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Graphene is a perfect 2D crystal of covalently bonded carbon atoms and constitutes the building block for all graphitic structures. Its superior properties make it an attractive material for a variety of technological applications. However, mass production does not meet the initial expectations. Chemical Vapor Deposition (CVD) is currently the only available method for large‐scale automated production, but the produced graphene sheets suffer from structural and morphological defects that degrade considerably the mechanical and other physical properties of synthesized graphene. Recently, the use of liquid metal catalysts (LMCat) has been proposed as an alternative platform for facile and high‐quality synthesis of single‐crystal graphene. Herein, simultaneous Raman spectroscopy combined with mechanical testing is adopted confirming that the reinforcing efficiency of the LMCat graphene is greatly improved. In fact, the effective Young's modulus of LMCat graphene has been found ≈630 GPa, which is significantly higher than the graphene grown on solid Cu substrate due to differences in the morphology of Cu substrate. Overall, this work paves the way for the development of defect‐free graphene of quality comparable to exfoliated flakes, and this will have a major technological impact for many applications. [ABSTRACT FROM AUTHOR]

Graphene and other two-dimensional materials (2DMs) have been shown to be promising candidates for the development of flexible and highly-sensitive strain sensors. However, the successful implementation of 2DMs in practical applications is slowed down by complex processing and still low sensitivity. Here, we report on a novel development of strain sensors based on Marangoni self-assemblies of graphene and of its hybrids with other 2DMs that can both withstand very large deformation and exhibit highly sensitive piezoresistive behaviour. By exploiting the Marangoni effect, reference films of self-assembled reduced graphene oxide (RGO) are first optimized, and the electromechanical behaviour has been assessed after deposition onto different elastomers demonstrating the potential of producing strain sensors suitable for different fields of application. Hybrid networks have been then prepared by adding hexagonal boron nitride (hBN) and fluorinated graphene (FGr) to the RGO dispersion. The hybrid integration of 2D materials is demonstrated to become a potential solution to increase substantially the sensitivity of the produced resistive strain sensors without compromising the mechanical integrity of the film. In fact, for large quasi-static deformations, a range of gauge factor values up to 2000 were demonstrated, while retaining a stable performance under cyclic deformations. [ABSTRACT FROM AUTHOR]

The very serious problem of temperature and humidity regulation, especially for small and medium-sized museums, galleries, and private collections, can be mitigated by the introduction of novel materials that are easily applicable and of low cost. Within this study, archive boxes with innovative technology are proposed as "smart" boxes that can be used for storage and transportation, in combination with a nanocomposite material consisting of polyvinyl alcohol (PVA) and graphene oxide (GO). The synthesis and characterization of the PVA/GO structure with SEM, Raman, AFM, XRD, Optical Microscopy, and profilometry are fully discussed. It is shown that the composite material can be integrated into the archive box either as a stand-alone film or attached onto fitting carriers, for example, those made of corrugated board. By applying the PVA/GO membrane this way, even with strong daily temperature fluctuations of ΔT = ±24.1 °C, strong external humidity fluctuations can be reduced by −87% inside the box. Furthermore, these humidity regulators were examined as Volatile Organic Compounds (VOCs) adsorbers since gas pollutants like formic acid, formaldehyde, acetic acid, and acetaldehyde are known to exist in museums and induce damages in the displayed or stored items. High rates of VOC adsorption have been measured, with the highest ones corresponding to formic acid (521% weight increase) and formaldehyde (223% weight increase). [ABSTRACT FROM AUTHOR]

Laser‐fabrication of graphene from cellulose‐based feedstock materials often requires extensive preprocessing. This work demonstrates laser fabrication of porous, 3D graphene from a new class of marine‐based sustainable materials–chitosan biopolymers. The biopolymer films contain only chitosan, acetic acid, glycerol, and water. Fourier transform infrared spectroscopy studies indicate that the cured chitosan films still retain a significant water content (≈30%), enabling production of flexible films. A simple 3‐step laser fabrication process is presented using low‐cost infrared (CO2, 2.1 W) and visible (405 nm, 0.5 W) hobbyist laser engravers, with measured sheet resistance values as low as 40 ohms sq.−1. Transient electrochemical detection of an inner sphere redox molecule is demonstrated using a graphene‐like carbon working electrode fabricated on a water‐soluble chitosan substrate. [ABSTRACT FROM AUTHOR]

