Mechanism of Formation and Chemical Structure of Graphene Oxide

© 2017 John Wiley & Sons, Ltd.This chapter presents the most recent view on fundamental aspects of graphene oxide (GO) chemistry. The mechanism of GO formation, its transformation during aqueous work-up and the fine chemical structure are introduced sequentially, in a way typical of textbooks. Re-examination of GO acidity overflows into discussion of the dynamic structural model. A new type of GO material with low density of defects, and thus termed "oxo-functionalized graphene" is introduced next. The challenges brought by the two-component GO structural model are then addressed. The chapter ends with a brief review of different bulk forms of graphite oxide

Functionalization and Reduction of Graphene Oxide

© 2017 John Wiley & Sons, Ltd.The chemistry of graphene oxide (GO) is a growing field of research. The modification of the surface properties of GO is the main goal in application-driven research. Successful functionalization protocols must be interpreted in accordance with the chemical structure of the original GO, and therefore, in this chapter, crucial aspects of the chemical structure of GO are introduced first. Next, the thermal and chemical stability of GO is reviewed, followed by introducing wet-chemical non-covalent and covalent reaction principles. The covalent functionalization of GO requires special attention. When chemical reaction principles, well known from organic chemistry, are applied to GO, it remains challenging to prove the successful accomplishment of reactions by analyzing the as-modified GO product. We pay special attention to the reactivity of the edges of defects and provide alternative explanations for interpreting experimental results, where necessary. Next, chemical reduction methods are summarized; special accent is placed on differentiating true chemical reduction from so-called "thermal reduction". Several examples for the functionalization of reduced graphene oxide (RGO) are considered next. While discussing GO chemical properties, in parallel with typical GO, we discuss these properties for the oxo-functionalized graphene (oxo-G1), a type of GO with very low density of structural defects. This sheds additional light on the role of defects in GO chemistry. Finally, additional properties of oxo-G1 are introduced. Oxo-G1 can act as a compound that enables the controlled chemistry for the design and synthesis of functional materials and devices

Graphene Oxide: Fundamentals and Applications

© 2017 John Wiley & Sons, Ltd. All rights reserved.Due to its unique properties, graphene oxide has become one of the most studied materials of the last decade and a great variety of applications have been reported in areas such as sensors, catalysis and biomedical applications. This comprehensive volume systematically describes the fundamental aspects and applications of graphene oxide. The book is designed as an introduction to the topic, so each chapter begins with a discussion on fundamental concepts, then proceeds to review and summarize recent advances in the field. Divided into two parts, the first part covers fundamental aspects of graphene oxide and includes chapters on formation and chemical structure, characterization methods, reduction methods, rheology and optical properties of graphene oxide solutions. Part Two covers numerous graphene oxide applications including field effect transistors, transparent conductive films, sensors, energy harvesting and storage, membranes, composite materials, catalysis and biomedical applications. In each case the differences and advantages of graphene oxide over its non-oxidised counterpart are discussed. The book concludes with a chapter on the challenges of industrial-scale graphene oxide production. Graphene Oxide: Fundamentals and Applications is a valuable reference for academic researchers, and industry scientists interested in graphene oxide, graphene and other carbon materials

Distribution of Gd(III) ions at the graphene oxide/water interface

© 2018 Elsevier Inc. Graphene oxide (GO) have emerged recently as a novel material for sorbing metal cations from aqueous media. However, the literature data on sorption capacity differ by more than one order in magnitude, and the nature of the chemical bonding between GO and metal cations remains unclear. In this work we show that Gd3+ ions are bound to GO by both coordinate-covalent bonding and electrostatic attraction with prevailing the former. We provide the complete account for the GO sorption toward Gd3+ as the function of the Gd3+/GO ratio and pH of solution. The upper limits of the strong bonding are determined as 0.70 and 0.16 mmol(Gd3+)/g(GO) in the neutral and in the intrinsically acidic solutions, respectively. At large excess of Gd3+ in the neutral solutions, the sorption capacity reaches 1.45 mmol(Gd3+)/g(GO). The effectiveness of water, hydrochloric acid and EDTA as desorbing eluents is compared. We experimentally demonstrate the existence of the Gd3+ concentration gradient within the diffuse layer at the GO/water interface, and its exponential character on the distance from the GO surface. The thickness of the diffuse layer and the position of the slipping plane are estimated. Such characteristics, typical for colloid systems, show that in solutions, GO flakes form distinct phase, even though they are just one atom thick

New Details to Relaxation Dynamics of Dielectric Composite Materials Comprising Longitudinally Opened Carbon Nanotubes

© 2017 American Chemical Society. The difference between intact and longitudinally opened multiwalled carbon nanotubes (referred to as CNT and OCNT) has been studied in their application as conductive filler in polymer composite materials. The dielectric properties have been studied in a broad frequency range at the temperatures varying from 293 K through 373 K. Introduction of as little as 0.5% and 1.0% of the conductive filler dramatically increased both parts of the complex permittivity. The percolation threshold is registered at ∼1.5% filling fraction. The main frequency dispersion of the dielectric permittivity lies in the low frequency end of the tested spectrum: from 10 2 Hz through 10 4 Hz. At equal filling fractions, the permittivity of the OCNT-based samples exceeds that of the intact CNT-based samples. The relaxation dynamics is largely affected by the nanoscale geometry of the filler: the temperature dependence of such parameters as dielectric strength, activation energy, and relaxation time demonstrated significant difference between the charge transfer mechanism in the CNT-based and OCNT-based samples. The obtained activation energy is 150 and 85 kJ/mol for materials comprising CNTs and OCNTs, respectively. The relaxation mechanism is complex, and the exact factors behind the macroscopic dielectric properties of the tested materials cannot be singled out with certainty. Several experimental data points suggest that the individual nanotubes, not their aggregates, play the major role in the observed electrical properties of the composites. At the low loading fractions, we attained the highest dielectric strength values among all the data reported by the present day for the CNT/polymer host systems

