X-ray Photoemission Spectroscopy Analysis Research Articles

Overcoming poisoning issues in hydrogen fuel cells with face-centered tetragonal FePt bimetallic catalysts

Hydrogen fuel cells are expected to play a central role in the next-generation energy paradigm. However, owing to practical limitations, hydrogen is supplied in the form of refined hydrocarbons or alcohols in industrial applications. Among them, methanol is widely used as a hydrogen source, and CO is inevitably generated during its oxidation process. Even a small amount of CO (∼20 ppm) strongly binds to Pt used as a catalyst, and deactivates it. In addition to CO, surface adsorption of organic cations by binder or ionomer use in alkaline fuel cells is also one of the poisoning issues to be overcome. Herein, we propose FePt bimetallic catalysts that can resist unavoidable CO and organic cation poisoning. Our synthetic strategy, including annealing and acid treatment, allows the catalysts to possess different alloying degrees and surface structures, which in turn induce different levels of resistance to CO and organic-cation poisonings. The correlation between the surface and bulk structures of the catalysts and poisoning resistance was elucidated through X-ray photoemission spectroscopy and electrochemical analysis. The results revealed that an FePt catalyst having an ordered atomic arrangement displayed a better poisoning resistance than that having a disordered arrangement.

Atmospheric plasma treatment: an alternative of HF etching in lithium disilicate glass-ceramic cementation.

Objectives: This study aimed to investigate whether the atmospheric pressure plasma jet (APPJ) could modify the surface of lithium disilicate glass ceramics (LDC) instead of hydrofluoric acid (HF) in LDC resin cementation. Methods: Two hundred and thirty-two LDC blocks were randomly divided into seven groups: Group 1 (16 specimens) was the blank control group (without HF or APPJ treatment); Group 2 (36 specimens) was etched by HF; Groups 3-7 (36 specimens each) were treated with APPJ, and the relative air humidity (RAH) of the discharge was 22.8%, 43.6%, 59.4%, 75.2%, and 94.0%, respectively. Three LDC blocks in each group were characterized via X-ray photoemission spectroscopy (XPS) analyses, 3 blocks via contact angle measurements, and other 10 blocks via surface roughness measurements. The residual LDC blocks in groups 2-7 were cemented to composite cylinders. Testing the cemented specimens' shear bond strength (SBS) before and after thermocycling (6,500 cycles of 5°C and 55°C) revealed fracture patterns. Data were analyzed by ANOVA (post hoc: Bonferroni) (α = 0.05). Results: After APPJ treatment, the water contact angle values of APPJ treated blocks dropped from 31.37° to 5.66°, while that of HF etched ones dropped to 18.33°. The O/C ratio increased after HF etching or APPJ treatment according to the calculated results, except for the APPJ-treated samples at a RAH of 22.8%. The surface roughness of LDC blocks showed no statistic difference before and after APPJ treatment, but experienced significant difference after HF etching. The O/Si and O/C ratios varied after HF etching or APPJ treatment. No significant difference in SBS values could be found among groups 2-7 before or after artificial aging (p > 0.05). All specimens showed mixed failure patterns. Conclusion: The APPJ treatment method reported in this study is a promising novel strategy for surface modification of the LDC. With acceptable bonding strength, it might be an alternative to HF in LDC-resin cementation.

Mitigation of arsenic stress in Brassica juncea L. using zinc oxide-nanoparticles produced by novel hydrothermal synthesis

