Miniaturization of electronics demands electromagnetic interference (EMI) shielding of nanoscale dimension. The authors report a systematic exploration of EMI shielding behavior of 2D Ti3C2Tx MXene ...assembled films over a broad range of film thicknesses, monolayer by monolayer. Theoretical models are used to explain the shielding mechanism below skin depth, where multiple reflection becomes significant, along with the surface reflection and bulk absorption of electromagnetic radiation. While a monolayer assembled film offers ≈20% shielding of electromagnetic waves, a 24‐layer film of ≈55 nm thickness demonstrates 99% shielding (20 dB), revealing an extraordinarily large absolute shielding effectiveness (3.89 × 106 dB cm2 g−1). This remarkable performance of nanometer‐thin solution processable MXene proposes a paradigm shift in shielding of lightweight, portable, and compact next‐generation electronic devices.
Self‐assembly of monolayer MXene and systematic exploration of the electromagnetic interference shielding behavior of 2D Ti3C2Tx MXene are presented. Theoretical models explain the shielding mechanism below skin depth. A monolayer assembled MXene film (2.3 nm) and 24‐layer film (≈55 nm) offer ≈20% and 99% shielding, respectively. The extraordinarily large absolute shielding effectiveness reaches 3.89 × 106 dB cm2 g−1.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
Engineering electrode nanostructures is critical in developing high‐capacity, fast rate‐response, and safe Li‐ion batteries. This study demonstrates the synthesis of orthorhombic Nb2O5@Nb4C3Tx (or ...@Nb2CTx) hierarchical composites via a one‐step oxidation —in flowing CO2 at 850 °C —of 2D Nb4C3Tx (or Nb2CTx) MXene. The composites possess a layered architecture with orthorhombic Nb2O5 nanoparticles decorated uniformly on the surface of the MXene flakes and interconnected by disordered carbon. The composites have a capacity of 208 mAh g−1 at a rate of 50 mA g−1 (0.25 C) in 1–3 V versus Li+/Li, and retain 94% of the specific capacity with 100% Coulombic efficiency after 400 cycles. The good electrochemical performances could be attributed to three synergistic effects: (1) the high conductivity of the interior, unoxidized Nb4C3Tx layers, (2) the fast rate response and high capacity of the external Nb2O5 nanoparticles, and (3) the electron “bridge” effects of the disordered carbon. This oxidation method was successfully extended to Ti3C2Tx and Nb2CTx MXenes to prepare corresponding composites with similar hierarchical structures. Since this is an early report on producing this structure, there is much room to push the boundaries further and achieve better electrochemical performance.
The oxidation of Nb4C3Tx MXene in CO2 results in a hierarchical T‐Nb2O5@Nb4C3Tx layered composite, that combines the high capacity of the external orthorhombic T‐Nb2O5, coupled with the high electrical conductivity of the interior unoxidized Nb4C3Tx and the electron bridge effect of the disordered carbon. This composite exhibits high capacity at high rate when used as Li‐ion battery anode.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SAZU, SBCE, SBMB, UL, UM, UPUK
In this work, we demonstrate that gas adsorption is significantly higher in edge sites of vertically aligned MoS2 compared to that of the conventional basal plane exposed MoS2 films. To compare the ...effect of the alignment of MoS2 on the gas adsorption properties, we synthesized three distinct MoS2 films with different alignment directions ((1) horizontally aligned MoS2 (basal plane exposed), (2) mixture of horizontally aligned MoS2 and vertically aligned layers (basal and edge exposed), and (3) vertically aligned MoS2 (edge exposed)) by using rapid sulfurization method of CVD process. Vertically aligned MoS2 film shows about 5-fold enhanced sensitivity to NO2 gas molecules compared to horizontally aligned MoS2 film. Vertically aligned MoS2 has superior resistance variation compared to horizontally aligned MoS2 even with same surface area exposed to identical concentration of gas molecules. We found that electrical response to target gas molecules correlates directly with the density of the exposed edge sites of MoS2 due to high adsorption of gas molecules onto edge sites of vertically aligned MoS2. Density functional theory (DFT) calculations corroborate the experimental results as stronger NO2 binding energies are computed for multiple configurations near the edge sites of MoS2, which verifies that electrical response to target gas molecules (NO2) correlates directly with the density of the exposed edge sites of MoS2 due to high adsorption of gas molecules onto edge sites of vertically aligned MoS2. We believe that this observation extends to other 2D TMD materials as well as MoS2 and can be applied to significantly enhance the gas sensor performance in these materials.
