Metal Oxide Nanomaterials Research Articles

Green synthesis of doped Co3O4 nanocatalysts using organic template for fast azo dye degradation from aqueous environment

AbstractBACKGROUNDDuring recent years, great efforts have been devoted towards the functionalization of metal oxide nanomaterials with various carbonaceous groups to enhance their catalytic performance for environmental remediation applications such as dye degradation. Here, we synthesized Co3O4, Co3O4:NiO and Co3O4:PdO/Pd nanomaterials via organic compounds of Abies pindrow Royle following a hydrothermal route and then investigated them as catalysts for the degradation of methyl orange in aqueous solution in the presence of solar light as well as under dark ambient conditions.RESULTSThe chemical composition and phase analysis of Co3O4, Co3O4:NiO and Co3O4:PdO/Pd were confirmed using X‐ray diffraction, energy‐dispersive X‐ray spectroscopy and Raman spectroscopy, while spherical nanostructures were observed using field emission scanning electron microscopy. Carbon‐ and oxygen‐containing functional groups were revealed using Fourier transform infrared spectroscopy and gas chromatography–mass spectrometry. The catalytic efficiency of the functionalized nanocatalysts was enhanced to 99% and 98% by incorporation of NiO and PdO/Pd, respectively, within 15 min in the presence of solar light. Whereas, under dark conditions, the degradation efficiency of Co3O4:PdO/Pd and Co3O4:NiO was calculated as 75% and 77%, respectively. The catalysts demonstrated excellent reusability in four cycles of experiments with pseudo‐first‐order kinetics (R2 < 1) in the light and under dark conditions.CONCLUSIONSThe findings demonstrated an efficient and sustainable bio‐templated synthesis of nanocatalysts for removal of organic dyes from aqueous environment. The excellent photocatalytic potential of phytosynthesized Co3O4:PdO/Pd and Co3O4:NiO was attributed to nanostructures as well as to incorporated carbonaceous compounds. © 2020 Society of Chemical Industry

Formation of Metal–Oxide Nanostructures during Oxidation of Cuts of Plastically Deformed Iron

The morphology and composition of an oxide layer on the surface of iron chipping cuts obtained using metal-working under conditions of intense plastic shear deformation and subsequent thermal oxidation have been investigated by scanning electron microscopy with an X-ray probe, Raman spectroscopy, and thermogravimetry. It is shown that agglomerations of metal–oxide nanoparticles and nanostructures (whiskers, nanotips, and nanoleaves), which are promising for production of new composites with ultra-fine-grained metal–oxide filler, are formed with a high rate on the surface of metal chippings during annealing in air at 800°C. The economic and ecological benefits due to recycling of metalworking wastes for producing new metal–oxide nanomaterials and related composites appear to be significant.

Suspended 1D Metal Oxide Nanowire Junction Networks for Use As Highly Sensitive Gas Sensors

