Functional Groups Of Graphene Oxide Research Articles

Desalination across a graphene oxide membrane via direct contact membrane distillation

We demonstrate the immobilization of graphene oxide on polytetrafluoroethylene (PTFE) membrane surface for desalination via direct contact membrane distillation. The graphene oxide immobilized membrane significantly enhanced the overall permeate flux with complete salt rejection, and the flux reached as high as 97kg/m2h at 80°C. We attribute this enhancement in flux to multiple factors including selective sorption, nanocapillary effect, reduced temperature polarization as well as the presence of polar functional groups in graphene oxide.

Effect of Microbes on the Adsorption of Naphthalene by Graphene Oxide

The adsorption of naphthalene on graphene oxide (GO) nanosheets in presence of Paecilomyces cateniannulatus (P. cateniannulatus) was conducted by the batch techniques. The morphology and nanostructure of GO were characterized by SEM, TEM, FTIR, XPS, and Raman. The adsorption kinetics indicated that the adsorption of naphthalene on GO and GO + P. catenlannulatus can be satisfactorily fitted pseudo-first-order and pseudo-second-order kinetic model, respectively. P. catenlannulatus inhibited the adsorption of naphthalene on GO at pH<4.0, whereas the increased adsorption was observed at pH>4.0. The adsorption of naphthalene on GO and GO + P. catenlannulatus can be better fitted by Langmuir and Freundlich model, respectively. The change in the conformation of GO was responsible to the increased adsorption of naphthalene by SEM and TEM images. According to FTIR analysis, naphthalene was absorbed by the oxygen-containing functional groups of GO, especially for –COOH. The finding in the study provides the implication for the preconcentration and removal of polycyclic aromatic hydrocarbons from environment cleanup applications.

High‐Power Supercapacitive Properties of Graphene Oxide Hybrid Films with Highly Conductive Molybdenum Disulfide Nanosheets

AbstractBy introducing a graphene oxide (GO) sheet as a phase stabilizer and a mechanical supporter, MoS2/GO hybrid films consisting of a high concentration of distorted 1T‐MoS2 are successfully fabricated through a post‐annealing process in air with the form of a restacked film. After the annealing process, the MoS2 nanosheets undergo direct binding with the oxygen functional groups of GO, maintaining their highly conducting 1T phase and leading to distorted 1T‐MoS2 or 1T′‐MoS2. A hybrid film‐based supercapacitor reveals significantly enhanced electrochemical properties, such as an ultrahigh volumetric power density (≈207 W cm−3), high volumetric capacitance (≈380 F cm−3 at 10 mV s−1), superior rate capability, and a semi‐permanent cycle life (95 % retention after 10 000 cycles) in an aqueous electrolyte.

Aggregation and Stability of Reduced Graphene Oxide: Complex Roles of Divalent Cations, pH, and Natural Organic Matter.

The aggregation and stability of graphene oxide (GO) and three successively reduced GO (rGO) nanomaterials were investigated. Reduced GO species were partially reduced GO (rGO-1h), intermediately reduced GO (rGO-2h), and fully reduced GO (rGO-5h). Specifically, influence of pH, ionic strength, ion valence, and presence of natural organic matter (NOM) were studied. Results show that stability of GO in water decreases with successive reduction of functional groups, with pH having the greatest influence on rGO stability. Stability is also dependent on ion valence and the concentration of surface functional groups. While pH did not noticeably affect stability of GO in the presence of 10 mM NaCl, adding 0.1 mM CaCl2 reduced stability of GO with increased pH. This is due to adsorption of Ca(2+) ions on the surface functional groups of GO which reduces the surface charge of GO. As the concentration of rGO functional groups decreased, so did the influence of Ca(2+) ions on rGO stability. Critical coagulation concentrations (CCC) of GO, rGO-1h, and rGO-2h were determined to be ∼ 200 mM, 35 mM, and 30 mM NaCl, respectively. In the presence of CaCl2, CCC values of GO and rGO are quite similar, however. Long-term studies show that a significant amount of rGO-1h and rGO-2h remain stable in Call's Creek surface water, while effluent wastewater readily destabilizes rGO. In the presence NOM and divalent cations (Ca(2+), Mg(2+)), GO aggregates settle from suspension due to GO functional group bridging with NOM and divalent ions. However, rGO-1h and rGO-2h remain suspended due to their lower functional group concentration and resultant reduced NOM-divalent cation bridging. Overall, pH, divalent cations, and NOM can play complex roles in the fate of rGO and GO.

