How Do Aryl Groups Attach to a Graphene Sheet?

Evidence for Trans-Oligoene Chain Formation in Graphene Induced by Iodine

Functionalization of pristine graphene by hydrogen and fluorine is well studied, resulting in graphane and fluorographene structures. In contrast, functionalization of pristine graphene with iodine has not been reported. Here, the functionalization of graphene with iodine using photochemical activation is presented, which is thermally reversible at 400 °C. Additional dispersive dominant Raman modes that are probed by resonance Raman spectroscopy are observed. Additionally, iodinated graphene is probed by Kelvin probe force microscopy and by transport measurements showing p-doping surpassing non-covalent iodine doping by charge transfer-complex formation. The emergent Raman modes combined with strong p-doping indicate that iodine functionalization is distinct from simple iodine doping. A reaction mechanism based on these findings is proposed, identifying the large size of iodine atoms as the probable cause governing regiochemically controlled addition due to steric hinderance of reactive sites. The modification of the electronic structure is explained by the confinement of 1D trans-oligoene chains between sp3-defects. These results demonstrate the uniqueness of iodine reactivity toward graphene and the modification of the electronic structure of iodinated graphene, highlighting its dependence on the spatial arrangement of substituents.

Mechanistic Insights on Functionalization of Graphene with Ozone

The exposure of graphene to O3 results in functionalization of its lattice with epoxy, even at room temperature. This reaction is of fundamental interest for precise lattice patterning, however, is not well understood. Herein, using van der Waals density functional theory (vdW-DFT) incorporating spin-polarized calculations, we find that O3 strongly physisorbs on graphene with a binding energy of -0.46 eV. It configures in a tilted position with the two terminal O atoms centered above the neighboring graphene honeycombs. A dissociative chemisorption follows by surpassing an energy barrier of 0.75 eV and grafting an epoxy group on graphene reducing the energy of the system by 0.14 eV from the physisorbed state. Subsequent O3 chemisorption is preferred on the same honeycomb, yielding two epoxy groups separated by a single C-C bridge. We show that capturing the onset of spin in oxygen during chemisorption is crucial. We verify this finding with experiments where an exponential increase in the density of epoxy groups as a function of reaction temperature yields an energy barrier of 0.66 eV, in agreement with the DFT prediction. These insights will help efforts to obtain precise patterning of the graphene lattice.

Unraveling the electronic influence and nature of covalent bonding of aryl and alkyl radicals on the B12N12 nanocage cluster

Carbon nanocage structures such as fullerene, nanotubes, nanocapsules, nanopolyhedra, cones, cubes, and onions have been reported since the discovery of C60, and they offer tremendous promise for investigating materials of low dimensions in an isolated environment. Boron Nitride (BN) nanomaterials such a: nanotubes, nanocapsules, nanoparticles, and clusters have been described in several studies and are predicted to be useful as electronic devices, high heat-resistance semiconductors, nanocables, insulator lubricants, and gas storage materials. The interaction, and electronic of octahedral B₁₂N₁₂ nanocage cluster covalently modified from the attachment of alkyl and aryl radicals were analyzed using Density Functional Theory calculations. The work discusses for the first time to our knowledge the complete investigation of the impact of the grafted aryl and alkyl groups on the electronic, bang gap, and density of states on the B₁₂N₁₂. Furthermore, this is the first complete description of these radicals attaching to a surface of B₁₂N₁₂ nanocage cluster.

Graphene-Dominated Hybrid Coatings with Highly Compacted Structure on Stainless Steel Bipolar Plates

Highly conductive corrosion protection coatings are necessary for metallic bipolar plates (BPs) of the proton-exchange membrane fuel cell. Graphene coatings have the potential of protecting metal substrates from corrosion without obscuring their excellent electrical conductivity. The electron transfer in the coatings facilitates the formation of galvanic cells, so the challenge is to block the mass transfer of the corrosion process. Here, we constructed highly compacted hybrid coatings with aligned water-dispersible graphene layers. The water-dispersible graphene (SG) held an electrical conductivity of >270 S cm^-1 while providing an unprecedented dispersibility, which can be redispersed from filter cake with a concentration of 120 mg mL^-1 or even dry state. The cohesion of the hybrid coatings was attributed to the interaction between highly aligned SG layers and the heterointerface between SG and polydopamine (PDA), as proven by the molecular dynamics simulations. The hybrid coatings presented a corrosion current density of 0.023 μA cm^-2 and an interfacial contact resistance of 9.94 mΩ cm², which meets the requirements of corrosion protection and electron transfer for the coatings on metallic BPs. The water-based fabrication method of the graphene-dominated hybrid coatings was a promising alternative of the vacuum-based deposition method for industrial production.