Ultra-sensitive and responsive humidity sensors were fabricated by deposition of graphene oxide (GO) on laser-induced graphene (LIG) electrodes fabricated by a low-cost visible laser scribing tool. The effects of GO layer thickness and electrode geometry were investigated. Sensors comprising 0.33 mg/mL GO drop-deposited on spiral LIG electrodes exhibited high sensitivity up to 1800 pF/% RH at 22 °C, which is higher than previously reported LIG/GO sensors. The high performance was ascribed to the high density of the hydroxyl groups of GO, promoted by post-synthesis sonication treatment, resulting in high water physisorption rates. As a result, the sensors also displayed good stability and short response/recovery times across a wide tested range of 0–97% RH. The fabricated sensors were benchmarked against commercial humidity sensors and displayed comparable performance and stability. Finally, the sensors were integrated with a near-field communication tag to function as a wireless, battery-less humidity sensor platform for easy read-out of environmental humidity values using smartphones. [ABSTRACT FROM AUTHOR]

The use of graphene in a form of discontinuous flakes in polymer composites limits the full exploitation of the unique properties of graphene, thus requiring high filler loadings for achieving- for example- satisfactory electrical and mechanical properties. Herein centimetre-scale CVD graphene/polymer nanolaminates have been produced by using an iterative 'lift-off/float-on' process and have been found to outperform, for the same graphene content, state-of-the-art flake-based graphene polymer composites in terms of mechanical reinforcement and electrical properties. Most importantly these thin laminate materials show a high electromagnetic interference (EMI) shielding effectiveness, reaching 60 dB for a small thickness of 33 μm, and an absolute EMI shielding effectiveness close to 3·105 dB cm2 g−1 which is amongst the highest values for synthetic, non-metallic materials produced to date. The properties of graphene/polymer composites are usually limited by the use of discontinuous graphene flakes. Here, the authors report a fabrication method to realise continuous cm-scale graphene/polymer nanolaminates with enhanced electromagnetic interference shielding effectiveness, conductivity and mechanical properties. [ABSTRACT FROM AUTHOR]

Achieving structural superlubricity in graphitic samples of macroscale size is particularly challenging due to difficulties in sliding large contact areas of commensurate stacking domains. Here, we show the presence of macroscale structural superlubricity between two randomly stacked graphene layers produced by both mechanical exfoliation and chemical vapour deposition. By measuring the shifts of Raman peaks under strain we estimate the values of frictional interlayer shear stress (ILSS) in the superlubricity regime (mm scale) under ambient conditions. The random incommensurate stacking, the presence of wrinkles and the mismatch in the lattice constant between two graphene layers induced by the tensile strain differential are considered responsible for the facile shearing at the macroscale. Furthermore, molecular dynamic simulations show that the stick-slip behaviour does not hold for incommensurate chiral shearing directions for which the ILSS decreases substantially, supporting the experimental observations. Our results pave the way for overcoming several limitations in achieving macroscale superlubricity using graphene. Superlubricity in macro-scale graphitic samples is hampered by commensurate stacking domains that prevent facile sliding between adjacent graphene layers. Here, the authors show the presence of macroscale structural superlubricity between two randomly stacked graphene layers produced by both mechanical exfoliation and CVD upon the imposition of a tensile stress. [ABSTRACT FROM AUTHOR]

In this study, we explore the effect of carbon support on the performance of anodic electrodes for polymer electrolyte membrane fuel cells (PEMFCs). Pt−Ru catalysts supported on different carbon materials were synthesized by wet impregnation method and characterized by means of Raman, XRD, TEM, and N2 adsorption analysis. The electrocatalytic activity of the prepared catalysts was studied during hydrogen oxidation reaction experiments (HOR) as well as during the operation of a fuel cell using pure H2, and H2‐carbon monoxide anode feeding. The results show that the crystalline phase and the point of zero charge (pzc) of the carbon supports play an important role in the metal particle size and consequently in the catalyst electrocatalytic activity. Carbon supports with amorphous phase and high values of pzc, result in catalysts with large metal particle size leading to low electrocatalytic activity. On the other hand, using graphene derivative or carbon nanotubes (CNT) in different catalysts generates smaller metal particle size which results in higher electrocatalytic activity. [ABSTRACT FROM AUTHOR]

