Bare Nanorods Research Articles

NO2 sensing characteristics by α-Fe2O3 nanorod arrays with atomic layer deposited amorphous Al2O3 overlayer

We have grown α-Fe2O3 nanorods by solution processing followed by the deposition of Al2O3 overlayer using atomic layer deposition. Al2O3 layer was deposited for two different thicknesses 4 nm and 8 nm and a post-deposition annealing at 550 °C for 2 h in air atmosphere was performed. Crystallinity analysis through x-ray diffraction (XRD) reveals that the α-Fe2O3 nanorods crystallized into rhombohedral structure, whereas the outer Al2O3 layers remained largely amorphous. Interestingly, the interface showed signs of AlFexOy formation as observed through high-resolution transmission electron microscopy images. Gas sensing characteristics were studied using NO2 with 10, 50, and 100 ppm concentrations at operating temperatures of 30 °C, 100 °C, 150 °C and 190 °C. The room temperature sensitivity values obtained in response to 10 ppm NO2 were 31%, which surpassed the previously reported values. A higher concentration of surface adsorbed oxygen on the Al2O3 overlayer, as revealed by the x-ray photoelectron spectroscopy (XPS) analysis, led to enhanced NO2 sensing at room temperature. A lower activation energy (0.29 eV) of barrier to charge transport for Al2O3 coated α-Fe2O3 nanorods compared to that of bare nanorods (0.45 eV), as calculated from the temperature dependent I-V measurements, supported observation of higher sensitivity at room temperature.

Capillary Condensation Mediated Fluidic Straining for Enhanced Bacterial Inactivation

AbstractBiomaterials capable of continuously inactivating pathogens are essential for suppressing transmission of infectious diseases, such as epidemic cerebrospinal meningitis and pulmonary tuberculosis. Here, capillary condensation of air moisture within nano‐confined spaces between superhydrophilic rigid nanorods is shown and target microbiology spontaneously stretch and inactivate aerosolized microorganisms. Specifically, the negative Gaussian curvature‐shaped water condensate causes fluidic straining, comprising surface tension and Laplace pressure, strong enough to deform and eliminate the selected bacteria. Plate counting quantifies the sharply reduced contact‐killing period for superhydrophilic and bare nanorods (6 vs 100 min for E. coli, 20 vs 120 min for S. aureus) under relative humidity of 70%. Theoretical calculations and experimental studies indicate increased mechanical straining and mechano‐bactericidal by improving air moisture content. To further illustrate utility, long‐term antibacterial medical masks are fabricated by integrating such nanorods onto commercial fabrics. Collectively, these findings highlight the immense potential of capillary condensation‐induced fluidic straining as an eco‐friendly, broad‐spectrum, and highly efficient antibacterial strategy.

Enhancement of electrochromic efficiency of TiO2 nanorods

In this study, the rutile TiO2 nanorods thin films were deposited via hydrothermal method on fluorine-doped tin oxide (FTO) substrate. To form a porous morphology layer, a thin film of amorphous titanium oxide (TiOx) was deposited on the TiO2 nanorods through sputtering at high pressure. The samples were annelid at 450ᵒC to transform the amorphous surface to anatase phase. Structural, optical, morphology and electrochemical properties of the samples were examined via X-ray diffraction (XRD), Raman scattering, UV–Vis NIR and photoluminescence (PL) spectroscopies, field-emission scanning electron microscopy (FE-SEM) and Potentiostat device respectively. The samples exhibited a large optical bandgap of 3.35–3.40 eV and high transparency of over 77 % at a wavelength of 555 nm. Raman analysis confirmed the formation of anatase phase on the rutile nanorods under thermal treatment. PL analysis indicated that the oxygen vacancies reached their maximum after sputtering, while the intensity of PL emission significantly increased after annealing. Investigation of the electrochromic properties revealed an increase in coloration efficiency from 2.6 C−1cm2 for bare nanorods to 10.0 C−1cm2 for nanorods after sputtering deposition, which decreased to 5.4 C−1cm2 after thermal treatment.

