Reduction Degree Of Graphene Oxide Research Articles

One-pot radiolytically synthesized reduced graphene oxide-gold nanoparticles composites and exploration in energy storage

Graphene and its composites are of primary importance, particularly in the field of energy storage. Numerous bottom-up and top-down methods have been proposed in the literature to produce these materials with enhanced physicochemical properties. Recently, an innovative and green methodology was developed based on ionizing radiation, allowing the quantitative synthesis of graphene oxide-based materials. With the aim to extend this strategy for the preparation of hybrid nanomaterials, the objective of this work was the one-pot synthesis of nanocomposites composed of reduced graphene oxide – gold nanoparticles (rGO-AuNPs) via gamma ray-induced radiolytic reduction. UV–Vis Absorption Spectroscopy, Fourier Transform Infrared Spectroscopy, Raman Spectroscopy and X-ray Photoemission Spectroscopy were utilized to comprehensively evaluate the reduction degree of graphene oxide and the formation of gold nanoparticles. Atomic Force Microscopy and Scanning Electron Microscopy were employed to obtain the morphological and topographical information on synthesized nanocomposites. Thermal properties were investigated by Thermogravimetric Analysis and electrical properties were investigated using Cyclic Voltammetry and Potentiostatic Charge and Discharge method. The results demonstrated the successful reduction of graphene oxide and gold ions through the drastic transformation of oxygen-containing functional groups and the formation of gold nanoparticles. Electrical characterization results highlighted the excellent electrical properties of radiosynthesized rGO-AuNPs composites and their great potential for supercapacitance application.

R-HGO/MXene composite membrane with enhanced permeability and rejection performance for water treatment

Pure graphene oxide (GO) membranes have a tendency to swell in water and have a relatively low flux, making them impractical for water treatment applications. Herein, a novel two-dimensional (2D) composite membrane based on reduced-holey GO (r-HGO) and MXene materials was developed. As a consequence of synergistic effects arising from its unique heterogeneous structure, the r-HGO/MXene composite membrane exhibited an exemplary performance for water treatment, in terms of its permeability and pollutant rejection, and high physical stability. The preparation conditions, especially the reduction degree of GO and the proportions of r-HGO and MXene, determine the properties and performance of the composite membrane. The water flux of the r-HGO/MXene composite membrane with a r-HGO/MXene mass ratio of 1/1 achieved 121.0 L m−2 h−1·bar−1, which was 23 times higher than that of pure GO membrane (∼5.2 L m−2 h−1·bar−1). The removal rates of Coomassie brilliant blue, Methyl blue, Crystal violet, Rhodamine B, Methylene blue, were all above 90 %. Furthermore, the r-HGO/MXene composite membrane was found to be physically stable for more than a week in an aqueous environment. The results of this work show that the r-HGO/MXene composite membrane has great potential as a separation method in water treatment by overcoming some of the important limitations of other current 2D materials.

Effect of Concentration and pH of GO Solutions on the Pd-rGO@NF Electrode Prepared by Spontaneous Reduction for H2O2 Reduction in Acidic Media

The Pd-rGO@NF composite electrodes were prepared by a simple and green two-step process of spontaneous reduction. Graphene oxide (GO) was first reduced directly by nickel foam (NF) to form a rGO@NF composite substrate. The effect mechanism of GO concentration and pH on the morphology and properties of rGO@NF was investigated by SEM, TEM, XRD and Raman. Increasing GO and H[Formula: see text] concentration can improve the reduction rate, deposit amount and reduction degree of GO on the surface of Ni foam. A uniform, compact and multi-fold rGO coating formed on the Ni skeleton surface at the GO concentration of 2[Formula: see text]g[Formula: see text]L[Formula: see text] and pH of 7. Then, Pd[Formula: see text] was reduced by rGO on the NF surface to construct the 3D Pd-rGO@NF composite electrodes, which showed superior catalytic activity and stability for H2O2 reduction in acidic media compared to Pd-NF due to a higher surface area and better anti-acid corrosion from rGO layers.

