Metal Oxide Nanostructures Research Articles

Ag and Cr oxide nanodots sputter decorated over Mn-Co-Cu ternary metal oxide nanostructures for high-performance supercapacitor

Hybrid nanostructures of quaternary composite of transition metal oxides (QCTMO) are fabricated by sputter depositing nano-dots of silver oxide or chromium oxide over flower-like nanostructures of manganese-cobalt-copper (MCC) ternary metal oxide. QCTMO electrodes are fabricated by magnetron assisted DC sputtering using different plasma powers. The presence of four different multivalent metal ions increases the redox sites, while the hybrid nature of the nanostructures increases the electrochemically active surface area. The synergistic effects result in enhancing the performance of the electrode. We showed that plasma power can be used to control the morphology and electrochemical properties of QCTMO electrodes. Chromium oxide nano-dots sputter deposited over MCC at 65 W showed the best performance with specific capacitance of 2261 F g−1 at a scan rate of 1 mV s−1 and specific capacity of 603 C g−1 at 5 mA cm−2. Solid-state symmetric supercapacitor fabricated with this electrode shows a retention in capacitance of 93 % after 4000 charge-discharge cycles and high energy density of 106 W h kg−1 at 3236.3 W kg−1 of power density.

Hierarchical SnO2 nanoparticles designed based on in situ derivatization strategy for rapid and sensitive imidacloprid detection

Designing sensitive and rapid sensing platforms for detection of pesticide residues is essential for food safety. Herein, we designed and synthesized the hierarchical SnO2 nanoparticles on carbon cloth (SnO2/CC) for the electrochemical detection of imidacloprid (IDP) based on in situ derivatization strategy. The hierarchical structure of SnO2/CC can maintain the original nanosheet morphology of SnS2 and prevent the aggregation of SnO2 nanoparticles, which endows SnO2/CC with a large specific surface area, abundant active sites, and fast electron transfer, which is beneficial to improve its electrocatalytic performance. Electrochemical studies showed that SnO2/CC exhibited favorable sensing performance for IDP under optimized conditions, including a linear range of 0.5–60 μM, extremely high sensitivity of 60.88 μA μM−1 cm−2, and a low detection limit of 0.056 μM. Additionally, the electrode was verified to have satisfactory feasibility by detecting IDP in grape and apple samples. This work opens a new perspective for the fabrication of high-performance IDP electrochemical sensors based on hierarchical nanostructured metal oxide.

Metal Oxides Nanoparticles: General Structural Description, Chemical, Physical, and Biological Synthesis Methods, Role in Pesticides and Heavy Metal Removal through Wastewater Treatment

Nanotechnology (NT) is now firmly established in both the private home and commercial markets. Due to its unique properties, NT has been fully applied within multiple sectors like pharmacy and medicine, as well as industries like chemical, electrical, food manufacturing, and military, besides other economic sectors. With the growing demand for environmental resources from an ever-growing world population, NT application is a very advanced new area in the environmental sector and offers several advantages. A novel template synthesis approach is being used for the promising metal oxide nanostructures preparation. Synthesis of template-assisted nanomaterials promotes a greener and more promising protocol compared to traditional synthesis methods such as sol-gel and hydrothermal synthesis, and endows products with desirable properties and applications. It provides a comprehensive general view of current developments in the areas of drinking water treatment, wastewater treatment, agriculture, and remediation. In the field of wastewater treatment, we focus on the adsorption of heavy metals and persistent substances and the improved photocatalytic decomposition of the most common wastewater pollutants. The drinking water treatment section covers enhanced pathogen disinfection and heavy metal removal, point-of-use treatment, and organic removal applications, including the latest advances in pesticide removal.

Silk and its composites for humidity and gas sensing applications.

