Presence Of Graphene Oxide Research Articles

Allylic and Allenylic Dearomatization of Indoles Promoted by Graphene Oxide by Covalent Grafting Activation Mode.

The site-selective allylative and allenylative dearomatization of indoles with alcohols was performed under carbocatalytic regime in the presence of graphene oxide (GO, 10 wt % loading) as the promoter. Metal-free conditions, absence of stoichiometric additive, environmentally friendly conditions (H2 O/CH3 CN, 55 °C, 6 h), broad substrate scope (33 examples, yield up to 92 %) and excellent site- and stereoselectivity characterize the present methodology. Moreover, a covalent activation model exerted by GO functionalities was corroborated by spectroscopic, experimental and computational evidences. Recovering and regeneration of the GO catalyst through simple acidic treatment was also documented.

Optical Investigation of TiO2/Graphene Oxide Thinfilm Prepared by Spin Coating Technique

Titanium dioxide/graphene oxide thin films with different concentrations of (0.0, 0.015, 0.030, 0.045 and 4.5 g/ml) graphene oxide were deposited on glass substrates at room temperature using spin coating method. Thin films were characterized by UV-Vis, FTIR and Raman spectroscopy. Presence of graphene oxide was confirmed with FTIR and Raman spectroscopy, too. The optical band gap of TiO2 with the addition of graphene oxide layer initially decreases, but by increasing the concentration of graphene oxide, the optical band gap increases to 2.9eV.

Lignin-graphene oxide inks for 3D printing of graphitic materials with tunable density

Graphitic structures, unlike polymers and metals, cannot be directly printed in 3D. We demonstrate here that graphitic structures can be shaped in 3D by using direct-ink writing (DIW) of lignin-graphene oxide solutions that are then dried and carbonized. Lignin is a promising precursor for the elaboration of bio-based carbon materials because of its low cost, natural availability and high carbon content. The rheology of the inks is controlled by the presence of graphene oxide (GO) in order to make the solutions viscoelastic and printable. The GO flakes are found to align during ink extrusion. This behavior is understood by considering the applied extrusion shear stress and the yield stress of the inks. By adjusting the relative fraction of GO and lignin, it is possible to change the density, the graphitic order, and thus the electrical and mechanical properties of the printed materials. In particular, GO promotes not only graphitic order but also porosity. By contrast, high amounts of lignin allow preparing denser but less ordered carbon structures. The possibility to vary density and properties offers an opportunity for the development of graphitic 3D materials with tunable properties.

Functional DNA Structures and Their Biomedical Applications

Since the discovery of the double-helix structure in 1953, nucleic acids have been developed from natural genetic codes into functional building blocks in a wide range of biotechnology and material...

Bifunctional Electrocatalytic Activity of Ordered Intermetallics Based on Pd and Sn

Structurally ordered intermetallic compounds are proven to be very promising for electrocatalysis owing to the homogeneous distribution of active sites, thermodynamic stability, and resistance toward surface rearrangement. Herein, we demonstrate a facile route for the synthesis of Sn- and Pd-based ordered intermetallics hybridized with reduced graphene oxide (rGO) and their bifunctional electrocatalytic performance toward oxygen reduction (ORR) and ethylene glycol oxidation reactions (EGOR). The coreduction of SnCl2 and K2PdCl4 in 1,5-pentanediol in the presence of graphene oxide and the subsequent thermal annealing in an inert atmosphere affords rGO hybridized intermetallics of three phases: primitive orthorhombic PdSn, base-centered orthorhombic PdSn2, and hexagonal Pd3Sn2. The electrocatalytic performance of the hybrid intermetallics toward EGOR and ORR is evaluated in alkaline and acidic electrolytes. Among the three intermetallics, PdSn has excellent electrocatalytic performance toward EGOR and ORR. The PdSn/rGO hybrid catalyst outperforms the other two intermetallics toward EGOR in alkaline pH and ORR in acidic as well as alkaline pH in terms of onset potential and mass specific activity. The enhanced performance of PdSn/rGO catalyst is attributed to (i) a change in the Pd d-band center, (ii) a Pd–Pd interatomic distance in a unit cell, and (iii) weak adsorption of in-situ-generated oxygen-containing intermediates species. The lattice strain due to the presence of dissimilarly sized Sn and Pd in a unit cell and the high oxophilicity of Sn downshifts the d-band center of Pd and facilitate the electron transfer kinetics. The catalyst support, rGO, prevents the unwanted aggregation of the active catalyst. The density functional theory calculations show that the oxygen-containing species weakly adsorb on the PdSn surface compared to the other intermetallics, supporting the high electrocatalytic activity of PdSn/rGO.

