Morphology Of Oxide Research Articles

Evolution of the oxide layers of an aluminum-forming austenitic heat-resistant steel with high-Mn substitution for Ni: Experiment and first-principle calculations

High Mn (8 wt%) was used to save Ni resources to replace 10 wt% Ni in Aluminum-forming austenitic (AFA) heat-resistant steel; the changes in oxidation resistance and morphology evolution of multiple oxide scales for the 8Mn-AFA steel were then studied. The 8Mn-AFA steel formed a three-layer scale on the surface oxidized at 750 °C for 100 h: inner dense Al2O3 sub-layer closed to the austenite matrix, intermediate Cr2O3 sub-layer with partial Cr substituted by Mn, and outer loose Mn2O3 + Mn3O4 sub-layer with FeMnO3 surface nodules. Mn from the matrix to the α-Al2O3 diffusion is spontaneous. However, Mn moving from an α-Al2O3 to α-Cr2O3 leads to partial Cr in the Cr2O3 sub-layer was substituted by Mn. When the 8Mn-AFA steel oxidated at 750 °C for 360 h, the Mn oxides, including Mn2O3, Mn3O4 and FeMnO3, increased significantly with the prolongation of the oxidation time. First-principle calculations based on density functional theory (DFT) also confirmed the diffusion of Mn did not destroy the dense Al2O3 scale. The oxidation weight gain of 8Mn-AFA steel oxidized at 750 °C in the air for 360 h follows a parabolic law, and the oxidation rate constant is 2.65 × 10−4.

Ligand-engineered Ru-doped cobalt oxides derived from metal-organic frameworks for large-current-density water splitting

The influence of the preorganized structure and chemical composition of metal-organic frameworks (MOFs) on the morphology, surface properties, and catalytic activity of the MOFs-derived metal oxides is yet to be revealed. In this work, two types of Co-MOFs with different coordination configurations are synthesized for the preparation of the structure-engineered ruthenium (Ru)-doped cobalt oxides. The effect of the preorganized coordination structure of the MOFs on the morphology and surface properties is investigated. Interestingly, the oxalate-based MOFs derived Ru-doped cobalt oxide (OX-Co3O4-Ru) exhibits much better surface wettability and more oxygen vacancies than the zeolitic imidazolate framework-67 derived Ru-doped cobalt oxide. As expected, the OX-Co3O4-Ru owns excellent catalytic properties towards both hydrogen evolution reaction and oxygen evolution reaction with an overpotential of 49 and 286 mV, respectively at a current density of 100 mA cm−2 in 1.0 M KOH. Importantly, the bifunctional OX-Co3O4-Ru catalyst offers an extremely high current density of 500 mA cm−2 at a cell voltage of 1.71 V for overall water splitting and as well demonstrates robust working stability.

Beam intensity of N2 plasma controlled surface engineering on WO3 for enhanced hydrogen evolution and oxygen evolution

Tungsten oxide is a promising electrocatalyst for water splitting reactions, due to its flexible chemical state, strong structural malleability and good corrosion resistance. Herein, the surface engineering on WO3 was conducted by a controllable N2 plasma for enhancing the performance of water splitting reactions. Under the specific N2 plasma treatment, the surface crystalline phase and the surface morphology of the tungsten oxide can be changed, as well as the creation of oxygen vacancies. These changes lead to a greatly increased electrochemical surface area, a narrowed bandgap, and a distorted crystal lattice. For oxygen evolution reaction (OER) in 1.0 M KOH, the activity of the modified tungsten oxide electrodes presents a positive correlation with the input plasma, and an optimal overpotential of 269 mV @ 10 mA cm−2 is achieved with a Tafel slope of 122 mV dec-1. With a high N2 plasma flux, the W-N bond can be formed on the tungsten oxide surface, which contributes to the promotion of the hydrogen evolution reaction (HER) activity, and an overpotential of 93 mV @ 10 mA cm−2 in 1.0 M KOH is exhibited, and the Tafel slope largely reduced to 76 mV dec-1. Such a facile strategy provides an engineering route of preparing efficient electrodes for water splitting reactions.