Low-Temperature Processed Brookite Interfacial Modification for Perovskite Solar Cells with Improved Performance.

The scaffold layer plays an important role in transporting electrons and preventing carrier recombination in mesoporous perovskite solar cells (PSCs), so the engineering of the interface between the scaffold layer and the light absorption layer has attracted widespread concern. In this work, vertically grown TiO2 nanorods (NRs) as scaffold layers are fabricated and further treated with TiCl4 aqueous solution. It can be found that a thin brookite TiO2 nanoparticle (NP) layer is formed by the chemical bath deposition (CBD) method on the surface of every rutile NR with a low annealing temperature (150 °C), which is beneficial for the infiltration and growth of perovskite. The PSC based on the TiO2 NR/brookite NP structure shows the best power conversion of 15.2%, which is 56.37% higher than that of the PSC based on bare NRs (9.72%). This complex structure presents an improved pore filling fraction and better carrier transport capability with less trap-assisted carrier recombination. In addition, low-annealing-temperature-formed brookite NPs possess a more suitable edge potential for electrons to transport from the perovskite layer to the electron collection layer when compared with high-annealing-temperature-formed anatase NPs. The brookite phase TiO2 fabricated at a low temperature presents great potential for flexible PSCs.

Enhanced Resonant Energy Transfer by Decorating Au Nanoparticles on the Sidewalls of InGaN Multiple‐Quantum‐Well Nanorods

An enhanced resonant energy transfer (RET) process between green InGaN multiple quantum wells (MQWs) and CdSe/ZnS quantum dots (QDs) is investigated by decorating the sidewalls of InGaN MQW nanorods with Au nanoparticles. The InGaN MQW nanorods are shallow‐etched to the region of InGaN MQWs or deep‐etched through InGaN MQWs completely. The Au nanoparticles can provide localized surface plasmon coupling to both InGaN MQWs and QDs, leading to accelerated decay rates. The localized surface plasmons also enhance the RET process between InGaN MQWs and QDs. Compared to the bare nanorods without Au nanoparticles, the enhancement factors of the RET process are 1.8 and 5.6 for shallow‐ and deep‐etched MQW nanorods, respectively. The larger enhancement factor for deep‐etched nanorods is mainly attributed to the weaker localized surface plasmon coupling with InGaN MQWs, which is proposed to compete with the RET process. The RET efficiency in the deep‐etched InGaN MQW nanorods is calculated as 62%, demonstrating high potential for usage in energy conversion devices.

Cellular Uptake of Gold Nanorods in Breast Cancer Cell Lines.

Nanosized materials have been proposed for a wide range of biomedical applications, given their unique characteristics. However, how these nanomaterials interact with cells and tissues, as well as how they bio-distribute in organisms, is still under investigation. Differences such as the nanoparticle size, shape, and surface chemistry affect the basic mechanisms of cellular uptake and responses, which, in turn, affects the nanoparticles’ applicability for biomedical applications. Thus, it is vital to determine how a specific nanoparticle interacts with cells of interest before extensive in vivo applications are performed. Here, we delineate the uptake mechanism and localization of gold nanorods in SKBR-3 and MCF-7 breast cancer cell lines. Our results show both differences and similarities in the nanorod–cell interactions of the two cell lines. We accurately quantified the cellular uptake of gold nanorods in SKBR-3 and MCF-7 using inductively coupled plasma mass spectrometry (ICP-MS). We found that both cell types use macropinocytosis to internalize bare nanorods that aggregate and associate with the cell membrane. In addition, we were able to qualitatively track and show intracellular nanoparticle localization using transmission electron microscopy. The results of this study will be invaluable for the successful development of novel and “smart” nanodrugs based on gold nano-structural delivery vehicles, which heavily depend on their complex interactions with single cells.

Anatase-Wrapped Rutile Nanorods as an Effective Electron Collector in Hybrid Photoanodes for Visible Light-Driven Oxygen Evolution.

