Dual path mechanism in the thermal reduction of graphene oxide

Biobased waterborne hyperbranched polyurethane/NiFe2O4@rGO nanocomposite with multi-stimuli responsive shape memory attributes

A biobased waterborne hyperbranched polyurethane nanocomposite was in situ fabricated with nickel ferrite/reduced graphene oxide nanohybrid (NiFe₂O₄@rGO) as stimuli responsive shape memory material.

Oscillatory behaviour of the surface reduction process of multilayer graphene oxide at room temperature

We report the observation of oscillatory redox reactions on the surface of multilayer graphene oxide (GO) films at room temperature.

Thermochemistry and kinetics of graphite oxide exothermic decomposition for safety in large-scale storage and processing

The success of graphene technologies will require the development of safe and cost-effective nano-manufacturing methods. Special safety issues arise for manufacturing routes based on graphite oxide (GO) as an intermediate due to its energetic behavior. This article presents a detailed thermochemical and kinetic study of GO exothermic decomposition designed to identify the conditions and material compositions that avoid explosive events during storage and processing at large scale. It is shown that GO becomes more reactive for thermal decomposition when it is pretreated with OH^- in suspension and the effect is reversible by back-titration to low pH. This OH^- effect can lower the decomposition reaction exotherm onset temperature by up to 50 degrees of Celsius, causing overlap with common drying operations (100-120°C) and possible self-heating and thermal runaway during processing. Spectroscopic and modeling evidence suggest epoxide groups are primarily responsible for the energetic behavior, and epoxy ring opening/closing reactions are offered as an explanation for the reversible effects of pH on decomposition kinetics and enthalpies. A quantitative kinetic model is developed for GO thermal decomposition and used in a series of case studies to predict the storage conditions under which spontaneous self-heating, thermal runaway, and explosions can be avoided.

Carbon dioxide reduction on Ir(111): stable hydrocarbon surface species at near-ambient pressure

Stable hydrocarbon surface species in the carbon dioxide hydrogenation reaction were identified on Ir(111) under near-ambient pressure conditions.

Laser-induced chemical transformation of free-standing graphene oxide membranes in liquid and gas ammonia environments

A fast and versatile method is developed for laser-induced reduction and nitrogen doping of free-standing graphene oxide membranes.

One-step grafting of polymers to graphene oxide

The direct grafting of poly(N-isopropylacrylamide) to the basal plane of graphene oxide has been achieved in a single step: cleavage of the terminal thiocarbonylthio group on RAFT grown poly(N-isopropylacrylamide) reveals a reactive thiol that attacks the epoxides present across the surface of graphene oxide. The new composite material was characterised by a combination of SSNMR, FTIR, Raman, EDX, XPS, TGA and contact angle measurement; it shows enhanced thermal stability and solubility in water.

Visualizing chemical states and defects induced magnetism of graphene oxide by spatially-resolved-X-ray microscopy and spectroscopy

This investigation studies the various magnetic behaviors of graphene oxide (GO) and reduced graphene oxides (rGOs) and elucidates the relationship between the chemical states that involve defects therein and their magnetic behaviors in GO sheets. Magnetic hysteresis loop reveals that the GO is ferromagnetic whereas photo-thermal moderately reduced graphene oxide (M-rGO) and heavily reduced graphene oxide (H-rGO) gradually become paramagnetic behavior at room temperature. Scanning transmission X-ray microscopy and corresponding X-ray absorption near-edge structure spectroscopy were utilized to investigate thoroughly the variation of the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups, as well as the C 2p(σ*)-derived states in flat and wrinkle regions to clarify the relationship between the spatially-resolved chemical states and the magnetism of GO, M-rGO and H-rGO. The results of X-ray magnetic circular dichroism further support the finding that C 2p(σ*)-derived states are the main origin of the magnetism of GO. Based on experimental results and first-principles calculations, the variation in magnetic behavior from GO to M-rGO and to H-rGO is interpreted, and the origin of ferromagnetism is identified as the C 2p(σ*)-derived states that involve defects/vacancies rather than the C 2p(π*) states that are bound with oxygen-containing and hydroxyl groups on GO sheets.

