Morphological Evolution of Carbon Nanofibers Encapsulating SnCo Alloys and Its Effect on Growth of the Solid Electrolyte Interphase Layer

Two distinctive one-dimensional (1-D) carbon nanofibers (CNFs) encapsulating irregularly and homogeneously segregated SnCo nanoparticles were synthesized <i>via</i> electrospinning of polyvinylpyrrolidone (PVP) and polyacrylonitrile (PAN) polymers containing Sn–Co acetate precursors and subsequent calcination in reducing atmosphere. CNFs synthesized with PVP, which undergoes structural degradation of the polymer during carbonization processes, exhibited irregular segregation of heterogeneous alloy particles composed of SnCo, Co₃Sn₂, and SnO with a size distribution of 30–100 nm. Large and exposed multiphase SnCo particles in PVP-driven amorphous CNFs (SnCo/PVP-CNFs) kept decomposing liquid electrolyte and were partly detached from CNFs during cycling, leading to a capacity fading at the earlier cycles. The closer study of solid electrolyte interphase (SEI) layers formed on the CNFs reveals that the gradual growth of fiber radius due to continuous increment of SEI layer thickness led to capacity fading. In contrast, SnCo particles in PAN-driven CNFs (SnCo/PAN-CNFs) showed dramatically reduced crystallite sizes (<10 nm) of single phase SnCo nanoparticles which were entirely embedded in dense, semicrystalline, and highly conducting 1-D carbon matrix. The growth of SEI layer was limited and saturated during cycling. As a result, SnCo/PAN-CNFs showed much improved cyclability (97.9% capacity retention) and lower SEI layer thickness (86 nm) after 100 cycles compared to SnCo/PVP-CNFs (capacity retention, 71.9%; SEI layer thickness, 593 nm). This work verifies that the thermal behavior of carbon precursor is highly responsible for the growth mechanism of SEI layer accompanied with particles detachment and cyclability of alloy particle embedded CNFs

In Situ Coupling of Multidimensional MOFs for Heterogeneous Metal-Oxide Architectures: Toward Sensitive Chemiresistors

Metal–organic frameworks (MOFs) are used as a new intriguing class of templates, which enable the creation of porous inorganic nanostructures via calcination. In this work, we first introduce in situ coupling of multidimensional MOFs for producing heterogeneous metal-oxide composite with multiple p–n junctions. Controlling relative ratios of two mixed solvents (water and ethanol), in zeolitic imidazolate framework (ZIF) growth, leads to the distinctive morphological evolution such as rod, sheet, and polyhedron particles. One-pot hybridization of ZIF-8 (sheet) with ZIF-67 (rods) results in the generation of hierarchically assembled 1D ZIF-67 rods anchored on a 2D ZIF-8 sheet. Through the calcination of such hybridized ZIFs, we successfully prepared hierarchically assembled 1D Co₃O₄ rods immobilized in a 2D ZnO sheet, possessing numerous n-type ZnO/p-type Co₃O₄ heterogeneous interfaces. This unique structure offers a remarkably enhanced chemiresistive sensing performance (<i>R</i>_a/<i>R</i>_g = 29 at 5 ppm acetone)

Novel Templating Route Using Pt Infiltrated Block Copolymer Microparticles for Catalytic Pt Functionalized Macroporous WO₃ Nanofibers and Its Application in Breath Pattern Recognition

