Surfaces

In order to synthesize chemical filters for the selective removal of volatile fluorides, commercial magnesium fluoride MgF₂ with high specific surface area (HSA) was investigated. The amount of -OH groups substituting fluorine is not negligible, partly due to the high surface area, but also due to the synthesis route. These hydroxyl groups induce a Lewis basicity on the surface of metal fluorides. The amount of these Lewis basic sites has been tailored using fluorination with F₂ gas. The sorption of VOF₃, used as model gas, onto these fluorides was investigated. The versatility of surface chemistry as a function of a number of Lewis basic sites opens the way to filter selectivity mixture of volatile fluorides depending on their Lewis acidity. HSA MgF₂ acts as a stable matrix towards the gas to be purified, and the selectivity may be achieved by a higher Lewis acidity of the gaseous impurity. Full article

Cu₂ZnSnSe₄ thin films have been synthesized by employing two magnetron-sputtering depositions, interlaced with two sequential post-deposition heat treatments in low vacuum, Sn+Se and Se–rich atmospheres at 550 °C. By employing successive structural analysis methods, namely Grazing Incidence X–Ray Diffraction (GIXRD) and Raman Spectroscopy, secondary phases such as ZnSe coexisting with the main kesterite phase have been identified. SEM peered into the surface morphology of the samples, detecting structural defects and grain profiles, while EDS experiments showed off–stoichiometric elemental composition. The optical bandgaps in our samples were calculated by a widely used extrapolation method from recorded transmission spectra, holding values from 1.42 to 2.01 eV. Understanding the processes behind the appearance of secondary phases and occurring structural defects accompanied by finding ways to mitigate their impact on the solar cells’ properties is the prime goal of the research beforehand. Full article

The research purpose of this work is to examine the adsorption interaction of gaseous molecules (GMs), such as NO, NO₂, SO, SO₂, and SO₃, with the surface of sodium magnesium phosphate NaMgPO₄ (033), in a neutral medium, using two different computational methods: density functional theory (DFT) and Monte Carlo dynamic simulation (MCDS). Various quantum and dynamic descriptors, such as global and local quantum descriptors and the radial distribution function (RDF), are also evaluated and discussed. The data obtained revealed that the NO₂ molecule has a small energy gap (0.363 eV) when compared to the other molecules, which means that it is highly reactive and is liable to adsorb, or stick, to the surface of NaMgPO₄ (033). Furthermore, this NO₂ molecule exhibits good adsorption in aqueous media, returning to the lowest global hardness value (0.1815 eV). MCDS predicted adsorption energies of −874.03, −819.94, −924.81, −876.33, and −977.71 kcal/mol for NO, NO₂, SO, SO₂, and SO₃, respectively. These energies are negative, implying that adsorption occurs spontaneously. Thus, the side views indicated which SO, NO, and SO₃ molecules are adsorbed in parallel to NaMgPO₄ and the other SO₂ and NO₂ molecules are adsorbed horizontally. Eventually, the theoretical results reveal that the studied gaseous molecules interact strongly with NaMgPO₄. The result obtained by radial distribution function (RDF) analysis for all complexes below 3.5 Å confirm that the adsorption is of the chemi1cal type. Full article

