Functional Groups Of Graphene Oxide Research Articles

Investigation of water-oil separation via graphene oxide membranes: A molecular dynamics study

Recently, graphene oxide has been widely used for the extraction of hydrocarbon compounds. In the present work, the separation of water from a water-oil mixture by two-layer graphene oxide has been studied using molecular dynamics simulation. Several interlayer spacing of graphene oxide layers was considered, and for each gap in each layer of graphene oxide, several sizes were considered and it was determined the efficient interlayer distance as well as gap size which gives highest water-oil separation. The simulation results unveil that as the interlayer spacing and the size of the gap is reduced, the flux and permeability of the water molecules decrease, but the amount of water molecules separating from the oil increases. To study the number of layers’ impact for higher separation efficiency, a system containing a graphene oxide layer was also studied and the importance of the number of graphene layers was highlighted. Also, for the analysis of graphene oxide functional groups’ effect on separation, a system containing graphene layers was also investigated and the role of functional groups was revealed in hydrogen bond formation between graphene oxide and water molecules. By calculating PMF, the effect of functional groups on the repelling oil molecules from the graphene oxide’s gaps was investigated.

Synthesis and characterization of the thermally reduced graphene oxide in argon atmosphere, and its application to construct graphene paste electrode as a naptalam electrochemical sensor

New insight into the preparation of sensitive carbon–based electrochemical electrode is provided by examining the properties of thermally reduced graphene oxide (TRGO). In this paper, TRGO was prepared by thermal reduction of graphene oxide (GO) in argon atmosphere, and characterized by Fourier transform infrared (FTIR) spectroscopy, transmission electron microscopy (TEM), selected area electron diffraction (SAED), and atomic force microscopy (AFM). Results showed that thermal reduction in argon was effective to remove oxygen-containing functional groups in GO, and graphene sheets were obtained. Furthermore, TRGO was used to prepare thermally reduced graphene oxide paste electrode (TRGOPE) which showed excellent conductivity and fast electron transfer kinetics confirmed by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV). The electrode was applied to determination of the pesticide naptalam (Nap) in square–wave voltammetric (SWV) mode. The corresponding current at approx. +1.0 V increased linearly with the Nap concentration within two linear dynamic ranges (LDR) of 0.1–1.0 μmol L−1 (LDR1) and 1.0–10.0 μmol L−1 (LDR2). The limits of detection (LOD) and quantification (LOQ) for Nap were calculated as 0.015 μmol L−1 and 0.051 μmol L−1, respectively. In comparison to the carbon paste electrode (CPE) the results showed that the TRGOPE possesses advantages in terms of linearity, sensitivity and detectability.

Preparation of Polydopamine-Modified Graphene Oxide/Chitosan Aerogel for Uranium(VI) Adsorption

The relatively low density of functional groups of graphene oxide (GO) and the difficulty to completely recover after adsorption limit its application in uranium (U(VI)) removal from aqueous soluti...

Determination of the crucial functional groups in graphene oxide for vanadium oxide nanosheet fabrication and its catalytic application in 5-hydroxymethylfurfural and furfural oxidation

Abstract Graphene oxide (GO) sheets are emerging as a new class of carbocatalyst, and also a perfect platform for metal-oxide catalyst assembling. The oxygen groups on either side of GO basal plane can be functioned as the anchor by employing GO as scaffolds. Vanadium-oxo nanosheets (VON) were assembled onto the surface of GO material from homogeneously dissolved VO(acac)2 solution via a facile route. Control experiments with different methods prepared graphene materials illustrate the nucleation and fabrication process of VON on GO surface with detailed TEM and XPS investigation. The evolution of oxygen groups in graphene material was also investigated. Hydroxyl/epoxy in GO sheets was considered to be important and favorable for the fabrication of VON on GO surface. The developed material was shown to be an efficient and recyclable heterogeneous catalyst for aerobic oxidation of 5-hydroxymethyfurfural (HMF) and furfural into maleic anhydride. Up to 90.9% yield of maleic anhydride from HMF and 59.9% from furfural were achieved under optimized reaction conditions, the reaction rate difference between HMF and FAL was studied on the basis of oxidation mechanism and their molecular structures.