Introduction Over the last few decades, research has been conducted to build sensitive, reliable and high-performance gas monitoring systems that meet the demands of industrial sites. In particular, 1D metal oxide (MOx) nanomaterials have been actively studied as a gas sensing material because of its excellent sensing performance, low cost, and suitability for a micro/nano device [1]. Besides, the MOx 1D nanostructures are relatively easy to synthesize, easy to control morphology and have various options including surface functionalization to make even further enhancement of the sensing performance [2]. In particular, when the MOx 1D nanostructures linked together and form a junction structure, an additional current path is generated through the formed junction and this forms additional potential barriers. Thus, an additional gas sensing mechanism can be utilized to further improve sensing performance as shown in Figure 1 [3]. In general, however, the fabrication process of MOx nanostructure networks including dense junctions requires complex and precise techniques. In addition, the nanostructure networks are positioned on the substrates. Therefore, gas access to the junctions and mass transfer to the sensing sites are limited. In this study, we report a novel gas sensor architecture including a suspended carbon mesh integrated with ZnO nanowires networks. The nanowires are grown on single carbon wires of the mesh and meet at the void regions of mesh structures. Thus, dese nanowire junctions can be formed in a suspended form (Figure 2). Owing to the suspended architecture, gas access to the sensing sites is effective and the sensing signal is free from the effect of the substrate [4]. The suspended carbon nanomesh was fabricated using the carbon-MEMS process consisting of simple photolithography and pyrolysis processes. The ZnO nanowire networks were precisely patterned at the suspended mesh using the hydrothermal method. The length of the nanowires was adjusted for good junction formation and the advantage of the suspended junctions was evaluated. Method Suspended carbon nanomesh was fabricated by photolithography and pyrolysis (Vacuum, 700°C) processes. Via two successive exposure steps in photolithography, suspended polymer mesh was defined without complex lithography techniques. After the pyrolysis process, microscale polymer mesh was converted into nano-sized carbon mesh because of the large volume reduction (up to 90%) in pyrolysis. After a thin ZnO seed layer was selectively coated on the suspended carbon mesh, ZnO nanowires were grown on the patterend seed layer by a hydrothermal process (Zn(NO3)2 25mM, HMTA 25mM ). The pristine ZnO nanostructures were annealed using RTA (N2 atmosphere, 300°C) for better adhesion and connection. Results and Conclusions Figure 2 shows the SEM images of the fabricated suspended carbon nanomesh (width ~140μm, thickness ~400nm, line spacing ~6μm) and ZnO nanowire networks (diameter ~100 nm, length ~3.5 μm). ZnO nanowires were well grown to form uniform and dense junctions. To characterize the effect of the nanowire junctions, NO2 gas sensing responses were compared between a nanomesh-based gas sensor and a single suspended carbon wire-based sensor. As shown in Figure 3. the suspend mesh-based sensor exhibited higher response and wider linear range due to the effect of junctions. This novel sensor architecture can be widely utilized because all the fabrication processes of the presented sensor were carried out at a wafer-level making it cost-effective and various MOx nanowires can be simple integrated with a bunch of junctions.

Ppb-Level of Ammonia Sensor on Reduced-Graphene Oxide Nanocomposite By the Supercritical Fluid Technique

Ammonia is an important indicator for the environment quality and agriculture safety applications. Besides, various medical reports have indicated that exhaled ammonia gas is considered to be a non-invasive biomarker of liver and kidney diseases. The exhaled ammonia gas concentration for healthy human is in the range of 200-2000 ppb [1], and for the environmental quality evaluation it should be lower than 50 ppb [2]. Due to the low concentration and the complicate sample gases, it is important to develop a highly sensitive and selective ammonia sensor. Several materials such as metal oxide, conducting polymer and carbon nanomaterials have been extensively examined for ammonia gas sensing. In this study, tungsten oxide and polyaniline was incorporated into easily functionalized reduced graphene in supercritical fluid to form a p-type nanocomposite. Metallic nanocatalyst was doped to enhance the sensitivity and selectivity. Ammonia was adsorbed onto the sensing membrane and then oxidized at room-temperature. Therefore, the resistance of sensing membrane increased with ammonia concentration. The sensor could detect the ammonia concentration in the range from 0 to 100 ppm at room temperature. The sensitivity was enhanced 4 times by the nanocatalyst, and the lower detection limit was 50 ppb. The effect of interference gases, including nitric oxide (NO), carbon monoxide (CO), carbon dioxide (CO2), sulfur dioxide (SO2) has been evaluated as well, and all the cross-talk was less than 10%. Furthermore, ammonia gas is highly water soluble, the sensing resistance could shift significantly with humidity, especially in higher humid atmosphere. In order to solve the problem, the electrode surface was designed to be more hydrophobic. After surface modification, the humidity effect decreased. The sensing mechanism of electrode and effect of humidity was also investigated. The experimental result suggested that the catalyst doped nanocomposite had high sensitivity, stability and selectivity for low concentration ammonia sensing at room temperature. A room temperature operated ppb-level ammonia sensor could be valuable solution for exhaled gas or environmental quality monitoring.[1] S. Abdulla, J. Dhakshinamoorthy, V. Mohan, D. V. Ponnuvelu, V. K. Kallidaikuruchi, L. M. Thalakkotil, B. Pullithadathil. J. Breath Res. 13 (2019) 046005; doi: https://doi.org/10.1088/1752-7163/ab278b[2] M. Insaustia, R. Timmis, R. Kinnersley , M. C. Rufino. Sci. Total Environ. (2019) 135124； doi: https://doi.org/10.1016/j.scitotenv.2019.135124.

Influence of metallic species for efficient photocatalytic water disinfection: bactericidal mechanism of in vitro results using docking simulation.