Lipopeptide and glycolipid assisted growth of ZnO micro-/nano-structures: Evaluating the role of chemical and microbial green surfactant

Micro-/nano-structured biomaterials with tuneable architectures and functionalities have found promising applications and facile fabrication strategies play a key role in controlling the morphological aspects. Here, green surfactants, rhamnolipid and surfactin were used to cap and stabilize zinc oxide at basic pH and compared with that synthesized using a synthetic surfactant, i.e., sodium dodecyl sulphate. The surfactant@ZnO was characterized by XRD, TGA, FTIR, SEM-EDS, TEM, XPS, AFM, DLS, UV–Vis and PL tests. The XRD, FTIR and XPS data show the successful formation of surfactant@ZnO. The SEM and TEM studies have revealed the various morphologies of ZnO. The UV–Vis and PL studies established the optical characteristics of the surfactant@ZnO. The AFM and DLS were used to examine the effect of surfactant on the size and stability of the ZnO micro- and nanostructures. It is found that the green surfactant@ZnO are more effective in controlling the crystallite size to as low as 13 nm. It is observed that the bio-surfactants meet the bare minimum criteria of a green template to control the size, morphology and optical properties of zinc oxide through a characteristic self-assembly route, essential for the rational development of nano-biomaterials which are anticipated to be widely used in industrial applications.

Analysis of neptunium oxides produced through modified direct denitration

Production of neptunium-237 (237Np) target materials for plutonium-238 (238Pu) radioisotope thermoelectric generators (RTGs) for deep space exploration requires advanced chemistry and engineering development. Currently, the domestic Pu-238 Supply Program at Oak Ridge National Laboratory produces neptunium dioxide (NpO2) for target material using a modified direct denitration (MDD) flowsheet. Although the chemistry, reaction mechanisms, and product characteristics of MDD are well understood for uranium, corresponding studies of the neptunium system are still needed to continue optimization of target material properties, production equipment design, and production flowsheets. The objective of this work is to characterize crystalline phases, morphology, surface texture, and particle size of NpO2 produced via MDD reactions. Solid-phase characterization techniques, including powder X-ray diffraction (pXRD) and scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), were employed to achieve this objective. Subsequent data processing using the Morphological Analysis for Material Attribution (MAMA) software was performed to analyze particle morphology and size. Broadly, the powders were found to contain a mixture of NpO2 and Np2O5 after denitration with a variety of morphologies. After high-firing, the product was found to be NpO2 with a typical polycrystalline oxide morphology and a grain size ranging from 0.72 to 0.94 µm. These analyses provide knowledge on the reaction pathway for a non-traditional NpO2 synthesis method and offer additional unique insight into production-scale environments for transuranic materials.

Mechanism of Electrochemical Oxidation of Titanium Via Isotopic Labeling, Medium Energy Ion Scattering, Nuclear Reaction Profiling, in-Situ Rutherford Backscattering Spectrometry, and Electrochemical Impedance Spectroscopy