Efficient Direct Reduction of Graphene Oxide by Silicon Substrate

Graphene has been studied for various applications due to its excellent properties. Graphene film fabrication from solutions of graphene oxide (GO) have attracted considerable attention because these procedures are suitable for mass production. GO, however, is an insulator, and therefore a reduction process is required to make the GO film conductive. These reduction procedures require chemical reducing agents or high temperature annealing. Herein, we report a novel direct and simple reduction procedure of GO by silicon, which is the most widely used material in the electronics industry. In this study, we also used silicon nanosheets (SiNSs) as reducing agents for GO. The reducing effect of silicon was confirmed by various characterization methods. Furthermore, the silicon wafer was also used as a reducing template to create a reduced GO (rGO) film on a silicon substrate. By this process, a pure rGO film can be formed without the impurities that normally come from chemical reducing agents. This is an easy and environmentally friendly method to prepare large scale graphene films on Si substrates.

Understanding the formation mechanism of graphene frameworks synthesized by solvothermal and rapid pyrolytic processes based on an alcohol-sodium hydroxide system

The determination of ways to facilitate the 2D-oriented assembly of carbons into graphene instead of other carbon structures while restraining the π-π stacking interaction is a challenge for the controllable bulk synthesis of graphene, which is vital both scientifically and technically. In this study, graphene frameworks (GFs) are synthesized by solvothermal and rapid pyrolytic processes based on an alcohol-sodium hydroxide system. The evolution mechanism of GFs is investigated systematically. Under sodium catalysis, the abundant carbon atoms produced by the fast decomposition of solvothermal intermediate self-assembled to graphene. The existence of abundant ether bonds may be favorable for 3D graphene formation. More importantly, GFs were successfully obtained using acetic acid as the carbon source in the synthetic process, suggesting the reasonability of analyzing the formation mechanism. It is quite possible to determine more favorable routes to synthesize graphene under this cognition. The electrochemical energy storage capacity of GFs was also studied, which revealed a high supercapacitor performance with a specific capacitance of 310.7 F/g at the current density of 0.2 A/g.

Environmentally benign and facile reduction of graphene oxide by flash light irradiation

In this work, we demonstrate an environmentally benign and facile flash light irradiation process to reduce graphene oxide (GO). GO thin films were prepared by a vacuum filtration process, and these films were reduced by exposure to flash light irradiation for a few milliseconds at room temperature under ambient conditions. Flash light conditions such as energy, pulse width, and pulse number were varied to determine optimal conditions for this photothermal reduction of GO. The flash light irradiation treatment completely reduced the GO thin films, transforming them into pure graphene films. The resulting graphene films were characterized by x-ray diffraction, x-ray photoelectron spectroscopy, Raman spectroscopy, transmission electron microscopy, and thermogravimetric analysis.

Roles of water molecules in trapping carbon dioxide molecules inside the interlayer space of graphene oxides

Density functional theory (DFT) calculations were employed to investigate the energetics of carbon dioxide migration within hydrated or anhydrous graphene oxides (GOs). When anhydrous GO structures contain a carbon dioxide molecule, the carbon dioxide interacts repulsively with the GO layers to increase the interlayer spacing. The repulsive electrostatic interactions are reduced by the insertion of water molecules into CO2-containing GO structures due to the occurrence of attractive water-layer interactions through hydrogen bonding. Consequently, the interlayer spacings in CO2-containing hydrated structures are shortened compared with those in the anhydrous structures. The results indicate that the intercalated water molecules have the ability to connect the GO layers in the presence of carbon dioxide. Furthermore, the DFT calculations indicated that the GO interlayer spacings, which are influenced by the intercalation of water molecules, control carbon dioxide migration within the GO layers. The importance of the interlayer spacings on the migration of carbon dioxide arises from the occurrence of repulsive interactions between CO2 and oxygen-containing groups attached on the graphene sheets. When the GO interlayer spacings are short due to the presence of intercalated water molecules, the repulsive interactions between carbon dioxide and the GO layers are strong enough to prevent CO2 from migrating from its original position. Such repulsive interactions do not occur during the migration of CO2 within anhydrous GO structures because of the relatively longer interlayer spacing. Accordingly, CO2 migrates within anhydrous GO with a less significant barrier, indicating that carbon dioxide molecules are easily released from the GO.

