Search Results (2,422)

The buckling-like mechanical behavior of functionally graded graphene platelet-reinforced composite (FG-GPLRC) structures is increasingly attracting research attention. However, buckling behavior has previously been studied separately as thermal buckling and mechanical buckling. In this context, this study investigates the buckling behavior of FG-GPLRC plates under combined thermal and mechanical loads. The coupled buckling problem is formulated according to the minimum potential energy theorem using first-order shear deformation theory (FSDT). In addition, the problem is approximated by the 2-D natural element method (NEM), and the resulting coupled eigen matrix equations are derived to compute the critical buckling temperature rise (CBTR) and the mechanical buckling load. The developed numerical method can solve thermal, mechanical, and coupled thermo-mechanical buckling problems, and its reliability is examined through convergence and benchmark tests. Using the developed numerical method, the buckling behavior of FG-GPLRC plates under thermal and mechanical buckling loads is examined in depth with respect to the key parameters. In addition, a comparison with functionally graded CNT-reinforced composite (FG-CNTRC) plates is also presented. Full article

In this work, an amino-functionalized graphene oxide/polypyrrole (AMGO/PPy) composite-based novel sensing platform was established to monitor lead ions (Pb²⁺) at high sensitivity. AMGO was synthesized through a hydrothermal process and later formed a composite with PPy at varying concentrations. A physicochemical investigation of the synthesized materials was carried out using various characterization tools, while the electrochemical properties were examined by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) methods. The AMGO/PPy composite was deposited on a glassy carbon electrode (GCE), which was used for the real-time electrochemical detection of Pb²⁺. The AMGO/PPy sensor exhibited lower limits of detection (LOD) of 0.91 nM. In addition, the developed Pb²⁺ sensor exhibited excellent reproducibility, repeatability, selectivity, sensitivity, and long-term stability for 25 days. The AMGO/PPy composite emerges as a ground-breaking material for the electrochemical detection of Pb²⁺, holding significant potential for environmental monitoring and the protection of human health. Full article

Azulene-based polycyclic hydrocarbons have garnered much attention as potential materials for organic optoelectronic devices and as molecular models for graphene nanosheets with structural defects. Although various methods for ring fusions to an azulene core have been established for ring fusions to an azulene core, efficient synthetic methodologies for ortho- and peri-fusion to an azulene core are still lacking, which hinders the investigation of the effect of the ortho- and peri-fusion on the electronic properties of the embedded azulene core. Herein, we describe the synthesis and characterization of quinoxaline-fused cyclopenta[cd]azulene 4 as a new ortho- and peri-fused azulene derivative. The target molecule 4 was successfully synthesized in four steps from 4-methylazulene. The ring annulation decreased the lowest excitation energy compared with that of azulene and its structural isomer 5 and led to multiple reversible reduction processes. Characterization of the molecular geometry and optoelectronic properties of 4 revealed that the embedded azulene core preserves its original aromaticity, while the fused quinoxaline acts as a nucleophilic and basic site. These features suggest that 4 could serve as a metal ligand, a near-infrared absorber, and a component in organic functional devices. Full article

Kynurenic acid (KA), a key metabolite of tryptophan (TRP) via the kynurenine pathway, plays a significant role in various physiological and pathological conditions, including neurodegenerative diseases, depression, and schizophrenia. This study aims to develop a flexible and sensitive electrochemical sensor platform for the direct detection of KA in biological fluids. Custom carbon-based electrodes were fabricated using specialized inks and a flexible plastic substrate, followed by functionalization with a composite film of gold nanoparticles, graphene oxide (GO), and polyethyleneimine (PEI). The GO was electrochemically reduced to enhance conductivity and sensitivity for the target analyte. The sensor platform was characterized using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), scanning electron microscopy (SEM), and atomic force microscopy (AFM). An optimized differential pulse voltammetry (DPV) method was employed for KA detection. The developed sensor demonstrated a detection limit of 0.3 nM and was effective across a concentration range of 1 nM to 500 µM. These findings highlight the potential of this electrochemical sensor as a reliable, rapid, and cost-effective tool for KA detection in various biological samples, offering significant advantages over traditional methods in terms of sensitivity and simplicity. Full article

