Understanding the Bonding Nature of Uranyl Ion and Functionalized Graphene: A Theoretical Study

Preparation and modification mechanism analysis of graphene oxide modified asphalts

Adsorption is widely regarded as the most promising method for uranium extraction. Among the various materials that have been studied, graphene oxide (GO) has attracted intensive interest because of its large specific surface area and abundant oxygen-containing functional groups. However, the layers tend to aggregate owing to pronounced Van der Waals forces, which reduce the surface area and diminish the likelihood of contact between uranyl ions and adsorption sites. Graphite oxide is an intermediate product of GO, with a simple preparation process and low cost. In this study, graphite oxide nanosheets (GONs) were synthesized using graphite oxide powder as the raw material and the NaOH activation method. GONs possessed a larger specific surface area and more carboxyl groups, which resulted in an excellent uranium adsorption capacity. The maximum adsorption capacity was found to be 578.0 mg·g−1, and the adsorption rate was 90.8% within 30 min. The adsorption process closely resembled the pseudo-second-order model and the Langmuir model. The mechanism of uranium adsorption by GONs was the synergistic coordination of -COOH and -OH with U(VI). This research suggests that the novel uranium adsorbent GONs can be applied to efficiently capture U(VI) from radioactive wastewater.

Theoretical insights into origin of graphene oxide acidity and relating behavior of oxygen-containing groups in water

A bioinspired method was used to synthesise graphene oxide (GO) based noble metal (Au) nanocomposite (GO/Au nanocomposite) using chemical exfoliated graphene oxide as the base matrix and biosynthesised gold (Au) nanoparticles. The morphological characterization of GO and the GO/Au nanocomposite was determined using TEM and SEM analysis. The amount of Au nanoparticles conjugated with GO was determined using an EDAX analysis. The absorption and emission properties of GO and GO/Au nanocomposite are revealed through optical studies. FTIR analysis revealed the presence of different functional groups in GO and GO/Au nanocomposite, while XRD analysis confirmed the formation of crystalline GO and GO/Au nanocomposite of different sizes. TGA analysis was used to determine the degradation behaviour of the two products with respect to temperature. An LCR analysis was used to characterise the electrical characteristics of GO dielectric features as a function of frequency between 1 Hz and 1 MHz. The dielectric permittivity and electrical conductivity of GO were very frequency-driven. The results demonstrated that GO has direct current and correlated barrier hopping conductivity processes in the low and high frequency bands. The dielectric constant and loss factors of the GO/Au nanocomposite show that the bioinspired approach includes organic macromolecules capable of modest GO reduction and so modifying the C/O ratio, resulting in an enhancement in the matrix's dielectric characteristics. This study further demonstrates that high-performance electronic devices, as well as electrical and energy storage systems based on high dielectrics, might be scaled using GO-based materials.

Graphene oxide incorporated functional materials: A review

We investigate the role of structure and chemical composition on the uptake of poly(ethylene oxide) by a series of graphite oxides (GOs) and thermally reduced GOs, leading to the formation of polymer-intercalated GO and polymer-adsorbed graphene nanostructures. To this end, a series of poly(ethylene oxide) (PEO) - GO hybrid materials exhibiting a variable degree of GO oxidation and exfoliation has been investigated in detail using a combination of techniques including X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetry, scanning-electron microscopy, and nitrogen adsorption. Intercalation of the polymer phase into well-defined GO galleries is found to correlate well with both the degree of GO oxidation and with the presence of hydroxyl groups. The latter feature is an essential prerequisite to optimize polymer uptake owing to the predominance of hydrogen-bonding interactions between intercalant and host. Unlike the bulk polymer, these intercalation compounds show neither crystallisation nor glass-transition associated with the polymer phase. Exfoliation and reduction of GO result in high-surface-area graphene layers exhibiting the highest polymer uptake in these GO-based materials. In this case, PEO undergoes surface adsorption, where we observe the recovery of glass and melting transitions associated with the polymer phase albeit at significantly lower temperatures than the bulk.

