Search

[Display omitted] • Synthesis of atomically thin 2D metal oxide NSs by a chemical exfoliation process. • A comparative study on the humidity sensing performances of 2D Ru oxide and Mn oxide NSs. • Demonstration of real-time breath humidity monitoring using a wearable sensing module. Collecting real-time breath humidity data is important for calibrating gas sensors from interfering signals in breath components, ultimately for accurately monitoring a patient's physiological information for applications in non-invasive and point-of-care diagnostics. In this work, atomically thin 2D metal oxide nanosheets (NSs) were synthesized by a liquid phase exfoliation process and their humidity sensing properties were investigated. Interestingly, Opposite humidity sensing responses (R D /R H) were observed between semiconducting oxide and metallic oxide NSs. For the semiconducting manganese (Mn) oxide NSs, decreasing resistance transitions were obtained with the response of 24.01 at 44.5% RH at low humidity levels (i.e., 6.1–45% RH), which was governed by proton (H+) conduction. On the other hand, the metallic ruthenium (Ru) oxide NSs exhibited increasing resistance transitions with the response of 0.28 at 96.3% RH at a high humidity range (i.e., 50–99.9% RH) as a result of proton trapping by accepting electrons upon the exposure to excess water molecules. Ru oxide NSs exhibited the response and recovery times of 68 sec and 8 sec, respectively, at 96.3% RH. Real-time breath humidity monitoring is demonstrated by integrating Ru oxide NSs with a wristband-type wireless sensing module, which can transmit the sensing data to a mobile device. [ABSTRACT FROM AUTHOR]

Silicon-coated molybdenum sulfide nanosheets were prepared in a thin-film shape (Si–MoS 2 TFs) through metal organic chemical vapor deposition (MOCVD) and radio frequency (RF) sputtering. By using MOCVD, the MoS 2 thin films composed of nanosheets were vertically grown on stainless steel substrates. To address the problem of polysulfide dissolution and shuttling effect of MoS 2 during discharge and charge reactions in thin-film Li-ion batteries, the entire surfaces of MoS 2 TFs were covered with silicon layers using RF sputtering. Compared with pristine MoS 2 TFs without protection, the Si–MoS 2 TFs showed excellent reversibility with a high capacity of ∼2000 mAh g−1 for 500 cycles in thin-film Li-ion batteries. Both materials – MoS 2 and Si – were synergistically taken into account to enhance the ability to store Li ions in the host structures and complement each other during repeated conversion and alloying reactions. The underlying reaction principle was elucidated, which provides insight into developing MoS 2 -based thin-film cathodes. [ABSTRACT FROM AUTHOR]

[Display omitted] Electrodeposition and electropolymerization have emerged as versatile tools for the fabrication of chemical and biosensors. The literature in this area, published since 2017, is the main focus of this review. Electropolymerization has played a particularly prominent role in sensor development since its discovery in 1980 by Diaz at IBM. The ability to entrain receptors such as antibodies, engineered virus particles, and metal chelating agents into a conductive polymer sensing element during electropolymerization has proven to be a powerful means of preparing chemiresistors for a variety of analyses. Electrodeposition has also been used to prepare nanostructured metal indicator microelectrodes, enabling of a new modality for transducing biosensors. Electrodeposited metal nanowires have formed the basis for rapid and sensitive sensors for hydrogen gas. Electrodeposition has also been exploited as a powerful means for amplifying weak biosensor signals, extending their dynamic range. Opportunities for the application of electrodeposition and electropolymerization for chemical and biological sensor fabrication and function are discussed. [ABSTRACT FROM AUTHOR]

[Display omitted] van der Waals heterostructures (vdWHs), consisting of more than one type of atomically thin 2D crystal layers are emerging platforms for interesting electrical, optical, and catalytic applications. High yield production of vdWHs with atomic scale precision is crucial prerequisite for practical utilization. Here we present a generalized approach of random solution phase, high yield heteroassembly of semiconducting vdWHs by exploiting inherent surface charge states of 2D materials as well as chemical affinity of specific ligand end-functionalities. Facile removal of noncovalent functionalized ligands via simple pH reversal enables clean interfaces within vdWHs, yielding outstanding optoelectrical and electrochemical properties driven by fluent interfacial charge transfer among the layered 2D structures. The generality of this procedure is demonstrated by the formation of a series of different vdWHs such as WSe 2 -MoS 2 , graphene–MoS 2 - and phospherene–WSe 2 heterostructures. Atomically thin WSe 2 –MoS 2 phototransistor displayed an exceptionally fast response time with high sensitivity. Graphene–MoS 2 overcomes the inherent charge transfer issue of MoS 2 for electrochemical catalyst. Phospherene–WSe 2 successfully addresses poor ambient stability of phospherene together with enhanced surface activity towards chemical sensing. [ABSTRACT FROM AUTHOR]