Electrochemical Detection Platform Based on RGO Functionalized with Diazonium Salt for DNA Hybridization

In this paper, we propose an improved electrochemical platform based on graphene for the detection of DNA hybridization. Commercial screen-printed carbon electrodes (SPCEs) were used for this purpose due to their ease of functionalization and miniaturization opportunities. SPCEs were modified with reduced graphene oxide (RGO), offering a suitable surface for further functionalization. Therefore, aryl-carboxyl groups were integrated onto RGO-modified electrodes by electrochemical reduction of the corresponding diazonium salt to provide enough reaction sites for the covalent immobilization of amino-modified DNA probes. Our final goal was to determine the optimum conditions needed to fabricate a simple, label-free RGO-based electrochemical platform to detect the hybridization between two complementary single-stranded DNA molecules. Each modification step in the fabrication process was monitored by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) using [Fe(CN)6]3-/4- as a redox reporter. Although, the diazonium electrografted layer displayed the expected blocking effect of the charge transfer, the next steps in the modification procedure resulted in enhanced electron transfer properties of the electrode interface. We suggest that the improvement in the charge transfer after the DNA hybridization process could be exploited as a prospective sensing feature. The morphological and structural characterization of the modified electrodes performed by scanning electron microscopy (SEM) and Raman spectroscopy, respectively, were used to validate different modification steps in the platform fabrication process.

Oxygen Interactions with Covalently Grafted 2D Nanometric Carboxyphenyl Thin Films—An Experimental and DFT Study

Surface modification is a hot topic in electrochemistry and material sciences because it affects the way materials are used. In this paper, a method for covalently attaching carboxyphenyl (PhCOOH) groups to a gold electrode is presented. These groups were grafted onto the electrode surface electrochemically via reduction of aryldiazonium salt. The resulting grafted surface was characterized using cyclic voltammetry (CV) before and after the functionalization procedure to validate the presence of the grafted layer. The grafting of PhCOOH groups was confirmed by analyzing electrode thickness and composition by ellipsometry and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) calculations indicated that the grafted layers provide a stable platform and resolved, for the first time, their interactions with oxygen.

Electrochemical and electronic detection of biomarkers in serum: a systematic comparison using aptamer-functionalized surfaces

Sensitive and selective detection of biomarkers in serum in a short time has a significant impact on health. The enormous clinical importance of developing reliable methods and devices for testing serum levels of cardiac troponin I (cTnI), which are directly correlated to acute myocardial infarction (AMI), has spurred an unmatched race among researchers for the development of highly sensitive and cost-effective sensing formats to be able to differentiate patients with early onset of cardiac injury from healthy individuals with a mean cTnI level of 26 pg mL^-1. Electronic- and electrochemical-based detection schemes allow for fast and quantitative detection not otherwise possible at the point of care. Such approaches rely largely on voltammetric and field-effect-based readouts. Here, we systematically investigate electric and electrochemical point-of-care sensors for the detection of cTnI in serum samples by using the same surface receptors, cTnI aptamer-functionalized CVD graphene-coated interdigated gold electrodes. The analytical performances of both sensors are comparable with a limit of detection (LoD) of 5.7 ± 0.6 pg mL^-1(electrochemical) and 3.3 ± 1.2 pg mL^-1 (electric). However, both sensors exhibit different equilibrium dissociation constant (K_D) values between the aptamer-linked surface receptor and the cTnI analyte, being 160 pg mL^-1 for the electrochemical and about three times lower for the electrical approach with K_D = 51.4 pg mL^-1. This difference is believed to be related to the use of a redox mediator in the electrochemical sensor for readout. The ability of the redox mediator to diffuse from the solution to the surface via the cTnI/aptamer interface is hindered, correlating to higher K_D values. In contrast, the electric readout has the advantage of being label-free with a sensing limitation due to ionic strength effects, which can be limited using poly(ethylene) glycol surface ligands.

