From Nanographene and Graphene Nanoribbons to Graphene Sheets: Chemical Synthesis

Facile and Green Synthesis of Graphene-Based Conductive Adhesives via Liquid Exfoliation Process

In this study, we report a facile and green process to synthesize high-quality and few-layer graphene (FLG) derived from graphite via a liquid exfoliation process. The corresponding characterizations of FLG, such as scanning electron microscopy (SEM), transmission electron microscope (TEM), atomic force microscopy (AFM) and Raman spectroscopy, were carried out. The results of SEM show that the lateral size of as-synthesized FLG is 1–5 μm. The results of TEM and AFM indicate more than 80% of graphene layers is <10 layers. The most surprising thing is that D/G ratio of graphite and FLG are 0.15 and 0.19, respectively. The result of the similar D/G ratio demonstrates that little structural defects were created via the liquid exfoliation process. Electronic conductivity tests and resistance of composite film, in terms of different contents of graphite/polyvinylidene difluoride (PVDF) and FLG/PVDF, were carried out. Dramatically, the FLG/PVDF composite demonstrates superior performance compared to the graphite/PVDF composite at the same ratio. In addition, the post-sintering process plays an important role in improving electronic conductivity by 85%. The composition-optimized FLG/PVDF thin film exhibits 81.9 S·cm⁻¹. These results indicate that the developed FLG/PVDF composite adhesives could be a potential candidate for conductive adhesive applications.

Temperature-Responsive Electrocatalysis Based on Poly(N-Isopropylacrylamide)-Modified Graphene Oxide (PNIPAm-GO)

Poly(N-isopropylacrylamide)-modified graphene oxide (PNIPAm-GO), which is a type of thermally responsive GO, was designed and synthesized through a covalent "grafting-from" strategy. The as-prepared modified nanosheets integrated the individual advantages of two components, such as the thermal sensitivity of the PNIPAm terminal as well as the conductivity and the open 2D structure of the GO substrate. PNIPAm-GO was able to perform the reversible regulation of hydrophilicity/hydrophobicity in aqueous solution upon variations in the temperature. Such a unique property might also lead to the utilization of PNIPAm-GO as an intelligent electrode material to achieve a switchable electrochemical response toward a [Fe(CN)₆ ]^3-/4- probe. The PNIPAm-GO modified glassy carbon electrode (PNIPAm-GO/GC electrode) was able to exhibit better electrochemical performance in an ON/OFF switching effect than the PNIPAm-modified glassy carbon electrode (PNIPAm/GC electrode) without GO owing to the intrinsic properties and large surface area of the introduced GO. Moreover, it was found that the PNIPAm-GO/GC electrode also displayed excellent thermally responsive electrocatalysis toward the detection of 1,4-dihydro-β-nicotinamide adenine dinucleotide (NADH) and dopamine (DA), which resulted in two different catalytic statuses on the same electrode. This kind of switchable catalytic performance of the PNIPAm-GO/GC electrode might greatly enhance the flexibility of its application, and thus it is expected to have wide potential for applications in the fields of biosensors and biocatalysis.

Alternating oligo(o,p-phenylenes) via ruthenium catalyzed diol-diene benzannulation: orthogonality to cross-coupling enables de novo nanographene and PAH construction

Ruthenium(0) catalyzed diol-diene benzannulation is applied to the conversion of oligo(p-phenylene vinylenes) 2a-c, 5 and 6 to alternating oligo(o,p-phenylenes) 10a-c, 11-13. Orthogonality with respect to conventional palladium catalyzed biaryl cross-coupling permits construction of p-bromo-terminated alternating oligo(o,p-phenylenes) 10b, 11-13, which can be engaged in Suzuki cross-coupling and Scholl oxidation. In this way, structurally homogeneous nanographenes 16a-f are prepared. Nanographene 16a, which incorporates 14 fused benzene rings, was characterized by single crystal X-ray diffraction. In a similar fashion, p-bromo-terminated oligo(p-phenylene ethane diol) 9, which contains a 1,3,5-trisubstituted benzene core, is converted to the soluble, structurally homogeneous hexa-peri-hexabenzocoronene 18. A benzothiophene-terminated pentamer 10c was prepared and subjected to Scholl oxidation to furnish the helical bis(benzothiophene)-fused picene derivative 14. The steady-state absorption and emission properties of nanographenes 14, 16a,b,d,e,h and 18 were characterized. These studies illustrate how orthogonality of ruthenium(0) catalyzed diol-diene benzannulation with respect to classical biaryl cross-coupling streamlines oligophenylene and nanographene construction.