Electrospinning–etching strategy was employed to synthesize Pt-loaded SnO 2 hollow microbelts (Pt_SnO 2 HBLs) based chemiresistive-type sensor demonstrating high sensitivity and selectivity toward acetone gas. This strategy overcomes a major hurdle toward achieving ubiquitous gas diffusion in electrospun structures, and provides highly porous thin-walled HBLs with large surface area and small crystallites. [Display omitted] • In situ templating of SnO 2 with SiO 2 was employed to form Pt-loaded SiO 2 @SnO 2 core–shell microbelts. • Etching away of SiO 2 in the Pt-loaded SiO 2 @SnO 2 microbelts yielded Pt-loaded SnO 2 hollow microbelts. • The Pt-loaded SnO 2 hollow microbelts exhibited good response (R a /R g = 93.5) and selectivity toward 2 ppm acetone at 350 °C. Challenges for ubiquitous diffusion of gas analytes into semiconducting metal oxides (SMOs) based sensing layers have necessitated the introduction of unprecedented synthesis techniques for thin, porous and high-performance gas sensing materials. In this work, electrospinning and calcination were employed to prepare unprecedented SiO 2 –SnO 2 core–shell microbelts (hereinafter referred to as SiO 2 @SnO 2 BLs) followed by etching away of SiO 2 in NaOH solution (pH 12) to achieve hollow SnO 2 BLs (hereinafter referred to as SnO 2 HBLs) with mean crystal size of 14.01 nm, large BET surface area (143.5 m2‧g–1), high porosity (mean pore size of 5.7 nm), and shell thickness of 58.3 ± 11.4 nm. Sensitization of SnO 2 HBLs with apoferritin-templated platinum nanoparticles (Pt NPs) enhanced their detection capability toward acetone. Response (defined as R a /R g , where R a and R g are sensor resistances in air and target gas, respectively) of Pt(0.12 %)_SnO 2 HBLs toward 2 ppm acetone was up to 7.8 times higher compared to that of pristine SnO 2 HBLs, and exhibited faster response (9.2 s). The Pt(0.12 %)_SnO 2 HBLs based sensor indicated a promising long-term stability, and outstanding repeatability of response (R a /R g = 93.7 ± 0.89) toward 25 cycles of 2 ppm acetone exposure in a humid environment of 90 % relative humidity. This performance could be attributed to the unique morphology of HBLs, sensitization effects of catalytic Pt NPs, and enlargement of the electron-depleted layer resulting from a Schottky barrier between Pt NPs and SnO 2 grains. [ABSTRACT FROM AUTHOR]

[Display omitted] • pDE nanocoating imparts anti-microbial, non-cytotoxic properties to the filter without filtration performance loss. • pDE-coated nanofiber filter provides superior long-term anti-bacterial and anti-viral efficacy. • pDE-coated nanofiber filter exhibits enhanced durability in highly humid conditions. We fabricated a multi-use face mask with anti-bacterial and anti-viral, but non-cytotoxic properties by adding a functional nanocoating on an electrospun nanofiber filter. The nanocoating consists of a copolymer synthesized from dimethyaminomethyl styrene (DMAMS) monomer containing anti-microbial tertiary amine moiety, and a biocompatible crosslinker, ethylene glycol dimethylacrylate (EGDMA). Initiated chemical vapor deposition process is utilized to deposit the nanocoating in order to impart desired functionalities conformally onto the nanofiber filter without deforming its highly porous structure. The synthesized non-cytotoxic copolymer of p(DMAMS-co-EGDMA), or pDE film showed excellent biocidal efficacy of > 99.995% and > 99.985% against Escherichia coli O157: H7 (E. coli O157: H7) and Staphylococcus aureus , respectively. The pDE-coated nanofiber filter shows a filtration efficiency of 91% with extremely low air resistance of ∼ 50 Pa. In highly humid conditions, the pDE-coated nanofiber filter shows long-term anti-microbial efficacy of 99.89% for E. coli O157: H7 up to 168 h, 99.21%, and 99.23% for human influenza virus (H1N1) strain A/Puerto Rico/8/1934 and human beta-coronavirus strain OC43 up to 100 h, without sacrificing breathability, and filtration performance. Furthermore, the surface-modified filter can easily eliminate dead pathogens with a simple water rinse, which enabled the full retention of the filtration efficiency even in six washing cycles, proving excellent reusability. We envision the highly breathable, antimicrobial, multi-use face mask will serve as an environmentally free platform for personal protective equipment against future viral threats. [ABSTRACT FROM AUTHOR]

