Nanostructured Metal Oxide Materials Research Articles

Characterization and Photocatalytic and Antibacterial Properties of Ag- and TiOx-Based (x = 2, 3) Composite Nanomaterials under UV Irradiation.

Metal and metal oxide nanostructured materials have been chemically and physically characterized and tested concerning methylene blue (MB) photoremoval and UV antibacterial activity against Escherichia coli and Staphylococcus aureus. In detail, silver nanoparticles and commercial BaTiO3 nanoparticles were modified to obtain nanocomposites through sonicated sol-gel TiO2 synthesis and the photodeposition of Ag nanoparticles, respectively. The characterization results of pristine nanomaterials and synthetized photocatalysts revealed significant differences in specific surface area (SSA), the presence of impurities in commercial Ag nanoparticles, an anatase phase with brookite traces for TiO2-based nanomaterials, and a mixed cubic-tetragonal phase for BaTiO3. Silver nanoparticles exhibited superior antibacterial activity at different dosages; however, they were inactive in the photoremoval of the dye. The silver-TiOx nanocomposite demonstrated an activity in the UV photodegradation of MB and UV inhibition of bacterial growth. Specifically, TiO2/AgNP (30-50 nm) reduced growth by 487.5 and 1.1 × 103 times for Escherichia coli and Staphylococcus aureus, respectively, at a dose of 500 μg/mL under UV irradiation.

Physical properties of thermal annealing induced In2O3 thin films for sensing layer applications

Detection and monitoring of flammable, toxic and explosive gases are crucial, where active research on nanostructured metal oxide materials and thin films is enthusiastically performed to explore new paths for improving the characteristic parameters of sensors. The higher stability and appropriate electrical properties along with wide band gap of In2O3 material make it suitable for active layer to gas sensors where properties of In2O3 films could be engineered by post treatments. The present work demonstrates an influence of thermal annealing on structural, optical, topographical, morphological, elemental and electrical properties of In2O3 films for gas sensor applications. The In2O3 films of thickness 500 nm are grown onto soda lime glass and conducting ITO substrates employing physical vapor deposition based thermal evaporation technique followed by thermal annealing at 200 °C, 300 °C and 400 °C for one hour in air atmosphere. The XRD analysis indicated phase transformation from metastable rhombohedral to stable cubic phase where crystallite size corresponding to associated preferred (110) and (222) peaks is tuned in range of 32–51 nm with annealing. Optical analysis unveiled higher transmittance in ultraviolet and visible regions whereas absorbance of films is fluctuated with thermal annealing. All the In2O3 films indicated the Ohmic nature where the resistivity is detected to be enhanced with annealing. EDS patterns confirmed deposition of the films. The SEM analysis showed nanospheres like grain morphology and such well connected nanospheric features offer large surface area and stimulate adsorption of gas effectively. Hence structural, optical, electrical and morphological properties of gas sensitive In2O3 layers are greatly stimulated by thermal annealing.

Observing resistive switching behaviors in single Ta2O5 nanotube-based memristive devices

Recently, one-dimensional (1D) metal oxide nanostructured materials have attracted considerable attention owing to their appealing properties and functionalities. In previous studies, 1D metal oxide materials have been widely applied to electronic components; among them, resistive switching memristive devices are one of the most promising applications. The resistive switching mechanism in thin-film dielectric layers is widely explored, but understanding of that in 1D materials is insufficient. Moreover, a direct evidence regarding the switching behavior resulting from the formation and dissolution of conductive filaments is still lacking. In this study, a single Ta2O5 nanotube (NT) was fabricated as an Ag/Ta2O5 NT/Ag device, and its electrical properties were examined, which demonstrated a stable resistance state with a large memory window of approximately 107. The in-situ transmission electron microscopy (TEM), high-resolution TEM, energy dispersive spectroscopy techniques and electron energy loss spectroscopy (EELS) were used to establish a unique resistive switching mechanism in such devices for the first time. In addition, the crystallinity of the Ta2O5 NTs was well-controlled through rapid thermal annealing and furnace. The relationship between crystallinity and electrical properties was investigated. Oxygen vacancies play a crucial role in resistance switching, and thus, their amounts were determined using EELS. Therefore, the established mechanism revealed the dynamic behavior of Ta2O5 NTs in memristive devices, which allows the exploration of a wide range of NT materials for memory applications.