In the current study, we successfully synthesized the zinc oxide nanoparticles (ZnO-NPs) via an efficient, facile, and cost-effective method of the modified hydrothermal synthesis approach, and examined their effectiveness in alleviating arsenic (As) stress in Brassica juncea. The synthesized ZnO-NPs were analyzed using a variety of experimental techniques viz. XRDs, SEM micrographs, EDAX/Mapping pattern, Raman Spectroscopy Pattern, and X-ray photoemission spectroscopy analysis. All of these analyses revealed that ZnO-NPs were highly pure with no internal defects and could potentially be used in plant applications. Hence, we further determined the effect of these nanoparticles in modulation of As tolerance in B. juncea plants by examining the various growth attributes, photosynthesis parameters, antioxidant activities, and enzyme activities. Our results demonstrated that As-stress inhibited growth, photosynthesis-related parameters, reduced protein content, as well as carbonic anhydrase, nitrate reductase, and RuBisCO; however, these attributes were substantially up-regulated by the supply of ZnO-NPs to the leaves. Furthermore, As stress-induced increases in malondialdehyde and H2O2 levels are partially reversed by ZnO-NP in the As-stressed plants. Overall, supplementation positively regulated As tolerance in B. juncea by altering the key enzymes involved in ROS detoxification, which in turn prevented As-induced oxidative damage to the plant tissues. Hence, our study clarified the potential involvement of the newly synthesized ZnO-NPs in alleviating As stress in plants. Furthermore, this is the first report to elucidate the effect of the ZnO-NPs synthesized by the hydrothermal reaction route on As-stress modulation in B. juncea.

Enhancing arsenic adsorptions by optimizing Fe-loaded biochar and preliminary application in paddy soil under different water management strategies.

Arsenic (As) is widely distributed in nature and is a highly toxic element impacting human health through drinking water and rice. In this study, an optimized approach was attempted to improve As adsorption capabilities by combining pre- and post-pyrolysis modification of Fe(oxy)hydroxides to rice husk biochar (FRB), of which the method is rarely addressed in previous studies. Maghemite and goethite were successfully loaded onto biochar, characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and X-ray photoemission spectroscopy (XPS) analyzer. The FRB had maximum As(III) and As(V) adsorption capabilities of 7908 and 11,268mg/kg, respectively, which was significantly higher than that of Fe-modified biochar in the pre-pyrolysis and/or post-pyrolysis process. Adsorption mechanisms for As explored by Fourier-transform infrared spectroscopy (FTIR), XPS analysis mainly included electronic attraction and ligand exchange with hydroxyl groups on the FRB. It was noteworthy that more than half of the As(II) species loaded on FRB were converted into less toxic As(V) species, which could be mediated by the redox-active groups on the biochar. The preliminary application of FRB in soil indicated that it has an effective remediation potential for As-contaminated soil under flooded conditions, while promoted As release under dry conditions. Finding of this study highlighted that the loading of metal oxides onto biochar by combining pre- and post-pyrolysis modification could potentially increase As adsorption capabilities and further help in strategic water management.

Synthesis and comprehensive synchrotron-based structural analysis of Si-doped nanodiamond composite films deposited on cemented carbide

Si-doped nanodiamond composite (NDC) films were deposited on unheated WC − Co substrates by coaxial arc plasma deposition for advanced cutting tools applications. The nanoindentation test revealed changes in films hardness and Young's modulus attributed to various Si doping concentrations (0, 1, 5, and 20 at.%) and the catalytic effects of Co diffused from the substrate surface into the films. To reveal the physical origin behind these changes, the films' structure was examined by synchrotron-based Auger electron spectroscopy (AES), soft X-ray photoemission spectroscopy (XPS), and near edge X-ray absorption fine structure spectroscopy (NEXAFS). The AES and XPS analysis showed a consistent correlation between nanoindentation measurements and the estimated C sp3 fraction in the films. The NEXAFS spectra revealed intense C − C σ* resonance, consistent with the measured film hardness. The 1 at.% Si-doped film, deposited with an undoped NDC buffer layer to mitigate the Co catalytic effects, exhibited the highest hardness of 60 GPa, the largest C sp3 fraction, and the most intense CC σ* peak. Si doping resulted in the formation of C − Si sp3 bonds at the expense of C sp2 bonds, increasing the fraction of C sp3 bonds and enhancing film hardness. The synchrotron-based analysis effectively revealed the electronic states of NDC hard coatings, particularly after the removal of surface contaminants through mechanical polishing.