The few nanometres of titanium oxide present on titanium and Ti alloy surfaces are responsible for protecting the underlying metal from oxidation and enabling its use in many high-performance applications. The oxide provides a hard, uniform, and thermodynamically stable protective coating on an otherwise soft and very reactive metal. Because of its passivating oxide film, titanium has found uses in biomedical implants, aerospace engineering, corrosive industrial piping, and other areas where high strength and low weight are required.Our project is aimed at understanding the atomistic mechanisms of TiO2 formation and growth. We have taken several different approaches to investigate the details of this process. In one approach, the electrochemical oxidation mechanism of titanium at applied potentials between 0 and 10 V vs the saturated calomel reference electrode (SCE) was examined for ultra-thin Ti films sputtered onto Si(001) substrates and exposed in-situ to H2 18O, and then anodized in D2 16O. The effects of this isotopic labeling procedure were studied using medium energy ion scattering (MEIS) and nuclear reaction profiling (NRP). Both MEIS and NRP results are consistent in showing that the titanium oxide layer is composed of two distinct regions (Ti16O2/Ti18O2/Ti/Si) for the entire range of the formation voltages (0–10 V vs SCE). The oxygen component of the outermost region consists entirely of 16O, and the 18O region is always adjacent to the Ti metal. No Ti or 18O loss into the electrolyte solution during anodization was detected. The oxide thickened linearly as a function of potential in the 0–10 V range vs SCE, with experimental anodization ratio of 24.5±0.6 Å V−1. Mott–Schottky (MS) analyses showed positive slopes, indicating formation of an n-type TiO2 semiconductor, with O vacancies (or Ti interstitials) as major charge carriers in the 0–10 V range. Charge carrier densities, ND = (0.8-5.0)×1021 cm−3 were calculated from Mott–Schottky analysis and were well within the range of results reported in the literature. We observed a decrease in the charge carrier densities above ∼4 V vs SCE, that can be connected to defect annihilation or minor modification in the structure (electrostatic annealing) of the growing TiO2 film.In a second approach, we are using Rutherford backscattering spectrometry (RBS) for elemental depth profiling during oxide growth to determine oxidation rates and the role of the anodization potential on the Ti oxide layer structure and morphology. RBS is a powerful ion beam-based analytical tool used to determine thickness at the nanometer scale and elemental depth distribution, making it an excellent choice for studying the thin oxide on titanium. A difficulty with using RBS for such studies has been that RBS must function under ultra-high vacuum, and this has made it incompatible with performing aqueous electrochemistry; therefore, RBS had to be performed as an ex situ analysis, like MEIS and NRP. We are overcoming this limitation by using a specially designed in-situ cell with an ion-permeable silicon nitride window to provide a barrier between the ultra-high vacuum (UHV) required to perform RBS and the aqueous electrolyte solution required for anodization. In this cell, the thin silicon nitride window is coated with titanium and functions as the working electrode when exposed to the aqueous electrolyte solution. RBS measurements are taken as the titanium metal is anodized to titanium oxide. RBS is then performed during in-situ anodization, to obtain information about the growth mechanism of titanium oxide. Our initial in-situ RBS results show a significant increase in the oxidation rate of titanium compared to equivalent ex-situ measurements, and we also observe spontaneous TiO2 film growth without applying an anodic polarization. These effects are likely generated by strongly oxidizing water radiolysis products (e.g., H2O2 or ·OH) formed by the action of high-energy He+ ions interacting with the electrolyte solution.This paper discusses our experimental methods and presents an overview of the results and conclusions of this work.

Observing the Evolution of Metal Oxides in Liquids.

Metal oxides with diverse compositions and structures have garnered considerable interest from researchers in various reactions, which benefits from transmission electron microscopy (TEM) in determining their morphologies, phase, structural and chemical information. Recent breakthroughs have made liquid-phase TEM a promising imaging platform for tracking the dynamic structure, morphology, and composition evolution of metal oxides in solution under work conditions. Herein, this review introduces the recent advances in liquid cells, especially closed liquid cell chips. Subsequently, the recent progress including particle growth, phase transformation, self-assembly, core-shell nanostructure growth, and chemical etching are introduced. With the late technical advances in TEM and liquid cells, liquid-phase TEM is used to characterize many fundamental processes of metal oxides for CO2 reduction and water-splitting reactions. Finally, the outlook and challenges in this research field are discussed. It isbelieved this compilation inspires and stimulates more efforts in developing and utilizing in situ liquid-phase TEM for metal oxides at the atomic scale for different applications.

