Three-dimensional graphene-based polymer nanocomposites: preparation, properties and applications

Construction of sandwich-like porous structure of graphene-coated foam composites for ultrasensitive and flexible pressure sensors

Ultrasensitive and flexible pressure sensors that can perceive and respond to environmental stimuli have attracted considerable attention due to their potential applications in wearable electronics and electronic skin devices. Here, we report a simple and low-cost strategy to fabricate high-performance pressure sensors via constructing a unique conductive/insulating/conductive sandwich-like porous structure (SPS). Interpenetration of the conductive graphene network throughout the porous insulating interlayer produces a highly efficient transition from the non-conductive to the conductive state. Consequently, the SPS sensors exhibit an extreme resistance-switching behavior (resistance change of >105 at 30 kPa), high sensitivity (∼0.67 kPa-1, <1.5 kPa), fast response/recovery time (∼10 and ∼16 ms) and outstanding mechanical stability. Such SPS pressure sensors are applicable for detecting various mechanical deformation modes (press, bend and torsion) and different stress/strain levels (from gait feature, finger/wrist/elbow movement to breathing monitoring and real-time pulse wave), providing a new concept of device design for wearable electronic applications.

One-step reducing and dispersing graphene oxide via hydroxypropyl hydrazine and its applications in Cu2+ removal

Graphene is widely used in numerous scientific fields including physics, chemistry and materials science due to its exceptional electrical, thermal, optical and mechanical properties. However, the poor solubility/dispersibility strongly limits the practical applications of graphene. In this work, hydroxypropyl hydrazine (HPH) was synthesized to reduce graphene oxide (GO) under mild conditions. The as-produced graphene sheets with a 3D-porous structure show admirable dispersion stability in N,N-dimethylacetamide (DMAc) and the graphene sheets are more effective absorbents for Cu²⁺ removal than those reduced by hydrazine hydrate. A mechanism for removal of epoxides and carboxides from GO by HPH has been proposed. This one-step reducing and dispersing process of GO is more efficient, environmentally benign and safer for the bulk-scale production of 3D porous graphene.

Multifunctional films with a highly oriented "nano-brick wall" structure by regulating modified TiO2@graphene oxide/poly(vinyl alcohol) nanocomposites

High-performance packaging materials featuring a superior gas barrier and UV resistance as well as excellent mechanical properties are highly desirable but are still encountering serious challenges in the food, pharmaceutical and electronic industries. Here, a multifunctional film based on a modified titanium dioxide@graphene oxide/poly(vinyl alcohol) (TiO2@GO/PVA) nanocomposite with a multilayer nano-brick wall structure is rationally designed and fabricated by a facile solution casting approach. The modified TiO2 nanoparticles, assembled on the surface and edges of GO, are employed as bridges to construct the GO edge-to-edge alignment. Then, they tightly combine with PVA chains, acting as the mortar, to form a multilayer compact film. Therefore, the oxygen permeability of the nanocomposite film decreases to 0.119 × 10-17 cm3·cm (cm2·s·Pa)-1 with the addition of 1.0 wt% GO and 1.2 wt% modified TiO2, reduced by 93% compared with pure PVA film. More impressively, it is increased by only 5.9% after 9 h of ultraviolet light irradiation, which shows its exceptional UV resistance ability. In addition, the mechanical performance, thermal stability and water resistance are substantially improved. The developed modified TiO2@GO/PVA nanocomposite films with outstanding performance can be perceived as a green biodegradable material for a wide range of packaging industries.

Polymer nanocomposites having a high filler content: synthesis, structures, properties, and applications

The recent development of nanoscale fillers, such as carbon nanotubes, graphene, and nanocellulose, allows the functionality of polymer nanocomposites to be controlled and enhanced. However, conventional synthesis methods of polymer nanocomposites cannot maximise the reinforcement of these nanofillers at high filler content. Approaches for the synthesis of high content filler polymer nanocomposites are suggested to facilitate future applications. The fabrication methods address the design of the polymer nanocomposite architecture, which encompasses one, two, and three dimensional morphologies. Factors that hamper the reinforcement of nanostructures, such as alignment, dispersion of the filler and interfacial bonding between the filler and polymer, are outlined. Using suitable approaches, maximum potential reinforcement of nanoscale fillers can be anticipated without limitations in orientation, dispersion, and the integrity of the filler particle-matrix interface. High filler content polymer composites containing emerging materials such as 2D transition metal carbides, nitrides, and carbonitrides (MXenes) are expected in the future.

