture through a filter funnel containing the synthesized porous material rGO@PU. The result indicated that the separation efficiency of the material was 85%. The recyling test was conducted by squeezing the saturated absorbed sponges and applying the desorbed sponges for the next cycle tests. After 10 times of recycling, the amounts of kerosene absorption on the rGO@PU were maintained from 4.39 - 5.33 g, implying the excellent recyclability of the material.

Enhanced adhesion and corrosion resistance of reduced graphene oxide coated-steel with iron oxide nanoparticles

Despite its potential for use in coating applications, graphene can promote corrosion at exposed graphene-metal interfaces because it presents cathodic properties when exposed to most metals. Moreover, such exposed areas can accelerate localized corrosion, which may lead to serious damage of the coated metal. This study describes a method for preparing reduced graphene oxide (RGO) coatings with iron oxide nanoparticles (Fex−1Ox), which exhibit improved adhesion strength and oxidation resistance on steel substrates. A suspension that contained a mixture of graphene oxide (GO) and graphene oxide with Fex−1Ox (GO/Fex−1Ox) was formulated and applied to a large area on a steel substrate using electrophoretic deposition. Mechanical and electrochemical characterizations of the RGO and RGO/Fex−1Ox coatings were conducted after thermal reduction at 810 °C in a 10 % Ar/H2 atmosphere. A 138 % improvement in adhesion tensile strength was measured using a mechanical test derived from the standard pull-out test. Moreover, the enhanced oxidation resistances of RGO and RGO/Fex−1Ox coatings were confirmed after thermal reduction using electrochemical impedance spectroscopy and the potentiodynamic polarization method. From calculation of corrosion rate, RGO/Fex−1Ox coatings were corroded by 4 and 13 times slower than RGO coatings and bare steel, respectively. These results suggest that graphene coatings with iron oxide nanoparticles could serve as effective adhesion-promoting intermediary layers that retard steel corrosion in certain applications.

Constructing reduced graphene oxide and polypyrrole coatings on glass fiber to enhance its absorbing performance

AbstractIn this work, a new route for improving the absorbing performance of glass fibers (GFs) composites by introducing the reduced graphene oxide (RGO)/polypyrrole (PPy)/RGO coatings through the self‐assembly method and then the in‐situ polymerization method was proposed. The corresponding microstructure and electromagnetic parameters were measured by scanning electron microscopy, X‐ray photoelectron spectroscopy, and vector network analyzer. The result indicated that the RGO/PPy/RGO coatings can adjust the absorbing performance of GFs composites by its synergistic effect, thus exhibiting optimum impedance matching degree and high conduction loss ability. The minimum reflection loss value of the synthesized RGO/PPy/RGO/GFs composite can reach −55.8 dB with the thickness of 4.3 mm, and the effective absorption bandwidths (≤−10 dB) covered the entire X‐band. This work proved that the RGO/PPy/RGO coatings can be used to adjust the radar absorbing performance of GFs composites.

Suppression of secondary electron emission on oxygen-free copper surface of reduced graphene oxide coatings prepared by electrophoretic deposition

We proposed a new carbon coating to inhibit secondary electron emission. Graphene oxide(GO) coatings were prepared on the surface of oxygen-free copper by DC electrophoretic deposition, and reduced graphene oxide(rGO) coatings were obtained by hydrogen thermal reduction. The X-ray photoelectron spectroscopy (XPS) analysis shows that the oxygen content of the coating reduced from 26.37 at.% to 9.89 at.% after thermal reduction, The XPS and Raman analysis shows that rGO still maintained the sp2 hybrid structure. The inhibitory effect of rGO coatings on secondary electron emission was tested. It was found that the maximum total secondary electron yield (δmax) of the oxygen-free copper surface reduced from 1.38 to 1.09 after the preparation of rGO coating. The total secondary electron yield did not decrease further with the film thickness increasing when the rGO coating reached a certain thickness. Our research provides a new perspective on the preparation of carbon coatings to reduce the secondary electron yield.

Tailored electromagnetic and microwave absorbing properties of multiscale composites by coating reduced graphene oxide over glass fiber

ABSTRACT Through the formation of a conduction layer of reduced graphene oxide (RGO) on the surface of the insulation glass fabrics (GFs) seems to be an effective method to enhance the electromagnetic wave absorbing properties of GFs composites. In this work, the graphene oxide (GO) coatings were prepared by the layer-by-layer (LBL) method, and then they were chemically reduced to RGO coatings over GFs (RGO/GFs). The micromorphology of RGO/GFs can be adjusted by the LBL parameters, such as GO concentration, repeat times, and chemical reduction time. Furthermore, RGO/GFs multiscale composites were processed and their electromagnetic parameters and absorbing properties were characterized and analyzed. When the concentration of GO, the repeat times, and the chemical reduction time were 4 mg/ml, 6 and 95 min, respectively, the RGO/GFs multiscale composites with the thickness of 3.6 mm have better absorbing performance with the effective absorption bandwidths (≤−10 dB) of 4.2 GHz. The high absorbing performance of RGO/GFs multiscale composites can be attributed to the high conduction loss caused by the introduced RGO and good impedance matching degree. This work provided a new route for synthesizing high-performance radar-absorbing materials.