TiO2-based heterogeneous photocatalysis systems have been reported with remarkable efficiency to decontaminate and mineralize a range of pollutants present in air and water medium. In the present study, a series of visible light active metal oxide TiO2 nanoparticle were synthesized and evaluated for their photodegradation efficiency against emerging textile pollutant (Reactive Yellow 145) and antibacterial applications. In the first phase, nanomaterial synthesis was carried out following various synthesis parameters like addition of metallic impurities (different types and concentration) and calcination temperature. In the second phase, synthesized nanomaterials were screened for their performance in terms of photocatalytic degradation of RY145 and the best one (Fe-1-T-3 with 100% RY145 removal within 80min of irradiation) was further optimized against various reaction parameters. To get knowledge about the insights of nanomaterial performance for degradation of different environmental pollutants, the most important is to understand their physicochemical properties utilizing different characterization techniques. The physical morphology and elemental dispersion of metal-doped TiO2 nanomaterials were analyzed and results indicated that added metallic impurities were well dispersed onto the substrate surface. The efficient nanomaterials selected from initial screening were further assessed for photocatalytic disinfection efficiency against human pathogenic bacterial strains. Antimicrobial activities of the metal oxide nanomaterial were tested against gram-positive and gram-negative pathogenic bacterial strains. Possible mode of interaction of nanomaterial with bacterial DNA for bacterial cell inactivation was predicted using molecular docking simulation. The research project has the potential to contribute to multiple disciplines like material synthesis, water disinfection, and as green solutions for the textile industry replacing traditional technologies.

Suspended Heater Embedded Metal Oxide Nanowire Based Gas Sensor Platform

Introduction Over the past few decades, different types of gas sensors have been developed based on different sensing materials and methods. Among them, semiconducting metal oxide nanomaterials are suitable for gas sensing applications due to their high electron mobility, high surface-to-volume ratio, high crystallinity, and long-term stability. Considerable efforts have been made to improve the performance indicators of metal oxide gas sensors such as sensitivity, selectivity, reaction and recovery time [1]. However, in recent years, there has been growing demand for miniaturization, low power consumption, low cost and mass production, which are the characteristics required for continuous and systematically integrated monitoring and management in the sensor market [2].Besides, widely used materials for metal oxide gas detection are wide-bandgap semiconducting oxides such as zinc oxide, tin oxide, gallium oxide or indium oxides, which are operate at elevated temperatures (250–600°C) since enough thermal energy of surface redox reaction is required to overcome the activation energy barrier and increase the reaction kinetics in order to realize sensing measurement. Therefore, additional heater systems are required to metal oxide gas sensor and it may cause high power consumption, high cost or occupying a lot of space. Hearin, we propose a nano-heater integrated metal oxide gas sensor that capable of sensing with low power consumption and fast response and of being fabricated at a wafer level through C-MEMS which facilitated sub-micrometer-level carbon patterning due to a dramatic volume reduction during the polymer pyrolysis. The temperature of the metal oxide, the sensing material, can be heated immediately to 600°C within a low power of 7mW. In addition, the maximum temperature of the metal oxide can be easily controlled according to the applied voltage. Therefore, only a voltage source is needed to heat the sensing material. Method Our sensor platforms as shown in Figure a, were fabricated in several steps. First, eave structures for the selective metal coating on a suspended carbon nanowire were fabricated by oxide etching and isotropic silicon etching. Then, the suspended carbon nanowire was fabricated through C-MEMS consisting of two successive photolithography and polymer pyrolysis [3]. Then, we deposited gold on a carbon wire using evaporation as a heater line. Owing to the eave structure and anisotropic evaporation, the gold layer could be connected only through the suspended wire as shown in Figure b. The next step was the deposition of HfO2 as an insulation layer by Atomic Layer Deposition. In what follows, the ZnO nanowire forest (Figure c) was integrated selectively on the middle of a suspended wire structure via seed layer patterning and a hydrothermal process in an autoclave [4]. Due to the high aspect ratio of the carbon nanowire, heat is hard to be released to both posts, resulting in a uniform temperature distribution over 80% of the total length of the wire. Therefore, we used ZnO nanowire forest as a sensing site by growing in the center of the carbon nanowire selectively where the temperature is kept uniform and within the range of the sensing target temperature according to the simulation results (Figure d). In the last, to obtain the electrical signal of sensing material, we deposited gold once more using an E-beam evaporator. Results and Conclusions We have identified the possibility of gas sensing with heater integrated metal oxide sensor platform. Observing that the resistance of the metal oxide decreased rapidly when a voltage was applied, we speculated that the temperature of the metal oxide would have risen immediately according to the Joule-heating principle. Furthermore, the resistance of the metal oxide decreased continuously as the applied-voltage gradually increased. When we applied 1.2V to a gold heater, the resistance of the ZnO dropped to about 1/20 of its room temperature resistance (Figure e) similar when it is heated by an external heater to about 250℃, which is occasionally used temperature condition in the MOS type gas sensor. Detailed gas sensing results will be presented at the conference.