Lithium – sulfur (Li-S) battery, with highest predicted theoretical capacity of ~1675 mAh/g, is a promising technology meeting the demands of next-generation electric vehicles. Abundance of sulfur and environmental friendliness are major factors that make Li-S batteries interesting and important. However, Li-S battery is plagued by its own limitations, which include low electrical conductivity of pure sulfur cathode and loss of active material due to dissolution of intermediate polysulfides from the cathode during reduction reactions. These factors limit the performance of Li-S batteries. Developing superior cathode structures to mitigate these problems has been the major focus of research in recent times. Carbon-based materials such as fibers, nanospheres and nanotubes embedded with sulfur are being explored as cathodes for Li-S batteries. In particular, graphene, which has superior electrical conductivity and mechanical flexibility, has been studied as potential candidate for cathodes and cathode supports in Li-S batteries. However, economical synthesis of pure graphene is a major hurdle for their use in commercially-viable Li-S batteries. Graphene oxide – sulfur composite based structures are viable alternatives that could provide required electrical conductivity, based on the concentration of functional groups (epoxy and hydroxyl). Additionally, graphene oxides are believed to act like anchors to sulfur/polysulfides particles and help reduce their dissolution, leading to significantly improved performance of Li-S batteries. However, leveraging the advantages of enhanced electrical conductivity and reduced polysulfide shuttle requires tuning of the functional groups present in the graphene oxide. In an effort to determine the most favorable graphene oxide structure, we performed molecular dynamics (MD) simulations to calculate the mobility of polysulfide species in the vicinity of different graphene oxide structures with varying concentration of functional groups. Diffusion coefficients of polysulfides were calculated along the surface of these graphene oxide sheets using MD simulations. Initially graphene oxide sheets with pure epoxy and hydroxyl functional groups were simulated. Partial charge on carbon atoms in graphene oxide with epoxy and hydroxyl groups were evaluated from the optimized structures obtained using Density Functional Theory (DFT) calculations. Bond, angle and dihedral parameters along with partial charges on sulfur particles in polysulfides S8 2- were evaluated from the optimized structure using DFT. A standard electrolyte DME – DOL in 1:1 v/v ratio, modeled using OPLS force filed parameters, was used in all the MD simulations. The density of equilibrated solvent was within 5% of the experimental value. A system comprising graphene oxide solvated with electrolyte containing polysulfides was simulated at 300K. Overall charge neutrality of the system was maintained by incorporating counter ions, while using specific strategy to screen out long range electrostatic interactions between the polysulfides and counter ions. The surface diffusion coefficients of polysulfide was evaluated in the vicinity of graphene oxide and compared to that near pure graphene. Our simulations evaluated the effectiveness of various groups in reducing dissolution of polysulfides. The concentration of polysulfides in the vicinity of the graphene/graphene oxide structures tend to increase from graphene to graphene oxide with pure epoxy groups and maximizes for graphene oxide with pure hydroxyl functional groups. The relatively greater binding of polysulfides to graphene oxide structures leads to reduced surface diffusion coefficients for polysulfides on graphene oxide compared to that near graphene interfaces.

Reducing and chemically functional modification of graphene oxide (GO) has attracted much attention in nanomaterial fields due to the outstanding properties of the graphene. In this article, water, a low cost and environmentally friendly reduction agent, to reduce selectively GO to form reduced GO (rGO) was applied, followed by modifying rGO with functional monomer octadecylamine (ODA), and subsequently polypropylene (PP) based nanocomposites containing functional graphene were fabricated via masterbatch‐melt blending technique. The effects of reduction and functionalization on the microstructural and chemical–physical properties of GO were investigated comparatively by using X‐ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and X‐ray photoelectron spectroscopy (XPS). The dispersibility of functional graphene before and after reduction was verified by using various agents. The experimental results showed that GO has been reduced selectively by water. Functional monomer ODA has been grated successfully on the surface of rGO and GO. The prepared graphene/PP nanocomposites were characterized by using Differential scanning calorimetric (DSC), XRD, scanning electron microscope (SEM), tensile, and impact tests. The results showed that the crystallization temperature (Tc) and melting temperature (Tm) of PP in the nanocomposites increased when the functional graphene was incorporated. The functional graphene has been dispersed uniformly in the PP matrix. Tensile tests showed that rG‐ODA could improve the tensile strength and elastic modulus of composites more effectively than G‐ODA. But G‐ODA was more effectively in improving the toughness of PP than rG‐ODA, as indicated by impact tests. POLYM. COMPOS., 38:E221–E228, 2017. © 2015 Society of Plastics Engineers

