Organic synthesis on graphene

Low-dimensional nanostructures for monolithic 3D-integrated flexible and stretchable electronics

Flexible/stretchable electronics, which are characterized by their ultrathin design, lightweight structure, and excellent mechanical robustness and conformability, have garnered significant attention due to their unprecedented potential in healthcare, advanced robotics, and human-machine interface technologies. An increasing number of low-dimensional nanostructures with exceptional mechanical, electronic, and/or optical properties are being developed for flexible/stretchable electronics to fulfill the functional and application requirements of information sensing, processing, and interactive loops. Compared to the traditional single-layer format, which has a restricted design space, a monolithic three-dimensional (M3D) integrated device architecture offers greater flexibility and stretchability for electronic devices, achieving a high-level of integration to accommodate the state-of-the-art design targets, such as skin-comfort, miniaturization, and multi-functionality. Low-dimensional nanostructures possess small size, unique characteristics, flexible/elastic adaptability, and effective vertical stacking capability, boosting the advancement of M3D-integrated flexible/stretchable systems. In this review, we provide a summary of the typical low-dimensional nanostructures found in semiconductor, interconnect, and substrate materials, and discuss the design rules of flexible/stretchable devices for intelligent sensing and data processing. Furthermore, artificial sensory systems in 3D integration have been reviewed, highlighting the advancements in flexible/stretchable electronics that are deployed with high-density, energy-efficiency, and multi-functionalities. Finally, we discuss the technical challenges and advanced methodologies involved in the design and optimization of low-dimensional nanostructures, to achieve monolithic 3D-integrated flexible/stretchable multi-sensory systems.

Photo-Enhanced Chemo-Transistor Platform for Ultrasensitive Assay of Small Molecules

Compared with traditional assay techniques, field-effect transistors (FETs) have advantages such as fast response, high sensitivity, being label-free, and point-of-care detection, while lacking generality to detect a wide range of small molecules since most of them are electrically neutral with a weak doping effect. Here, we demonstrate a photo-enhanced chemo-transistor platform based on a synergistic photo-chemical gating effect in order to overcome the aforementioned limitation. Under light irradiation, accumulated photoelectrons generated from covalent organic frameworks offer a photo-gating modulation, amplifying the response to small molecule adsorption including methylglyoxal, p-nitroaniline, nitrobenzene, aniline, and glyoxal when measuring the photocurrent. We perform testing in buffer, artificial urine, sweat, saliva, and diabetic mouse serum. The limit of detection is down to 10^-19 M methylglyoxal, about 5 orders of magnitude lower than existing assay technologies. This work develops a photo-enhanced FET platform to detect small molecules or other neutral species with enhanced sensitivity for applications in fields such as biochemical research, health monitoring, and disease diagnosis.

Graphene oxide-catalyzed trifluoromethylation of alkynes with quinoxalinones and Langlois' reagent

The direct C–H trifluoromethylation of alkynes and quinoxalinones has been achieved using a graphene oxide/Langlois' reagent system. This multi-component tandem reaction using graphene oxide as the catalyst and Langlois' reagent as the robust CF₃ radical source results in the formation of olefinic C–CF₃ to access a series of 3-trifluoroalkylated quinoxalin-2(1H)-ones.

The direct C–H trifluoromethylation of alkynes and quinoxalinones using a graphene oxide/Langlois' reagent system.

Ultrasensitive Field-Effect Biosensors Enabled by the Unique Electronic Properties of Graphene

This review provides a critical overview of current developments on nanoelectronic biochemical sensors based on graphene. Composed of a single layer of conjugated carbon atoms, graphene has outstanding high carrier mobility and low intrinsic electrical noise, but a chemically inert surface. Surface functionalization is therefore crucial to unravel graphene sensitivity and selectivity for the detection of targeted analytes. To achieve optimal performance of graphene transistors for biochemical sensing, the tuning of the graphene surface properties via surface functionalization and passivation is highlighted, as well as the tuning of its electrical operation by utilizing multifrequency ambipolar configuration and a high frequency measurement scheme to overcome the Debye screening to achieve low noise and highly sensitive detection. Potential applications and prospectives of ultrasensitive graphene electronic biochemical sensors ranging from environmental monitoring and food safety, healthcare and medical diagnosis, to life science research, are presented as well.