Impact of annealing on charge storage capability of thermally evaporated molybdenum oxide thin films

Rapid technological advancements in recent years have necessitated the creation of energy-related devices. Due to their unique properties, including an exceptional cycling life, safe operation, low processing cost, and a higher power density than batteries, supercapacitors (SCs) have been identified as one of the most promising candidates to meet the demands of human sustainability. To increase the energy density of SCs, several advanced electrode materials and cell designs have been researched during the past few years. Utilizing the Faradaic charge storage process of transition metal cations, transition metal compounds have recently received attention as prospective electrode materials for SCs with high energy densities. In this work, the structure, morphology and electrochemical properties of molybdenum oxide (MoO3) films deposited via thermal evaporation technique and annealed at various temperatures were systematically investigated in order to examine the potential use of MoO3 for supercapacitors. Electrochemical analysis confirmed the pseudocapacitance characteristics of the synthesized films. The annealing temperature affects the oxidation and reduction observed in the cyclic voltammetry (CV) plots. Areal capacitance of thin films annealed at 150°C was found to be maximum and this could be attributed to the formation of hollow tube-like nanostructures which provided more active sites, than films annealed at higher temperatures. This also influences the charge storage ability of the synthesized films. It would be logical to assume that additional research in this area will result in more interesting discoveries and, eventually, the vi-ability of those promising Mo-based compounds in high-tech energy storage systems.

Understanding the evolution of microstructure, phase homogeneity, electrochemical characteristics and surface chemistry of electrodeposited MnCrCoFeNiCu high entropy alloy coating with reinforcement of carbon nanotubes

MnCrCoFeNiCu high entropy alloy (HEA) coatings with varying volume fractions of carbon nanotube (CNT) were electrodeposited on mild steel. Morphology, phase constitution, wettability, surface oxide chemistry and corrosion of coatings were examined. Coating morphology became finer with initial CNT incorporation and then transformed to rougher surface for higher CNT volume fractions. Pristine HEA coating contained mixture of body centre cubic (bcc) and face centre cubic (fcc) phases. With the CNT addition phase homogenization happened and for the HEAC3 coating (from electrolyte with 5 mg/L concentration of CNT) single phase bcc microstructure was obtained. The phase mixture however re-evolved for the higher CNT incorporation due to CNT agglomeration and reduction in the metal-CNT interfaces. Water contact angle was 127° for HEA_C3 coating. All the HEA-CNT coatings exhibited higher corrosion resistance than the pristine HEA coating, corrosion rate trend was however not monotonic with CNT volume fraction and maximum corrosion resistance was observed for the HEA_C3 coating. Surface oxide chemistry of exposed sample showed stabler oxide over the HEA-CNT coatings when compared to the oxides of the pristine HEA coating. Higher corrosion resistance of the HEA_C3 coating was due to compact morphology, hydrophobicity, phase homogenization and evolution of stable surface oxides.

Simple express precursor synthesis of erbium-doped yttrium oxide luminescent material for optical thermometry

A new, simple and inexpensive method for the preparation of nanosized (Y1-xErx)2O3 oxides, including the stages of synthesis and thermolysis of Y1-xErx(HCOO)3 precursors, has been developed. The precursors were obtained by the interaction of mixtures of yttrium and erbium nitrates with formic acid. The effect of erbium concentration on the structure, morphology, and optical properties of (Y1-xErx)2O3 oxides was studied using X-ray diffraction, scanning electron microscopy, and optical absorption methods. Under UV excitation (Y1-xErx)2O3 oxides with 0.005≤x ≤ 0.25 exhibit strong green luminescence related to the 2H11/2/4S3/2 → 4I15/2 transitions and weak red luminescence associated with the 4F9/2 → 4I15/2 transition. According to the CIE chromaticity coordinates, the oxides demonstrate a yellowish-green color emission. A noticeable decrease in the luminescence intensity was recorded for oxides with erbium concentrations above 2.5 mol.% (x = 0.025). Yellowish-green and yellow green upconversion emission resulting from the 4S3/2 → 4I15/2 and the 4F9/2 → 4I15/2 transitions of Er3+ ions were observed upon continuous 980 nm diode laser excitation. When the concentration of erbium in (Y1-xErx)2O3 oxides increases, the luminescence color changes and the intensity of upconversion emission rises. The maximum intensity of upconversion emission was observed for the (Y0.9Er0.1)2O3 oxide. A two-photon upconversion mechanism was established based on the pumping power dependence of UC luminescence intensity. The thermoluminescence characteristics of (Y0.9Er0.1)2O3 oxides based on the ratio of the intensities of the lines corresponding to thermal-coupled 2H11/2 and 4S3/2 levels were determined, the absolute and relative sensitivity values was calculated, and the prospects for using this oxide in non-contact optical thermometers were estimated.