To realize simple and intelligent electrochemical ammonia (NH₃) detection in water, highly dense colloidal copper nanoparticles (CuNPs) were prepared and subsequently deposited onto a glassy carbon electrode (GCE). The CuNPs/GCE was then placed in an oven at 60 °C to intelligently transform CuNPs into cuprous oxide (Cu₂O) thin film. The colloidal CuNPs were characterized by ultraviolet-visible (UV-Vis) spectroscopy, whereas the fabricated Cu₂O/GCE was subjected to Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and electrochemical impedance spectroscopy (EIS). The XRD of Cu₂O/GCE showed the crystalline nature of the thermally converted Cu₂O thin film, whereas XPS demonstrated that the thin film formed on the surface of GCE was primarily composed of Cu₂O. The SEM images of Cu₂O/GCE revealed Cu₂O crystals with hexapod morphology. The EIS study exhibited substantially higher charger transfer activity of Cu₂O/GCE compared to bare GCE. The drop coating of ammonia (NH₃) solution onto Cu₂O/GCE enabled the fabricated electrode to be utilized as an electrochemical sensor for NH₃ detection in water. The cyclic voltammetric (CV) behavior of NH₃/Cu₂O/GCE was investigated in 0.1 M pH 7 phosphate buffer, which led to the formation of a copper-ammonia complex and revealed the nobility of the fabricated electrode. The square wave voltammetric (SWV) response was linear over the 10 µM and 1000 µM ranges with a detection limit of 6.23 µM and good reproducibility. The NH₃/Cu₂O/GCE displayed high selectivity for the detection of NH₃ in the presence of various coexisting cations and anions in 0.1 M pH 7 phosphate buffer. The recovery of NH₃ in the drinking water sample varied from 98.2% to 99.1%. Full article

Employing a self-combustion method supported by egg white, pure and Fe-doped ZnO/C nanoparticles successfully biosynthesized. XRD, FTIR, Raman, SEM/EDS and TEM measurements were used to characterize the pure and doped systems. The materials under investigation’s optical, surface and magnetic characteristics were recognized. Only one zinc oxide crystalline phase exhibiting a hexagonal shape comparable to wurtzite was present in the systems of pure and Fe-doped ZnO/C. Due to the variation in ionic radii, doping ZnO/C system with iron ions resulted in a decrease in unit cell volume; it revealed that ions of iron had been integrated into the lattice of zinc oxides. FTIR analysis shows characteristic vibration modes related to ZnO and that of carbon groups, confirming the formation of the ZnO/C system. In a perfect match with the IR data, which represent two bands at 1120 and 1399 cm⁻¹ attributed to carbon groups, the Raman analysis shows that in the freshly manufactured materials, sp² and disordered G and D carbon bands have both graphitized. Fe-doping of the ZnO/C system with different amounts of iron ions resulted in the change in the size and agglomeration of the particle’s system. The doped ZnO/C system has a surface area smaller than that of the pure system due to the decrease in both the mean pore radius and the total pore volume. Doping the ZnO/C system with 2 and 5 mol% Fe₂O₃ resulted in optical band gaps expanding from 3.17 eV to 3.27 eV and 3.57 eV, respectively. Due to the doping with iron ions, a magnetic transition from a fully diamagnetic state to a slightly ferromagnetic state was detected. Full article

Researchers have just discovered an alternative to synthetic corrosion inhibitors, which are hazardous and terrible for the ecosystem, to prevent rusting in the environment. A metal corrodes when it is subjected to corrosive media (acid, base, or saline) and they deteriorate, leading to failure. The most straightforward and affordable corrosion protection and prevention technique in acidic environments has been proven to be corrosion inhibitors. On industrial surfaces, pieces of machinery, or vessels, these inhibitors slow the rate of corrosion, preventing the monetary losses brought on by metallic corrosion. Recently, attention has been directed to developing ecologically appropriate corrosion retardation methods because inorganic and organic inhibitors are harmful and expensive. Recent studies have focused on green mild steel (MS) corrosion inhibitors that mimic industrial processes in acidic conditions. This presentation briefly covers the many types of corrosion, the corrosion process and the most recent studies on using natural plant extracts as corrosion inhibitors. Since they are safe and cost-effective, green corrosion inhibitors are a new trend in preventing corrosion. These inhibitors are produced from various plant parts, and inhibition efficiency (IE) also depends on them. To ascertain the IE of the corrosion inhibitor, some experiments, including computational studies (quantum calculations and MD simulations), electrochemical measurements (electrochemical impedance (EIS) and potentio-dynamic polarization), surface morphology atomic force microscopy (AFM), scanning electron microscopy (SEM)/energy-dispersive X-ray analysis (EDX) and UV–visible spectroscopy are carried out. It has been demonstrated that the IE is maximum for green corrosion inhibitors compared to synthetic inhibitors. This paper provides an overview of the properties, mechanism of corrosion inhibitors, nature of green corrosion inhibitors and their IE obtained by performing tests. This review article discussion shows that reinforcement with plant extract performs well in aggressive environments, which is evident from electrochemical studies and surface analysis when compared to reinforcement with inhibitors. Full article