Graphene oxide: a green oxidant-acid bifunctional carbon material for the synthesis of functionalized isoindolin-1-ones via formal amide insertion and substitution

A formal amide insertion and substitution reaction using graphene oxide as an oxidant-acid bifunctional carbon material

A Chemical Blowing Strategy to Fabricate Biomass-Derived Carbon-Aerogels with Graphene-Like Nanosheet Structures for High-Performance Supercapacitors

The efficient exploitation and utilization of low-cost and biomass-derived carbon materials will play an active role in developing sustainable energy storage systems. However, the difficult morphology control and incomplete activation limits their pervasive application in electrochemical energy storage. Inspired by the famous Chinese folk handicraft of sugar-figure blowing, biomass-derived carbon aerogels (GCA) with 2 D graphene-like thin nanosheets were fabricated by a simple chemical blowing strategy from a viscous agaric solution obtained through hydrothermal treatment of agaric. A chemical blowing agent (NH₄ Cl) was used to effectively exfoliate the bulk biomass-derived carbon flake into 2 D graphene-like nanosheets, which resulted in a highly porous structure and high specific area (2200 m²  g^-1 ) after the activation process. As a result, a high specific capacitance of 340 F g^-1 at 3 A g^-1 and a high specific energy of 25.5 Wh kg^-1 at a power density of 2 kW kg^-1 was obtained for the GCA electrode, which can be attributed to the abundant electrochemically active surfaces, short ion transport paths, and effective electrolyte infiltration.. This work demonstrates an effective and low-cost strategy to prepare hierarchical and well-organized porous biomass carbon materials with graphene-like nanosheets for high-performance supercapacitors.

Graphene oxide as a green carbon material for cross-coupling of indoles with ethers via oxidation and the Friedel–Crafts reaction

The first example of using GO as a carbon material facilitated C(sp²)–C(sp³) bond formation.

Controllable Bipolar Doping of Graphene with 2D Molecular Dopants

The fine control of graphene doping levels over a wide energy range remains a challenging issue for the electronic applications of graphene. Here, the controllable doping of chemical vapor deposited graphene, which provides a wide range of energy levels (shifts up to ± 0.5 eV), is demonstrated through physical contact with chemically versatile graphene oxide (GO) sheets, a 2D dopant that can be solution-processed. GO sheets are a p-type dopant due to their abundance of electron-withdrawing functional groups. To expand the energy window of GO-doped graphene, the GO surface is chemically modified with electron-donating ethylene diamine molecules. The amine-functionalized GO sheets exhibit strong n-type doping behaviors. In addition, the particular physicochemical characteristics of the GO sheets, namely their sheet sizes, number of layers, and degree of oxidation and amine functionality, are systematically varied to finely tune their energy levels. Finally, the tailor-made GO sheet dopants are applied into graphene-based electronic devices, which are found to exhibit improved device performances. These results demonstrate the potential of GO sheet dopants in many graphene-based electronics applications.

Rapid synthesis and decoration of reduced graphene oxide with gold nanoparticles by thermostable peptides for memory device and photothermal applications

This article presents novel, rapid, and environmentally benign synthesis method for one-step reduction and decoration of graphene oxide with gold nanoparticles (NAuNPs) by using thermostable antimicrobial nisin peptides to form a gold-nanoparticles-reduced graphene oxide (NAu-rGO) nanocomposite. The formed composite material was characterized by UV/Vis spectroscopy, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and high-resolution transmission electron microscopy (HR-TEM). HR-TEM analysis revealed the formation of spherical AuNPs of 5-30 nm in size on reduced graphene oxide (rGO) nanosheets. A non-volatile-memory device was prepared based on a solution-processed ZnO thin-film transistor fabricated by inserting the NAu-rGO nanocomposite in the gate dielectric stack as a charge trapping medium. The transfer characteristic of the ZnO thin-film transistor memory device showed large clockwise hysteresis behaviour because of charge carrier trapping in the NAu-rGO nanocomposite. Under positive and negative bias conditions, clear positive and negative threshold voltage shifts occurred, which were attributed to charge carrier trapping and de-trapping in the ZnO/NAu-rGO/SiO2 structure. Also, the photothermal effect of the NAu-rGO nanocomposites on MCF7 breast cancer cells caused inhibition of ~80% cells after irradiation with infrared light (0.5 W cm-2) for 5 min.