Graphene and carbon nanotubes interfaced electrochemical nanobiosensors for the detection of SARS-CoV-2 (COVID-19) and other respiratory viral infections: A review

Recent COVID-19 pandemic has claimed millions of lives due to lack of a rapid diagnostic tool. Global scientific community is now making joint efforts on developing rapid and accurate diagnostic tools for early detection of viral infections to preventing future outbreaks. Conventional diagnostic methods for virus detection are expensive and time consuming. There is an immediate requirement for a sensitive, reliable, rapid and easy-to-use Point-of-Care (PoC) diagnostic technology. Electrochemical biosensors have the potential to fulfill these requirements, but they are less sensitive for sensing viruses/viral infections. However, sensitivity and performance of these electrochemical platforms can be improved by integrating carbon nanostructure, such as graphene and carbon nanotubes (CNTs). These nanostructures offer excellent electrical property, biocompatibility, chemical stability, mechanical strength and, large surface area that are most desired in developing PoC diagnostic tools for detecting viral infections with speed, sensitivity, and cost-effectiveness. This review summarizes recent advancements made toward integrating graphene/CNTs nanostructures and their surface modifications useful for developing new generation of electrochemical nanobiosensors for detecting viral infections. The review also provides prospects and considerations for extending the graphene/CNTs based electrochemical transducers into portable and wearable PoC tools that can be useful in preventing future outbreaks and pandemics.

Controlled covalent functionalization of a graphene-channel of a field effect transistor as an ideal platform for (bio)sensing applications

The controlled covalent functionalization of the graphene channel of a field effect transistor, based on interdigitated gold electrodes (source and drain), via electrochemical grafting, using specifically designed aryl diazonium species is demonstrated to allow the simple fabrication of a general platform for (bio)sensing applications. The electrochemical grafting of a protected ethynylphenyl diazonium salt leads to the deposition of only a monolayer on the graphene channel. This controlled covalent functionalization of the graphene channel results in a charge mobility of the GFET of 1739 ± 376 cm² V^-1 s^-1 and 1698 ± 536 cm² V^-1 s^-1 for the holes and electrons, respectively, allowing their utilization as (bio)sensors. After deprotection, a dense and compact ethynylphenyl monolayer is obtained and allows the immobilization of a wide range of (bio)molecules by a "click" chemistry coupling reaction (Huisgen 1,3-dipolar cycloaddition). This finding opens promising options for graphene-based (bio)sensing applications.

A chemisorbed interfacial layer for seeding atomic layer deposition on graphite

The integration of graphene, and more broadly two-dimensional materials, into devices and hybrid materials often requires the deposition of thin films on their usually inert surface. As a result, strategies for the introduction of surface reactive sites have been developed but currently pose a dilemma between robustness and preservation of the graphene properties. A method is reported here for covalently modifying graphitic surfaces, introducing functional groups that act as reactive sites for the growth of high quality dielectric layers. Aryl diazonium species containing tri-methoxy groups are covalently bonded (grafted) to highly oriented pyrolytic graphite (HOPG) and graphene, acting as seeding species for atomic layer deposition (ALD) of Al₂O₃, a high-κ dielectric material. A smooth and uniform dielectric film growth is confirmed by scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrical measurements. Raman spectroscopy showed that the aryl groups gradually detach from the graphitic surface during the Al₂O₃ ALD process at 150 °C, with the surface reverting back to the original sp²-hybridized state and without damaging the dielectric layer. Thus, the grafted aryl groups can act as a sacrificial seeding layer after healing the defects of the graphitic surface with annealing treatment.

Aryl Migration on Graphene

The design and synthesis of molecular systems able to carry out movements resembling macroscopic objects is an exciting and challenging endeavor. Molecules that can walk covalently on a track have been demonstrated, and we now report how aryl groups that can migrate over a graphene surface. Specifically, we describe a system comprised of covalently functionalized aryl groups on graphene that undergo continuous aryl shifts. The dynamic aryl shift allows the aryl groups on graphene to effectively migrate step-by-step wherein each step involves reversible bond breaking and making that is initiated by a combination of an activated arene and p-doping of the graphene surface. Raman spectroscopic mapping of the distribution of the covalent attachment revealed that activated 4-methoxyphenyl groups migrate several microns from regions of high functionalization to regions with no prior functionalization.

Diazonium Modification of Inorganic and Organic Fillers for the Design of Robust Composites: A Review

This review focuses on fillers modified with diazonium salts and their use in composites. We reviewed scientific publications and presented information about such diazonium-modified fillers as boron nitride, carbon fillers, cellulose, clay, silica, titanium dioxide, and zeolite. The fillers were divided into two groups. The first group includes those that form covalent bonds with the polymer, while the second includes those that do not form them. This review indicates a tremendous impact of filler modification using diazonium salts on the properties of composites. The review presents examples of the impact of filler on such properties as thermal conductivity, thermal stability, and mechanical properties (e.g., interfacial shear strength, compressive strength, flexural strength). The presented review indicates the enormous potential of composites with diazonium-modified fillers in control drug release, antistatic coatings, electrode materials, photocatalysts, bone tissue engineering scaffolds, fuel cell applications, abrasive tools, and electromechanical strain sensor. We hope that this review will help both research groups and industry in choosing fillers for given types of polymers and obtaining composites with even better properties.

