Reduction Process Of Graphene Oxide Research Articles

Influence of the thermal reduction process on the tribological and conductive properties of single-layer graphene oxide

Graphene oxide (GO) can be intentionally modified by the reduction process to tune some of its physical properties. This allows the application of GO as a thin film interface in various technologies, especially MEMS devices. One of the key factors when considering GO as a nanocoating in MEMS is its ability to reduce friction and increase electrical conductivity. Here, we exemplify a simple adjustment of the friction and conductance of a single GO flake at the nanoscale by the thermal reduction process, which results in morphological, chemical, and structural changes. The core of this experimental work is based on atomic force microscopy (AFM), in particular AFM topography imaging, force spectroscopy, lateral force microscopy, and conductive AFM. Additional measurements were performed using optical microscopy, Fourier-transform infrared spectroscopy, Raman spectroscopy, and wetting angle measurements. The physical properties were measured as a function of the reduction temperature for isolated single-layer GO flakes. In our research, we have identified a temperature threshold at which structural and morphological changes occur. The conversion of the properties of GO as conductivity, thickness, adhesive, and friction force, as well as defect level was shown to occur at most at 130 °C. However, some effects start even at 100 °C. We have found a non-monotonic friction dependence as a function of the sliding velocity, close to our published results for fluoroalkylsilanes [1]:Weiss M. et al. (2021), Tribology International, 162, 107133], which exhibits a characteristic friction minimum. It corresponds to the lowest possible energy dissipation in the system for a given sliding velocity and load. To extend the range of accessible sliding velocities and gain insight into the molecular details of the friction process, molecular dynamics simulations were performed. In conclusion, by controlling the thermal reduction process of GO, it is possible to influence the properties of the GO system, such as adhesion, friction, and electrical conductivity, which can enhance the performance of materials in various applications, including MEMS devices.

Crystal Structure Parameter Analysis of Reduced Graphene Oxide (rGO) from Coconut Shell Charcoal

In this research, reduced graphene oxide (rGO) material from coconut shell charcoal was synthesized using the modified Hummer method. The reduction process of Graphene Oxide (GO) to rGO uses the reducing agent L-Ascorbic Acid (LAA) and is assisted by microwave radiation. The samples obtained were then characterized using XRD to analyze the crystal structure parameters of the rGO samples obtained. Based on the XRD results, the data obtained was then analyzed using the Scherrer and modified Scherrer equations to determine the crystal size in the sample. In addition, the Williamson-Hall equation is also used to analyze crystal size and lattice strain. This article also analyzes XRD data using the Rietveld method using Rietica software. The output from the Rietica software obtained lattice parameter values a ≠ b ≠ c and angle α = β = γ = 90° which indicates an orthorhombic crystal lattice structure. In the refinement process, Rietica's software affects the suitability parameters in the form of R and GOF indicator values. The sample obtained was also measured for the electrical conductivity value of the rGO sample using an LCR meter.

Significantly enhanced photo response of hydrazine hydrate reduced graphene oxide films modified with swift heavy ion irradiation of silver (Ag8+) ions

In this paper, a multistep reduction process of graphene oxide (GO) is discussed. It is basically a two-step reduction process. In the first step, the GO sample is reduced by hydrazine hydrate. In the second step, it is further reduced by a swift heavy ion irradiation beam of silver (Ag8+) ions of 100 MeV energies. Ion beam irradiation causes defects in the hydrazine hydrate reduced graphene oxide (rGO) samples. FTIR study confirms the removal of oxygen containing functional groups. The pore volume and pore density of the samples seem to increase with increase in the ion irradiation doses. It is also seen that the electrical conductivity and specific surface area increases with dose of ion irradiation. The prepared samples were tested for photo response measurement and among all the sample, R5 had the highest photo response of 6.25 % at 30 mW/cm2. The photodetection response seems to increase with increase in intensity of light.