Electrically erasable writing properties of ZnS films by conductive atomic force microscopy

Resistive switching cycles were realized in Au/ZnS/substrate (indium–tin oxide (ITO), Cu, Si) structures, and electrically erasable writing operations were achieved in the Au/ZnS/Si structure using conductive atomic force microcopy. High-resolution transmission electron microscopy revealed that high resistance state was a mixture of amorphous and nanocrystalline state, while the frequency response of alternating current conductivity indicated that the low resistance state (LRS) was only nanocrystalline. Electric field and thermal effects contributed to the distribution of conductive defects in the ZnS film, and nearest-neighbor hopping conduction controlled the electrical resistance of the Au/ZnS/ITO structure. X-ray photoemission spectroscopy analysis of conductive defects of ZnS films in the LRS revealed that they were zinc-rich or sulfur-poor. This study confirms the intrinsic resistive switching characteristic of ZnS films, which can serve as nonoxide materials for nonvolatile memory application.

Intrinsic resistive switching in ultrathin SiOx memristors for neuromorphic inference accelerators

Two-dimensional (2D) materials are promising memristive materials owing to their outstanding physical properties, electrical tunability and fast switching capability. However, 2D layered materials generally require sophisticated deposition techniques at the expense of limited large-scale homogeneity and high growth temperatures. Furthermore, the variability and reliability of the 2D materials based memristor should be further improved. Here, we report an intrinsic memristor based on ultrathin 2D-like nonlayered amorphous SiOx which is derived from a native oxidation process at ambient temperature. Such 2D-like memristors demonstrate low switching variability (3.7 %), nanosecond switching speed (15 ns), good endurance (>106 cycles) and high retention (>103 s at 85 °C). We verified the resistive switching mechanism via in-depth X-ray photoemission spectroscopy (XPS) analysis at different resistance states and confirmed the oxygen vacancies movement under the electric field between the SnOx reservoir layer and the SiOx layer. Moreover, Simulation results for an MNIST image classifier based on the ultrathin SiOx memristor show a high recognition accuracy of ∼ 98 %, manifesting its potential for the practical implementation of nonlayered 2D-like materials based neural network inference accelerator.

Flower-like Layered NiCu-LDH/MXene Nanocomposites as an Anodic Material for Electrocatalytic Oxidation of Methanol

Direct methanol fuel cell (DMFC) technology has grabbed much attention from researchers worldwide in the realm of green and renewable energy-generating technologies. Practical applications of DMFCs are marked by the development of highly active, efficient, economical, and long-lasting anode catalysts. Layered double hydroxide (LDH) nanohybrids are found to be efficient electrode materials for methanol oxidation. In this study, we synthesized NiCu-LDH/MXene nanocomposites (NCMs) and investigated their electrochemical performance for methanol oxidation. The formation of NCM was verified through field emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Brunauer-Emmett-Teller (BET), and X-ray photoemission spectroscopy (XPS) analyses. The cyclic voltammetry, chronoamperometry, and electron impedance spectroscopy techniques were carried out to assess the electrocatalytic ability of the methanol oxidation reaction. The incorporation of MXene enhanced the methanol oxidation 2-fold times higher than NiCu-LDH. NCM-45 exhibited high peak current density (86.9 mA cm-2), enhanced electrochemical active surface area (7.625 cm2), and long-term stability (77.8% retention after 500 cycles). The superior performance of NCM can be attributed to the synergistic effect between Ni and Cu and, further, the electronic coupling between LDH and MXene. Based on the results, NCM nanocomposite is an efficient anodic material for the electrocatalytic oxidation of methanol. This study will open the door for the development of various LDH/MXene nanocomposite electrode materials for the application of direct methanol fuel cells.

Synthesis and crystallization of (Co, Cr, Fe, Mn, Ni)3O4 high entropy oxide: The role of fuel and fuel-to-oxidizer ratio

