Graphene-related Materials Research Articles

Evidencing opposite charge-transfer processes at TiO2/graphene-related materials interface through a combined EPR, photoluminescence and photocatalysis assessment

Combining TiO2 with graphene or with graphene related materials (GRMs) is an attractive strategy for enhancing the TiO2 photocatalytic activity through charge separation at the TiO2/GRMs hetero-interface. With the aim of shed light on the various factors that can affect the actual TiO2/GRMs charge transfer behavior, in the present work two series of TiO2(P25)/GRM composites containing growing amount (up to 10 wt.%) of GRMs (rGO and graphene-like layers, GL) were considered. The experimental campaign was carried out by combining standard characterization techniques, EPR analysis, excitation-resolved photoluminescence (PLE) spectroscopy and methylene blue photodegradation tests coupled with scavenging tests. Although 1% GRM load improves MB photodegradation of both P25/GRM composites, no significant MB photodegradation activity differences among the employed P25/GRM composites were highlighted by standard photocatalytic tests. Nevertheless, EPR, PLE and photodegradation analyses with scavenging agents evidenced basic differences in the two P25/GRM composites. EPR analysis showed that the spin density in rGO and GL respectively increase and decrease, as they are brought in contact with P25 in the composites. The photoluminescence (PL) spectral shape of P25 were not modified by interaction with rGO, and its intensity was uniformly and smoothly quenched as the rGO load was increased. On another hand, P25 in P25-GL composites exhibited an enhanced and spectrally-modified PL intensity, with a sharp decrease vs GL load. Hole and ROS scavenging tests evidenced that the oxidation by reactive radicals formed from photoexcited electrons is negligibly affected by the presence of the two GRMs, while the oxidation by reactive radicals formed from photoinduced holes is enhanced in P25-rGO composites and hindered in P25-GL ones. These findings suggested that two opposite charge-transfers mechanisms occur, namely electron transfer from P25 to rGO and hole transfer from P25 to GL.

Graphene-like layers as promising chemiresistive sensing material for detection of alcohols at low concentration

In the manifold of materials for Volatile Organic Compound (VOC) sensing, graphene related materials (GRMs) gain special attention thanks to their versatility and overall chemico-physical tunability as a function of specific applications. In this work, the sensing performances of graphene-like (GL) layers, a new material belonging to the GRM family, are tested against ethanol and n-butanol. Two typologies of GL samples were produced by employing two different approaches and tested in view of their application as VOC sensors. The experiments were performed under atmospheric pressure, in dry air, and at room temperature and demonstrated that the sensing capabilities are related to the film surface features. The results indicated that GL films are promising candidates for the detection of low concentrations of VOCs at room temperature. The present investigation thus paves the way for VOC sensing optimization using cost-effective and easily scalable materials.

Renaissance of graphene-related materials in photovoltaics due to the emergence of metal halide perovskite solar cells

This literature review presents the research progress and future perspectives of graphene-based based mesoscopic and planar perovskite solar cells.

Graphene oxide electrochemistry: the electrochemistry of graphene oxide modified electrodes reveals coverage dependent beneficial electrocatalysis.

The modification of electrode surfaces is widely implemented in order to try and improve electron transfer kinetics and surface interactions, most recently using graphene related materials. Currently, the use of ‘as is’ graphene oxide (GO) has been largely overlooked, with the vast majority of researchers choosing to reduce GO to graphene or use it as part of a composite electrode. In this paper, ‘as is’ GO is explored and electrochemically characterized using a range of electrochemical redox probes, namely potassium ferrocyanide(II), N,N,N′,N′-tetramethyl-p-phenylenediamine (TMPD), dopamine hydrochloride and epinephrine. Furthermore, the electroanalytical efficacy of GO is explored towards the sensing of dopamine hydrochloride and epinephrine via cyclic voltammetry. The electrochemical response of GO is benchmarked against pristine graphene and edge plane-/basal plane pyrolytic graphite (EPPG and BPPG respectively) alternatives, where the GO shows an enhanced electrochemical/electroanalytical response. When using GO as an electrode material, the electrochemical response of the analytes studied herein deviate from that expected and exhibit altered electrochemical responses. The oxygenated species encompassing GO strongly influence and dominate the observed voltammetry, which is crucially coverage dependent. GO electrocatalysis is observed, which is attributed to the presence of beneficial oxygenated species dictating the response in specific cases, demonstrating potential for advantageous electroanalysis to be realized. Note however, that crucial coverage based regions are observed at GO modified electrodes, owing to the synergy of edge plane sites and oxygenated species. We report the true beneficial electrochemistry of GO, which has enormous potential to be beneficially used in various electrochemical applications ‘as is’ rather than be simply used as a precursor to making graphene and is truly a fascinating member of the graphene family.