Strategies for the Formation of Monolayers From Diazonium Salts: Unconventional Grafting Media, Unconventional Building Blocks

Pioneered by J. Pinson and coll. in 1990s, the reductive grafting of aryldiazonium salts has become a powerful method for surface functionalization. Highly robust interfaces result from this surface attachment, resistant to heat, chemical degradation and ultrasonication. Importantly, this approach can be applied to many materials, ranging from conducting, semi-conducting, oxides to insulating substrates. In addition, either massive, flat surfaces or nanomaterials can be functionalized. The method is easy to process and fast. The grafting process involves the formation of highly reactive aryl radicals able to attack the substrate. However, the generated radicals can also react with already-grafted aryl species, leading to the formation of loosely-packed polyaryl multilayer films, typically of 10-15 nm thick. It is thus highly challenging to control the vertical extension of the deposited layer and to form well-ordered monolayers from aryldiazonium salts. In this mini review, we briefly describe the different strategies that have been developed to prepare well-ordered monolayers. We especially focus on two strategies successfully used in our laboratories, namely the use of unconventional solvents, i.e., room temperature ionic liquids (RTILs), as grafting media and the use of calixarene macrocycles by taking benefit of their pre-organized structure. These strategies give large possibilities for the structuring of interfaces with the widest choice of materials and highlight the potential of aryldiazonium grafting as a competitive alternative to self-assembled monolayers (SAMs) of alkyl thiols.

Interface Chemistry of Graphene/Cu Grafted By 3,4,5-Tri-Methoxyphenyl

Chemical reaction with diazonium molecules has revealed to be a powerful method for the surface chemical modification of graphite, carbon nanotubes and recently also of graphene. Graphene electronic structure modification using diazonium molecules is strongly influenced by graphene growth and by the supporting materials. Here, carrying on a detailed study of core levels and valence band photoemission measurements, we are able to reconstruct the interface chemistry of trimethoxybenzenediazonium-based molecules electrochemically grafted on graphene on copper. The band energy alignment at the molecule-graphene interface has been traced revealing the energy position of the HOMO band with respect to the Fermi level.

Use of calixarenes bearing diazonium groups for the development of robust monolayers with unique tailored properties

Calixarene-based diazonium salts can be easily synthesized in a few steps. This review surveys recent examples that illustrate the key advantages of these highly reactive molecular platforms for surface modification.

Electrochemical modification of platinum and glassy carbon surfaces with pyridine layers and their use as complexing agents for copper (II) ions

The electrochemical grafting of the “in-situ” prepared diazopyridinium salt have permitted the attachment of pyridine moieties onto platinum and glassy carbon surfaces. The modification of the electrode surfaces is observed by a redox probe. The ability of the film for the complexation of copper (II) ions is demonstrated by square wave voltammetry. After 45 min accumulation of copper (II) ions onto the grafted electrode surfaces, the electrode signal obtained by square wave voltammetry measurement served to discriminate the adsorbed heavy metal ions. Such measurements showed that the grafted pyridine has the ability to display complexing behavior toward some heavy metal ions. DFT calculations support a strong binding of the pyridine moieties onto the Pt surface. The most favorable complexation mode of copper (II) ions as suggested from DFT is the bidentate complex. This strategy is vital in constructing a wide range of different electrochemical sensors.

The influence of the grafted aryl groups on the solvation properties of the graphyne and graphdiyne - a MD study

The mechanism of the adsorption and grafting of diazonium cations onto the surface of graphyne and graphdiyne was investigated using Density Functional Theory (DFT). The adsorption energy (both in vacuum and water as solvent) of the phenyl diazonium cation was evaluated at three different positions of the graphyne and graphdiyne surface. Moreover, the lowest energy adsorption sites were used to calculate and plot Non-covalent Interactions (NCI). The Bond Dissociation Energy (BDE) results (up to 66 kcal/mol) for the scission of the phenyl group support the remarkable stability of the grafted layer. As both of these materials are non-dispersible in aqueous solution, in this work through the use of Molecular Mechanics (MM) and Molecular Dynamics (MD) we explored also the effect of the grafted substituted aryl groups derived from aryldiazonium salts onto the solvation properties of these materials.