Hydrous ruthenium oxide (RuO 2) has been considered a potential electrode for supercapacitors. However, RuO 2 is not easy to be hydrous, which impedes advancement in RuO 2 -based supercapacitors. Here, strontium cation (Sr2+) – with a lower oxidation state than Ru4+ – doping effects on improving the capability of RuO 2 to be hydrous are reported. The Sr2+ doping in the RuO 2 was simply possible using electrospinning and subsequent calcination, affecting hydrous properties and promoting miniaturization of nanograins in one-dimensional (1D) nanofibers. The compositions of hydrous Sr2+-doped RuO 2 (H-Sr x Ru 1−x O 2−x) nanofibers were optimized considering correlations between synthesis temperature and degree of hydration. It was found that the H-Sr 0.2 Ru 0.8 O 1.8 nanofibers synthesized at 400 °C were hydrous compared with the pristine RuO 2 and H-Sr 0.1 Ru 0.9 O 1.9 nanofibers. The H-Sr 0.2 Ru 0.8 O 1.8 nanofibers (400) could possess the smallest nanocrystallites, increasing electrochemically active surface area and satisfying specific capacitance of 612.6 A/g at a scan rate of 50 mV s–1. • A Sr2+-doped RuO 2 nanofibers were successfully fabricated by electrospinning and calcination. • Sr2+ doping enabled RuO 2 nanofibers to be hydrous and to possess miniaturized nanograins. • Sr2+ doping in RuO 2 was optimized for annealing temperature and composition. • The highly hydrous Sr 0.2 Ru 1.8 O 1.8 nanofibers boost the capacitance performance. [ABSTRACT FROM AUTHOR]

• The morph-genetic method was innovatively used to fabricate the ABH actuator. • The ABH actuator exhibits promising comprehensive performance. • The assembled biomimetic actuators show excellent synergistic performance. • The biomimetic actuator shows potential for a variety of applications. Stimuli-responsive hydrogels are most promising for the fabrication of autonomous bio-mimetic soft actuators. However, their weak actuation forces and isotropic volume change hinder their practical utilization as versatile actuators, owing to their fragility. Herein, we used the morph-genetic method to fabricate anisotropic bamboo/poly(N-isopropylacrylamide) hydrogel (ABH) complex for use as soft actuator. First of all, the bamboo fiber structure provides an anisotropic framework for the ABH actuator to achieve precise deformational programmability. Secondly, benefiting from the ultra-high directional strength (110 MPa) of bamboo, ABH actuator exhibits sufficiently robust mechanical property, which generates a powerful actuating force. Lastly, owing to the regulation of bamboo sheet and PNIPAM hydrogel, the ABH actuator not only achieves ultra-fast response speed (825°/s of the bending speed), but also has excellent synergetic performance. We demonstrate several bio-mimetic actuating devices based on ABH actuator, inspired by the intricate motions of natural organisms, to highlight how the specific materials properties and their synergy can be systematically exploited for the rational design of soft actuators. Henceforth, it is anticipated that the development of hydrogel actuators could continue to benefit from the use of various naturally-anisotropic materials, such as shape-memory polymers or liquid crystals, for the preparation of further advanced hydrogel actuators by the morph-genetic method. [ABSTRACT FROM AUTHOR]

