Surface Composition Research Articles

Catalytic ammonia synthesis by supported molybdenum nitride: insight into the support effect

The influence of the support on the performance of Mo nitrides has been investigated in ammonia synthesis and decomposition. A series of Mo‐N catalysts supported on different materials, namely SiO2 (commercial, SBA‐15), Al2O3 and CeO2, were prepared. The results showed that, despite high dispersion of Mo species in all catalysts, large disparities in activity for ammonia synthesis exist. Initial rates of ~ 1208, ~ 481 and ~ 372 µmol gactive phase‐1 h‐1 are obtained over 10‐Mo‐N/SBA‐15, 10‐Mo‐N/SiO2 and 10‐Mo‐N/Al2O3 respectively. However, no catalytic activity was registered when Mo species were supported on CeO2. Furthermore, 10‐Mo‐N/Al2O3 deactivated after few hours of reaction. The surface composition was studied by means of XPS to probe the origin of the catalytic activity differences, and the results showed that a range of various oxidation states of Mo was detected depending on the support. The difference in catalytic behavior could not be solely explained by the differences in Mo‐N species concentrations. In situ EPR analysis showed that the mechanism of MoO3 nitridation could differ depending on the support, leading to the formation of different Mo‐N species. The effect of support was however not as severe in ammonia decomposition as it was the case of ammonia synthesis.

Development of phage-containing hydrogel for treating Enterococcus faecalis-infected wounds.

Chronic wound infections caused by Enterococcus faecalis pose formidable challenges in clinical management, exacerbated by the emergence of vancomycin-resistant strains. Phage therapy offers a targeted approach but encounters delivery hurdles. Due to their biocompatibility and controlled release properties, hydrogels hold promise as carriers. This study aimed to fabricate phage-containing hydrogels using sodium alginate (SA), carboxymethyl cellulose (CMC), and hyaluronic acid (HA) to treat E. faecalis-infected wounds. We assessed the efficacy of these hydrogels both in vitro and in vivo. The hydrogel was prepared using SA-CMC-HA polymers. Phage SAM-E.f 12 was incorporated into the SA-CMC-HA hydrogel. The hydrogel's swelling index was measured after 24 h, and degradation was assessed over seven days. Surface morphology and composition were analyzed using Scanning Electron Microscopy (SEM) and Fourier-transform infrared spectroscopy (FTIR). Antibacterial activity was tested via optical density (OD) and disk diffusion assays. Phage release and stability were evaluated over a month. In vivo efficacy was tested in mice through wound healing and bacterial count assays, with histopathological analysis. Hydrogels exhibited a swelling index of 0.43, a water absorption rate of %30, and 23% degradation over seven days. FTIR confirmed successful polymer incorporation. In vitro studies demonstrated that phage-containing hydrogels significantly inhibited bacterial growth, with an OD of 0.3 compared to 1.1 for the controls. Hydrogels remained stable for four weeks. In vivo, phage-containing hydrogels reduced bacterial load and enhanced wound healing, as shown by improved epithelialization and tissue restoration. Phage-containing hydrogels effectively treat wounds infected with E. faecalis-infected wounds, promoting wound healing through controlled phage release. These hydrogels can improve clinical outcomes in the treatment of infected wounds.

Microstructure and mechanical properties of Al2O3/AZ61 Mg alloy surface composite developed using friction stir processing and groove reinforcement filling processes

Abstract In this work, the alumina (Al2O3) particles-reinforced AZ61 magnesium (Mg) alloy surface composite was fabricated using friction stir processing (FSP) and groove reinforcement filling methods. The Mg alloy surface composites were developed with and without the addition of Al2O3 reinforcing particles, and their mechanical performance was compared with each other and with unprocessed base metal (BM). The Al2O3 powder was compressed into a groove of 4.5 mm depth that had been created in AZ61 Mg alloy plates. The volume fraction of Al2O3 powder was increased to 5, 10, and 15 vol.% depending on the width of the groove. Results disclosed that the problem of cluster formation of reinforcing Al2O3 particles was minimized by performing FSP in five number of passes. The ultimate tensile strength (UTS) and hardness of AZ61 Mg alloy were enhanced by 6.07 % and 22.23 % when it was subjected to FSP. This is primarily correlated to the significant refining of grains due to the severe plastic deformation associated with FSP. The 15 vol.%-FSPed Al2O3/AZ61 Mg alloy surface composite showed a higher UTS of 630 MPa and hardness of 300 HV. This is due to the integration of a greater quantity of Al2O3 particles with substantial grain refining.