Supramolecular Assemblies on Surfaces: Nanopatterning, Functionality, and Reactivity

Understanding how molecules interact to form large-scale hierarchical structures on surfaces holds promise for building designer nanoscale constructs with defined chemical and physical properties. Here, we describe early advances in this field and highlight upcoming opportunities and challenges. Both direct intermolecular interactions and those that are mediated by coordinated metal centers or substrates are discussed. These interactions can be additive, but they can also interfere with each other, leading to new assemblies in which electrical potentials vary at distances much larger than those of typical chemical interactions. Earlier spectroscopic and surface measurements have provided partial information on such interfacial effects. In the interim, scanning probe microscopies have assumed defining roles in the field of molecular organization on surfaces, delivering deeper understanding of interactions, structures, and local potentials. Self-assembly is a key strategy to form extended structures on surfaces, advancing nanolithography into the chemical dimension and providing simultaneous control at multiple scales. In parallel, the emergence of graphene and the resulting impetus to explore 2D materials have broadened the field, as surface-confined reactions of molecular building blocks provide access to such materials as 2D polymers and graphene nanoribbons. In this Review, we describe recent advances and point out promising directions that will lead to even greater and more robust capabilities to exploit designer surfaces.

Facile room temperature synthesis of large graphene sheets from simple molecules

The simplest way to produce large graphene sheets starting from simple molecules (benzene or n-hexane) under ambient conditions (temperature and pressure).

The largest graphene sample obtained through a chemical reaction under ambient conditions (temperature and pressure), using simple molecules such as benzene or n-hexane as precursors, is reported. Starting from a heterogeneous reaction between solid iron chloride and the molecular precursor (benzene and n-hexane) at a water/oil interface, graphene sheets with micrometric lateral size are obtained as a film deposited at the liquid/liquid (L/L) interface. The pathway involving the cyclization and aromatization of n-hexane to benzene at the L/L interface, and the sequence of conversion of benzene to biphenyl and biphenyl to condensed rings (which originates the graphene structures) was followed by different characterization techniques and a mechanistic proposal is presented. Finally, we demonstrate that this route can be extended for the synthesis of N-doped graphene, using pyridine as the molecular precursor.

Synthesis of Triply Fused Porphyrin-Nanographene Conjugates

Two unprecedented porphyrin fused nanographene molecules, 1 and 2, have been synthesized by the Scholl reaction from tailor-made precursors based on benzo[m]tetraphene-substituted porphyrins. The chemical structures were validated by a combination of high-resolution matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (HR MALDI-TOF MS), IR and Raman spectroscopy, and scanning tunnelling microscopy (STM). The UV-vis-near infrared absorption spectroscopy of 1 and 2 demonstrated broad and largely red-shifted absorption spectra extending up to 1000 and 1400 nm, respectively, marking the significant extension of the π-conjugated systems.

A Phenylene-Bridged Cyclohexa-meta-phenylene as Hexa-peri-hexabenzocoronene Precursor

A phenylene-bridged cyclohexa-meta-phenylene was synthesized via intramolecular Yamamoto coupling of an appropriate p-quinquephenyl derivative carrying four m-chlorophenyl substituents. The structural proof could be obtained by single-crystal X-ray diffraction analysis, which also revealed a slightly strained structure with an internal phenylene bridge. Notably, this cyclo-meta-phenylene served as a novel precursor for hexa-peri-hexabenzocoronene (HBC). The cyclodehydrogenation proceeded smoothly, providing the corresponding HBC derivative as confirmed by MALDI-TOF-MS, and UV/Vis spectroscopy.