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IJS, KILJ, NUK, PNG, UL, UM
Two-dimensional (2D) transition metal carbides (MXenes) exhibit outstanding performances in many applications, such as energy storage, optoelectronics, and electrocatalysts. However, colloidal ...solutions of Ti3C2Tx MXene flakes deteriorate rapidly under ambient conditions due to the conversion of the titanium carbide to titanium dioxide. Here, we discuss the dominant factors influencing the rate of oxidation of Ti3C2Tx MXene flakes, and present guidelines for their storage with the aim of maintaining the intrinsic properties of the as-prepared material. The oxidation stability of the Ti3C2Tx flakes is dramatically improved in a system where water molecules and temperature were well-controlled. It was found that aqueous solutions of Ti3C2Tx MXene can be chemically stable for more than 39 weeks when the storage temperature (−80 °C) is sufficiently low to cease the oxidation processes. It was also found that if the Ti3C2Tx flakes are dispersed in ethanol, the degradation process can be significantly delayed even at 5 °C. Moreover, the oxidation stability of the Ti3C2Tx flakes is dramatically improved in both cases, even in the presence of oxygen-containing atmosphere. We demonstrate practical applications of our approach by employing Ti3C2Tx in a gas sensor showing that when oxidation is inhibited, the device can retain the original electrical properties after 5 weeks of storage.
Though anodes with high Li gravimetric capacities, beyond commercial graphite, have been intensively studied, gravimetric capacity does not precisely reflect the performance of a packed cell. Li ...anodes with high mass loadings, which can achieve high areal capacities, are required for many commercial applications. Herein, anodes with high mass loadings were fabricated using two-dimensional transition metal carbides (MXenes). Powders of the latter were cold pressed, without binders, at a pressure of 1GPa, to create ∼300μm thick, free-standing discs. When Ti3C2 was used as the anode for lithium, the initial reversible areal capacity was ∼15mAh/cm2, which decreased to 5.9mAh/cm2 after 50 cycles, but the decrease after the first ∼20 cycles was very gradual. The latter is one of the highest values ever reported to date. When Nb2C was used as the anode instead, the initial reversible capacity was ∼16mAh/cm2; this value decreased to 6.7mAh/cm2 after 50 cycles, which is about a 14% increase compared to Ti3C2. As the research on MXenes for lithium ion batteries has just begun, there is certainly room for further improving their electrochemical performance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
Oxidation-resistant titanium carbide MXene films Lee, Yonghee; Kim, Seon Joon; Kim, Yong-Jae ...
Journal of materials chemistry. A, Materials for energy and sustainability,
2020, Volume:
8, Issue:
2
Journal Article
Peer reviewed
Two-dimensional transition metal carbides (MXenes) have attracted much attention due to their excellent electrical conductivity and outstanding performances in energy storage, telecommunication, and ...sensing applications. It is known that MXene flakes are readily oxidized in either humid air or aqueous environments. While the chemical instability of MXenes may limit their use in applications involving ambient environments and long-term operation, oxidation behaviour of MXene films has not been addressed. In this work, we demonstrate a hydrogen annealing method to increase the oxidation stability of Ti
3
C
2
MXene in two different aspects: (1) dramatic improvement in the oxidation stability of pristine MXene films against harsh conditions (100% relative humidity, 70 °C), and (2) large recovery in the electrical conductivity of previously oxidized Ti
3
C
2
MXene films. We also demonstrate an electric-field-induced heater capable of stable operation under highly oxidizing conditions, based on the oxidation-resistant MXene film. A total loss of heat generation ability was observed for the as-prepared MXene film, while the hydrogen-annealed one maintained its bright infrared radiation, under the highly oxidizing conditions. This work offers a solution to industrial applications of unprotected MXene films, securing their stable and long-term operation in humid conditions.
We have demonstrated a highly stable electric heater made of oxidation-resistant MXene film, which was capable of stable operation in air under highly oxidizing conditions (70 °C, 100% RH).
