O4 Nanorods Research Articles

NiO Nanoparticles Anchored on Phosphorus-Doped α-Fe2 O3 Nanoarrays: An Efficient Hole Extraction p-n Heterojunction Photoanode for Water Oxidation.

The photoelectrochemical (PEC) water-splitting efficiency of a hematite-based photoanode is still far from the theoretical value due to its poor surface reaction kinetics and high density of surface trapping states. To solve these drawbacks, a photoanode consisting of NiO nanoparticles anchored on a gradient phosphorus-doped α-Fe2 O3 nanorod (NR) array (NiO/P-α-Fe2 O3 ) was fabricated to achieve optimal light absorption and charge separation, as well as rapid surface reaction kinetics. Specifically, a photoanode with the NR array structure allowed a high mass-transport rate to be achieved, while phosphorus doping effectively decreased the number of surface trapping sites and improved the electrical conductivity of α-Fe2 O3 . Furthermore, the p-n junction that forms between NiO and P-α-Fe2 O3 can further improve the PEC performance due to efficient hole extraction and the water oxidization catalytic activity of NiO. Consequently, the NiO/P-α-Fe2 O3 NR photoanode produced a high photocurrent density of 2.08 mA cm-2 at 1.23 V versus a reversible hydrogen electrode and a 110 mV cathodic shift of the onset potential. This rational design of structure offers a new perspective in exploring high-performance PEC photoanodes.

Synthesis and characterization of high-performance RGO-modified LiNi0.5Mn1.5O4 nanorods as a high power density cathode material for Li-ion batteries

Micronanosized LiNi0.5Mn1.5O4 nanorods coated with reduced graphene oxide is successfully synthesized by a hydrothermal-assembly method. The as-prepared samples are characterized by X-ray diffraction, Raman spectroscopy, field emission scanning electron microscope, and electrochemical tests. The XRD and Raman results show that the LiNi0.5Mn1.5O4 nanorods have disordered structure of Fd-3m space group. The SEM characterization exhibits that LiNi0.5Mn1.5O4 nanorods are about 200–400 nm in diameter, and the RGO is well dispersed on the surface of LiNi0.5Mn1.5O4 nanorods. Moreover, a RGO layer coated on the surface of LiNi0.5Mn1.5O4 can suppress the interfacial side reactions. The electrochemical tests show that the RGO-LNMO composites reveal high specific capacity and excellent cyclic stability at high rates. The 1%-RGO-LNMO composite can still possess the capacity of 71.4 mAh g−1 and excellent capacity retention about 99% after 1000 cycles at 10 C rate. The excellent performance of RGO-LNMO composites makes it a promising candidate as lithium-ion battery cathode materials.

Synthesis of Porous Magnetic Ni0.6Fe2.4O4 Nanorods for Highly Efficient Adsorption of U(VI)

In this study, porous magnetic Ni0.6Fe2.4O4 nanorods (MNs) were successfully synthesized just by calcining the Ni0.6Fe2.4C2O4·2H2O precursor. MNs exhibited porous structure with disorderly nanorods based on the characterizations. Experimental results showed that the removal of U(VI) by MNs can reach equilibrium within 150 min at 293 K with a maximal adsorption capacity of 57.7 mg/g. Besides, the adsorption performance was highly dependent on solution pH values, while ion strength and ion species had little influence. The U(VI) adsorption onto the MNs was fitted better by the pseudo-second-order kinetic model, and the isothermal data can be better described by the Langmuir model, suggesting a monolayer adsorption process. Thermodynamic studies indicated the adsorption process to be spontaneous and endothermic. In addition, this magnetic material can achieve convenient separation using an external magnet. Hence, the MNs can be utilized as an effective candidate to enrich and separate U(VI) from aqueous solu...

