Well-aligned Nanorods Research Articles

Memristive gas sensor (gasistor) based on Ag/ordered TiO2 nanorods/FTO sandwich structure for evaluation of ethanol concentration in mixed ambient

Herein, we designed a memoristor-type gas sensor (gasistor) with Ag/ordered TiO2 nanorods/FTO sandwich structure for recognizing ethanol concentration in ethanol-methanol mixtures. The gas adsorption characteristics of different TiO2 substrates were first investigated by first-principle calculations. The results showed that the TiO2 surface in the low resistance state exhibited better immunity to other interfering gas molecules. However, similar adsorption energies and charge transfers calculated for adsorption of methanol and ethanol mean that the interference of methanol to the response of ethanol cannot be completely ignored. In next experiments, the Ag/TiO2/FTO gasistor with well-aligned TiO2 nanorods as the resistive layer was constructed successfully and demonstrated the stable resistive switching function and excellent retention characteristic. Further device tests confirm the ability of the gasistor in the low resistance state to discriminate between ethanol and methanol, as well as better anti-interference for other organic vapors. Also, an ultra-short recovery time (∼1.8 s) was observed by applying a direct current scanning voltage to the gasistor. Finally, to improve the recognition rate of ethanol in ethanol-methanol mixed atmosphere, a neural network algorithm based on back-propagation was incorporated and good prediction accuracy was obtained at ethanol concentrations ≥ 5 ppm.

A 3D hierarchical TiO2/CaIn2S4/C3N4 arrays photoanode with dual-heterojunction for enhanced photoelectrochemical performance

A novel 3D hierarchical TiO2/CaIn2S4/C3N4 arrays with dual heterojunctions photoanode is constructed by stepwise deposition of CaIn2S4 nanosheets and ultrathin C3N4 onto the well-aligned TiO2 nanorods arrays. Integrating the merit of the superior ability of CaIn2S4 and C3N4 to harvest visible light, dual type-Ⅱ heterojunction band structure and one-dimensional ordered nanostructures, the TiO2/CaIn2S4/C3N4 photoanode exhibits simultaneous significant improvements in visible-light harvesting, charge separation and electron transfer capability. At 1.23 V (versus reversible hydrogen electrode) under AM 1.5 G irradiation, the TiO2/CaIn2S475/C3N4 photoanode exhibits a photocurrent density of 4.5 mA cm−2, which is 5.2 and 51.1-fold higher than that of TiO2/CaIn2S475 and pristine TiO2 photoanode, respectively. Moreover, the applied bias photo-to-current efficiency (ABPE) of the TiO2/CaIn2S475/C3N4 photoanode reaches 3.5% at 0.36 V (versus reversible hydrogen electrode). These results are helpful for fabricating more efficient heterostructure photoelectrodes.

The facile synthesis of 3D hierarchical flower-like TiO2 microspheres with enhanced photocatalytic activity

A 3D hierarchical flower-like rutile TiO2 microspheres assembled by well-aligned 1D nanorods were efficiently synthesized using the solvothermal method at a temperature of 140 °C for 5 h. The synthesized TiO2 microspheres have an average crystallite size of about 6.9–8.4 nm. According to SEM, FESEM and TEM analysis, flower-like TiO2 microspheres are made up of nanorods that grow radially from the center and are several nm thick on average. The XRD, EDS and XPS analysis revealed that titanium and oxygen peaks were present with no other impurity peaks. The volume ratio of water and toluene plays a vital role that was significantly affecting the chemical properties of synthesized TiO2 materials. Compared to other samples, the hierarchical 3D TiO2 microspheres Ti(1:1) had a small crystallite size, a lower bandgap, a comparatively large BET surface area of about 130 m2/g and a pore volume of 0.179 cm3/g, which revealed more favorable for photocatalytic activity. Ti(1:1) photocatalyst degraded MO by almost 96 and 94% within 50 and 40 min, respectively, when exposed to mercury light and sunlight. Also, it showed that within 60 min of mercury light irradiation, RhB degraded up to 65%. Additionally, an LC-MS study was performed for the degradation of MO dye solution and a possible degradation path was proposed.