Ultra-strong and conductive graphene fiber via sacrificial layer technology

Microfluidic spinning technology (MST) is an emerging method specialized in the construction of multi-component and multi-structure fibers. In this study, we designed an ultra-strong coaxial graphene oxide (GO) fiber by employing sodium alginate (SA) as sheath flow via MST. The diameter of the fiber and the arrangement of GO molecules could be controlled by adjusting process parameters. More importantly, the outer SA layer could be removed during a subsequent reduction process of GO, which served as a sacrificial layer to GO fiber formation and enhanced the fiber strength. Ultimately, this could achieve a conductive graphene fiber with a maximum strength of 365.2 MPa and electrical conductivity of 52 Ω/cm via a common wet spinning mechanism.

Unveiling the reduction process of graphene oxide by ascorbic acid; grafting and reduction sequences for high surface area graphene materials.

We synthesized high surface area reduced graphene oxides using L-ascorbic acid as a reducing agent by precisely controlling the interaction between graphene oxide and L-ascorbic acid. Based on the structural characterization, such as textural properties (specific surface area, pore structure), crystallinity, and carbon chemical state, we identified that the temperature and reaction time are critical parameters to control the stacking degree of the final product. Besides, by performing a time course analysis of the reaction, we identified the side products of the reducing agent by LC-MS and verified the reduction mechanism. Following our results, we proposed an optimum condition for producing a high-surface area graphene derivative that can work as an adsorbent in an aqueous solution for organic and inorganic pollutants such as methylene blue, methyl orange, and cadmium.

Pedot:PSS/Graphene Oxide (GO) Ternary Nanocomposites for Electrochemical Applications.

Among conductive polymers, poly(3,4 ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) has been widely used as an electrode material for supercapacitors, solar cells, sensors, etc. Although PEDOT:PSS-based thin films have acceptable properties such as good capacitive and electrical behaviour and biocompatibility, there are still several challenges to be overcome in their use as an electrode material for supercapacitors. For this reason, the aim of this work is to fabricate and characterise ternary nanocomposites based on PEDOT:PSS and graphene oxide (GO), blended with green additives (glucose (G) or ascorbic acid (AA)), which have the benefits of being environmentally friendly, economical, and easy to use. The GO reduction process was first accurately investigated and demonstrated by UV-Vis and XRD measurements. Three-component inks have been developed, and their morphological, rheological, and surface tension properties were evaluated, showing their printability by means of Aerosol Jet® Printing (AJ®P), an innovative direct writing technique belonging to the Additive Manufacturing (AM) for printed electronics applications. Thin films of the ternary nanocomposites were produced by drop casting and spin coating techniques, and their capacitive behaviour and chemical structures were evaluated through Cyclic Voltammetry (CV) tests and FT-IR analyses. CV tests show an increment in the specific capacitance of AAGO-PEDOT up to 31.4 F/g and excellent overtime stability compared with pristine PEDOT:PSS, suggesting that this ink can be used to fabricate supercapacitors in printed (bio)-electronics. The inks were finally printed by AJ®P as thin films (10 layers, 8 × 8 mm) and chemically analysed by FT-IR, demonstrating that all components of the formulation were successfully aerosolised and deposited on the substrate.

Investigating the Extracellular-Electron-Transfer Mechanisms and Kinetics of Shewanella decolorationis NTOU1 Reducing Graphene Oxide via Lactate Metabolism

Microbial graphene oxide reduction is a developing method that serves to reduce both production costs and environmental impact in the synthesis of graphene. This study demonstrates microbial graphene oxide reduction using Shewanella decolorationis NTOU1 under neutral and mild conditions (pH = 7, 35 °C, and 1 atm). Graphene oxide (GO) prepared via the modified Hummers' method is used as the sole solid electron acceptor, and the characteristics of reduced GO (rGO) are investigated. According to electron microscopic images, the surface structure of GO was clearly changed from smooth to wrinkled after reduction, and whole cells were observed to be wrapped by GO/rGO films. Distinctive appendages on the cells, similar to nanowires or flagella, were also observed. With regard to chemical-bonding changes, after a 24-h reaction of 1 mg mL-1, GO was reduced to rGO, the C/O increased from 1.4 to 3.0, and the oxygen-containing functional groups of rGO were significantly reduced. During the GO reduction process, the number of S. decolorationis NTOU1 cells decreased from 1.65 × 108 to 1.03 × 106 CFU mL-1, indicating the bactericide effects of GO/rGO. In experiments adding consistent concentrations of initial bacteria and lactate, it was shown that with the increase of GO additions (0.5-5.0 mg mL-1), the first-order reaction rate constants (k) of lactate metabolism and acetate production increased accordingly; in experiments adding consistent concentrations of initial bacteria and GO but different lactate levels (1 to 10 mM), the k values of lactate metabolism did not change significantly. The test results of adding different electron transfer mediators showed that riboflavin and potassium ferricyanide were able to boost GO reduction, whereas 2,6-dimethoxy-1,4-benzoquinone and 2,6-dimethyl benzoquinone completely eliminated bacterial activity.

