The porous alumina ceramics with closed pores were fabricated using C@Al2O3 microspheres as pore-forming agent. The closed pores with a diameter about 5μm were successfully obtained in the dense ...matrix, owing to the additive C@Al2O3 microspheres. Different amount of C@Al2O3 microspheres was added to investigate the effects of closed pores on thermal, dielectric and mechanical properties. With the increasing microspheres amount, the closed porosity of alumina ceramics ranges from 5.82 to 14.5%, the thermal conductivity decreases continuously at the temperature ranging from 30 to 1200°C, and the flexural strength and fracture roughness decrease. As the closed porosity increases, the real permittivity decreases, while the tangent loss has a slight increase. When the mass ratio of C@Al2O3 microspheres is 10wt.%, the porous alumina ceramics with the thermal conductivity (13.07–3.8W·m−1·K−1), the flexural strength (97.05±18MPa), and the fracture roughness (2.65±0.13MPa·m1/2) can be obtained.
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•The closed pores in alumina ceramics were achieved using core-shell structured C@Al2O3 microspheres as pore-forming agent.•The closed pores significantly decreased the thermal conductivity to 3.8W·m−1·K−1 at 1200°C.•The closed pores decreased the real permittivity from 9.74 to 7.48 with a slight increase of the imaginary permittivity.
Achieving pseudocapacitive intercalation in MXenes with neutral aqueous electrolytes and driving reversible redox reactions is scientifically appealing and practically useful. Here, we report that ...the partial oxidation of MXene intensifies pseudocapacitive Li+ intercalation into Ti3C2T x MXene from neutral water-in-salt electrolytes. An in situ X-ray absorption near-edge structure analysis shows that the Ti oxidation state changes during the Li+ intercalation, indicating the presence of a surface redox reaction. The Ti oxidation/reduction is further confirmed by an in situ extended X-ray absorption fine structure analysis, which shows a reversible contraction/expansion of the Ti–C interatomic distance. The intensified Li+ pseudocapacitive intercalation can be explained by the higher oxidation state of Ti at the open circuit potential. This work demonstrates the possibility of tuning the pseudocapacitive intercalation by adjusting the initial oxidation state of the transition metal on the MXene and offers a facile way to enhance the pseudocapacitance of various MXenes.
Two-dimensional transition metal carbides, nitrides and carbonitrides, popular by the name MXenes, are a promising class of materials as they exhibit intriguing optical, optoelectronic and ...electrochemical properties. Taking advantage of their metallic conductivity and hydrophilicity, titanium carbide MXenes (Ti3C2Tx and others) are used to fabricate solution processable transparent conducting electrodes (TCEs) for the design of three-electrode electrochromic cells. However, the tunable electrochromic behavior of various titanium-based MXene compositions across the entire visible spectrum has not yet been demonstrated. Here, we investigate the intrinsic electrochromic properties of titanium-based MXenes, Ti3C2Tx, Ti3CNTx, Ti2CTx, and Ti1.6Nb0.4CTx, where individual MXenes serve as a transparent conducting, electrochromic, and plasmonic material layer. Plasmonic extinction bands for Ti3C2Tx, Ti2CTx and Ti1.6Nb0.4CTx are centered at 800, 550 and 480 nm, which are electrochemically tunable to 630, 470 and 410 nm, respectively, whereas Ti3CNTx shows a reversible change in transmittance in the wide visible range. Additionally, the switching rates of MXene electrodes with no additional transparent conductor electrodes are estimated and correlated with the respective electrical figure of merit values. This work demonstrates that MXene-based electrochromic cells are tunable in the entire visible spectrum and suggests the potential of the MXene family of materials in optoelectronic, plasmonic, and photonic applications, such as tunable visible optical filters and modulators, to name a few.