We propose a new route for transferring catalysts onto macroporous metal oxide nanofibers (NFs) using metallic nanoparticles (NPs) infiltrated block copolymer microparticles as sacrificial templates. Pt decorated polystyrene-<i>b</i>-poly­(4-vinylpyridine) (PS-<i>b</i>-P4VP) copolymer microparticles (Pt-BCP MPs), produced from oil-in-water emulsions, were uniformly dispersed within electrospun PVP/W precursor composite NFs. The macropore-loaded WO₃ NFs (macroporous Pt-WO₃ NFs), which are additionally functionalized by Pt NPs (10 nm), were achieved by decomposition of polymeric components and oxidization of W precursor after high-temperature calcination. In particular, macropores with the similar size distribution (50–300 nm) with BCP MPs were also formed on interior and exterior of WO₃ NFs. Chemical sensing performance of macroporous Pt-WO₃ NFs was investigated for pattern recognition of simulated breath gas components at highly humid ambient (95% RH). The result revealed that superior hydrogen sulfide sensitivity (<i>R</i>_air/<i>R</i>_gas = 834.2 ± 20.1 at 5 ppm) and noticeable selectivity were achieved. In addition, H₂S pattern recognition against other chemical components (acetone, toluene, and methyl mercaptan) was clearly identified without any overlapping of each pattern. This work demonstrates the potential application of BCP-templated maroporous Pt-WO₃ NFs in exhaled breath analysis for noninvasive monitoring of physical conditions

Metal Organic Framework-Templated Chemiresistor: Sensing Type Transition from P‑to‑N Using Hollow Metal Oxide Polyhedron via Galvanic Replacement

Facile synthesis of porous nanobuilding blocks with high surface area and uniform catalyst functionalization has always been regarded as an essential requirement for the development of highly sensitive and selective chemical sensors. Metal–organic frameworks (MOFs) are considered as one of the most ideal templates due to their ability to encapsulate ultrasmall catalytic nanoparticles (NPs) in microporous MOF structures in addition to easy removal of the sacrificial MOF scaffold by calcination. Here, we introduce a MOFs derived n-type SnO₂ (n-SnO₂) sensing layer with hollow polyhedron structures, obtained from p–n transition of MOF-templated p-type Co₃O₄ (p-Co₃O₄) hollow cubes during galvanic replacement reaction (GRR). In addition, the Pd NPs encapsulated in MOF and residual Co₃O₄ clusters partially remained after GRR led to uniform functionalization of efficient cocatalysts (PdO NPs and p-Co₃O₄ islands) on the porous and hollow polyhedron SnO₂ structures. Due to high gas accessibility through the meso- and macrosized pores in MOF-templated oxides and effective modulation of electron depletion layer assisted by the creation of numerous p–n junctions, the GRR-treated SnO₂ structures exhibited 21.9-fold higher acetone response (<i>R</i>_air/<i>R</i>_gas = 22.8 @ 5 ppm acetone, 90%RH) compared to MOF-templated p-Co₃O₄ hollow structures. To the best of our knowledge, the selectivity and response amplitudes reported here for the detection of acetone are superior to those MOF derived metal oxide sensing layers reported so far. Our results demonstrate that highly active MOF-derived sensing layers can be achieved via p–n semiconducting phase transition, driven by a simple and versatile GRR process combined with MOF templating route

Glassy Metal Alloy Nanofiber Anodes Employing Graphene Wrapping Layer: Toward Ultralong-Cycle-Life Lithium-Ion Batteries

Amorphous silicon (a-Si) has been intensively explored as one of the most attractive candidates for high-capacity and long-cycle-life anode in Li-ion batteries (LIBs) primarily because of its reduced volume expansion characteristic (∼280%) compared to crystalline Si anodes (∼400%) after full Li⁺ insertion. Here, we report one-dimensional (1-D) electrospun Si-based metallic glass alloy nanofibers (NFs) with an optimized composition of Si₆₀Sn₁₂Ce₁₈Fe₅Al₃Ti₂. On the basis of careful compositional tailoring of Si alloy NFs, we found that Ce plays the most important role as a glass former in the formation of the metallic glass alloy. Moreover, Si-based metallic glass alloy NFs were wrapped by reduced graphene oxide sheets (specifically Si₆₀Sn₁₂Ce₁₈Fe₅Al₃Ti₂ NFs@rGO), which can prevent the direct exposure of a-Si alloy NFs to the liquid electrolyte and stabilize the solid-electrolyte interphase (SEI) layers on the surfaces of rGO sheets while facilitating electron transport. The metallic glass nanofibers exhibited superior electrochemical cell performance as an anode: (i) Si₆₀Sn₁₂Ce₁₈Fe₅Al₃Ti₂ NFs show a high specific capacity of 1017 mAh g^–1 up to 400 cycles at 0.05C with negligible capacity loss as well as superior cycling performance (nearly 99.9% capacity retention even after 2000 cycles at 0.5C); (ii) Si₆₀Sn₁₂Ce₁₈Fe₅Al₃Ti₂ NFs@rGO reveals outstanding rate behavior (569.77 mAh g^–1 after 2000 cycles at 0.5C and a reversible capacity of around 370 mAh g^–1 at 4C). We demonstrate the potential suitability of multicomponent a-Si alloy NFs as a long-cycling anode material