Facile h-MoO3 synthesis for NH3 gas sensing application at moderate operating temperature

One dimensional (1D) transition metal oxide nano-structured materials have high possibilities in the field of sensor applications. In the current work, we have investigated gas sensing response of the less explored hexagonal-Molybdenum Oxide (h-MoO3) for ammonia (NH3) gas. We have synthesized h-MoO3 nano-rods by facile chemical bath technique (CBT). To fabricate sensors, thin films were deposited on glass substrates using spin coating technique. Change in resistance of the film on NH3 exposure was recorded with time. The gas sensing response was measured at different concentration levels of NH3 ranging from 5 ppm to 100 ppm at 200 °C. We observed comparatively high sensing percentage for low to high concentration of NH3 gas at moderate operating temperature. h-MoO3 nano-structured rods based ammonia sensors lend a promising prospective in industrial applications like fertilizer, refrigeration industries etc.

RH Sensing by Means of TiO2 Nanoparticles: A Comparison among Different Sensing Techniques Based on Modeling and Chemical/Physical Interpretation

TiO2 nanoparticles coating has been proven to be an extremely performing sensing material for relative humidity (RH) measurements. The chemical activity of TiO2 toward water vapor adsorption and the very large surface to volume ratio typical of nanostructures are ideal characteristics for the development of RH fast and sensitive sensors. Different sensor technologies can be used in conjunction with this material to realize devices with satisfactory performance. In this paper, the authors aim to describe and discuss the main different possible choices and highlight the advantages and disadvantages, and linking them both to the underlying mechanism of water adsorption on the TiO2 sensing layer and to the modification of the electrical behavior due to the water adsorption. In particular, the authors start from results obtained by depositing TiO2 nanoparticles on a novel MEMS microbalance operating at low frequency, which allows to sense only the adsorbed water mass, and they exploit the sensor output to obtain a dynamic model of the water adsorption. They also link these results to those obtained with a Quartz Crystal Microbalance (QCM) functionalized with the same material operating at 10 MHz as a part of an oscillator. Finally, they establish a link with the results obtained by an RH impedance sensor, which exploits the same active material and the same deposition technique. With this sensor technology, the conductive and electrical behavior of the sensing and adsorbed films play a role. The whole work tries to unravel the different phenomena that contribute to the response of RH sensors not only based on TiO2 nanoparticles but also, more generally, based on nanostructured metal oxide materials.

Physio-Chemical Properties and Dielectric Behavior of As-Grown Manganese Oxide (γ-Mn2O3) Nanoparticles

Semiconducting metal oxide nanostructured materials are demonstrating efficient use and functional properties in devices. Manganese oxide (Mn2O3) is one of the smart semiconductor metal oxides. The hydrothermal method was found suitable to prepare γ-Mn2O3 nanoparticles. The nanostructural characterization using various advanced tools confirmed the purity and polymorph of the as-prepared γ-Mn2O3 nanoparticles. Optical analyses exposed the presence of a possible dual-band-gap in γ-Mn2O3 nanoparticles. A strong blue shift of 1.3 eV estimates the activation energy (Ea) of the nanoparticles. Furthermore, γ-Mn2O3 nanoparticles were used as dielectrics to explore the dielectric response of the material in a broad frequency domain (50 Hz–30 MHz). The dielectric spectroscopy analyses revealed the regular value of the dielectric constant (∼ 9) in the high-frequency domain, the low value of the tangent loss (0.05 ≤ tanδ ≥ 1.34), the frequency power law-dependent ac conductivity, the occurrence of single dielectric relaxation process of relaxation time 160 μs, and a non-Debye-type relaxation behavior in the γ-Mn2O3 nanoparticles. The properties assessed here indicate the functional-behavior and prospective application of the γ-Mn2O3 nanoparticles in devices.

Effect of Ni2+ doping on chemocatalytic and supercapacitor performance of biosynthesized nanostructured CuO

The synthesis of metal oxide nanostructured materials derived from plant extract embraces the futuristic design of an eco friendly system by reducing the hazardous toxic chemicals. In the present work, copper oxide nanoparticles (CuO NPs) and Ni2+ doped (0.003, 0.006 and 0.009 M) CuO NPs were prepared by green method using Azadirachta indica (A. indica) leaf extract. The XRD pattern reveals that the synthesized CuO NPs exhibits monoclinic structure. Nanoflower like morphology is observed in FESEM and TEM analysis. The oxidation states of Cu (2p), Ni (2p) and O (1s) have been identified in XPS spectra. The weight loss and thermal effects were investigated in TG–DSC analysis. The green synthesized materials effectively degrade the hazardous water pollutants like methylene blue, methyl orange and eosin yellow. The pseudocapacitive properties of CuO and Ni doped CuO NPs have been investigated through cyclic voltammetry and galvanostatic charge–discharge (GCD) studies. The Ni doped (0.009 M) CuO NPs exhibited high specific capacitance of 511 F/g at a current density of 1 A/g, and good reversibility with cycling efficiency of 88% after 3000 GCD cycles for S4 electrode, suggesting its use as promising electrode material in supercapacitors.

