Well-aligned Nanostructures Research Articles

Large-Scale, Proteinaceous Nanotube Arrays with Programmable Hydrophobicity, Oleophilicity, and Gas Permeability

Nanotubular structures possess remarkable advantages in a broad range of areas, such as catalysis, sensing, microencapsulation, selective mass transport, filtration, and drug delivery. While the fields of carbon nanotubes and nanotubes made of several noncarbon materials (e.g., metals, oxides, semiconductors) have been progressing rapidly, proteinaceous nanotubes remained largely underexplored. Here, by retrofitting a template wetting approach with multiple silk-based suspensions, we present a rapidly scalable and robust technology for fabricating large arrays (e.g., 20 × 20 cm2) of well-aligned 1D nanostructures made of silk proteins. Benefiting from the polymorphic nature of silk, precise control over the size, density, aspect ratio, and morphology (tubes versus pillars) of silk nanostructures is achieved, which then allows for programmable modulation of the end materials' functions and properties (e.g., hydrophobicity, oleophilicity, and gas permeability). The silk nanotube arrays fabricated present great utility as antifouling coatings against marine algae and in oil extraction from oil-water mixtures.

Moving toward Smart Hybrid Vertical Carbon/MoS2 Binder-Free Electrodes for High-Performing Sodium-Ion Batteries

Finding potential electrodes with smart construction and design is one of the major tasks in the development of advanced sodium-ion batteries (SIBs) and in bridging the gap by bringing them to realization. In this work, we report on the design of such a binder-free composite anode realized by combining vertical carbon nanotube/molybdenum sulfide (VCNT/MoS2) hybrid nanostructures. The well-aligned vertical nanostructures in the binder-free VCNT/MoS2 hybrid composite electrode enhance the electrolyte penetration into the electrode and shorten the ion diffusion channels. Moreover, the VCNT provides better ion/electron conductivity for the electrode. Due to these favorable characteristics, binder-free VCNT/MoS2 hybrid composite electrodes exhibit superior electrochemical properties when employed as an anode for SIBs, especially superior rate capability with a specific discharge capacity of 403 mA h g–1 at a high current density of 3200 mA g–1. The findings are expected to lead us in the direction of designing smart electrodes with hybrid nanostructured active materials, completely free of any binder for high-performing electrochemical energy storage applications.

Improved performance of flexible supercapacitor using naphthalene sulfonic acid‐doped polyaniline/sulfur‐doped reduced graphene oxide nanocomposites

In this study, we followed a facile method to grow well-aligned PANI nanostructures on S-doped reduced graphene oxide nanosheets (SPANI/S-rGO) using hydrothermal method combined with soft template polymerization of aniline where naphthalene sulfonic acid is used as a dopant for PANI as well as the soft template. The effect of using different wt% of S-rGO on the structural, morphology, and electrochemical performance of SPANI/S-rGO composites has been evaluated. Supercapacitor fabricated using SPANI/S-rGO10 (10 wt% of S-rGO) composite based electrodes delivered a high specific capacitance of 347.5 F/g at a current density of 1 A/g in symmetrical cell design (the specific capacitance was calculated based on a single electrode). Only 11% of its initial capacitance is lost after 2500 cycles at a current density of 2 A/g. The enhanced performance is attributed to the optimum loading of S-rGO in designing binary composite, well-aligned growth of SPANI nanostructures on S-rGO sheets, and synergistic effect of both S-rGO and SPANI. The facile synthesized SPANI/S-rGO composite electrode material with the aforementioned features is considered to be a promising candidate for a high-performance supercapacitor.

Enhancing ionic conductivity in tablet–bottlebrush block copolymer electrolytes with well-aligned nanostructures via solvent vapor annealing

Solvent vapor annealing was employed to obtain tablet–bottlebrush block copolymer electrolytes (BCPEs) with well-aligned lamellar nanostructures stable at high temperatures above 200 °C. The alignment greatly enhances the ionic conductivity of the BCPE, with value reaching 2.19 mS cm−1 at 200 °C.

