Assembly Of Graphene Research Articles

On nonlinear 3D electro-elastic numerical modeling of two-phase inhomogeneous FG piezocomposites reinforced with GNPs

The novelty here comes from not only the perfect nonlinear three-dimensional (3D) electro-elasticity investigation but also the mixed material itself. The literature widely showed mechanical assessments on the piezoelectric structures; however, a lack of nonlinear three-dimensional elasticity studies has been witnessed on these kinds of smart materials. Therefore, a nonlinear 3D elasticity-piezoelectricity coupling is considered in this study. What is more, this research brings about an era in the field of sensing manufacturing such as sensors and actuators by proposing the construction of these devices in an advanced composite framework. The piezoelectric medium can be electro-mechanically improved with the aggregation of graphene platelets/nanoplatelets (GPLs/GNPs) based on the functionally graded (FG) composition. The assumption for such a smart composite has been made to provide higher flexibility smart tools while their elastic strength can also get further. To accomplish this, the derivation of a rigorous mathematical model has come out for a transversely isotropic inhomogeneous FG-piezoelectric beam-like sensor/actuator using 3D kinematic displacements, geometrically nonlinear strains, Lagrange technique, 3D stress-strains tensors, linear elastic material, and in particular Halpin-Tsai micro-mechanic model. Numerical modeling has been built by the generalized differential quadrature (GDQ) technique. A comprehensive parametric study has also been established for intelligent FG beams.

Achieving high electrothermal and mechanical performance for Graphene/Poly(hexamethylene terephthalamide) composite films via interfacial engineering with two-dimensional polyarylamide nanosheets

Although graphene-based polymer electrothermal films have received great attention, the graphene aggregation restricts the improvement in electrothermal performance. This study reports graphene (GN)/two-dimensional polyarylamide nanosheets (2DPA) filled poly (hexamethylene terephthalamide) (PA6T) composite film with outstanding electrothermal and mechanical performance. Owing to the addition of 2DPA, the as-prepared 2DPA-GN/PA6T composite film can attain a high heating-up rate of 25.5 °C/s, 1.8 times higher than that of GN/PA6T composite film (14.1 °C/s). Furthermore, the 2DPA-modified composite film showed a remarkable heating temperature rise to ∼230 °C, 80 °C higher than that of GN/PA6T composite film (∼150 °C). Additionally, the film had excellent mechanical performance with tensile strength and modulus of elasticity of 32.5 MPa and 4.6 GPa, which were 24.2 % and 52.3 % higher than that of GN/PA6T composite film, respectively. Such outstanding performance came from strong interfacial adhesion between GN and PA6T, induced by 2DPA nanosheets through hydrogen bonding and π-π interactions, which were confirmed by FTIR and UV–Vis measurements. Besides improving interfacial adhesion, 2DPA can also reduce the surface defect density of the GN through π-π conjugation. Both improved interfacial adhesion and reduced defects of GN contributed to the formation of electrically conductive and stress transfer pathways, which supported the excellent electrothermal and mechanical properties of 2DPA-GN/PA6T composite films. This study demonstrates an effective way to prepare high-performance graphene composites for electrothermal applications, with expected uses in aerospace, industry, and other technological fields.

Graphene Composites and its Application in Environmental Treatment

Graphene, as a new two-dimensional material, is an ideal material for pollutant adsorption because of its large specific surface area and strong adsorption capacity. Moreover, graphene has an ultra-high electron transport capacity and can be used as a carrier of photocatalysis to further treat pollutants, so it has a wide range of applications in the field of environmental governance. However, with the application of graphene in the field of environmental treatment, the shortcomings of graphene are gradually exposed, such as easy aggregation, easy oxidation and biological toxicity. In recent years, in order to better meet the needs of removing pollutants in the environment and solve the shortcomings of graphene, graphene composites came into being. In this paper, three kinds of graphene composites which can solve the problems of easy aggregation, easy oxidation and biological toxicity of graphene are found out from thousands of graphene composites, and the basic properties, preparation methods and applications in environmental treatment are summarized respectively. They are graphene/metal oxide composites, porous foam/graphene oxide composites and graphene oxide/chitosan composites. At the same time, the application of graphene composites in pollutant adsorption and degradation and the problems existing in this process are also introduced in detail.