The main object of this study is to synthesize (Co, Cr, Fe, Mn, Ni)3O4 high-entropy oxide through the solution combustion synthesis (SCS) method in the presence of different fuels at various fuel-to-oxidizer (F/O) ratios. Differential thermal analysis (DTA) and in-situ high-temperature XRD (HT-XRD) results demonstrated the high degree of thermal stability of the synthesized powder up to 1100 ​°C. According to XRD results, the single-phase high-entropy oxide was crystallized at fuel-lean conditions without any heat treatment. However, the single-phase high-entropy oxide was crystallized in all samples when they were heat-treated at 600 ​°C. X-ray photoemission spectroscopy (XPS) analysis and elemental-mapping analysis results clarified the high homogeneity of the obtained powder. Statistical analysis of results revealed a direct correlation of F/O, crystallinity, crystallite size, and lattice distortion values with magnetization saturation (Ms). Besides, the data represent an indirect correlation between micro-strain and Ms. The highest amount of Ms (14.6 emu/g) was obtained for the synthesized sample with a lattice distortion of 10.28%. Moreover, a specific surface area (SBET) value of 121 ​m2/g was obtained. In summary, the results indicated the significant role of fuel type and F/O ratio in improving the physicochemical properties of SCS synthesized (Co, Cr, Fe, Mn, Ni)3O4 high-entropy oxide.

Biofunctionalization of Porous Titanium Oxide through Amino Acid Coupling for Biomaterial Design.

Porous transition metal oxides are widely studied as biocompatible materials for the development of prosthetic implants. Resurfacing the oxide to improve the antibacterial properties of the material is still an open issue, as infections remain a major cause of implant failure. We investigated the functionalization of porous titanium oxide obtained by anodic oxidation with amino acids (Leucine) as a first step to couple antimicrobial peptides to the oxide surface. We adopted a two-step molecular deposition process as follows: self-assembly of aminophosphonates to titanium oxide followed by covalent coupling of Fmoc-Leucine to aminophosphonates. Molecular deposition was investigated step-by-step by Atomic Force Microscopy (AFM) and X-ray Photoemission Spectroscopy (XPS). Since the inherent high roughness of porous titanium hampers the analysis of molecular orientation on the surface, we resorted to parallel experiments on flat titanium oxide thin films. AFM nanoshaving experiments on aminophosphonates deposited on flat TiO2 indicate the formation of an aminophosphonate monolayer while angle-resolved XPS analysis gives evidence of the formation of an oriented monolayer exposing the amine groups. The availability of the amine groups at the outer interface of the monolayer was confirmed on both flat and porous substrates by the following successful coupling with Fmoc-Leucine, as indicated by high-resolution XPS analysis.

Bifunctional electrocatalytic activity of two-dimensional multilayered vanadium carbide (MXene) for ORR and OER

MXenes are a new class of 2D materials that demonstrate effective bifunctional electrocatalytic activity for oxygen reduction (ORR) and evolution reactions (OER). We synthesized V2C (VC–HF) MXene from V2AlC (VAC) via etching using HF at low temperatures. The structure, composition, and morphology of VC-HF MXene were determined using X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS), Scanning electron microscopy (SEM), and Transmission electron microscopy (TEM) analysis. The XPS analysis demonstrated that VC-HF contained a small amount of Al, suggesting the presence of unreacted VAC even after etching. With an impressive ΔE of ∼0.90 V (the potential difference between ORR and OER), the VC-HF MXene exhibited excellent ORR and OER catalytic activity. This electrocatalyst showed an Eonset of 0.87 V for the reduction of O2, which is remarkable compared to those of the reported bifunctional oxygen catalysts, and exhibited a 430 mV OER overpotential value (η10) at 10 mA cm−2. Besides higher catalytic activity, VC-HF MXene demonstrated good catalytic stability over 10000 s. This work suggests that VC-HF is a promising and efficient bifunctional catalyst for use in various oxygen-based electrochemical devices.

Fabrication of Antibacterial TiO2 Nanostructured Surfaces Using the Hydrothermal Method.