Controlled synthesis of graphite oxide: Formation process, oxidation kinetics, and optimized conditions

Graphite oxide (GO) is one of the most extensively studied materials and has been tested for numerous applications due to its unique properties. Nevertheless, a quantitative description of complicated transfer and reaction rates of the oxidation of graphite is still not available, which essentially hinders large-scale production of high-quality GO and other graphene related materials. In this work, GO is prepared from flake graphite (FG) by a modified Hummers method. Size and color evolutions of time-dependent complementary domains, i.e. the starting GO domain and the remaining FG domain, are monitored during the entire oxidation process. The oxidation of FG in acidic oxidizing medium can be interpreted as a contracting area process controlled by phase boundary. Reaction rate constant (k) and kinetic parameters (Ea, lnA) are obtained after a systematic investigation of the influence of reaction temperature, concentration of sulfuric acid, and oxidizing agent on the oxidation, with the aid of R2 mathematical model. Using the kinetic results, the oxidation process and the conversion rate from FG to GO thus become controllable. Both intermediate products and final GO products are studied using XRD, TGA, and XPS to reveal the oxidation mechanism. The degree of oxidation of FG and the content of major functional groups on the surface of products can thus be optimized. Our research results are valuable to understanding fundamental mechanism of graphite oxidation and to achieving industrial production of high-quality GO with controllable degree of oxidation and tunable proportion of oxygen-containing functional groups for a variety of applications.

Evaluation of Graphene Aerogel Monolith-Based Solid-Phase Extraction for the Separation of Pyrethroids from Water Samples

Graphene aerogel monolith was synthesized directly in the solid-phase extraction cartridge through template-free “sol-cryo” method and used for the separation of pyrethroids insecticides from water samples, followed by gas chromatography–mass spectrometry analysis. Graphene sheets, the basic components of graphene aerogel, extracted the analytes from water samples through π–π stacking interaction and hydrophobic interaction. Then the targets were desorbed in ethyl acetate for subsequent analysis. Several parameters such as adsorption property, the type of the elution solvent and elution volume, the loading volume and its pH were investigated to achieve the best solid-phase extraction performance. Low limits of detection in the range of 0.83–9.31 ng L−1 and acceptable precision (RSDs 3.8–11.7%) were achieved under the optimized conditions. The developed method was applied to extract pyrethroids from real water samples with satisfactory recoveries between 76.2 and 106.0%. The present work extends the application of graphene related materials in separation science.

Graphene oxide on magnetron sputtered silver thin films for SERS and metamaterial applications

Abstract In the last years the potential of combining the attractive materials characteristics of graphene related materials and silver nanostructures for SERS and metamaterials has emerged. Here, we report of graphene oxide thin films deposited by dip-coating on magnetron sputtered silver thin films. Our work represents a novelty in the field of the study of graphene oxide- silver composites, since magnetron sputtering deposition is an alternative way to silver thin films fabrication; previous works used instead silver nitrate aqueous solution mixed with the graphene oxide. Micro-Raman technique, morphological analysis and variable angle spectroscopic ellipsometry were performed. The final SERS signal intensity was investigated and we found Raman peaks dependent on the intensity of the laser and the thickness of silver and GO films. These results could open somestudies on plasmonics and on the reduction of graphene oxide mediated by silver thin films. Moreover, effective medium theory calculations show the possible use of these graphene oxide/silver thin films in multilayer hyperbolic metamaterials for optical applications.