Growth of highly aligned ZnO nanorod arrays on zinc plates: Morphological and structural characterization

In this work, uniform and highly aligned ZnO nanorod arrays were simply synthesized on zinc plates by hydrothermal method using zinc–ammonia complex solution. Effects of ZnO seed layer formation, Zn(NO3)2 concentration and NH3/Zn(NO3)2 mole ratio (R) in the reaction medium on the morphology and crystal structure of nanorods were investigated in detail. ZnO nanorods grown on zinc surfaces were highly crystalline and had a hexagonal wurtzite structure, as revealed by XRD analysis. In addition, the dominant crystal growth direction was in c-axis, indicating the verticality of the nanorods. SEM images showed that one-dimensional (1D) ZnO nanorods with high verticality and number density were synthesized on seeded plates whereas randomly oriented arrays were grown on non-seeded surfaces. Increase in the Zn2+ concentration changed the top ends of the rods from tapering to hexagonal ends; and also led to an increase in the average size and verticality of the nanorods. The increase in R value (or i.e., amount of NH3) caused the rods to misalign on the surface and decrease in size. The size of well-aligned nanorods can be adjusted from 50 to 260 nm in diameter and 0.11 to 6 m in length by changing the reaction parameters, implying their large potential to be used in photocatalytic and also in electronic applications.

An ordered conductive Ni-CAT nanorods array as all-round polysulfide regulator for lithium-sulfur batteries

The effective suppression of polysulfide shuttle is indispensable for the commercialization of lithium-sulfur batteries (LSBs). In this work, an ordered conductive metal-organic framework (MOF) Ni-CAT nanorods array rooted on carbon nanotube film (Ni-CAT/CNTF) is proposed for this subject. The well-aligned MOF nanorods array possesses a unique vertical structure, presenting an incompact upper part and dense root, which guarantee the highly efficient adsorption and selective sieving towards polysulfides, respectively, as well as a fast Li+ transfer. What's more, the good electrical property and fully exposed Ni-based catalytic sites are qualified to boost the electrochemical kinetics. Consequently, LSBs with this fully functional MOF nanorods array exhibit an astonishing capacity of 1087 mAh g−1 and an extraordinary cyclability with a finite capacity-fading of only 0.026% per cycle for 1000 cycles at 1 C, along with an exceptional rate performance of 754 mAh g−1 at 5 C. Moreover, outstanding cycle and rate performance can be maintained under elevated sulfur loadings with a reduced electrolyte content. This work offers new insights into the rational design of polyfunctional nanostructures in LSBs.

PH Controlled Nanostructure and Optical Properties of ZnO and Al-Doped ZnO Nanorod Arrays Grown by Microwave-Assisted Hydrothermal Method.

The low-temperature microwave-assisted hydrothermal method was used to successfully grow pure and Al-doped ZnO (AZO) nanorod (NR) arrays on glass substrates. The combined effects of doping and pH on the structural properties, surface chemistry, and optical properties of all samples were investigated. Thermodynamic-based simulations of the growth solution were performed and a growth mechanism, that considers the effects of both the pH and Al-doping, is proposed, and discussed. Tuning the solution pH is key parameter to grow well-aligned, single crystal, highly packed, and high aspect ratio nanorod arrays. Moreover, the optical absorption in the visible range is enhanced by controlling the pH value. The PL spectra reveal a shift of the main radiative emission from the band-to-band into a transition involving deep defect levels of Zinc interstitial Zni. This shift is caused by an enhancement of the non-radiative components (phonon relaxation) at high pH values. The production of well-ordered ZnO and AZO nanorod arrays with visible-active absorption/emission centers would increase their potential use in various applications.

Enhanced sensitivity of low-cost fabricated fluorine doped ZnO metal semiconductor metal photodetector