Oxide films produced from plasma electrolytic oxidation are porous in structure. While they have some passivating effect in Mg alloys, the pores still lead to corrosion over long periods of exposure. In this study, spray pyrolysis was used to seal the porous oxide layer developed through the plasma electrolytic oxidation method on Mg alloy AZ31. The PEO coating acted as a good base for the application of spray pyrolysis due to its morphology. Three different kinds of coatings were obtained using different precursors: zinc acetate for ZnO, phosphoric acid for phosphate (P), and a mixture of zinc acetate and sodium phosphate for ZnO+P. The corrosion performance of all three coatings was studied by performing electrochemical impedance and polarization tests on the samples. Mass loss over a duration of 1 week was measured in 3% NaCl solution using immersion gravimetry. The coating with only phosphate (P) was found to be most corrosion-resistant with 52 times lower rate of corrosion and 50 times more polarization potential. The chemical composition of the corrosion products was studied using XRD and SEM-EDS analysis. Mass loss in ZnO+P was the highest, at up to 1.4 and 5.1 times higher than ZnO and P, respectively. Full article

Metal–organic chemical vapor deposition (MOCVD) is a key method for scalable synthesis of two-dimensional transition metal dichalcogenide (2D-TMDC) layers. However, it faces several challenges, such as the unintentional co-deposition of carbon impurities resulting from the pyrolysis of metal–organic precursors. This study investigates the chemical features of carbon and its impact on the photoluminescence property and air stability of 2D-MoS₂. Using X-ray photoemission spectroscopy (XPS), it was found that the carbon impurities show characteristics similar to those of sp²-bonded graphitic carbon. Upon prolonged (20–40 weeks) exposure to the atmosphere, the incorporated carbon appears to react with 2D-MoS_2, forming a MoS_2−xC_x solid solution. At the same time, a gradual decrease in the S/Mo ratio implies the formation of sulfur vacancies was also observed. These two processes lead to crystal degradation over time, as evidenced by the gradual quenching of the Raman and photoluminescence (PL) peaks. More detailed PL analyses suggest a charge transfer mechanism between sp²-carbon/2D-MoS₂ and 2D-MoS₂/air-adsorbates, which, in the short term, could alter PL emissions and appear to further intensify the degradation of 2D-MoS₂ in the long-term. The findings highlight the strong impact of unintentionally co-deposited carbon on the optical properties and air stability of MOCVD 2D-MoS₂ layers. Full article

Advances in nanotechnology have contributed to many innovative approaches in the forensic sciences, including the development of new techniques and protocols for latent fingermark detection. Among other nanomaterials, metal-based nanoparticles have been explored as suitable developers for fingermarks present on surfaces that challenge traditionally established methods. The present study explored, for the first time in the forensic science literature, the application of greenly synthesized silver nanoparticles (AgNPs) for latent fingermark surface-assisted laser desorption/ionization mass spectrometry (SALDI MS) analysis. A leaf extract of a native plant from the Cerrado biome was used for green synthesis of the AgNPs, and their hydrodynamic diameter, polydispersity index (PdI), and Zeta potential values were evaluated. Latent fingermarks were produced by three distinct donors and treated with α-CHCA matrix or AgNP suspension and were further investigated using commercial matrix assisted laser desorption/ionization (MALDI)-TOF MS equipment in the m/z range of 100–1000. Characterization results of the AgNPs indicated an average hydrodynamic diameter of 25.94 ± 0.30 nm, a PdI of 0.659 ± 0.085, and a Zeta potential of −33.4 ± 2.6 mV. The silver ions detected showed a relative intensity at least 20× higher for greenly synthesized AgNPs than for AgNO₃ suspension, which may be advantageous for the detection of molecular species, especially olefins, present in forensic traces. The AgNP-based SALDI MS approach for the analysis of latent fingermarks showed intense ions at m/z 106.9, 215.8, and 322.7, referring to silver cation species that have been reported as important internal calibrants. The detection of components from endogenous and exogenous sources in latent fingermarks was achieved using the present approach. Greenly synthesized AgNPs may offer a new cost-effective, eco-friendly, and easily scaled up method for application in the chemical analysis of fingermarks. Full article