Light and atmosphere affect the Quasi-equilibrium states of graphite oxide and graphene oxide powders

Graphite oxide (GiO) and graphene oxide (GeO) possess wide applicability in technological devices. The exact chemical compositions, structures, and properties of these materials remain vague to the graphene community despite being heavily researched. As metastable materials, the properties of GiO and GeO are easily manipulated under various conditions of temperature, light, and atmosphere. Although these aspects are important considerations for long-term storage of the materials, they are not well understood. In this experimental work, investigations are performed to determine how light and atmosphere contribute to the characteristics of GiO and GeO powders. The study shows that, at room-temperature, the quasi-equilibrium states of both materials, in specific the O/C ratios, vary according to the storage conditions. Drastic disparities between GiO and GeO are observed. GiO kept away from light and GeO kept under inert atmosphere maintain relatively high O/C ratios. As the metastable states of the materials are governed by the diffusion of oxygen functionalities, the presence of epoxide groups diminishes while negligible changes occur to the sp(2) lattice size. This experimental work lays out fundamental aspects that govern the stability of frequently mass-produced GiO and GeO powders under different environments, with major implications on their optimal storage conditions.

Graphene oxide thin films: influence of chemical structure and deposition methodology

We synthesized graphene oxide sheets of different functionalization by oxidation of two different starting materials, graphite and GANF nanofibers, followed by purification based on alkaline washing. The chemical structure of graphene oxide materials was determined by X-ray photoelectron spectroscopy (XPS), and the nanoplatelets were characterized by ζ potential and dynamic light scattering (DLS) measurements. The XPS results indicated that the chemical structure depends on the starting material. Two different deposition methodologies, Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS), were employed to build the graphene oxide thin films. The film morphology was analyzed by scanning electron microscopy (SEM). The SEM images allow us to conclude that the LB methodology provides the highest coverage. This coverage is almost independent of the chemical composition of sheets. Conversely, the coverage obtained by the LS methodology increases with the percentage of C-O groups attached to sheets. Surface-pressure isotherms of these materials were interpreted according to the Volmer model.

Polymer composites prepared by low-temperature post-irradiation polymerization of C2F4 in the presence of graphene-like material: synthesis and characterization

Study of PTFE–microwave exfoliated graphene oxide (MEGO) composites synthesized using a low temperature post-irradiation polymerization technique. SEM images of MEGO (left) and PTFE–MEGO composite (right).

Superior CO2 adsorption from waste coffee ground derived carbons

Utilising waste from spent coffee grounds KOH activated highly microporous carbons with surface areas of 2785 m² g⁻¹ and micropore volumes of 0.793 cm³ g⁻¹ were synthesised that are capable of uptake capacities near 3 mmol g⁻¹ at 50 °C and 1 bar.

Fabrication of reduced graphene oxide/metal (Cu, Ni, Co) nanoparticle hybrid composites via a facile thermal reduction method

Reduced graphene oxide/metal (e.g., Cu, Ni, Co) nanoparticle hybrid composites were prepared via a facile thermal reduction method at 500 °C under flowing argon without any usage of external reductive gases.

In situ observation of facet-dependent oxidation of graphene on platinum in an environmental TEM

The facet-dependent oxidation reactionvia in situETEM.