The literature mostly reports on thin-film fluorine-doped zinc oxide (FZnO) and has yet to fabricate metal semiconductor metal (MSM) photodetectors (PDs) based on FZnO nanostructures for the enhancement of photoresponse parameters despite their huge potential. In this work, ZnO film of 32 nm-thick was deposited and used as a seed layer on silicon (Si) substrates with the aid of the radio frequency (RF) magnetron sputtering method. Vertically well-aligned FZnO nanorods (NRs) were later grown on the seeded substrates via a hydrothermal method and annealed for 1 h at 400 °C. The formation of well-aligned hexagonal NRs at low fluorine doping was revealed by field emission scanning microscopy (FESEM), and energy-dispersive X-ray (EDX) analysis confirmed the presence of fluorine doping. X-ray diffraction (XRD) investigation confirmed the growth of good crystal quality hexagonal wurtzite F–ZnO NRs along the (002) direction, and bandgaps were estimated using UV–Vis–NIR spectroscopy. Photoluminescence (PL) measurement has revealed the main emission peak for ultraviolet (UV) is centered at 375 nm and a red-shifted emission with fluorine doping has been identified. An F2 UV MSM PD device is fabricated. Upon exposure to UV light (395 nm) at 4 V, it displayed a high sensitivity of 1.1 × 105%, responsivity of 0.66 A/W, detectivity of 1.30 × 1010 Jones, a response time of 90 ms, and recovery time of 110 ms.

Electrodeposition of vertically aligned Sb2Se3 nanorods array for photocatalytic reduction of methylene blue

Sb2Se3, as a new class of functional materials, has recently emerged for solar energy conversion owing to its low cost and high activity. In this paper, a facile electrodeposition method allows uniform formation of vertically aligned Sb2Se3 nanorods arrays. The physical and chemical properties of Sb2Se3 films can be modulated by varying the used substrates. A more uniform nanorod-shaped Sb2Se3(Se) film is developed on the Se-coated Ni substrate with better crystallinity, improved light absorption ability, suitable band structure, efficient photogenerated carriers transport. Additionally, the Sb2Se3(Se) film exhibits the better photocatalytic activity, and degrades 74.7% methylene blue (MB) after irradiation for 60 ​min, as compared to the Sb2Se3(Ni) film. The research provides an effective approach for synthesizing well-aligned Sb2Se3 nanorods arrays, and reveals a new direction for designing high-efficiency photocatalysis.

Aligned TiO2 nanorod arrays decorated with closely interconnected Au/Ag nanoparticles: Near-infrared SERS active sensor for monitoring of antibiotic molecules in water

Near-infrared (NIR) excited surface-enhanced Raman scattering (SERS) spectroscopy is expected to have more appealing multiple-features than that of traditional ultraviolet (UV) or visible light excitation. Herein, we demonstrate an interesting and highly active hybrid semiconductor-based NIR-SERS sensor via well-aligned TiO2 nanorod arrays (NRAs) decorated with bimetallic Au/Ag nanoparticles (NPs). The obtained Au/Ag NPs-TiO2 NRAs with a stronger absorption capacity in 400–1300 nm region exhibit a remarkable higher NIR-SERS activity than that of monometallic Au or Ag loaded on TiO2 NRAs. Then, the established NIR-SERS sensor can provide ultrasensitive 785 nm laser excited-SERS detection of antibiotic ciprofloxacin and chloramphenicol in real-world water samples with detection limits as low as 10–9 M and 10–8 M, respectively. Interestingly, superior to the present bare metallic nanosubstrates, the Au/Ag NPs-TiO2 NRAs with unique heterostructures can also be served as reusable NIR-SERS sensor due to its excellent photocatalytic degradation ability, and ~84.2% residual SERS activity can be maintained after 5 recycling tests. Therefore, it is believed that the established multifunctional NIR-SERS sensor holds greater potential for ultrasensitive monitoring of diverse biomolecules in many specific applications.

Structural and morphological tuning of Cu-based metal oxide nanoparticles by a facile chemical method and highly electrochemical sensing of sulphite

A facile one-step chemical method is introduced for the successful synthesis of Cu2O, CuO and CuNa2(OH)4 crystal structures and their electrochemical properties were also investigated. X-ray diffraction studies revealed that these copper-based oxide nanoparticles display different crystal structures such as cubic (Cu2O), monoclinic (CuO) and orthorhombic [CuNa2(OH)4]. The microstructural information of nanoparticles was investigated by transmission electron microscopy. It shows attractive morphologies of different orientation such as rod like structure, nanobeads and well-aligned uniform nanorod for Cu2O, CuO and CuNa2(OH)4, respectively. Electrochemical sensing of sulphite (SO32−) on these three copper-based oxide modified electrodes was investigated. Among the three different crystal structures, CuO shows promising electrocatalytic activity towards oxidation of sulphite. A linear variation in peak current was obtained for SO32− oxidation from 0.2 to 15 mM under the optimum experimental condition. The sensitivity and detection limit were in the order of 48.5 µA cm−2 mM−1 and 1.8 µM, respectively. Finally, practical utility of CuO modified electrode was demonstrated for the estimation of sulphite in commercial wine samples.