Preparation of β-cyclodextrin/graphene oxide and its adsorption properties for methylene blue

Graphene oxide (GO)-based materials offer great potential for biofunctionalization with applications ranging from biosensing to drug delivery. Such biofunctionalization utilizes specific functional groups, typically a carboxyl moiety, as anchoring points for biomolecule. However, due to the fact that the exact chemical structure of GO is still largely unknown and poorly defined (it was postulated to consist of various oxygen-containing groups, such as epoxy, hydroxyl, carboxyl, carbonyl, and peroxy in varying ratios), it is challenging to fabricate highly biofunctionalized GO surfaces. The predominant anchoring sites (i.e., carboxyl groups) are mainly present as terminal groups on the edges of GO sheets and thus account for only a fraction of the oxygen-containing groups on GO. Herein, we suggest a direct solution to the long-standing problem of limited abundance of carboxyl groups on GO; GO was first reduced to graphene and consequently modified with only carboxyl groups grafted perpendicularly to its surface by a rational synthesis using free-radical addition of isobutyronitrile with subsequent hydrolysis. Such grafted graphene oxide can contain a high amount of carboxyl groups for consequent biofunctionalization, at which the extent of grafting is limited only by the number of carbon atoms in the graphene plane; in contrast, the abundance of carboxyl groups on "classical" GO is limited by the amount of terminal carbon atoms. Such a graphene platform embedded with perpendicularly grafted carboxyl groups was characterized in detail by X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy, and its application was exemplified with single-nucleotide polymorphism detection. It was found that the removal of oxygen functionalities after the chemical reduction enhanced the electron-transfer rate of the graphene. More importantly, the introduction of carboxyl groups promoted a more efficient immobilization of DNA probes on the electrode surface and improved the performance of graphene as a biosensor in comparison to GO. The proposed material can be used as a universal platform for biomolecule immobilization to facilitate rapid and sensitive detection of DNA or proteins for point-of-care investigations. Such reactive carboxyl groups grafted perpendicularly on GO holds promise for a highly efficient tailored biofunctionalization for applications in biosensing or drug delivery.

Graphene oxide (GO), an up-and-coming material rich in oxygenated groups, shows much promise in pollution management. GO is synthesised using several synthetic routes, and the adsorption behaviour of GO is investigated to establish its ability to remove the heavy-metal pollutants of lead and cadmium ions. The GO is synthesised by Hummers' (HU), Hofmann's (HO) and Staudenmaier's (ST) methodologies. Characterisation of GO is performed before and after adsorption experiments to investigate the structure-function relationship by using Fourier-transform infrared spectroscopy and X-ray photoelectron spectroscopy. Scanning electron microscopy coupled with elemental detection spectroscopy is used to investigate morphological changes and heavy-metal content in the adsorbed GO. The filtrate, collected after adsorption, is analysed by inductively coupled plasma mass spectrometry, through which the efficiency and adsorption capacity of each GO for heavy-metal-ion removal is obtained. Spectroscopic analysis and characterisation reveal that the three types of GO have different compositions of oxygenated carbon functionalities. The trend in the affinity towards both Pb(II) and Cd(II) is HU GO>HO GO>ST GO. A direct correlation between the number of carboxyl groups present and the amount of heavy-metal ions adsorbed is established. The highest efficiency and highest adsorption capacity of heavy-metal ions is achieved with HU, in which the relative abundance of carboxyl groups is highest. The embedded systematic study reveals that carboxyl groups are the principal functionality responsible for heavy-metal-ion removal in GO. The choice of synthesis methodology for GO has a profound influence on heavy-metal-ion adsorption. A further enrichment of the carboxyl groups in GO will serve to enhance the role of GO as an adsorbent for environmental clean-up.