Density functional theory modeling of multilayer "epitaxial" graphene oxide

CONSPECTUS: Graphene oxide (GO) is a complex material of both fundamental and applied interest. Elucidating the structure of GO is crucial to achieve control over its properties and technological applications. GO is a nonstoichiometric and hygroscopic material with a lamellar structure, and its physical chemical properties depend critically on synthesis procedures and postsynthesis treatments. Numerous efforts are in place to both understand and exploit this versatile layered carbon material. This Account reports on recent density functional theory (DFT) studies of "epitaxial" graphene oxide (hereafter EGO), a type of GO obtained by oxidation of graphene films grown epitaxially on silicon carbide. Here, we rely on selected X-ray photoelectron spectroscopy (XPS), infrared spectroscopy (IR), and X-ray diffraction (XRD) measurements of EGO, and we discuss in great detail how we utilized DFT-based techniques to project out from the experimental data basic atomistic information about the chemistry and structure of these films. This Account provides an example as to how DFT modeling can be used to elucidate complex materials such as GO from a limited set of experimental information. EGO exhibits a uniform layered structure, consisting of a stack of graphene planes hosting predominantly epoxide and hydroxyl groups, and water molecules intercalated between the oxidized carbon layers. Here, we first focus on XPS measurements of EGO, and we use DFT to generate realistic model structures, calculate core-level chemical shifts, and through the comparison with experiment, gain insight on the chemical composition and metastability characteristics of EGO. DFT calculations are then used to devise a simplistic but accurate simulation scheme to study thermodynamic and kinetic stability and to predict the intralayer structure of EGO films aged at room temperature. Our simulations show that aged EGO encompasses layers with nanosized oxidized domains presenting a high concentration of oxygen functionalities and local structural order, surrounded by regions of pristine graphene. Through the analysis of XRD and IR measurements, our DFT calculations finally show that in EGO, the oxidized domains of stacked layers overlap and locally confine about a monolayer of water molecules. The overall water content in EGO remains below 10%, and intralayer and interlayer spatial ditribution of oxygen species in EGO lead to a layered porous film with an interlayer spacing of about 10 Å. The basic insight gained from our DFT studies, from chemical composition to a nanoscale characterization of the film structure, will be used to fine-tune synthesis methods and EGO properties.

Scalable holey graphene synthesis and dense electrode fabrication toward high-performance ultracapacitors

Graphene has attracted a lot of attention for ultracapacitor electrodes because of its high electrical conductivity, high surface area, and superb chemical stability. However, poor volumetric capacitive performance of typical graphene-based electrodes has hindered their practical applications because of the extremely low density. Herein we report a scalable synthesis method of holey graphene (h-Graphene) in a single step without using any catalysts or special chemicals. The film made of the as-synthesized h-Graphene exhibited relatively strong mechanical strength, 2D hole morphology, high density, and facile processability. This scalable one-step synthesis method for h-Graphene is time-efficient, cost-efficient, environmentally friendly, and generally applicable to other two-dimensional materials. The ultracapacitor electrodes based on the h-Graphene show a remarkably improved volumetric capacitance with about 700% increase compared to that of regular graphene electrodes. Modeling on individual h-Graphene was carried out to understand the excellent processability and improved ultracapacitor performance.

Facile aerosol synthesis and characterization of ternary crumpled graphene-TiO₂-magnetite nanocomposites for advanced water treatment

In this work, the synthesis and characterization of multifunctional crumpled graphene-based ternary nanocomposite photocatalysts for advanced water treatment applications is described. Currently, a major hurdle for the scale-up and optimization of aqueous, graphene-based photocatalysts is restacking of graphene nanosheets due to strong π-π interactions. To overcome this hurdle, a fast and facile aerosol technique to synthesize monomeric, aggregation-resistant, crumpled graphene-based photocatalysts was developed. The aerosol route utilizes water evaporation-induced confinement forces to effectively crumple graphene oxide and subsequently encapsulate commercially available TiO2 and magnetite nanoparticles. The as-synthesized crumpled graphene-TiO2-magnetite (GOTIM) ternary core-shell nanostructures are shown to possess superior aqueous-based photocatalytic properties (over a 20-fold enhancement in some cases) compared to TiO2 alone. Total GOTIM photocatalytic reactivity is confirmed to also include efficient photoreduction reaction pathways, in addition to expected oxidation routes typical of TiO2-based photocatalysts, significantly expanding photocatalytic application potential compared to TiO2 alone. Reaction kinetics and proposed mechanisms (both oxidative and reductive) are described for a model organic compound, here as methyl orange. Further, with the addition of hole scavengers such as EDTA, and/or lowering the O2 concentration, we demonstrate enhancement of photocatalyzed reduction reactions, suggesting potential for directed, controlled reduction applications. In addition to robust aqueous stability, low-field magnetic susceptibility is demonstrated, allowing for low-energy, in situ material separations, which are critical for material recycling and reuse.