Transition metal-assisted carbonization of small organic molecules toward functional carbon materials

Nanostructured carbon materials with large surface area and desired chemical functionalities have been attracting considerable attention because of their extraordinary physicochemical properties and great application potentials in catalysis, environment, and energy storage. However, the traditional approaches to fabricating these materials rely greatly on complex procedures and specific precursors. We present a simple, effective, and scalable strategy for the synthesis of functional carbon materials by transition metal-assisted carbonization of conventional small organic molecules. We demonstrate that transition metals can promote the thermal stability of molecular precursors and assist the formation of thermally stable polymeric intermediates during the carbonization process, which guarantees the successful preparation of carbons with high yield. The versatility of this synthetic strategy allows easy control of the surface chemical functionality, porosity, and morphology of carbons at the molecular level. Furthermore, the prepared carbons exhibit promising performance in heterogeneous catalysis and electrocatalysis.

Green and facile synthesis of few-layer graphene via liquid exfoliation process for Lithium-ion batteries

A green and facile method using jet cavitation (JC) was utilized to prepare few layer graphene (FLG) derived from artificial graphite delamination without adding any strong acids and oxidants. The JC method not only provides high quality FLG with high yield but also demonstrate excellent electrochemical performance as anode materials for Li-ion batteries. Raman spectroscopy, scanning electron microscopy (SEM), and transmission electron microscopy (TEM) as well as BET isotherms and XPS are carried out in this study. The results of atomic force microscopy (AFM) further revealed that up to 85% of the prepared FLG were less than 10 layers. This exfoliation process happened mainly due to the cavitation-induced intensive tensile stress acting on the layered materials. Electrochemical measurements demonstrate that graphite anode delivered only 240 mAh/g while FLG anode achieved more than 322 mAh/g at 5C rate test. These results indicate that JC method not only paves the way for cheaper and safer production of graphene but also holds great potential applications in energy-related technology.

A thiadiazole-capped nanoribbon with 18 linearly fused rings

Polycyclic aromatic hydrocarbons that extend over 2 nm in one dimension are seen as monodisperse graphene nanoribbons, which have attracted significant attention for a broad range of applications in organic electronics and photonics. Herein we report the synthesis of a stable bisthiadiazole-capped pyrene-containing nanoribbon with 18 linearly fused rings (NR-18-TD). Thanks to the presence of alternating tert-butyl and tri-iso-butylsilyl groups, NR-18-TD is highly soluble in organic solvents and therefore its structure and fundamental optoelectronic, redox and electrical properties could be unambiguously established. This work illustrates that NR-18-TD is a promising soluble NR-based n-type semiconductor for applications in organic electronics.

Experimental Study of the Structural Effect on the Nanosecond Nonlinear Optical Response of O-Doped Polycyclic Aromatic Hydrocarbons

The nonlinear optical response of some O-doped polycyclic aromatic hydrocarbons (PAHs) is systematically investigated in the present work aiming to understand the influence of structural effects on their nonlinear optical response. In that view, the third-order nonlinear optical properties of these PAHs were measured under 4 ns visible (532 nm) and infrared (1064 nm) laser excitation. The O-doped PAHs were found to exhibit large saturable absorption and negative sign nonlinear refraction under visible excitation, increasing both with the addition of naphthalene units and with the number of O atoms. Their nonlinear optical response was found to be negligible under infrared excitation. Similar measurements performed on thin films of these PAHs have shown that they maintain their large nonlinear optical response even in the solid state, confirming their high potential for optoelectronic and photonic applications.