Structural, compositional study, and thermal behavior of TiO2/Cr2O3/GO nanocomposite for methylene blue degradation

This study emphasizes the methylene blue (MB) dye degradation potential of mixed systems of TiO2, Cr2O3, and graphene oxide (GO) based nanocomposites (NCs). Structural and thermal studies for TiO2, Cr2O3, TiO2/GO, Cr2O3/GO, TiO2/Cr2O3, and TiO2/Cr2O3/GO compositions are executed. XRD, FTIR, and EDX confirm the lack of impurities within compositions. Additionally, the EDX, and FTIR results are agreeing with each other in highly oxygenated NC formation. Regarding the morphological study, TEM micro-graphing supports TNC formation owing to aggregation-growing inhibition that causes surface area widening and enhances dye removal potential. On the other hand, FESEM is agreeing with TEM that TNC shows a lowering in grains size and aggregations that TiO2, and Cr2O3 record 60, and 75 nm, respectively. This agreement with TEM, and FESEM in widening surface area and adding crystallinity defects raising which recommended the occurrence of chemical decontamination operation. The thermodynamic study reports almost equal values of enthalpy (ΔH) and activation energy (i.e. according to the CR model: 155.6, 147.7 KJ mole−1, respectively), this is explained by the presence of TNC in the condensed phase through the temperature scope (545–750 °C), besides its significant stability. Moreover, the EDX, and FTIR results are agreeing TiO2/Cr2O3NC shows intermediate thermal behavior between its pure ingredient, leaving 97.3 % as a residual. TNC total weight loss hits 9.2 %. This percentage is contributed to four stages, 1.3 % (30–300 °C/dehydration), 2.3 % (300–545 °C/structure rearrangement), 3.5 % (545–750 °C/GO reduction process & structure rearrangement), and 2.1 % (750–100 °C/GO reduction). The inorganic compositions show acceptable thermal stability for environmental usage. The stated NCs able to be recycled that TiO2/Cr2O3/GO shows a minor decline in MB degradation potential that decreases from 98.8 to 87.5 % after five cycles.

Development of stripping voltammetry using glassy carbon electrode modified with electrochemical reduced graphene oxide for the determination of amaranth in soft drink and candy samples

In this study, the manufacturing conditions of glassy carbon electrode modified with electrochemical reduced graphene oxide (ErGO/GCE) were elucidated to determine amaranth in soft drink and candy samples by adsorptive stripping voltammatry. The ErGO/GCE was fabricated through an electrochemical reduction process of graphene oxide in the potential range from 0 V to −1.5 V using cyclic voltammetry method. Characteristics of graphene oxide and reduced graphene oxide were studied by FT-IR, XRD, TEM, SEM. Amaranth is adsorbed on the ErGO/GCE working electrode surface through an irreversible oxidation process. The optimal conditions used to determine amaranth are Britton-Robinson buffer solution of pH 3.0, an adsorption potential at 0 V, an adsorption time of 30 s, at a scan rate of 20 mV/s, a linearity range from 1.0 × 10−7 mol. L−1 to 1.0 × 10−6 mol. L−1, a (LOD) detection limit of 2.8 × 10−8 mol. L−1 and a (LOQ) qualification limit of 9.3 × 10−8 mol. L−1. The proposed method can be applied to determine amaranth dye in food.