Size Effect in Nanostructured SnO2/TiO2 Gas Sensors

Introduction Size effect in resistive-type responses to gases has been demonstrated for the first time in the case of SnO2 polycrystalline sensors [1]. Since then it is believed that the smallest the grain size, the higher change in the electrical resistivity of metal oxide nanomaterials can be expected upon interaction with oxidizing or reducing gases. This belief is based on the argument that the surface-to-volume ration increases with a decrease in the grain diameter and as a gas adsorption is a surface process this in consequence leads to an increased density of active sites available for gas-solid interaction [2-3].Therefore, the size reduction has been considered as a fundamental strategy for nanosensors, justifying an enormous effort towards application of nanotechnology in gas sensing devices.A closer look at this issue reveals that such simplified reasoning is not always true. Geometrical decrease in the grain size below 10 nm for SnO2 does not necessarily mean to be a good solution for other oxides such as TiO2. In fact, the most important is a comparison between the grain diameter d and the Debye length λD defined as: λD={(ε ε0φS)/(eND)}1/2 where ε and ε0 denote relative permittivity of the material and vacuum permittivity, respectively, φ S is the surface potential, e represents electron charge and ND stands for donor concentration.When the condition d << λD is fulfilled, the size effect should play a substantial role in gas sensing. Therefore, the aim of this work is to investigate the size effect in the electrical resistivity of SnO2/TiO2 upon interaction with oxidizing/reducing gases by intentional modification of λD by influencing: the electrical properties through donor concentration ND the structural properties through anatase to rutile ratio thus affecting relative permittivity, εmorphology through its impact on the surface potential, φ S Technology TiO2/SnO2 bi-layer nanoheterostructures have been synthesized in a two-step process: (i) magnetron sputtering, MS, followed by (ii) Langmuir-Blodgett, LB technique [4]. Mixed TiO2/SnO2 composites have been obtained by means of Flame Spray Synthesis, FSS [5], sol-gel [6] and by mechanical mixing of commercial Sigma-Aldrich nanopowders [7]. Experimental Methods Crystallographic structure of the nanocomposites was studied by X-ray diffraction in Bragg-Brentano geometry while that of thin films was determined by X-ray diffraction in grazing incidence GID geometry using Philips X’pert Pro diffractometer. Scanning electron microscopy SEM investigations were carried out with the use of FEI Nova Nano SEM 200 microscope. Transmission electron microscopy TEM was employed to study the morphology of the nanopowders. FEI Tecnai TF 20 X-TWIN microscope was used. Gas sensing properties were established by measuring resistive-type responses to hydrogen, and NO2 vs. time, within a temperature range of 200-400oC both in dc and ac mode. The experimental setup for sensor characterization was already described in [8]. Sensitivity of the sensors to the reducing gas was defined as R0/R while that to the oxidizing as R/R0, where R0 is the baseline resistance in the reference gas, i.e. in air. Results and Conclusions Nanopowders of TiO2 with different crystallite size, grown by FSS, demonstrate a size effect in the electrical conductivity (Fig.1a) which can be attributed to the activation energy decreasing with the particle size. No grain size effect in hydrogen sensing has been observed.Bi-layered heterostructures synthesized on special gas sensor substrates with precisely defined interdigital electrodes were tested towards NO2 detection over the low concentration range from 200 ppb to 20 ppm.High response to low concentration of NO2 (Fig. 1b) could be accounted for by two factors: particular morphology of SnO2 base layer with small, well-dispersed grains indicating possibility of a grain size effectwell-developed, rough surface of TiO2 overlayer grown by the LB technique. Acknowledgement National Science Center NCN, Poland project no. 2016/23/B/ST7/00894 is acknowledged.