Asymmetric cove-edged graphene nano-ribbons were employed as metallic electrodes in a hybrid gap device structure with zig-zag graphene nano-ribbons terminations for amino acid recognition and peptide sequencing. On a theoretical basis, amino acid recognition is attained by calculating, using the non equilibrium Green function scheme based on density functional theory, the transversal tunnelling current flowing across the gap device during the peptide translocation through the device. The reliability and robustness of this sequencing method versus relevant operations parameters, such as the bias, the gap size, and small perturbations of the atomistic structures, are studied for the paradigmatic case of Pro-Ser model peptide. I evidence that the main features of the tunnelling signal, that allow the recognition, survive for all of the operational conditions explored. I also evidence a sort of geometrical selective sensitivity of the hybrid cove-edged graphene nano-ribbons versus the bias that should be carefully considered for recognition. Full article

Carbon fibre-reinforced polymers (CFRPs) are a lightweight alternative solution for various applications due to their mechanical and structural properties. However, debonding at the fibre–matrix interface is an important failure mechanism in composite materials. Proposed solutions include using nano-scale reinforcements to strengthen and toughen structural composites. This study covers a comprehensive approach for evaluating occupational hazards during the sizing of 6k carbon fibres using multi-walled functionalized carbon nanotubes (MWCNTs) and few-layer graphene (FLG) at a pilot scale. Material hazard and exposure banding showed elevated risks of exposure to nanomaterials during the sizing process, while a ‘what-if’ process hazard analysis allowed for the evaluation of hazard control options against the hypothetical process failure scenarios of human error and utilities malfunctioning. On-site measurements of airborne particles highlighted that using MWCNTs or FLG as a sizing agent had negligible effects on the overall exposure potential, and higher micro-size particle concentrations were observed at the beginning of the process, while particle size distribution showcased high concentrations of particles below 50 nm. This analysis provides a thorough investigation of the risks and potential exposure to airborne hazardous substances during CF sizing while providing insights for the effective implementation of a safe-by-design strategy for designing targeted hazard control systems. Full article

Coal tar, a by-product of the pyrolysis of coal, is rich in aromatic compounds that have the potential to facilitate the synthesis of graphene, a high-quality carbon material, via low-temperature chemical vapor deposition (CVD). This approach offers a promising avenue for the cost-effective and large-scale industrial production of graphene while minimizing energy consumption. Nevertheless, there is a paucity of research focused on the low-temperature synthesis mechanisms of graphene derived from aromatic compounds in the context of graphene growth. To achieve high-quality graphene synthesis from coal tar and its aromatic constituents at reduced temperatures, a comprehensive investigation into the reaction pathways of these aromatic compounds is essential. In this study, we meticulously simulate the pyrolysis of benzene, a key aromatic component of coal tar, across various temperature settings utilizing reactive force field (ReaxFF) methodology. Furthermore, we apply density functional theory (DFT) calculations, executed through the Vienna Ab initio Simulation Package (VASP), to assess the dehydrogenation energy associated with the adsorption of benzene on vapor-deposited copper foils. Our molecular dynamics simulations, enhanced by a mixed force field approach, revealed that the dehydrogenated benzene ring (C₆ intermediate) acts as a critical precursor for graphene synthesis. This research significantly elucidates the reaction pathways of aromatic benzene in coal tar through molecular simulations conducted at different temperatures, both in the gas phase and on solid copper foil substrates. Full article

Metronidazole, an antibiotic widely used in human and veterinary medicine, poses significant environmental risks when discharged into aquatic environments. This study explores the potential of functionalized graphene membranes for the removal of metronidazole from industrial and pharmaceutical wastewater. Employing molecular simulations and the AM1 semi-empirical-calculation method in solvent (water), we designed and simulated functionalized membranes to enhance metronidazole removal efficiency. Pharmaceutical effluent that contains metronidazole can have detrimental effects on aquatic ecosystems, including toxicity to aquatic organisms and the potential development of antibiotic-resistant bacteria. Our findings show that specific functionalized membranes exhibit selective adsorption for metronidazole, indicating promising results for efficient wastewater treatment. In the study, it was confirmed that a significant drop occurs in the adsorptive property of all functions for metronidazole removal, except for membranes decorated with aldehyde (-CHO) and secondary amine (-CHNH) function. Further analysis of the functionalized graphene membranes confirms one decorated with aldehyde function to have demonstrated superior selective adsorption of metronidazole over water, compared to the other membrane decorated with other functions in the presence of water. The use of functionalized graphene membranes for metronidazole removal shows great potential in mitigating the environmental risks associated with pharmaceutical effluent, which is in line with the study findings and related literature. By improving our understanding of adsorption processes and membrane interactions, we can develop more effective wastewater treatment technologies to safeguard our environment. Full article