Insight into hydrogen bonds and characterization of interlayer spacing of hydrated graphene oxide.

The number of hydrogen bonds and detailed information on the interlayer spacing of graphene oxide (GO) confined water molecules were calculated through experiments and molecular dynamics simulations. Experiments play a crucial role in the modeling strategy and verification of the simulation results. The binding of GO and water molecules is essentially controlled by hydrogen bond networks involving functional groups and water molecules confined in the GO layers. With the increase in the water content, the clusters of water molecules are more evident. The water molecules bounding to GO layers are transformed to a free state, making the removal of water molecules from the system difficult at low water contents. The diffuse behaviors of the water molecules are more evident at high water contents. With an increase in the water content, the functional groups are surrounded by fewer water molecules, and the distance between the functional groups and water molecules increases. As a result, the water molecules adsorbed into the GO interlamination will enlarge the interlayer spacing. The interlayer spacing is also affected by the number of GO layers. These results were confirmed by the calculations of number of hydrogen bonds, water state, mean square displacement, radial distribution function, and interlayer spacing of hydrated GO. Graphical Abstract This work research the interaction between GO functional groups and confined water molecules. The state of water molecules and interlayer spacing of graphene oxide were proved to be related to the number of hydrogen bonds.

Observation of negative differential resistance in mesoscopic graphene oxide devices

The fractions of various functional groups in graphene oxide (GO) are directly related to its electrical and chemical properties and can be controlled by various reduction methods like thermal, chemical and optical. However, a method with sufficient controllability to regulate the reduction process has been missing. In this work, a hybrid method of thermal and joule heating processes is demonstrated where a progressive control of the ratio of various functional groups can be achieved in a localized area. With this precise control of carbon-oxygen ratio, negative differential resistance (NDR) is observed in the current-voltage characteristics of a two-terminal device in the ambient environment due to charge-activated electrochemical reactions at the GO surface. This experimental observation correlates with the optical and chemical characterizations. This NDR behavior offers new opportunities for the fabrication and application of such novel electronic devices in a wide range of devices applications including switches and oscillators.

Novel application of graphene oxide to improve hydrophilicity and mechanical strength of aramid nanofiber hybrid membrane

The synergy effect of nano-materials with composite membrane has provided numerous opportunities to strengthen the performance of the membrane in all-around research territories. Previous studies have demonstrated that bulk aramid macroscale fibers can be effectively split into aramid nanofibers (ANFs) by dissolution in dimethylsulfoxide (DMSO) in the presence of potassium hydroxide (KOH). Addressed herein is a facile and low-cost approach to endow hydrophobic Kevlar nanofiber membranes with reliable hydrophilicity and improved mechanical strength. Introduction of Graphene oxide (GO) into the structure of ANFs membranes was realized through π-π stacking interactions and aramid nanofiber-graphene oxide (ANFGs) hybrid membranes contained gradient concentrations of GO with enhanced hydrophilicity and mechanical strength were synthesized. The structure, composition and mechanical properties of hybrid membranes were characterized by FT-IR, XRD, SEM and Universal pull machine. Within the range of GO loadings assessed in this work, it was found that the ANFGs with GO 0.75 wt.% and 1.0 wt.% provide optimal potentiation both on tensile strength (377 ± 3 MPa) and Young’s modulus (18.36 ± 0.87 GPa). The hydrophilicity of the ANFGs membranes was assessed by water contact angle measurements which showed that medium GO content (1 wt.%) result in the most hydrophilic coating with the lowest contact angle of 53 ± 0.4°. ANFGs hybrid membranes offered not only remarkable mechanical performance, but also better hydrophilicity which should be due to abundant functional groups in GO, indicating great potential of such membranes in water industry.