Assisted Tip Sonication Approach for Graphene Synthesis in Aqueous Dispersion

Graphene (G) is a newcomer material that holds promising properties for many applications. The production of high quality G with a good yield is a long-standing goal for many researchers. This work emphasizes synthesis of dispersed graphene nanoplatelets (DGP) through aqueous dispersion technique in surfactant/water solution with the aid of tip sonication. A chemical method was also used to prepare graphene oxide (GO) and reduced graphene oxide (RGO) for comparison. Elemental analysis revealed the C:O ratio to be 12:1 for DGP but much lower for other graphene structures. Optical characterization of DGP, GO and RGO with UV and Raman spectroscopy confirmed the ideal structure of DGP. Moreover, X-ray diffraction (XRD) revealed the amorphous structure of DGP. Transmission electron microscope (TEM) imaging showed that DGP was composed of a few flat layers, unlike the wrinkled and partially bent multilayered G. Topological study of the DGP surface with scanning electron microscope (SEM) depicted its rough surface with (ra) value of 35 nm, as revealed using an atomic force microscope (AFM). Electrochemical measurements confirmed the higher conductivity of DGP over graphene prepared by chemical method due to lack of structural defects. Its perfect structure facilitates the mobility of charge carriers that makes it preferable in optoelectronic applications.

Toward Full Zigzag-Edged Nanographenes: peri-Tetracene and Its Corresponding Circumanthracene

Zigzag-edged nanographene with two rows of fused linear acenes, called as n- peri-acene (n-PA), is considered as a potential building unit in the arena of organic electronics. n-PAs with four ( peri-tetracene, 4-PA), five ( peri-pentacene, 5-PA) or more benzene rings in a row have been predicted to show open-shell character, which would be attractive for the development of unprecedented molecular spintronics. However, solution-based synthesis of open-shell n-PA has thus far not been successful because of the poor chemical stability. Herein we demonstrated the synthesis and characterization of the hitherto unknown 4-PA by a rational strategy in which steric protection of the zigzag edges playing a pivotal role. The obtained 4-PA possesses a singlet biradical character ( y₀ = 72%) and exhibits remarkable persistent stability with a half-life time ( t_1/2) of ∼3 h under ambient conditions. UV-vis-NIR and electrochemical measurements reveal a narrow optical/electrochemical energy gap (1.11 eV) for 4-PA. Moreover, the bay regions of 4-PA enable the efficient 2-fold Diels-Alder reaction, yielding a novel full zigzag-edged circumanthracene.

Enantiopure distorted ribbon-shaped nanographene combining two-photon absorption-based upconversion and circularly polarized luminescence

Herein we describe a distorted ribbon-shaped nanographene exhibiting unprecedented combination of optical properties in graphene-related materials, namely upconversion based on two-photon absorption (TPA-UC) together with circularly polarized luminescence (CPL). The compound is a graphene molecule of ca. 2 nm length and 1 nm width with edge defects that promote the distortion of the otherwise planar lattice. The edge defects are an aromatic saddle-shaped ketone unit and a [5]carbohelicene moiety. This system is shown to combine two-photon absorption and circularly polarized luminescence and a remarkably long emission lifetime of 21.5 ns. The [5]helicene is responsible for the chiroptical activity while the push-pull geometry and the extended network of sp2 carbons are factors favoring the nonlinear absorption. Electronic structure theoretical calculations support the interpretation of the results.

Metal Free Graphene Oxide (GO) Nanosheets and Pristine-Single Wall Carbon Nanotubes (p-SWCNTs) Biocompatibility Investigation: A Comparative Study in Different Human Cell Lines