Improvement in Long-Term Stability of Field Effect Transistor Biosensor in Aqueous Environments Using a Combination of Silane and Reduced Graphene Oxide Coating

Improvement in Long-Term Stability of Field Effect Transistor Biosensor in Aqueous Environments Using a Combination of Silane and Reduced Graphene Oxide Coating

Suppression of Secondary Electron Emission on Oxygen-Free Copper Surface of Reduced Graphene Oxide Coatings Prepared by Electrophoretic Deposition

Suppression of Secondary Electron Emission on Oxygen-Free Copper Surface of Reduced Graphene Oxide Coatings Prepared by Electrophoretic Deposition

Enhanced Boiling Heat Transfer by Nucleation Patterning with Self-Assembly of Reduced Graphene Oxide Coating

Enhanced Boiling Heat Transfer by Nucleation Patterning with Self-Assembly of Reduced Graphene Oxide Coating

Charge Capacitance and Hydrogen Storage Capacity of Drop Cast and Electrodeposited Reduced Graphene Oxide Coatings

Drop cast (DC) and electrodeposited (ED) graphene-based coatings on glassy carbon (GC) electrodes were subjected to various electro-reduction degrees. The ED coatings were characterized by more accumulated graphene sheets imperfections as observed by cross section TEM analysis. These coatings, when reduced at −1.6 V vs Hg/HgO showed more efficient removal of phenolic groups than DC ones treated at the same potential (remaining contents of 2.1 and 18.1%, respectively). They also showed lower charge transfer resistance (5.2 and 28 Ω cm2, respectively), higher capacitance (73.2 and 42.6 F g−1, respectively), and higher hydrogen storage capacity (119 and 57 mAh g−1, respectively). Moreover, they showed higher stability towards H2 charge/discharge cycles (retained hydrogen capacities of 95 and 40% after 15 and 6 cycles for ED and DC coatings reduced at −1.5 V, respectively). The superior performance properties of coatings obtained by ED and subsequently electro-reduced make them promising electrode materials for energy storage.

Functionalization of graphene oxide coatings with phosphorus atoms and their corrosion resistance in sodium chloride environment

In this work, we compared corrosion resistance of graphene oxide, and phosphorus functionalized reduced graphene oxide coatings obtained as a result of electrophoretic deposition on the copper substrate. Doping graphene oxide with phosphorus atoms was performed by a hydrothermal method in the presence of different amounts of phosphoric acid. Structural studies confirmed the insertion of phosphorus atoms into the graphene oxide structure. FTIR spectra showed peaks at 1020 cm−1 and 1131–1450 cm−1 which can be assigned to phosphorus groups. XPS analysis indicated that phosphorus atoms were inserted in an amount of around 5%. The stable and uniform suspension of functionalized graphene precursors of coatings allowed electrodeposition. These coatings show good protective properties due to hydrophobic and intact surfaces without significant damages.

Effect of Functionalization of Reduced Graphene Oxide Coatings with Nitrogen and Sulfur Groups on Their Anti-Corrosion Properties.

Electrophoretic production of anticorrosion carbonaceous coatings on copper could be successfully performed by anodic oxidation of negatively charged graphene platelets suspended in an aqueous solution. The various platelets were synthesized by Hummer’s method followed by a hydrothermal reduction in the presence of NH4SCN which was expected to substitute some parts of graphene structure with nitrogen and sulfur groups. X-ray photoelectron spectroscopy analysis confirmed that the graphene precursors, as well as the coatings, contained typical nitrogen groups, such as pyridinic and pyrrolic, and sulfur groups, such as thiol, thiophene, or C-SO2. However, due to oxidation during deposition, the qualitative and quantitative composition of the graphene coatings changed relative to the composition of the precursors. In particular, the concentration of nitrogen and sulfur dropped and some thiophene groups were oxidized to C-SO2. Studies showed the functionalized coatings had a uniform, defect-free, hydrophobic, more adhesive surface than nonmodified films. The corrosion measurements demonstrated that these coatings had better protective properties than the ones without these heteroatoms. This behavior can be assigned to the catalytic activity of nitrogen towards oxidation of C-SO2 groups to C-SO3H with oxygen.