Surface interaction of tetrabromobisphenol A, bisphenol A and phenol with graphene-based materials in water: Adsorption mechanism and thermodynamic effects

Carbon-based materials, especially graphene nanocomposites (GNS) have attracted wide attention in recent years. In this study, graphene oxide (GO) and reduced graphene oxide (rGO) were prepared using the Improved Hummers method and were investigated for their adsorption behavior of emerging contaminants such as tetrabromobisphenol A (TBBPA), bisphenol A (BPA), and a conventional contaminant, phenol. The adsorption capacity seemed to slightly increase with increasing reduction degree of GO, highlighting its hydrophobic effect. The adsorption kinetics and isotherms were well delineated using pseudo-second-order and Langmuir equations respectively. At higher temperatures, the adsorption of these selected organic contaminants on GO and rGO slightly increased, also indicating the slight effect of temperature on the adsorption in the environment. From a thermodynamic analysis, the endothermic and spontaneous reaction was observed. The adsorption mechanisms included hydrophobicity, π- π interactions and π electron acceptor and donor ones. GNS can suspend in water even after adsorbing pollutants at the water interface. This would enhance the transport of these contaminants with nanomaterials in the environment. These findings are valuable to elucidate the interaction mechanism between phenol, BPA, and TBBPA on GNS while further understanding the physicochemical behavior of these organic contaminants in the environment.Summary: Adsorption capacities of emerging contaminants, BPA and TBBPA, as well as phenol on graphene oxide (GO) and reduced GO (rGO), were similar. Higher temperatures slightly increased the adsorption of these phenolic compounds on GO and rGO, which also indicated an endothermic and spontaneous process.

Vitamin C aqueous solution assisted in-situ reduction of graphene oxide in flexible thermoplastic polyurethane

Graphene oxide (GO) is usually used as a precursor of reduced GO (rGO) in polymer matrices for improving their properties. However, reduction degree of GO in conventional melt mixing is usually limited. In this work, thermoplastic polyurethane (TPU)/rGO nanocomposite is prepared via water-assisted mixing extrusion with vitamin C (VC) aqueous solution injection. In situ chemical reduction (ISCR) by the VC and in situ thermal reduction (ISTR) by the thermal energy from both extruder barrel heating and screw shear are simultaneously enhanced for the GO, which are indicated by disappearances of O–H peak at the FTIR spectrum and O–C=O peak at the XPS spectrum of the rGO powder extracted from the prepared nanocomposite. Thus high reduction degree of the GO is obtained (with C/O atom ratio of 9.83 for the extracted rGO powder). This is attributed to the following two aspects: (1) TPU chains plasticized by water can better intercalate into GO galleries, thus enhancing the stripping of oxygen-containing groups from GO surface and the ISTR of the GO; (2) the screw shear action helps to disperse the VC of the injected VC aqueous solution in the TPU melt and increase the contact between the VC and GO, therefore enhancing the ISCR of the GO. The prepared TPU/GO nanocomposite exhibits enhanced dielectric permittivity.

Spectral and Structural Properties of High-Quality Reduced Graphene Oxide Produced via a Simple Approach Using Tetraethylenepentamine.

A simple temperature-assisted solution interaction technique was used to functionalize and reduce graphene oxide (GO) using tetraethylenepentamine (TEPA) with less chemicals, low temperature, and without using other reducing agents. GO nanosheets, produced using a modified Hummers’ method, were functionalized using two different GO:TEPA ratios (1:5 and 1:10). The reduction of GO was evaluated and confirmed by different spectroscopic and microscopic techniques. The FTIR and XPS spectra revealed that most of the oxygenated groups of GO were reduced. The emergence of amide groups in the XPS survey of the rGO-TEPA samples confirmed the successful reaction of TEPA with the carboxyl groups on the edges of GO. The replacement of the oxygenated groups increased the carbon/oxygen (C/O) ratio of GO by approximately 60%, suggesting a good reduction degree. It was found that the I2D/ID+D′ ratio and the relative intensity of the D″ band clearly increased after the reduction reaction, suggesting that these bands are good estimators for the reduction degree of GO. The morphological structure of GO was also affected by the reaction with TEPA, which was confirmed by SEM and TEM images. The TEM images showed that the transparent GO sheets became denser and opaque after functionalization with TEPA, indicating an increase in the stacking level of the GO sheets. This was further confirmed by the XRD analysis, which showed a clear decrease in the d-spacing, caused by the removal of oxygenated groups during the reduction reaction.