Bioinspired Robust Gas-Permeable On-Skin Electronics: Armor-Designed Nanoporous Flash Graphene Assembly Enhancing Mechanical Resilience.

Soft on-skin electrodes play an important role in wearable technologies, requiring attributes such as wearing comfort, high conductivity, and gas permeability. However, conventional fabrication methods often compromise simplicity, cost-effectiveness, or mechanical resilience. In this study, a mechanically robust and gas-permeable on-skin electrode is presented that incorporates Flash Graphene (FG) integrated with a bioinspired armor design. FG, synthesized through Flash Joule Heating process, offers a small-sized and turbostratic arrangement that is ideal for the assembly of a conductive network with nanopore structures. Screen-printing is used to embed the FG assembly into the framework of polypropylene melt-blown nonwoven fabrics (PPMF), forming a soft on-skin electrode with low sheet resistance (125.2 ± 4.7 Ω/□) and high gas permeability (≈10.08mg cm⁻2 h⁻¹). The "armor" framework ensures enduring mechanical stability through adhesion, washability, and 10,000 cycles of mechanical contact friction tests. Demonstrating capabilities in electrocardiogram (ECG) and electromyogram (EMG) monitoring, along with serving as a self-powered triboelectric sensor, the FG/PPMF electrode holds promise for scalable, high-performance flexible sensing applications, thereby enriching the landscape of integrated wearable technologies.

Electricity/light-heat-hygro multi-responsive soft luminescent systems for rewritable and programmable information display

Rewritable luminescent materials are attracting widespread attention for information storage and display as they can help to reduce environmental wastes caused by the abuse of single-use and transient systems. Nevertheless, since most reported systems are chemical-stimuli-responsive and single-stimuli-responsive, it remains challenging to achieve the rewritable and programmable display of multiple information in one single system, which is essential to enhance information richness and display intelligence. In this work, an ideal kind of multi-responsive soft luminescent display systems are reported, which consist of heat/humidity-responsive fluorescence-phosphorescence dual-emission film and stacked graphene assembly (SGA) film by using thin poly (dimethyl siloxane) (PDMS) as middle connecting layer. In such multilayer structure, the heat generated by electricity connection or light illumination of bottom SGA film can be instantly transferred across the middle PDMS layer to cause heat-triggered red-to-blue emission color change, or to evaporate water for blue-to-red emission color recovery. Owing to the “residual-free” nature of these electricity, light and water stimuli, multi-responsive rewritability is guaranteed to enable the reversible writing and complete erasure of various letter/pattern information. On this basis, robust electricity/light-heat-hygro multi-responsive soft luminescent display systems are demonstrated, in which diverse letter/pattern information could be facilely programmed to be successively displayed and then completely reset to enable another data writing/erasing cycle by sequential modulation of different environmental stimuli. This study brings programmable merit for rewritable luminescent display systems and is expected to inspire more intelligent ones.

The effect of processing/curing temperature and viscosity of epoxy resins on the flexural/tensile properties of GNP-epoxy resin nanocomposites

Despite the problem of graphene aggregation in cured epoxy resin, no studies have clarified the tendency of graphene aggregation in a wide variety of material systems and process. We hypothesized that the use of epoxy resins at high temperatures leads to an extreme decrease in resin surface tension and viscosity of epoxy, which would cause re-aggregation of graphene once dispersed. So, we examined process/material with/without high temperature treatment and epoxy resins of different viscosities, and properties of nanocomposites were evaluated by flexural/tensile test. Experiments revealed that the process not including high temperature treatment suppressed graphene re-aggregation and maintained the high mechanical properties of nanocomposites. In particular, the increased tensile modulus by 18.44% and flexural strength by 2.81% (@ 1 wt% graphene loading), which were quite high for non-functionalized graphene, were recorded when epoxy was treated and cured at 20 ˚C at all times to keep the surface tension of epoxy desirable.