Excellent Tribological Properties of Lower Reduced Graphene Oxide Content Copper Composite by Using a One-Step Reduction Molecular-Level Mixing Process.

Reduced graphene oxide (RGO) composite copper matrix powders were fabricated successfully by using a modified molecular-level mixing (MLM) method. Divalent copper ions (Cu2+) were adsorbed in oxygen functional groups of graphene oxide (GO) as a precursor, then were reduced simultaneously by one step chemical reduction. RGO showed a distribution converting from a random to a three-dimensional network in the copper matrix when its content increased to above 1.0 wt.% The tribological tests indicated that the friction coefficient of the composite with 1.0 wt.% RGO decreased markedly from 0.6 to 0.07 at an applied load of 10 N, and the wear rate was about one-third of pure copper. The excellent tribological properties were attributed to a three-dimensional and uniform distribution, which contributes to improving toughness and adhesion strength.

Synthesis of fluorinated graphene oxide by using an easy one-pot deoxyfluorination reaction

The fluorination of two types of graphene oxides conducted by an easy and scalable deoxyfluorination reaction is reported. This reaction was carried out using diethylaminodifluorosulfinium tetrafluoroborate, a stable compound and an efficient reagent for replacing oxygenated functional groups of graphene oxide by fluoride. The graphene oxide produced by the Hummers’ method (GOH) showed lower reactivity than that produced by the Brodie’s method (GOB). X-ray photoelectron spectroscopy indicated that the highest fluorination degree achieved was 4.7 at.% when GOB was used, and the CF character corresponds to semi-ionic bonds. Additionally, a partial reduction of GO was concomitant with the functionalization reaction. The deoxyfluorination reaction changed the crystalline structure of GO, favoring the reconstruction of Csp2 structure of the graphene lattice and reducing the number of stacked layers. The fluorination led to the modification of the electronic band structure of this material, increasing the band gap from 2.05 eV for GOB to 3.88 eV for fluorinated GOB, while for GOH the low flurionation led to a slight increase of the band gap, from 3.48 eV to 3.57 eV.

Solution-processed highly adhesive graphene coatings for corrosion inhibition of metals

The corrosion of metals can be induced by different environmental and operational conditions, and protecting metals from corrosion is a serious concern in many applications. The development of new materials and/or technologies to improve the efficiency of anti-corrosion coatings has attracted renewed interest. In this study, we develop a protective coating composed of a bilayer structure of reduced graphene oxide (RGO)/graphene oxide (GO) applied to Cu plates by spray-coating and subsequent annealing. The annealing of the GO/Cu plates at 120 °C produces a bilayer structure of RGO/GO by the partial reduction of the spray-coated GO layer. This induces superior corrosion resistance and adhesion strength compared to those of GO/Cu and RGO/Cu plates because of the hydrophobic nature of the RGO surface exposed to the surroundings and the formation of Cu–O bonds with the O-based functional groups of GO. This approach provides a viable and scalable route for using graphene coatings to protect metal surfaces from corrosion.

Pore channel surface modification for enhancing anti-fouling membrane distillation

Membrane surface modification by forming a functional layer is an effective way to improve the anti-fouling properties of membranes; however, the additional layer and the potential blockage of bulk pores may increase the mass transfer resistance and reduce the permeability. In this study, we applied a novel method of preparing anti-fouling membranes for membrane distillation by dispersing graphene oxide (GO) on the channel surface of polyvinylidene fluoride membranes. The surface morphology and properties were characterized by scanning electron microscopy, atomic force microscope, and Fourier transform infrared spectrometry. Compared to the membrane surface modification by nanoparticles (e.g. SiO2), GO was mainly located on the pore surface of the membrane bulk, rather than being formed as an individual layer onto the membrane surface. The performance was evaluated via a direct-contact membrane distillation process with anionic and cationic surfactants as the foulants, separately. Compared to the pristine PVDF membrane, the anti-fouling behavior and distillate flux of the GO-modified membranes were improved, especially when using the anionic surfactant as the foulant. The enhanced anti-fouling performance can be attributed to the oxygen containing functional groups in GO and the healing of the membrane pore defects. This method may provide an effective route to manipulate membrane pore surface properties for anti-fouling separation without increasing mass transfer resistance.