Thermal reduced graphene oxide enhanced in-situ H2O2 generation and electrochemical advanced oxidation performance of air-breathing cathode

Developing highly efficient catalysts with high ORR activity and H2O2 selectivity is an important challenge for producing H2O2 through 2e− oxygen reduction reaction (ORR). In this work, we tuned the reduction degree of graphene oxide by controlling reducing temperature and prepared graphite-TRGO hybrid air breathing cathodes (ABCs). The H2O2 production rate of TRGO-1100 (with highest reduction degree) modified ABC exhibits highest H2O2 generation rate of 20.4 ± 0.8 mg/cm2/h and current efficiency of 94 ± 2%. The charge transfer resistance of TRGO-1100 decreases by 2.5-fold compared with pure graphite cathode. Unreduced GO shows high H2O2 selectivity and low ORR activity, while TRGO shows lower H2O2 selectivity but higher ORR activity. Though the 2e− ORR selectivity of TRGO decreased TRGO with all reduction degrees, the H2O2 production increased in all forming electrodes. Superior performance of TRGO modified ABCs is attributed to high oxygen adsorption and low charge transfer resistance. TRGO possesses super-hydrophobicity and large surface area for oxygen adsorption. Besides, TRGO provides abundant electrochemically active sites to facilitate the electron transfer and formed more mesopores for H2O2 release. Electro-Fenton using TRGO-1100-ABC exhibited great performance for Persistent Organic Pollutants (POPs) degradation, which removed 66% of tetracycline in 5 min.

Redox-active engineered holey reduced graphene oxide films for K+ storage

Graphene film is promising candidate as free-standing electrodes for potassium-ion batteries (KIBs) owing to its intrinsic nature of mechanical strength and high electrical conductivity. However, its performance is usually restricted by the tightly stacked structure and sluggish insertion/deinsertion K storage mechanism. Herein, a redox-active engineered holey reduced graphene oxide (HRGO) film anode was prepared by using the carboxylic acid functionalized polystyrene (PS-COOH) spheres as the template. The holey ion diffusion network channels and the oxygen functional groups can be optimized during the PS-COOH spheres decomposition process, which largely promote the enhancement of electrochemical performance because the oxygen functional groups can serve as the surface-redox sites increasing surface-driven reactions and holey channels provide more ion-accessible area for K-ion storage. Moreover, the reduction degree of graphene oxide also be simply tuned by changing the annealing temperature, which can improve the K+ bulk intercalation reaction. As a result, the optimized HRGO-900 (HRGO sample obtained at 900 °C) films exhibits a superior areal capacity (0.80 mAh cm−2 at 0.1 mA cm−2). The electrode design and construction strategies can be effectively applied in other 2D materials, which exhibits practical applications in energy storage devices.

Manipulating Exciton Transfer between Colloidal Quantum Dots and Graphene Oxide

Colloidal quantum dots and graphene oxide composite are promising semiconductor nanomaterials for optoelectronic devices due in part to their tunable light absorption and extraordinary carrier transport properties. We investigate the exciton interaction between them during laser irradiation by transient absorption spectroscopy. In the transient measurement, an exciton bleach buildup signal is exhibited before its recovery at the long probe wavelength. It can be attributed that the trapped electron of graphene oxide backward transfers to the conduction band of quantum dots. With the reduction degree of graphene oxide being increased by laser irradiation, backward electron transfer would take place at both longwave and shortwave, resulting in a broader and stronger exciton bleach feature. Subsequently, exciton bleach disappeared at longwave because of hole trapping by graphene oxide. Exciton transfer of quantum dots and graphene oxide composite has been efficiently manipulated by laser irradiation.