Low-temperature thermal reduction of graphene oxide nanobrick walls: unique combination of high gas barrier and low resistivity in fully organic polyelectrolyte multilayer thin films

Layer-by-layer assembly from aqueous solutions was used to construct multilayer thin films (<200 nm) comprising polyethylenimine and graphene oxide. Low-temperature (175 °C) thermal reduction of these films improved gas barrier properties (e.g., lower permeability than SiOx), even under high humidity conditions, and enhanced their electrical conductivity to 1750 S/m. The flexible nature of the aforementioned thin films, along with their excellent combination of transport properties, make them ideal candidates for use in a broad range of electronics and packaging applications.

Facile preparation of Pd nanoparticles supported on single-layer graphene oxide and application for the Suzuki-Miyaura cross-coupling reaction

Pd nanoparticles supported on single layer graphene oxide (Pd-slGO) were prepared by gentle heating of palladium(ii) acetate (Pd(OAc)2) and GO in ethanol that served as a mild reductant of the Pd precursor. Pd-slGO showed a high catalytic performance (TON and TOF = 237 000) in the Suzuki-Miyaura cross-coupling reaction.

Sulfur-functionalized graphene oxide by epoxide ring-opening

The treatment of graphene oxide (GO) with potassium thioacetate followed by an aqueous work-up yields a new material via the ring-opening of the epoxide groups. The new material is a thiol-functionalized GO (GO-SH) which is able to undergo further functionalization. Reaction with butyl bromide gives another new material, GO-SBu, which shows significantly enhanced thermal stability compared to both GO and GO-SH. The thiol-functionalized GO material showed a high affinity for gold, as demonstrated by the selective deposition of a high density of gold nanoparticles.

Revealing the adsorption mechanisms of nitroxides on ultrapure, metallicity-sorted carbon nanotubes

Carbon nanotubes are a natural choice as gas sensor components given their high surface to volume ratio, electronic properties, and capability to mediate chemical reactions. However, a realistic assessment of the interaction of the tube wall and the adsorption processes during gas phase reactions has always been elusive. Making use of ultraclean single-walled carbon nanotubes, we have followed the adsorption kinetics of NO2 and found a physisorption mechanism. Additionally, the adsorption reaction directly depends on the metallic character of the samples. Franck-Condon satellites, hitherto undetected in nanotube-NOx systems, were resolved in the N 1s X-ray absorption signal, revealing a weak chemisorption, which is intrinsically related to NO dimer molecules. This has allowed us to identify that an additional signal observed in the higher binding energy region of the core level C 1s photoemission signal is due to the C ═ O species of ketene groups formed as reaction byproducts . This has been supported by density functional theory calculations. These results pave the way toward the optimization of nanotube-based sensors with tailored sensitivity and selectivity to different species at room temperature.

Origin of the chemical and kinetic stability of graphene oxide

At moderate temperatures (≤ 70°C), thermal reduction of graphene oxide is inefficient and after its synthesis the material enters in a metastable state. Here, first-principles and statistical calculations are used to investigate both the low-temperature processes leading to decomposition of graphene oxide and the role of ageing on the structure and stability of this material. Our study shows that the key factor underlying the stability of graphene oxide is the tendency of the oxygen functionalities to agglomerate and form highly oxidized domains surrounded by areas of pristine graphene. Within the agglomerates of functional groups, the primary decomposition reactions are hindered by both geometrical and energetic factors. The number of reacting sites is reduced by the occurrence of local order in the oxidized domains, and due to the close packing of the oxygen functionalities, the decomposition reactions become - on average - endothermic by more than 0.6 eV.