Radial assembly of graphene nanoplates via ice-template method to construct 3D thermally conductive phase change materials

Phase change material (PCM) with the capacity to store and release substantial thermal energy, has drawn significant attention. However, its large-scale application is still hindered by inadequate thermal management capacity and unsatisfactory thermal conductivity. In this study, graphene nanoplates were assembled into a 3D thermally conductive scaffold using a specialized ice template method. By virtue of the unique growth of ice crystals in radial pattern, a series of multidirectional thermal conduction pathways were successfully constructed within PCM, which has provided microscopically interconnected pathways for thermal transport. Consequently, a remarkable 5.2-fold increment in thermal conductivity (1.365 W m−1 K−1) in comparison to pure paraffin was achieved by incorporating a mere 6 vol% of GNP, which therefore enables excellent thermal cycling stability, remarkable latent heat storage capacity exceeding 175 J/g, together with leak-proof properties even under extended high-temperature conditions. Moreover, the solar-to-thermal energy storage efficiency is up to 85.8 % due to its efficient photothermal effect. This work presents an innovative approach to design PCMs with enhanced thermal conductivity and photothermal efficiency, offering promising applications in advanced thermal storage.

N-doped hollow carbon nanospheres embedded in N-doped graphene loaded with palladium nanoparticles as an efficient electrocatalyst for formic acid oxidation

Efficient electrocatalysts with a low cost, high activity and good durability play a crucial role in the use of direct formic acid fuel cells. Pd nanoparticles supported on N-doped hollow carbon nanospheres (NHCNs) embedded in an assembly of N-doped graphene (NG) with a three-dimensional (3D) porous structure by a simple and economical method were investigated as direct formic acid fuel cell catalysts. Because of the unique porous configuration of interconnected layers doped with nitrogen atoms, the Pd/NHCN@NG catalyst with Pd nanoparticles has a large catalytic active surface area, superior electrocatalytic activity, a high steady-state current density, and a strong resistance to CO poisoning, far surpassing those of conventional Pd/C, Pd/NG, and Pd/NHCN catalysts for formic acid electrooxidation. When the HCN/GO mass ratio was 1:1, the Pd/NHCN@NG catalyst had an outstanding performance in the catalytic oxidation of formic acid, with an activity 4.21 times that of Pd/C. This work indicates a way to produce superior carbon-based support materials for electrocatalysts, which will be beneficial for the development of fuel cells.

Graphene and MOF Assembly: Enhanced Fabrication and Functional Derivative via MOF Amorphization.

The integration of graphene and metal-organic frameworks (MOFs) has numerous implications across various domains, but fabricating such assemblies is often complicated and time-consuming. Herein, a one-step preparation of graphene-MOF assembly is presented by directly impregnating vertical graphene (VG) arrays into the zeolitic imidazolate framework (ZIF) precursors under ambient conditions. This approach can effectively assemble multiple ZIFs, including ZIF-7, ZIF-8, and ZIF-67, resulting in their uniform dispersion on the VG with adjustable sizes and shapes. Hydrogen defects on the VG surface are critical in inducing such high-efficiency ZIF assembly, acting as the reactive sites to interact with the ZIF precursors and facilitate their crystallisation. The versatility of VG-ZIF-67 assembly is further demonstratedby exploring the process of MOF amorphization. Surprisingly, this process leads to an amorphous thin-film coating formed on VG (named VG-IL-amZIF-67), which preserves the short-range molecular bonds of crystalline ZIF-67 while sacrificing the long-range order. Such a unique film-on-graphene architecture maintains the essential characteristics and functionalities of ZIF-67 within a disordered arrangement, making it well-suited for electrocatalysis. In electrochemical oxygen reduction, VG-IL-amZIF-67 exhibits exceptional activity, selectivity, and stability to produce H2O2 in acid media.

Low friction coefficient bioinspired copper/graphene nanolaminates with high content graphene

Graphene is widely used in metal matrix composites (MMC) to improve the tribological properties of metal due to its special lamellar structure and excellent tribological properties. However, because the aggregation of graphene, it is difficult to increase the content of graphene in metal materials, which seriously hinders the further optimization of friction coefficient. In this paper, we report a bioinspired strategy to fabricate nacre-like copper/graphene nanolaminates through chemical intercalation of copper precursor into the interlayer space of expandable graphite and subsequent reduction. The regular parallel arrangement of graphene can greatly improve the agglomeration phenomenon and the aspect ratio of graphene, which harden the copper matrix by effectively restricting the motion of dislocation and also form continuous lubricating film on the surface. A low dry sliding friction coefficient 0.13 is thus obtained among copper-based composites without severely deteriorating the electrical properties, providing new prospect in sliding electrical contact applications.