3D Conformal Modification of Electrospun Silk Nanofibers with Nanoscaled ZnO Deposition for Enhanced Photocatalytic Activity.

Nanostructured metal oxide materials have drawn great attention because of their enhanced semiconducting, electrical, optical, sensing, and chemical catalyzing properties. The application of metal oxides in biomedicine has recently emerged as a promising field, especially in the format of organic/metal oxide composites. However, the existing methods for fabricating organic/metal oxide materials revealed limitations on the precise control over the deposition of metal oxides and the maintenance of organic nanostructures. Here, we developed an approach for the fabrication of composite materials by depositing metal oxides on the nanostructured organic templates through atomic layer deposition (ALD). With this method, we fabricated a series of silk fibroin/ZnO composites at varied deposition temperatures. The results demonstrated that the ZnO layer had a 3D conformality and hexagonal wurtzite structure, and the deposition thickness was well controlled. The photocatalytic activity of silk/ZnO composites was confirmed by the photodegradation of Rh-B under UV exposure, and the efficiency was found to be temperature dependent. These results demonstrated the successful integration of organic materials with metal oxides through an easy and controllable approach for the development of multifunctional organic/metal oxide biomaterials.

Sputtered Synthesis of MnO2 Nanorods as Binder Free Electrode for High Performance Symmetric Supercapacitors

Among numerous active electrode materials, manganese oxides are promising electrodes in supercapacitors. Manganese oxides research has thus far focused on the synthesis of one-dimensional (1-D) metal oxide nanostructured materials, which can have superior electrochemical performance. Several chemical methods are used to synthesize metal oxide nanostructured which involve toxic reagents, solvents and introduction of byproducts. However, physical method offers an eco-friendly path to develop contamination free 1-D metal oxide nanostructured materials. Here, we report the fabrication of binder free supercapacitor electrode of MnO2 nanorods on Nickel (Ni) coated porous anodic aluminum oxide (AAO) by DC magnetron sputtering for first time. Ni coated porous AAO substrate act as excellent current collector, enhancing the specific capacitance of MnO2 to 649F/g. The binder free symmetric supercapacitor device delivered a high areal capacitance (112.6 mF/cm2), specific capacitance (194.23 Fg−1), good cyclic ability (89.83%) retention in capacitance after 5000 cycles), energy density (4.2 Whkg−1), and power density (1.4 kWkg−1 at 0.718 Whkg−1). These outstanding electrochemical performances, suggest their tremendous potential as supercapacitor electrode in energy storage application.

WO3 Nanograined Chemosensor: A Model of the Sensing Behavior

The sensing mechanism of resistive metal oxide gas sensors is quite complicated. Many factors determine the sensitivity and the response of these devices. In the past, many research works pointed out that an improved sensitivity and faster responses can be obtained, given a certain material, by using nano-grained or nanostructured metal oxide materials. This is due to the obvious reason that the grain size reductions imply the surface to volume ratio enhancement, and, consequently, the sensor response enhancement, being the sensing determined by surface phenomena. Actually, this intuitive explanation is not exhaustive, so in this paper the authors present a novel model for nano-grained metal oxide gas sensors, that is used to highlight the main factors influencing their sensing properties. The developed model, describing spherical grains, is applied to WO3 for NO2 detection, and is compared with different models already in the literature. What emerges as an interesting result is that the usual model of large grained films can give a rough but meaningful idea of the sensor sensitivity magnitude, whereas more fine models have to be used in order to predict some peculiar behaviors related to nano-sized grains.