In this study, we developed a facile one-pot synthesis of a nanocomposite consisting of silver nanoparticles (AgNPs) growing over graphene oxide (GO) nanoflakes (AgNPs@GO). The process consists of the in situ formation of AgNPs in the presence of GO nanosheets via the spontaneous decomposition of silver(I) acetylacetonate (Ag(acac)) after dissolution in water. This protocol is compared to an ex situ approach where AgNPs are added to a waterborne GO nanosheet suspension to account for any attractive interaction between preformed nanomaterials. The systems under investigation are characterized by UV/vis absorption spectroscopy, dynamic light scattering (DLS), zeta potential (Z-Pot), and scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDX). The stability of the AgNPs@GO composite suspension is tested as a function of GO concentration (0–67 μg/mL) while maintaining a constant Ag content (14.4 μg/mL), exhibiting excellent stability over time up to an Ag-to-GO mass ratio of 0.58. Full article

Lubricant friction modifier additives are used on lower viscosity engine oils to mitigate boundary friction. This work presents the development of a graphene-based material as an oil friction modifier additive, from formulation to actual vehicle tests. The graphene material was initially characterized using scanning electron microscopy (SEM) and Raman spectroscopy, which revealed the predominance of graphene nanoplatelets (GNPs) with an average of nine layers. After functionalization, two GNP additive variants were initially mixed with a fully formulated SAE 0W-20 engine oil and tribologically evaluated using reciprocating sliding tests at 40 and 120 °C and Hertzian pressure up to 1.2 GPa when both variants presented friction reduction. Then, the GNP additive variant with better performance was evaluated in a vehicle emission test using a fully formulated 5W-20 SAE oil as a reference. The addition of 0.1% of GNPs reduced fuel consumption by 2.6% in urban conditions and 0.8% in highway ones. The urban test cycle was FTP75 and higher benefits of the GNP additive occurred especially on the test start, when the engine and oil were still cold and on test portions where the vehicle speed was lower. Full article

The large-scale implementation of 2D material-based membranes is hindered by mechanical stability and mass transport control challenges. This work describes the fabrication, characterisation, and testing of self-standing graphene oxide (GO) membranes cross-linked with oxides such as Fe₂O₃, Al₂O₃, CaSO₄, Nb₂O₅, and a carbide, SiC. These cross-linking agents enhance the mechanical stability of the membranes and modulate their mass transport properties. The membranes were prepared by casting aqueous suspensions of GO and SiC or oxide powders onto substrates, followed by drying and detachment to yield self-standing films. This method enabled precise control over membrane thickness and the formation of laminated microstructures with interlayer spacings ranging from 0.8 to 1.2 nm. The resulting self-standing membranes, with areas between 0.002 m² and 0.090 m² and thicknesses from 0.6 μm to 20 μm, exhibit excellent flexibility and retain their chemical and physical integrity during prolonged testing in direct contact with ethanol/water and methanol/water mixtures in both liquid and vapour phases, with stability demonstrated over 24 h and up to three months. Gas permeation and chemical characterisation tests evidence their suitability for gas separation applications. The interactions promoted by the oxides and carbide with the functional groups of GO confer great stability and unique mass transport properties—the Nb₂O₅ cross-linked membranes present distinct performance characteristics—creating the potential for scalable advancements in cross-linked 2D material membranes for separation technologies. Full article