Innovative Nanosensor for Disease Diagnosis

ConspectusAs a futuristic diagnosis platform, breath analysis is gaining much attention because it is a noninvasive, simple, and low cost diagnostic method. Very promising clinical applications have been demonstrated for diagnostic purposes by correlation analysis between exhaled breath components and specific diseases. In addition, diverse breath molecules, which serve as biomarkers for specific diseases, are precisely identified by statistical pattern recognition studies. To further improve the accuracy of breath analysis as a diagnostic tool, breath sampling, biomarker sensing, and data analysis should be optimized. In particular, development of high performance breath sensors, which can detect biomarkers at the ppb-level in exhaled breath, is one of the most critical challenges. Due to the presence of numerous interfering gas species in exhaled breath, selective detection of specific biomarkers is also important.This Account focuses on chemiresistive type breath sensors with exceptionally high sensitivity and selectivity that were developed by combining hollow protein templated nanocatalysts with electrospun metal oxide nanostructures. Nanostructures with high surface areas are advantageous in achieving high sensitivity because the sensing signal is dominated by the surface reaction between the sensing layers and the target biomarkers. Furthermore, macroscale pores between one-dimensional (1D) nanostructures can facilitate fast gas diffusion into the sensing layers. To further enhance the selectivity, catalytic functionalization of the 1D metal oxide nanostructure is essential. However, the majority of conventional techniques for catalytic functionalization have failed to achieve a high degree of dispersion of nanoscale catalysts due to aggregation on the surface of the metal oxide, which severely deteriorates the sensing properties by lowering catalytic activity. This issue has led to extensive studies on monolithically dispersed nanoscale particles on metal oxides to maximize the catalytic performances.As a pioneering technique, a bioinspired templating route using apoferritin, that is, a hollow protein cage, has been proposed to obtain nanoscale (∼2 nm) catalyst particles with high dispersity. Nanocatalysts encapsulated by a protein shell were first used in chemiresistive type breath sensors for catalyst functionalization on 1D metal oxide structures. We discuss the robustness and versatility of the apoferrtin templating route for creating highly dispersive catalytic NPs including single components (Au, Pt, Pd, Rh, Ag, Ru, Cu, and La) and bimetallic catalysts (PtY and PtCo), as well as the core–shell structure of Au–Pd (Au-core@Pd-shell). The use of these catalysts is essential to establish high performance sensors arrays for the pattern recognition of biomarkers. In addition, novel multicomponent catalysts provide unprecedented sensitivity and selectivity. With this in mind, we discuss diverse synthetic routes for nanocatalysts using apoferritin and the formation of various catalyst–1D metal oxide composite nanostructures. Furthermore, we discuss detection capability of a simulated biomarker gas using the breath sensor arrays and principal component analysis. Finally, future prospects with the portable breath analysis platform are presented by demonstrating the potential feasibility of real-time and on-site breath analysis using chemiresistive sensors

Sub-Parts-per-Million Hydrogen Sulfide Colorimetric Sensor: Lead Acetate Anchored Nanofibers toward Halitosis Diagnosis