Surface modification of carbon fibre using graphene–related materials for multifunctional composites

Abstract Graphene-related materials (GRMs) have been identified as excellent nano-reinforcements for carbon fibre reinforced polymers (CFRPs) with regard to a wide range of engineering applications. GRMs are easily produced from their chief source, graphite, which is relatively affordable and abundantly available around the globe. The outstanding properties of GRMs, such as their large surface area, high mechanical strength and low manufacturing cost bring them to be distinguished nano-reinforcements for CFRPs to form multi-functional and multiscale composites. In this paper, the importance of using GRMs to enhance the properties of CFRPs is highlighted. Different synthesis methods for depositing GRMs onto the surface of carbon fibre and their effectiveness of improving the properties of host materials are reviewed and discussed. At this stage, more works are still needed to understand the basic stress transfer mechanism of GRM-coated CF composites. Their property enhancement at cryogenic environment are crucial for new aircraft and space engineering development.

Heat-Treated Transition Metal Hexacyanometallates with Trace Amount of Pt As Electrocatalysts for the Oxygen Reduction Reaction Based on Nitrogen Doped Graphene: Catalysts Development and Electrode Structure Design

In the recent research years is observed huge interest in design of new functional nanomaterials for developing new electrocatalysts for oxygen reduction reaction (ORR) in acid and alkaline media. The research has been focused on developing carbon nanostructures especially graphene/graphene oxide materials with the different transition metals (e.g. Co, Ni, Ag, Au, Cu, Mn) analogue of polynuclear Prussian Blue, namely with ultra-thin Co, and Ni hexacyanoferrate layers and trace amount of platinum for fuel cell applications. Electrocatalysts based on graphene and graphene-oxide (GO) are more homogeneous and possess properties such as excellent conductivity, good chemical stability and can be functionalized in a controlled manner. Following the heat-treatment step at higher temperatures, some thermal decomposition of the cyanometallate network occurs and, consequently, metallic sites are generated. Their formation and distribution are facilitated by the voltammetric potential cycling in acid and alkaline electrolytes. The most promising electrocatalytic results with respect to the reduction of oxygen (the highest currents and the most positive electroreduction potentials) have been obtained when graphene nanostructures are combined with analogue of polynuclear Prussian Blue and trace amount of Pt nanoparticles. What is even more important that, due to the presence of the polynuclear cyanoferrate modifier or linker, the amounts of the undesirable hydrogen peroxide intermediate are significantly decreased. An electrocatalytic system, that utilizes metal hexacyanometallates nanoparticles with trace amount of Pt modified graphene and graphene related materials, is developed and characterized here using transmission electron microscopy and such electrochemical diagnostic techniques as cyclic volammetry and rotating ring-disk voltammetry in a 0.5 M H2SO4 electrolyte and in a 0.1 M KOH electrolyte and upon introduction (as cathode) to the low-temperature hydrogen-oxygen fuel cell. Comparative measurements have been performed against the model noble metal (Vulcan-supported platinum nanoparticles) catalyst.

Environmental‐Friendly Assembly of Functional Graphene Hydrogels with Excellent Antibacterial Properties

AbstractBacterial contamination, harmful to human beings health and well‐being, has been a serious issue in china, even in the modern world. Graphene‐based materials have been found to have good antimicrobial properties. However, the research on three‐dimensional graphene related material with excellent antimicrobial activity is quite limited, which hinders its usage in protection of environment and sustainable development, such as in water treatment. In this work, we successfully design a facile, green and efficient strategy to fabricate three‐dimensional graphene hydrogel monoliths with excellent antibacterial properties by zinc ions coordination. The presence of zinc ions can maintain the structural integrity and the resulting sample exhibits excellent antimicrobial activities toward E. coli (99.5 ±3.6 %) and S. aureus (96.4 ±4.6 %) with increased glutathione oxidation capacity. The mechanism is also intensively investigated. The whole preparation process is carried out without using any toxic reducing agent, which may offer an alternative strategy for the fabrication of graphene related materials with excellent antibacterial properties.

Quercetin-mediated synthesis of graphene oxide-silver nanoparticle nanocomposites: a suitable alternative nanotherapy for neuroblastoma.