Development of a new synthetic strategy for highly reduced graphene oxide-CdS quantum-dot nanocomposites and their photocatalytic activity

Cadmium sulfide (CdS) is a vital wide-bandgap semiconductor that plays an important role in many fields. In this study, we grew CdS quantum dots on graphene oxide (GO) sheets using a novel chemical bath deposition approach. Highly reduced graphene oxide-CdS (rGO-CdS) nanocomposites were successfully obtained. H2S/N2 gas played a key role in the preparation of these nanocomposites, as it provided a source of S and reduced the GO. The size distribution and crystal structure of the CdS quantum dots and the reduction degree of GO in the rGO-CdS nanocomposites were investigated using various characterization techniques and the results showed that the GO was successfully reduced. Furthermore, CdS quantum dots (approximately 5–6 nm in size) with a hexagonal wurtzite structure were uniformly distributed on the rGO layers. The pollutant degradation performances of the rGO-CdS nanocomposites under visible light were studied, and the degradation mechanism was analyzed in detail.

Hydrothermal reduced graphene oxide membranes for dyes removing

Graphene oxide (GO) has potential application in membrane separation owing to its extraordinary permeance. In this paper, the reduced graphene oxide (rGO) was synthesized by a green hydrothermal reduction method, and the rGO membranes was prepared on polyvinylidene fluoride (PVDF) supporting membranes by vacuum filtration. The interlayer structure of GO and the permeability of rGO membranes can be controlled by adjusting the reduction degree of GO through changing the hydrothermal reaction time. The disorder and defects of rGO nanosheets, the less oxygen-containing functional group and the enhanced hydrophobicity facilitate transport of water molecular in relatively smaller interlayer space owing to hydrothermal reduction. Compared with the GO membranes, the hydrothermally reduced rGO membranes showed a more excellent permeability without sacrificing rejection. The rejection of the prepared rGO membrane for Methyl blue, Congo red and Crystal violet all exceed 99%.

A fast self-healing and conductive nanocomposite hydrogel as soft strain sensor

Remarkable progress achieved for conductive hydrogels has been witnessed in recent years. However, hydrogels are easily damaged during the course of use, which limits their applications as soft conductors. Here, the nanocomposite hydrogels with fast self-healing property, conductive capability and strain-sensitive performance are successfully obtained via simple synthesis routes. Dynamic diol-borate eater bonds built from polyvinyl alcohol (PVA) and borax mainly allow nanocomposite hydrogels to display decent self-healing behaviors in mechanical (restore 92.89% of original tensile strength within 60 s), electrical (restore 96.7 ± 2% of original resistance within 4.2 s) and rheological recovery experiments without any external stimuli. Meanwhile, hydrogen bonds in prepared networks can endow hydrogels with self-healing property to a certain extent. Graphene oxide (GO) is partially reduced under the oxidative self-polymerization of dopamine (DA), providing conductivity for nanocomposite hydrogels (2.7 mS cm−1). Besides, the mechanical property and conductivity of nanocomposite hydrogels are controlled by the reduction degree of GO. Due to physical interactions formed among oxygen functional groups, the nanocomposite hydrogels show greater behaviors in mechanical, rheological and swelling tests verse pure PVA hydrogels. Furthermore, the acquired hydrogels demonstrate strain sensitivity in the designed LED bulb circuit. In view of no apparent anaphylaxis of nanocomposite hydrogels to human skins, the soft stain sensor prepared by designed hydrogel can be fabricated to detect human activities, such as bending and sitting. Our work offers an effective approach to synthesize a fast self-healing, conductive and strain-sensitive hydrogel applied as soft strain sensor for human movement monitoring.