Control of Manganese Oxide Hybrid Structure through Electrodeposition and SILAR Techniques for Supercapacitor Electrode Applications

Manganese oxide has been studied as a promising supercapacitor electrode due to its high theoretical capacitance, low cost, and environmental friendliness. Supercapacitor performance such as specific capacitance, resistance, and cycle life greatly depends on the morphology and crystal structure of manganese oxide. In this study, a Mn3O4 hybrid structure was successfully synthesized using electrodeposition and successive ionic layer adsorption and reaction (SILAR) techniques which are simple, cost-effective, and low-temperature wet chemical processes. It was found that Mn3O4 morphology is different depending on manganese precursors and synthesis techniques. Sea-grape-like and bird nest-like morphologies were obtained via the electrodeposition technique, while flower-like and nanoparticle morphologies were formed via the SILAR technique using manganese acetate and manganese sulfate as precursors, respectively. The hybrid structure of the nanoparticle-decorated bird nest-like heterostructure was prepared using manganese sulfate electrodeposition and subsequent SILAR deposition of manganese acetate. X-ray photoelectron spectroscopy confirmed the Mn3O4 formation. Electrochemical properties of manganese oxide hybrid structure were systematically studied with cyclic voltammetry and galvanostatic charge–discharge, showing the highest areal capacitance of 390 mF cm−2 at 0.1 mA cm−2 with series and charge transfer resistances down to 4.55 and 4.91 Ω in 1 M sodium sulfate electrolyte.

Development of hydrogen reduction method for La–Fe–Si materials from oxalate precursors

ABSTRACT Hydrogen reduction was used to synthesise LaFeSi-based materials from lanthanum, cerium, iron oxalates, and silicon dioxide. The process involved the pre-reduction of the precursor powder mixture at 650°C under N2 for 1 h, followed by a full reduction under H2 for 2 h at 900°C. The predominant phases in the synthesised materials were a-Fe, lanthanum, cerium, and silicon oxides. A decrease in the La/Ce ratio in the main composition resulted in an increase in the a-Fe phase. The rest of the non-oxidized materials showed an Fm-3 m structure. Both XRD and EDS analyses indicated the presence of metal/oxide composite structure in the synthesised materials. The oxide morphology observed in SEM images exhibited a porous media. The room temperature VSM analysis showed that x = 0.3 product had the highest coercivity as 26 Oe and the lowest saturation magnetisation as 106.3 emu/g.

Coaxially swirled porous disks flow simultaneously induced by mixed convection with morphological effect of metallic/metallic oxide nanoparticles

This study focuses on the numerical modeling of coaxially swirling porous disk flow subject to the combined effects of mixed convection and chemical reactions. We conducted numerical investigations to analyze the morphologies of aluminum oxide (Al2O3) and copper (Cu) nanoparticles under the influence of magnetohydrodynamics. For the flow of hybrid nanofluids, we developed a model that considers the aggregate nanoparticle volume fraction based on single-phase simulation, along with the energy and mass transfer equations. The high-order, nonlinear, ordinary differential equations are obtained from the governing system of nonlinear partial differential equations via similarity transformation. The resulting system of ordinary differential equations is solved numerically by the Runge–Kutta technique and the shooting method. This is one of the most widely used numerical algorithms for solving differential equations in various fields, including physics, engineering, and computer science. This study investigated the impact of various nanoparticle shape factors (spherical, platelet and laminar) subject to relevant physical quantities and their corresponding distributions. Our findings indicate that aluminum oxide and copper (Al2O3-Cu/H2O) hybrid nanofluids exhibit significant improvements in heat transfer compared to other shape factors, particularly in laminar flow. Additionally, the injection/suction factor influences the contraction/expansion phenomenon, leading to noteworthy results concerning skin friction and the Nusselt number in the field of engineering. Moreover, the chemical reaction parameter demonstrates a remarkable influence on Sherwood’s number. The insights gained from this work hold potential benefits for the field of lubricant technology, as they contribute valuable knowledge regarding the behavior of hybrid nanofluids and their associated characteristics.