Graphene oxide as a water transporter promoting germination of plants in soil

Graphene oxide (GO) is a graphene derivative bearing various oxygen-containing functional groups attached to the basal plane and to the edges of the graphene lattice and hence has a unique structure in which numerous hydrophobic sp2 clusters are isolated within the hydrophilic sp3 C–O matrix. In this study, the hydrophilic nature and water-transporting properties of GO were exploited to promote germination and growth of plants. It was found that a low dose of GO significantly promoted the germination of spinach and chive in soil. The oxygen-containing functional groups of GO collected water, and the hydrophobic sp2 domains transported water to the seeds to accelerate the germination of plants. The strong interaction between GO and the surfaces of soil grains stabilized GO in the soil and prevented dissipation of GO. In addition, no GO was detected either on the surface or inside the cells of plants; this finding confirmed that GO was not phytotoxic. Therefore, GO may serve as a promising nontoxic additive to increase a plant yield.

Poly (vinyl alcohol) supported thermally reduced graphene oxide (TRGO) nanosheets exhibit enhanced electrical and mechanical behavior

In the present work thermally reduced graphene oxide was reinforced into polyvinyl alcohol (PVA) film by the solution cast method. The structural and morphological characterization of prepared nanocomposite materials was done using Fourier transform infrared (FTIR), X-ray diffraction (XRD), and Raman spectroscopy, scanning electron microscopy(SEM), field emission gun-transmission electron microscopy (FEG-TEM) and atomic force microscopy (AFM) techniques. The microscopic observations revealed by the SEM and TEM suggested for complete dispersion of thermally reduced graphene oxide (TRGO) into the PVA film. The XRD studies of nanocomposite revealed an enhanced crystallinity in comparison to the native PVA film. The thermal reduction process enabled homogenous dispersion of reduced graphene oxide sheets and improved the electrical conductivity of nanocomposites due to their low damage level of conjugate-structures. As a result, the percolation threshold of PVA-TRGO nanocomposites was ∼0.189 wt% which is lower than the presently reported one (2 to 10 wt%). At the TRGO content of 2 wt%, the electrical conductivity of PVA-TRGO nanocomposite reached from 0.2491 to 0.2631Scm−1. The enhancement mechanism of the composite was explained by the existence of multi-hydrogen bonds between the hydroxyl (-OH) groups of PVA and oxygen-containing functional groups of graphene oxide (GO). The AC electrical conductivity and mechanical studies results indicated that the performance of nanocomposites was significantly improved as compared to the native PVA and offered the possibilities to use the prepared nanocompsoite films to be used in electronic devices.

The effect of oxygen–containing functional groups on the H2 adsorption of graphene–based nanomaterials: experiment and theory

The oxygen–containing functional groups of graphene oxide (GO) play an important role in hydrogen storage. In addition to the contribution of the specific surface area and micro–porous porosity, the interactions of the functional groups with H2 molecules are also an important factor in the aspect of GO hydrogen storage. This paper explores the oxygen–containing functional groups affecting the hydrogen physisorption capacity of the GO and reduced graphene oxide (RGO) by experimental H2 adsorption measurement and theoretical calculation. Experimental results related to synthesis of GO and RGO via the modified Hummer's method and characterized using SEM, TEM, SAED, XRD, FTIR, TGA and Raman spectroscopy, are presented. Compared with RGO, the surface and edge of GO contain a large amount of oxygen–containing functional groups and its specific surface area is slightly increased through BET measurement. GO is found to exhibit better H2 uptake capacity (0.74 wt%) as compared to RGO (0.47 wt%) at 77 K and pressure up to 10 bars. The density functional theory is applied to optimize the adsorption configurations of H2 on the surface of samples. Calculation results show that the adsorption on the GO can be promoted by surface functional groups epoxy, hydroxyl, carboxyl and carbonyl; the enhancement of hydroxyl is greater than other species on the surface and the maximal adsorption energy reaches to −0.112 eV which is about twice that of graphene. As indicated above, these functional groups could be formed easily on the graphene surface, which not only enhance specific surface area and interlayer spacing, but also significantly change the location of carbons, redistributing the electron structure of graphene and enhancing the adsorption energy.