Room-temperature, high selectivity and low-ppm-level triethylamine sensor assembled with Au decahedrons-decorated porous α-Fe2O3 nanorods directly grown on flat substrate

Chemiresistive based gas sensors with low operating temperature (e.g. room-temperature), high selectivity, and fast response for specific target gas are highly desired. Herein, we successfully construct triethylamine (TEA) gas sensors with gold (Au) decahedrons (DHs)-decorated porous α-Fe2O3 nanorods, which can work at 40 °C and exhibit high selectivity and low-ppm-level response. Porous α-Fe2O3 nanorods with high specific surface area are directly grown on seeded flat substrate with electrodes by a cost-effective hydrothermal method. Au DHs synthesized by one-pot polyol reaction method are deposited onto such α-Fe2O3 nanorods by spin-coating. Such Au DHs/α-Fe2O3 nanorods sensor working at temperature as low as 40 °C and relative humidity (RH) of 30% exhibits high response (17–50 ppm TEA), low detection concentration (∼1 ppm), and short response/recovery time (12/8 s), which are all much better than the control α-Fe2O3 nanorods sensor. When the RH increases, the sensor response decreases due to the water molecules adsorption. Furthermore, the enhanced sensing properties toward TEA are discussed in terms of the formation of Au/Fe2O3 metal/semiconductor Schottky contact and the catalytic activity of Au DHs.

Sb-Doped SnO2 Nanorods Underlayer Effect to the α-Fe2 O3 Nanorods Sheathed with TiO2 for Enhanced Photoelectrochemical Water Splitting.

Here, a Sb-doped SnO2 (ATO) nanorod underneath an α-Fe2 O3 nanorod sheathed with TiO2 for photoelectrochemical (PEC) water splitting is reported. The experimental results, corroborated with theoretical analysis, demonstrate that the ATO nanorod underlayer effect on the α-Fe2 O3 nanorod sheathed with TiO2 enhances the PEC water splitting performance. The growth of the well-defined ATO nanorods is reported as a conductive underlayer to improve α-Fe2 O3 PEC water oxidation performance. The α-Fe2 O3 nanorods grown on the ATO nanorods exhibit improved performance for PEC water oxidation compared to α-Fe2 O3 grown on flat fluorine-doped tin oxide glass. Furthermore, a simple and facile TiCl4 chemical treatment further introduces TiO2 passivation layer formation on the α-Fe2 O3 to reduce surface recombination. As a result, these unique nanostructures show dramatically improved photocurrent density (139% higher than that of the pure hematite nanorods).

Ceramic hyperbranched alkyd/γ-Al2O3 nanorods composite as a surface coating

The work reports engineering an eco-friendly series of ceramic hyperbranched alkyd/γ-Al2O3 nanorods composite coatings via solution casting method and auto-oxidation curing mechanism. Sunflower oil based hyperbranched alkyd resin was successfully prepared by using polyesterification method. Controlled synthesis of single crystal γ-Al2O3 nanorods with 20 nm average diameter exposed by {400} crystal plane was carried out via hydrothermal and decomposition methods The effects of dispersing different concentrations of one-dimensional ceramic γ-Al2O3 nanorod filler in the alkyd matrix were studied. The tailored alkyd/single crystal γ-Al2O3 nanocomposites were applied for mechanical and anticorrosive coatings. Coatings' surface and anticorrosive properties were investigated via water contact angle, scanning electron microscopy and salt spray test. Studying the mechanical properties, stability against chemicals and thermal behavior of the ceramic alkyd nanocomposites were also considered. Results approved that the highest improvement was achieved with nanofiller insertion up to 0.5% γ-Al2O3 nanorods in the alkyd composites.

LiMn1.8Ni0.2O4 nanorods obtained from a novel route using α-MnOOH precursor as cathode material for lithium-ion batteries

Nanorod structures of LiMn1.8Ni0.2O4 applicable as active cathode material for Li-ion batteries were synthesized from α-MnOOH and α-MnO2 initial phases. The LiMn1.8Ni0.2O4 spinel nanorods obtained from α-MnOOH using a novel, eco-friendly method showed higher purity than the traditional spinel obtained from α-MnO2. The showed charge capacity that was in the order of 122 mA h g−1 higher than similar active material reported in the literature, and it was able to keep >80% of initial capacity at a charge rate of 5 C.