Graphene-assisted biosensing based on terahertz nanoslot antennas

We report on improvement of sensitivity for molecular detection utilizing terahertz time domain spectroscopy. Based on confining and enhancing electromagnetic field with metallic nanoslot antennas, we additionally employ monolayer graphene sheet whose edge and hydrophobic surface nature lead to increase detecting performance. Terahertz transmittance in monolayer graphene/metallic nanoslot structure exhibits more unambiguous change after lactose molecules are attached, compared to that in metallic nanoslot structure without monolayer graphene. We attribute the prominent change to that more lactose molecules are guided inside/near the metal gap region due to edge and hydrophobic surface nature of monolayer graphene. This monolayer graphene/metallic nanoslot structure can be expanded in other organic or bio-molecular detection.

Alkyl-Modified Gold Surfaces: Characterization of the Au-C Bond

The surface of gold can be modified with alkyl groups through a radical crossover reaction involving alkyliodides or bromides in the presence of a sterically hindered diazonium salt. In this paper, we characterize the Au-C(alkyl) bond by surface-enhanced Raman spectroscopy (SERS); the corresponding peak appears at 387 cm^-1 close to the value obtained by theoretical modeling. The Au-C(alkyl) bond energy is also calculated, it reaches -36.9 kcal mol^-1 similar to that of an Au-S-alkyl bond but also of an Au-C(aryl) bond. In agreement with the similar energies of Au-C(alkyl) and Au-S-(alkyl), we demonstrate experimentally that these groups can be exchanged on the surface of gold.

Ionic liquids plus microwave irradiation: a general methodology for the retro-functionalization of single-walled carbon nanotubes

One of the most important objectives nowadays in the field of chemical modification of carbon nanotubes (CNTs) is to control the degree of functionalization, since excessive modification can disrupt the π-conjugated system and adversely affect their useful properties. Covalent functionalization is one of the most common methods for the modification of single-walled carbon nanotubes (SWCNTs). However, only a few examples have appeared in the last few years regarding the control of the functionalization degree and the reversibility of the reaction. We present here an approach for the retro-functionalization of SWCNTs which could be applied to different types of covalent functionalizations, allowing the restoration of the π-conjugated structure. The process is performed through the combination of ionic liquids plus microwave irradiation and it is applicable to the retro-arylation and retro-cycloaddition reactions on SWCNTs. The successful retro-functionalization is monitored by Raman spectroscopy, thermogravimetric analysis and UV-Vis-NIR spectroscopy.

Oxo-Functionalized Graphene: A Versatile Precursor for Alkylated Graphene Sheets by Reductive Functionalization

Controlled covalent functionalization of graphene remains a challenging task owing to the heterogeneous nature of materials. Functionalization approaches for graphene either lack in quantifying the degree of functionalization or they do not discriminate between covalent and non-covalent functionalization. Here, graphite is oxidized and exfoliated in a three-step procedure and subsequently reduced and functionalized by hexylation. Although Raman spectroscopy is powerful to determine the degree of in-plane lattice defects (θ_LD ) and functionalization (θ_FD ), the method fails at detecting introduced hexyl groups at a concentration of about 0.03 %, next to the pre-existing in-plane lattice defects of 0.7 %. However, sensitive thermogravimetric analysis coupled with gas chromatography and mass spectrometry (TGA-GC/MS) can prove the hexylation reaction. The efficiency of functionalization is comparable to reductive functionalization of pristine chemical vapor deposition (CVD)-graphene and bulk graphite.

A photochemical approach for a fast and self-limited covalent modification of surface supported graphene with photoactive dyes

Herein, we report a simple method for a covalent modification of surface supported graphene with photoactive dyes. Graphene was fabricated on cubic-SiC/Si(001) wafers due to their low cost and suitability for mass-production of continuous graphene fit for electronic applications on millimetre scale. Functionalisation of the graphene surface was carried out in solution via white light induced photochemical generation of phenazine radicals from phenazine diazonium salt. The resulting covalently bonded phenazine-graphene hybrid structure was characterised by scanning tunnelling microscopy (STM) and spectroscopy (STS), Raman spectroscopy and density functional theory (DFT) calculations. It was found that phenazine molecules form an overlayer, which exhibit a short range order with a rectangular unit cell on the graphene surface. DFT calculations based on STM results reveal that molecules are standing up in the overlayer with the maximum coverage of 0.25 molecules per graphene unit cell. Raman spectroscopy and STM results show that the growth is limited to one monolayer of standing molecules. STS reveals that the phenazine-graphene hybrid structure has a band gap of 0.8 eV.