Controlled Functionalization of Graphene by Oxo-addends

The single carbon layer graphene and especially its oxidized derivatives, such as graphene oxide (GO), are in the focus of research that started already 150 years ago [1–6]. GO is a collective term for various single layers of graphene (with lattice defects) functionalized by oxo-addends. The type of oxo-groups is not defined, but epoxy and hydroxyl groups dominate the structure in addition to in-plane lattice defects on the percent scale. Those defects are rarely considered in chemical functionalization approaches and it is impossible to distinguish between functionalization of surface oxo-groups and in-plane oxo-groups.

This chapter focuses on functionalized derivatives of graphene with an almost intact carbon framework, termed “oxo-functionalized graphene” (oxo-G1, index indicates the number of layers). Avoiding in-plane defects further allows the development of a controlled chemistry of graphene with oxo-addends. However, general approaches of conventional GO chemistry are summarized in a separate section.

Molecular assembly on two-dimensional materials

Molecular self-assembly is a well-known technique to create highly functional nanostructures on surfaces. Self-assembly on two-dimensional (2D) materials is a developing field driven by the interest in functionalization of 2D materials in order to tune their electronic properties. This has resulted in the discovery of several rich and interesting phenomena. Here, we review this progress with an emphasis on the electronic properties of the adsorbates and the substrate in well-defined systems, as unveiled by scanning tunneling microscopy. The review covers three aspects of the self-assembly. The first one focuses on non-covalent self-assembly dealing with site-selectivity due to inherent moiré pattern present on 2D materials grown on substrates. We also see that modification of intermolecular interactions and molecule-substrate interactions influences the assembly drastically and that 2D materials can also be used as a platform to carry out covalent and metal-coordinated assembly. The second part deals with the electronic properties of molecules adsorbed on 2D materials. By virtue of being inert and possessing low density of states near the Fermi level, 2D materials decouple molecules electronically from the underlying metal substrate and allow high-resolution spectroscopy and imaging of molecular orbitals. The moiré pattern on the 2D materials causes site-selective gating and charging of molecules in some cases. The last section covers the effects of self-assembled, acceptor and donor type, organic molecules on the electronic properties of graphene as revealed by spectroscopy and electrical transport measurements. Non-covalent functionalization of 2D materials has already been applied for their application as catalysts and sensors. With the current surge of activity on building van der Waals heterostructures from atomically thin crystals, molecular self-assembly has the potential to add an extra level of flexibility and functionality for applications ranging from flexible electronics and OLEDs to novel electronic devices and spintronics.

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.

Chemical reactivity of graphene oxide towards amines elucidated by solid-state NMR

Graphene oxide (GO) is an attractive nanomaterial for many applications. Controlling the functionalization of GO is essential for the design of graphene-based conjugates with novel properties. But, the chemical composition of GO has not been fully elucidated yet. Due to the high reactivity of the oxygenated moieties, mainly epoxy, hydroxyl and carboxyl groups, several derivatization reactions may occur concomitantly. The reactivity of GO with amine derivatives has been exploited in the literature to design graphene-based conjugates, mainly through amidation. However, in this study we undoubtedly demonstrate using magic angle spinning (MAS) solid-state NMR that the reaction between GO and amine functions occurs via ring opening of the epoxides, and not by amidation. We also prove that there is a negligible amount of carboxylic acid groups in two GO samples obtained by a different synthesis process, hence eliminating the possibility of amidation reactions with amine derivatives. This work brings additional insights into the chemical reactivity of GO, which is fundamental to control its functionalization, and highlights the major role of MAS NMR spectroscopy for a comprehensive characterization of derivatized GO.