Patterning of graphene into micro- and nano-ribbons allows for tunability in emerging fields such as flexible electronic and optoelectronic devices, and is gaining interest for the production of more efficient reinforcement for composite materials. In this work we fabricate micro-ribbons from graphene synthesized via chemical vapor deposition (CVD) by combining ultraviolet (UV) photolithography and dry etching oxygen plasma treatments. We used Raman spectral imaging to confirm the effiectiveness of the patterning procedure, which is suitable for large-area patterning of graphene on wafer-scale, and confirms that the quality of graphene remains unaltered. The produced micro-ribbons were finally transferred and embedded into a polymeric matrix and the mechanical response was investigated by in-situ mechanical investigation combining Raman spectroscopy and tensile/compressive tests. [ABSTRACT FROM AUTHOR]

Mechanical properties of graphene prepared by chemical vapour deposition (CVD) are not easily comparable to the properties of nearly perfect graphene prepared by mechanical cleavage. In this work, we attempt to investigate the mechanical performance of CVD graphene (simply supported or embedded in polymer matrix), transferred by two different techniques, under uniaxial loading with simultaneous in situ monitoring by Raman microspectroscopy. The level of charge transfer doping and strain is assessed using the vector analysis modified for uniaxial strain. The strain distribution across the samples varies significantly, owing to the growth and transfer process, which induces wrinkles and faults in the CVD graphene. In simply supported specimens, the stress transfer efficiency is generally very low and the changes in Raman spectra are dominated by variations in the charge transfer originating from the realignment of the domains on the substrate upon the application of strain. In contrast, samples covered with an additional polymer layer exhibit an improved stress transfer efficiency, and the alterations of charge doping levels are negligible. In fully embedded specimens, the variations in stress transfer efficiencies are caused by the size of the effective graphene domains defined by cracks, folds and/or wrinkles. [ABSTRACT FROM AUTHOR]

Exfoliated monolayer graphene flakes were embedded in a polymer matrix and loaded under axial compression. By monitoring the shifts of the 2D Raman phonons of rectangular flakes of various sizes under load, the critical strain to failure was determined. Prior to loading care was taken for the examined area of the flake to be free of residual stresses. The critical strain values for first failure were found to be independent of flake size at a mean value of -0.60% corresponding to a yield stress up to -6 GPa. By combining Euler mechanics with a Winkler approach, we show that unlike buckling in air, the presence of the polymer constraint results in graphene buckling at a fixed value of strain with an estimated wrinkle wavelength of the order of 1-2 nm. These results were compared with DFT computations performed on analogue coronene/ PMMA oligomers and a reasonable agreement was obtained. [ABSTRACT FROM AUTHOR]

Front Cover: Effect of Carbon Support on the Electrocatalytic Properties of Pt-Ru Catalysts (ChemElectroChem 19/2019) Keywords: PEM fuel cells; Pt-Ru catalysts; graphene; biochar; carbon black; carbon nanotubes PEM fuel cells, Pt-Ru catalysts, graphene, biochar, carbon black, carbon nanotubes. [Extracted from the article]