열처리된 그래핀 산화물을 정공주입층으로 이용한 유기발광 다이오드

Article history: This paper reports on thermally adjusted graphene oxide (GO) as the hole transport layer (HTL) for organic light-emitting diodes (OLEDs). GO is generally not suitable for HTL of OLEDs because of intrinsic specific resistance. In this paper, the specific resistance of GO is adjusted by the thermal annealing process. The optimum specific resistance of HTL is found to be 10 2 Ω·m, and is defined by the maximum current efficiency of OLEDs, 2 cd/A. In addition, the reasons for specific resistance change are identified by x-ray photoelectron spectroscopy (XPS). First, the XPS results show that several functional groups of GO were detached by thermal energy, and the amount of epoxide changed substantially following the temperature. Second, the full width at half maximum (FWHM) of the C-C bond decreased during the process. That means the crystallinity of the graphene improved, which is the scientific basis for the change in specific resistance.

In-situ investigation of graphene oxide under UV irradiation: Evolution of work function

Using in-situ Kelvin probe force microscopy (KPFM) to measure surface potential, we investigated the time-dependent work function evolution of solution-processed graphene oxide (GO) under ultraviolet (UV) irradiation. We found that the work function of GO exposed in UV shows a notable decrease with increasing irradiation time, which is proposed to be attributed to the gradual disappearance of oxygen-containing functional groups in GO during the UV-induced reduction reaction process. Fourier transform infrared spectrum and Raman spectrum were used to confirm the reduction of GO under UV irradiation. Our study would give an insight into understanding the transformation of GO’s electronic structures during the reduction process.

Using silane-functionalized graphene oxides for enhancing the interfacial bonding strength of carbon/epoxy composites

Silane-functionalized graphene oxides (sGOs) were fabricated with four different self-assembled monolayers (SAMs) to reinforce an epoxy adhesive, with the aim of improving the bonding strength of carbon/epoxy composites. The oxygen-containing groups on the surface of graphene oxide (GO) were converted by the SAMs to amine, epoxy, or alkyl groups. The successful reaction between the silane molecules of the SAMs and functional groups of GO was evidenced by the results of different characterization methods such as Fourier transform infrared spectroscopy. It was found that the average thickness of the sGO flakes was higher than that of GO flakes. The bonding strength of a carbon fiber/epoxy composite, tested with a single lap joint bonded with an epoxy adhesive, was increased by 53% after the addition of a sGO that contained amine groups. These results show that sGOs, especially those containing amine functional groups, can strengthen the interfacial bonding between the carbon fibers and epoxy adhesive.

Role of oxygen functional groups in graphene oxide for reversible room-temperature NO2 sensing

Reduced graphene oxide (rGO) is one of the promising sensing elements for high-performance chemoresistive sensors because of its remarkable advantages such as high surface-to-volume ratio, outstanding transparency, and flexibility. In addition, the defects on the surface of rGO, including oxygen functional groups, can act as active sites for interaction with gaseous molecules. However, the major drawback of rGO-based sensors is the extremely sluggish and irreversible recovery to the initial state after a sensing event, which makes them incapable of producing repeatable and reliable sensing signals. Here, we show that pristine GO can be used as the active sensing material with reversible and high response to NO2 at room temperature. First-principles calculations, in conjunction with experimental results, reveal the critical role of hydroxyl groups rather than epoxy groups in changing metallic graphene to the semiconducting GO. We show that the adaptive motions of the hydroxyl groups, that is, the rotation of these groups for the adsorption of NO2 molecules and relaxation to the original states during the desorption of NO2 molecules, are responsible for the fast and reversible NO2 sensing behavior of GO. Our work paves the way for realizing high-response, reversible graphene-based room-temperature chemoresistive sensors for further functional convergence.

Enhanced photocatalytic properties of a novel GO-Ag-C6H5Ag3O7 nanocomposite

A novel graphene oxide-Ag-C6H5Ag3O7 nanocomposite was prepared by a facile precipitation reaction with the aid of photo-reduction. The rich surface functional groups of graphene oxide (GO) interacted with silver cations, provided the nucleation sites and induced the formation of C6H5Ag3O7 nanoparticles on the GO surface uniformly. The nanocomposite displayed an enhanced photocatalytic activity compared with pure C6H5Ag3O7 and GO under simulated sunlight, due to the reduced recombination of plasmon-induced electron–hole pairs on the Ag nanoparticles by the GO. This study likely provides one possibility of exploiting stable Ag/silver (I) complex photocatalysts in dealing with environmental contaminants.