Unveiling the Reaction Mechanism of Metal Oxide Based Anode Materials with High Abnormal Capacity for Lithium-Ion Batteries By Using Synchrotron X-Ray Techniques

Graphitic carbon is extensively used as anode material in most of the commercial lithium-ion batteries due to its low cost and high coulombic efficiency. However, capacity of carbon anode (372mAh/g and 830mAh/mL) is limited by the reversible electrochemical intercalation of lithium ions in its structure. So, alternative research directions and different anode materials are currently being investigated with an aim to achieve high capacity and cycling stability. Recently, nano-material research has shed light on many high performing materials. Among these, metal oxide based materials such as SnO2, MoO2, Co(OH)2 have been recognized as one of the potential candidates for anode material of lithium–ion batteries because of its higher specific lithium storage capacity [1, 2, 3]. But, their poor capacity retention over long-term charge-discharge cycling due to low electrical conductivity has prevented its use as commercial anode material in lithium-ion batteries. Furthermore, during the electrochemical cycling, metal oxides typically break into small metal clusters, resulting in a large volume expansion and a loss of capacity [4]. For improving the performance of metal oxide based materials, nanostructured materials have received much attention as battery electrodes due to the short transport lengths for both electrons and Li ions, higher electrode-electrode contact area, and better accommodation of the strain of Li insertion/extraction [5]. Although there have been reports in the electrochemical behavior and performance improvement on metal oxide based anode materials for lithium ion batteries, it is still difficult to prove the reaction mechanism and abnormal capacity clearly. For accurate explanation of reaction mechanism and abnormal capacity, it is important to analyze each region systematically. Herein, we successfully synthesized nano-structured metal oxide materials through simple synthetic strategy. This research also included its novel reaction mechanism during electrochemical cycling with lithium. Structure and electrochemical properties of synthesized material were studied by diverse electrochemical tests, combination of the synchrotron radiation XRD and XAS techniques. Especially, the changes in the local structures during cycling were investigated systematically on the basis of XAS analysis. Based on these results, novel reaction mechanism about the nano-structured metal oxide based anode material during electrochemical cycling was suggested specifically. This finding will not only be helpful in a more complete understanding of the reaction mechanism of metal oxide based anode materials but also will offer valuable guidance for developing new anode materials with abnormal high capacity for next generation rechargeable batteries. More detailed discussion will be presented at the time of meeting. [1]. Dong, Q et al., Materials Research Bulletin, 2011. 46(8): p. 1156-1162. [2]. I. A. Courtney and J. R. Dahn, J. Electrochem. Soc., 1997, 144, 2045 [3]. Wang, Z. Y et al., Chem. Commun. 2010, 46, 6906−6908 [4]. Poizot, P et al., Nature 2000, 407, 496−499 [5]. Maier, J et al., Nat. Mater. 2005, 4, 805−815.

Evidence of Extra Capacity in Conversion Reaction of Ruthenium Oxide: A Cyclic Voltammetry Study

ABSTRACTSynthesis and understanding of metal oxide nanomaterials with improved electrochemical properties can play a big role in the development of high capacity electrochemical cells for application in lithium-ion batteries (LIBs). Metal oxide nanostructured materials have shown exceptional storage capabilities through conversion reaction. But, excess reversible capacity is usually observed in these systems. To understand the origin of the excess capacity, we have prepared nanostructured ruthenium oxide (RuO2) directly on stainless steel current collectors using low pressure chemical vapor deposition. The crystal structure of the as-prepared materials were examined by powder X-ray diffraction and indexed to the rutile structure. Field emission scanning electron microscopy revealed 3D pyramidal shape architectures that self-assembled into columns creating high surface area. Galvanostatic charge-discharge measurements were performed versus Li/Li+ in the range of 4.0 to 0.1 V. We have observed a reversible capacity of 1150 mAh/g which is equivalent to 5.70 Li per mol of RuO2. The expected capacity of RuO2 is 806 mAh/g which is approximately 4 Li per mol of RuO2 based on this equation: RuO2 + Li + 4e- ↔ Ru0 + 2Li2O. The excess capacity is approximately 435 mAh/g. The origin of the excess capacity was investigated using cyclic voltammetry, which was performed at two different range of voltage.

The Fabrication of NiO Microtubes Using Bacillus subtilis/Bacteria

The nickel oxide microtubes with high surface-to-volume ratio have been achieved using the Bacillus subtilis bacteria. Surface properties of the metal-oxide nanostructured materials were investigated by electron microscopy. The surface area of that was also studied by the Brunauer Emmett Teller analysis method. The materials were used at the construction of supercapacitor as an electrode active material.