BackgroundGraphene and graphene-related materials have gained substantial interest from both academia and industry for the development of unique nanomaterials for biomedical applications. Graphene oxide (GO) and silver nanoparticles (AgNPs) are a valuable platform for the development of nanocomposites, permitting the combination of nanomaterials with different physical and chemical properties to generate novel materials with improved and effective functionalities in a single platform. Therefore, this study was conducted to synthesize a graphene oxide–silver nanoparticle (GO-AgNPs) nanocomposite using the biomolecule quercetin and evaluate the potential cytotoxicity and mechanism of GO-AgNPs in human neuroblastoma cancer cells (SH-SY5Y).MethodsThe synthesized GO-AgNPs were characterized using various analytical techniques. The potential toxicities of GO-AgNPs were evaluated using a series of biochemical and cellular assays. The expression of apoptotic and anti-apoptotic genes was measured by quantitative real-time reverse transcription polymerase chain reaction. Further, apoptosis was confirmed by caspase-9/3 activity and a terminal deoxynucleotidyl transferase dUTP nick end labeling assay, and GO-AgNPs-induced autophagy was also confirmed by transmission electron microscopy.ResultsThe prepared GO-AgNPs exhibited significantly higher cytotoxicity toward SH-SY5Y cells than GO. GO-AgNPs induced significant cytotoxicity in SH-SY5Y cells by the loss of cell viability, inhibition of cell proliferation, increased leakage of lactate dehydrogenase, decreased level of mitochondrial membrane potential, reduced numbers of mitochondria, enhanced level of reactive oxygen species generation, increased expression of pro-apoptotic genes, and decreased expression of anti-apoptotic genes. GO-AgNPs induced caspase-9/3-dependent apoptosis via DNA fragmentation. Finally, GO-AgNPs induced accumulation of autophagosomes and autophagic vacuoles.ConclusionIn this study, we developed an environmentally friendly, facile, dependable, and simple method for the synthesis of GO-AgNPs nanocomposites using quercetin. The synthesized GO-AgNPs exhibited enhanced cytotoxicity compared with that of GO at very low concentrations. This study not only elucidates the potential cytotoxicity against neuroblastoma cancer cells, but also reveals the molecular mechanism of toxicity.

Interaction of different forms of graphene with chicken embryo red blood cells

With the rapid development of graphene synthesis and functionalization approaches, graphene and its related derivatives have shown great potential in many applications in material science, including biomedical applications. Several in vitro and in vivo studies clearly showed no definitive risks, while others have indicated that graphene might become health hazards. In this study, we explore the biocompatibility of graphene-related materials with chicken embryo red blood cells (RBC). The hemolysis assay was employed to evaluate the in vitro blood compatibility of reduced graphene, graphene oxide, and reduced graphene oxide, because these materials have recently been used for biomedical applications, including injectable graphene-related particles. This study investigated structural damage, ROS production and hemolysis of chicken embryo red blood cells. Different forms of graphene, when incubated with chicken embryo RBC, were harmful to cell structure and induced hemolysis.

Uptake of label-free graphene oxide by Caco-2 cells is dependent on the cell differentiation status

BackgroundUnderstanding the interaction of graphene-related materials (GRM) with human cells is a key to the assessment of their potential risks for human health. There is a knowledge gap regarding the potential uptake of GRM by human intestinal cells after unintended ingestion. Therefore the aim of our study was to investigate the interaction of label-free graphene oxide (GO) with the intestinal cell line Caco-2 in vitro and to shed light on the influence of the cell phenotype given by the differentiation status on cellular uptake behaviour.ResultsInternalisation of two label-free GOs with different lateral size and thickness by undifferentiated and differentiated Caco-2 cells was analysed by scanning electron microscopy and transmission electron microscopy. Semi-quantification of cells associated with GRM was performed by flow cytometry. Undifferentiated Caco-2 cells showed significant amounts of cell-associated GRM, whereas differentiated Caco-2 cells exhibited low adhesion of GO sheets. Transmission electron microscopy analysis revealed internalisation of both applied GO (small and large) by undifferentiated Caco-2 cells. Even large GO sheets with lateral dimensions up to 10 µm, were found internalised by undifferentiated cells, presumably by macropinocytosis. In contrast, no GO uptake could be found for differentiated Caco-2 cells exhibiting an enterocyte-like morphology with apical brush border.ConclusionsOur results show that the internalisation of GO is highly dependent on the cell differentiation status of human intestinal cells. During differentiation Caco-2 cells undergo intense phenotypic changes which lead to a dramatic decrease in GRM internalisation. The results support the hypothesis that the cell surface topography of differentiated Caco-2 cells given by the brush border leads to low adhesion of GO sheets and sterical hindrance for material uptake. In addition, the mechanical properties of GRM, especially flexibility of the sheets, seem to be an important factor for internalisation of large GO sheets by epithelial cells. Our results highlight the importance of the choice of the in vitro model to enable better in vitro-in vivo translation.