Silk fibroin (SF) is a natural protein largely used in the textile industry with applications in bio-medicine, catalysis as well as in sensing materials. SF is a fiber material which is bio-compatible, biodegradable, and possesses high tensile strength. The incorporation of nanosized particles into SF allows the development of a variety of composites with tailored properties and functions. Silk and its composites are being explored for a wide range of sensing applications like strain, proximity, humidity, glucose, pH and hazardous/toxic gases. Most studies aim at improving the mechanical strength of SF by preparing hybrids with metal-based nanoparticles, polymers and 2D materials. Studies have been conducted by introducing semiconducting metal oxides into SF to tailor its properties like conductivity for use as a gas sensing material, where SF acts as a conductive path as well as a substrate for the incorporated nanoparticles. We have reviewed gas and humidity sensing properties of silk, silk with 0D (i.e., metal oxide), 2D (e.g., graphene, MXenes) composites. The nanostructured metal oxides are generally used in sensing applications, which use its semiconducting properties to show variation in the measured properties (e.g., resistivity, impedance) due to analyte gas adsorption on its surface. For example, vanadium oxides (i.e., V2O5) have been shown as candidates for sensing nitrogen containing gases and doped vanadium oxides for sensing CO gas. In this review article we provide latest and important results in the gas and humidity sensing of SF and its composites.

New Advances into Nanostructured Oxides

Inorganic nanostructured (metal) oxides are a large class of inorganic materials extensively investigated for their unique and outstanding properties that allow for their use within a multitude of technological fields of emerging interest, such as (photo)catalysis, environmental remediation processes, energy storage, controlled transport and/or release of drugs and chemicals, biomedicine, sensing, development of smart materials, stimuli-responsive materials, and nanocomposites [...]

GAS SENSORS BASED ON METAL OXIDE NANOPARTICLES AND THEIR APPLICATION FOR ENVIRONMENTALLY HAZARDOUS GASES DETECTION A MINI-REVIEW

Hazardous gases have adverse effects on living organisms and the environment. They can beclassified into two categories, i.e. toxic gases (e.g. H2S, SO2, CO, NO2, NO and NH3) and greenhousegases (e.g. N2O, CH4 and CO2). Moreover, their presence in confined areas may lead to fireaccidents, cause serious health problems or even death. Therefore, monitoring of these substanceswith gas sensors allows assessing the quality of the atmosphere, helps avoiding accidents and saveslives. Metal oxide semiconductor gas sensors (MOS) are one of the most popular choices for theseapplications owing to their numerous advantages, i.e. high sensitivity, long lifetime and shortresponse time. However, these devices have their limitations as well. They exhibit baseline drift,sensor poisoning and poor selectivity. Although much has been done in order to deal with thoseproblems, the improvement of MOS sensors continues to attract researchers attention.The strict control of gas sensing materials preparation is one of the approaches that helps to improveMOS sensors performance. Nanomaterials have been found to be more suitable candidates for gasdetection than materials designed at microscale. Moreover, it was found that the regular and orderedmorphology of metal oxide nanostructures, their loading with noble metals, or the formation ofheterojunctionscan exert additional influence on the properties of these nanostructures andimprove their gas sensing performance, which will be described in the following sections of thispaper. Following a discussion of the operation principle of MOS sensors, a comprehensive review ofthe synthesis and application of metal oxide nanoparticles in the construction of the MOS sensorsdedicated for environmentally hazardous gases is presented. The paper discusses also present issuesand future research directions concerning application of nanotechnology for gas sensing.

Correction: Recent progress in the fabrication of nanostructured zinc-based ternary metal oxides for high-performance lithium-ion batteries

Correction: Recent progress in the fabrication of nanostructured zinc-based ternary metal oxides for high-performance lithium-ion batteries

WO3 Nanorods Decorated with Very Small Amount of Pt for Effective Hydrogen Evolution Reaction