Raman scattering study of IrxRu1−xO2 mixed metal oxide nanowires (0 ≤ x ≤ 1)

Recent interests in mixed metal oxide nanostructured materials especially IrxRu1−xO2 compounds have been mainly driven by the technological application as electrocatalyst and electrode materials. We present room temperature Raman scattering results of single crystalline IrxRu1−xO2 (0 ≤ x ≤ 1) nanowires grown by atmospheric pressure chemical vapor deposition. We observed that the Eg, the A1g, and the B2g phonon modes of a single IrxRu1−xO2 nanowire are blue-shifted linearly with respect to the Ir contents from which we could get stoichiometry information. We also observed that the asymmetric lineshape and the broadening of the full width at half maximum of the Eg mode that involves the out-of-plane oxygen vibration. The unusual asymmetric broadening of the Eg phonon can be explained by the activation of the non-zone-center phonons due to substitutional disorder present in the system. We also found that there is a mixed mode of the A1g and the B2g phonons due to the substitutional disorder, in the range of 630–750 cm−1.

Monolithic co-aerogels of carbon/titanium dioxide as three dimensional nanostructured electrodes for energy storage

Conductive fillers, such as amorphous carbon, carbon nanotube and graphene etc., are generally mixed with nanostructured metal oxide materials to improve the performance of electrode materials in energy storage devices. However, the conductive framework that provides path for electric conduction does not normally form a well-connected and robust 3-D network to ensure optimized ions transport. Here, we report a convenient, inexpensive and scalable method for synthesizing hybrid carbon and titanium dioxide co-gels and co-aerogels to improve the electrochemical capacity by combining both the lithium insertion and the surface storage mechanisms in Li ion batteries (LIBs) anodes. A monolithic piece of a hybrid C/TiO2 co-aerogel can be directly used as an active electrode without the addition of binders, such as polyvinylidene fluoride (PVDF). As a result, the performance of LIB anodes using the hybrid co-aerogel is significantly improved over current LIBs based on carbon/titanium oxide composites. The reversible discharge capacity was stabilized at ∼400 mAh g−1 at a 168 mA g−1 scan rate and an operating voltage between 3.0 and 0.05 V vs. Li+/Li with excellent cyclic capacity retention. This approach, however, is not limited to only C/TiO2 system but can be extended to other metal oxides to form co-gels with carbon to improve their potential use in numerous electrochemical, photocatalytic, and photoelectronic devices.

Metal Oxides Mono‐Dimensional Nanostructures for Gas Sensing and Light Emission

The present Review opens with an overview of metal oxides and the description of their material properties. The first part mainly deals with various preparation techniques and growth mechanisms, which have been largely developed in the last few decades to fabricate different types of metal oxide nanostructures. The second part, on the other hand, will provide the Reader with an up‐to‐date summary of different applications in which metal oxides nanostructures have been successfully implemented and/or suggested. In particular, great attention will be dedicated to the implementation of metal oxide nanostructures for gas sensing as well as light emission applications, for which both working principles and integration, as well as the latest reported cutting edge results are herein reported. Finally, we emphasize on the current potentials of metal oxide nanostructured materials and future challenges that this field in continuous expansion is currently facing.

Preparation of low temperature nano-structured ZnO and RhO2 on titanium substrates, and evaluation for phenol electro-catalytic oxidation

An approach based on a thermodynamical growth control concept of ZnO and RhO2 nano-structured metal oxides on a titanium substrate for electro-catalytic oxidation of phenol is demonstrated. These nano-structured metal oxide materials prepared via a low temperature thin film growth technique were characterized by scanning electron microscopy. The effect of the method employed, i.e. three-dimensional arrays, could be clearly seen in the estimated values of surface roughness. The scanning electron technique confirmed the sizes of the metal titanium oxide materials in the nano range: The diameter of the ZnO rods ranges from 50–150 nanometers and the lengths from 1–2 μm. The diameters of RhO2 showed oval structures from 10–100 nanometers. Thermogravimetric analyses showed that at 450 °C and 800 °C (the calcination temperature) no further structural changes occurred due to mass loss for ZnO and RhO2 respectively. Cyclic voltammetry (CV) showed that both the Ti/ZnO and Ti/RhO2 nano-structured electrodes can be used for phenol electro-catalytic oxidation and that the Ti/RhO2 electrode can also be used as a sensor for the detection of phenol.

Preparation of Helical Transition-Metal Oxide Tubes Using Organogelators as Structure-Directing Agents

We prepared novel transition-metal (Ti, Ta, V) oxide fibers with chiral, helical, and nanotubular structures. The nanostructured metal oxide materials were provided by the sol-gel polymerization of metal alkoxides using chiral self-assemblies of organogelators as structure-directing agents. The chiral structures of the metal oxide fibers can be created by the formation of chiral self-assemblies constructed by organogelators and the transcription of the organogel superstructure into metal oxides.