Carbon Nanoparticle Oxidation by NO2and O2: Chemical Kinetics andReaction Pathways.

Carbon nanoparticle interactions with gases are central to many environmental and technical processes, but the underlying reaction kinetics and mechanisms are not well understood. Here, we investigate the oxidation and gasification of carbon nanoparticles by NO2and O2under combustion exhaust conditions. We build on a comprehensive experimental data set and use a kinetic multilayer model (KM-GAP-CARBON) to trace the uptake and release of gas molecules alongside the temporal evolution of particle size and surface composition. The experimental results are captured by a model mechanism that involves different types of carbon atoms (edge/plane-like) and the formation of a reactive oxygen intermediate (activated CO complex) as the rate-limiting step. A transition between distinct chemical regimes driven by NO2at lower temperatures and O2at higher temperatures is reflected by an increase in the observable activation energy from ~60 kJ/mol to ~130 kJ/mol. We derive energy profiles for three alternative reaction pathways that involve uni- or bimolecular decomposition of reactive oxygen intermediates.

Carbon Nanoparticle Oxidation by NO2 and O2: Chemical Kinetics and Reaction Pathways

Carbon nanoparticle interactions with gases are central to many environmental and technical processes, but the underlying reaction kinetics and mechanisms are not well understood. Here, we investigate the oxidation and gasification of carbon nanoparticles by NO2 and O2 under combustion exhaust conditions. We build on a comprehensive experimental data set and use a kinetic multilayer model (KM‐GAP‐CARBON) to trace the uptake and release of gas molecules alongside the temporal evolution of particle size and surface composition. The experimental results are captured by a model mechanism that involves different types of carbon atoms (edge/plane‐like) and the formation of a reactive oxygen intermediate (activated CO complex) as the rate‐limiting step. A transition between distinct chemical regimes driven by NO2 at lower temperatures and O2 at higher temperatures is reflected by an increase in the observable activation energy from ~60 kJ/mol to ~130 kJ/mol. We derive energy profiles for three alternative reaction pathways that involve uni‐ or bimolecular decomposition of reactive oxygen intermediates.

Ultrafast laser-induced simultaneous carbonization and texturization of titanium alloy surface and its tribological properties

Due to the poor tribological properties, the applications of titanium alloy are restricted. Both laser texturing and surface coating are effective methods to enhance the tribological properties of titanium alloy surfaces. Hence, this study proposed a new ultrafast laser-induced simultaneous carbonization and texturization of titanium alloy surfaces to improve its tribological properties by modifying titanium alloy’s surface composition and micro-nanostructures in one step. A polymer film (polyimide, PI) was selected as the carbon source preplaced on the titanium alloy (Ti-6Al-4 V, TC4) surface. On the one hand, under ultrafast laser (picosecond 355 nm laser) irradiation, the laser-induced photothermal effect led to the carbonization of the polymer film and the formation of the pyrolytic carbon coating on the titanium alloy surface. Pyrolytic carbon also reacted with titanium alloy to form titanium carbides. On the other hand, ultrafast lasers also led to the melting and ablation of the titanium alloy surface, creating micro-nanostructures with interlocking micro-holes and micro-bumps. The coefficient of friction (COF) and wear rate of the titanium alloy surfaces were significantly reduced due to the synergistic effects of carbon coating and micro-nanostructures. It showed great significance in improving the tribological properties and the surface treatment of metallic materials.

Influence of processing variables on fabrication of AA7475/B4C/Al2O3 hybrid surface composites via FSP

The motive of this research is to fabricate AA7475/B4C/Al2O3 hybrid surface composites (HSCs) using friction stir processing (FSP) for various applications in aerospace, marine, and automotive industries. The research systematically varied key processing variables, including rotational speed (900–1300 rpm), feed rate (30–60 mm/min), and reinforcement ratios (from 30% B4C and 70% Al2O3 to 70% B4C and 30% Al2O3), to optimize responses such as ultimate tensile strength (UTS), tensile elongation (TE), and microhardness (MH). A face-centered central composite design (FCCCD) of response surface methodology (RSM) was employed to develop mathematical models correlating the input parameters with the response variables. An analysis of variance (ANOVA) was conducted to assess the effects and interactions of the processing parameters on the composite properties. A validation test confirmed the reliability of these optimal conditions. ANOVA results indicated that the tool rotational speeds had the most significant effect on the tensile, ductility, and hardness properties of the HSCs. However, changes in feed rate and reinforcement ratio had minimal impact on these properties. The study identified optimal conditions for different responses: UTS of 452.62 MPa, TE of 6.89%, and MH of 168.52 HV at a rotational speed of 1300 rpm, feed rate of 45 mm/min, and a 50:50% reinforcement ratio (50% B4C and 50% Al2O3). The HSCs fabricated at 1300 rpm, 45 mm/min, and a 50:50% reinforcement ratio exhibited significant necking before failure, leading to a ductile failure mode.