Arrays of single crystal TiO2 rutile nanorods (RNRs) appear highly promising as electron-collecting substrates in hybrid photoanodes as the RNRs offer direct charge carriers transport pathways, contrary to the conventional electrodes prepared from TiO2 powders that suffer from the numerous charge traps at the grain boundaries. However, the specific surface area of the nanorods is highly limited by their smooth morphology, which might be detrimental in view of utilizing the RNR as a substrate for immobilizing other functional materials. In this study, we developed a novel anatase-wrapped RNR (ARNR) material fabricated by a facile seed layer-free hydrothermal method. The ARNR comprises polycrystalline anatase nanoparticles formed on the surface of RNR, resulting in a large surface area that provides more deposition sites compared to the bare nanorods. Herein, we functionalize ARNR and RNR electrodes with polymeric carbon nitride (CNx) coupled with a CoO(OH)x cocatalyst for dioxygen evolution. The anatase wrapping of the rutile nanorod scaffold is found to be crucial for effective deposition of CNx and for improved photoanode operation in visible light-driven (λ > 420 nm) oxygen evolution, yielding a significant enhancement of photocurrent (by the factor of ∼3.7 at 1.23 V vs. RHE) and faradaic efficiency of oxygen evolution (by the factor of ∼2) as compared to photoanodes without anatase interlayer. This study thus highlights the importance of careful interfacial engineering in constructing photoelectrocatalytic systems for solar energy conversion and paves the way for the use of ARNR-based electron collectors in further hybrid and composite photochemical architectures for solar fuel production.

Influence of ZnO nanorod surface chemistry on passivation effect of TiO2 shell coating

Core–shell structures with ZnO cores have been widely investigated due to their effectiveness in suppressing surface defects of ZnO nanostructures. As the surface defects are hugely dependent on the synthesis conditions, it is important to understand the interactions between shell material and ZnO with different surface chemistry. Here we produce well-aligned ZnO nanorods using two growth methods, leading to ZnO with different surface chemistries. A thin layer of TiO2 shell is applied via layer-by-layer adsorption method. The core–shell structure is confirmed via high-resolution transmission electron microscopy. The optical properties and chemical states of both bare nanorods and core–shell structures are investigated and compared using photoluminescence (PL) measurement and x-ray photoelectron spectroscopy (XPS). Both PL and XPS results suggest surface defects are passivated by TiO2 shell coating. The shell coating has a stronger effect on ZnO synthesized in OH− rich environment, due to excessive hydroxyl groups provided during synthesis, which remain even after annealing-induced crystallization.

Colorimetric determination of Hg(II) by combining the etching and aggregation effect of cysteine-modified Au-Ag core-shell nanorods

Abstract In this report, a simple and effective approach for colorimetric detection of Hg2+ based on surface etching and aggregation effect of cysteine-modified Au-Ag core-shell nanorods has been investigated. When the addition of Hg2+ has a low concentration under 60 μM, electrostatic interaction-induced intense aggregation of colloidal Au-Ag core-shell nanorods takes place. Thus the longitudinal plasmonic absorption peak decreases rapidly, which also leads to the colloidal color become shallow. Whereas when the addition of Hg2+ has a high concentration greater than 60 μM, the adherent cysteine molecules break away from the surface of nanorods due to the intense Hg-S bond. Then the bare nanorods have been etched under the action of Hg2+. The decrease of the Ag shell results in the red shift of the longitudinal absorption peak, which further leads to the color change of the colloids. The sensing based on particle aggregation-induced absorption decrease has a linear response for Hg2+ from 1 to 60 μM with a theoretical detection limit of 0.273 μM. The sensing based on etching effect-induced red shift has a logarithmic response for Hg2+ from 60 to 250 μM with a theoretical detection limit of 1.065 μM. Interference test and real samples detection results show that Hg2+ could be specifically detected by using this probe based on Au-Ag core-shell nanorods.