Carbon-coated hierarchical spinel Fe1.5V1.5O4 nanorods: A promising anode material for enhanced lithium storage

In this work, a facile synthesis strategy was used to fabricate the carbon-coated new spinel Fe1.5V1.5O4 nanorods. The initial obtained precursor was prepared by a facile solvothermal process. After it was treated by different methods, hierarchical Fe1.5V1.5O4@C nanorods consisted of Fe1.5V1.5O4 primary nanoparticles with different particle sizes could be obtained. As anode materials for lithium ion batteries, the hierarchical Fe1.5V1.5O4@C nanorods composed of smaller primary particles show higher reversible capacity, better cycling performance and rate capability. Its reversible capacity can retain at 753 mAh g−1 and 709 mAh g−1 even cycled at 0.5 A g−1 and 2 A g−1 after 100 cycles and 1000 cycles, respectively. The excellent lithium storage performance of carbon-coated Fe1.5V1.5O4 nanorods is dependent on the spinel crystal structure, unique hierarchical structure, and synergistic effect of active materials and carbon layer in the composites. The results of CV curves imply that the overall capacity upon cycling is determined by both of the surface-controlled capacitive contribution and diffusion-controlled Li+ intercalation process.

Core-Shell Nitrogen-Doped Carbon Hollow Spheres/Co3 O4 Nanosheets as Advanced Electrode for High-Performance Supercapacitor.

Co3 O4 /nitrogen-doped carbon hollow spheres (Co3 O4 /NHCSs) with hierarchical structures are synthesized by virtue of a hydrothermal method and subsequent calcination treatment. NHCSs, as a hard template, can aid the generation of Co3 O4 nanosheets on its surface; while SiO2 spheres, as a sacrificed-template, can be dissolved in the process. The prepared Co3 O4 /NHCS composites are investigated as the electrode active material. This composite exhibits an enhanced performance than Co3 O4 itself. A higher specific capacitance of 581 F g-1 at 1 A g-1 and a higher rate performance of 91.6% retention at 20 A g-1 are achieved, better than Co3 O4 nanorods (318 F g-1 at 1 A g-1 and 67.1% retention at 20 A g-1 ). In addition, the composite is employed as a positive electrode to fabricate an asymmetric supercapacitor. The device can deliver a high energy density of 34.5 Wh kg-1 at the power density of 753 W kg-1 and display a desirable cycling stability. All of these attractive results make the unique hierarchical Co3 O4 /NHCS core-shell structure a promising electrode material for high-performance supercapacitors.

High-performance piezoelectric energy harvesting of vertically aligned Pb(Zr,Ti)O3 nanorod arrays

Recent developments of self-powered devices and systems have attracted much attention. Lead zirconate titanate (PZT) has been regarded as one of the most promising materials for building high-performance nanogenerators. Herein, vertically aligned PZT nanorod arrays were synthesized on a pre-oxidized Ti substrate in the presence of a surfactant by a one-step hydrothermal method. The PZT nanorod arrays consist of an initial layer of a PZT film and well aligned nanorods with (001)-orientated tetragonal single crystalline structures. The PZT nanorods exhibited a high piezoelectric response with a d33 value of up to 1600 pm V−1. A piezoelectric energy harvester was fabricated based on the PZT nanorod arrays, which exhibited outstanding energy harvesting performance with an open-circuit output voltage of 3.3 V and 8 V when the devices were pressed by a compressive 10 N force and a finger tapping motion, respectively. Moreover, the average power density generated by those two mechanical stimulations were up to 3.16 and 5.92 μW cm−2 with the external load of 1 MΩ.

Improved Dehydrogenation Properties of LiBH4 Using Catalytic Nickel- and Cobalt-based Mesoporous Oxide Nanorods.

Lithium borohydride (LiBH4 ) with a theoretical hydrogen storage capacity of 18.5 wt % has attracted intense interest as a high-density hydrogen storage material. However, high dehydrogenation temperatures and limited kinetics restrict its practical applications. In this study, mesoporous nickel- and cobalt-based oxide nanorods (NiCo2 O4 , Co3 O4 and NiO) were synthesized in a controlled manner by using a hydrothermal method and then mixed with LiBH4 by ball milling. It is found that the dehydrogenation properties of LiBH4 are remarkably enhanced by doping the as-synthesized metal oxide nanorods. When the mass ratio of LiBH4 and oxides is 1:1, the NiCo2 O4 nanorods display the best catalytic performance owing to the mesoporous rod-like structure and synergistic effect of nickel and cobalt active species. The initial hydrogen desorption temperature of the LiBH4 -NiCo2 O4 composite decreases to 80 °C, which is 220 °C lower than that of pure LiBH4 , and 16.1 wt % H2 is released at 500 °C for the LiBH4 -NiCo2 O4 composite. Meanwhile, the composite also exhibits superior dehydrogenation kinetics, which liberates 5.7 wt % H2 within 60 s and a total of 12 wt % H2 after 5 h at 400 °C. In comparison, pure LiBH4 releases only 5.3 wt % H2 under the same conditions.