Application of response surface methodology for simultaneous removal of major cations from seawater using metal oxide nanostructures

&#x0D; The objectives of this study were to assess the suitability of metal oxide nanomaterials for removal of major cations Na+, K+, Ca2+ and Mg2+ from seawater. The as-synthesised nanomaterials were characterized using different techniques, such as XRD, TEM, and BET. The simultaneous removal of Na+, K+, Ca2+ and Mg2+ ion from aqueous solutions by α-Fe2O3 and SiO2/Nb2O5/Fe2O3 nanostructures was studied using batch method. The influence of different experimental parameters (such as initial metal ion concentrations, mass of adsorbent, sample pH and contact time) that affect the simultaneous removal of metal ions was studied using response surface methodology (RSM) based on small central composite design (SCCD). Under optimised conditions, the highest percentage removal was 75%, 92%, 93% and 85% for Na+, K+, Ca2+ and Mg2+, respectively.

Application of response surface methodology for simultaneous removal of major cations from seawater using metal oxide nanostructures

&#x0D; The objectives of this study were to assess the suitability of metal oxide nanomaterials for removal of major cations Na+, K+, Ca2+ and Mg2+ from seawater. The as-synthesised nanomaterials were characterized using different techniques, such as XRD, TEM, and BET. The simultaneous removal of Na+, K+, Ca2+ and Mg2+ ion from aqueous solutions by α-Fe2O3 and SiO2/Nb2O5/Fe2O3 nanostructures was studied using batch method. The influence of different experimental parameters (such as initial metal ion concentrations, mass of adsorbent, sample pH and contact time) that affect the simultaneous removal of metal ions was studied using response surface methodology (RSM) based on small central composite design (SCCD). Under optimised conditions, the highest percentage removal was 75%, 92%, 93% and 85% for Na+, K+, Ca2+ and Mg2+, respectively.

Two-Dimensional Earth-Abundant Transition Metal Oxides Nanomaterials: Synthesis and Application in Electrochemical Oxygen Evolution Reaction.

Development of a universal synthetic strategy for two-dimensional (2D) Earth-abundant transition metal oxides nanomaterials is highly vital toward numerous electrochemical applications. Herein, a facile and general synthesis of highly ordered two-dimensional metal oxides nanomaterials includes Co3O4, NiO, CuO, and Fe3O4 nanosheets as an electrocatalyst for oxygen evolution reaction (OER) is demonstrated. Among the synthesized 2D transition metal oxides, the Co3O4 nanosheet exhibits smallest overpotential (η) of ∼384.0 mV at a current density of 10.0 mA cm-2 and Tafel slope of ∼52.0 mV dec-1, highest mass activity of ∼112.3 A g-1 at the overpotential of ∼384.0 mV, and high turn over frequency (TOF) of 0.099 s-1, which is relatively favorable with state-of-the-art RuO2 catalyst. The present synthetic approach may unlock a brand new pathway to prepare shape-controlled Earth-abundant transition metal oxides nanomaterials for electrocatalytic OER.

Fabrication of electrospun Co3O4/CuO p-p heterojunctions nanotubes functionalized with HFIP for detecting chemical nerve agent under visible light irradiation

Organic functionalized composite metal oxide nanomaterials are promising for reliable selective and high sensitive gas sensors based on their chemical bonding with the targeted molecules and rapid transport pathways of charges. The selectivity of semiconducting metal oxides (SMOs) still insufficient and its mechanism is not clearly demonstrated, which restricts their application. Herein, hexafluoroisopropanol (HFIP) groups were grafted on the composite Co3O4/CuO nanotubes as a hybrid sensing material for detecting dimethyl methylphosphonate (DMMP), sarin nerve agent simulant. Porous composite Co3O4/CuO nanotubes were fabricated via electrospun of a polymeric blend as a sacrificial template to construct nanotubes (NTs) based on the phase separation property. The designed hybrid HFIP-Co3O4/CuO NTs showed high response (8.8 Rg/Ra at 90 °C), rapid response (7.3 s)-recovery (5.2 s) times and excellent selectivity to 0.5 ppm DMMP under light irradiation compared to un-functionalized sample and the response in dark, indicating to the specific bonding between HFIP and DMMP via hydrogen bonds and photo-generation of charge carriers. The hybrid sample showed high reversibility and humidity independence under light, approving the repeatability of the chemisorption processes and the hydrophobic behavior of HFIP groups. The enhanced DMMP detection is attributed to the photoactivation of p-p heterojunctions Co3O4/CuO NTs and HFIP functionalization.