The electrochemical hydrogen evolution reaction (HER) is one of the most promising green methods for the efficient production of renewable and sustainable H2, for which platinum possesses the highest catalytic activity. Cost-effective alternatives can be obtained by reducing the Pt amount and still preserving its activity. The Pt nanoparticle decoration of suitable current collectors can be effectively realized by using transition metal oxide (TMO) nanostructures. Among them, WO3 nanorods are the most eligible option, thanks to their high stability in acidic environments, and large availability. Herein, a simple and affordable hydrothermal route is used for the synthesis of hexagonal WO3 nanorods (average length and diameter of 400 and 50 nm, respectively), whose crystal structure is modified after annealing at 400 °C for 60 min, to obtain a mixed hexagonal/monoclinic crystal structure. These nanostructures were investigated as support for the ultra-low-Pt nanoparticles (0.2-1.13 μg/cm2): decoration occurs by drop casting some drops of a Pt nanoparticle aqueous solution and the electrodes were tested for the HER in acidic environment. Pt-decorated WO3 nanorods were characterized by performing scanning electron microscopy (SEM), X-ray diffraction analysis (XRD), Rutherford backscattering spectrometry (RBS), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry. HER catalytic activity is studied as a function of the total Pt nanoparticle loading, thus obtaining an outstanding overpotential of 32 mV at 10 mA/cm2, a Tafel slope of 31 mV/dec, a turn-over frequency of 5 Hz at -15 mV, and a mass activity of 9 A/mg at 10 mA/cm2 for the sample decorated with the highest Pt amount (1.13 μg/cm2). These data show that WO3 nanorods act as excellent supports for the development of an ultra-low-Pt-amount-based cathode for efficient and low-cost electrochemical HER.

Successful Growth of TiO2 Nanocrystals with {001} Facets for Solar Cells

The growth of nanocrystals (NCs) from metal oxide-based substrates with exposed high-energy facets is of particular importance for many important applications, such as solar cells as photoanodes due to the high reactivity of these facets. The hydrothermal method remains a current trend for the synthesis of metal oxide nanostructures in general and titanium dioxide (TiO2) in particular since the calcination of the resulting powder after the completion of the hydrothermal method no longer requires a high temperature. This work aims to use a rapid hydrothermal method to synthesize numerous TiO2-NCs, namely, TiO2 nanosheets (TiO2-NSs), TiO2 nanorods (TiO2-NRs), and nanoparticles (TiO2-NPs). In these ideas, a simple non-aqueous one-pot solvothermal method was employed to prepare TiO2-NSs using tetrabutyl titanate Ti(OBu)4 as a precursor and hydrofluoric acid (HF) as a morphology control agent. Ti(OBu)4 alone was subjected to alcoholysis in ethanol, yielding only pure nanoparticles (TiO2-NPs). Subsequently, in this work, the hazardous chemical HF was replaced by sodium fluoride (NaF) as a means of controlling morphology to produce TiO2-NRs. The latter method was required for the growth of high purity brookite TiO2 NRs structure, the most difficult TiO2 polymorph to synthesize. The fabricated components are then morphologically evaluated using equipment, such as transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), electron diffraction (SAED), and X-ray diffraction (XRD). In the results, the TEM image of the developed NCs shows the presence of TiO2-NSs with an average side length of about 20-30 nm and a thickness of 5-7 nm. In addition, the image TEM shows TiO2-NRs with diameters between 10 and 20 nm and lengths between 80 and 100 nm, together with crystals of smaller size. The phase of the crystals is good, confirmed by XRD. The anatase structure, typical of TiO2-NS and TiO2-NPs, and the high-purity brookite-TiO2-NRs structure, were evident in the produced nanocrystals, according to XRD. SAED patterns confirm that the synthesis of high quality single crystalline TiO2-NSs and TiO2-NRs with the exposed {001} facets are the exposed facets, which have the upper and lower dominant facets, high reactivity, high surface energy, and high surface area. TiO2-NSs and TiO2-NRs could be grown, corresponding to about 80% and 85% of the {001} outer surface area in the nanocrystal, respectively.

Synergistic Enhancement of CoMoO4@Ni(OH)2 Electrode Materials for High Performance Capacitors

Electrode materials with excellent electrochemical performance have been ascribed to the significant for energy storage devices. Nanostructures of metal oxides have attracted much attention in the field of supercapacitors because of their rapid charge transport processes. In this work, we prepared CoMoO4@Ni(OH)2 nanowire through a simple hydrothermal methods. The as-fabricated product exhibits a specific capacitance of 1026 Fg−1 at 1 Ag−1. In addition, the samples exhibited a good capacitance retention of 83% after 10000 cycles. This superior electrochemical performance can be ascribed to the unique spatial structure, demonstrating the potential application in next generation micro/nanodevices.