Nanorod Mn3O4 anchored on graphene nanosheet as anode of lithium ion batteries with enhanced reversible capacity and cyclic performance

Nanorod Mn3O4 anchored on graphene nanosheet (Mn3O4@GNS) using GNSs and MnSO4·H2O as precursor materials have been prepared by a simple, effective and scalable method. The nanorod Mn3O4@GNS as anode materials in lithium-ion batteries exhibits the better electrochemical properties in the composite than the bare nanorod Mn3O4 owing to its special structure, including a maximum reversible specific capacity of 1155.2 mA h g−1 at 100 mA g−1, and the extraordinary cycling stability, with no decay in capacity for up to 100 cycles. The nanorod Mn3O4@GNS could be a promising candidate material for high reversible specific capacity, stable columbic efficiency, long cycle life and outstanding rate capacity. This study would offer a new method to improve the properties of insulating materials, holding a promising potential for high-performance lithium-ion batteries in energy storage fields.

Growth of hybrid carbon nanostructures on iron-decorated ZnO nanorods

A novel carbon-based nanostructured material, which includes carbon nanotubes (CNTs), porous carbon, nanostructured ZnO and Fe nanoparticles, has been synthetized using catalytic chemical vapour deposition (CVD) of acetylene on vertically aligned ZnO nanorods (NRs). The deposition of Fe before the CVD process induces the presence of dense CNTs in addition to the variety of nanostructures already observed on the process done on the bare NRs, which range from amorphous graphitic carbon up to nanostructured dendritic carbon films, where the NRs are partially or completely etched. The combination of scanning electron microscopy and in situ photoemission spectroscopy indicate that Fe enhances the ZnO etching, and that the CNT synthesis is favoured by the reduced Fe mobility due to the strong interaction between Fe and the NRs, and to the presence of many defects, formed during the CVD process. Our results demonstrate that the resulting new hybrid shows a higher sensitivity to ammonia gas at ambient conditions (∼60 ppb) than the carbon nanostructures obtained without the aid of Fe, the bare ZnO NRs, or other one-dimensional carbon nanostructures, making this system of potential interest for environmental ammonia monitoring. Finally, in view of the possible application in nanoscale optoelectronics, the photoexcited carrier behaviour in these hybrid systems has been characterized by time-resolved reflectivity measurements.

Performance improvement of organic solar cells with the introduction of branched zinc oxide nanorods

Zinc oxide (ZnO) nanorods with branches are synthesised through facile hydrothermal approach at relatively low temperature. With the prepared ZnO nanostructures as the hole-blocking layer, organic solar cells based on poly(3-hexylthiophene): 1-(3-methoxycarbonyl) propyl-1-phenyl[6,6]C61 are fabricated. For comparison, devices with planar ZnO thin film and bare ZnO nanorods are manufactured as well. J-V curves show that the best device performance is achieved by the branched nanorod-based solar cell. Owing to the decreased charge carrier travelling length, the nanorod-based device shows higher short circuit current (Jsc) than that of the device with planar ZnO layer. Moreover, the solar cell with branched nanorods shows larger open-circuit voltage (Voc) than that with bare nanorods. Therefore, the performance of organic photovoltaic is enhanced with the introduction of branched ZnO nanorods. Finally, the mechanism of device performance improvement upon the introduction of branched nanorods is discussed. c 2015 The Institution of Engineering and Technology.

Facile Preparation of TiO2 Nanobranch/Nanoparticle Hybrid Architecture with Enhanced Light Harvesting Properties for Dye‐Sensitized Solar Cells

We report TiO2 nanobranches/nanoparticles (NBN) hybrid architectures that can be synthesized by a facile solution phase method. The hybrid architecture simultaneously improves light harvesting and charge collection performances for a dye‐sensitized solar cell. First, TiO2 nanorods with a trunk length of 2 μm were grown on a fluorine‐doped tin oxide (FTO)/glass substrate, and then nanobranches and nanoparticles were deposited on the nanorods’ trunks through a solution method using an aqueous TiCl3 solution at 80°C. The relative amount of nanobranches and nanoparticles can be controlled by multiplying the number of TiCl3 treatments to maximize the amount of surface area. We found that the resultant TiO2 NBN hybrid architecture greatly improves the amount of dye adsorption (five times compared to bare nanorods) due to the enhanced surface area, while maintaining a fast charge collection, leading to a three times higher current density and thus tripling the maximum power conversion efficiency for a dye‐sensitized solar cell.