Layered double hydroxides derived NiCo-sulfide as a cathode material for aluminum ion batteries

Aluminum-ion batteries (AIBs) is a type of emerging device for large scale energy storage. Developing new and efficient cathode materials is a hotspot in this research area. Herein, a strategy combining the layer double hydroxides (LDHs) synthesis in the presence of graphene oxide (GO) and subsequent sulfidation is developed to prepare a composite of nickel-cobalt sulfides and reduced graphene oxide (rGO). The resulting sulfurized product (S–NiCo@rGO) exhibits a high discharge capacity of 248.2 mA h g−1 at the current density of 1 A g−1 and maintains a discharge capacity of 83 mA h g−1 with nearly 100% coulombic efficiency after 100 cycles. The energy storage mechanism of this material is disclosed to be due to the substitution of Ni2+ and Co2+/Co3+ by Al3+. The material and the finding obtained in this work are significant for the development of high performance AIBs using LDH-derived materials.

Synthesis of graphene oxide-polychrysoidine nanocomposite for supercapacitor applications

Abstract In this study, a quite simple method has been represented for the fabrication of polymeric crosslinked graphene nanocomposite and examined for supercapacitance properties. Since most of the azo dyes display the conjugated structures, their contribution to enhance the conductivity and capacitance of carbon containing compounds such as graphene could be an interesting area. Therefore, in the present work, chrysoidine (CHRYS) was polymerized in the presence of graphene oxide (GO) in which the produced polychrysoidine (PCHRYS) acted as a cross linker for GO nanosheets. The optimized components ratio of GO:PCHRYS forms the efficient porous graphene oxide-polychrysoidine (GO-PCHRYS) nanocomposite which easily stores charge and represents a rather high specific capacitance of 715.3 F g−1 at the current density of 0.5 A g−1. The electrode stability was determined after 10000 cycles via comparing initial and final capacitance and the results indicated that 89.8% of the initial capacitance had been maintained .

Silicon photovoltaic cell based on graphene oxide as an active layer

This paper presents the fabrication and characterization of spin coated multilayer graphene oxide/p-silicon heterojunction solar cell. Liquid graphene oxide is synthesized from graphite sheets using electrochemical process. XRD confirms the presence of graphene oxide. Surface morphology of spin coated on graphene oxide on silicon wafer was investigated by scanning electron microscopy. The current–voltage characterization has been studied to investigate photovoltaic performance of fabricated solar cell. Further two diode model was also designed for this solar cell.

Synthesis and micromechanical properties of graphene oxide-based polymer nanocomposites