Facile preparation and antibacterial activity of zinc oxide nanobullets

Bacterial infections and emergence of many multidrug resistant bacterial pathogens are serious threats to human health. Nanostructured metal oxides are now used as antibacterial additives in various products of everyday usage, but their mode of antibacterial action still remains unclear. ZnO nanobullets were synthesized using a surfactant-free and template-free simple chemical route and well characterized by using FESEM, TEM, HRTEM, XRD, Raman and UV-vis spectroscopy. FESEM and TEM revealed bullet-shaped ZnO nanostructures with average size 50 nm. XRD analysis confirmed hexagonal wurtzite structure of ZnO nanobullets with crystallite size of 24 nm. We explored the antibacterial effects of ZnO nanobullets on gram-negative (Escherichia coli) and gram-positive (Bacillus oceanisediminis), and investigated the underlying mechanism using morphological analysis by SEM, ROS scavenging by histidine, thiobarbituric acid reactive species (TBARS) assay, analysis of potassium ion leakage and Bradford assay. Our results demonstrated that ZnO nanobullets efficiently inhibited the growth of both Escherichia coli and Bacillus oceanisediminis bacteria. Furthermore, various biochemical and molecular assays have provided evidence that the strong antibacterial action of ZnO nanobullets can be attributed to ROS induced oxidative stress resulting in enhanced lipid peroxidation and cell membrane damage, which subsequently caused protein leakage. In summary, our results show that ZnO nanobullets exhibit a strong antibacterial activity against both Escherichia coli and Bacillus oceanisediminis under ambient lighting, which is exciting for practical applications.

Drastic Gas Sensing Selectivity in 2-Dimensional MoS2 Nanoflakes by Noble Metal Decoration.

Noble metal nanoparticle decoration is a representative strategy to enhance selectivity for fabricating chemical sensor arrays based on the 2-dimensional (2D) semiconductor material, represented by molybdenum disulfide (MoS2). However, the mechanism of selectivity tuning by noble metal decoration on 2D materials has not been fully elucidated. Here, we successfully decorated noble metal nanoparticles on MoS2 flakes by the solution process without using reducing agents. The MoS2 flakes showed drastic selectivity changes after surface decoration and distinguished ammonia, hydrogen, and ethanol gases clearly, which were not observed in general 3D metal oxide nanostructures. The role of noble metal nanoparticle decoration on the selectivity change is investigated by first-principles density functional theory (DFT) calculations. While the H2 sensitivity shows a similar tendency with the calculated binding energy, that of NH3 is strongly related to the binding site deactivation due to preferred noble metal particle decoration at the MoS2 edge. This finding is a specific phenomenon which originates from the distinguished structure of the 2D material, with highly active edge sites. We believe that our study will provide the fundamental comprehension for the strategy to devise the highly efficient sensor array based on 2D materials.

Reduced graphene oxide decorated transition metal manganese vanadium oxide nanorods for electrochemical supercapacitors and photocatalytic degradation of pollutants in water

BackgroundGraphene-based nanostructured metal oxides have great attention in the field of electrochemistry and photochemistry due to their electrochemical, optical, and electronic properties. This Mn2V2O7-rGO hybrid catalyst demonstrated excellent stability and reusability, indicating that it is an efficient, cost-effective, and environmentally friendly catalyst. MethodsOur research aims to develop effective supercapacitor (SC) electrodes and photocatalysts by incorporating reduced graphene oxide (rGO) into manganese vanadium oxide (Mn2V2O7) nanorods to generate a Mn2V2O7-rGO hybrid composite via a single-step hydrothermal process. As prepared catalysts are investigated using different analytical methods such as optical, morphological, XPS, and ESR for radical analysis. Significant findingsThe Mn2V2O7-rGO nanorods coated on a carbon sheet exhibited a specific capacitance of 882 Fg−1 at 0.6 current density. The Mn2V2O7-rGO supercapacitor also exhibited long-term cyclic stability, with 88% of its original specific capacitance remaining after 2000 cycles. These findings open a new pathway for SCs as promising electrode materials. The Mn2V2O7-rGO hybrid was then tested for photocatalytic activity using ciprofloxacin (CIP). The photocatalytic reduction process destroyed >96% of the CIP after 60 min. The prepared catalyst was then used to investigate the electron transfer mechanism. The combination of rGO and Mn2V2O7 formed a conductive nano-network, yielding a highly active material.