Lightweight and ultrathin materials with superior electromagnetic interference (EMI) shielding performance are highly desirable for next-generation electronic devices. Herein, we fabricate a lightweight, thin, and flexible composite film, composed of Ti 3 C 2 T x MXene and nanoparticles of Galinstan liquid metal, by simple vacuum-assisted filtration as a promising candidate for EMI shielding. The resultant composite film with highly conductive liquid metal between the MXene nano sheets exhibits enhanced electrical conductivity (4955 S cm−1), superior EMI shielding effectiveness (66.28 dB), and an absolute shielding effectiveness (15,029 dB cm2 g−1) at a thickness of 15 μm in the X-band (8.2–12.4 GHz) frequency range that is one of the highest among those of MXenes hybrid composites. [Display omitted] • Lightweight and ultrathin EMI shielding materials were fabricated. • MXene-Galinstan liquid metal hybrid yields superior electrical conductivity. • It exhibited shielding effectiveness of 66.3 dB and an absolute shielding effectiveness of 15,029 dB cm2 g−1. • Such properties attributed to the bridging effect of liquid metal in the hybrid. [ABSTRACT FROM AUTHOR]

[Display omitted] • 2D-MOF is connected to 3D-MOF with coordination bond to form Ni-HHTP@UiO-66NH 2. • 2D-MOF@3D-MOF affords porosity, conductivity, and active interface for sensing. • Ni-HHTP@UiO-66NH 2 shows superior sensitivity and low detection limit toward H 2 S. • A plausible mechanism is proposed from the joint experimental/computational data. Research to develop ideal sensing devices for toxic gases is on the rise, and amongst various materials, metal–organic frameworks (MOFs) have opened up promising vistas as chemiresistive sensors due to their high structural and functional tunability. Here, we report the composites of dimensionally (2D and 3D) and functionally (conductive and porous) different two MOFs in the form of a well-integrated core–shell structure. The hierarchically assembled 2D-MOF@3D-MOF exhibits new interfacial properties that are responsible for synergetically enhanced sensing performances toward toxic H 2 S gas with the lowest recorded limit of detection (1.4 ppb), superior sensitivity (ΔR/R 0 = 3.37), and outstanding selectivity at room temperature in air. The sensing mechanisms are proposed by combinational studies of experiments and calculation, which indicates that multiple changes (e.g., local structural change of the shell MOF, secondary binding sites generation from the core MOF, and free radicals formation) play a critical role in achieving synergetic chemiresistive sensing. [ABSTRACT FROM AUTHOR]

The lack of bifunctional features of perovskite oxide toward the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) significantly limits its use as a cathode catalyst for rechargeable Zn–air batteries (ZABs). Thus far, numerous techniques to disperse additional catalysts on a perovskite host have been suggested to overcome this problem; however, cost-effectiveness and catalyst lifespan remain unsatisfactory. Herein, we present cobalt-based-nanoparticle-decorated Sr 0.95 Nb 0.1 Co 0.7 Fe 0.2 O 3–δ (S0.95NCF) by a simple ex-solution method and use it as a novel air-electrode catalyst. We successfully implemented the socketed nanoparticles with various compositions at different reduction temperatures, achieving notably enhanced activity towards OER and ORR. More importantly, the newly designed catalyst exhibits record-high charge/discharge durability over 500 h (or 1500 consequent cycles) when used as the ZABs cathode. Our findings provide essential guidelines for designing heterostructured electrocatalysts for future energy devices, in which multifunctionality is desirable. [Display omitted] • Ex-solution is applied to Sr 0.95 Nb 0.1 Co 0.7 Fe 0.2 O 3 –δ at various reduction temperatures. • The exsolved metals are elaborately explored depending on ex-solution conditions. • CoFe-nanoalloy ex-solution enhances electrochemical performances for OER and ORR. • The designed catalyst exhibits record-high durability for the Zinc-air batteries. [ABSTRACT FROM AUTHOR]