The authors have studied the effect of small (≤ 1 wt%) additions of thermally reduced graphene oxide on the microhardness and microindentation kinetics in two types of polymers: polystyrene (i.e. thermoplastic with a glass transition temperature of Tg ≈ 373 K) and polyester resin (i.e. thermosetting plastic, Tg ≈ 300 K). The room temperature creep of nanocomposites under an indenter is described using a three-element rheological Kelvin–Voigt model. The study determines the parameters of this model and how graphene oxide (GO) affects them. In a polystyrene nanocomposite with 0.3 wt % graphene oxide, unrelaxed and relaxed elastic moduli, and the modulus characterizing high-elastic deformation, increase by 11%, 40% and 87%, respectively, as compared to the initial polystyrene; at the same time, microhardness increases by 38% and 45% for the different series of samples. The results obtained indicate that the presence of graphene oxide in the nanocomposite severely restricts the mobility of molecular segments. The addition of 0.3 wt% graphene oxide to polyester resin is accompanied by an increase in the mechanical glass transition temperature of the resin by at least 5 K. This leads to a change in the relaxation state of this polymer: while at room temperature the polyester resin behaves like an elastomer, a polyester resin nanocomposite with 0.3 wt% graphene oxide exhibits glassy properties. At room temperature, the microhardness of polyester resin-glass fabric-graphene oxide nanocomposites with a GO content of 0.5 and 1 wt% increases by 20% and 80% respectively, as compared to that of a polyester resin-glass fabric composite. The authors have obtained the temperature dependences of the microhardness of nanocomposites with a polyester matrix in the range 77–298 K, and have also identified temperature regions where the microdeformation of composites is reversible, which is associated with the formation of crazes with a lower glass transition temperature.

Effects of graphene oxide on the crystallization behavior of VS55 during cooling and warming

The present work aims to investigate the crystallization behavior of VS55 in the presence of graphene oxide (GO) by Differential Scanning Calorimetry (DSC) and Cryomicroscopy system. The DSC results show that the higher GO concentration increase crystallization enthalpy Hf for 2.1 M&4.2 M VS55 but has little effects on 8.4 M VS55 during cooling processes. The recrystallization enthalpy HTd of VS55 + GO decreased with increasing concentrations of GO during warming processes significantly. Especially, when increasing both cooling and warming rates, the HTd of VS55 drops more obviously once adding higher concentration of GO, which indicates that the critical cooling rate and warming rate may be smaller for the purpose of practical application. The Cryomicroscopy results show that the crystal regrowth can be watched only for high concentration VS55 (i.e. 8.4 M) due to devitrification, and the growth rates become smaller when increasing cooling rates as well as GO concentration, which certainly confirms the results of DSC.

Space-confined iron nanoparticles in a 3D nitrogen-doped rGO-CNT framework as efficient bifunctional electrocatalysts for rechargeable Zinc–Air batteries

Abstract Transitional metal nitrogen-doped carbon catalysts are increasingly attractive due to their high bifunctional activities in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) of rechargeable zinc-air batteries. In the present work, space-confined iron nanoparticles in a 3D nitrogen-doped reduced graphene oxide-carbon nanotube (rGO-CNT) framework (Fe-NCNTs/NG) were synthesized by pyrolysis of a compound comprising urea, anhydrous ferric chloride (FeCl3) and ammonium chloride (NH4Cl) in the presence of graphene oxide (GO). Carbon nanotubes (CNTs) were grown from urea under the catalysis of iron before the pyrolysis to obtain Fe-NCNTs/NG. Nitrogen was introduced into the rGO-CNT framework from urea and NH4Cl in the pyrolysis process at a temperature of 700/800/900/1000 °C. XRD, SEM, HRTEM and XPS techniques were employed to characterize Fe-NCNTs/NG and showed iron and/or Fe3O4 nanoparticles are confined in the 3D nitrogen-doped rGO-CNT framework. The electrochemical test results demonstrate that as-prepared Fe-NCNTs/NG can conduct better catalytic performances than Pt/C and IrO2 in the aspects of a higher half-wave potential and a lower overpotential. Specifically, the best catalytic performance of Fe-NCNTs/NG was achieved when it was prepared by a 30:1 mass ratio of urea to FeCl3 and pyrolyzed at a temperature of 900 °C. Furthermore, a home-made zinc-air battery loading a Fe-NCNTs/NG electrode showed better charge-discharge stability and higher power density than a Pt/C loaded zinc-air battery. The present work demonstrates that the Fe-NCNTs/NG framework is promising to be an alternative to Pt/C and/or IrO2 in the rechargeable zinc-air battery industry.

