Ultralong Nanowires Research Articles

Progressively Oriented Attachment-Enabled Ultralong Single-Crystalline Upconversion Nanowires for Multidirectional Strain Sensing.

Fabricating one-dimensional (1D) single-crystalline nanostructures with the necessary characteristics for interconnects and functional units in nanodevices poses a major challenge. Traditional solution-based synthesis methods, driven by oriented attachment mechanisms, have limited the growth of either ultrathin crystalline nanowires or short rod-like nanocrystals due to stringent orientation requirements. The construction of single-crystalline ultralong nanowires with both an elongated length and moderate thickness has remained elusive. Here we introduce a growth mechanism based on progressively oriented attachment that enables the attachment of larger crystals while preserving the alignment of the crystal lattice. Using this mechanism, we achieve 1D single-crystalline lanthanide-doped nanowires (K2YF5:Yb/Er) with lengths up to 9 μm and a moderate thickness of approximately 20 nm. These nanowires can be integrated into a flexible film that exhibits stretching-dependent upconverted luminescence behavior. The mechanical toughness and elongated morphology of the nanowires facilitate the development of a wearable device dedicated to multidirectional strain sensing with high responsivity and excellent stability, withstanding repeated stretching and releasing for up to 1000 cycles.

Large‐Area Freestanding Bi2S3 Nanofibrous Membranes for Fast Photoresponse Flexible IR Imaging Photodetector (Adv. Funct. Mater. 24/2023)

Flexible IR Imaging Photodetectors In article number 2300159, Jinzhong Wang, Shiyong Gao, and co-workers, successfully prepared, a large-area freestanding Bi2S3 nanofibrous membrane (NFM) with high flexibility, which is self-assembled from ultralong Bi2S3 nanowires. The flexible photodetector based on the as-prepared Bi2S3 NFM exhibits high responsivity, fast response, excellent stability and splendent imaging capability under both flat and bent state. The as-prepared Bi2S3 NFM has great potential in flexible and wearable optoelectronic devices.

One-Step Preparation of Si-Doped Ultra-Long β-Ga2O3 Nanowires by Low-Pressure Chemical Vapor Deposition

In this work, we prepared ultra-long Si-doped β-Ga2O3 nanowires on annealed Al2O3-film/Si substrate by low-pressure chemical vapor deposition (LPCVD) assisted by Au as catalyst. The length of nanowires exceeds 300 μm and diameters range from ~30 to ~100 nm in one-dimensional structures. The nanowires show good crystal quality and exhibit (201) orientation, confirmed by transmission electron microscopy and X-ray diffraction analysis. The PL spectrum obtained from these β-Ga2O3 nanowires has three obvious blue luminescence peaks at 398 nm (3.12 eV), 440 nm (2.82 eV), and 492 nm (2.51 eV). The electrical properties obtained from Si-doped β-Ga2O3 nanowires exhibit good conductivity. A metal-semiconductor-metal device is made by using Ti/Au as the electrode, and the device current reaches 200 pA at a bias voltage of 3 V. Our results show that ultra-long Si-doped β-Ga2O3 nanowires can be grown directly on the surface of Al2O3-film/Si substrates. These nanowires have a very high length-diameter ratio and good electrical properties. A possible mechanism for Si doping is also presented.

Phase transformation of α-MnO2 to β- MnO2 induced by Cu doping: Improved electrochemical performance for next generation supercapacitor

With the advent of wearable/portable electronics and hybrid electric vehicles, supercapacitors have gained much interest owing to their high-power density. This work deals with ultralong MnO2 nanowires reinforced with different Cu contents as a new electrode material for supercapacitors fabrication. X-ray diffraction (XRD) results showed the MnO2 phase transformation from α-MnO2 to β- MnO2 induced by Cu doping. β-MnO2 due to its highest structural stability is expected to show the excellent cyclic stability of the electrode material. Field emission scanning electron microscopy (FESEM) confirmed the ultralong nanowires morphology. Ultralong nanowires with extremely interconnected network enable efficient electron transport between them, further enhancing the electrical conductivity of the material. Redox peaks present in the CV profile revealed that the preferred charge storage follows faradic mechanism, which was further confirmed by rate law. Nanosized morphology and spongy structure of the current collector exposed the maximal electrode area in conjunction with shielding from electrode pulverization.