Ultra-high dispersion of graphene in polymer composite via solvent free fabrication and functionalization.

The drying process of graphene-polymer composites fabricated by solution-processing for excellent dispersion is time consuming and suffers from a restacking problem. Here, we have developed an innovative method to fabricate polymer composites with well dispersed graphene particles in the matrix resin by using solvent free powder mixing and in-situ polymerization of a low viscosity oligomer resin. We also prepared composites filled with up to 20 wt% of graphene particles by the solvent free process while maintaining a high degree of dispersion. The electrical conductivity of the composite, one of the most significant properties affected by the dispersion, was consistent with the theoretically obtained effective electrical conductivity based on the mean field micromechanical analysis with the Mori-Tanaka model assuming ideal dispersion. It can be confirmed by looking at the statistical results of the filler-to-filler distance obtained from the digital processing of the fracture surface images that the various oxygenated functional groups of graphene oxide can help improve the dispersion of the filler and that the introduction of large phenyl groups to the graphene basal plane has a positive effect on the dispersion.

1-Aza-15-Crown-5 Functionalized Graphene Oxide for 2D Graphene-Based Li⁺-ion Conductor.

Attachment of Li(+) ion on graphene surface to realize Li(+)-ion conductor is a real challenge because of the weak interaction between the ions and the functional groups of graphene oxide; although, a large number of theoretical results are already available in the literature. To overcome this problem, graphene oxide is functionalized by 1-aza-15-crown-5, the cage-like structure containing four oxygens that can bind Li(+) ion through electrostatic interaction. Li(+) migration on graphene surface has been investigated using ac relaxation mechanism. Perfect Debye-type relaxation behavior with β (relaxation exponent) value ≈1 resulting from single ion is observed. The activation energy of Li(+) migration arising due to cation-π interaction is found to be 0.37 eV, which agrees well with recently reported theoretical value. It is believed that this study will help to design isolated ion conductors for Li(+)-ion battery.

Carbon nanostructures reduced from graphite oxide as electrode materials for supercapacitors

In this review we present information about obtaining and properties of carbon nanomaterials (graphite oxide, grapheme oxide, reduced graphene oxide), which are used as electrodes for supercapacitors (SC). This review describes methods of obtaining graphite oxide, followed by separation of graphene oxide and reducing graphene oxide by thermal, photochemical and chemical methods. Information on the composition and concentration of functional groups in graphene oxide and the elemental composition is described in detail. Results of the analysis of еру physical, electrochemical, thermal and optical properties of the graphene oxide and its derivatives are shown. The ratio of oxygen-containing functional groups was estimated by XPS. The presence of partial surface reduction is found. Hydroge-containing functional groups are characterized by IR spectroscopy. Method of estimating the size of graphene crystallites by Raman spectroscopy is shown. Mass loss upon heating is analyzed by thermogravimetry. The gassing of graphene oxide at thermal and photochemical reduction is studied by mass spectrometry. The difference between the abovementioned reduction methods is clearly demonstrated by the difference in the composition of the evolved gases. Also the chemical method of graphene oxide reduction with hydrazine is described. Review considers the literature data which illustrate the most interesting, from the Authors׳ point of view, aspects of that field of research.

外电场中单层氧化石墨烯的透射特性与成像

The recent boom in graphene oxide (GO) based sensor and optical materials requires to improve and control the GOs optoelectronic properties. It is reported here that the optical transmission and fluorescence spectra of monolayer GO can be controlled by means of external electric field. The imaging of GO under electric fields shows the absorption and emission anisotropy, the transmission and fluorescence spectra demonstrate the electrically reversible features. The polarity effects of the functional groups in GO under electric field induced changes of electronic density of localized states as well as the optical properties, meanwhile, demonstrated the electric field direction dependent polarity results.

Effects of functional groups of graphene oxide on the electrochemical performance of lithium-ion batteries

Graphene oxide (GO) with different ratios of functional groups is prepared via low temperature directional thermal reduction and re-oxidization by nitric acid.