Photoelectrochemical degradation of perfluorooctanoic acid (PFOA) with GOP25/FTO anodes: Intermediates and reaction pathways

Perfluorooctanoic acid (PFOA) have been widely studied due to their persistence, bioaccumulation and possible toxic effects. In this work, we investigated a photoelectrochemical (PEC) system consisting of a graphene oxide-titanium dioxide (GOP25) anode coated on fluorine-doped tin oxide (FTO) glass for removal of PFOA in an aquatic environment. The GOP25/FTO anode was fabricated and well characterized. Nearly complete decomposition of 0.5 mg/L PFOA was achieved after 4 h of PEC treatment with an initial pH of 5.3 and a current density of 16.7 mA cm−2. The presence of graphene oxide (GO) on the TiO2 anode could enhance its electrochemical performance, thereby leading to increased decomposition efficiency. A total of 18 PFOA transformation products, including short-chain perfluoroalkyl acids, are reported in this work, and 13 products were observed for the first time. Four possible routes of PFOA decomposition, namely, decarboxylation followed by oxidation, defluorination, hydroxylation and Cl atom substitution, were determined. The presence of chlorinated byproducts in the system indicated that reactive chlorine species contributed to PFOA degradation.

Superhigh-exfoliation graphene with a unique two-dimensional (2D) microstructure for lubrication application

Graphene being a two-dimensional (2D) nanomaterial, is highly regarded in scientific researches and industrial applications for reducing friction energy consumption and improving anti-wear durability. Excellent friction reduction and wear resistance properties can be effectively achieved by microstructural design of graphene. In this study, superhigh-exfoliation reduced graphene oxide (SRGO), synthesized in the presence of graphene oxide (GO), was thermally reduced via the activation of KOH. The SRGO nanosheets show a unique 2D microstructure with little restack and agglomeration. Particularly, SRGO has very large values of specific surface area (1665 m2/g) and of interlayer spacing (4.25 Å). The nanosheets with superhigh degree of exfoliation are studied as lubricant additives for the first time. They show excellent tribological properties, and the coefficient of friction (COF) of base oil can be reduced by 70% and the wear volume by >60%, which are mainly attributed to the unique microstructure, good self-dispersed stability and sliding-oriented transformation of SRGO. The results provide an efficient way to design the microstructure of graphene as a promising candidate for reducing consumption and saving energy.

Bottom-up Design of Bimetallic Cobalt-Molybdenum Carbides/Oxides for Overall Water Splitting.

Earth‐abundant transition‐metal‐based catalysts for electrochemical water splitting are critical for sustainable energy schemes. In this work, we use a rational design method for the synthesis of ultrasmall and highly dispersed bimetallic CoMo carbide/oxide particles deposited on graphene oxide. Thermal conversion of the molecular precursors [H3PMo12O40], Co(OAc)2 ⋅4 H2O and melamine in the presence of graphene oxide gives the mixed carbide/oxide (Co6Mo6C2/Co2Mo3O8) nanoparticle composite deposited on highly dispersed, N,P‐doped carbon. The resulting composite shows outstanding electrocatalytic water‐splitting activity for both the oxygen evolution and hydrogen evolution reaction, and superior performance to reference samples including commercial 20 % Pt/C & IrO2. Electrochemical and other materials analyses indicate that Co6Mo6C2 is the main active phase in the composite, and the N,P‐doping of the carbon matrix increases the catalytic activity. The facile design could in principle be extended to multiple bimetallic catalyst classes by tuning of the molecular metal oxide precursor.