Photoluminescence, electrical and mechanical properties of ultra-long single crystalline Al4O4C nanowires

Ultra-long single-crystalline orthorhombic Al4O4C nanowires (NWs) were synthesized via annealing a mixture of Ta, Al, and graphite powders at 1500 °C for 1 h in a flowing argon atmosphere based on the vapor-liquid-solid (VSL) mechanism. The molten Al-Ta droplets formed by adding Ta resulted in its growth along the [101] direction. Therefore, highly crystalline Al4O4C NWs possessed rough surfaces, a high aspect ratio (∼2200) with diameters ranging from 100 nm to 500 nm and lengths up to hundreds of micrometers (660 μm). They exhibited a decreased bandgap of 2.63 eV and broad emission bands in yellow/near-infrared light region under the excitation of 532 nm, which was originated by Ar doping and surficial defects. Furthermore, the single nanowire electrode devices were fabricated using the FIB-SEM technique to accurately measure the electrical and mechanical properties. Al4O4C NWs possessed the intrinsic resistivity of 202.61 Ω·m, Young's modulus of 93.89 ± 13.34 GPa, and yield strength of 4.08 ± 0.51 GPa, and therefore it is potential for nanodevice applications.

Improved photocatalytic performance of Li+/Eu3+-co-doped V2O5 ultralong nanowires

Layered-structure V2O5 has attracted extensive research attention as an ideal electrode material for lithium batteries and gas sensors, among others. In this study, we investigated the effects of Li+ and Eu3+ single- and co-doping on the electronic structure, optical properties, and pollutant-photodegradation efficiency of V2O5. All the samples were fabricated by a simple one-step hydrothermal method using NH4VO3 and phthalic acid as precursors. Pure and Eu3+-doped V2O5 developed into short, thick nanorods, while, Li+/Eu3+-co-doped V2O5 crystallized into ultralong nanowires. Furthermore, Li+ and Eu3+ doping significantly increased the ability of V2O5 to photodegrade Rhodamine B in solution. In order to elucidate the mechanism of this photochemical enhancement, the multivalence of V, charge dispersion characteristics, luminescence, and carrier lifetime were measured. The improved photocatalysis of Li+/Eu3+-co-doped V2O5 was found to be related to its increased specific surface area, multivalent V4+/5+ ions, prolonged charge lifetime, and accelerated charge dispersion. Experimental results showed that Eu3+ and Li + ions are present in the interlayers of V4O5 as pillars. Thus, co-doping represents a viable strategy to improve the photochemical properties of layered V2O5.

A Flexible Humidity Sensor with Wide Range, High Linearity, and Fast Response Based on Ultralong Na2Ti3O7 Nanowires.

A flexible humidity sensor with wide sensing range, superior sensitivity, high linearity, and advanced response/recovery capabilities is extremely desirable for practical applications in human body-related (HBR) monitoring and human-machine interaction (HMI). However, the practical sensor lacks a versatile nanomaterial integrated with sensing capabilities and mechanical flexibility to meet the criteria. Herein, a comprehensive flexible humidity sensor with ultralong Na2Ti3O7 nanowires (>120 μm) is subtly constructed for the first time. Owing to the distinguish nanowires network structure, the sensor exhibits wide sensing range (11-95% RH), high sensitivity (>103), high linearity (R2 > 0.98), and fast response/recovery capability (8.9/2.1 s), as well as excellent respiratory stability (>5000 s). In addition, the Na2Ti3O7-based humidity sensor demonstrates superior flexibility and antibacteria capabilities, and exhibits diverse applications in respiration monitoring, noncontact detection, as well as dynamic interactive display. This work provides a multifunctional humidity sensor with excellent practicability, suggesting the great potential in next-generation human-related flexible/wearable devices.