Terahertz detection using mechanical resonators based on 2D materials

We have investigated a THz detection scheme based on mixing of electrical signals in a voltage-dependent capacitance made out of suspended graphene. We have analyzed both coherent and incoherent detection regimes and compared their performance with the state of the art. Using a high-amplitude local oscillator, we anticipate potential for quantum limited detection in the coherent mode. The sensitivity stems from the extraordinary mechanical and electrical properties of atomically thin graphene or graphene-related 2D materials.

Recent Advances on Anilato-Based Molecular Materials with Magnetic and/or Conducting Properties

The aim of the present work is to highlight the unique role of anilato-ligands, derivatives of the 2,5-dioxy-1,4-benzoquinone framework containing various substituents at the 3 and 6 positions (X = H, Cl, Br, I, CN, etc.), in engineering a great variety of new materials showing peculiar magnetic and/or conducting properties. Homoleptic anilato-based molecular building blocks and related materials will be discussed. Selected examples of such materials, spanning from graphene-related layered magnetic materials to intercalated supramolecular arrays, ferromagnetic 3D monometallic lanthanoid assemblies, multifunctional materials with coexistence of magnetic/conducting properties and/or chirality and multifunctional metal-organic frameworks (MOFs) will be discussed herein. The influence of (i) the electronic nature of the X substituents and (ii) intermolecular interactions i.e., H-Bonding, Halogen-Bonding, π-π stacking and dipolar interactions, on the physical properties of the resulting material will be also highlighted. A combined structural/physical properties analysis will be reported to provide an effective tool for designing novel anilate-based supramolecular architectures showing improved and/or novel physical properties. The role of the molecular approach in this context is pointed out as well, since it enables the chemical design of the molecular building blocks being suitable for self-assembly to form supramolecular structures with the desired interactions and physical properties.

Graphene oxide nanosheets induced genotoxicity and pulmonary injury in mice

Graphene and graphene-related materials have broadly applied in biomedical purposes due to their unique properties, thus safety evaluation of them is crucial. This study was performed to explore the genotoxic and pulmonary toxic potential of different doses of graphene oxide nanosheets’ (GOs) in mice.A total of 90 male mature mice were randomly divided into six groups of fifteen mice per each, five groups were intraperitoneally injected by GO at doses of 10, 50, 100, 250 and 500μg/kg b.w once weekly in addition to the control group that was injected intraperitoneally with 0.2ml saline solution. Five animals from each group were euthanized after 7, 28 and 56days post treatment. Evaluation of genotoxicity was performed through detection of chromosomal aberrations in bone marrow while assessment of lung injury was made by determination of DNA fragmentation in lung specimens using the alkali Comet assay, pulmonary oxidative markers estimation and finally histopathological investigations. Results revealed that GOs induced variable structural chromosomal aberrations (SCA) in bone marrow and DNA damage of lung cells that were time and dose dependent and represented by increase in%DNA in comet tail, tail moment and tail length and decrease in% head DNA in nuclei of lung of GOs-treated mice versus control groups in addition, GOs induced various changes in pulmonary oxidative stress parameters that were affected by dose and duration of treatment compared with the control as well as various pulmonary histopathological alterations were detected indicating lung injury. Conclusion: GO potentiate the induction of genotoxicity and pulmonary injury in mice in time and dose dependent manner.