Antiviral and antibacterial violacein embedded porous nanofiber that can sterilize itself is proposed as an effective solution to prevent aerosol and post-contact transmission of pathogens viruses for safer personal protective equipments. [Display omitted] • Self-sterilizable nanofiber filter with naturally occurring violacein is developed. • Remarkable biocidal activities against infectious viruses and bacteria are achieved. • Viricidal efficacy for influenza and human coronavirus is studied by TCID 50 analysis. • Porous nanofiber matrix immobile pathogens and prevents aerosol transmission. • Violacein endows nanofibers with UV shielding property to help protect skin. Most respiratory masks are made of fabrics, which only capture the infectious virus carriers into the matrix. However, these contagious viruses stay active for a long duration (∼7 days) within the fabric matrix possibly inducing post-contact transmissions. Moreover, conventional masks are vulnerable to bacterial growth with prolonged exposure to exhaled breaths. Herein, we combined violacein, a naturally-occurring antimicrobial agent, with porous nanofiber membranes to develop a series of functional filters that autonomously sterilizes viruses and bacteria. The violacein-embedded membrane inactivates viruses within 4 h (99.532 % reduction for influenza and 99.999 % for human coronavirus) and bacteria within 2 h (75.5 % reduction). Besides, its nanofiber structure physically filters out the nanoscale (<0.8 μm) and micron-scale (0.8 μm − 3 μm) particulates, providing high filtration efficiencies (99.7 % and 100 % for PM 1.0 and PM 10, respectively) with long-term stability (for 25 days). In addition, violacein provides additional UV-resistant property, which protects the skin from sunlight. The violacein-embedded membrane not only proved the sterile efficacy of microbe extracted pigments for biomedical products but also provided insights to advance the personal protective equipment (PPE) to fight against contagious pathogens. [ABSTRACT FROM AUTHOR]

[Display omitted] • A simple but powerful solution to overcome the chronic bottleneck of the nanocatalyst delivery on oxide support: the carbothermal shock driven nanocatalyst formation on carbon nanofibers (CNFs) with small sizes and fine distribution can be delivered to oxide structures of choice while retaining high uniformity. • Fabrication of catalyst delivered porous oxide structures: the asymmetric sputtering of oxide on CNFs can induce the formation of openly porous hemi-tubular structures with tunable porosity and thickness. A simple subsequent calcination results in the transfer of catalysts from the CNF template to the porous oxide structures. • Superior hydrogen sulfide sensing properties: Uniform distribution of Pt nanoparticles on SnO 2 hemitubes showed superior H 2 S sensing performances (Response Rair/Rgas > 1500 at 5 ppm H 2 S) compared to state-of-the-art H 2 S sensors. To achieve powerful gas sensors oxide semiconductor chemiresistors, the uniform functionalization of nanocatalysts on the desired metal oxides is considered as a key strategy. However, still, it is challenging to achieve the nanocatalysts decoration on desired oxides without deterioration of target materials. In this study, thermal-shock (rapid joule-heating method) was applied to uniformly decorate Pt nanoparticles (NPs) on the surface of carbon nanofibers (CNFs) to achieve the uniform distribution of Pt NPs on one-dimensional structures. And then, SnO 2 was physically deposited on the Pt NPs loaded CNFs and continuous heat-treatment was conducted to transfer the Pt NPs to desired SnO 2 porous hemitubes. Thanks to the well-distributed Pt NPs on porous SnO 2 hollow structures, the Pt laoded SnO 2 hemitubes showed an exceptional sensitivity (R air /R gas = 1500 at 5 ppm) in H 2 S. Also, it showed high selectivity for H 2 S and high stability even under continuous gas exposure, confirming its potential as an effective H 2 S sensor. [ABSTRACT FROM AUTHOR]

• The non-noble metals are introduced on graphene-based fiber as a sensitizer for the high-performance chemiresistor. • Metal oxides on graphene fibers naturally are converted into metals at a relatively low temperature annealing (under 700 °C) due to catalytic effect of graphene. • The graphene fiber acts as a flexible conductive support as well as a catalyst for the deoxidation of metal oxide. • The metal/metal oxide/graphene fibers exhibited a 16 times higher response to NO 2 gas and recovery than metal oxide/graphene fiber without metal. • The proposed strategy opens a new avenue for the realization of high-performance devices, such as chemical catalysts, photoactive devices. [Display omitted] Noble metal/metal-oxide-based hybrid gas sensors exhibit a low operating temperature, remarkable sensitivity, and fast recovery. As additives, noble metals induce a catalytic sensitization effect, which promotes charge transfer from the metal oxide to the analyte molecules, the so-called spillover mechanism. This suggests that metal catalysts can improve gas sensing performance. Herein, for the first time, non-noble metals are introduced on hybrid metal oxide/graphene fibers as sensitizers to fabricate high-performance chemiresistive sensors. The formation of metal components can be effectively controlled by annealing the metal oxide on graphene. Remarkably, compared with the corresponding metal oxide/graphene fiber sensors without metal components, the metal/metal oxide/graphene fiber sensors exhibit over a 16-fold higher response to NO 2 gas as well as effective recovery characteristics. Specifically, the Cu/Cu 2 O/graphene and Ni/NiO/graphene fiber sensors operating at 150 °C exhibit sensitivities of 18.90 % and 0.82 %, respectively, for 5 ppm NO 2 gas. The proposed strategy to achieve flexible graphene fiber chemiresistors by decorating them with non-noble metal and metal oxide nanoparticles opens a new avenue for realizing high-performance devices, such as photovoltaic devices, photocatalysts, and chemical catalysts. [ABSTRACT FROM AUTHOR]