Durable Machine-Washable Wool via AOX-Free Plasma-Mediated Coating with Keratin

ABSTRACT Although their favorable performance, appearance, and comfort attributes, woolen garments have the tendency to felt unenviably during washing. In this work, an eco-friendly, energy-saving, non-deteriorative process for the fabrication of machine-washable wool tops (WTs) was proposed. WTs were exposed to atmospheric air or an argon plasma treatment at different powers for various durations, followed by coating with a protein biopolymer, namely keratin, using the pad-dry-cure technique. The felting resistance of the finished WTs was evaluated, and the results revealed that the finished sample has an enhanced felting resistance to the extent of machine-washable wool (no felt ball is formed), whereas the untreated sample forms a felt ball with a diameter of 2.166 cm after undergoing the felting test. The treated WTs maintained their felting resistance after 20 wash cycles. The surface composition of the plasma-treated WTs was examined using X-ray photoelectron spectroscopy. The change in the chemical structure of the treated WTs was monitored by determining the cystine content, alkali solubility, base-combining capacity, and affinity to anionic dye. The dye exhaustion of the untreated and finished samples after 60 min was 66% and 98.8%, respectively. Scanning electron microscopy was used to study the wool fibers’ topography.

Exploring Platinum Thin Films as Electrodes for High‐Temperature and ‐Pressure Electrochemical Studies in Aqueous Systems

ABSTRACTThis work reports a methodology for the fabrication of Pt thin‐film electrodes for electrochemical studies in hydrothermal systems. The research process was meticulous, with particular attention paid to the multilayer Ti/Pt/Ti/Al2O3 film structure and annealing conditions that are expected to impact the morphology of the films, surface composition and electrochemical response. The findings of this study are significant, as they provide valuable insights into the behaviour of Pt thin‐film electrodes in various media and conditions. Two different approaches were adopted for the preparation of the electrodes: in one case, the Ti/Pt/Ti/Al2O3 films deposited on sapphire wafers were exposed to rapid thermal annealing at 900°C under argon for 5 min, followed by argon ion milling to etch the final electrode pattern (Pt‐RA(900)), while in the other case, uncapped Pt films were annealed, after etching, in a tubular oven under argon at specific temperatures between 200°C and 900°C (Pt‐TO). Rapid annealing at 900°C on capped films resulted in the formation of a Pt3Ti intermetallic alloy with remarkable mechanical and chemical stability even after 10 h of immersion in deionised water, acid (0.1 M H2SO4) and alkaline media (0.1 M KOH) conditions at temperatures up to 150°C, despite the dissolution of the Al2O3 top layer at 150°C and long immersion times (> 10 h). In the case of uncapped Pt films, diffusion and oxidation of Ti through the Pt film at high temperature resulted in the formation of TiO2 on the surface of Pt. The results were confirmed by using a comprehensive suite of ex‐situ characterisation techniques to follow changes in the Pt electrode surface morphology and composition before and after immersion in H2O, 0.1 M H2SO4 and 0.1 M KOH solutions under argon. Ex‐situ electrochemical characterisation studies were also conducted to correlate the changes in the electrode surface properties, including the electrochemical surface area, with different annealing conditions and after various hydrothermal treatments in neutral, alkaline and acidic media.

Enhancing reflectivity of tantalum oxide coatings through plasma spraying and annealing techniques

Tantalum oxides, widely used as a high-reflectivity infrared material in aerospace and optoelectronics, often experiences a significant reduction in coating performance post-plasma spraying due to the emergence of oxygen defects. To overcome this shortcoming, this study comprehensively examined the effects of spray parameters and annealing processes on coating reflectivity. Our findings revealed that while optimizing spray parameters can modify micromorphology, these changes exert limited improvement on reflectivity (<2%). Conversely, muffle and laser annealing markedly enhance reflectivity by altering the surface composition and the valence of tantalum. Notably, post-laser annealing increased the reflectivity to 57 % from the original 12 % at 1070 nm. These results offer valuable insights into the development of high-reflectivity tantalum oxide coatings.