We present a versatile method for synthesizing high-quality molybdenum disulfide (MoS₂) crystals on graphite foil edges via chemical vapor deposition (CVD). This results in MoS₂/graphene heterostructures with precise epitaxial layers and no rotational misalignment, eliminating the need for transfer processes and reducing contamination. Utilizing in situ transmission electron microscopy (TEM) equipped with a nano-manipulator and tungsten probe, we mechanically induce the folding, wrinkling, and tearing of freestanding MoS₂ crystals, enabling the real-time observation of structural changes at high temporal and spatial resolutions. By applying a bias voltage through the probe, we measure the electrical properties under mechanical stress, revealing near-ohmic behavior due to compatible work functions. This approach facilitates the real-time study of mechanical and electrical properties of MoS₂ crystals and can be extended to other two-dimensional materials, thereby advancing applications in flexible and bendable electronics. Full article

Green chemistry seeks to find alternative synthesis routes that are less harsh to living organisms and the environment. In this communication, a microwave-assisted hydrothermal technique and a thermal annealing method were used in the reduction of graphene oxide (GO) to make reduced GO (rGO). Graphite powder was oxidised using the Improved Hummers’ method, exfoliated, and freeze-dried. Thereafter, an aqueous suspension of GO was reduced under microwave (MW) irradiation for 10 min at 600 W with and without the help of a reducing agent (hydrazine hydrate). Thermal annealing reduction was also conducted under a nitrogen atmosphere at 300 °C for 1 h. Prepared samples were analysed using Raman laser spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), the Brunauer–Emmett–Teller (BET) method, and X-ray photoelectron spectroscopy (XPS). A successful reduction in the GO functional groups between the sheets was established using XRD. In the Raman analysis, the ratio of the intensity of the D and G band (I_D/I_G) in graphene sheets assisted in assessing the quality of the graphene films. An estimation of the number of structural defects was calculated using the I_D/I_G ratio. The Raman analysis showed an increase in the I_D/I_G ratio after both oxidation and reduction processes. The defect densities of both MW-treated samples were comparable while an increased defect density was evident in the thermally annealed sample. TEM micrographs confirmed the sheet-like morphology of the samples. The rGO sheets obtained from the MW-treated method appeared to be smaller when compared to the rGO ones obtained by thermal treatment. It was also evident from XRD analysis that thermal treatment promoted the coalition of graphitic layers, such that the estimated number of layers was larger than that of GO. The elemental analysis showed that the C/O ratio of GO increased from 2 to 7.8 after MW hydrazine reduction. Full article

Graphene and its derivatives (GDs) have been applied in many fields, like photocatalysts, sensors, and biomedical delivery, due to its excellent physicochemical properties. However, the widespread use of GDs has significantly increased human exposure to these materials. Some health risks of exposure to GDs have been identified, including organ fibrosis, inflammation, DNA damage, etc. Given that graphene is a novel concern, we especially emphasized the various exposure pathways and potential health risks of exposure to GDs. People get exposed to GDs mainly through inhalation, ingestion, dermal contact, etc. GDs could transfer to the circular system of people and accumulate in blood, cells, and major organs. GDs exposure could induce organ and cell inflammatory responses and damage, such as disrupted kidney function, declined cell vitality, cytotoxicity, etc. These changes at the organ and cell levels might lead to adverse tangible influences on people, like decreased locomotor activity, the accelerated aging process, and even abnormal offspring development. We also summarized the characterization and detection methods of GDs. In addition, we compared the studies of exposure to dust and GDs in the aspects of health risks and study methods. This review could offer a comprehensive summary related to GDs and provide helpful references for further graphene-related studies. Full article

The large-scale microwave plasma synthesis of graphene and nitrogen-doped graphene with tailored structural properties, crucial for their successful usage applications, has been demonstrated. The developed atmospheric pressure plasma method offers several advantages, including the continuous production of high-quality, free-standing graphene without the use of chemicals, solvents, catalysts, or additional heating. This non-toxic process eliminates the need for vacuum systems while achieving high temperatures. The method enables the precise control over graphene’s properties, such as the layer number, defects, sheet size, uniformity, and functionality, as well as the doping type and configuration, by adjusting the plasma parameters. Protocols for the synthesis of specific nanostructures with a controlled structural quality, production rate, and chemical composition have been established using methane and methylamine as precursors. The comprehensive physicochemical characterization of the graphene and nitrogen-doped graphene was carried out using scanning electron microscopy, high-resolution transmission electron microscopy, Raman spectroscopy, X-ray diffraction, and X-ray photoelectron spectroscopy. Full article