The in vitro biocompatibility of Graphene Oxide (GO) nanosheets, which were obtained by the electrochemical exfoliation of graphite electrodes in an electrolytic bath containing salts, was compared with the pristine Single Wall Carbon Nanotubes (p-SWCNTs) under the same experimental conditions in different human cell lines. The cells were treated with different concentrations of GO and SWCNTs for up to 48 h. GO did not induce any significant morphological or functional modifications (demonstrating a high biocompatibility), while SWNCTs were toxic at any concentration used after a few hours of treatment. The cell viability or cytotoxicity were detected by the trypan blue assay and the lactate dehydrogenase LDH quantitative enzymatic test. The Confocal Laser Scanning Microscopy (CLSM) and transmission electron microscopy (TEM) analysis demonstrated the uptake and internalization of GO sheets into cells, which was localized mainly in the cytoplasm. Different results were observed in the same cell lines treated with p-SWCNTs. TEM and CLSM (Confocal Laser Scanning Microscopy) showed that the p-SWCNTs induced vacuolization in the cytoplasm, disruption of cellular architecture and damage to the nuclei. The most important result of this study is our finding of a higher GO biocompatibility compared to the p-SWCNTs in the same cell lines. This means that GO nanosheets, which are obtained by the electrochemical exfoliation of a graphite-based electrode (carried out in saline solutions or other physiological working media) could represent an eligible nanocarrier for drug delivery, gene transfection and molecular cell imaging tests.

Behaviour of the XH-*-π and YX-*-π interactions (X, Y = F, Cl, Br and I) in the coronene π-system, as elucidated by QTAIM dual functional analysis with QC calculations

The dynamic and static nature of XH-*-π and YX-*-π in the coronene π-system (π(C24H12)) is elucidated by QTAIM dual functional analysis, where * emphasizes the presence of bond critical points (BCPs) in the interactions. The nature of the interactions is elucidated by analysing the plots of the total electron energy densities H b(r c) versus H b(r c) - V b(r c)/2 [=(ħ 2/8m)∇2 ρ b(r c)] for the interactions at BCPs, where V b(r c) are the potential energy densities at the BCPs. The data for the perturbed structures around the fully optimized structures are employed for the plots in addition to those of the fully optimized structures. The plots are analysed using the polar coordinate of (R, θ) for the data of the fully optimized structures, while those containing the perturbed structures are analysed using (θ p, κ p), where θ p corresponds to the tangent line of each plot and κ p is the curvature. Whereas (R, θ) show the static nature, (θ p, κ p) represent the dynamic nature of the interactions. All interactions in X-H-*-π(C24H12) (X = F, Cl, Br and I) and Y-X-*-π(C24H12) (Y-X = F-F, Cl-Cl, Br-Br, I-I, F-Cl, F-Br and F-I) are classified by pure CS (closed shell) interactions and are characterized as having the vdW nature, except for X-H = F-H and Y-X = F-Cl, F-Br and F-I, which show the typical-HB nature without covalency. The structural features of the complexes are also discussed.

Functionalization of Graphene Aerogels and their Applications in Energy Storage and Conversion

Functionalized graphene aerogels (GAs) not only own the advantages of the original ones like large specific surface area, three-dimensional porous structures, high specific capacitance and excellent cyclic stability, but also realize the function expansion due to the collective properties endowed via different methods. These characteristics make them advantageous in some promising applications. In this minireview, we focus on the various functionalization methods of GAs and especially their use in the applications of energy storage and conversion like batteries, supercapacitors and fuel cells, etc.

Efficient energy transfer between coronene-modified permethyl-β-cyclodextrins and porphyrin for light induced DNA cleavage

A novel supramolecular assembly was constructed by the noncovalent complexation of hexa-cata-hexabenzocoronene modified permethyl-β-cyclodextrins with tetrasodium tetraphenylporphyrintetrasulfonate in water, exhibiting highly efficient excited energy transfer behaviors and a promising DNA photocleavage ability.

Dehydrogenative homocoupling of tetrafluorobenzene on Pd(111) via para-selective C-H activation

Aryl homocoupling reactions via meta- and ortho-selective C-H activation have been achieved on surfaces, but the highly important para-selective C-H activation has not been reported yet. Combined with scanning tunneling microscopy, time-of-flight secondary ion mass spectrometry and density functional theory, here we describe dehydrogenative homocoupling of tetrafluorobenzene on Pd(111) via para-selective C-H activation to form perfluorinated oligo(p-phenylene)s.