Development of Cu-(Gr + W) Hybrid Surface Composites Fabricated through Friction Stir Processing

Development of Cu-(Gr + W) Hybrid Surface Composites Fabricated through Friction Stir Processing

Impact of Boron Nitride(H) reinforcement on the properties of 5.8% copper-based aluminium alloy surface composite done by friction stir processing

ABSTRACT Numerous experiments and research is underway within the realm of aluminium metal matrix surface composites (MMSCs). This material has been applied in various marine, and aerospace industries, on account of its remarkable mechanical properties and desirable weight to strength ratio. The current study is focused on the synthesis of surface composites comprising of BN(H) reinforced 5.8% Cu aluminium alloy matrix composites. Boron Nitride(H) was reinforced on the surface of the Aluminum Alloy by FSP. Grooves were machined on the surface of the matriux and compacted with reinforcement particles. The wear rate, tensile behaviour, and microhardness were evaluated for the fabricated surface composites. The microstructural analysis was done via EDAX and FE-SEM to establish the presence of the reinforced particles. The tensile strength increased marginally with an increase in microhardness and reduction in elongation percenatge. The wear morphology aided in identifying the various wear mechanisms observed.

Adsorbate Resonance Induces Water-Metal Bonds in Electrochemical Interfaces.

This study delves into the intricate interactions between surface-near species, OH and H2O, on electrodes in electrochemical interfaces. These species are an inevitable part of many electrocatalytic energy conversion reactions such as the oxygen reduction reaction. In our modeling, we utilize high statistics on a dataset of complex solid solutions with high atomic variability to show the emergence of H2O-metal covalent bonds under specific conditions. Based on density functional theory (DFT) calculations ofadsorption energies onmany thousands of different surface compositions, we provide a quantifiable physical understanding of this induced water covalency, which is rooted in simple quantum mechanics. Directional hydrogen bonding between surface-near H2O and OH, enables surface bonding electrons to delocalize mediatedby near-symmetrical adsorbate resonance structures. The different adsorbate resonance structures differ by surface coordination explaining the induced H2O-metal bonding.

Adsorbate Resonance Induces Water‐Metal Bonds in Electrochemical Interfaces

This study delves into the intricate interactions between surface‐near species, OH and H2O, on electrodes in electrochemical interfaces. These species are an inevitable part of many electrocatalytic energy conversion reactions such as the oxygen reduction reaction. In our modeling, we utilize high statistics on a dataset of complex solid solutions with high atomic variability to show the emergence of H2O‐metal covalent bonds under specific conditions. Based on density functional theory (DFT) calculations of adsorption energies on many thousands of different surface compositions, we provide a quantifiable physical understanding of this induced water covalency, which is rooted in simple quantum mechanics. Directional hydrogen bonding between surface‐near H2O and OH, enables surface bonding electrons to delocalize mediated by near‐symmetrical adsorbate resonance structures. The different adsorbate resonance structures differ by surface coordination explaining the induced H2O‐metal bonding.

Impact of Ar plasma bombardment on the composition and surface roughness of GaAs wafer

The surface property of GaAs has an important impact on device performance, so how to improve the surface quality in reactive ion etching process is one of the key issues. In this paper, the composition and roughness changes of GaAs surface subjected to Ar plasma bombardment were investigated. It was found that the relative contents of Ga2O3 and As2O3 of the surface decreased with the increase of RF power, and the distribution depths of the compositions were different. In addition, dielectric constant increased with the increase of RF power. It was found that the surface roughness can be reduced after the plasma bombardment. Furthermore, the surface roughness and Ga/As component ratio followed a certain trend with the RF power. When the RF power was lower than 150 W, the surface roughness and Ga/As component ratio had the same trend, and when the RF power was higher than 150 W, they had the opposite trend. These results are helpful for the improvement of GaAs-based wafer-bonding strength and the performance of optoelectronic structures.

Machine Learning Aided Design and Optimization of Antifouling Surfaces.

Antifouling surfaces, renowned for their strong surface resistance to proteins, cells, or tissues in various biological and environmental conditions, have broad applications in implanted devices, antibacterial coatings, biosensors, responsive materials, water treatment, and lab-on-a-chip. While extensive experimental research exists on antifouling surfaces, machine learning studies on this topic are relatively few. This perspective specifically focuses on exploring the complex relationships between the composition, structure, and properties of antifouling surfaces, examining how these factors correlate with surface hydration and protein adsorption. Different machine learning models have been developed to analyze and predict single and multiple protein adsorptions on various types of surfaces, ranging from structureless surfaces to well-ordered and rigid self-assembled monolayers, dynamically ordered polymer brushes, and complex filtration membranes. These models not only identify key descriptors or functional groups critical for antifouling performance (surface hydration, protein adsorption) but also predict the antifouling properties for a specific surface. Recognizing current challenges, this perspective delineates future research directions in the antifouling field. By leveraging and comparing current machine learning approaches, it aims to advance both the design and fundamental understanding of antifouling surfaces, thereby pushing the boundaries of innovation in this critical field.