Understanding the etching mechanisms of MXene and obtaining direct insights into the influence of etchants on structural features and defects are of critical importance for improving MXene ...properties, optimization of etching protocols, and exploring new MXene compositions. Despite their importance, such studies have been challenging because of the monoatomic thickness of the A-element layers being etched and aggressive etchants that hinder in situ studies. Here, we visualize the etching behavior of the Ti3AlC2 MAX phase in different etchants at the atomic scale using focused ion beam and electron microscopy. We also report on the structural changes in the Ti3AlC2 phase as a function of etching time and etchant type (LiF/HCl, HF, or NH4HF2) to reveal the etching mechanism for the first time. Interestingly, direct visualization reveals an unexpected stepwise etching where the edge Al atoms at the middle layers of the MAX particle are not etched despite contact with the acidic etchant counterintuitively. Also, while the propagation of the etching front occurs in the direction normal to the inner basal plane for all etchants, we reveal that HF and NH4HF2 etch the grain boundaries of polycrystal MAX particles to expose more edge sites to the etchant, which is not observed for LiF/HCl.
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IJS, KILJ, NUK, PNG, UL, UM
Cancer immunotherapy has emerged as a promising cancer treatment. However, the presence of immune-refractory tumor cells limits its clinical success by blocking amplification of anti-tumor immunity. ...Previously, we found that immune selection by immunotherapy drives the evolution of tumors toward multi-modal resistant and stem-like phenotypes via transcription induction of AKT co-activator TCL1A by NANOG. Here, we report a crucial role of HSP90A at the crossroads between NANOG-TCL1A axis and multi-aggressive properties of immune-edited tumor cells by identifying HSP90AA1 as a NANOG transcriptional target. Furthermore, we demonstrate that HSP90A potentiates AKT activation through TCL1A-stabilization, thereby contributing to the multi-aggressive properties in NANOG
tumor cells. Importantly, HSP90 inhibition sensitized immune-refractory tumor to adoptive T cell transfer as well as PD-1 blockade, and re-invigorated the immune cycle of tumor-reactive T cells. Our findings implicate that the HSP90A-TCL1A-AKT pathway ignited by NANOG is a central molecular axis and a potential target for immune-refractory tumor.
MXenes are a prominent family of two-dimensional materials because of their metallic conductivity and abundant surface functionalities. Although MXenes have been extensively studied as bulk particles ...or free-standing films, thin and transparent films are needed for optical, optoelectronic, sensing, and other applications. In this study, we demonstrate a facile method to fabricate ultrathin (∼10 nm), Ti3C2T x MXene films by an interfacial assembly technique. The self-assembling behavior of MXene flakes resulted in films with a high stacking order and strong plane-to-plane adherence, where optimal films of 10 nm thickness displayed a low sheet resistance of 310 Ω/□. By using surface tension, films were transferred onto various types of planar and curved substrates. Moreover, multiple films were consecutively transferred onto substrates from a single batch of solution, showing the efficient use of the material. When the films were utilized as gas sensing channels, a high signal-to-noise ratio, up to 320, was observed, where the gas response of films assembled from small MXene flakes was 10 times larger than that from large flakes. This work provides a facile and efficient method to allow MXenes to be further exploited for thin-film applications.
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IJS, KILJ, NUK, PNG, UL, UM
Exosomes are extracellular vesicles that mediate intercellular communication, immune response, and tumour metastasis. However, exosome isolation from the blood is complicated because their size and ...density are similar to those of blood lipoproteins. Here, we employed field programming frit-inlet asymmetrical flow field-flow fractionation (FIAF4) coupled with multiangle light scattering (MALS) for the effective separation of exosomes from free unbound proteins and lipoproteins present in serum samples using different pre-treatment methods, namely, a commercial exosome isolation kit, ultracentrifugation (UC), and a simple centrifugation followed by ultrafiltration (UF). Sizes of the eluted exosomes, as calculated by MALS signals, approximated well with the results of batch dynamic light scattering of the collected fractions and with the sizes of polystyrene particles. Exosome separation from lipoproteins was validated by western blotting with several markers of exosomes and lipoproteins, followed by proteomic analysis using nanoflow ultrahigh-performance liquid chromatography-electrospray ionisation-tandem mass spectrometry. UC requires relatively large amounts of serum samples (at least 2 mL) but is more efficient at removing lipoproteins. The UF method with a centrifugal concentrator (300 kDa) was found to be more effective in retrieving exosomes with low serum volumes (50 μL). Altogether, this study demonstrates the application of field programming FIAF4 for the isolation/purification of exosomes from proteins and lipoproteins in the serum.
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•FlFFF-MALS was employed to investigate the isolation efficiency of serum exosomes.•Exosomes can be separated from serum HDL and LDL by FlFFF with field programming.•Ultrafiltration showed better retrieval with less volume than ultracentrifugation.•Ultrafiltration with FlFFF-MALS can be a simple method for isolating serum exosomes.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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