A Novel Approach to Synthesise a Dual-Mode Luminescent Composite Pigment for Uncloneable High-Security Codes to Combat Counterfeiting.

A strategy is demonstrated to protect valuable items, such as currency, pharmaceuticals, important documents, etc. against counterfeiting, by marking them with luminescent security codes. These luminescent security codes were printed by employing luminescent ink formulated from a cost effective dual-mode luminescent composite pigment of Gd1.7 Yb0.2 Er0.1 O3 and Zn0.98 Mn0.02 S phosphors using commercially available PVC Gold medium. In the composite, Gd1.7 Yb0.2 Er0.1 O3 and Zn0.98 Mn0.02 S account for upconversion and downconversion processes, respectively. The synthesis procedure of the composite involves the admixing of Gd1.7 Yb0.2 Er0.1 O3 nanorods and Zn0.98 Mn0.02 S phosphor, synthesised by hydrothermal and facile solid-state reaction methods, respectively. The structural, morphological, microstructural, and photoluminescent features of Gd1.7 Yb0.2 Er0.1 O3 nanorods, Zn0.98 Mn0.02 S phosphor and composite were characterised by using XRD, SEM, TEM, and photoluminescence (PL) techniques, respectively. The distribution of PL intensity of the printed pattern was examined by using confocal PL mapping microscopy. The obtained results reveal that security codes printed using ink formulated from this bi-luminescent composite pigment provide dual-stage security against counterfeiting.

Engineering Magnetic and Tunneling Magnetoresistance Properties of CoxFe3−xO4 Nanorods

A simple cation exchange reaction has been adapted to produce the CoxFe3−xO4 nanorods with different concentration of Co. The substitution of Fe2+ with Co2+ ions increase the magnetocrystalline anisotropy and coercivity of pristine superparamagnetic Fe3O4 nanorods. Atomic concentration of 5–11% of Co2+ in Fe3O4 nanorods renders coercivity of 300–460 Oe at room temperature and 2200–4050 Oe at 10 K. Hydrocarbon long‐chain amine (oleylamine) functionalized nanorod assemblies form a multiple tunnel junction, where organic amine monolayers act as insulating tunnel barriers. CoxFe3−xO4 nanorods show a magnetoresistance switching behavior at room temperature and the switching field is consistent with the magnetic coercivity. A 14–15% TMR is recorded at room temperature in CoxFe3−xO4 nanorod assemblies, which increases to 23–26% at 150 K at a magnetic field of ±2 T. The calculated spin polarization for Co0.33Fe2.67O4 nanorods at room temperature is 52%. A similar spin polarization and TMR as Fe3O4 in Co‐doped Fe3O4 nanorod assemblies is obtained. Thus, controlled doping of Co ions engineers the coercivity and remanence of the “super‐paramagnetic” Fe3O4 without hindering their TMR performances, which could be very useful for memory devices.

Enhanced cycling properties and better rate capabilities of Al-doped LiMn2O4 nanorods and nanospheres

The paper reports a facile synthesis of Al-doped LiMn2O4 nanorods and the oleic-acid-treated LiMn2O4 nanospheres without the use of MnO2 as templates in a single step solution combustion process. The as synthesized pristine LiMn2O4, LiMn1.6Al0.4O4 nanorods and LiMn1.6Al0.4O4 nanospheres are characterized for the structural and morphological characteristics by using x-ray diffraction spectroscopy (XRD), energy-dispersive x-ray spectroscopy (EDX) and field effect scanning electron microscopy (FESEM). The LiMn2O4 pristine sample and Al-doped LiMn2O4 nanorods and nanospheres have been explored as lithium ion battery cathodes. The results reveal the enhanced structural and electrochemical properties of the samples with the Al-doping. The oleic acid treated sample shows the best cycling properties and higher rate capabilities even at large discharge current rates of up to 2000 mA g−1.