Facile Synthesis of Anisotropic Au Nanostructures by Laser Irradiation and Study of Their Optical and Electrokinetic Properties

This work describes a cost-effective single step technique for the preparation of Au nanostructures of many anisotropic shapes from Au nanorods by irradiating them with different laser energies (2.71, 2.54, and 2.41 eV). A variety of many irregular Au nanomorphologies such as multifaceted polygonal spheres (10–20 nm), low aspect ratio rods, oval egg shapes, squares, pentagons, and nanocapsules of varying sizes were formed after laser exposure. The small irregular shaped particles with new surface exposed atoms having cutting edges and sharp corners affect the optical, electrokinetic, and catalytic properties of fragmented Au nanoparticles. The percentage decomposition of Au nanorods is found to increase as 59% > 69% > 72% with increased energy of laser exposure; 2.41 eV (514.7 nm) > 2.50 eV (488 nm) > 2.71 eV (457.9 nm), as determined from the TEM images. The formation of quantum sized paticles upon laser irradiation results in the increase of zeta potential from +50.0 to +57.5 mV and conductance values. The co-catalytic activity of photofragmented Au nanorods is ∼20–25% higher than that of bare nanorods for benzaldehyde photooxidation.

A method to obtain the thermal parameters and the photothermal transduction efficiency in an optical hyperthermia device based on laser irradiation of gold nanoparticles.

Optical hyperthermia systems based on the laser irradiation of gold nanorods seem to be a promising tool in the development of therapies against cancer. After a proof of concept in which the authors demonstrated the efficiency of this kind of systems, a modeling process based on an equivalent thermal-electric circuit has been carried out to determine the thermal parameters of the system and an energy balance obtained from the time-dependent heating and cooling temperature curves of the irradiated samples in order to obtain the photothermal transduction efficiency. By knowing this parameter, it is possible to increase the effectiveness of the treatments, thanks to the possibility of predicting the response of the device depending on the working configuration. As an example, the thermal behavior of two different kinds of nanoparticles is compared. The results show that, under identical conditions, the use of PEGylated gold nanorods allows for a more efficient heating compared with bare nanorods, and therefore, it results in a more effective therapy.

Electrical investigation and ultraviolet detection of ZnO nanorods encapsulated with ZnO and Fe-doped ZnO layer

Encapsulated ZnO nanorod arrays were fabricated using a two-step method; hydrothermal followed by dip-coating. Intensity of X-ray diffraction peaks of ZnO nanorod films increased by encapsulation with ZnO and Fe doped ZnO layer. Encapsulation process increased diameter of the rods in a range of 20–40 nm. The optical studies indicated that the band-gap decreased with increment of the nanorod diameter, and increased with Fe doping in the ZnO layer. The electrical resistance of the samples demonstrated a remarkable reduction due to encapsulation, especially in the sample encapsulated with Fe doped-ZnO layer. The photoresponse behavior of ZnO nanorod films was investigated under different powers of ultraviolet illumination. The photoresponsivity was improved for encapsulated nanorods as compared to bare nanorods.