Fine tuning of graphene properties by modification with aryl halogens

Graphene and its derivatives belong to one of the most intensively studied materials. The radical reaction using halogen derivatives of arene-diazonium salts can be used for effective control of graphene's electronic properties. In our work we investigated the influence of halogen atoms (fluorine, chlorine, bromine and iodine) as well as their position on the benzene ring towards the electronic and electrochemical properties of modified graphenes. The electronegativity as well as the position of the halogen atoms on the benzene ring has crucial influence on graphene's properties due to the inductive and mesomeric effects. The results of resistivity measurement are in good agreement with the theoretical calculations of electron density within chemically modified graphene sheets. Such simple chemical modifications of graphene can be used for controllable and scalable synthesis of graphene with tunable transport properties.

Halogenation of epitaxial graphene grown on the Si-face of the SiC(0001) substrate and its further reaction with Grignard reagent

F-, Cl-, and Br-terminated epitaxial graphene (EG) on SiC were achieved but only chlorinated EG undergoes reaction with Grignard reagent.

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.).

3D graphene nanomaterials for binder-free supercapacitors: scientific design for enhanced performance

Because of the excellent intrinsic properties, especially the strong mechanical strength, extraordinarily high surface area and extremely high conductivity, graphene is deemed as a versatile building block for fabricating functional materials for energy production and storage applications. In this article, the recent progress in the assembly of binder-free and self-standing graphene-based materials, as well as their application in supercapacitors are reviewed, including electrical double layer capacitors, pseudocapacitors, and asymmetric supercapacitors. Various fabrication strategies and the influence of structures on the capacitance performance of 3D graphene-based materials are discussed. We finally give concluding remarks and an outlook on the scientific design of binder-free and self-standing graphene materials for achieving better capacitance performance.

Hybrids of cationic porphyrins with nanocarbons

In the review hybrids of cationic porphyrins (i.e. porphyrins functionalized by quaternary pyridinium groups) with nanocarbons such as fullerenes, carbon nanotubes and graphene are described. Selected examples of these species are characterized in regard of their properties and possible applications.

Au/graphene oxide/carbon nanotube flexible catalyst film: synthesis, characterization and its application for catalytic reduction of 4-nitrophenol

We report a simple approach for fabricating flexible, free-standing and catalytic film composed of graphene oxide/carbon nanotube-Au. It shows excellent catalytic property in the reduction of 4-nitrophenol to 4-aminophenol reaction.

Doping graphene with an atomically thin two dimensional molecular layer

Atomically thin and chemically versatile GO sheets are used as p-type dopants of CVD-graphene. This method enables the strong, stable, large-scale, low-temperature, and controllable p-doping of graphene with preserved charge mobility, intrinsic roughness, and transmittance.

Strain engineering the properties of graphene and other two-dimensional crystals

This perspective discusses recent advances in using strain to engineer the properties of thin-layer materials such as graphene and transition metal dichalcogenides (TMDs).

Pyrene-fullerene C60 dyads as light-harvesting antennas

A series of pyrene-fullerene C₆₀ dyads bearing pyrene units (PyFC₁₂, PyFPy, Py₂FC₁₂ and PyFN) were synthesized and characterized. Their optical properties were studied by absorption and fluorescence spectroscopies. Dyads were designed in this way because the pyrene moeities act as light-harvesting molecules and are able to produce “monomer” (PyFC₁₂) or excimer emission (PyFPy, Py₂FC₁₂ and PyFN). The fluorescence spectra of the dyads exhibited a significant decrease in the amount of pyrene monomer and excimer emission, without the appearance of a new emission band due to fullerene C₆₀. The pyrene fluorescence quenching was found to be almost quantitative, ranging between 96%–99% depending on the construct, which is an indication that energy transfer occurred from one of the excited pyrene species to the fullerene C₆₀.