Reduction degree regulated room-temperature terahertz direct detection based on fully suspended and low-temperature thermally reduced graphene oxides

A series of fully-suspended reduced graphene oxide (RGO) room-temperature THz detectors were fabricated based on low-temperature (from 100 to 350 °C) thermally-reduced free-standing graphene oxide (GO) thin films. The suspended configuration results in a four-fold increase in responsivity and at least one order of magnitude increase in response speed compared to the substrate-supported detector. More importantly, the responsivity can be adjusted over a wide range from 10−2–102 mA W−1 and simultaneously the response speed can be adjusted on the order of tens of milliseconds by only tuning the reduction temperature of GO namely the reduction degree of GO. The regulation mechanism was revealed at the molecular level, i. e., the content of C=O functional group and the O/C ratio inside RGO, which are vary with the reduction degree of GO, are closely related to THz absorbance and electrical conductivity of RGO thin films, respectively. The experimental results demonstrated that the as high as possible content of C=O functional group and simultaneously a moderate O/C ratio can achieve optimal synergy between the THz absorption and electrical conductivity of the RGO thin films, thereby achieving an optimal THz detection performance.

The Control of Reduction Degree of Graphene Oxide

The Control of Reduction Degree of Graphene Oxide

Reduced graphene oxide as saturable absorbers for erbium-doped passively mode-locked fiber laser**Project supported by the Central University Special Fund for Basic Research and Operating Expenses, China (Grant No. GK201702005), the Natural Science Foundation of Shaanxi Province, China (Grant No. 2017JM6091), the National Natural Science Foundation of China (Grant No. 61705183), and the Fundamental Research Funds for the Central Universities (Grant

We demonstrate a nanosecond mode-locked erbium-doped fiber laser (EDFL) based on a reduced graphene oxide (RGO) saturable absorber (SA). The RGO SA is prepared by depositing the graphene oxide (GO) on fluorine mica through thermal reduction of GO. A scanning electron microscope (SEM), Raman spectrometer, and x-ray photoelectron spectroscopy (XPS) are adopted to analyze the RGO characteristics. The results show that the reduction degree of graphene oxide is very high. By embedding the RGO SA into the EDFL cavity, a stable mode-locked fiber laser is achieved with a central wavelength of 1567.29 nm and repetition rate of 12.66 MHz. The maximum output power and the minimum pulse duration are measured to be 18.22 mW and 1.38 ns respectively. As far as we know, the maximum output power of 18.22 mW is higher than those of other nanosecond mode-locked oscillators reported. Such a nanosecond pulse duration and megahertz repetition rate make this mode-locked erbium-doped fiber laser a suitable seed oscillator for high-power applications and chirped pulse amplifications.

Conductive Graphene-Melamine Sponge Prepared via Microwave Irradiation.

A conductive graphene-melamine sponge (MS) prepared via microwave irradiation is reported in this paper. Graphene oxide supported on the MS was prereduced first at 100 °C and then further reduced in a household microwave oven at over 1000 °C. It was surprising to find that graphene oxide on the MS was reduced perfectly while the three-dimensional structure of the MS was kept well after high-temperature reduction via microwave irradiation. Slight pyrolysis of MS was also found during 5 s microwave irradiation, resulting in nitrogen generation from the pyrolysis of the MS being doped into graphene, which could benefit the electric conductivity of the prepared graphene-MS. The electric conductivity of the prepared graphene-MS is about 0.12-1.0 S/m because of the high reduction degree of graphene oxide and nitrogen doping. On the other hand, different from the pure MS, the newly developed conductive graphene-MS possesses superhydrophobic and superoleophilic properties. Overall, the newly developed conductive graphene-MS contained 94.3 wt % MS and 5.7 wt % N-doped graphene and is a cost-effective material with good elasticity, high conductivity, superhydrophobicity, and superoleophilicity.