Pillared Graphene for Supercapacitor Applications

Since the discovery of graphene in 2004 [1], it has been considered a “Wonder” material with lots of potential due to its attractive properties. Owing to such properties, graphene is theoretically expected to have an electrochemical double layer capacitance of 550 F/g [2]. However, due to the high cost and difficulty of producing and handling single sheets of graphene, the presence of graphene in the market was hindered. Luckily, many methods were devised to synthesize graphene-like materials that would be easier and cheaper to produce. Unfortunately such methods end up producing reduced Graphene Oxide (rGO) with stacked graphene layers due to pi-pi interactions, which impedes the full utilisation of the graphene’s surface area. Pillaring the graphene using organic linkers was proven to be one of the useful techniques in partially preventing the restacking of the graphene sheets in rGO [3].Herein, three molecular pillars with different chemical nature and lengths will be presented as pillaring agents for graphene and the performance of their corresponding pillared graphene assemblies as electrode materials for supercapacitors will be assessed against that of rGO as a reference sample. To assess the success of the pillaring technique and to decipher the chemical composition of the samples, various characterization techniques were employed such as XRD, TGA, XPS, EA, SEM, FT-IR, Raman spectroscopy and conductivity measurements. Different electrolytes were used to test the electrochemical performance in different environments (acidic and neutral with different cation sizes). The pillared graphene assemblies demonstrated an enhanced capacitive performance compared to reference samples and a correlation between such performance and the different physico-chemical characteristics is to be highlighted.

Fabrication of Polyurethane/Laponite/Graphene Transparent Coatings with High Surface Hardness

A polyurethane/Laponite/graphene transparent coating with high surface hardness, obtained by dispersing the Laponite–graphene oxide (Lap-GO) in polyurethane for UV reduction, is reported. Lap-GO improves the hardness of the coating, where Laponite is intercalated between graphene layers through electrostatic action, preventing the re-accumulation or aggregation of graphene and ensuring the transparency of the coating. The analysis of pencil hardness and light transmittance shows that when the Lap-GO content is 0.05 wt‰ and the UV reduction is 10 min, the hardness of the coated pencil increases to 5H, and the light transmittance remains above 85%. Furthermore, the polyurethane/Laponite/graphene transparent coating also has excellent cold liquid resistance and meets specific usage standards. The prepared polyurethane/Laponite/graphene transparent coatings are promising for broad application prospects in cover and protective coatings.

Stable hydrogen evolution catalysis: Nitrogen-carbon-stabilized platinum on a microporous carbon-based framework

Hydrogen produced from water electrolysis powered by renewable energy is an environmentally friendly fuel. However, the wide commercialization of water electrolysis is hindered by the high cost and low stability of the state-of-the-art Pt/C electrocatalysts. In this work, interconnected 3D carbon-based framework with a microporous configuration supported Pt nanoparticles (Pt/rGO1-FHCNs4) was proposed, and exhibited significantly enhanced catalytic activity and stability towards hydrogen evolution. The strong metal–N interactions between Pt nanoparticles and the functionalized support kept Pt nanoparticles in a well dispersed state and modified the electron structure of platinum nanoparticles during HER. The three-dimensional structure of carbon-based supports enhanced the access of active sites to reactant. The graphene contributed to the conductivity of the catalysts. In addition, the hollow structure of the carbon support act as an efficient nano spacer and a cross-linker for the 3D assembly of graphene due to electrostatic interaction. This work provides the approaches to fabricate metal nanoparticle/3D carbon-based support composites with potential applications as high performance electrocatalysts.