Binary nickel cobalt oxide (NixCo3-xO4) nanostructures as stable and high-energy density asymmetric supercapacitor electrode material

Nickel cobalt oxides are very desirable for a wide range of scientific research and practical applications due to their smooth redox activity and unquestionable parameter optimization freedom. This report examines the capacitive behaviour of hydrothermally fabricated nickel cobalt oxide nanostructures for potential application in the field of energy storage. According to the findings of our research, the morphology of the nickel-cobalt oxides is highly dependent on reaction time as well as the ratio of Ni/Co. When NiO, NixCox-3O4(I) and NixCox-3O4(II) are deposited on nickel foam, the fabricated electrodes show a specific capacitance of 291, 590, 1948 F g-1 respectively, scanned at 5 mVs−1 in an aqueous electrolyte containing 4 M KOH. The NixCox-3O4(II) electrode shows less cycle fatigue as its initial capacitance dropped by just 17% even after 10k cycles and demonstrating low impedance confirmed by electrochemical impedance spectroscopy (EIS). Moreover, the solid state asymmetric capacitor fabricated by using NixCox-3O4(II) as positive and activated carbon as negative electrode demonstrates the specific energy and power of 38 Whkg−1, 3.3 kW kg−1respectively. These remarkable electrochemical properties, characterized by exceptional stability and high energy density, demonstrated by the NixCox-3O4(II) based electrode unequivocally establish it as an indispensable and highly promising electrode material for utilization in electrochemical energy storage devices.

Effects of Zr and/or Ti addition on the morphology, crystal and metal/oxide interface structures of nanoparticles in FeCrAl-ODS steels

FeCrAl oxide dispersion strengthened (ODS) steel is one of the most promising candidate cladding materials for Generation IV nuclear reactors due to its superior high temperature strength and excellent resistance to creep, corrosion and irradiation. The morphologies of matrix grains and oxides, the crystal and metal/oxide interface structures of nanoparticles in two FeCrAl ODS steels, i.e., 3.3Al–0.5Zr (Fe–15Cr–2W–3.3Al–0.5Zr–0.35Y2O3) and 3.7Al–0.1Ti–0.6Zr (Fe–15Cr–2W–3.7Al–0.1Ti–0.6Zr–0.35Y2O3), were studied by transmission electron microscopy (TEM), scanning transmission electron microscopy (STEM) and high resolution transmission electron microscopy (HRTEM). The average matrix grain sizes of 3.3Al–0.5Zr ODS steel and 3.7Al–0.1Ti–0.6Zr ODS steel are 1.01 and 0.97 μm, respectively. The dispersion morphology of oxides in 3.7Al–0.1Ti–0.6Zr ODS steel is much better, relative to that of 3.3Al–0.5Zr ODS steel. Crystal & interface structures of 88 and 171 oxides in 3.3Al–0.5Zr ODS steel and 3.7Al–0.1Ti–0.6Zr ODS steel were characterized, respectively. The proportions of Y–Zr–O, Y–Al–O, Y–Cr–O, ZrO2 and Y2O3 in 3.3Al–0.5Zr ODS steel are 77.2%, 9.1%, 2.3%, 2.3% and 2.3%, respectively and, however, the proportions of Y–Zr–O, Y–Ti–O, Y–Al–O and ZrO2 in 3.7Al–0.1Ti–0.6Zr ODS steel are 86.5%, 8.3%, 3.5% and 1.7%, respectively. The much better dispersion morphology of oxides in 3.7Al–0.1Ti–0.6Zr ODS steel, relative to that of 3.3Al–0.5Zr ODS steel, is due to the much higher proportion of Y–Zr–O, the considerably lower proportion of Y–Al–O and the fairly high number fraction of Y–Ti–O. The mechanisms of the formation and polymorphic transition of various kinds of oxides and, moreover, the strengthening mechanisms in both ODS steels were discussed.