Conversion of p to n-type reduced graphene oxide by laser annealing at room temperature and pressure

Physical properties of reduced graphene oxide (rGO) are strongly dependent on the ratio of sp2 to sp3 hybridized carbon atoms and the presence of different functional groups in its structural framework. This research for the very first time illustrates successful wafer scale integration of graphene-related materials by a pulsed laser deposition technique, and controlled conversion of p to n-type 2D rGO by pulsed laser annealing using a nanosecond ArF excimer laser. Reduced graphene oxide is grown onto c-sapphire by employing pulsed laser deposition in a laser MBE chamber and is intrinsically p-type in nature. Subsequent laser annealing converts p into n-type rGO. The XRD, SEM, and Raman spectroscopy indicate the presence of large-area rGO onto c-sapphire having Raman-active vibrational modes: D, G, and 2D. High-resolution SEM and AFM reveal the morphology due to interfacial instability and formation of n-type rGO. Temperature-dependent resistance data of rGO thin films follow the Efros-Shklovskii variable-range-hopping model in the low-temperature region and Arrhenius conduction in the high-temperature regime. The photoluminescence spectra also reveal less intense and broader blue fluorescence spectra, indicating the presence of miniature sized sp2 domains in the vicinity of π* electronic states, which favor the VRH transport phenomena. The XPS results reveal a reduction of the rGO network after laser annealing with the C/O ratio measuring as high as 23% after laser-assisted reduction. The p to n-type conversion is due to the reduction of the rGO framework which also decreases the ratio of the intensity of the D peak to that of the G peak as it is evident from the Raman spectra. This wafer scale integration of rGO with c-sapphire and p to n-type conversion employing a laser annealing technique at room temperature and pressure will be useful for large-area electronic devices and will open a new frontier for further extensive research in graphene-based functionalized 2D materials.

A novel approach to decrease friction of graphene

Graphene as a well-known solid lubricant is widely used in micro- and nano-scale mechanical devices, decreasing the friction of graphene as far as possible is a perpetual task to improve the performance of these devices. A novel approach was proposed to decrease the friction of graphene against atomic force microscopy (AFM) tip by plasma treatment of the substrate. The plasma treatment of the substrate enhances the adhesive attraction between graphene and SiO2 substrate by generating stronger van der Waals attraction. Enhancing the adhesive attraction can indeed decrease the friction of graphene, regardless of the thickness of graphene and the kinds of AFM tip. Longer time of plasma treatment results in stronger adhesive attraction, leads to smaller friction. The decreased friction is mainly due to the combined action of the suppressed puckering of graphene and the reduced ability of graphene to adjust its atomic configuration. This novel approach will promote the engineering application of graphene and other related 2D materials as lubricants in MEMS/NEMS.

Graphene-based field effect transistors as biosensors

Graphene and graphene-related materials exhibit switchable charge-carrier mobility induced by applying a potential or by interaction with molecules. The short review summarizes concepts for the development of solution-gated field effect transistors using graphene or related substances as gate material focusing on applications in biosensors.

Disentangling contributions of point and line defects in the Raman spectra of graphene-related materials

The transition from graphene to a fully disordered sp2 carbon material can be idealized by either cutting graphene into smaller and smaller pieces, or adding more and more point defects. In other words, from the dimensionality standpoint, defects in two-dimensional (2D) systems can be either one- (1D) or zero-dimensional (0D). From an application point of view, both in terms of bottom-up as well as top-down approaches, the discrimination between these two structural disorder in two-dimensional systems is urgently desired. In graphene, both types of defects produce changes in the Raman spectrum, but identifying separately the contribution from each defect-type has not yet been achieved. Here we show that a diagram can be built for disentangling contributions of point-like and line-like defects to the Raman spectra of graphene-related materials embracing, from the topology point of view, all possible structures from perfect to fully disordered sp2 bonded carbons. Two sets of graphene-related samples, produced by well-established protocols that generate either 0D or 1D defects in a controlled way, are analysed with our model and used to parameterize the limiting values of the phase space. We then discuss the limitations and apply our new methodology to analyse the structure of two-dimensional nanocarbons generated from renewable gas, used to produce inks and conducting coatings.