Implant-associated infections (IAI) are a common cause for implant failure, increased medical costs, and critical for patient healthcare. Infections are a result of bacterial colonization, which leads to biofilm formation on the implant surface. Nanostructured surfaces have been shown to have the potential to inhibit bacterial adhesion mainly due to antibacterial efficacy of their unique surface nanotopography. The change in topography affects the physicochemical properties of their surface such as surface chemistry, morphology, wettability, surface charge, and even electric field which influences the biological response. In this study, a conventional and cost-effective hydrothermal method was used to fabricate nanoscale protrusions of various dimensions on the surface of Ti, Ti6Al4V, and NiTi materials, commonly used in biomedical applications. The morphology, surface chemistry, and wettability were analyzed using scanning electron microscopy (SEM), X-ray photoemission spectroscopy (XPS), and water contact angle analysis. The antibacterial efficacy of the synthesized nanostructures was analyzed by the use of Escherichia coli bacterial strain. XPS analysis revealed that the concentration of oxygen and titanium increased on Ti and Ti6Al4V, which indicates that TiO2 is formed on the surface. The concentration of oxygen and titanium however decreased on the NiTi surface after hydrothermal treatment, and also a small amount of Ni was detected. SEM analysis showed that by hydrothermal treatment alterations in the surface topography of the TiO2 layer could be achieved. The oxide layer on the NiTi prepared by the hydrothermal method contains a low amount of Ni (2.8 atom %), which is especially important for implantable materials. The results revealed that nanostructured surfaces significantly reduced bacterial adhesion on the Ti, Ti6Al4V, and NiTi surface compared to the untreated surfaces used as a control. Furthermore, two sterilization techniques were also studied to evaluate the stability of the nanostructure and its influence on the antibacterial activity. Sterilization with UV light seems to more efficiently inhibit bacterial growth on the hydrothermally modified Ti6Al4V surface, which was further reduced for hydrothermally treated Ti and NiTi. The developed nanostructured surfaces of Ti and its alloys can pave a way for the fabrication of antibacterial surfaces that reduce the likelihood of IAI.

The photocatalytic degradation of phenol under solar irradiation using microwave-assisted Ag-doped ZnO nanostructures

The contamination of water resources in the world is increasing daily and is a significant environmental concern for humanity. Phenol and its derivatives are the most hazardous water pollutants emerging from industries. Therefore, developing a cost-effective technique to remove phenol from contaminated water is essential. With the advent of nanotechnology, many types of research have been conducted to use this technology to filter water. In this study, silver-doped zinc oxide NRs of varying doping concentrations were synthesized by microwave-assisted technology for the degradation of phenol under sunlight light. After the synthesis, Ag–ZnO NRs were annealed at 550 °C. The morphology and crystallinity of the samples were studied with X-ray diffraction (XRD) and Field Emission Scanning Electron Microscopy (FESEM). The results showed two distinct types of structures, hexagonal and cubic. Silver doping into the zinc oxide lattice was validated by X-ray photoemission spectroscopy (XPS) and Energy dispersive X-Ray analysis (EDX). The optical properties of these NRs were also studied and showed a significant improvement in the energy band gap due to doping with silver. In photocatalysis performance, the 0.5 at.% Ag-doped ZnO NRs are the best candidate for removing phenol contamination under solar light irradiation. The photocatalytic kinetics in 0.5% Ag–ZnO are observed to be seven times greater than that achieved in 0% Ag - ZnO NRs, and the degradation rate reaches 98.5% after 5 h for removing phenol contamination under solar light irradiation.

Insights into manganese ferrite anchored graphene oxide to remove Cd(II) and U(VI) via batch and semi-batch columns and its potential antibacterial applications

The bioaccumulation, non-biodegradability, and high toxicity of Cd(II) and U(VI) in water is a serious concerns. Manganese ferrite/graphene oxide (GMF) nanocomposites were synthesized, characterized, and used to efficiently remove Cd(II) and U(VI) from an aqueous solution in this study. X-ray diffraction (XRD) and X-ray photoemission spectroscopy (XPS) analyses, respectively, confirmed the formation of GMF and the adsorptive removal mechanism. The XRD results revealed an amorphous structure when MnFe2O4 was loaded onto the GO surface. XPS results suggest that C = C, C−OorOH, and metal oxides are responsible for the removal of Cd(II) and U(VI) via electrostatic and chemical interaction. According to the Brunauer Emmett and Teller (BET), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) characterization analysis, GMF has a high surface area (117.78 m2/g) and a spherical shape with even distribution. The kinetics data were successfully reproduced by a pseudo-second-order non-linear model indicating the complexity of the sorption mechanism was rate-limiting. The maximum Langmuir uptake ability of GMF for Cd(II) and U(VI) was calculated to be 232.56 mg/g and 201.65 mg/g, respectively. Using external magnetic power, the prepared GMF can easily separate from the aqueous solution and can keep both metal ions under Environmental protection agency standards in water for up to six cycles of re-use of GMF. Finally, the GMF nanocomposite demonstrated significant promise as an adsorbent for removing Cd(II) and U(VI) from actual contaminated water samples. The antibacterial test was expanded to include gram-negative E. coli and gram-positive S. aureus to better understand GMF's bacterial inhibition efficacy.