Breaking Down the Performance Losses in O2-Evolution Stability Tests of IrO2-based Electrocatalysts

Understanding the deactivation mechanisms affecting the state-of-the-art, Ir oxide catalysts employed in polymer electrolyte water electrolyser (PEWE-) anodes is of utmost importance to guide catalyst design and improve PEWE-durability. With this motivation, we have tried to decouple the contributions of various degradation mechanisms to the overall performance losses observed in rotating disk electrode (RDE) tests on three different, commercial Ir oxide catalysts (pure or supported on Nb2O5). Specifically, we investigated whether these performance decays stem from an intrinsic deactivation of the catalysts caused by alterations in their oxidation state, crystalline structure, morphology and/or Ir-dissolution, and also assessed possible decreases in the catalyst loading caused by the delamination of the materials over the course of these OER-stability tests. Additionally, we also examined recently reported artifacts related to the use of RDE voltammetry for such measurements and found that neither these nor the above mechanisms (or combinations thereof) can cause the totality of the observed performance losses. Beyond these uncertainties, complementary PEWE-tests showed that this apparent RDE-instability is not reproduced in this application-relevant environment.

Effect of mixing ratios of SiO[formula omitted] nanoparticles synthesized from metakaolin on the physicochemical properties of ZnO/SiO[formula omitted] nanocomposites

Nanomaterials have distinguished themselves as an outstanding class of materials due to their unique physical and chemical characteristics compared to bulk materials. The physicochemical properties of nanomaterials can be improved by forming nanocomposites and manipulating different nanoparticles by varying their mixing ratios. In this study, ZnO and SiO2 nanoparticles and ZnO/SiO2 nanocomposites were produced using a sol–gel method based on the variation of mixing ratios (1:1, 1:2 and 2:1). The monometallic oxide nanoparticles (ZnO, SiO2) and the corresponding nanocomposites (ZnO/SiO2) were characterized using HRSEM, EDX, XRD, FTIR, BET and XPS. Regardless of the mixing ratio of ZnO and SiO2 nanoparticles used, the HRSEM pictures demonstrated a morphological change from the irregular and spherical forms produced for SiO2 and ZnO nanoparticles to rod-like shapes for the ZnO/SiO2 nanocomposite. The quartz phase of SiO2 nanoparticles, with a crystallite size of 43.67 nm, and the hexagonal wurtzite phase of ZnO nanoparticles, with a crystallite size of 31.52 nm, were both synthesized, as revealed by the XRD results. As opposed to this, the XRD patterns of the ZnO/SiO2 nanocomposites synthesized with 1:1, 1:2 and 2:1 mixing ratios showed a mixture of α-quartz (SiO2) and hexagonal wurtzite (ZnO) with crystallite sizes of 21.24, 29.56 and 15.36 nm, respectively. The EDS results confirmed the existence of Zn and O for ZnO; Si and O for SiO2 nanoparticles and Zn, Si and O in the prepared ZnO/SiO2 nanocomposite, irrespective of the mixing ratios. The XPS results showed the existence of Zn in the +1 oxidation state in ZnO/SiO2 compared to single ZnO with the Zn2+ valence. The BET surface area indicates that the ZnO/SiO2 nanocomposites had a higher surface area (1:1 (39.042 m2/g), 1:2 (55.602 m2/g) and 2:1 (82.243 m2/g)), irrespective of the mixing ratios, compared to the surface area for the ZnO (8.620 m2/g) and SiO2(0.386 m2/g) nanoparticles. The mixing ratio of the ZnO and SiO2 nanoparticles influenced the crystallite sizes, surface elements oxidation states and morphology of the ZnO/SiO2 nanocomposite formed and the optima mixing ratio for the formation of ZnO/SiO2 nanocomposite was found to be 2:1 of ZnO:SiO2 nanoparticles.