As an emerging class of materials, nanocarbons have attracted significant interest for practical applications due to their remarkable mechanical, electrical and thermal properties coupled with high surface areas and tunable surface chemistry. However, challenges like high aspect ratios and poor dispersibility in polymer matrices hinder their widespread use in technological applications. The problems are most prominently resolved with the use of free-standing nanocarbon sheets. The present paper reviews recent advancements in fabricating and utilizing free-standing sheets consisting of various nanocarbons: carbon nanotubes and 2D materials like graphene, graphene oxide, and reduced graphene oxide. It initially delves into the nanomechanics of these sheets, focusing on inter-particle cross-linking and nacre-like microstructures. Energy storage applications are also examined, with emphasis on the role of nanocarbon-based sheets in the enhancement of specific energy capacity and performance retention of batteries, electric double layer supercapacitors, and pseudocapacitors. In the field of electromagnetic interference shielding, the sheets' superior electrical conductivity and microstructures, which amplify internal reflections in the GHz and THz regions, are showcased. Their potential in heat dissipation, owing to their high thermal conductivity and large surface area, is also explored. Additionally, they are reviewed for membrane-based separation processes, specifically gas separation, reverse osmosis, forward osmosis, and pervaporation, highlighting properties like ion selectivity and chlorine resistance. The last discussion concerns the role of nanocarbon-based sheets in catalysis where they can enhance reaction efficiencies and promote sustainable solutions. Either as catalysts and/or supports, with key features such as high surface area, electrical conductivity, and adaptable functionalities, they showcase significant potential in various catalytic processes like electrocatalysis and environmental remediation. [Display omitted] • Mechanical strengthening via cross-linking of nanocarbons and nacre microstructure. • Nanocarbon-based energy storage devices with increased capacity and stability. • EMI shielding applications of nanocarbon sheets in the GHz and THz range. • Methods to increase in-plane and cross-plane thermal conductivity of the sheets. • Use of nanocarbon sheets in RO, NF, FO and gas separation applications. [ABSTRACT FROM AUTHOR]

A method that utilises atomic trajectories and velocities from molecular dynamics simulations has been suitably adapted and employed for the implicit calculation of the phonon dispersion curves of graphene. Classical potentials widely used in the literature were employed. Their performance was assessed for each individual phonon branch and the overall phonon dispersion, using available inelastic x-ray scattering data. The method is promising for systems with large scale periodicity, accounts for anharmonic effects and non-bonding interactions with a general environment, and it is applicable under finite temperatures. The temperature dependence of the phonon dispersion curves has been examined with emphasis on the doubly degenerate Raman active Γ-E2g phonon at the zone centre, where experimental results are available. The potentials used show diverse behaviour. The Tersoff-2010 potential exhibits the most systematic and physically sound behaviour in this regard, and gives a first-order temperature coefficient of χ = −0.05 cm−1/K for the Γ-E2g shift in agreement with reported experimental values. [ABSTRACT FROM AUTHOR]

Push-to-pull (PTP) testing is employed to probe the uniaxial tensile response of freestanding monolayer graphene. Various analytical approaches are employed to estimate the elastic modulus of end-clamped graphene samples, combining in-situ Raman spectroscopy and scanning electronic microscope (SEM) measurements. The utilization of spatially resolved Raman-derived strains for assessing the elastic properties of monolayer graphene leads to results consistent with previous experimental and theoretical values of the elastic modulus (approximately 1 TPa). Molecular dynamics (MD) simulations of (pristine and defective) freestanding graphene sheets uniaxially loaded under varying clamping conditions are performed to support the experimental observations. The computational results indicate that the mechanical responses of the sheets are affected by the type, the spatial profile, and the heterogeneity of the clamping. When uniaxial pulling of end-clamped graphene is applied by a substrate adhering to the graphene sheet through van der Waals forces (as in PTP testing), the elastic modulus may be highly underestimated due to often inhomogeneous stress distribution and slippage processes. The MD simulations predict that the elastic modulus of pristine monolayer graphene is approximately 1 TPa, whereas its fracture strength can reach values of up to 110 GPa. Overall, this study underscores the limitations of traditional analyses of PTP experiments (utilizing indentation readouts and SEM imaging) and proposes new potential avenues (involving Raman measurements) for future research on the elastic properties of 2D materials. [Display omitted] • Push-to-pull uniaxial straining is coupled with SEM and Raman spectroscopy. • In-situ Raman spectroscopy quantifies the deformation states of 2D materials. • Measurement of ultra-high elastic modulus (1 TPa) of monolayer graphene. • MD simulations reveal the influence of defects and clamping. [ABSTRACT FROM AUTHOR]