Cobalt monosulfide nanofibers: ethanol sensing and magnetic properties

Metal sulfide nanomaterials have attracted great interest because of their excellent properties and promising applications in sensing, energy harvesting, magnetic and optoelectronic devices, especially their well-aligned crystalline nanostructures are highly desirable for the enhanced performance and novel applications. In this study, the cobalt monosulfide (CoS) nanofibers with uniform shape and good crystallinity were firstly obtained via electrospinning and atmospheric calcination routes under controllable conditions. It was found that the CoS nanofibers exhibited ethanol sensing properties at the optimum working temperature of 200 °C, the response was 11.6 toward 100 × 10−6 ethanol gas, and the CoS nanofibers-based sensor exhibits a short response time and recovery time of 5 and 6 s at the optimum temperature, respectively, the result also shows that the sensor has good stability after 50 days, which would be a favorable characteristic as a promising sensor. In addition, the Pauli paramagnetic property of CoS nanofibers was also investigated at room temperature.

Well-aligned periodic germanium nanoisland arrays with large areas and improved field emission performance induced by femtosecond laser

Si-based field emitters with high and stable current densities have gained increasing attention owing to their relevant compatibility with other silicon-based microelectronic and photonic devices. Currently, well-aligned Ge nanostructure arrays can be used in fabrication of Si-based field emitters with excellent performance. In this study, large-area well-aligned Ge nanoisland arrays are induced by femtosecond laser (120 fs, 800 nm, 1 kHz). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), atomic force microscopy (AFM), Raman analyses, and X-ray photoelectron spectroscopy (XPS) reveal that well-aligned Ge nanoisland arrays with good quality. Field emission (FE) measurements indicate Ge nanoisland arrays with high emission current densities and good stability. Overall, the excellent FE properties of the proposed Ge nanoisland arrays will make them potential for applications in high-performance field emitters integrated with Si nanodevices.

Scalable Direct Writing of Lanthanide-Doped KMnF3 Perovskite Nanowires into Aligned Arrays with Polarized Up-Conversion Emission.

The use of one-dimensional nano- and microstructured semiconductor and lanthanide materials is attractive for polarized-light-emission studies. Up-conversion emission from single-nanorod or anisotropic nanoparticles with a degree of polarization has also been discussed. However, microscale arrays of nanoparticles, especially well-aligned one-dimensional nanostructures as well as their up-conversion polarization characterization, have not been investigated yet. Herein, we present a novel and facile paradigm for preparing highly aligned arrays of lanthanide-doped KMnF3 (KMnF3:Ln) perovskite nanowires, which are good candidates for polarized up-conversion emission studies. These perovskite nanowires, with a width of 10 nm and length of a few micrometers, are formed through the oriented attachment of KMnF3:Ln nanocubes along the [001] direction. By the employment of KMnF3:Ln nanowire gel as nanoink, a direct-writing method is developed to obtain diverse types of aligned patterns from the nanoscale to the wafer scale. Up-conversion emissions from the highly aligned nanowire arrays are polarized along the array direction with a polarization degree up to 60%. Taking advantage of microscopic nanowire arrays, these polarized up-conversion emissions should offer potential applications in light or information transportation.

Pr3+ doped biphasic TiO2 (rutile-brookite) nanorod arrays grown on activated carbon fibers: Hydrothermal synthesis and photocatalytic properties

Praseodymium-doped biphasic TiO2 (rutile-brookite) nanorod arrays (Pr-TiO2 NRAs) were successfully prepared via a two-step hydrothermal reaction on activated carbon fibers (ACFs) which pre-coated with TiO2 nanoparticles at first step. The bicrystalline arrays grown on ACFs are primarily constructed by the well-aligned TiO2 nanorods growing along [0 0 1] direction, which were indicated by the results of SEM and XRD. The nanorods are uniform in diameter and length with about 250 nm and 2.5 μm. The composite photocatalyst with high specific surface area and well-aligned nanostructure are beneficial to enhance the adsorption capacity and even help to suppress electron-hole recombination effectively, which consequently revealed much better (2 times) catalytic performance than that of commercially available P25 TiO2 on methylene blue(MB) photodegradation. In addition, the existence of praseodymium in TiO2 gives rise to shift of absorption edge towards long wavelength, which was indicated by the results of UV-vis DRS. Photodegradation results reveal that Pr-doping significantly improves the activity of TiO2, which was 20% higher than that of undoped TiO2 NRAs for the photodegradation of MB in aqueous medium under visible light irradiation. Meanwhile, the doped amount of Pr had a tiny influence on the photocatalytic performance of the composites. In our experiment, 3% Pr-doped molar concentration was proven to be the relatively optimal dopant concentration for the doping of TiO2 NRAs. Moreover, the photocatalyst grown on ACFs substrates is favorable to reuse and photodegradation rate kept on 76% even after 4 times of reuse.