Lead­(II) acetate [Pb­(Ac)₂] reacts with hydrogen sulfide to form colored brownish precipitates of lead sulfide. Thus far, in order to detect leakage of H₂S gas in industrial sectors, Pb­(Ac)₂ has been used as an indicator in the form of test papers with a detection limit only as low as 5 ppm. Diagnosis of halitosis by exhaled breath needs sensors able to detect down to 1 ppm of H₂S gas. In this work, high surface area and porous Pb­(Ac)₂ anchored nanofibers (NFs) that overcome limitations of the conventional Pb­(Ac)₂-based H₂S sensor are successfully achieved. First, lead­(II) acetate, which melts at 75 °C, and polyacrylonitrile (PAN) polymer are mixed and stirred in dimethylformamide (DMF) solvent at 85 °C, enabling uniform dispersion of fine liquid droplets in the electrospinning solution. During the subsequent electrospinning, Pb­(Ac)₂ anchored NFs are obtained, providing an ideal nanostructure with high thermal stability against particle aggregation, numerous reactions sites, and enhanced diffusion of H₂S into the three-dimensional (3D)-networked NF web. This newly obtained sensing material can detect down to 400 ppb of H₂S at a relative humidity of 90%, exhibiting high potential feasibility as a high-performance colorimetric sensor platform for diagnosis of halitosis

Abnormal Optoelectric Properties of Two-Dimensional Protonic Ruthenium Oxide with a Hexagonal Structure

Two-dimensional structures can potentially lead to not only modulation of electron transport but also the variations of optical property. Protonic ruthenium oxide, a two-dimensional atomic sheet material, has been synthesized, and its optoelectric properties have been investigated. The results indicate that protonic ruthenium oxide is an excellent candidate for use as a flexible, transparent conducting material. A hydrated-ruthenium-oxide sheet has been first prepared via the chemical exfoliation of sodium intercalated ruthenium oxide (NaRuO₂) and, subsequently, converted into a protonic ruthenium oxide sheet using thermal treatment. A thermally activated transport mechanism is dominant in hydrated ruthenium oxide but diminishes in protonic ruthenium oxide; this resulted in a high electrical conductivity of ∼200 S/cm of the protonic sheet. Because of the unique interband and intraband structure, protonic ruthenium oxide has a small optical absorption coefficient of ∼1.62%/L. Consequently, such high conductivity and low absorption coefficient of protonic ruthenium oxide results in excellent transparent conducting properties

Cu Microbelt Network Embedded in Colorless Polyimide Substrate: Flexible Heater Platform with High Optical Transparency and Superior Mechanical Stability

Metal nanowires have been considered as essential components for flexible transparent conducting electrodes (TCEs) with high transparency and low sheet resistance. However, large surface roughness and high interwire junction resistance limit the practical use of metal wires as TCEs. Here, we report Cu microbelt network (Cu MBN) with coalescence junction and low surface roughness for next-generation flexible TCEs. In particular, the unique embedded structure of Cu MBN in colorless polyimide (cPI) film was achieved to reduce the surface roughness as well as enhance mechanical stability. The TCEs using junction-free Cu MBN embedded in cPI exhibited excellent mechanical stability up to 100 000 bending cycles, high transparency of 95.18%, and a low sheet resistance of 6.25 Ω sq^–1. Highly robust Cu MBN-embedded cPI-based TCE showed outstanding flexible heater performance, i.e., high saturation temperature (120 °C) at very low voltage (2.3 V), owing to the high thermal stability of cPI and excellent thermal conductivity of the Cu MBN

Induction of Nrf2-downstream genes by 4-HBA in C6 cells.

<p>(A-B) Cells were treated with 4-HBA (100 or 500 μM) for 3, 6, 9, or 12 hrs and protein levels of HO-1, NQO1, GCLM, and ɑ-tubulin were determined by immunoblotting. (C-D) Cells were pre-treated with 4-HBA (100 μM) for 6 or 9 hrs, treated with H₂O₂ (100 μM) for 1 hr, and protein levels of HO-1, NQO1, GCLM, and ɑ-tubulin were determined 1 hr later. (B, D) Protein levels determined in three independent experiments are presented as means±SEMs. **p<0.01, ^$$<0.01, ^#<0.05, ^## <i>p</i> < 0.01 between indicated groups.</p