Subnanometer vacancy defects introduced on graphene by oxygen gas

The basal plane of graphene has been known to be less reactive than the edges, but some studies observed vacancies in the basal plane after reaction with oxygen gas. Observation of these vacancies has typically been limited to nanometer-scale resolution using microscopic techniques. This work demonstrates the introduction and observation of subnanometer vacancies in the basal plane of graphene by heat treatment in a flow of oxygen gas at low temperature such as 533 K or lower. High-resolution transmission electron microscopy was used to directly observe vacancy structures, which were compared with image simulations. These proposed structures contain C═O, pyran-like ether, and lactone-like groups.

Reduction of graphene oxide – a comprehensive electrochemical investigation in alkaline and acidic electrolytes

Electrochemical characterization to investigate the extent of reduction and the nature of reminiscent oxygen moieties in GO-based materials.

Structural and electronic properties of Pd-decorated graphene oxides and their effects on the adsorption of nitrogen oxides: insights from density functional calculations

The Pd decoration on graphene oxides effectively modifies the structural and electronic properties of nanomaterials and improves the adsorption of nitrogen oxides.

Fabrication of multi-functional PVDF/RGO composites via a simple thermal reduction process and their enhanced electromagnetic wave absorption and dielectric properties

The PVDF/RGO composites synthesized by a thermal reduction process exhibit high values of reflection loss and excellent dielectric properties with low filler loading.

Large-scale production of high-quality graphene using glucose and ferric chloride

A novel method to prepare high-quality graphene is developed using simple calcination of a mixture of glucose and FeCl₃.

Sulfuric acid intercalated graphite oxide for graphene preparation

Graphene has shown enormous potential for innovation in various research fields. The current chemical approaches based on exfoliation of graphite via graphite oxide (GO) are potential for large-scale synthesis of graphene but suffer from high cost, great operation difficulties, and serious waste discharge. We report a facile preparation of graphene by rapid reduction and expansion exfoliation of sulfuric acid intercalated graphite oxide (SIGO) at temperature just above 100°C in ambient atmosphere, noting that SIGO is easily available as the immediate oxidation descendent of graphite in sulfuric acid. The oxygenic and hydric groups in SIGO are mainly removed through dehydration as catalyzed by the intercalated sulfuric acid (ISA). The resultant consists of mostly single layer graphene sheets with a mean diameter of 1.07 μm after dispersion in DMF. This SIGO process is reductant free, easy operation, low-energy, environmental friendly and generates graphene with low oxygen content, less defect and high conductivity. The provided synthesis route from graphite to graphene via SIGO is compact and readily scalable.

Diffusion and desorption of oxygen atoms on graphene

To understand the reversible oxidation of graphene in a recent experiment, a density-functional theory study is performed. The adsorption energy of isolated oxygen atom on graphene is 2.3 eV, indicating a strong interaction between them. However, the migration barrier of oxygen atoms on graphene is only 0.8 eV and oxygen diffusion is still possible. Provided with this possibility, we find that, although a single oxygen atom is very difficult to desorb, cooperative desorption of two oxygen atoms is feasible.

Hydrothermal deoxygenation of graphene oxide: chemical and structural evolution

A green and facile approach for the partial deoxygenation of graphene oxide (GO) at moderate temperature (100 °C) and under atmospheric pressure, catalyzed by acidic conditions in water is reported. The chemical and structural changes in GO as a function of hydrothermal time were probed to understand the deoxygenation events. The brown GO dispersion in water was found to gradually turn black over the hydrothermal-treatment time on account of the increasing graphitic content. FTIR, thermogravimetric (TG), Raman, and XRD analyses revealed that the labile oxygen functionalities are progressively eliminated, thereby partially restoring the π-conjugated network. This was further corroborated by X-ray photoelectron spectroscopy (XPS) studies based on quantitative analysis of each carbon component associated with the different chemical functionalities. Carbonyl, carboxyl, ether, and phenolic groups were found to be thermally stable, which hinders complete deoxygenation of GO and makes their dispersion in water stable, as monitored by the ζ potential. It is worth noting that deoxygenation events are expedited under acid-catalyzed hydrothermal treatment relative to thermal deoxygenation in air.