Multicolour and nearly white light emission in YP0.8V0.2O4:Sm3+ nanorods: Controlled energy transfer

Nanorods of YP0.8V0.2O4:Sm3+ have been synthesized under hydrothermal conditions. Substitution of vanadium (V5+) sites in YVO4 by phosphorus ions (P5+) has been confirmed by Fourier transform infrared spectroscopy, X-ray diffraction and transmission electron microscopy. Careful selection of Sm3+ concentration in YP0.8V0.2O4 enables to achieve the controlled energy transfer from the VO43− absorption to the excited states of Sm3+ ions. The controlled energy transfer has been confirmed from the steady state luminescence and decay lifetime studies of VO43− emission. With the controlled retention of VO43− emission, tuning of light emission from the singly (Sm3+) doped YP0.8V0.2O4 nanorods is realized. At a particular doping concentration of Sm3+ (1.25 at.%), a nearly white light emission is observed. The quantum yield of this nearly white light emission is found to be ∼28%. Tunability of the light and white light emission are supported by CIE chromaticity. The energy transfer efficiency from the VO43− absorption to the excited states of Sm3+ ion in YP0.8V0.2O4 reaches upto ∼86% with the doping concentration of 2.25 at.%.

High-Performance 2.6 V Aqueous Asymmetric Supercapacitors based on In Situ Formed Na0.5 MnO2 Nanosheet Assembled Nanowall Arrays.

The voltage limit for aqueous asymmetric supercapacitors is usually 2 V, which impedes further improvement in energy density. Here, high Na content Birnessite Na0.5 MnO2 nanosheet assembled nanowall arrays are in situ formed on carbon cloth via electrochemical oxidation. It is interesting to find that the electrode potential window for Na0.5 MnO2 nanowall arrays can be extended to 0-1.3 V (vs Ag/AgCl) with significantly increased specific capacitance up to 366 F g-1 . The extended potential window for the Na0.5 MnO2 electrode provides the opportunity to further increase the cell voltage of aqueous asymmetric supercapacitors beyond 2 V. To construct the asymmetric supercapacitor, carbon-coated Fe3 O4 nanorod arrays are synthesized as the anode and can stably work in a negative potential window of -1.3 to 0 V (vs Ag/AgCl). For the first time, a 2.6 V aqueous asymmetric supercapacitor is demonstrated by using Na0.5 MnO2 nanowall arrays as the cathode and carbon-coated Fe3 O4 nanorod arrays as the anode. In particular, the 2.6 V Na0.5 MnO2 //Fe3 O4 @C asymmetric supercapacitor exhibits a large energy density of up to 81 Wh kg-1 as well as excellent rate capability and cycle performance, outperforming previously reported MnO2 -based supercapacitors. This work provides new opportunities for developing high-voltage aqueous asymmetric supercapacitors with further increased energy density.

CdS/Zr:Fe2O3 Nanorod Arrays with Al2O3 Passivation Layer for Photoelectrochemical Solar Hydrogen Generation

CdS-sensitized 1 D Zr:Fe2 O3 nanorod arrays were synthesized on fluorine-doped tin oxide substrates by a two-step hydrothermal method. The photoelectrochemical results demonstrate that the current density (4.2 mA cm-2 at 0 V vs. Ag/AgCl) recorded under illumination for the CdS/1 D Zr:Fe2 O3 photoanodes is 2.8 time higher than the bare 1 D Zr:Fe2 O3 . The extended absorbance spectrum, the reduced recombination, and the effective transport of photogenerated holes in CdS to the electrolyte facilitate enhancement in the photoelectrochemical performance. From X-ray photoelectron spectroscopy and TEM observations of the bare and aluminum oxide-treated CdS/1 D Zr:Fe2 O3 photoanodes, we could confirm that the 1 D Zr:Fe2 O3 nanorods were covered by the CdS layer and Al2 O3 layer present on surface of CdS. Furthermore, the photocurrent and stability of the CdS/1 D Zr:Fe2 O3 nanorods was significantly enhanced by Al2 O3 compared to bare CdS/1 D Zr:Fe2 O3 heterojunction owing to its ability to act as an effective holetransport- as well as photocorrosion-protecting layer. These remarkable enhancements in light-energy harvesting, improvement in charge transport, and stability directly suggest the usefulness of photoanodes for solar hydrogen generation.