• Porosity control of nanofibers: The high porosity of the metal oxide nanofibers is the key to achieving the dual sensitization owing to their high gas permeability and numerous active sites. Both saponin and water-ethanol co-solvent play critical roles in modifying morphology of nanofibers into elliptical nanofibers during electrospinning. Additionally, saponin forms numerous pores in the nanofibers when being burnt out during calcination. These porous, elliptical nanofibers possess a larger surface area and porosity.Saponin and water-ethanol co-solvent enabled porous, elliptical nanofibers to emerge. • Bifunctional Ga doping: Ga dopants enhanced sensing performance via conductivity improvement and grain growth inhibition. • Functionalization of Pt catalysts : Spill-over effects and chemical sensitization of remarkably improved C 2 H 2 sensitivity. Herein, we demonstrate a sensitization strategy via solid-solution doping and catalytic metal nanoparticles (NPs) onto porous metal oxide nanofibers (NFs) for superior acetylene (C 2 H 2) sensing capabilities. The introduction of dopants and catalysts not only increases the inherent reactivity of metal oxides, but also induces the spillover of C 2 H 2 onto metal oxides, significantly improving the sensing properties. We elucidate that the high porosity of the metal oxide NFs, prepared by electrospinning and utilizing saponin as a sacrificial template, is the key to achieving high gas permeability and numerous active sites. Consequently, Ga-doped ZnO porous NFs functionalized with Pt catalysts exhibited the highest C 2 H 2 sensing responses among the current state-of-the-art C 2 H 2 sensors (R a /R g = 26.2 at 400 °C) with a fast response time (10.2 s), at a particularly low concentration of 5 ppm. Moreover, these NFs showed excellent selectivity against the interfering gas (H 2 , C 7 H 8 , CO, CH 4 , C 8 H 10 , CH 3 COCH 3 , HCHO and C 2 H 5 OH) and outstanding stability up to 20 sensing cycles to 0.4 ppm of C 2 H 2. These results provide an efficient strategy to tailor composites of metal oxide nanostructures, dopants, and catalysts for highly sensitive gas sensors. [ABSTRACT FROM AUTHOR]

• Synthesis of CA-CNF by insulating block electrospinning & carbonization. • Formation of cross-aligned network even after heat treatment. • Faster reaction kinetics and regular electron pathway of CA-CNF. • High-rate cyclability of CA-CNF (259.4 mAh g−1 at 3000 mA g−1). The conventional use of metallic current collector in an electrochemical cell results in decreased loading of active materials and hence limited capacity in consideration of all the inactive current collector components. In response to this trend, a number of conductive, free-standing materials have been proposed as electrodes, which would act as both current collector and active materials. Here, in this study, we have firstly developed the cross-aligned carbon nanofiber (CA-CNF) for efficient Li storage, especially at high current densities. Using the insulating block electrospinning, the nanofibers can be aligned in a certain direction, where it is viable to fabricate cross-aligned nanofibers in a cost-effective and scalable manner. Attributed to faster kinetics and regular electron pathway arising from CA-CNF, it exhibits an excellent high-rate cyclability (259.4 mAh g−1 at a current density of 3000 mA g−1). This work builds up a milestone in suggesting a cross-aligned carbon nanofibrous network as efficient Li storage, which can also be applied to various electrode materials embedded cross-aligned conductive composite materials. [Display omitted] [ABSTRACT FROM AUTHOR]