Mechanics of assembling two-dimensional materials on a solid substrate by droplet drying

Assembly of two-dimensional (2D) nanomaterials by droplet drying offers a straightforward and low-cost route to obtain their bulk forms for widespread applications in manufacturing and printing of functional structures and devices. However, unlike rigid nanoparticles that usually do not experience mechanical deformation, 2D nanomaterials are easily deformed and folded during assembly by evaporative drying, and traditional assembly theory that can address these fundamental deformation mechanisms is currently lacking. In the present study, we have developed an energy-based rotational spring-mechanical slider mechanics model to describe the mechanical deformation and assembly of 2D material graphene on a solid substrate during the evaporation of its droplet solution. In the development of theory, the mechanical folding deformation of 2D material graphene itself is modeled by the rotational spring, and the folding-induced interior interactions of graphene itself and its assembly interactions with neighboring ones and solid substrate all due to van der Waal force are modeled by the mechanical sliders. The surface wettability of substrate and the evaporative modes of droplet on substrate including constant contact angle (CCA), constant contact radius (CCR), and their combination are also incorporated into the mechanics model. In parallel, large-scale molecular dynamics (MD) simulations with the development of coarse-grained model of 2D graphene and its virtual force field interaction with liquid is performed and show remarkable agreement with theoretical predictions on both assembly patterns and dimensional sizes. The effect of graphene size and its interaction strength with substrate on assembly is also elucidated. This work uncovers fundamental assembly mechansim of mechanically deformable nanomaterials by solution drying, and also provides immediate application guidance to ink-based printing techniques for manufacturing deformable nanomaterials-enabled devices with controlled patterns on substrates.

Encapsulating flower-like MoS2 nanosheets into interlayer of nitrogen-doped graphene for high-performance lithium-ion storage

Layered molybdenum disulfide (MoS2) is a promising anode material for lithium-ion storage and its coupling with graphene can further improve the specific capacity and cycling stability. In this work, a feasible polyacrylamide (PAM)-assisted approach to prepare the flower-like MoS2 nanosheets encapsulated by nitrogen-doped graphene (FL-MoS2/N-G) is proposed. The PAM is taken as the directing agent for the layered assembly of graphene and further confined growth of FL-MoS2 in the interlayers of the graphene. The unique encapsulation construction of MoS2 and N-doped graphene leads to the high loading of active species and stabilized structural integrity after the continuous Li+ ion intercalations. Theoretical simulation results reveal that the MoS2 nanosheets coupled with N-doped graphene can accelerate the charge transfer process and create extra lithiation sites with decreased diffusion resistance of Li+ ions. As the anode material in lithium-ion batteries (LIBs), the target FL-MoS2/N-G composite exhibits a high reversible capacity of about 1202 mAh g−1 at 0.2 A g−1 and it can remain 835 mAh g−1 even at 5 A g−1, highlighting an excellent rate capacity. Additionally, the FL-MoS2/N-G anode is also capable of delivering a long-term cycling performance with a capacity retention of about 78% after 800 cycles. Furthermore, benefiting from the fast charge transfer process of the FL-MoS2/N-G dominated by surface capacitive behavior, the lithium-ion hybrid capacitor with good electrochemical performance was fabricated to brighten its practical application prospect. The current work presents a new insight into the fabrication of high-loading MoS2/N-doped graphene composites with unique nanostructures for high-performance lithium-ion storage.

Laser direct writing graphene assembly film for realizing plasmon-induced transparency at terahertz region

Laser direct writing graphene assembly film for realizing plasmon-induced transparency at terahertz region

Exploring and Understanding the Multiscale Mechanical Degradation in Graphene Assemblies via Practical Microstructure Guided Modeling

AbstractExploring and understanding the structure‐mechanical property relations in hierarchical graphene assemblies is crucial for optimizing their mechanical properties and developing new functionalities, as the tensile strength is two orders of magnitude degradation from pristine graphene to graphene assemblies. Yet, quantifying the strength degradation across multiscale is a challenge due to the complex hierarchical structures. Thus, key structures and dominated factors at different lengthscales that affect the mechanical properties of graphene assemblies should be extracted for the reasonable unveiling of this problem. In this study, the multiscale mechanical degradation of graphene assemblies through practical microstructure‐guided multiscale modeling is characterized. Combining with experimental observations, three representative models are developed to study the mechanical behaviors of graphene assemblies at different lengthscales. Then, the dominated factors affecting the strength at these lengthscales are identified, that is the defects in monolayer graphene, tension‐shear load transfer for stacked graphene, and uniformity of graphene assemblies. Based on the simulation results, the structure‐strength relation of graphene assemblies is given, and practical strategies are proposed followed by experimental realization, to significantly improve the mechanical properties of graphene‐based nanocomposites.