3D heteroatom-doped graphene-wrapped flexible carbon fiber microsensor for real-time hydrogen peroxide detection in live cancer cells

Balancing electrostatic repulsive force and bonding interactions are the key principles for constructing 3D graphene architecture on single carbon fiber (CF). Herein, we present a simple and facile method to modify 3D porous N, B co-doping graphene on single CF (CF@3D-NBG). In the process, the Ni nanoparticles were deposited on CF and used as a reductant for reducing graphene oxide (GO), promising graphene-wrapped CF at low temperature. Ionic liquids were introduced to prevent re-aggregation of graphene sheets during the reduction process of GO, but also acted as heteroatom sources for doping graphene, which provides high electrical conductivity, numerous doping sites and edges for H2O2 electrocatalysis reduction. It is found that the CF@3D-NBG flexible microelectrodes show a broad linear range from 0.5 μM to 4.25 mM and a low detection limit of 100 nM for H2O2 detection. When applied to track the amount of H2O2 generated from real samples, the sensor exhibits desirable performance in distinguishing cancer cells from normal cells and further assessing the therapeutic effect of antitumor drugs on live cancer cells. Therefore, this study may offer an attractive method for synthesizing advanced graphene-based electrodes with great promise for biosensors.

Revisiting the two-dimensional structure and reduction process of graphene oxide with in-plane X-ray diffraction

The unique characteristics and low cost of graphene oxide (GO) make it a promising nanocarbon material for many practical applications. However, despite intensive studies with advanced spectroscopic and microscopic methods as well as theoretical calculation, the two-dimensional structure of GO remains controversial due to the structural complexity, inhomogeneity, and instability. Here, we employed a synchrotron in-plane X-ray diffraction (XRD) technique to elucidate its true 2D structure. An overall feature of the in-plane XRD profiles of GOs obtained by Hummers' and Brodie's methods revealed that the graphene-like hexagonal lattice was preserved without amorphization after severe chemical oxidation. The 10 reflection peak was analyzed to probe the intraplane lattice expansion, shrinkage, and microstrain that depend on the oxidation and reduction conditions due to the interconnected oxygen functional groups and carbon defects in a single crystalline domain. Based on the correlation between the global and local structures and the chemical composition, we established a three-step reduction process of GO consisting of deoxygenation, diffusionless lattice modification, and diffusional lattice modification. The updated 2D structural model and the generalized reduction process will facilitate the design and interpretation of GO-related materials.

Li₄Ti₅O₁₂/Graphene composite as an anode for Li-ion battery

Spinel structured Li4Ti5O12 (LTO) is one of the most promising candidate anode material for Li-ion battery known as zero strain material, it has poor intrinsic electronic properties. In order to enhance it, graphene was used as additive. The LTO and graphene composites were synthesized by reduction process of graphene oxide via hydrothermal treatment. Thepowders were characterized by X-Ray diffraction (XRD), Infrared spectroscopy (FT-IR).For the galvanostatic discharge and charge measurements were performed at roomtemperature against Li/Li+ metal electrode.

Synthesis of semiconductors nanocomposites of polymethyl methacrylate and reduced graphene oxide by ultraviolet radiation

Polymeric nanocomposites of polymethylmethacrylate (PMMA) added with up to 20wt.% of graphene oxide (GO) were synthesized by the solvent evaporation technique and, for the first time, irradiated with ultraviolet radiation (UV-B) to reduce GO and obtain novel films of electrically semiconductive nanocomposites (PMMA-rGO). The exposition times to reduce the GO in these nanocomposites were 48 and 96 h. Chemical, physical, and electrical conductivity analyses were performed, and both GO and rGO added PMMA nanocomposites results were compared before and after UV-B radiation. Plain PMMA results were also compared as control. These results showed that the addition of GO flakes and its reduction (rGO) by UV-B radiation promoted better thermal stability and stiffness to the nanocomposites than to plain PMMA, as demonstrated by the thermogravimetric and differential scanning calorimetry analyses. High resolution scanning electron microscopy demonstrated well distributed rGO particles in the PMMA matrix. FTIR and Raman confirm the reduction process of GO after being UV-B rays irradiated. The colorimetric analyses showed that the GO and rGO flakes and the PMMA matrix presented an excellent superficial interaction. The results of electrical conductivity for the PMMA matrix (4.50 × 10−9 S/m) and the nanocomposites with 2 wt. % GO (1.21 × 10−9 S/m) revealed an insulating behavior, whcich decreases for an addition of 20 wt.% GO. The electrical conductivity displayed a significant improvement with UV-B radiation, such that with 20 wt.% rGO exposed to 48 and 96 h of UV-B radiation, the PMMA-rGO nanocomposites became semiconductor.