As being only one atom thick, most of the device applications require graphene to be partially or fully supported by a substrate, which is typically silicon dioxide (SiO 2). According to a common understanding, graphene interacts with SiO 2 through weak, long-range van der Waals forces, emerging between instantaneous/induced dipoles, in contrast to the experimental evidence that reveals a surprisingly high interaction between graphene and SiO 2. In order to get further insight into this phenomenon, we carried out diverse physical measurements on SiO 2 substrates, prepared via different fabrication protocols, with and without graphene on top. As a result, the role of the oxide surface charges is recognized for the first time as a main factor causing graphene to strongly interact with SiO 2. Our findings provide guidelines for designing 2D materials interaction with a substrate through modulation of surface charges. This, in turn, can facilitate the development of new graphene based microelectronic devices. Image 1 [ABSTRACT FROM AUTHOR]

Graphene was successfully employed as a catalyst for the activation of sodium persulfate, towards the effective degradation of propylparaben, an emerging micro-pollutant, representative of the parabens family. A novel process is proposed which utilizes a commercial graphene nano-powder as the catalyst and sodium persulfate as the oxidizing agent. It was found that over 95% of micro-pollutant degradation occurs within 15 min of reaction time. The effects of catalyst loading (75 mg/L to 1 g/L), sodium persulfate (SPS) concentration (10 mg/L to 1 g/L), initial solution pH (3–9) and initial paraben concentration (0.5 mg/L to 5 mg/L) were examined. Experiments were carried out in different aqueous conditions, including ultrapure water, bottled water and wastewater in order to investigate their effect on the degradation rate. The efficiency of the process was lower at complex water matrices signifying the role of organic matter as scavenger of the oxidant species. The role of radical scavengers was also investigated through the addition of methanol and tert-butanol in several concentrations, which was found to be important only in relatively high values. An experiment in which propylparaben was substituted by methylparaben was conducted and similar results were obtained. The consumption of SPS was found to be high in all pH conditions tested, surpassing 80% in near neutral environment. However, the results indicate that the sulfate radicals formed react with water in alkaline conditions, which are the optimal for the reaction, producing hydroxyl radicals which appear to be the dominant species leading to the rapid degradation of propylparaben. To the best of our knowledge, this is the first time pristine graphene has been implemented as an activator of sodium persulfate for the effective oxidation of micro-pollutants. [ABSTRACT FROM AUTHOR]

High quality graphene was produced by electrochemical exfoliation of graphite. The obtained material was dispersible in several organic solvents and when applied on a Si/SiO 2 substrate it formed thin sheets mostly of 1–3 layers with lateral dimensions ranging between 1 and 10 μm. The number of defects in these sheets was quite low as detected by Raman spectroscopy. Graphene was transferred on FTO electrodes by its dispersion in isopropanol and produced thin transparent films, which were combined with electrochemically deposited PEDOT and were used as counter electrodes in dye-sensitized solar cells. The synergy between the two materials was remarkable and the obtained hybrid electrocatalyst outperformed standard Pt nanoparticle electrocatalyst. [ABSTRACT FROM AUTHOR]

Abstract: A simple and efficient approach to exfoliate graphene sheets in solution was reported. The principle of this strategy involved the utilization of binary solvent mixtures which exhibit moderate miscibility. At certain composition, these solvent mixtures showed much more efficient graphene exfoliation, greater than in the case of neat solvents. By adopting a combination of short-time sonication and gradual centrifugation, the resulting suspensions were found to be highly enriched in mono- and few-layer graphene sheets. The structure and morphology of nanosheets were characterized using imaging techniques and spectroscopies. Statistical analysis from imaging techniques showed that 90% of graphene aggregates were less than five layers thick with a monolayer fraction of about 10%. [Copyright &y& Elsevier]

Abstract: A chemical vapor deposition (CVD) process for the production of continuous-high quality-graphene layers based on camphor decomposition on polycrystalline Ni foil, is demonstrated. In situ X-ray diffraction at the pyrolysis temperature of the Ni foil indicates the presence of dominant Ni <111> grains which play an important role in the carbon nucleation and growth. The topography of the grown graphene layers is studied by scanning electron microscopy and atomic force microscopy which show that the Ni surface is covered by continuous and wrinkled graphene carpets. Raman spectroscopy reveals the high quality of the graphene film which appears to be only a few monolayers thick. X-ray photoelectron spectroscopy indicates the existence of graphitic layers and the absence of any spectral features associated with carbides (NixC). The proposed CVD process is a sufficient method for large scale production of graphene films. [Copyright &y& Elsevier]