Review of Photodetectors for Space Lidars

Photodetectors play a critical role in space lidars designed for scientific investigations from orbit around planetary bodies. The detectors must be highly sensitive due to the long range of measurements and tight constraints on the size, weight, and power of the instrument. The detectors must also be space radiation tolerant over multi-year mission lifetimes with no significant performance degradation. Early space lidars used diode-pumped Nd:YAG lasers with a single beam for range and atmospheric backscattering measurements at 1064 nm or its frequency harmonics. The photodetectors used were single-element photomultiplier tubes and infrared performance-enhanced silicon avalanche photodiodes. Space lidars have advanced to multiple beams for surface topographic mapping and active infrared spectroscopic measurements of atmospheric species and surface composition, which demand increased performance and new capabilities for lidar detectors. Higher sensitivity detectors are required so that multi-beam and multi-wavelength measurements can be performed without increasing the laser and instrument power. Pixelated photodetectors are needed so that a single detector assembly can be used for simultaneous multi-channel measurements. Photon-counting photodetectors are needed for active spectroscopy measurements from short-wave infrared to mid-wave infrared. HgCdTe avalanche photodiode arrays have emerged recently as a promising technology to fill these needs. This paper gives a review of the photodetectors used in past and present lidars and the development and outlook of HgCdTe APD arrays for future space lidars.

Designed magnetic nanoparticles for ferroptosis: Release of iron ions from metal-organic frameworks modified with iron oxides

The unique chemical properties of the catalytic and biocompatible metal organic framework MIL88b allow for considering it as prooxidant agent. The authors hypothesize whether additional modification of the MIL88b with an additional iron source as Fe3O4 nanoparticles can increase both pro-oxidant activity and provide magnetic properties contributing to target delivery. The prooxidant activity of the Fe3O4-MOF was studied using electron paramagnetic resonance spectroscopy and methylene blue degradation reactions in the presence of hydrogen peroxide. To understand the reaction mechanism, the authors studied the released iron ions, as well as the surface composition using the X-ray photoelectron spectroscopy method. The addition of iron oxide leads to a more prolonged release of iron ions and the production of hydroxyl radicals within 24 h. The native MIL88b demonstrates the highest Fenton reaction rate due to "sacrificial" behavior (despite lower concentration of iron ions in the composition and on the surface compared to the modified sample) and the blocking of the active centers of MIL88b by Fe3O4 on the surface.

Regeneration of spent graphite via graphite-like turbostratic carbon coating for advanced Li ion battery anode

Recycling spent graphite (SG) from lithium-ion batteries is an effective approach to reduce resource waste and address environmental issues. The main reasons for the capacity degradation of graphite anode are the structural destruction and changes in surface composition during the cycling process. However, repairing the graphite with satisfactory electrochemical properties remains a significant challenge due to the lack of efficient recycling methods. Herein, a low-temperature magnesium catalytic method is developed to reconstruct turbostratic carbon coating and repair defects in SG at 900 °C. The dense turbostratic carbon not only effectively repairs the surface damage of the SG and mitigates the occurrence of side reactions but also improves the Li+ and electron transfer kinetics of SG. The regenerated graphite anode exhibits high initial Coulombic efficiency (ICE) of 86.2 %, a high capacity of 350 mAh g−1 after 500 cycles at 0.5 C with a capacity retention of 96.5 %, which reaches the requirements of commercial applications. Furthermore, a techno-economic analysis shows that this strategy has higher environmental and economic benefits compared to conventional recycling methods.

Cu(I) and Cu(II) in mixed bismuth tantalate pyrochlores according to XPS and NEXAFS spectroscopy

Mixed copper-containing pyrochlores Bi2Co1/2Cu1/2Ta2O9+Δ, Bi2Ni1/2Cu1/2Ta2O9+Δ, Bi2Co1/3Cu1/3Ni1/3Ta2O9+Δ (sp.gr. Fd-3 m) were synthesized by the solid-phase reaction method. The surface composition and chemical state of transition element atoms in pyrochlores were characterized by XPS, NEXAFS spectroscopy. According to the XPS spectra, bismuth and tantalum cations have an effective charge of + 3 and +(5-δ). The NEXAFS Cu2p spectra of pyrochlores are shown to represent a superposition with the CuO and Cu2O spectra in terms of the main spectral characteristics. This indicates a variable Cu ion content in oxide pyrochlores in the form of Cu(I,II) ions.