Synthesis and enhanced gas sensing properties of flower-like ZnO/α-Fe2O3 core-shell nanorods

This paper reports a facile two-step synthesis route for the preparation of flower-like ZnO/α-Fe2O3 nanorods (NRs). Flower-like ZnO NRs with the average diameter about 810nm and length about 4.5µm were firstly synthesized via a chemical solution method, and then ZnO NRs was coated with a continuous α-Fe2O3 layer to form ZnO/α-Fe2O3 core-shell structure through an ionic-layer adsorption and reaction method. The gas-sensing results show that the ZnO/α-Fe2O3 NRs exhibit excellent sensitivity, selectivity, and response-recovery capacity to ethanol vapor at a low optimum temperature of 240°C. In particular, compared with pure ZnO NRs and α-Fe2O3 nanoparticles (NPs), the ZnO/α-Fe2O3 NRs show an obvious improvement in gas sensing properties. The substantial improvement of sensing properties may be attributed to the unique microstructure and heterojunction formed between ZnO and α-Fe2O3.

Iron-cobalt bimetal oxide nanorods as efficient and robust water oxidation catalysts.

Cobalt-based oxides are considered as potential water oxidation catalysts for future artificial photosynthetic systems because of their high abundance, strong stability and efficient performance. Herein, a series of cobalt-based oxides, MnCo3-nO4 (M = Mn, Fe, Co) samples, were synthesized through changing the metal sources by a low-temperature coprecipitation method. These catalysts were investigated under photochemical and electrochemical water oxidation conditions. And they all exhibited efficient activity for water oxidation under alkaline, acidic and neutral conditions under visible light irradiation. An excellent O2 yield of 90.4% for Fe-Co bimetal oxide (Fe1.1Co1.9O4) nanorods was obtained under optimal conditions (photoirradiation at λ ≥ 420 nm, [Ru(bpy)3](ClO4)2 as the photosensitizer, Na2S2O8 as the oxidant in borate buffer at pH = 9.0, bpy = 2,2-bipyridine). Among MnCo3-nO4 samples, Fe1.1Co1.9O4 nanorods were proved to be the optimal electrocatalytic water oxidation catalyst as well. Multiple experiments (SEM, FT-IR, XRD, XPS, Bulk electrolysis) were used to test the stability of Fe1.1CO1.9O4 and these results indicate that Fe1.1CO1.9O4 nanorods are highly stable. Furthermore, based on Mott-Schottky and cyclic voltammetry analysis, the best balanced flat-band potential of Fe1.1CO1.9O4 nanorods is just located at the middle position between the oxidation potential of O2/H2O and the half-wave potential of [Ru(bpy)3]3+/2+, which was probably responsible for their superior photocatalytic water oxidation performance.

Synthesis and Characterization Studies of Pb:Zr:/O2 Nanorods for Optoelectronic Applications

Synthesis and Characterization Studies of Pb:Zr:/O2 Nanorods for Optoelectronic Applications In the present work, we have synthesized ZrO2 doped PbO2 nanocrystals were successfully prepared by hydrothermal method which is Zirconium nitrate hydrate (Zr(NO3)4.5H2O) and lead nitrate (Pb(NO3)2) were used as a precursor. In the experimental results show that the amount of Iodine (I) and the NaOH concentration plays a important roles in the formation of hexagonal defined amount of ethylene glycol at 900 °C within 21 hrs. In the physiochemical properties of Zr doped lead oxide nanorod were determined by using X-ray diffraction (XRD), ultraviolet–visible spectroscopy (UV-vis), Fourier Transform Infrared spectroscopy (FTIR) and Transmission electron microscope (TEM). In Zr doped Pb oxide nanorods were the highest photon activity under both UV and visible light irradiation.