Electrophilic radical coupling at the edge of graphene

We report the selective functionalization of an edge of graphene via the electrografting of 4-nitrobenzene diazonium tetrafluoroborate. The edge - a single line of carbon atoms - forms during the process of cutting a graphene monolayer with an atomically sharp microtome knife. Embedded in a polymeric matrix, the just cut bare graphene edge efficiently transfers electrons to a ferricyanide probe in solution. By monitoring the electron exchange reactions of the edge upon functionalization, we observe an annihilation of the reduction and oxidation peaks of the ferricyanide probe, characteristic of the formation of a nitroaryl passivation layer on the edge of graphene. For the first time, the chemical state of a single line of carbon atoms is influenced and monitored using an electrochemical cell, therefore bypassing the usual requirements of atomic resolution characterization techniques, which often demand very clean graphene samples and vacuum processing.

Characterisation, coverage, and orientation of functionalised graphene using sum-frequency generation spectroscopy

We report the unambiguous detection of phenyl groups covalently attached to functionalised graphene using non-linear spectroscopy. Sum-frequency generation was employed to probe graphene on a gold surface after chemical functionalisation using a benzene diazonium salt. We observe a distinct resonance at 3064 cm-1 which can clearly be assigned to an aromatic C-H stretch by comparison with a self-assembled monolayer on a gold substrate formed from benzenethiol. Not only does sum-frequency generation spectroscopy allow one to characterise functionalised graphene with higher sensitivity and much better specificity than many other spectroscopic techniques, but it also opens up the possibility to assess the coverage of graphene with functional groups, and to determine their orientation relative to the graphene surface.

Sensing at the Surface of Graphene Field-Effect Transistors

Recent research trends now offer new opportunities for developing the next generations of label-free biochemical sensors using graphene and other two-dimensional materials. While the physics of graphene transistors operated in electrolyte is well grounded, important chemical challenges still remain to be addressed, namely the impact of the chemical functionalizations of graphene on the key electrical parameters and the sensing performances. In fact, graphene - at least ideal graphene - is highly chemically inert. The functionalizations and chemical alterations of the graphene surface - both covalently and non-covalently - are crucial steps that define the sensitivity of graphene. The presence, reactivity, adsorption of gas and ions, proteins, DNA, cells and tissues on graphene have been successfully monitored with graphene. This review aims to unify most of the work done so far on biochemical sensing at the surface of a (chemically functionalized) graphene field-effect transistor and the challenges that lie ahead. The authors are convinced that graphene biochemical sensors hold great promise to meet the ever-increasing demand for sensitivity, especially looking at the recent progresses suggesting that the obstacle of Debye screening can be overcome.

Occurrence of photoinduced charge separation by the modulation of the electronic coupling between pyrene dimers and chemically converted graphenes

The photoexcitation of the pyrene dimer on graphene resulted in the final formation of a charge-separated (CS) state following an exciplex formation, while that of the pyrene monomer on graphene generated the corresponding exciplex solely.

Protection of carbon steel corrosion in 3.5% NaCl medium by aryldiazonium grafted graphene coatings

Modification of CS/G by 1,8 ND containing two phenyl rings and two azo groups led to higher protection efficiency.

Graphene Coatings as Barrier Layers to Prevent the Water-Induced Corrosion of Silicate Glass

Corrosion-protective coatings for silicate glass based on the transfer of one or two layers of graphene grown on copper by chemical vapor deposition have been demonstrated. The effectiveness of graphene to act as a glass corrosion inhibitor was evaluated by water immersion testing. After 120 days of immersion in water, bare glass samples had a significant increase in surface roughness and defects, which resulted in a marked reduction in fracture strength. In contrast, the single- and double-layer graphene-coated glasses experienced negligible changes in both fracture strength and surface roughness. The anticorrosion mechanism was also studied.

Synergistic effect of pyrroloquinoline quinone and graphene nano-interface for facile fabrication of sensitive NADH biosensor

A self-assembly composite of graphene-pyrroloquinoline quinone (PQQ) was fabricated and modified on glassy carbon electrode (GCE) for sensitive detection of nicotinamide adenine dinucleotide (NADH). Chitosan (CTS) was applied to disperse graphene to form a stable robust film on GCE. A synergistic effect between PQQ and graphene was observed during the electrocatalytic oxidation of NADH, with about 260mV reduction in the oxidation potential and 2.5-fold increase in the oxidation current compared with those on the bare GCE. The electrochemical sensors based on the modified electrodes allowed the detection of NADH with a good linear dependence from 0.32 to 220µM with a high sensitivity of 0.421µAµM^-1cm^-2 and a low detection limit of 0.16µM (S/N=3). It could also eliminate the interference of electroactive substances like ascorbic acid (AA), uric acid, and dopamine and its derivatives. The outstanding performances of graphene-PQQ/CTS composite capable of improving the electrical conductivity and accelerating the electron transport suggested its promising applications for design of different graphene based composites used in electrochemical sensing and energy fields.