In situ growth of hexagonal-shaped α-Fe2O3 nanostructures over few layered graphene by hydrothermal method and their electrochemical performance

A simple in situ hydrothermal method was developed to anchor α-Fe2O3 (hematite) on reduced graphene oxide (rGO) surfaces. The impact of functional groups of graphene oxide (GO) and the coordination between metal and carbonyl group was studied by Fourier transform infrared spectroscopy. The crystallographic structure of the hybrid composite material was examined by X-ray diffraction (XRD) analysis. The microscopic images indicate the decoration of Fe2O3 nanostructures with an average size of 35–40 nm were encapsulated in rGO sheets. The XPS and Raman spectroscopy results further corroborate that α-Fe2O3 is successfully formed on the rGO matrix, which is in good accordance with XRD results. The presence of α-Fe2O3 nanostructures between the graphene layers avoids the restacking efficiently and increases the surface area accessibility. α-Fe2O3/rGO nanocomposites modified electrode exhibits 894 F g−1 specific capacitance at a current density of 0.5 A g−1 in 1 M H2SO4 electrolyte. Furthermore, these trouble-free and cost effectively-prepared hierarchical materials showed high rate capability and excellent cycle stability.

Graphene oxide encapsulated in alginate beads for enhanced sorption of uranium from different aquatic environments

Single step sol gel method was used for synthesising new generation hybrid material (Cal-Alg-GO beads) by impregnating graphene oxide (GO) in calcium alginate (Cal-Alg). The optimum composition of the hybrid material was 8% loading of graphene oxide into 4% Ca-alginate matrix. Although alginate itself have tendency for uranium uptake from aquatic medium, impregnation of GO enhanced it several times. Uptake studies were carried out in batch mode and the Cal-Alg-GO beads were found to be highly efficient for uranium decontamination (>90%) in the pH range of 4–5. Beads were successfully tested for uptake of uranium from groundwater/river water/lake water. Sorption isotherm was seen to follow Langmuir model (R2 = 0.98) and the uptake capacity evaluated was 29.4 mg g−1. Mechanism of sorption was proposed based on the zeta potential values of the GO and presence of various species of uranium at different pH. High sorption of uranium was attributed to the interaction of oxygen containing functional groups of GO with positively charged species of uranium while the negatively charged functional groups of alginate further enhanced the sorption.

Analiza površinskih funkcionalnih grupa termički redukovanog grafen oksida metodom temperaturski programirane desorpcije

In this paper the influence of thermal reduction on oxygen functional groups of graphene oxide, synthesized by modified Hummer's method, has been investigated. The graphene oxide was characterized by X-ray diffraction analysis, ultraviolet-visible spectroscopy, scanning and transmission electron microscopy. Atomic force microscopy was used for thickness analysis of graphene oxide layers before and after of thermal reduction. Changes in surface functional groups of thermally reduced graphene oxide were monitored by temperature programmed desorption method (TPD). TPD analysis of the samples showed removal of surface groups whose stability range is below temperature of the thermal reduction. It was shown that thermal reduction at 300 °C induces desorption of epoxy, alkoxy and carboxyl groups as well as carbonyl groups prone to transformation to α-substituted ketones and aldehydes. Similarly, thermal reduction at 600 °C is capable of desorbing carboxylic anhydrides. TPD analysis of samples recorded certain period of time after thermal reduction showed partial restoring of surface oxygen groups with time.