Synthesis of 2D and 3D hierarchical β-FeOOH nanoparticles consisted of ultrathin nanowires for efficient hexavalent chromium removal

The self-assembly of 1-dimensional nanorods into free-standing multi-dimensional (2D and 3D) nanostructures is a considerable challenge. Here, 2D β-FeOOH nanobundles (NBs) and 3D spiky particles (SPs) were prepared without a substrate using a one-pot hydrothermal method. The oriented aggregation of nanoparticles (NPs) induced at the initial stage an unusual growth pathway beyond a reversed crystal growth route, forming spindle-like or spiky structure, which was confirmed by structural analyses. Then, with a surface-to-core extension of crystallization and nanorod self-assembly, 2D NBs with ultrathin and well-aligned nanorods and 3D SPs were finally generated. The reduction of the surface free energy served as a primary driving force for the oriented self-assembly. The initial concentrations of sodium sulfate and polyethyleneimine, which are used as reducing reagent and electrostatic stabilizer, are crucial adsorption parameters. The adsorption capacity of the NBs and SPs for Cr(VI) was 68.3 mg g−1 and 83.4 mg g−1, respectively. The adsorption mechanism study showed that electrostatic interaction and reduction concomitantly affected the adsorption. The molecular dynamic simulation indicated that the adsorption performance depends on the crystallographic surface of the materials. The suggested synthesis route provides an atypical strategy to prepare 2D and 3D nanostructures with promising sorbent characteristics.

High Sensitivity and Selectivity of Array Gas Sensor through Glancing Angle Deposition Method

In this study, we propose an array-type gas sensor with high selectivity and response using multiple oxide semiconductors. The sensor array was composed of SnO2 and In2O3, and the detection characteristics were improved by using Pt, Au, and Pd catalysts. All samples were deposited directly on the Pt interdigitated electrode (IDE) through the e-beam evaporator glancing angle deposition (GAD) method. They grew in the form of well-aligned nanorods at off-axis angles. The prepared SnO2 and In2O3 nanorod samples were exposed to CH3COCH3, C7H8, and NO2 gases in a 300℃ dry condition. Au-decorated SnO2, Au-decorated In2O3, and Pd-decorated In2O3 exhibited high selectivity for CH3COCH3, C7H8, and NO2, respectively. They demonstrated a high detection limit of the sub ppb level computationally. In addition, measurements from each sensor were executed in the 40% relative humidity condition. Although there was a slight reduction in detection response, high selectivity and distinguishable detection characteristics were confirmed

Charge transfer plasmon coupled surface photosensing in ZnO nanorods–Au array hetero-nanostructures

Well-aligned zinc oxide nanorods (ZnO NRs) array have been grown by wet chemical method on seeded substrates at low temperature. Gold nanosheet has been deposited by DC magnetron sputtering on the surrounding of the ZnO NRs array at glancing angle, thus creating a three-dimensionally (3D) plasmonic hetero-nanostructure (HNS). The localized surface plasmon resonance (LSPR) is tuned and blue-shifted as the thickness of the gold nanosheet increased. The efficient surface plasmon (SP) excitation, and charge transfer plasmon through tunneling transport and junction conductance elevates the locally electromagnetic field and subsequently enhances surface Raman scattering in ZnO NRs-Au array HNS. An enhanced factor (EF) of 500 can be obtained for the surface enhancement Raman scattering (SERS) response for ZnO NRs-Au array HNS. Photoluminescence spectrum shows Au- mediated blue emission enhancement. The ZnO NRs–Au HNSs show high nonlinear refractive index and nonlinear optical absorption coefficient around 10−5 cm2/W and 1 cm/W, respectively. The ZnO NRs-Au array HNS can provide the figures of merit w = 209.83 and t = 0.59 for the optical switching devices. Photosensitivity and photocatalytic activity are elevated in ZnO NRs-Au array HNS. The ZnO NRs-Au array HNS shows maximal photocurrent enhancement of 69.38% in comparison to the bare ZnO NRs array.