Outsole is a crucial component of a shoe’s bottom that directly contacts the ground. Comfort and durability are the most expected characteristics of outsoles. Various nanocomposites are utilized to increase the thermal stability, light weightiness, microporosity, and durability of polymeric materials. In this research, PVC soling composites were prepared using synthesized graphene oxide (GO) from a modified Hummer method. The goal is to improve physical properties like thermal stability or durability, lightweight, tensile strength, and hardness. The GO content in developed soling composites ranged from 0.1% to 0.4% by the colloidal blending method. FTIR, TGA, XRD, and SEM characterized GO and GO/PVC soling composites. The presence of the functional groups C=C, C-O-C, -C=O, and -OH was confirmed by the FTIR spectra of GO, while oxygen-holding functional groups to the layered structure caused the separation of the interlayer space to grow from 0.34 nm to 0.86 nm, according to GO XRD data. XRD results revealed that the GO layers were uniformly distributed in the polymeric matrix of composites. TGA results exhibited that the percentage of mass loss for GO was 81.96% at 800 °C and for soling composites it decreased continuously with an increase in the content of GO, respectively. SEM analysis revealed that the composites with GO showed a homogeneous composite with significantly porous surface morphology. Proportional improvement of tensile strength and hardness for GO-based soling materials were in an increased proportion and density were in a decreased proportion, making the outsole lightweight and durable. Finally, the results suggest that GO/PVC soling composites can improve the durability, mechanical and thermal stability, light weightiness, and microporosity of PVC soles, while the best performance was found for PVC/GO-0.4% soling composites.

The synthesis of graphene oxide (GO)-based benzimidazole-crosslinked network (GOBIN) materials is presented. These materials are prepared by the covalent crosslinking of GO sheets using a condensation reaction between the carboxylic acid moieties on the GO surface and the o-aminophenyl end groups of 3,3'-diaminobenzidine (or 1,2,4,5-benzenetetraamine tetrahydrochloride). An efficient one-pot catalyst- and template-free synthesis was performed. The obtained porous GO-based materials possess a Brunauer-Emmett-Teller specific surface area ranging from 260 to 920 m(2) g(-1). Electrochemical testing indicates that the GOBIN materials display a specific capacitance up to 370 F g(-1) at a current density of 0.1 A g(-1) and about 90% of the original capacitance is retained after 5000 cycles at a current density of 3 A g(-1). Therefore, GOBIN materials can be employed as promising electrode materials for high-performance supercapacitors with outstanding cycling stability. Furthermore, owing to their significantly high specific surface area, these materials also show hydrogen uptake (up to 1.24 wt%, at 77 K and 1.0 bar) and carbon dioxide capture (up to 14.2 wt%, at 273 K and 1.0 bar) properties. As a result, these GO-based porous materials improve both the supercapacitor performance and gas sorption property, which demonstrate an excellent performance in the practical application of energy storage.

Mimicking the graphene oxide structure in solutions by interaction of Fe(III) and Gd(III) with model small-size ligands. The NMR relaxation study

In order to reduce the harm of nitrous oxide (N2O) on the environment, it is very important to find an effective way to capture and decompose this nitrous oxide. Based on the density functional theory (DFT), the adsorption mechanism of N2O on the surfaces of M-decorated (M = Mg, Cu or Ag) graphene oxide (GO) was studied in this paper. The results show that the effects of N2O adsorbed onto the surfaces of Mg–GO by O-end and Cu–GO by N-end are favorable among all of the adsorption types studied, whose adsorption energies are −1.40 eV and −1.47 eV, respectively. Both adsorption manners belong to chemisorption. For Ag–GO, however, both the adsorption strength and electron transfer with the N2O molecule are relatively weak, indicating it may not be promising for N2O removal. Moreover, when Gibbs free energy analyses were applied for the two adsorption types on Mg–GO by O-end and Cu–GO by N-end, it was found that the lowest temperatures required to undergo a chemisorption process are 209 °C and 338 °C, respectively. After being adsorbed onto the surface of Mg–GO by O-end, the N2O molecule will decompose into an N2 molecule and an active oxygen atom. Because of containing active oxygen atom, the structure O–Mg–GO has strong oxidizability, and can be reduced to Mg–GO. Therefore, Mg–GO can be used as a catalyst for N2O adsorption and decomposition. Cu–GO can be used as a candidate material for its strong adsorption to N2O.