Analysis of arrayed nanocapacitor formed on nanorods by flow-rate interruption atomic layer deposition

Flow-rate interruption (FRI) atomic layer deposition (ALD) technique was adopted to fabricate AZO/Al2O3/AZO thin film on a ZnO nanorod array template at low temperature. The high quality amorphous dielectric Al2O3 layer was deposited at 50°C. The template with an average of 0.73μm in length was made by a simple hydrothermal method on a c−plane sapphire with an AZO seed layer. Using Polystyrene (PS) microspheres were served as a mask to form vertical and well-aligned ZnO nanostructures. Field-emission scanning electron microscope (FESEM) and transmission electron microscope (TEM) images show ALD to have achieved good step coverage and thickness control in the thin films structure coating. The capacitance density of the arrayed template nanocapacitor increased more than 100% than those of the thin film capacitor at an applied frequency of 10 kHz. These results suggest that the ZnO-arrayed template could enhance energy storage capability by providing significant surface area. This structure provides a concept for high surface-area nanocapacitor applications.

Synthesis of porous SnO2 hexagon nanosheets loaded with Au nanoparticles for high performance gas sensors

Two-dimensional (2D) porous nanostructures with more active areas and less agglomeration represent an alternative option for new generation of gas sensors. In addition, surface functionalization with noble metals is considered as an effective strategy to improve gas sensing properties of metal oxide-based gas sensors. In this work, a novel gas sensing material was synthesized by decorating Au nanoparticles (Au NPs) on very low thickness SnO2 nanosheets (SnO2 NSs) with side length of 100–300nm. Furthermore, the nanosheets are porous with pore diameter of 5–10nm and a high specific surface area (64.2 m2g−1). Due to the well-aligned 2D nanostructures and the incorporation of the interface between Au nanoparticles and SnO2 nanosheets, the gas sensors based on Au-SnO2 nanocomposites show excellent sensitivity and selectivity to ethanol at the operating temperature of 160°C, giving a response of about 70.2–100ppm ethanol, which was about 3 times higher than that of the sensor based on pure SnO2.

Low-temperature hydrothermally grown 100 μm vertically well-aligned ultralong and ultradense ZnO nanorod arrays with improved PL property

The hydrothermal synthesis of ZnO nanorods (NRs) has been investigated using ammonium hydroxide and polyethyleneimine as additives to the conventional nitrate based synthesis route, to obtain thin-films of well-aligned, ultradense and ultralong nanostructures. ZnO NRs longer than 60 μm were obtained in a one-cycle growth run and rod lengths ∼100 μm by a two-cycle growth. The lengths of the rods were distributed uniformly across the substrate in all samples and highly dense NR arrays were observed. These conditions were obtained by a careful review of the nucleation and growth kinetics for this material system, such that the supersaturation of the solution was only relieved by precipitation on and in the presence of crystalline ZnO, and by the exploitation of a second growth phase due to the chelating behave of PEI and the products of HMTA. Also, the growth behavior was correlated to the solution pH values. The structural and optical data were found to be supportive of the growth conditions. The photoluminescence (PL) spectra from as-grown ultralong ZnO NRs exhibited a strong broad (520–800 nm) visible emission peak. However, annealing in a forming gas atmosphere at 350 °C revealed a PL spectrum with a significantly decreased visible emission and an increased near band gap UV emission at 379 nm. Thus, the mechanisms associated with ammonium hydroxide and PEI addition provide a simple route for synthesizing ultralong and dense arrays of ZnO NRs at low temperature i.e. 95 °C.

Transparent and flexible films of horizontally aligned carbon nanotube/polyimide composites with highly anisotropic mechanical, thermal, and electrical properties

Flexible anisotropic films manufactured from one-dimensional aligned nanomaterials can be potentially used in electronic skin and thermal interface applications due to their anisotropic properties. However, high anisotropy also makes the fabrication of aligned polymeric composites with a highly ordered structure and good interface properties very problematic. In this work, transparent, flexible, and robust anisotropic films containing aniline-grafted horizontally aligned carbon nanotube (G−HACNT)/polyimide (PI) composites have been synthesized. The obtained uniform G−HACNT/PI composite films are characterized by a variety of excellent anisotropic properties. Thus, the film electrical (σ) and thermal (κ) conductivities in the longitudinal direction are one order of magnitude higher than the corresponding values measured in the transverse direction (σ//:σ⊥ = 15.3, κ///κ⊥ = 10.1). Furthermore, the tensile strength in the longitudinal direction exceeds that in the transverse direction by 52.9%. The high anisotropy of the flexible films (observed even at 200 °C) with extremely low contents of G−HACNTs (less than 0.1 wt%) originates from the well-aligned nanostructures and preferentially oriented crystalline PI chains. Hence, the flexible and robust G−HACNT/PI composite films with uniformly aligned structures pave the way for fabricating in-plane anisotropic polymeric nanocomposites by controlling interactions between the nanotube and PI components.