Large‐Area Freestanding Bi2S3 Nanofibrous Membranes for Fast Photoresponse Flexible IR Imaging Photodetector

AbstractFilms with excellent flexibility and mechanical stability are important for flexible and wearable devices. However, most films reported are prepared on substrates, and the synthesis of freestanding flexible films remains a challenge. Herein, a freestanding Bi2S3 nanofibrous membrane (NFM) is successfully prepared via a one‐step hydrothermal method, which is self‐assembled from ultralong Bi2S3 nanowires (NWs) over a length of millimeter‐scale crisscrossing each other. Significantly, the Bi2S3 NFM can be bent or clipped into an arbitrarily desired form. Based on the freestanding Bi2S3 NFM, an IR photodetector is fabricated, depicting a robust responsivity of 2.23 (2.06) µA W−1 under 850 (940) nm illumination. The Bi2S3 NFM photodetector exhibits a relatively fast response time (47.1 ms), which is attributed to high‐speed carrier transport efficiency in the NWs network. Under the bending states, the device still exhibits excellent detection performance, maintaining more than 86% of the initial photocurrent even after 1000 bending‐flattening times. The robust photoresponse of the Bi2S3 NFM photodetector after 2 months of storage in air and after 1 week in the bending state illustrates its excellent air stability and flexible detection ability. Besides, the photodetector can clearly identify the target image, indicating widespread potential applications in flexible and wearable fields.

Efficient reduction of Cr(VI) and elimination of total Cr with S-bridged Ni3S2/MoS2 nanowire electrode

Electrochemical reduction of Cr(VI) is eco-friendly and cost-effective for eliminating the environmental risk of Cr-contaminated water. Herein, a novel Ni3S2/MoS2 nanowire electrode with a unique stem-leaf structure was synthesized for this purpose. Self-supported ultra-long Ni3S2 nanowires bearing MoS2 nanoflakes were in-situ grown from Ni foam with a hydrothermal method, in which Ni3S2 and MoS2 grow accompanied with each other by sharing some S atoms. Consequently, highly conductive out-stretched MoS2 nanoflakes wrap the Ni3S2 nanowires, providing aligned pathways for directional electron transfer and huge networks for the efficient reduction of Cr(VI) and high uptake of generated Cr(OH)3. The highest Cr(VI) removal rate attained at − 1.2 V approaches 0.005 mg/cm2 min, and elimination efficiency of total Cr is high up to 90.81 %. Although the adsorbed Cr(OH)3 on Ni3S2/MoS2 decreases the activity after repeated runs, the electrode can be restored by a simple pickling process with dilute acid, which has promising application prospects in the electrochemical reduction of Cr-contained wastewater.

A Simple Route to Fabricate Ultralong and Uniform Polypyrrole Nanowires with High Electrochemical Capacitance for Supercapacitor Electrodes

This work demonstrated a straightforward strategy to fabricate ultralong interconnected polypyrrole (PPy-GS) nanowires with a gemini surfactant (GS) as a soft template and dopant. Pure PPy particles and a PPy nanowire doped with CTAB (PPy-CTAB) were prepared for comparison. The results showed that the electrochemical performances, conductivity, and morphology of PPy-GS could be significantly changed by changing the concentration of GS in the aqueous phase owing to the different self-assembly behaviors. When the molar ratio of pyrrole, APS, and GS was 1:1:0.4, an interconnected ultralong and uniform PPy-GS nanowire with the largest surface area, the smallest average pore size, the lowest contact angle, and the highest conductivity can be obtained, resulting in the formation of effective electrolyte transport channels and faster electron transport pathways. Compared with pure PPy particles and the PPy-CTAB nanowire, the incorporation of GS significantly enhanced the conductivity and specific capacitance of PPy-GS-40%. The conductivity of PPy-GS-40% was up to 13.54 S/cm compared with 1.17 S/cm for PPy particles and 3.84 S/cm for the PPy-CTAB nanowire. Also, the highest specific capacitance of PPy-GS reached up to 556 F/g at 1 A/g compared with 233 F/g for PPy particles and 397 F/g for the PPy-CTAB nanowire. A total of 85.4% of the initial capacitance was retained even after 2000 cycles at 1.0 A/g. The energy density and power density of the PPy-GS-40% symmetrical supercapacitor were 49.4 Wh/kg and 400 W/kg, respectively. The good electrochemical properties of the PPy-GS electrode suggest a tremendous potential in the high-performance electrode not only for supercapacitors but extensively for various energy storage applications.