Free-Green Synthesis and Dynamics of Reduced Graphene Sheets via Sun Light Irradiation

It is universally known that the preparation of high quality graphene on a large scale and in a cost-effective manner is essential for many technological applications. Graphene oxide (GO) has emerged as the precursor of choice for bulk production of graphene-based materials, as it can be synthesized from inexpensive graphite powders. In this paper, a simple method is described for reduction of GO solution by a free and green irradiation based technique. The majority of oxygen-containing functional groups of GO are removed by sun light. This methodology provides an effective way to quantitatively produce high quality graphene sheets. This paper presents irradiation by sun light of synthesized graphene oxide nano-flakes prepared by Hummer’s method. These nano-flakes have been successfully reduced while the dynamic of this irradiation process is discussed. The irradiated nano-flakes of graphene oxide have been investigated using X-Ray diffraction, ATR-FTIR and UV-Vis-NIR.

Influences of sodium dodecyl sulfate on vulcanization kinetics and mechanical performance of EPDM/graphene oxide nanocomposites

In this work, influence of SDS presence on the physical interactions between EPDM macromolecules and graphene oxide functional groups are investigated.

Effect of the oxygen-containing functional group of graphene oxide on the aqueous cadmium ions removal

The adsorption process of graphene oxide (GO) with oxygen-containing functional groups towards cadmium ions was investigated. GO synthesized from graphite by using the modified Hummers method was characterized by scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared spectrometer (FT-IR) and X-ray photoelectron spectroscopy (XPS). The oxygen-containing groups on the surfaces of GO played an important role in Cd(II) ion adsorption onto GO. The results of batch experiments indicated that maximal adsorption, which was found to be 23.9mg/g, could be achieved over the broad pH range of 6.0–7.0. Adsorption isotherms were better fitted by Freundlich model than by Langmuir model and kinetic studies suggested that adsorption was controlled by chemical adsorption. According to FT-IR and XPS analyses of before and after Cd(II) adsorption on GO, electrostatic attraction and cation exchange between Cd(II) and O-containing functional groups on GO were the dominant mechanisms responsible for Cd(II) sorption.

Polystyrene–graphene oxide (GO) nanocomposite synthesized by interfacial interactions between RAFT modified GO and core–shell polymeric nanoparticles

Here we report simple and robust one-pot method for the preparation of polystyrene (PS)/graphene oxide (GO) nanocomposite using reversible addition fragmentation chain transfer (RAFT) modified GO in surfactant free emulsion polymerization (SFEP). The results suggested that ionic comonomer, styrene sulfonate sodium salt (SS-Na), concentration plays vital role in forming PS/GO nanocomposite. X-ray and electron diffraction studies suggest that there is no recombination of GO sheets when moderate SS-Na concentration is used, resulting complete exfoliation of GO sheets in the PS/GO nanocomposite. The formation of core–shell particles in which PS is the core and polystyrene sulfonate sodium salt (PSS–Na) is the shell, and the specific interactions between functional groups of GO and PSS–Na are attributed as the driving forces for the PS/GO nanocomposite formation.

Facile self-assembly of magnetite nanoparticles on three-dimensional graphene oxide–chitosan composite for lipase immobilization

Three dimensional (3D) magnetic graphene oxide–chitosan (GO–CS) composites with orderly self-assembled magnetite (Fe3O4) nanoparticles (GO–CS–Fe3O4) were successfully fabricated. First, the covalent functionalization of graphene oxide (GO) using chitosan (CS) was successfully accomplished via a facile amidation process, forming a 3D network. In the as-fabricated GO–CS composites, GO sheets remained less aggregated, exhibiting a large surface area, and the interconnected pores in the hydrogels allowed object molecules to diffuse easily into the composites. Subsequently, the GO–CS–Fe3O4 composites were synthesized using FeCl3·6H2O and GO–CS composite as the starting materials through a solvothermal reaction. The resulting composite combined the features of the high surface area of GO, abundant amino, and hydroxyl functional groups of CS, and the magnetic response of magnetic nanoparticles. For further application, these composites were utilized to immobilize Candida rugosa lipase via different routes, and they showed excellent immobilization capacities.

Simultaneously functionalization and reduction of graphene oxide containing isocyanate groups

A facile and efficient approach is developed to simultaneously functionalize and reduce graphene oxide (GO) containing isocyanate groups with toluene-2,4-diisocyanate (TDI). In this approach, the reaction between some isocyanate groups of TDI and oxygen containing functional groups of GO has occurred, with the GO reducing. The result can be found that others active isocyanate groups of TDI remain upon surface of GO, and the surface of GO changes from hydrophile to hydrophobic. In order to obtain the largest amount of isocyanate groups on surface of TDI-rGO, appropriate temperature and equilibrium time of the reaction are determined to be 75°C and 5h.