Temperature-triggered sensitive resistance transition of graphene oxide wide-ribbons wrapped sponge for fire ultrafast detecting and early warning

Fire prevention and safety of combustible materials is a global challenge. To reduce their high fire risk, traditional smoke detectors are widely used indoor via detecting smoke product after combustion; however, they usually show a long response time and limitation for outdoor use. Herein, we report a temperature-induced electrical resistance transition of graphene oxide wide-ribbon (GOWR) wrapped sponges to reliably monitor fire safety of the combustible materials. Novel rectangle-like GOWR sheets are synthesized from unzipping carbon nanofibers and used to fabricate GOWR wrapped melamine formaldehyde sponges with multi-functionalities, e.g. lightweight, good hydrophobicity, reversible compressibility, excellent acidic/alkaline tolerance and flame resistance. The GOWR sheets on the sponge skeleton can be in-situ thermally reduced once encountering a flame attack or abnormal high temperature, inducing a distinct transition in electrical resistance. Consequently, an ultrafast alarm response of ∼2 s to flame attack is triggered, and rapid fire early warning signals to abnormal high temperatures, e.g. ∼33 s at 300 °C, are achieved below ignition temperature of most combustible materials. This method drives substantial motivation and opportunity to develop advanced fire detection and early warning sensors for reducing the high fire risk of various combustible materials in outdoor applications.

Hydrothermal Synthesis of Graphene Quantum Dots Supported on Three-Dimensional Graphene for Supercapacitors

Incorporation of new functional components into a three-dimensional graphene (3DG) framework improves the performance of supercapacitors based on 3DG as electrodes by tailoring the framework's structure and properties. In this work, graphene quantum dots (GQDs) were incorporated into 3DG via one-step hydrothermal treatment of GQDs and graphene oxide (GO). By simply adjusting the GQDs/GO feeding ratio by weight, various GQDs/3DG composites were formed. The maximum feeding ratio was 80%, and the prepared composites possessed saturated GQDs loading on the 3DG framework, whereas composites obtained with a GQDs/GO feeding ratio of 40% as electrodes exhibited optimal specific capacitance of 242 F·g-1 for supercapacitors, an increase of 22% compared with that of pure 3DG electrodes (198 F·g-1). This improved performance was mainly due to better electrical conductivity and larger surface area for GQDs/3DG composites with moderate GQDs content. The fabricated GQDs/3DG composites as electrodes for supercapacitors revealed high electrochemical stability. Their capacitance kept 93% of the initial value after 10,000 charge-discharge cycles.

Mechanically robust nanocomposites from screen-printable polymer/graphene nanosheet pastes

Innovative methods for producing graphene-based polymer nanocomposites with excellent mechanical robustness have become a focus for their practical utilization, existing solutions suffer from drawbacks such as limited laboratory-scale fabrication, affordability, and inadequate processability. To address these issues, we proposed a screen printing approach utilizing formulated graphene-modified water-based printable pastes to achieve inexpensive and scalable manufacturing of graphene-reinforced polymer nanocomposites. Leveraging this simple and versatile manufacturing process, mass production, as well as personalized-patterned bulk materials, can be efficiently produced using easily obtainable substrates. The surface-tailored graphene (PEI-rGO) can improve the dispersion quality and strengthen the interfacial bonding with a waterborne polyurethane (WPU) matrix, yielding an optimized enhancement effect and enhancing the tensile strength and Young's modulus about 9.46 and 19.8 times higher than those of the pure WPU, respectively. In particular, their utility as an anti-wear modifier through direct printing on textile and wear-reduction performance were investigated. Our study establishes screen printing as a general strategy to achieve facile fabrication of polymer nanocomposites at an industrial-scale in an economically viable manner, which can to a great extent bridge the gap between scientific research and real-world applications.

Strain-sensitive electrical conductivity of carbon nanotube-graphene-filled rubber composites under cyclic loading

Conductive rubber nanocomposites have been attracting interest for strain sensing applications owing to their large deformation and high sensitivity. In this paper, the strain sensing behavior of room temperature vulcanized (RTV) hybrid silicone rubber composites containing carbon nanotubes and graphene was systematically investigated. We studied the effects of the nanofiller content and strain amplitude on the strain sensing behavior of the nanocomposites, and found good stability and durability during cyclic loading. The shoulder peaks appeared in the cyclic loading curves owing to the competition between the reconstruction process of the conductive network during deformation and time-dependent features of the polymer material. Furthermore, our test results of different loading histories indicated that a sufficient recovery time could reduce or even eliminate the shoulder peak. Finally, the mechanical structure with a negative Poisson's ratio is designed to regulate the resistance response of the RTV nanocomposites, exhibiting a monotonic and more sensitive resistance response. Our research results explain the main factors contributing to the shoulder peak phenomenon of conductive nanocomposites and provide a regulation strategy for achieving a monotonic and highly sensitive resistance response.