Synergistic Tailoring Reduced Graphene Oxide Coating for Natural Polymer-Based Gas Barrier Films

Improving the gas molecule barrier performance of biomass-derived bio-plastic films dramatically contributes to packaging and protective fields, such as food, agriculture, pharmaceuticals and electronic instruments et al. Herein, cellulose acetate (CA)/polyethyleneimine (PEI)/reduced graphene oxide (rGO)-NiCoFeOx nanocomposite film featured with high gas obstructing property was precisely tailored by two-terminal 'molecular glue' joints and targeted nano-patching engineering. Terminal amino groups enriched PEI functions as 'molecular glue' to tightly connect CA substrate with rGO via chemical bonds and the defective regions in rGO plane was nano-patched through hydrophilic interactions between edged oxygen-containing functional groups and ultrafine NiCoFeOx nanoparticles. Together with the reinforced atomic interfacial contact of CA/rGO and targeted nano-patching defect of rGO, the oxygen and moisture transmission rates of the prepared CA/PEI/rGO-NPs hybrid film were significantly reduced to 0.31 cm3*μm/(m2*d*kPa) and 314.23 g/m2*24h, respectively, which were 99.60% and 54.69% lower than pristine CA films. Meanwhile, the contact angle and tensile strength of hybrid film reached 97.74° and 40.67 MPa. Moreover, the resultant nanocomposite films possess excellent structure stability without GO shedding and hydrophobicity attenuation after persistent bending at least for 100 times. Such two-pronged manage strategy provides a prototype for designing and fabricating robust bio-plastic gas resistance films.

Solution‐processed graphene oxide coatings for enhanced heat transfer during dropwise condensation of steam

AbstractHydrophobic coatings have the ability to promote dropwise condensation on metal surfaces. In this work, reduced graphene oxide coatings are fabricated by dip coating copper substrates into a graphene oxide colloidal suspension, followed by thermal reduction. The formation of reduced graphene oxide is demonstrated by Raman and X‐ray photoelectron spectroscopy characterizations, while scanning electron microscopy, atomic force microscopy and dynamic water contact angle analyses are employed to verify the morphology and the wettability of the coatings. The prepared coatings demonstrate applicability in the promotion of dropwise condensation of pure steam, with an 8‐fold enhancement of the heat transfer coefficient compared to film‐wise condensation. In addition, durability of the reduced graphene oxide coatings of more than 100 hours in the tested condition is reported.

Comparison between Linear and Branched Polyethylenimine and Reduced Graphene Oxide Coatings as a Capture Layer for Micro Resonant CO2 Gas Concentration Sensors.

The comparison between potential coatings for the measurement of CO2 concentration through the frequency shift in micro-resonators is presented. The polymers evaluated are linear polyethylenimine, branched polyethylenimine and reduced graphene oxide (rGO) by microwave reduction with polyethylenimine. The characterization of the coatings was made by using 6 MHz gold-plated quartz crystals, and a proof-of-concept sensor is shown with a diaphragm electrostatic microelectromechanical systems (MEMS) resonator. The methods of producing the solutions of the polymers deposited onto the quartz crystals are presented. A CO2 concentration range from 0.05% to 1% was dissolved in air and humidity level were controlled and evaluated. Linear polyethylenimine showed superior performance with a reaction time obtained for stabilization after the concentration increase of 345 s, while the time for recovery was of 126 s, with a maximum frequency deviation of 33.6 Hz for an in-air CO2 concentration of 0.1%.

In situ real time monitoring of hygroscopic properties of graphene oxide and reduced graphene oxide

Graphene oxide (GO) and reduced graphene oxide (RGO) has gained much attention in the field of gas sensing. However to realize its full potential in this regard, it is important to understand the influence of moisture on GO and RGO. Therefore, in situ and real time monitoring of adsorption and desorption of water molecules on GO and RGO coatings were investigated using quartz crystal microbalance (QCM). Water adsorption were studied under constant relative humidity (RH) levels over a period of time. For both GO and RGO the results show that the adsorption is followed by an equilibrium state. It is shown that for GO the initial rate of water adsorption, the amount of water at the equilibrium and the time to reach the equlibrium vary with RH, where as for RGO no such variations were observed. These observations indicate that at low RH adsorption is primarily throught surface and the edges where as at high RHs water penetrate into the intersitial layers of GO. Thus the latter becoming the rate limiting step for water adsorption at high RH. The results also elucidate on the contribution of surface oxygen functional groups towards the water adsorption rate and the amount adsorbed. The above results provde important information that can be used during GO-based sensor design and calibration.