Emulsion Assembly of Graphene Oxide/Polymer Composite Membranes.

Graphene oxide/polymer composite water filtration membranes were developed via coalescence of graphene oxide (GO) stabilized Pickering emulsions around a porosity-generating polymer. Triptycene poly(ether ether sulfone)-CH2NH2:HCl polymer interacts with the GO at the water-oil interface, resulting in stable Pickering emulsions. When they are deposited and dried on polytetrafluoroethylene substrate, the emulsions fuse to form a continuous GO/polymer composite membrane. X-ray diffraction and scanning electron microscopy demonstrate that the intersheet spacing and thickness of the membranes increased with increasing polymer concentration, confirming the polymer as the spacer between the GO sheets. The water filtration capability of the composite membranes was tested by removing Rose Bengal from water, mimicking separations of weak black liquor waste. The composite membrane achieved 65% rejection and 2500 g m-2 h-1 bar-1. With high polymer and GO loading, composite membranes give superior rejection and permeance performance when compared with a GO membrane. This methodology for fabrication membranes via GO/polymer Pickering emulsions produces membranes with a homogeneous morphology and robust chemical separation strength.

Nucleate boiling enhancement on bubble-induced assembly of graphene oxide/carbon black hybrid networks

The efficiency and capacity of nucleate boiling can be enhanced by the bubble-induced assembly of nanoparticles, which are dispersed in a boiling liquid. Recently, carbon nanomaterials have attracted appreciable research interest for boiling heat transfer enhancement. This study presents nucleate boiling performance on interconnected graphene/carbon black hybrid films formed through the bubble-induced self-assembly of suspended particles. Aqueous graphene/carbon black hybrid solutions at varying concentration ratios (GO:CB; 1:0, 1:1, 1:5) were prepared via probe sonication. The solutions were then saturated and subjected to pool boiling under atmospheric pressure on a custom-made boiling test apparatus with a flat copper heating surface. Experiments were carried out at a stepwise increasing heat flux until the critical heat flux was reached. A heat transfer coefficient and critical heat flux enhancement of 223.0% and 182.4%, respectively, were achieved at a GO:CB concentration ratio of 1:5. The change in surface characteristics and, subsequently, the boiling performance were elaborated by conducting a series of surface characterizations such as Field Emission Scanning Electron Microscopy, Energy Dispersive X-Ray analysis, contact angle analysis, and surface profilometry. Nucleate boiling enhancement was attributed to the contribution of multiple factors such as surface roughening, increased effective surface area, decent interfacial contact within the assembly structure, improved capillarity, and lateral heat conduction.

Toward the Improvement of Silicon-Based Composite Electrodes via an In-Situ Si@C-Graphene Composite Synthesis for Li-Ion Battery Applications

Using Si as anode materials for Li-ion batteries remain challenging due to its morphological evolution and SEI modification upon cycling. The present work aims at developing a composite consisting of carbon-coated Si nanoparticles (Si@C NPs) intimately embedded in a three-dimensional (3D) graphene hydrogel (GHG) architecture to stabilize Si inside LiB electrodes. Instead of simply mixing both components, the novelty of the synthesis procedure lies in the in situ hydrothermal process, which was shown to successfully yield graphene oxide reduction, 3D graphene assembly production, and homogeneous distribution of Si@C NPs in the GHG matrix. Electrochemical characterizations in half-cells, on electrodes not containing additional conductive additive, revealed the importance of the protective C shell to achieve high specific capacity (up to 2200 mAh.g-1), along with good stability (200 cycles with an average Ceff > 99%). These performances are far superior to that of electrodes made with non-C-coated Si NPs or prepared by mixing both components. These observations highlight the synergetic effects of C shell on Si NPs, and of the single-step in situ preparation that enables the yield of a Si@C-GHG hybrid composite with physicochemical, structural, and morphological properties promoting sample conductivity and Li-ion diffusion pathways.