A facile one-pot synthesis of N-La codoped TiO2 porous materials with bio-hierarchical architectures and enhanced photocatalytic activity

Bio-hierarchical TiO2-based porous structures (denoted as morph-TiO2) with N and La co-doping (denoted as N-La-morph-TiO2) are successfully synthesized via a facile one-pot reaction by using butterfly wings as bio-template and surfactant as co-template. Due to the novel dual-template strategy, the well-aligned 3D bio-hierarchical porous structures in combination with N-La codoping not only modify the band structure of TiO2 to make it more responsive to visible light, but also increase the surface area and lead TiO2 to have enhanced photocatalytic activity for methyl orange (MO) degradation under UV and/or visible light illumination as compared with P25 TiO2 and pristine TiO2. The optimized N-La-morph-TiO2 nanostructures present a narrow pore size distribution with an average pore diameter of 8.7 nm and a high specific surface area (196 m2 g−1), which is nearly four times that of P25 TiO2. The enhanced photocatalytic activity is attributed to the combination of the doped inorganic elements, the fine hierarchical and well-aligned porous nanostructures as analyzed by SEM, TEM, XPS, BET, UV–vis absorption and photodegradation tests. The promotional mechanisms and principles reported in this work are believed to have great significance in heterogeneous photocatalysis.

Macroscopic Alignment of One-Dimensional Conjugated Polymer Nanocrystallites for High-Mobility Organic Field-Effect Transistors.

Controlling the morphology of polymer semiconductors remains a fundamental challenge that hinders their widespread applications in electronic and optoelectronic devices and commercial feasibility. Although conjugated polymer nanowires (NWs) are envisioned to afford high charge-carrier mobility, the alignment of preformed conjugated polymer NWs has not been reported. Here, we demonstrate an extremely simple and effective strategy to generate well-aligned arrays of one-dimensional (1D) polymer semiconductors that exhibit remarkable enhancement in charge transport using a solution shear-coating technique. We show that solution shear coating of poly(alkylthiophene) NWs induces extension or coplanarization of the polymer backbone and highly aligned network films, which results in enhanced intra- and intermolecular ordering and reduced grain boundaries. Consequently, highly aligned poly(3-hexylthiophene) NWs exhibited over 33-fold enhancement in the average carrier mobility, with the highest mobility of 0.32 cm(2) V(-1) s(-1) compared to pristine films. The presented platform is a promising strategy and general approach for achieving well-aligned 1D nanostructures of polymer semiconductors and could enable the next generation of high-performance flexible electronic devices for a wide range of applications.

Preparation of ZnO Nanorod/Graphene/ZnO Nanorod Epitaxial Double Heterostructure for Piezoelectrical Nanogenerator by Using Preheating Hydrothermal

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we describe a one-step fabrication technique to synthesis freestanding ZnO nanorod/graphene/ZnO nanorod double heterostructure. The preparation of the double heterostructure is performed by using thermal chemical vapor deposition (CVD) and preheating hydrothermal technique. In addition, the morphological properties were characterized by using the scanning electron microscopy (SEM). The utility of freestanding double heterostructure is demonstrated by fabricating the piezoelectric nanogenerator. The electrical output is improved up to 200% compared to that of a single heterostructure owing to the coupling effect of the piezoelectricity between the arrays of ZnO nanorods on the top and bottom of graphene. This unique double heterostructure have a tremendous potential for applications of electrical and optoelectrical devices where the high number density and specific surface area of nanorod are needed, such as pressure sensor, immuno-biosensor and dye-sensitized solar cells.

Preparation of ZnO Nanorod/Graphene/ZnO Nanorod Epitaxial Double Heterostructure for Piezoelectrical Nanogenerator by Using Preheating Hydrothermal.