Two-dimensional transition metal carbides and nitrides (MXenes) have accumulated tremendous interest recently due to their high conductivity and excellent figures of merit in electromagnetic ...interference shielding and other applications. Large-area freestanding films of MXenes are important for versatility in application; however, alternative processing methods are needed for large-scale production. In this work, we demonstrate fabrication of Ti3C2Tx MXene freestanding films through drop-casting onto hydrophobic plastic substrates. Freestanding MXene films prepared using the drop-casting method can be fabricated in large areas (>125 cm2) and thicknesses (23.2 μm), and have smooth surfaces (14 nm RMS roughness) while maintaining high electrical conductivity (~7,000 S cm−1). Moreover, these MXene films can be micropatterned in three dimensions by processing on commercially available microstructured plastics, resulting in a 38% increase in normalized electromagnetic interference shielding efficiency compared with flat films. The results presented here suggest a scalable path toward creating MXene freestanding films for prototypes and industrialization.
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•Freestanding MXene films are prepared using hydrophobic substrates•These films have smooth surfaces with good alignment between flakes•Using pre-patterned substrates, micrometer-scale patterns can be made in the films•Patterned films show a ~38% boost in electromagnetic interference shielding efficiency
Electromagnetic interference (EMI) can cause disruptions in communication in critical applications, resulting in potentially disastrous consequences. As electronics become portable, miniaturized, and wearable, it has become clear that traditional EMI shields require large thicknesses to be effective, hampering design flexibility. MXenes have accumulated tremendous interest due to their high conductivity and excellent figures of merit in EMI shielding and other applications. In this work, we demonstrate fabrication of MXene freestanding films through drop-casting onto hydrophobic substrates. These films can be patterned in three dimensions simply by using a pre-patterned substrate, leading to a significant enhancement in the normalized EMI shielding efficiency. We suggest that these micropatterned MXene films, prepared using a method that is scalable and allows for high throughput, can be readily used in EMI shielding, energy storage, and optoelectronics applications.
Electromagnetic interference (EMI) can cause disruptions in communication in critical applications, resulting in potentially disastrous consequences. MXenes have accumulated tremendous interest due to their high conductivity and excellent figures of merit in EMI shielding and other applications. Here, freestanding Ti3C2Tx MXene films are prepared through drop-casting onto hydrophobic plastic substrates. By drop-casting onto pre-patterned plastics, films can be patterned with macro- and microscopic features resulting in significant enhancement to EMI shielding properties.
The availability of MXenes and other two-dimensional conductive nanomaterials with tunable surface chemistry has reshaped the field of electromagnetic protection. However, the high electrical ...conductivity and low dielectric loss of titanium-based MXenes lead to strong reflection of electromagnetic waves, even when combined with polymers to form composites. Here, we report on the ability of vanadium-based MXenes to provide broadband microwave absorption. Polyurethane composites with ∼2 wt % Vn+1CnTx can absorb 90% of electromagnetic waves covering the entire X band. In addition, pure Vn+1CnTx films of submicrometer thickness can provide effective electromagnetic interference shielding. The free electron transport, surface terminations, native defects, and layers arrangement in composites have profound effects on electronic and dielectric properties of Vn+1CnTx MXenes. This study points toward a new frontier for development of thin and highly absorbing MXene-based electromagnetic protection materials.
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•Polyurethane composites with ∼2 wt % Vn+1CnTx absorb >90% of microwaves in X band•600-nm-thick Vn+1CnTx films provide effective electromagnetic interference shielding•The native defects and surface groups affect the microwave absorption behavior
Han et al. report that vanadium-based MXenes (V2CTx and V4C3Tx) can provide broadband microwave absorption with ultralow filler loading in polymer matrix. The free electron transport, surface terminations, native defects, and layers arrangement significantly affect electronic and dielectric properties of Vn+1CnTx MXenes.