Facile preparation of large-scale α-Fe2O3 nanorod/SnO2 nanorod composites and their LPG-sensing properties

α-Fe2O3 nanorods (NRs) with length and diameter of 300 and 50nm, and SnO2 NRs with length and diameter of 30 and 10nm, respectively, were prepared through hydrothermal treatment method. Morphologies of α-Fe2O3 and SnO2 NRs and their composites with different weight ratios were studied by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). The SEM and TEM images showed SnO2 NRs attached on (branch onto) the surface of the α-Fe2O3 NRs. Liquefied petroleum gas (LPG)-sensing properties of films with bare α-Fe2O3, SnO2 NRs, and their composite NRs were investigated. The composite of 75wt% α-Fe2O3/25wt% SnO2 exhibits the highest response to LPG at optimum operating temperature of 370°C. The improvement in the gas-sensing characteristics of the composite NRs compared with bare NRs is attributed to the formation of hetero-junctions in α-Fe2O3 NRs/SnO2 NRs and to their porous structure.

Fe2O3 nanorods/carbon nanofibers composite: Preparation and performance as anode of high rate lithium ion battery

A novel Fe2O3/carbon composite is prepared using a facile one-step hydrothermal method. Its structure, morphology and performance as anode of lithium ion battery are investigated with X-ray diffraction, scanning electron microscopy, thermogravimetry, cyclic voltammetry, galvanostatic charge/discharge, and electrochemical impedance spectroscopy. It is found that the as-prepared composite is composed of α-Fe2O3 nanorods of about 75 nm in diameter and 1 μm in length, which are enwrapped with soft and curly carbon nanofibers, and exhibits superior charge/discharge performance compared to bare α-Fe2O3 nanorods, especially at high current rate. The discharge capacity is 1069 mAh g−1 at the first cycle and remains 560 mAh g−1 after 30 cycles at 0.2C for the bare nanorods, but improved to 1278 mAh g−1 and 960 mAh g−1 for the composite. At 12C, the discharge capacity is only 798 mAh g−1 initially and becomes 98 mAh g−1 after 30 cycles for the bare nanorods, while 844 mAh g−1 and 292 mAh g−1 for the composite. The improved performance of the composite is attributed to the bondage from carbon nanofibers, which contributes to the improvement in electronic conductivity and structure stability of α-Fe2O3 nanorods.

A Quantitative Study of the Environmental Effects on the Optical Response of Gold Nanorods

The effects of the dielectric environment on the optical extinction spectra of gold nanorods were quantitatively studied using individual bare and silica-coated nanorods. The dispersion and amplitude of their extinction cross-section, dominated by absorption for the investigated sizes, were measured using spatial modulation spectroscopy (SMS). The experimental results were compared to calculations from a numerical model that included environmental features present in the measurements and the morphology and size of the corresponding nanorods measured by transmission electron microscopy. The combination of these experimental and theoretical tools permits a detailed interpretation of the optical properties of the individual nanorods. The measured optical extinction spectra and the extinction cross-section amplitudes were well reproduced by the numerical model for silica-coated gold nanorods, for which the silica shell provides a controlled environment. In contrast, additional environmental factors had to be assumed in the model for bare nanorods, stressing the importance of controlling and characterizing the experimental conditions when measuring the optical response of bare surface-deposited single metal nanoparticles.

Hollow core–shell nanostructure supercapacitor electrodes: gap matters

Hollow core–shell nanorods with a nanogap are designed and constructed with the assistance of atomic layer deposition (ALD) for energy storage applications. As a demonstration, CoO nanorods and NiO nanowalls are enclosed by a TiO2 nanotube shell, forming the “wire in tube” and “wall in box” structures, respectively. A thin sacrificial layer of Al2O3 is deposited by ALD and removed eventually, forming a nanogap between the CoO core (or the NiO nanowall) and the TiO2 shell. When they are tested as supercapacitor electrodes, an evident difference between the solid core–shell nanostructure and hollow ones can be found; for example, the hollow structure shows ∼2 to 4 times the capacitance compared to the solid wires. The electrochemical properties are also superior compared to the bare nanorods without the nanotube shell. The enhancement is ascribed to the conformal hollow design which provides enlarged specific surface areas and a shorter ion transport path. It is prospected that such a positive nanogap effect may also exist in other electrochemical cell electrodes such as lithium ion batteries and fuel cells.