Influence of Solvothermal Reaction Temperature on Hydroxyapatite Nanowires

Nowadays, nanomaterials have become the focus of many scientific researchers. As one of the mostly used biomaterials, the special structure and good performance of hydroxyapatite (HA) nanowires is a research hotspot. However, the synthesis of ultralong HA nanowires with highly efficiency and relatively low-cost is still a great challenge. In this work, HA nanowires are successfully synthesized through a simple solvothermal route, with calcium oleate and sodium hexametaphosphate as the calcium and phosphorus source, respectively. Influence of the solvothermal reaction temperature on the HA products are investigated. As the solvothermal temperature increases, the morphology of the HA crystals become nanowires and the length increases. This method is one-step and environmentally friendly without any pollution, since no organic solvent is allowed to be used in the whole experiment. The as-synthesized ultralong HA nanowires have enhanced mechanical properties and can be used in bone tissue engineering, drug delivery, adsorbents, and many other applications.

Balanced Mechanical and Biotribological Properties of Polymer Composites Reinforced by a 3D Interlocked Si3N4 Nanowire Membrane.

Polymer composites have great potential applications in the hip joint replacement, where the combinations of high mechanical strength and excellent biotribological properties are required. In this work, a well-dispersed three-dimensional (3D) silicon nitride nanowire membrane (SNm) designed as a reinforcement and brushite (Bs) served as bioactive filler are constructed into the polymer matrix, forming SNm-reinforced Bs/polymer composites (SNm-Bs/Pm). Especially, SNm could form a 3D interlocked structure, where the ultralong silicon nitride nanowires are entangled with each other. SNm could effectively facilitate the penetration of the polymer matrix and improve the cohesion strength of the polymer, thereby promoting mechanical and biotribological properties for SNm-Bs/Pm. The performances for polymer composites are optimized by increasing the layer number of preform. By comparing SNm-Bs/Pm with one-layer preform, the tensile strength of SNm-Bs/Pm with six-layer preforms reaches 83.3 MPa with an increase of 767.7%. In addition, the friction coefficient and wear rate of SNm-Bs/Pm with six-layer preforms in fetal bovine serum medium achieve 0.06 and 0.21 × 10-14 m3(N·m)-1 and decrease by 82.4 and 72.4%, respectively. The present work provides a promising methodology of preparing interlocked SNm-reinforced polymer composites with enhanced mechanical and biotribological properties that are potential for hip joint replacement applications.

Facile macro fabrication of ultra-fine, ultra-long silver nanowire and growth mechanism

Silver nanowire (AgNWs) with a fine diameter (< 20 nm) and large aspect ratio (>1000) is one of the requirements for good optoelectronic properties of a transparent conductive film. Herein we report a facile and high yield modified polyol synthesis of AgNWs with average diameters of ∼ 17 nm, aspect ratios up to 2600. And the synthesized AgNWs were applied in flexible transparent conductive films (TCF). Some crucial factors, such as illumination, solvent, and stirring impacting the diameter, and yield of AgNWs were discussed in detail. Illumination is the main factor that impact the yield of AgNWs. The probable growth mechanism of AgNWs was proposed. The sheet resistance of the AgNWs was 92 Ω/sq and the transmittance and haze were 90 % and 1.74 %, respectively.

Growing self-assisted GaAs nanowires up to 80 μm long by molecular beam epitaxy

Ultralong GaAs nanowires were grown by molecular beam epitaxy using the vapor–liquid–solid method. In this ultralong regime we show the existence of two features concerning the growth kinetic and the structural properties. Firstly, we observed a non-classical growth mode, where the axial growth rate is attenuated. Secondly, we observed structural defects at the surface of Wurtzite segments located at the bottom part of the nanowires. We explain these two phenomena as arising from a particular pathway of the group V species, specific to ultralong nanowires. Finally, the optical properties of such ultralong nanowires are studied by photoluminescence experiments.

Wet End Chemical Properties of a New Kind of Fire-Resistant Paper Pulp Based on Ultralong Hydroxyapatite Nanowires.