Enhanced reduction of sulfate and chromium under sulfate-reducing condition by synergism between extracellular polymeric substances and graphene oxide

Microbial reduction of sulfate and metal were simultaneously enhanced in the presence of graphene oxide (GO)-like nanomaterials, however, the mechanism remained unclear. In this study, bio-reduction of Cr was compared between free-living bacterium BY7 and immobilized BY7 (BY-rGO) on reduced GO particles. The role of extracellular polymeric substances (EPS) and rGO material on reduction of sulfate and Cr was investigated. Cr(VI) was reduced to Cr(III) and elemental Cr by BY-rGO particles up to 51% and 28%, respectively. EPS produced by the bacterium BY7 mainly consisted of proteins, polysaccharides, nucleic acids and humic substances. Concentration of EPS was sharply increased (about 54%) with the addition of graphene oxide, while the composition of EPS components was strongly affected by the exposure to Cr. By removing surface EPS without breaking the cells, reduction activities of sulfate and chromium by both BY-rGO particles and free-living BY7 cells were decreased. In contrast, reduction of sulfate and Cr by the free-living BY7 cells was enhanced with external addition of extracted EPS. Based on electrochemical analysis, the reduction peak indicating enhanced electron transfer was lost after removing EPS. Moreover, the contribution of each EPS fractions on sulfate and Cr reduction followed an order of polysaccharides > proteins > humic substances. Therefore, microbial sulfate and Cr reduction processes in the presence of BY-rGO particles were enhanced by the increasing amounts of EPS, which likely mediated electron transfer during sulfate and Cr reduction, and relieved bacteria from metal toxicity. Nevertheless, the presence of rGO was crucially important for elemental Cr production under sulfate-reducing condition, which might contribute to lowering electric potential or reducing activation energy for Cr(III) reduction. This work provided direct evidences for enhancing sulfate and Cr reduction activities by supplement of EPS as an additive to increase treatment efficiency in environmental bioremediation.

Graphene Oxide-Assisted Morphology and Structure of Electrodeposited ZnO Nanostructures.

In this paper, ZnO electrodeposition was studied with the presence of graphene oxide (GO) exploited as a possible structure-directing agent. The effect of deposition potential and duration on the morphology and structure of ZnO was analyzed. The morphology and structure of the hybrids was analyzed by Raman spectroscopy, X-ray diffraction (XRD), and Scanning Electron Microscopy (SEM). The Raman results indicate a successful modification of ZnO with GO sheets and a hybridization threshold of 10 mg L−1 by the evolution of the defect related band of ZnO at 580 cm−1. The morphology results show that a low GO content only slightly influences the morphology and orientation of ZnO nanostructures while a high content as 10 mg L−1 changes the morphology in nanoplates and growth orientation to lateral. The results show that while GO participated in the deposition reaction, it has a two-fold role, also by structure-controlling ZnO, indicating that the approach is valid for the use of GO as a structure-directing agent for the fabrication of ZnO nanostructures by electrodeposition with varying morphologies and orientations.

Binding modes of Fe(III) with graphene oxide in aqueous solutions. Competition with Sr2+, Cs+, Na+ ions and Fe(III) chelators

The work is devoted to the analysis of the state of the Fe(III) ions in aqueous solutions of graphene oxide (GO) using NMR-relaxation method. The presence of graphene oxide in solution suppresses the hydrolysis of Fe(III) in a wide pH range, and provides high values of the spin-spin relaxivity of the Fe(III)-GO system. Experiments with varying concentrations of Fe (III) and GO demonstrate the presence of the two types of the sites on GO surface: the A-type sides that strongly bind cations (the source of high relaxivity), and the B-type sites, weakly binding cations (providing lower relaxivity). Addition of the single charged (Cs+, Na+) or double charged (Sr2+) cations to the Fe(III)-GO solutions leads to a decrease in relaxivity due to the displacement of the Fe(III) ions from A to B-type sites with the Na+ < Cs+ < Sr2+ increasing efficiency. The possibility of releasing bound Fe(III) from GO by using two different chelators (ethylenediaminetetraacetic acid (EDTA) and 3,4-dihydroxybenzoic acid (3.4-DHB)) was tested in a wide range of pH.