Room temperature giant magneto-caloric effect in Ni45Mn44Sn11-XInX (X = 1, 3) disordered Heusler alloy: The role of martensite transition

Here, we report the first order martensite to austenite transition characterized through magnetic and calorimetric studies in (off-stoichiometric) shape memory Heusler alloy Ni45Mn44Sn11-XInX (X = 1; 3) in the proximity of room temperature. The structural properties of the alloys were checked with x-ray diffraction (XRD), x-ray photoemission spectroscopy (XPS) and energy dispersive x-ray analysis (EDXA). The dominance of a particular phase (martensite or austenite) at room temperature can be predicted from the structural study by XRD as two different phases (L21 and 10 M) were found at room temperature with different proportion for the two alloys. Martensite transition was observed near the room temperature for both samples which was monitored with differential calorimetry and magnetization study. A large magneto-caloric effect was found in the system near the room temperature observed from the magnetic measurements. The calculated entropy change (3.24 JKg−1K−1 and 11.2 JKg−1K−1 for X = 1 and 3 respectively) and the refrigerant capacity (27 JKg−1 and 40 JKg−1 for X = 1 and 3 respectively) for 3 T magnetic field were found to be significant for practical applications near room temperature. A small amount of In substitutions in Sn sites have influenced the martensite transition as a significant increase in the martensite transition temperature has been observed. The magnetocaloric effect in these materials has been understood in the realm of sharp magnetization change arising in the vicinity of metamagnetic transition from the martensite phase (weakly magnetic) to the austenite phase (ferromagnetic). The In substitution is thought to influence the hybridization between Ni-Mn bonds which in turn influence the martensite transition and thereby enhancing the magnetocaloric property of the materials.

High temperature crystallographic and low temperature magnetic phase transitions in Fe doped Sr2RuMnO6

Fe doped Sr2RuMnO6 (SRMO) double perovskites (Sr2RuMn1-xFexO6, x = 0, 0.1, 0.2 and 0.3) were prepared by solid-state route. Both x-ray diffraction and Raman spectroscopy were performed to investigate the crystal structure of the synthesized double perovskites. Rietveld refinement of the x-ray diffraction patterns confirmed a phase transition from tetragonal to cubic space group as a function of doping concentration of iron. Raman spectroscopy at room temperature and group theory analysis revealed the phonon modes associated with the space group of the samples. The temperature dependent Raman spectroscopy showed an anharmonic behaviour of the phonon modes of the Fe doped SRMO samples. The temperature evolution of the phononic modes in the range of 300 K–620 K is predominantly influenced by the lattice degrees of freedom. The presence of several oxidation states Mn (2+, 3+ and 4+) and Fe (3+ and 4+) was confirmed by an X-ray photoemission spectroscopy analysis of the highest doped sample (x = 0.3). The magnetic properties measurements showed that the samples were completely paramagnetic at room temperature. The samples exhibit antiferromagnetism at very low temperatures and we conclude that they exhibit ferrimagnetic ground state in the mid temperature region.