Surface Charge Research of Graphene Oxide, Chemically Reduced Graphene Oxide and Thermally Exfoliated Graphene Oxide

In this contribution, the surface electrical properties of graphene oxide (GO), chemically reduced graphene oxide (RGO) and thermally exfoliated graphene oxide (EGO) were characterized by zeta potential. Their surface morphologies were observed by scanning electron microscope. Then they were immobilized on glass carbon electrodes and their electrochemical behaviors for different charged redox systems were also investigated by using the cyclic voltammetry (CV) method. Results indicated that the density of surface negative charge on GO is much more than those on RGO and EGO. Furthermore, the electrochemical performances of electrodes modified with GO, RGO and EGO for detecting the model analyte Cu2+ by CV were compared. The results demonstrate that negative charge on the surface of graphene materials affects their performances as electrochemical sensors significantly.

Making graphene holey. Gold-nanoparticle-mediated hydroxyl radical attack on reduced graphene oxide

Graphene oxide (GO) and reduced graphene oxide (RGO) have important applications in the development of new electrode and photocatalyst architectures. Gold nanoparticles (AuNPs) have now been employed as catalyst to generate OH(•) and oxidize RGO via hydroxyl radical attack. The oxidation of RGO is marked by pores and wrinkles within the 2-D network. Nanosecond laser flash photolysis was used in conjunction with competition kinetics to elucidate the oxidative mechanism and calculate rate constants for the AuNP-catalyzed and direct reaction between RGO and OH(•). The results highlight the use of the AuNP-mediated oxidation reaction to tune the properties of RGO through the degree of oxidation and/or functional group selectivity in addition to the nanoporous and wrinkle facets. The ability of AuNPs to catalyze the photolytic decomposition of H2O2 as well as the hydroxyl radical-induced oxidation of RGO raises new issues concerning graphene stability in energy conversion and storage (photocatalysis, fuel cells, Li-ion batteries, etc.). Understanding RGO oxidation by free radicals will aid in maintaining the long-term stability of RGO-based functional composites where intimate contact with radical species is inevitable.

Controlling hydrogenation of graphene on Ir(111)

Combined fast X-ray photoelectron spectroscopy and density functional theory calculations reveal the presence of two types of hydrogen adsorbate structures at the graphene/Ir(111) interface, namely, graphane-like islands and hydrogen dimer structures. While the former give rise to a periodic pattern, dimers tend to destroy the periodicity. Our data reveal distinctive growth rates and stability of both types of structures, thereby allowing one to obtain well-defined patterns of hydrogen clusters. The ability to control and manipulate the formation and size of hydrogen structures on graphene facilitates tailoring of its properties for a wide range of applications by means of covalent functionalization.

Synthesis and electronic properties of chemically functionalized graphene on metal surfaces

A review on the electronic properties, growth and functionalization of graphene on metals is presented. Starting from the derivation of the electronic properties of an isolated graphene layer using the nearest neighbor tight-binding (TB) approximation for π and σ electrons, the TB model is then extended to third-nearest neighbors and interlayer coupling. The latter is relevant to few-layer graphene and graphite. Next, the conditions under which epitaxial graphene can be obtained by chemical vapor deposition are reviewed with a particular emphasis on the Ni(111) surface. Regarding functionalization, I first discuss the intercalation of monolayer Au into the graphene/Ni(111) interface, which renders graphene quasi-free-standing. The Au intercalated quasi-free-standing graphene is then the basis for chemical functionalization. Functionalization of graphene is classified into covalent, ionic and substitutional functionalization. As archetypical examples for these three possibilities I discuss covalent functionalization by hydrogen, ionic functionalization by alkali metals and substitutional functionalization by nitrogen heteroatoms.