Chemistry of graphene oxide. Reactions with transition metal cations

© 2017 Elsevier LtdThe main advantage of graphene oxide (GO) over its non-oxidized counterpart, is its ability to form stable solutions, due to exfoliation to single-atomic-layer sheets. At present day, the fine chemical structure of GO remains ambiguous, while the traditional characterization methods have exhausted their potentials in revealing GO chemistry. Here we employ the NMR relaxation method to monitor reactions between GO and the three transition metal cations Mn2+, Gd3+ and Fe3+ while in solution phase. We demonstrate that interaction between GO and metal cations is chemical in its nature. The GO functional groups serve as ligands replacing water molecules from the metal cations’ first coordination sphere. The functional groups interacting at different pH values have been identified and quantified. At least part of the functional groups interacting with metal cations in neutral and basic solutions are alcohols that have acidic character. The metal ion induced rearrangement of the oxygen functional groups on GO platform points at the highly dynamic nature of GO, confirming the main standing points of our earlier proposed Dynamic Structural Model. For Fe3+, the polynuclear complexes with hydroxide ion bridges form on the surface of GO; the process of the seeding the nanoparticles on GO surface is recorded

New insights into the solubility of graphene oxide in water and alcohols

© The Owner Societies 2017. One of the main advantages of graphene oxide (GO) over its non-oxidized counterpart is its ability to form stable solutions in water and some organic solvents. At the same time, the nature of GO solutions is not completely understood; the existing data are scarce and controversial. Here, we demonstrate that the solubility of GO, and the stability of the as-formed solutions depend not just on the solute and solvent cohesion parameters, as commonly believed, but mostly on the chemical interactions at the GO/solvent interface. By the DFT and QTAIM calculations, we demonstrate that the solubility of GO is afforded by strong hydrogen bonding established between GO functional groups and solvent molecules. The main functional groups taking part in hydrogen bonding are tertiary alcohols; epoxides play only a minor role. The magnitude of the bond energy values is significantly higher than that for typical hydrogen bonding. The hydrogen bond energy between GO functional groups and solvent molecules decreases in the sequence: water 4 methanol 4 ethanol. We support our theoretical results by several experimental observations including solution calorimetry. The enthalpy of GO dissolution in water, methanol and ethanol is 0.1815 0.0010, 0.1550 0.0012 and 0.1040 0.0010 kJ g1, respectively, in full accordance with the calculated trend. Our findings provide an explanation for the well-known, but poorly understood solvent exchange phenomenon

On the Solvation Behavior of Graphene Oxide in Ethylene Glycol/Water Mixtures

© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim The self-association and solvation pattern of graphene oxide (GO) in water, ethylene glycol (EG), and their mixtures were analyzed by means of UV/Vis spectrophotometry. A careful analysis of the absorbance dependencies vs. the GO concentration shows that self-association of the GO sheets in EG occurs at higher concentration compared to that in water. It was established that depending on the mixed solvent composition, two different types of the GO solvates are formed. The results of quantum chemical calculations allow one to suggest that in the water-rich compositions, the GO oxygen-containing groups are in direct contact with water molecules while in the glycol-rich media the EG molecules fully substitute water in the GO's first solvation layer

Magneto-Optical Properties of the Magnetite-Graphene Oxide Composites in Organic Solvents

Copyright © 2018 American Chemical Society. Graphene oxide (GO) aqueous solutions are known to form liquid crystals that can switch in electric fields. Magnetic fields as external stimuli are inefficient toward GO because of its diamagnetic properties, and GO is known to be insoluble in most of the organic solvents. In this study, composites of GO with oleate-protected magnetite nanoparticles were prepared as stable colloid solutions in the mixed isopropanol-chloroform solvents. The structure of the composite particles and the optical properties of their solutions can be controlled by the ratio of the mixing parent components. The as-prepared solutions are highly responsive to external magnetic field. As the consequence, the optical transmission and the direction of light scattering can be efficiently manipulated. These systems pave the way for fabricating functional materials, such as magneto-optical switches, density-gradient materials, and micromotors. Solubility in nonpolar organic solvents broadens the scope of their potential applications

Oxidatively modified carbon as efficient material for removing radionuclides from water

© 2017 Elsevier LtdThere is a constant need to develop advantageous materials for removing radioactive waste from aqueous systems. Here we propose a new carbon-based material prepared by oxidative treatment of various natural carbon sources. The as-prepared oxidatively modified carbon (OMC) has an oxygen-rich surface, and retains its particulate granular texture. It has relatively low cost and can be used in traditional filtration columns. The sorption ability of OMC toward several metal cations is demonstrated. It is especially efficient toward Cs+ cations, the species that are among the most difficult to remove from the waters at the Fukushima nuclear plant