Chrysanthemum-like high-entropy diboride nanoflowers: A new class of high-entropy nanomaterials

High-entropy nanomaterials have been arousing considerable interest in recent years due to their huge composition space, unique microstructure, and adjustable properties. Previous studies focused mainly on high-entropy nanoparticles, while other high-entropy nanomaterials were rarely reported. Herein, we reported a new class of high-entropy nanomaterials, namely (Ta0.2Nb0.2Ti0.2W0.2Mo0.2)B2 high-entropy diboride (HEB-1) nanoflowers, for the first time. Formation possibility of HEB-1 was first theoretically analyzed from two aspects of lattice size difference and chemical reaction thermodynamics. We then successfully synthesized HEB-1 nanoflowers by a facile molten salt synthesis method at 1423 K. The as-synthesized HEB-1 nanoflowers showed an interesting chrysanthemum-like morphology assembled from numerous well-aligned nanorods with diameters of 20–30 nm and lengths of 100–200 nm. Meanwhile, these nanorods possessed a single-crystalline hexagonal structure of metal diborides and highly compositional uniformity from nanoscale to microscale. In addition, the formation of the as-synthesized HEB-1 nanoflowers could be well interpreted by a classical surface-controlled crystal growth theory. This work not only enriches the categories of high-entropy nanomaterials but also opens up a new research field on high-entropy diboride nanomaterials.

Linearly Polarized Emission from Shear-Induced Nematic Phase Upconversion Nanorods.

Lanthanide-doped particles exhibit unique polarization-dependent luminescence due to the anisotropic crystalline local symmetry surrounding the emitter. Precise control of the orientation of particles shows great significance for exploiting the luminescent polarization and their potential applications. Here, we demonstrated a facile polypropylene-aided shear-driven method to obtain large-scale orientationally ordered upconversion nanorods, showing a liquid-crystalline nematic phase. Upconversion nanorods with low aspect ratios were well-aligned with the crystalline c-axis along the shearing direction using monodispersed colloid nanorods as the nanoink. The order parameter of aligned upconversion nanorods can reach up to 0.95. The nematic upconversion nanorods demonstrated strong polarization-dependent luminescence with the high degrees of polarization of the 4F9/2 sublevels at 657 and 661 nm being 0.47 and 0.59, respectively. Taking advantage of these mesoscopic well-aligned upconversion nanorods, their peculiar polarized emissions are potentially useful for some interdisciplinary applications such as polarization-sensitive bioprobes and anticounterfeiting.

Facile synthesis of schwertmannite@akaganeite core/shell nanostructure from pickling waste liquor: Formation mechanism and potential application

An environmentally friendly and low-cost synthesis of schwertmannite@akaganeite (Sch@Aka) core/shell nanostructure was achieved from hydrochloric pickling waste liquor (HPWL). The Sch@Aka nanostructure had a pincushion-like shape composed of radially well-aligned nanorods with an average length of about 250 nm and a mean diameter of about 60 nm. Trace SO42− ions played a key role in the formation of the Sch@Aka nanostructure. In the presence of Fe3+, Cl− and trace SO42− ions, schwertmannite was preferentially nucleated and then served as a core for akaganeite growth. The novel Sch@Aka nanostructure not only exhibited a higher adsorption capacity (43.0 mg g−1) for heavy metal Cr(VI) ions, but also delivered a larger reversible storage capacity of 1245 mA h·g−1 with Coulombic efficiency of close to 82% as the anode material in Li-ion batteries, indicating its potential application value.