Well-aligned ZnO nanostructures have been intensively studied over the last decade for remarkable physical properties and enormous applications. Here, we describe a one-step fabrication technique to synthesis freestanding ZnO nanorod/graphene/ZnO nanorod double heterostructure. The preparation of the double heterostructure is performed by using thermal chemical vapor deposition (CVD) and preheating hydrothermal technique. In addition, the morphological properties were characterized by using the scanning electron microscopy (SEM). The utility of freestanding double heterostructure is demonstrated by fabricating the piezoelectric nanogenerator. The electrical output is improved up to 200% compared to that of a single heterostructure owing to the coupling effect of the piezoelectricity between the arrays of ZnO nanorods on the top and bottom of graphene. This unique double heterostructure have a tremendous potential for applications of electrical and optoelectrical devices where the high number density and specific surface area of nanorod are needed, such as pressure sensor, immuno-biosensor and dye-sensitized solar cells.

Enhanced Photocatalytic Activity of TiO2 Nanorod Arrays Decorated with CdSe Using an Upconversion TiO2:Yb3+,Er3+ Thin Film

A new composite photocatalyst CdSe-sensitized TiO2 nanorod array (CdSe/TiO2 NRA) grown on fluorine-doped tin oxide (FTO) coated with a TiO2:Yb3+,Er3+ thin film was constructed. The TiO2:Yb3+,Er3+ thin film acted as a medium for converting near-IR light to visible light via an upconversion process and reduced electron–hole recombination. TiO2 NRAs with high specific surface areas and well-aligned nanostructures can provide a fast transfer pathway for photogenerated electrons. The CdSe/TiO2 NRAs extended the optical response from the ultraviolet to visible region, which can generate more electron–hole pairs. The composite photocatalyst TiO2 NRAs/TiO2:Yb3+,Er3+ exhibited excellent photocatalytic activity toward the degradation of Rhodamine B. The composite structure can not only extend the absorption of TiO2 but also consequently reduce electron–hole recombination, which improve the photocatalytic efficiency of the composite photocatalyst. Moreover, the photocatalyst grown on FTO substrates directly makes it...

Nanoconfined nonequilibrium electrodeposition of metal-metal hydroxide one-dimensional nanostructures

In this paper, we present a new insight into nonequilibrium electrodeposition. Owing to the nanoscale confinement effect of the template channels, the large overpotential leads to a highly nonequilibrium process and generates segmented metal-metal hydroxide one-dimensional (1D) nanostructures. The synthesized Ni-Ni(OH)x≈2 nanotubes vividly reflect the evolution of the local electrochemical environments, by which both the morphology and the composition have been modulated. The electrochemical mechanisms responsible for this unexpected deposition have been identified and discussed. It was exploited to obtain bi-segmented Ni nanowire-Ni(OH)x≈2 nanotube. This work opens the way to a versatile synthesis of metal-metal hydroxide 1D nanostructures that could be applicable for the integration of well-aligned metal-hydroxide nanostructures into large-scale energy-storage devices.

Optical properties of well-aligned ZnO nanostructure arrays synthesized by an electric field-assisted aqueous solution method

A simple electric field-assisted aqueous solution (EFAS) technique was successfully developed to prepare 1D ZnO nanostructures with different morphologies. Changing the current density between the substrate and the Pt wire as the anode can efficiently control the morphologies of the nanostructures. The structural and optical properties of the ZnO nanostructures including nanorods and nanocones were investigated by photoluminescence and Raman spectroscopy. Raman spectrum measurements confirmed that the ZnO nanorod arrays were vertically aligned and highly c-axis oriented, with the sample treated at 0.05mA demonstrating the best crystallization among all samples. The optical quality of the as-grown ZnO nanocones improved after thermal annealing at 500°C because of the released functional group elements and decreased deep-level defects. These findings indicate the potential of the EFAS method to grow high-quality ZnO nanostructures for field-emission and optical applications.

Fabrication of obliquely-aligned single crystalline diamond nanostructures and their arrays

The polycrystalline diamond film on silicon substrates is used as a starting material to fabricate three different single crystalline nanostructures by employing the bias-assisted reactive ion etching technique in hydrogen plasma. The gold layer was sputtered on the top of the films as an etching mask to produce the high-density arrays of nanocones, nanopillars and nanofibers. The well-aligned nanostructures are uniformly distributed over large surface areas, and have a tilted angle of 60° to the substrate. Meanwhile, Raman measurement confirms that no stress is introduced into the nanostructures during the etching process. The nanostructures with the unique morphologies have potential applications in various diamond-based devices.