Layer-by-layer decorated herbal cell compatible scaffolds for bone tissue engineering: A synergistic effect of graphene oxide and Cissus quadrangularis

Among various bone regenerative and repair methods, use of osteoinductive scaffold as bone grafts/substitute has gained wide importance worldwide. To develop such osteoinductive scaffold that is more natural and which spontaneously stimulates osteoblast formation without any differentiation media, we prepared electrospun poly ε-caprolactone scaffold which is further modified by means of layer-by-layer method using Cissus quadrangularis callus culture extract and graphene oxide (PCL-GO-CQ). The modified PCL-GO-CQ scaffold was compared with plain poly ε-caprolactone scaffold and poly ε-caprolactone coated only with graphene oxide. Physical properties, such as roughness, wettability, yield strength and tensile strength, of PCL-GO-CQ scaffold were found to be superior. Also, PCL-GO-CQ scaffold showed more in vitro cell compatibility with enhanced cellular proliferation on its surface. Presence of graphene oxide and Cissus quadrangularis callus in scaffold helped in the differentiation of human umbilical cord Wharton’s jelly-derived mesenchymal stem cells into osteogenic lineage without any differentiation media in less than 20 days. The synergistic effect of Cissus quadrangularis callus extract and graphene oxide in PCL-GO-CQ scaffold enhanced osteoblastic differentiation, osteoconduction and osteoinduction potential of scaffolds making them highly potential in bone regeneration and bone tissue engineering applications.

Hydration of C3A/gypsum composites in the presence of graphene oxide

The interactions between graphene oxide (GO) and individual clinker phases, which are critical for understanding the mechanism of GO during the hydration of cementitious materials, remain unclear. Therefore, this study investigated the effect of GO on the thermodynamic-based solution chemistry and hydration of tricalcium aluminate (C3A), which is a main constituent phase of Portland cement, in the presence of gypsum. The pore solution composition, phase content, and morphology of C3A/GO/gypsum composites were studied by inductively coupled plasma optical emission spectroscopy, X-ray diffraction, thermogravimetric analysis, and scanning electron microscopy. The experimental results showed that the incorporation of GO led to Ca2+ adsorption, which particularly decreased the local Ca2+ concentration near the surface of C3A. This increased the undersaturation levels of C3A and gypsum, thus facilitating their dissolution. A lower Ca2+ concentration led to a slight decrease in the supersaturation of hydrates after GO addition. Nevertheless, the introduction of GO improved the overall hydration degree, as confirmed by quantitative X-ray diffraction and thermogravimetric analysis. This improvement can be probably attributed to the higher number of nucleation sites provided by GO for precipitation. In addition, the scanning electron microscopy images of C3A/gypsum paste showed a cluster-like structure composed of coarse needle-like ettringites.

Polymer tethered graphene oxide influences miscibility and cooperative relaxation in LCST blends

The miscibility of a classical lower critical solution temperature (LCST) system; PMMA/SAN was probed by different rheological fingerprints such as isochronal temperature ramps, and isothermal frequency sweeps, in presence of graphene oxide (GO) and PMMA tethered GO. The chain length of the grafted polymer was varied to study its effect on miscibility, volume cooperativity, entanglement density and localization in the blends. The PMMA tethered GO alters the chain dynamics both at local and cooperative length scale through entropic and enthalpic interactions. It was perceived that the thermodynamic miscibility, cooperative relaxations and concentration fluctuation in PMMA/SAN blends are controlled by the spatial distribution of GO in the blend. By varying the chain length, we were able to understand that shorter tethered chains lead to early phase separation whereas the tethered chain length similar to that of the host matrix delays phase separation. Interestingly, irrespective of the length of the tethered polymer chain, the grafted GO sheets were not localized in the thermodynamically preferred phase (here PMMA). These findings are of great importance to further help us understand the theories and simulations which pertain to chain dynamics of PMMA/SAN blends containing polymer-tethered nanoparticles with large specific surface area like GO.