Engineering of mixed metal oxides photocatalysts derived from transition-metal-based layered double hydroxide towards selective oxidation of cyclohexane under visible light

In this work, visible-light-driven mixed metal oxide nanostructures were synthesized selecting layered double hydroxide (LDHs) as precursors. Such LDHs-derived mixed metal oxide photocatalysts possessed distinct difference in cyclohexane oxidation under visible light, which was mainly due to the controllable composition of metal cations. Through the analysis of photocatalytic performances, it was figured out that, Cr0.2Mg3AlO showed the best catalytic activity among the series of photocatalysts, possessing 12.5% conversion and 96.7% recyclability for oxidation of cyclohexane. The superior oxidation performance of Cr0.2Mg3AlO was largely dependent on the formation of MgAlO/MgCr2O4 heterojunction, and it matched band structure could effectively enhance the absorption of visible light and the separation of electron-holes, and therefore accelerated the photocatalytic activity. This work provided an effective strategy for the preparation of highly efficient photocatalysts toward oxidation of cyclohexane.

Highly Heterogeneous Morphology of Cobalt Oxide Nanostructures for the Development of Sensitive and Selective Ascorbic Acid Non-Enzymatic Sensor

The surface tailored metal oxide nanostructures for the development of non-enzymatic sensors are highly demanded, but it is a big task due to the wide range of complexities during the growth process. The presented study focused on the surface modification of the heterogeneous morphology of cobalt oxide (Co3O4) prepared by the hydrothermal method. Further surface modification was conducted with the use of sodium citrate as a reducing and surface modifying agent for the Co3O4 nanostructures through the high density of oxygenated terminal groups from the citrate ions. The citrate ions enabled a significant surface modification of the Co3O4 nanostructures, which further improved the electrochemical properties of the Co3O4 material toward the design of the non-enzymatic ascorbic acid sensor in a phosphate buffer solution of pH 7.4. The morphology and crystal arrays of the Co3O4 nanostructures were studied by scanning electron microscopy (SEM) and powder X-ray diffraction (XRD) techniques. These physical characterizations showed the highly tailored surface features of Co3O4 nanostructures and a significant impact on the crystal properties. The electrochemical activity of Co3O4 was studied by chronoamperometry, linear sweep voltammetry, and cyclic voltammetry (CV) for the detection of ascorbic acid. The linear range of the proposed sensor was measured from 0.5 mM to 6.5 mM and a low limit of detection of 0.001 mM was also estimated. The presented Co3O4 nanostructures exhibited significant surface roughness and surface area, consequently playing a vital role toward the selective, sensitive, and stable detection of ascorbic acid. The use of a low cost surface modifying agent such as sodium citrate could be of great interest for the surface roughness and high surface area of nanostructured materials for the improved electrochemical properties for the biomedical, energy storage, and conversion systems.

Review on Metals and Metal Oxides in Sustainable Energy Production: Progress and Perspectives

The exponential population growth on earth has put an enormous strain on energy resources, which come in various forms like fossil fuels, geothermal energy, and so on. Currently, fossil fuels are fulfilling most of our energy requirements. However, their nonrenewable nature and the production of toxic and greenhouse gases have forced the research community to explore different renewable and nontoxic energy resources. Among different renewable energy resources, hydrogen is considered an important alternative energy source. However, the production of hydrogen (H2) from water is a nonspontaneous process. Therefore, different processes like photocatalysis and photoelectrocatalysis are employed to carry out the water splitting. For these processes, there is a dire need to develop different substances that can act as catalysts. For energy applications, different metals (particularly noble metals) and metal oxides (mostly transition metal oxides) have shown promising catalytic applications in the past decade. Herein, we discuss the progress made in the synthesis of metal and metal oxide nanostructures, followed by a discussion regarding the advances made in the application of these nanostructures as photocatalysts, electrocatalysts, and photoelectrocatalysts. From an energy application standpoint, it is found that doping and heterostructure development are the most advantageous methods used to date to improve the efficiency of metal and metal oxide nanostructures. Also, the development of dye-sensitized metal oxide catalysts for energy applications is considered a powerful method to develop highly efficient photocatalysts and electro-/photoelectrocatalysts. Finally, the limitations and challenges facing the practical application of these nanostructures are also discussed.