Graphene-philic surfactants for nanocomposites in latex technology

Graphene is the newest member of the carbon family, and has revolutionized materials science especially in the field of polymer nanocomposites. However, agglomeration and uniform dispersion remains an Achilles' heel (even an elephant in the room), hampering the optimization of this material for practical applications. Chemical functionalization of graphene can overcome these hurdles but is often rather disruptive to the extended pi-conjugation, altering the desired physical and electronic properties. Employing surfactants as stabilizing agents in latex technology circumvents the need for chemical modification allowing for the formation of nanocomposites with retained graphene properties. This article reviews the recent progress in the use of surfactants and polymers to prepare graphene/polymer nanocomposites via latex technology. Of special interest here are surfactant structure-performance relationships, as well as background on the roles surfactant-graphene interactions for promoting stabilization.

Covalent functionalization of reduced graphene oxide with porphyrin by means of diazonium chemistry for nonlinear optical performance

Reduced graphene oxide (RGO)-porphyrin (TPP) nanohybrids (RGO-TPP 1 and RGO-TPP 2) were prepared by two synthetic routes that involve functionalization of the RGO using diazonium salts. The microscopic structures, morphology, photophysical properties and nonlinear optical performance of the resultant RGO-TPP nanohybrids were investigated. The covalent bonding of the porphyrin-functionalized-RGO nanohybrid materials was confirmed by Fourier transform infrared spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and thermogravimetric analysis. Attachment of the porphyrin units to the surface of the RGO by diazotization significantly improves the solubility and ease of processing of these RGO-based nanohybrid materials. Ultraviolet/visible absorption and steady-state fluorescence studies indicate considerable π-π interactions and effective photo-induced electron and/or energy transfer between the porphyrin moieties and the extended π-system of RGO. The nonlinear optical properties of RGO-TPP 1 and RGO-TPP 2 were investigated by open-aperture Z-scan measurements at 532 nm with both 4 ns and 21 ps laser pulses, the results showing that the chemical nanohybrids exhibit improved nonlinear optical properties compared to those of the benchmark material C₆₀, and the constituent RGO or porphyrins.

Efficient covalent modification of graphene by diazo chemistry

Functionalized graphene is prepared by an efficient and facile approach via diazo chemistry.

Mapping nanometric electronic property changes induced by an aryl diazonium sub-monolayer on HOPG

The morphology as well as the electric and electronic properties of aryl diazonium, in particular 4-nitrobenzene-diazonium (NBD), films on HOPG surfaces have been studied at the nanoscale level.

Functionalization of nanomaterials with aryldiazonium salts

This paper reviews the surface modification strategies of a wide range of nanomaterials using aryldiazonium salts. After a brief history of diazonium salts since their discovery by Peter Griess in 1858, we will tackle the surface chemistry using these compounds since the first trials in the 1950s. We will then focus on the modern surface chemistry of aryldiazonium salts for the modification of materials, particularly metallic, semiconductors, metal oxide nanoparticles, carbon-based nanostructures, diamond and clays. The successful modification of sp(2) carbon materials and metals by aryldiazonium salts paved the way to innovative strategies for the attachment of aryl layers to metal oxide nanoparticles and nanodiamonds, and intercalation of clays. Interestingly, diazotized surfaces can easily trap nanoparticles and nanotubes while diazotized nanoparticles can be (electro)chemically reduced on electrode/materials surfaces as molecular compounds. Both strategies provided organized 2D surface assembled nanoparticles. In this review, aryldiazonium salts are highlighted as efficient coupling agents for many types of molecular, macromolecular and nanoparticulate species, therefore ensuring stability to colloids on the one hand, and the construction of composite materials and hybrid systems with robust and durable interfaces/interphases, on the other hand. The last section is dedicated to a selection of patents and industrial products based on aryldiazonium-modified nanomaterials. After nearly 160 years of organic chemistry, diazonium salts have entered a new, long and thriving era for the benefit of materials, colloids, and surface scientists. This tempts us to introduce the terminology of "diazonics" we define as the science and technology of aryldiazonium salt-derived materials.