Nanocomposites based on the biomimetic brick and mortar architecture are gathering great attention recently due to the outstanding properties of the natural analogues. Thanks to the very high in-plane orientation of nanoplatelets and the low matrix content, these materials exhibit good mechanical performance combined with excellent functional properties based on the nanoplatelets characteristics. Key feature of these materials is the presence of a regular nanostructure that consists of alternated nanoplatelet and matrix layers. Such architecture is commonly attained by means of bottom-up manufacturing processes able to control the alternation of the two phases at the nanoscale. This differs markedly from the top-down manufacturing processes, which are suitable for an industrial scale up but fail to meet the expected requirements. In the present work, nacre-like graphene nanoplatelets (GNPs)/epoxy films at different filler content have been prepared by a top-down manufacturing technology and their mechanical properties in tension have been experimentally evaluated. The elastic modulus has been found to exhibit a maximum between 53 and 67 vol% filler content and then it starts dropping at higher loadings. This was attributed to the depletion of the polymeric matrix which disrupts the continuity of the matrix layer thus inducing incomplete GNP surface coverage. As a result, the effective area for stress-transfer is considerably reduced and this impairs the reinforcement efficiency. In order to explain this behaviour, a model is proposed for predicting the stress transfer characteristics in brick and mortar systems by paying attention to possible non-uniform matrix distribution over the nanoplatelets. The proposed analysis captures well the observed effects and paves the way for the development and further improvement of this new class of engineering materials. [Display omitted] [ABSTRACT FROM AUTHOR]

Fiber-reinforced composites (FRC) are nowadays one of the most widely used class of high-tech materials. In particular, sporting goods, cars and the wings and fuselages of airplanes are made of carbon fiber reinforced composites (CFRC). CFRC are mature commercial products, but are still challenging materials. Their mechanical and electrical properties are very good along the fiber axis, but can be very poor perpendicular to it; interfacial interactions have to be tailored for specific applications to avoid crack propagation– and delamination; fiber production includes high-temperature treatments of adverse environmental impact, leading to high costs. Recent research work shows that the performance of CFRC can be improved by addition of graphene or related 2-dimensional materials (GRM). Graphene is a promising additive for CFRC because: 1) Its all-carbon aromatic structure is similar to the one of carbon fiber (CF). 2) Its 2-dimensional shape, high aspect ratio, high flexibility and mechanical strength allow it to be used as a coating on the surface of fiber, or as a mechanical/electrical connection between different fiber layers. 3) Its tunable surface chemistry allows its interaction to be enhanced with either the fiber or the polymer matrix used in the composite and 4) in contrast to carbon fibers or nanotubes, it is easily produced on a large scale at room temperature, without metal catalysts. Here, we summarize the key strategic advantages that could be obtained in this way, and some of the recent results that have been obtained in this field within the Graphene Flagship project and worldwide. [ABSTRACT FROM AUTHOR]

Graphene wetting by polymers is a critical issue to both the success of polymer-aided transfer of large size sheets onto specific substrates and to the development of well performing nanocomposites. Here we show for the first time that high temperature contact angle measurements can be performed to investigate the wettability of CVD graphene by molten polymers. In particular, poly(methyl methacrylate), a widely used polymer support for CVD graphene transfer, has been adopted herein for this proof-of-concept study and the values of contact angle and work of adhesion have been provided in the temperature range 170–200 °C. Image 1 • We show that high temperature contact angle measurements can be performed to investigate the wettability of CVD graphene by molten polymers. • As proof-of-concept, the system molten PMMA on CVD graphene has been investigated in the temperature range 170 – 200 ° C. • Kinetics of wetting were studied and the duration of the transient is consistent with the characteristic time for interfacial-tension-driven motions. • The work of adhesion between graphene and PMMA has been calculated in the investigated temperature range. [ABSTRACT FROM AUTHOR]