Selective Reduction of Oxygen Functional Groups to Improve the Response Characteristics of Graphene Oxide-Based Formaldehyde Sensor Device: A First Principle Study

This paper presents a density functional theory-based first principle study to investigate the atomic-scale interactions of formaldehyde (H2CO) molecules with different oxygen containing functional groups of graphene oxide to identify which particular functional group possesses better adsorption capability toward H2CO molecule. The detailed study on formaldehyde adsorption has been conducted in terms of changes in structural, energetic, electronic, and transport properties of graphene oxides modeled with sp3 hybridized hydroxyl (-OH) and epoxy (C-O-C) groups on the carbon basal plane. Our computational results suggest that the graphene oxidized with only -OH group shows the highest affinity toward formaldehyde as compared with epoxy oxidized graphene and graphene oxide containing both the functional groups. The influence of vacancy defect on improving the sensing response of graphene oxide has also been studied. The results of current–voltage ( ${I}$ – ${V}$ ) characteristics reveal that graphene oxidized with only hydroxyl group can achieve an improvement in sensitivity by almost two times and five times as compared with graphene oxide containing both the functional groups and the pristine graphene sheet, respectively. Moreover, the selectivity test for some common indoor air pollutants was also carried out and the test results suggest that H2CO molecule is highly selective toward the -OH group of graphene oxide as compared with the epoxy group.

General Synthesis of Transition-Metal Oxide Hollow Nanospheres/Nitrogen-Doped Graphene Hybrids by Metal-Ammine Complex Chemistry for High-Performance Lithium-Ion Batteries.

We present a general and facile synthesis strategy, on the basis of metal-ammine complex chemistry, for synthesizing hollow transition-metal oxides (Co3 O4 , NiO, CuO-Cu2 O, and ZnO)/nitrogen-doped graphene hybrids, potentially applied in high-performance lithium-ion batteries. The oxygen-containing functional groups of graphene oxide play a prerequisite role in the formation of hollow transition-metal oxides on graphene nanosheets, and a significant hollowing process occurs only when forming metal (Co2+ , Ni2+ , Cu2+ , or Zn2+ )-ammine complex ions. Moreover, the hollowing process is well correlated with the complexing capacity between metal ions and NH3 molecules. The significant hollowing process occurs for strong metal-ammine complex ions including Co2+ , Ni2+ , Cu2+ , and Zn2+ ions, and no hollow structures formed for weak and/or noncomplex Mn2+ and Fe3+ ions. Simultaneously, this novel strategy can also achieve the direct doping of nitrogen atoms into the graphene framework. The electrochemical performance of two typical hollow Co3 O4 or NiO/nitrogen-doped graphene hybrids was evaluated by their use as anodic materials. It was demonstrated that these unique nanostructured hybrids, in contrast with the bare counterparts, solid transition-metal oxides/nitrogen-doped graphene hybrids, perform with significantly improved specific capacity, superior rate capability, and excellent capacity retention.

Enhanced electrocapacitive performance for the supercapacitor with tube-like polyaniline and graphene oxide composites

Polyaniline (PANI) is one of the most attractive materials for pseudocapacitors. To enhance the electrolyte diffusion and improve the electrochemical performance of the electrode, the well-designed morphology of PANI is required. Incorporating carbon materials is also benefic on enhancing the cycling stability as well as the mechanical and electrochemical properties of PANI. In this study, a simple solution method is applied to synthesize the particle-deposited tube-like PANI. Due to the well-defined structure, a specific capacitance (CF) of 437.8 F/g is achieved at the current density of 4 A/g. Furthermore, the self-synthesized graphene oxide (GO) is simply mixed with the particle-deposited tube-like PANI to make a more efficient electrocapacitive material. An enhanced CF value of 475.0 F/g is achieved for the optimized PANI/GO electrode, owing to the synergic effects of the pseudo-capacitance from PANI and the functional groups of GO, as well as the electrochemical double-layered capacitance from GO. After conducting 2000 cycles repeated charge/discharge process, the CF retention of 90% and the average Coulombic efficiency of higher than 90% are also attained for the optimized PANI/GO electrode.