In 2014, a new type of the fire-resistant paper based on ultralong hydroxyapatite (HAP) nanowires was reported by the author’s research group, which had superior properties and promising applications in various fields, such as high-temperature resistance, fire retardance, heat insulation, electrical insulation, energy, environmental protection, and biomedicine. The wet end chemical properties of the fire-resistant paper pulp are very important for papermaking and mechanical performance of the paper, which play a guiding role in the practical production of the fire-resistant paper. In this paper, the wet end chemical properties of a new kind of fire-resistant paper pulp based on ultralong HAP nanowires are studied for the first time by focusing on the wet end chemical parameters, the effects of these parameters on the properties such as flocculation, retention, draining, and white water circulation of the fire-resistant paper pulp, and their effects on the properties of the as-prepared fire-resistant paper. The experimental results indicated that the wet end chemical properties of the new kind of fire-resistant paper pulp based on ultralong HAP nanowires were unique and entirely different from those of the traditional paper pulp based on plant fibers. The wet end chemical properties of the fire-resistant paper pulp were significantly influenced by the inorganic adhesive and its content, which affected the runnability of the paper machine and the properties of the as-prepared fire-resistant paper. The flocculation properties of the fire-resistant paper pulp based on ultralong HAP nanowires were affected by the conductivity and Zeta potential. The addition of the inorganic adhesive in the fire-resistant paper pulp based on ultralong HAP nanowires could significantly increase the conductivity of the fire-resistant paper pulp, reduce the particle size of paper pulp floccules, and increase the tensile strength of the fire-resistant paper. In addition, the fire-resistant paper pulp based on ultralong HAP nanowires in the presence of inorganic adhesive exhibited excellent antibacterial performance. This work will contribute to and accelerate the commercialization process and applications of the new type of the fire-resistant paper based on ultralong HAP nanowires.

UV–Vis Transparent Conductive Film Based on Cross-Linked Ag Nanowire Network: A Design for Photoelectrochemical Device

The FTO/ITO transparent conductive films currently used in photoelectrochemical devices limit performance improvement due to their low conductivity, poor flexibility, and inability to transmit UV light. Ag nanowire-based films are a very promising alternative to address these problems, and are considered to be the next generation in transparent conductive film. Here, we prepared a cross-linked nano-network composed of ultra-long Ag nanowires by a special physical template method. The obtained Ag nanowire transparent conductive film has a transmittance of over 80% in a wide range of 200 nm–900 nm, a sheet resistance as small as 5.2 Ω/sq, and can be easily transferred to various substrates without damage. These results have obvious advantages over Ag nanowire films obtained by traditional chemical methods. Considering the special requirements of photoelectrochemical devices, we have multifunctionally enhanced the film by a TiO2 layer. The heat-resistant temperature of transparent conductive film was increased from 375 °C to 485 °C, and the mechanical stability was also significantly improved. The presence of the multifunctional layer is expected to suppress the carrier recombination in self-powered photoelectrochemical devices and improve the electron diffusion in the longitudinal direction of the electrode, while serving as a seed layer to grow active materials. The high-quality Ag nanowire network and functional layer synergize to obtain a UV–Visible transparent conductive film with good light transmittance, conductivity, and stability. We believe that it can play an important role in improving the performance of photoelectrochemical devices, especially the UV devices.

Microwave-Assisted Hydrothermal Rapid Synthesis of Ultralong Hydroxyapatite Nanowires Using Adenosine 5'-Triphosphate.