Sensitive detection of hydroquinone using exfoliated graphene-Au/glassy carbon modified electrode

Graphene nanosheets (EGr) were electrochemically prepared through one-step exfoliation of a graphite rod in a mixture of H₂SO₄:HNO₃ (3:1) at low bias (4 V). Subsequently, gold nanoparticles were attached to the graphene surface (EGr-Au) by the reduction of the metal precursor (HAuCl₄) in aqueous solution containing dispersed graphene sheets. According to the XRD investigation, the synthesized material consists of a mixture of few-layer (86%) and multi-layer (14%) graphene. The interlayer distance was found to be in the range of 0.466-0.342 nm, which is larger than the interlayer distance in graphite (0.335 nm). The average size of gold nanoparticles in the EGr-Au sample was 24 nm, in excellent agreement with the TEM results. The synthesized material was then employed to modify a glassy carbon (GC) substrate, in order to obtain a modified electrode (GC/EGr-Au). Next, the electrochemical behavior of hydroquinone (HQ) in the presence and absence of interfering species, catechol (CAT) and bisphenol A (BPA) was studied and the corresponding calibration curves were plotted. Thus, in solutions without interfering species, the GC/EGr-Au electrode has a wide linear range (3 × 10^-7-10^-4 M), high sensitivity (0.089 A M^-1) and low detection limit (LOD = 10^-7 M; S/N = 3). The presence of either catechol or bisphenol A leads to the increase of LOD to 2 × 10^-7 M, and in addition changes the electrode sensitivity, up to 0.146 A M^-1.

Monodisperse N-Doped Graphene Nanoribbons Reaching 7.7 Nanometers in Length

The properties of graphene nanoribbons are highly dependent on structural variables such as width, length, edge structure, and heteroatom doping. Therefore, atomic precision over all these variables is necessary for establishing their fundamental properties and exploring their potential applications. An iterative approach is presented that assembles a small and carefully designed molecular building block into monodisperse N-doped graphene nanoribbons with different lengths. To showcase this approach, the synthesis and characterisation of a series of nanoribbons constituted of 10, 20 and 30 conjugated linearly-fused rings (2.9, 5.3, and 7.7 nm in length, respectively) is presented.

On-Surface Route for Producing Planar Nanographenes with Azulene Moieties

Large aromatic carbon nanostructures are cornerstone materials due to their increasingly active role in functional devices, but their synthesis in solution encounters size and shape limitations. New on-surface strategies facilitate the synthesis of large and insoluble planar systems with atomic-scale precision. While dehydrogenation is usually the chemical zipping reaction building up large aromatic carbon structures, mostly benzenoid structures are being produced. Here, we report on a new cyclodehydrogenation reaction transforming a sterically stressed precursor with conjoined cove regions into a planar carbon platform by incorporating azulene moieties in their interior. Submolecular resolution STM is used to characterize this exotic large polycyclic aromatic compound on Au(111) yielding unprecedented insight into a dehydrogenative intramolecular aryl-aryl coupling reaction. The resulting polycyclic aromatic carbon structure shows a [18]annulene core hosting peculiar pore states confined at the carbon cavity.

The mechanochemical Scholl reaction – a solvent-free and versatile graphitization tool

Ball milling was applied to a Scholl reaction of dendritic oligophenylene precursors to produce benchmark nanographenes under solvent-free conditions.

Building a 22-ring nanographene by combining in-solution and on-surface syntheses

A nanographene formed by the fusion of 22 benzene rings has been prepared by combining in-solution cycloaddition reactions and on-surface cyclodehydrogenations.

Recent advances in three-dimensional graphene based materials for catalysis applications

This review presents recent theoretical and experimental progress in the construction, properties, and catalytic applications of 3D graphene-based materials.

Synthesis of distorted nanographenes containing seven- and eight-membered carbocycles

We highlight recent progress in bottom-up synthesis of well-defined distorted polyaromatic hydrocarbons with saddle shapes containing heptagonal and octagonal carbocycles.