The Covalent Functionalization of Graphene on Substrates

The utilization of grown or deposited graphene on solid substrates offers key benefits for functionalization processes, but especially to attain structures with a high level of control for electronics and "smart" materials. In this review, we will initially focus on the nature and properties of graphene on substrates, based on the method of preparation. We will then analyze the most relevant literature on the functionalization of graphene on substrates. In particular, we will comparatively discuss radical reactions, cycloadditions, halogenations, hydrogenations, and oxidations. We will especially address the question of how the reactivity of graphene is affected by its morphology (i.e., number of layers, defects, substrate, curvature, etc.).

Molecular interactions on single-walled carbon nanotubes revealed by high-resolution transmission microscopy

The close solid-state structure–property relationships of organic π−aromatic molecules have attracted interest due to their implications for the design of organic functional materials. In particular, a dimeric structure, that is, a unit consisting of two molecules, is required for precisely evaluating intermolecular interactions. Here, we show that the sidewall of a single-walled carbon nanotube (SWNT) represents a unique molecular dimer platform that can be directly visualized using high-resolution transmission electron microscopy. Pyrene is chosen as the π−aromatic molecule; its dimer is covalently linked to the SWNT sidewalls by aryl addition. Reflecting the orientation and separation of the two molecules, the pyrene dimer on the SWNT exhibits characteristic optical and photophysical properties. The methodology discussed here—form and probe molecular dimers—is highly promising for the creation of unique models and provides indispensable and fundamental information regarding molecular interactions.

Probing local molecular properties is crucial for the rational designs of functional organic materials. Here, Umeyama et al. prepare a dimeric structure of a model π-aromatic compound on the sidewall of a carbon nanotube to be visualized by transmission electron microscopy at a single-molecule level.

Metal-free ferromagnetic metal and intrinsic spin semiconductor: two different kinds of SWCNT functionalized BN nanoribbons

Two different kinds of SWCNT functionalized zigzag edge BN nanoribbons with n chains (n-ZBNNRs), namely, (a) B-edge functionalized by (m,m)SWCNT and N-edge modified with H (nZBNNR-B-(m,m)SWCNTs); and (b) the B-edge modified with H and the N-edge functionalized by (m,m)SWCNT (nZBNNR-N-(m,m)SWCNTs), have been predicted. Amazingly, we find that unlike the semiconducting and nonmagnetic H-modified n-ZBNNRs, the nZBNNR-B-(m,m)SWCNTs are intrinsic ferromagnetic metals, regardless of ribbon widths n and tube diameters (m,m). At a given (m,m), their local magnetic moments, at first, exhibit oscillation with increasing n, whereas when n is larger than 5, they are independent of n. In contrast, unlike the metallic and nonmagnetic (m,m)SWCNTs, the nZBNNR-N-(m,m)SWCNTs are ferromagnetic intrinsic spin-semiconductors with direct band gaps, regardless of n and (m,m). Their local magnetic moments and band gaps are independent of n and (m,m). The DFT calculations reveal that the process of SWCNT functionalization of the n-ZBNNRs does not need any activation energy. Moreover, the formation energies of the SWCNT functionalized n-ZBNNRs are always less than zero. Therefore, the SWCNT functionalized n-ZBNNRs are not only stable, but can also be spontaneously formed. Furthermore, compared with n-ZBNNRs, the SWCNT functionalized n-ZBNNRs show significant improvements in their thermal and mechanical stabilities. Thus, (m,m)SWCNT functionalization of n-ZBNNRs may open new routes toward practical nanoelectronic and optoelectronic as well as spintronic devices based on BNC-based materials.

Nanostructuring graphene for controlled and reproducible functionalization

The 'graphene rush' that started almost a decade ago is far from over. The dazzling properties of graphene have long warranted a number of applications in various domains of science and technology. Harnessing the exceptional properties of graphene for practical applications however has proved to be a massive task. Apart from the challenges associated with the large-scale production of the material, the intrinsic zero band gap, the inherently low reactivity and solubility of pristine graphene preclude its use in several high- as well as low-end applications. One of the potential solutions to these problems is the surface functionalization of graphene using organic building blocks. The 'surface-only' nature of graphene allows the manipulation of its properties not only by covalent chemical modification but also via non-covalent interactions with organic molecules. Significant amount of research efforts have been directed towards the development of functionalization protocols for modifying the structural, electronic, and chemical properties of graphene. This feature article provides a glimpse of recent progress in the molecular functionalization of surface supported graphene using non-covalent as well as covalent chemistry.