PVA assisted ZnO based mesoporous ternary metal oxides nanomaterials: synthesis, optimization, and evaluation of antibacterial activity

The poly (vinyl alcohol) (PVA) assisted highly mesoporous Zn-Fe-Mn oxides nanomaterials were synthesized using the sol-gel followed by the self-propagation techniques. The UV–vis spectroscopic technique was used to study the optical properties of the materials. The presence of metal-oxygen bond and deposited OH−/H2O species were characterized by FT-IR spectroscopic technique. The porous morphology and elemental analysis were confirmed by the SEM/EDX and further morphological and crystal structure studies were conducted using TEM/HRTEM techniques. The semi-crystallinity and composition analyses were verified from XRD patterns. Using the BET N2 adsorption-desorption analytical techniques; the porosity, specific surface area, and pore diameter enhancements were confirmed. The optima of PVA and precursors percentage were selected with the help of XRD, UV–Vis, and SEM techniques. The potential of the materials towards antibacterial activities was evaluated against both Gram-negative Escherichia coli and Gram-positive Staphylococcus aureus bacteria. The 50(0.7) PVA assisted ternary metal oxide nanocomposite (PVA-TMONC) with 125 μg ml−1 concentration showed better inhibition zone for both Escherichia coli and Staphylococcus aureus bacteria, with a value of 28 and 29 mm in diameter, respectively.

Controllable design, synthesis and characterization of nanostructured rare earth metal oxides

Abstract Rare earth metal oxide nanomaterials have drawn much attention in recent decades due to their unique properties and promising applications in catalysis, chemical and biological sensing, separation, and optical devices. Because of the strong structure–property correlation, controllable synthesis of nanomaterials with desired properties has long been the most important topic in nanoscience and nanotechnology and still maintains a grand challenge. A variety of methods, involving chemical, physical, and hybrid method, have been developed to precisely control nanomaterials, including size, shape, dimensionality, crystal structure, composition, and homogeneity. These nanostructural parameters play essential roles in determining the final properties of functional nanomaterials. Full understanding of nanomaterial properties through characterization is vital in elucidating the fundamental principles in synthesis and applications. It allows researchers to discover the correlations between the reaction parameters and nanomaterial properties, offers valuable insights in improving synthetic routes, and provokes new design strategies for nanostructures. In application systems, it extrapolates the structure–activity relationship and reaction mechanism and helps to establish quality model for similar reaction processes. The purpose of this chapter is to provide a comprehensive overview and a practical guide of rare earth oxide nanomaterial design and characterization, with special focus on the well-established synthetic methods and the conventional and advanced analytical techniques. This chapter addresses each synthetic method with its advantages and certain disadvantages, and specifically provides synthetic strategies, typical procedures and features of resulting nanomaterials for the widely-used chemical methods, such as hydrothermal, solvothermal, sol–gel, co-precipitation, thermal decomposition, etc. For the nanomaterial characterization, a practical guide for each technique is addressed, including working principle, applications, materials requirements, experimental design and data analysis. In particular, electron and force microscopy are illuminated for their powerful functions in determining size, shape, and crystal structure, while X-ray based techniques are discussed for crystalline, electronic, and atomic structural determination for oxide nanomaterials. Additionally, the advanced characterization methodologies of synchrotron-based techniques and in situ methods are included. These non-traditional methods become more and more popular because of their capabilities of offering unusual nanostructural information, short experiment time, and in-depth problem solution. Graphical Abstract:

Nano-Structured Dilute Magnetic Semiconductors for Efficient Spintronics at Room Temperature