Multifunctional WS2&M-AgNPs superhydrophobic conductive sponges for application in various sensors

Superhydrophobic conductive sponge is prepared by an easy method based on WS₂ nanosheets and modified Ag nanoparticles in this work, which is promising to apply in various sensors derived from superior liquid repellence, thermo stability, conductive property, mechanical and chemical durability.

Chitin nano-whiskers (CNWs) as a bio-based bio-degradable reinforcement for epoxy: evaluation of the impact of CNWs on the morphological, fracture, mechanical, dynamic mechanical, and thermal characteristics of DGEBA epoxy resin

Chitin nano-whiskers (CNWs) reinforcement for producing optically transparent epoxy nanocomposites with enhanced fracture, mechanical and thermal characteristics.

A Large-Sized Reduced Graphene Oxide with Low Charge-Transfer Resistance as a High-Performance Electrode for a Nonflammable High-Temperature Stable Ionic-Liquid-Based Supercapacitor

Large-sized reduced graphene oxide prepared was prepared by combined microwave intermittent heating and an extraction process (e.g., 900 W for 10 min (MRG-900-10)) with a lateral size of several micrometers and a thickness of 4-6 monosheets . The MRG-900-10 has a high C/O molar ratio (5.89) and a sp² C content of 69.0 %, which leads to a fast electronic transmission in the sample. In addition, MRG-900-10 possesses a large specific surface area of 568.2 m²  g^-1 , which increases the contact surface area between the active material and the electrolyte, thus enhancing the electron and ion transport in the interfaces when used as the electrode material in supercapacitors. MRG-900-10 possesses a low charge-transfer resistance (≈0.36 Ω). Used as the electrode material for a supercapacitor in 6 m KOH aqueous electrolyte, MRG-900-10 produces a high specific capacity of 327.6 F g^-1 at the current density of 0.5 A g^-1 . A specific capacity of 248.3 F g^-1 was obtained at a high current density of 100 A g^-1 , which indicated its high-rate ability. The initial capacity of 92 % can be maintained after 40 000 cycles at 5 A g^-1 , which indicated its high cycling stability. As for the MRG-900-10 symmetric supercapacitors, the energy densities of 11.0 and 36.2 Wh kg^-1 were obtained in 6 m KOH aqueous and 1 m tetraethylammonium tetrafluoroborate ([TEA]BF₄ )/acetonitrile (ACN) electrolytes, respectively. Importantly, a high energy density of 68.6 Wh kg^-1 was achieved in the nonflammable ionic liquid 1-ethyl-3-methylimidazolium bis(trifluoromethane)sulfonimide ([EMIM][TFSI])/ACN (80 vol % [EMIM][TFSI]), and the supercapacitor was effective from room temperature to 100 °C.

Achieving high-performance nitrate electrocatalysis with PdCu nanoparticles confined in nitrogen-doped carbon coralline

Complex porous carbon nanostructures with homogeneously embedded nanoparticles and intricate architectures show promise as high-performance catalysts. Herein, we demonstrate a direct surfactant co-assembly approach for the fabrication of well-dispersed PdCu nanoparticles encapsulated in N-doped porous carbon with three-dimensional coralline structures. Owing to their porous features and unique frameworks, the PdxCuy@N-pC coralline-like nanostructures offer large surface areas, accessible active sites, and excellent nitrate electrocatalytic ability. The composite catalyst Pd4Cu4@N-pC exhibits outstanding catalytic performance with a high nitrate removal rate of ∼95%, nitrogen selectivity of ∼80%, and removal capacity of 22 000 mg N per g PdCu. More importantly, the present work opens up a broad horizon for architectures of nanoparticles confined in coralline-like 3D porous carbon structures with superior performance and promising large-scale applications.

Thin Electric Heating Membrane Constructed with a Three-Dimensional Nanofibrillated Cellulose⁻Graphene⁻Graphene Oxide System

Nanofibrillated cellulose (NFC) and graphene oxide (GO) with reinforcing and film-forming properties were employed with graphene to develop a novel and thin electric heating membrane with heat dissipation controllability. A negative charge was found on the surface of GO and NFC in aqueous dispersions, which contributed to the homogeneous distribution of the graphene sheets. The membrane had a good laminated structure with three-dimensional interaction between GO and NFC, with embedded graphene sheets. Conductivity was characterized as a function of the amount of graphene, thus giving control over to the heating power by adjusting the ratio of graphene. Subsequent electric heating tests can remove irregularities on the GO and graphene sheet, improving the laminated structure further. The temperature on the surface of the membrane presented an exponential increasing regularity with time. Under the same power density and time, the stabilized temperature rise of membranes was higher when grammage was higher, which was characterized by the linear function of the power density. Low-grammage membranes (1 and 4 g·m⁻²) also exhibited regular and even stabilized temperature rises. The indicated structure and heating performance of the membrane, as well as the variation induced by Joule heating, would drive its applications.