Ultralong hydroxyapatite (HAP) nanowires are promising for various biomedical applications owing to their chemical similarity to the inorganic constituent of bone, high biocompatibility, good flexibility, excellent mechanical properties, etc. However, it is still challenging to control the formation of ultralong HAP nanowires because of the presence of free PO43− ions in the reaction system containing the inorganic phosphate source. In addition, it takes a long period of time (usually tens of hours) for the synthetic process of ultralong HAP nanowires. Herein, for the first time, we have developed an eco-friendly calcium oleate precursor microwave hydrothermal method using biocompatible adenosine 5′-triphosphate (ATP) as a bio-phosphorus source and water as the only solvent for the rapid synthesis of ultralong HAP nanowires. The controllable hydrolysis of ATP can avoid the premature formation of calcium phosphate nuclei and uncontrollable crystal growth. Microwave heating can significantly shorten the synthetic time from tens of hours required by the traditional heating to 1 h, thus achieving high efficiency, energy saving and low cost. The as-prepared ultralong HAP nanowires with high flexibility have lengths of several hundred micrometers and diameters of 10~20 nm, and they usually self-assemble into nanowire bundles along their longitudinal direction. The as-prepared ultralong HAP nanowire/chitosan porous scaffold has excellent bioactivity, good biodegradation and cytocompatibility owing to the bioactive adenosine adsorbed on the surface of ultralong HAP nanowires. It is expected that ultralong HAP nanowires will be promising for various applications in the biomedical fields, such as bone defect repair, skin wound healing, and as a drug nanocarrier.

Facile preparation of α-MnO2 nanowires for assembling free-standing membrane with efficient Fenton-like catalytic activity

Assembling MnO2 nanowires into macroscopic membrane is a promising engineered technology for catalyst separation and enhancement of Fenton-like reaction activity, yet its development is limited by the deficiencies in preparation and property modulation of the MnO2 nanowires. In this work, we developed a facile method using C2H5OH and CH3COOK as reductive and vital control reagents to react with KMnO4 by hydrothermal reaction at 140 °C for 12 h, to prepare the ultralong α-MnO2 nanowires up to tens of micrometers with high purity and aspect ratio. Such strategy not only had the advantages of being mild, easily controlled and environmental pollution-free, but also endowed α-MnO2 nanowires with excellent ability as a Fenton catalyst when assembled into free-standing membrane for degrading phenolic compounds (kobs = 0.0738 ∼ 0.1695 min−1) in a continuous flow reaction. The reactive oxygen species (i.e., •OH) from Fenton-like reaction were enriched within this α-MnO2 nanowire membrane via nanoconfinement effect, which further enhanced the mass transportation of •OH available for phenolic contaminants. MnO2 nanowire membrane using our method possessed the high practical potential for water purify due to its easy-preparation and enhanced catalytic performances.

Fabrication of oxygen-vacancy abundant MnO2 nanowires@ NiMnxOy-δ nanosheets core-shell heterostructure for capacity supercapacitors

Structure instability and poor electrical conductivity are two major obstacles to realizing high performance of MnO2-based pseudocapacitor material. The construction of unique hierarchical core-shell nanostructures, therefore, plays an important role in the efficient enhancement of the rate capacity and the stability of this material. Herein, a stable MnO2@NiMnxOy-δ core-shell heterostructure is prepared via a simple liquid-phase reaction combined with heat-treatment method, composed of ultrathin NiMnxOy-δ nanosheets with oxygen vacancies uniformly growing on the surface of ultralong MnO2 nanowires. Electrochemical test results show that the electrode exhibits a specific capacitance of 463.5 C g−1 at 1 A g−1 and has an excellent capacitance retention as high as 94.9% after 20,000 cycles. Compared with the MnO2@NiMnxOy nanowires, the introduction of oxygen vacancies in the ultrathin nanosheets of the MnO2@NiMnxOy-δ core-shell heterostructure can provide a large number of surface active sites to accelerate electron/ions transport during electrochemical reaction. Moreover, the interfacial behavior of the electrode reaction can be also adjusted due to the potential synergistic effect between one-dimensional nanowires and two-dimensional nanosheets, further the MnO2@NiMnxOy-δ core-shell heterostructure demonstrating the superior cyclic stability.

A perspective on ultralong silicon nanowires for flexible sensors

Flexible sensitive materials are important for the development of flexible sensors. As a dominant semiconductor, silicon is an excellent sensitive material for fabricating traditional rigid sensors. However, its applications in flexible sensors have been hindered by the rigidity and brittleness of commonly used Si wafers. In this Perspective, we focus on ultralong silicon nanowires (SiNWs), which are a kind of flexible Si materials. The synthesis of ultralong SiNWs, fabrication of SiNW fabrics, and their applications in flexible sensors are discussed. We also point out some challenges and future directions in this field.