Recent progress in the fabrication of nanostructured zinc-based ternary metal oxides for high-performance lithium-ion batteries

Recent progress in the fabrication of nanostructured zinc-based ternary metal oxides for high-performance lithium-ion batteries

Modulation of the Work Function of TiO2 Nanotubes by Nitrogen Doping: Implications for the Photocatalytic Degradation of Dyes

The work function engineering in metal-oxide nanostructures by judicious doping of impurities is not straightforward as it introduces multiple defects in the system. In this regard, understanding the nitrogen (N) doping-induced modulation of Fermi levels in TiO2 nanotubes (TNTs) is challenging for visible-range photocatalytic applications. Here, 50 keV N ions are implanted in TNTs with a fluence range of 1014–1016 ions/cm2. X-ray diffraction and micro-Raman analyses demonstrate the formation of anatase-TiO2 in pristine TNTs, while the crystalline quality is significantly affected by increasing ion fluence. The evolution of Ti3+ is also established by X-ray photoelectron spectroscopy, whereas ultraviolet photoelectron spectroscopy reveals the reduction in work function due to the formation of oxygen vacancies, in good agreement with X-ray absorption spectroscopy and photoluminescence results. The electron paramagnetic resonance study further identifies the evolution of Ti3+/N-substitutional defect centers. Finally, an enhancement in visible-light-assisted methylene blue and Rhodamine B dye degradation is recorded up to a fluence of 1 × 1015 ions/cm2, and it is correlated with the N-ion implantation-induced formation of electrochemically active states near the conduction band minimum and the valence band maximum. The decrease in degradation efficiency beyond a critical fluence of 1015 ions/cm2 is discussed on the ground of ion-beam-mediated amorphization and the subsequent increase in electron–hole recombination in the defect states.

A Review of Transition Metal Compounds as Functional Separators for Lithium‐Sulfur Batteries

AbstractLithium‐sulfur (Li−S) batteries have great potential for the development of next‐generation high‐energy‐density secondary batteries owing to their high theoretical energy density, active material (sulfur) environmental friendliness, and low cost. However, their application is still impeded by the inherent sluggish kinetics and solubility of intermediate products of the sulfur cathode. Interface design is an important direction to address challenges in the development of Li−S batteries. The modification of the separator has been shown to effectively suppress the shuttling effect of physical hindrance or chemical bonding without affecting the utilization of active materials. This review encompasses the application of nanostructured transition metal oxides (TMOs), transition metal sulfides (TMSs), transition metal nitrides (TMNs), transition metal phosphides (TMPs), such as incorporating functional separators beyond the approach for preparing novel cathodes, and discusses their composites in a new multifunctional barrier layer for Li−S batteries. The objective properties of various metal compounds and the effect of the shuttle effect in particular on the electrochemical performance in Li−S batteries are highlighted, and give an outlook on the promising approaches for the construction of reliable Li−S batteries.

Plasmonic Properties of SrVO3 Bulk and Nanostructures

AbstractCorrelated metals, such as SrVO3 (SVO) or SrNbO3, are promising materials for optical devices such as transparent conductors. Here, a real‐space and reciprocal‐space electron‐energy‐loss‐spectroscopy (EELS) investigation of SVO bulk and nanostructures is reported. An intense 1.35 eV excitation with a weak energy dispersion is observed in the loss function and is attributed to a bulk plasmonic excitation from the 3d‐t2g orbitals. Ab initio calculations done within a time‐dependent density functional theory framework reveal that a 1.5 band renormalization is sufficient to reproduce quantitatively this d–d plasmon energy and dispersion. The corresponding localized surface plasmon (LSP) peaks are measured by EELS on various nanostructures and are compared to finite‐difference time‐domain simulations. These LSPs exhibit quality factors above canonical materials (e.g., indium tin oxide) in the near‐infrared regime, demonstrating that SVO is also a material of high interest for plasmonic applications. Finally, by phasing out the surface plasmon contribution with EELS collected at minute off‐dipolar conditions, the bulk‐type plasmonic values are retrieved with nanometrical resolution. Core–shelled electronic structures are then observed for nanorods designed by focused ion beam (FIB), revealing a bandgap opening due to FIB damage. It is envisioned that similar bulk measurement can be feasible for most of the transition metal oxide nanostructures.