Non-covalent functionalization of graphene sheets by pyrene-endcapped tetraphenylethene: Enhanced aggregation-induced emission effect and application in explosive detection.

In this work, a dispersible graphene-based material with a characteristic of aggregation-induced emission (AIE) was prepared by wet chemical reduction of graphene oxide (GO). During the GO reduction process, a conjugated molecule TPEP containing tetraphenylethylene (TPE) and pyrene was employed as a stabilizer because of the π–π interactions and the wrapping effect. The as-prepared rGO-TPEP not only has good dispersion in solution but also processes the AIE feature. Its fluorescence intensity is 2.23 times higher than that of TPEP at the same condition. The unique optical properties and AIE effect enable the rGO-TPEP as a chemical sensor for highly sensitive explosive detection in aggregated state and solid state. In the aggregated state, trace 2,4-dinitrotoluene (DNT) can be detected by the rGO-TPEP even when the concentration is as low as 0.91 ppm, and the quenching constant is as high as 2.47 × 104 M-1.

Flexible humidity sensor based on light-scribed graphene oxide

The light scribe (LS) technique has been applied to reduce graphene oxide (LSGO) over a flexible substrate to be used as a humidity sensor. Graphene oxide (GO) suspension was drop casted over Polyethylene terephthalate (PET) substrate and then reduced inside a conventional light scribe digital video disc (DVD). Interdigitated electrode was precisely fabricated with dimensions of the finger length of 450 μm and width of 20 μm. The prepared material was characterized using X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and Raman spectroscopy. The results confirm the reduction process of GO using the LS technique. Moreover, the humidity sensing properties of the LSGO was evaluated. Results showed that the present light-scribed humidity sensor has many advantages including rapid response, highly precise due to light scribe technique, and more importantly sensors can be fabricated directly on flexible substrates which are highly favorable for future wearable smart electronics.

Bovine serum albumin-functionalized graphene-decorated strontium as a potent complex nanoparticle for bone tissue engineering

Graphene and its family have a great potential in tissue engineering because of their super mechanical properties, electrical conductivity and antibacterial properties. Considering other properties of graphene such as high surface area and ready-to-use functionalization according to the high oxygen-containing groups in graphene oxide family, some needs could be addressed in bone tissue engineering. Herein, we synthesized and decorated strontium nanoparticles (SrNPs) during the reduction process of graphene oxide using green and novel method. Without using hydrazine or chemical linkers, strontium NPs were synthesized and decorated on the surface of rGO simultaneously using BSA. The results of the UV–Vis, FTIR and Raman spectroscopy demonstrated that BSA could successfully reduce graphene oxide and decorated SrNPs on the surface of rGO. FESEM and TEM exhibited that in situ synthesized SrNPs had 25–30 nm diameter. Interestingly, cell viability for MC3T3-E1 cells treated with SrNPs-rGO, were significantly higher than BSA-rGO and GO in constant concentration. Furthermore, we investigated the alkaline phosphatase activity (ALP) of these nanosheets that the results demonstrated Sr-BSA-rGO enhanced ALP activity more than GO and BSA-rGO. Remarkably, the relative expression of RUNX 2 and Col1 genes of MC3T3-E1 cells was boosted when treated with Sr-BSA-rGO nanosheets. This study revealed that using proteins and other biomolecules as green and facile agent for decoration of smart nanoparticles on the surface of nanosheets, would be promising and assist researcher to replace the harsh and toxic hydrazine like materials with bio-friendly method. These results demonstrated that Sr-BSA-rGO had the excellent capability for regenerating bone tissue and could be used as an osteogenesis booster in implants.