New ultrathin and multifunctional electromagnetic interference (EMI) shielding materials are required for protecting electronics against electromagnetic pollution in the fifth-generation networks and ...Internet of Things era. Micrometer-thin Ti
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MXene films have shown the best EMI shielding performance among synthetic materials so far. Yet, the effects of elemental composition, layer structure, and transition-metal arrangement on EMI shielding properties of MXenes have not been explored, despite the fact that more than 30 different MXenes have been reported, and many more are possible. Here, we report on a systematic study of EMI shielding properties of 16 different MXenes, which cover single-metal MXenes, ordered double-metal carbide MXenes, and random solid solution MXenes of M and X elements. This is the largest set of MXene compositions ever reported in a comparative study. Films with thicknesses ranging from nanometers to micrometers were produced by spin-casting, spray-coating, and vacuum-assisted filtration. All MXenes achieved effective EMI shielding (>20 dB) in micrometer-thick films. The EMI shielding effectiveness of sprayed Ti
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film with a thickness of only ∼40 nm reaches 21 dB. Adjustable EMI shielding properties were achieved in solid solution MXenes with different ratios of elements. A transfer matrix model was shown to fit EMI shielding data for highly conductive MXenes but could not describe the behavior of materials with low conductivity. This work shows that many members of the large MXene family can be used for EMI shielding, contributing to designing ultrathin, flexible, and multifunctional EMI shielding films benefiting from specific characteristics of individual MXenes.
Water-based polyurethane/alumina hollow microsphere (WPU-hAl2O3) composite films were prepared via a facile spin coating method. The pristine WPU, as the matrix of the composite films, was ...tailor-made by hAl2O3 with the diameter of 2–5 μm to improve the mechanical and physical properties of the films. The hardness, surface morphology, infrared emissivity, wettability, and light transmittance of the WPU-hAl2O3 films with different hAl2O3 contents were investigated. The results indicate that the Vickers hardness, coefficient of friction, infrared emissivity at the wavelength of 2–22 μm, and wetting angle of the WPU-hAl2O3 films (30 wt%) increased by 53.6%, 51.7%, 21.1%, and 19.0%, respectively, compared with the pristine WPU films. Meanwhile, with the rising of hAl2O3 content, the light transmittance decreased by 75.3% at the wavelength of 400–800 nm. This work not only designs a kind of lightweight multifunctional composite film but also provides an effective route for extending further applications of hAl2O3 in the field of composite films.
Highly integrated, flexible, and ultrathin wireless communication components are in significant demand due to the explosive growth of portable and wearable electronic devices in the fifth-generation ...(5G) network era, but only conventional metals meet the requirements for emerging radio-frequency (RF) devices so far. Here, it is reported on Ti
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MXene microstrip transmission lines with low-energy attenuation and patch antennas with high-power radiation at frequencies from 5.6 to 16.4 GHz. The radiation efficiency of a 5.5 µm thick MXene patch antenna manufactured by spray-coating from aqueous solution reaches 99% at 16.4 GHz, which is about the same as that of a standard 35 µm thick copper patch antenna at about 15% of its thickness and 7% of the copper weight. MXene outperforms all other materials evaluated for patch antennas to date. Moreover, it is demonstrated that an MXene patch antenna array with integrated feeding circuits on a conformal surface has comparable performance with that of a copper antenna array at 28 GHz, which is a target frequency in practical 5G applications. The versatility of MXene antennas in wide frequency ranges coupled with the flexibility, scalability, and ease of solution processing makes MXene promising for integrated RF components in various flexible electronic devices.
High throughput manufacturing of regenerable nanomaterial-based flexible electronics represents an extreme challenge. Here we demonstrate a rapid and eco-friendly assembly and regeneration of ...nanomaterial networks (films) on a hydrophobic polymer substrate (i.e., polydimethylsiloxane) from a sonicated dispersion of hydrophobic nanoparticles in water. The self-limiting sono dip coating (SDC) assembly is characterized by an ultrafast withdrawal speed (16 m/min, one to five orders of magnitude greater than that of existing nanomaterial dip-coating processes) and insensitivity to substrate geometry. It is applicable to a wide range of hydrophobic nanomaterials, from graphene to carbon nanotubes and poly (methyl methacrylate) nanoparticles. The sono healing method requires only 1 min sonication in water to regenerate graphene/polydimethylsiloxane strain sensors. Furthermore, the SDC can be combined with other nanomaterial deposition methods (e.g., electroplating) to build heterostructures and integrated devices.
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