In recent years, many efforts have been made to develop advanced metal oxide semiconductor nanomaterials with exotic magnetic properties for modern applications w.r.t traditional analogues. Dilute magnetic semiconductor oxides (DMSOs) are promising candidates for superior control over the charge and spin degrees of freedom. DMSOs are transparent, wide band gap materials with induced ferromagnetism in doping, with a minor percentage of magnetic 3d cation to create a long-range antiferromagnetic order. Although significant efforts have been carried out to achieve DMSO with ferromagnetic properties above room temperature, it is a great challenge that still exists. However, TiO2, SnO2, ZnO and In2O3 with wide band gaps of 3.2, 3.6, 3.2 and 2.92 eV, respectively, can host a broad range of dopants to generate various compositions. Interestingly, a reduction in the size of these binary oxides can induce ferromagnetism, even at room temperature, due to the grain boundary, presence of defects and oxygen vacancies. The present review provides a panorama of the structural analysis and magnetic properties of DMSOs based on binary metal oxides nanomaterials with various ferromagnetic or paramagnetic dopants, e.g., Co, V, Fe and Ni, which exhibit enhanced ferromagnetic behaviors at room temperature.

Interaction of Slow Electrons with Thermally Evaporated Manganese(II) Acetylacetonate Complexes.

Complexes of metal acetylacetonate are used as general precursors for the synthesis of metal oxide nanomaterials. In the present work, we study the interaction of low-energy (<10 eV) electrons, produced abundantly as secondary electrons during the bombardment of the substrate by the primary particles, with thermally evaporated manganese(II) acetylacetonate complexes. We found that the acetylacetonate anion ([acac]-) is the major anionic species produced, while the second most abundant is the parent anion [Mn(II)(acac)2]-. This observation differs from those reported from electron attachment to Cu(acac)2, for which [Cu(II)(acac)2]- is the predominant anion [Kopyra et al. Phys. Chem. Chem. Phys. 2018, 20, 7746]. The experimental data are supported by theory to provide information on the physical-chemistry processes initiated by slow electrons to the organometallic precursor and to interpret the different behavior of Mn(acac)2 compared to Cu(acac)2.

Solvent effects on the heterogeneous growth of TiO2 nanostructure arrays by solvothermal synthesis

One-dimensional titanium dioxide (TiO2) nanostructure arrays (nanoarrays) are important metal oxide nanomaterials that can be synthesized via facile solvothermal methods. The properties of the organic solvents can impose significant effects on the microstructures and properties of the final products. However, the discussions were limited to the homogeneously nucleated TiO2 nanomaterials in free-standing powder form, while the solvent effects are less understood during the heterogeneous growth of TiO2 nanoarrays on a substrate surface. In this work, six organic compounds, namely 2-butanone, n-decane, n-hexane, toluene, ethylene glycol and ethanol, were selected as the solvents for the solvothermal synthesis of TiO2 nanoarrays on the cordierite monolithic substrates. Special attentions are paid to the morphology, crystallinity, specific surface area, and porosity of the samples. The heterogeneous growth of TiO2 nanoarrays on substrate surfaces is found to favor the solvents with moderate dielectric constants, which can be partially dissolved in the aqueous solution and modulate the reaction rate during the solvothermal synthesis. Organic solvents with low dielectric constants may result in a complete separation between the precursors and aqueous solution, and therefore slow down the overall reaction, causing the insufficient growth of the nanoarrays. The TiO2 nanoarrays are obtained with optimum morphology from the combination of 2-butanone and titanium (IV) butoxide as solvent and precusor, respectively, with a high specific surface area up to 56 m2/g including cordierite substrate given a micron thickness. When loaded with Pt catalyst, the TiO2 nanoarray-based monolithic catalysts show excellent low-temperature catalytic activity and hydrothermal stability for the CO and hydrocarbon oxidation under the simulated exhausted conditions. This work shall shed light on a better understanding of the growth mechanism and rational design of TiO2 nanoarrays for high-performance catalytic converters.

One Dimensional LaTiO3-δ Nanorods for Solid Oxide Fuel Cells

At present oxide materials in nano size provide new solutions and opportunities to guarantee better efficiency and stability for devices that produce or store sustainable energy. Due to their special shapes, compositions, chemical and physical properties, metal oxide nanomaterials are in the focus of current research efforts in all fields of science and technology. One-dimensional nanostructures, such as nanofibers, nanorods and nanotubes, have attracted significant attention due to the interesting confinement effects and the structure-related properties. One-dimensional nanostructures are attracting a great deal of attention due to their essential role in developing understanding of the fundamental concepts of quantum confinement effects. One-dimensional nanosized lanthanum titanate (LaTiO3−δ ) was synthesized using the hydrothermal technique to enhance the material’s electrical behavior. Using X-ray diffraction, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM), LaTiO3−δ was explored physicochemically. In SEM and TEM images, uniformly distributed nanorods were shown. Electrical properties analyzed using impedance spectroscopy revealed that the conductivity was in the order of 10−3–10−4 S/cm at a temperature range 500–630°C.