Barrier Layer Induced Switching Stability in Ga:ZnO Nanorods Based Electrochemical Metallization Memory

The effect of the TiW barrier layer on the switching properties of Ga-doped ZnO (GZO) nanorods based on Electrochemical Metallization Memory is investigated. Vertically well-aligned and uniform GZO nanorods having a diameter of approximately 35 nm are hydrothermally grown on a seeding layer of ZnO deposited on indium tin oxide (ITO) coated glass substrate, to fabricate Cu/TiW/nanorods/ITO/Glass devices. The remarkable enhancement in the memory window (on/off ratio) is achieved in the 5 nm TiW barrier layer embedded device. This device exhibits endurance of more than 103 cycles and a large memory window of ∼103. The conduction mechanism at different current regions is studied, and it is found that Schottky emission is dominated in the low field region. The TiW barrier layer helps to retain the Cu ions and control the Cu ions diffusion, hence control the filament growth into the resistive layer, confirmed from the X-ray photoelectron spectroscopy (XPS) analysis. This device is suitable for the future low power non-volatile memory devices.

Study on the role of growth time on structural, morphological and optical properties of un-capped and L-cyst.-capped ZnO nanorods grown on a GZO seeded thin film layer from an aqueous solution

The influence of the deposition time (ranging from 30 to 300 min) and the role of l-cysteine on the structural and optical properties of the un-capped and L-cyst.-capped ZnO nanorods (ZNRs) grown using the chemical bath deposition method was discussed. X-ray diffraction patterns showed that the estimated crystallite size increased with the deposition time up to 240 min for both capped and un-capped samples, while the calculated strain was found to decrease to a minimum for the 240 min deposition time. The Fourier transform infra-red spectroscopy of the as-grown ZNRs films showed various absorption bands in the range of 250–4000 cm-1 indicating the presence of different functional groups. Scanning electron microscopy analysis illustrated that the aspect ratios of the L-cyst.-capped ZNRs increased six-fold as the growth duration varied from 30 to 240 min, but decreased slightly at longer growth time. The root mean square roughness increased continuously from 10.9 to 36.3 nm as the growth time was raised from 30 to 240 min for the un-capped ZNRs. The samples deposited at 240 min exhibited the highest photoluminescence emission intensity ratios suggesting a low density of deep level defects. An inverse relation between the optical band gaps and growth time was observed. The highly luminescent cyst.-capped sample, with well-aligned nanorods and highest aspect ratio and good crystallization grown at 240 min growth time can be used as a possible photoanode component of dye-sensitized solar cells.

Jackfruit-like electrode design for advanced Na-Se batteries

Sodium-selenium (Na–Se) batteries are attracting much attention because of their high energy density. However, their practical application is still restricted by rapid capacity fading resulting from the inferior electrode kinetics, low utilization of Se and enormous volumetric expansion. Herein, a jackfruit-like electrode is designed for advanced Na–Se batteries to solve these problems. The carbon nanorods are well-aligned to form a jackfruit-like design as the Se host. Thanks to the unique structure, many hollow nanochannels between nanorods are able to provide multifold pathways for Na-ions diffusion and electrolyte penetration. Moreover, the nanopores in carbon nanorods can provide adequate space to store Se and to buffer volumetric expansion during cycling. More importantly, the well-aligned carbon nanorods can enable a fast electron transfer to improve the utilization of Se. As a result, the jackfruit-like Se-carbon electrodes exhibit a high capacity of 616 mAh g−1 at 0.2 C, outstanding rate capability and long cycling life up to 600 cycles at 2 C with a very low capacity decay of 0.066% per cycle.

Fabrication of Ag2S quantum dots sensitized CdSe photoelectrodes and its photoelectric performance

Well-aligned wheat-like CdSe nanorods array was fabricated by electrodeposition method, which was sensitized with Ag2S quantum dots (QDs) by using successive ionic layer adsorption and reaction (SILAR) method. The combination of five successive layers Ag2S QDs with CdSe shows maximum short-circuit photocurrent density of 36.88 mA/cm2. Compared with TiO2-based photoelectrode, the wheat-like CdSe nanorods array modified with Ag2S QDs exhibit improved photoelectrochemical (PEC) performance. The main reason for the enhancement of PEC is to use narrow band-gap semiconductor CdSe instead of the conventional wide band-gap oxide as the sensitized substrate of Ag2S QDs. In addition, the synthetic nanocomposites are characterized by analytical techniques such as XRD, UV–vis absorption spectroscopy, FESEM, HRTEM, EDX, XPS and EIS. The results indicate that Ag2S QDs are well grown on the surface of CdSe photoelectrodes. Meantime, the PEC performance of CdSe photoelectrodes has also been improved.