Giant exchange bias in antiferromagnetic Pr2CoFe0.5Mn0.5O6: a structural and magnetic properties study

Antiferromagnetic (AFM) materials with a colossal exchange bias (EB) effect find applications as high-density spintronic devices. We report structural (geometrical and electronic) and magnetic studies in the polycrystalline Pr2CoFe0.5Mn0.5O6 double perovskite system. The observed lack of training effect suggests the existence of robust EB. In addition, the detailed magnetic studies and Raman studies unravel the Griffith-like phase along with the spin-phonon coupling in the present system. The x-ray photoemission spectroscopy (XPS) analysis supports more than one valence state of B-site elements, which is accountable for the competition between ferromagnetic (FM) and AFM interactions in addition to the anti-site disorder in the system. The neutron measurement confirms the G-type AFM spin arrangement, accredited by the DFT calculation. The magnetic studies have correlated with the electronic structure, neutron study, and theoretical first principle calculations.

Hydrophobic properties and chemical state analysis of wear resistant coating prepared by electrical discharge process

Electrical discharge coating (EDC) process has been used to prepare a corrosion and wear resistant super-hydrophobic coating on the steel substrate. The coating process has been carried out by using three types of green compact tool electrodes (WS2/Cu, MoS2/Cu, and hBN/Cu). In these tool electrodes, powder mixing ratios (40:60, 50:50, 60:40) are varied, and their effect on coating characteristics (surface morphology, wettability, corrosion, and wear behaviour) has been studied. In this investigation, the morphology and chemical state of coating has been observed by using a scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS). SEM images of the applied coating show a porous and hierarchical structure. This hierarchical structure helps in raising the contact angle (CA) to 165.6° (super-hydrophobic state). The XPS analysis reveals that the deposition of solid lubricants takes place with their negligible disintegration into non-lubricating compounds. In addition, the prepared coating exhibits excellent resistance to wear and corrosion.

Bimetallic Au-Pd/α-MoO3 Catalyst with High Oxygen Vacancies for Selective Oxidation of Cinnamyl Alcohol

Supported Au-Pd nanoparticles (NPs) have been extensively studied in alcohol oxidation reactions. However, few studies use reducible metal oxides as support, which can activate oxygen molecules and boost the selectivity of the reaction. In this work, Au-Pd NPs were supported on α-MoO3 and evaluated in the selective oxidation of cinnamyl alcohol without solvent. The Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, and X-ray photoemission spectroscopy (XPS) analyses showed that the catalyst is richer in oxygen vacancies than the support, being probably responsible for the stability of the NPs (average size 4.62 ± 0.15 nm) and the high conversion and selectivity for the oxidation of cinnamyl alcohol. Furthermore, experiments have shown that the Au:Pd molar ratio influences the catalytic performance and can be optimized by controlling temperature, pressure, and reaction time. The catalyst proved to be active and selective for cinnamaldehyde in short reaction times. It showed satisfactory performance at 30 min and its best activity at 1 h with 94% conversion and 87% selectivity, without loss of activity and selectivity after four runs under the same reaction conditions.

Thickness-Dependent Structural and Electrical Properties of WS2 Nanosheets Obtained via the ALD-Grown WO3 Sulfurization Technique as a Channel Material for Field-Effect Transistors.

Ultrathin WS2 films are promising functional materials for electronic and optoelectronic devices. Therefore, their synthesis over a large area, allowing control over their thickness and structure, is an essential task. In this work, we investigated the influence of atomic layer deposition (ALD)-grown WO3 seed-film thickness on the structural and electrical properties of WS2 nanosheets obtained via a sulfurization technique. Transmission electron microscopy indicated that the thinnest (1.9 nm) film contains rather big (up to 50 nm) WS2 grains in the amorphous matrix. The signs of incomplete sulfurization, namely, oxysulfide phase presence, were found by X-ray photoemission spectroscopy analysis. The increase in the seed-film thickness of up to 4.7 nm resulted in a visible grain size decrease down to 15–20 nm, which was accompanied by defect suppression. The observed structural evolution affected the film resistivity, which was found to decrease from ∼106 to 103 (μΩ·cm) within the investigated thickness range. These results show that the thickness of the ALD-grown seed layer may strongly affect the resultant WS2 structure and properties. Most valuably, it was shown that the growth of the thinnest WS2 film (3–4 monolayers) is most challenging due to the amorphous intergrain phase formation, and further investigations focused on preventing the intergrain phase formation should be conducted.