Influence of zinc oxide morphology on its photocatalytic properties

The rapid development of industry, in addition to the positive impact, has led to environmental problems. The release of polluting waste containing substances such as dyes, pesticides, heavy metals and pharmaceutical waste leads to contamination of water reservoirs, that has a negative impact on humans and aquatic organisms. In this regard, the development of an inexpensive, effective, environmentally friendly method of waste water treatment from organic pollutants is an urgent research priority. Zinc oxide (ZnO) is one of the most active semiconductor photocatalysts. In this paper, the influence of the morphology of nanostructured zinc oxide synthesized by effective methods on photocatalytic properties with respect to the rhodamine-B dye (RhB)was investigated, and the influence of the length-to-thickness ratio (aspect ratio AR) of ZnO samples on its structural and optical properties was studied. The results of the study showed that an increase in the annealing temperature of zinc acetate in the atmosphere leads to an increase in the size of zinc oxide crystallites, while an increase in the concentration of alkali in the growth solution (synthesis of ZnO by chemical deposition from 0.4 M to 0.7 M) makes it possible to synthesize thinner extended 2D plates. It is shown that an increase in the AR value of the synthesized samples makes it possible to increase their photocatalytic activity.

Corrosion behavior of strontium modified Al-12Si cast alloys in flowing and stagnant chloride containing media

The Al-12Si alloy was modified with strontium varied from 0.1% to 0.35% in order to unveil its effect on corrosion resistance in static as well as in flowing solution with and without 3.5% NaCl at pH∼11. The Sr contents upto 0.18% changed the eutectic morphology to fine fibrous network beyond which, the acicular silicon begun to emerge. The corrosion resistance of both modified and unmodified Al-12Si alloy during flow reduced to as low as 30% of that observed during static condition. The 0.25% Sr containing alloy exhibited superior corrosion resistance to other variants including unmodified alloy. The Raman spectroscopy and XRD analyses of corrosion product unveiled the presence of bayerite on both unmodified and modified Al-12Si alloys, irrespective of presence of Cl- in the solution. The Sr additions, except 0.25%, degrades corrosion resistance of Al-12Si alloy in both during flow and static conditions. The corrosion resistance of 0.25% Sr is correlated to the evolution of thicker and different oxide morphology along with presence of relatively large silicon on the surface after corrosion.

Atomic-Scale Mechanisms of MoS2 Oxidation for Kinetic Control of MoS2/MoO3 Interfaces.

Oxidation of transition metal dichalcogenides (TMDs) occurs readily under a variety of conditions. Therefore, understanding the oxidation processes is necessary for successful TMD handling and device fabrication. Here, we investigate atomic-scale oxidation mechanisms of the most widely studied TMD, MoS2. We find that thermal oxidation results in α-phase crystalline MoO3 with sharp interfaces, voids, and crystallographic alignment with the underlying MoS2. Experiments with remote substrates prove that thermal oxidation proceeds via vapor-phase mass transport and redeposition, a challenge to forming thin, conformal films. Oxygen plasma accelerates the kinetics of oxidation relative to the kinetics of mass transport, forming smooth and conformal oxides. The resulting amorphous MoO3 can be grown with subnanometer to several-nanometer thickness, and we calibrate the oxidation rate for different instruments and process parameters. Our results provide quantitative guidance for managing both the atomic scale structure and thin-film morphology of oxides in the design and processing of TMD devices.