Natural printed silk substrate circuit fabricated via surface modification using one step thermal transfer and reduction graphene oxide

Graphene conductive silk substrate is a preferred material because of its biocompatibility, flexibility and comfort. A flexible natural printed silk substrate circuit was fabricated by one step transfer of graphene oxide (GO) paste from transfer paper to the surface of silk fabric and reduction of the GO to reduced graphene oxide (RGO) using a simple hot press treatment. The GO paste was obtained through ultrasonic stirring exfoliation under low temperature, and presented excellent printing rheological properties at high concentration. The silk fabric was obtained a surface electric resistance as low as 12.15 KΩ cm−1, in the concentration of GO 50 g L−1 and hot press at 220 °C for 120 s. Though the whiteness and strength decreased with the increasing of hot press temperature and time slowly, the electric conductivity of RGO surface modification silk substrate improved obviously. The surface electric resistance of RGO/silk fabrics increased from 12.15 KΩ cm−1 to 18.05 KΩ cm−1, 28.54 KΩ cm−1 and 32.53 KΩ cm−1 after 10, 20 and 30 washing cycles, respectively. Theresultsshowedthat the printed silk substrate circuit has excellent washability. This process requires nochemical reductant, and the reduction efficiency and reduction degree of GO is high. This time-effective and environmentally-friendly one step thermal transfer and reduction graphene oxide onto natural silk substrate method can be easily used to production of reduced graphene oxide (RGO) based flexible printed circuit.

Catalyst surfaces with tunable hydrophilicity and hydrophobicity: metal–organic frameworks toward controllable catalytic selectivity

This report describes a facile strategy that has the capability of adjusting different surface hydrophilicities/hydrophobicities of catalysts by covering metal-organic frameworks with graphene oxide and reduced graphene oxide. The catalysts exhibit remarkable catalytic selective performance for the hydrogenation of different hydrophobic and hydrophilic reactants.

Investigation of the Influences of Reaction Temperature and Time on the Chemical Reduction of Graphene Oxide by Conventional Method Using Vitamin C as a Reducing Agent

The aim of this work is to investigate the synthesis of reduced graphene oxide (rGO) aqueous suspension by a conventional heating method using vitamin C as a reducing agent. The influences of reaction temperatures (70, 90 and 100 °C) and heating times (30, 45 and 60 min) on the chemical reduction of graphene oxide (GO) were studied. Then, the obtained rGO samples were characterized by FT-IR, Raman and UV-Vis spectroscopy. The FT-IR and Raman results showed that the reduction degree of GO to rGO was increased with the rising of the reaction temperature and time. Moreover, the UV-Vis spectra demonstrated that the absorption band at around 230 nm (π-π*) of pristine GO had shift to the longer wavelength upon the chemical reduction, indicating that GO is reduced to rGO. The optimal condition of the chemical reduction of GO to achievable rGO was the temperature of 90 °C with the 45 min of heating time. This condition yielded the rGO black aqueous suspension with the high quality and stability. Thus, this method of synthesis has an advantage of the rGO dispersion which led to many potential applications.

Study of structural and optical properties of low temperature photo-activated ZnO-rGO composite thin film

Zinc oxide-reduced graphene oxide (ZnO-rGO) nanocomposite thin films were fabricated by dip-coating various substrates with a homogeneous dispersion of graphene oxide powder in a sol-gel derived ethanolic solution of zinc acetate and subsequent photo-annealing with deep-ultraviolet radiation. For comparison, ZnO thin films and ZnO-rGO thin films thermally annealed at 500°C were also prepared. The low temperature deep-ultraviolet irradiation resulted in crystallization of ZnO and reduction of graphene oxide which was confirmed by x-ray diffraction and Raman spectroscopy. Moreover, the Raman spectra also revealed that the reduction degree of graphene oxide was highest for deep-ultraviolet irradiated ZnO-rGO thin film. These results show that photo-chemical activation by deep-ultraviolet irradiation provides a low temperature, environment friendly technique to make ZnO-rGO thin films and can be used to fabricate semiconductor-graphene composite thin films on flexible substrates.