Preparation of graphene-starch composite film and its application in sensor materials

In this work, a composite film was prepared by combining reduced graphene oxide (RGO) and starch nanocrystals (SNC). The results show that SNC can be well dispersed on graphene after mixed with the graphene oxide solutions. SNC had a greater impact on the morphology and microstructure of the composite film. Moreover, the introduction of SNC and the efficient reduction process of graphene oxide (GO) render these composite films good mechanical properties as well as high electrical conductivity. The tensile strength of the composite film was improved after being combined with graphene. However, as the addition rate of SNC increased, the strain-to-failure of the composite film decreased. Therefore, 10% reduced graphene-starch nanocrystals (10%RGO-SNC) was used as multifunctional sensor materials. And it had strong responses to different external stimuli, such as, temperature, humidity, bending/stretching, and solutions.

Corrosion behavior of Q235 steel in graphene oxide aqueous dispersion

Conductive metals can speed up the self-assembly and reduction process of graphene oxide (GO) in liquid media, but there is little available information about the effect of this process on the corrosion rate of metal substrates. The corrosion performance of Q235 steel in GO aqueous solution was studied by comparing the influence of different GO concentrations and immersion times on the corrosion rate of steel. The result found that a GO layer will be formed on the surface of steel when immersing in the GO aqueous dispersion, which has a shielding effect on the diffusion process of ions and electrons, and effectively inhibits the steel corrosion. However, this inhibition effect of GO layer will disappear with the self-reduction of GO, which increasing the defect density and conductivity of the sedimentary layer on steel and thus the corrosion rate of steel will increase with the immersion time and the GO concentration in solution.

Electrically conductive, hydrophobic, UV protective and lightweight cotton spunlace nonwoven fabric coated with reduced graphene oxide.

In this study, cotton spunlace nonwoven fabrics with four different basis weights were coated with graphene oxide (GO) by conventional dip coating method which is one of the most simple and effortless process in textile industry. The graphene oxide coated cotton nonwoven fabrics were immersed in an aqueous sodium dithionite solution in order to obtain reduced graphene oxide (RGO) coated cotton spunlace nonwoven fabrics. The obtained nonwoven fabrics became electrically conductive with very low surface electrical resistivity of 5.98 × 102 W/sq for the 70 g/m2 basis weight nonwoven fabric. The color measurements and reflectance spectrophotometry were performed in order to identify the coating and reduction process of GO on cotton nonwoven fabrics. The hydrophobic characteristic of the GO and RGO coated cotton nonwoven fabrics were determined by the means of water contact angle. The ultraviolet (UV) blocking ability of the cotton nonwoven fabric both coated with GO and RGO were analyzed by the UV transmittance analyzer. The water contact angle results revealed that the hydrophilic cotton nonwoven fabric became hydrophobic due to the reduction of GO. It was also found that the ultraviolet protection factor (UPF) depends on the basis weight of the cotton nonwoven fabric and the reduction of GO.

Detailed thermal reduction analyses of graphene oxide via in-situ TEM/EELS studies

We report an in-depth study of the reduction of graphene oxide (GO) by in-situ thermal transmission electron microscopy (TEM) analysis. In-situ heating high-resolution TEM (HRTEM) imaging and electron energy-loss spectroscopy (EELS) measurements have been combined to identify the transformations of different oxygen functional groups, the desorption of physisorbed and chemisorbed water and the graphitisation as a function of the temperature in the range from 70 up to 1200 °C. A model for the general removal of water and OFGs is proposed based on different chemical and physical parameters that have been monitored. All this unique information provides a detailed roadmap of the thermal behaviour of GO at an extended range of temperature. This is not only of interest to understand the thermal reduction process of GO but also of critical relevance to the response of GO in applications when exposed to thermal effects.