Synthesis of Metal Oxide Nanomaterials for Early Lung Disease Detection

Metal oxide nanomaterials from bulk zinc oxide and tin oxide powders were synthesized via Horizontal Vapor Phase Crystal Growth deposition technique. Synthesized nanomaterials were deposited in a silica quartz tube where it acts as sensing element of the gas sensor. Volatile organic compounds (VOCs) were utilized as identifier for lung disease which served as analytes to interact with the gas sensor. The sensitivity test was measured using its response time and voltage difference. An immediate voltage response time with an average of 3 seconds was observed upon exposure of the analyte to the sensor. Selectivity test was analyzed through radar plots of tin oxide and zinc oxide which depicted that each metal oxides have distinct sensing capabilities in terms of sensed VOC gases.

Dual remediation of waste waters from methylene blue and chromium (VI) using thermally induced ZnO nanofibers

Electrospun zinc oxide (ZnO) nanofibers have been significantly improved via a simple heat treatment modification. The present work reports an intriguing cost-effective microstructure tuning, by drastically dropping the temperature of the calcined sample during the cooling period, to get highly photocatalytically active ZnO nanofibers. The calcination temperatures are deducted from thermogravimetric analysis, the phase and purity are confirmed by X-ray diffraction, while the morphology and texture have been revealed by field emission scanning electron microscopy and high-resolution transmission electron spectroscopy. X-ray photoelectron spectroscopy was conducted to get further insight on the surface composition and oxidation states, while N2-adsorption isotherms were analyzed using the Brunauer-Emmet-Teller methodology. The crystallinity, surface area, and porosity of the ZnO nanofibers, as well as the exposure of active sites, have been enhanced by the rapid cooling method. Photodegradation activity toward methylene blue was improved from 88% to 94%, and 85% to 97%, for free cooled and rapid cooled samples calcined at 300 °C and 500 °C respectively. The adsorption of chromium (VI) was also tested and reached around 85 mg/g at 100 ppm without being saturated, thereby highlighting one of the most cost-effective performance-enhancing modifications so far that could be extended on different metal oxide nanomaterials.

Numerical Differential Quadrature Examination of Steady Mixed Convection Nanofluid Flows Over an Isothermal Thin Needle Conveying Metallic and Metallic Oxide Nanomaterials: A Comparative Investigation

The significance of the local skin friction as well as the heat transfer rate on the motion of water $$ \left( {{\text{H}}_{2} {\text{O}}} \right) $$ and ethylene glycol $$ \left( {{\text{C}}_{2} {\text{H}}_{6} {\text{O}}_{2} } \right) $$ conveying metallic and metallic oxide nanoparticles (e.g., Al, Cu, Zn, Al203, CuO and ZnO) along a vertical thin needle is needed to improve the performance of chemical reactors, heat exchangers, pharmaceutical equipment and hybrid-powered engines. This led to the investigation of mixed convection flow and heat transfer of some nanofluids, in which the thermal conductivity and viscosity vary nonlinearly with the volume fraction. For simplifying the present investigation, appropriate variables were introduced successfully in the mathematical formulation to convert the governing nonlinear partial differential equations to coupled ordinary differential equations (ODEs). Moreover, the resulting ODEs were solved numerically via a robust differential quadrature algorithm. Furthermore, a comparative study with the existing literature is found to be in an excellent agreement. The enhancement of heat transfer in nanofluids is ascertained by increasing the convection ratio. Generally, the maximum improvement in the local skin friction was perceived for the flows of zinc–water-based nanofluids ( $$ {\text{Zn}} $$ – $$ {\text{H}}_{2} {\text{O}} $$ ) with the upsurge in the volume fraction of the nanoparticles $$ {\text{Zn}} $$ . On the contrary, the highest enhancement in the heat transfer rate was revealed for the flows of copper–ethylene glycol-based nanofluids ( $$ {\text{Cu}} $$ – $$ {\text{C}}_{2} {\text{H}}_{6} {\text{O}}_{2} $$ ) with the increase in the weight percent of the $$ {\text{Cu}} $$ nanomaterial loading.