Porous carbon is an emerging material for the capture of CO₂ from point sources of emissions due to its high structural, mechanical, and chemical stability, along with reusability advantages. Currently, research efforts are mainly focused on high- or medium-pressure adsorption, rather than low-pressure or DAC (direct air capture) conditions. Highly porous and functionalized carbon, containing heteroatoms (N, O, etc.), is synthesized using different activation synthesis routes, such as hard template, soft template, and chemical activation, to achieve high CO₂ capture efficiency at various temperatures and pressure ranges. Fundamental pore formation mechanisms with different activation routes have been evaluated and explored. Higher porosity alone can be ineffective without the presence of proper saturated diffusion pathways for CO₂ transfer. Therefore, it is imperative to emphasize more rational multi-hierarchical macro-/meso-/micro-/super-/ultra-pore design strategies to achieve a higher utilization efficiency of these pores. Moreover, the present research primarily focuses on powder-based hierarchical porous carbon materials, which may reduce the efficiency of the capture performance when shaping the powder into pellets or fixed-bed shapes for applications considered. Therefore, it is imperative to develop a synthesis strategy for pelletized porous carbon and to explore its mechanistic synthesis route and potential for CO₂ capture. Full article

Bacterial adhesion and biofilm formation on the surface of titanium implants are the main causes of implant-associated infection. An antibacterial coating on the implant surface can reduce the risk of biofilm formation. The aim of this study was to investigate the bactericidal effects of a van-comycin-loaded polymer coated on an implant surface. For this purpose, poly(N-isopropylacrylamide) (PNIPAAm) was first synthesized as a homopolymer or by co-polymerization with acrylamide (PNIPAAm-AAm) at a 5% weight ratio. Then, thin and uniform polymer coatings were prepared using the spin coating technique. The degree of surface hydro-philicity of the polymer coatings was evaluated by measuring the water contact angle (CA). For the antibacterial tests, the polymer-coated surfaces were loaded with vancomycin. The tests were performed in three conditions: on a glass surface (control), on a PNIPAAm-AAm-coated surface, and on a PNIPAAm-AAm-coated surface loaded with vancomycin. The death rates of the bacteria in contact with the coated surfaces were evaluated at different temperatures with fluorescence microscopy. A scanning electron microscopy (SEM) analysis of cross sections of the polymer coatings revealed a uniform thin film of approximately 200 nm in thickness. The water contact angle analysis performed at different temperatures revealed that the polymer-coated surfaces were more hydrophobic (CAs ranging between 53° and 63°) than the uncoated glass surface (CA ranging between 15° and 35°). The bacterial death rate, measured at 40 °C or while continuously switching the temperature between 37 °C and 40 °C, was higher in the presence of the surface coated with vancomycin-loaded PNIPAAm-AAm than when using the other surfaces (p-value ≤ 0.001). The vancomycin-loaded polymer coating evaluated in this study exhibited effective antibacterial properties when the polymer reached the phase transition temperature. Full article

The mechanism of the vapor–gas deposition of vinyltrimethoxysilane (VS) and ethylene glycol (EG) from azeotropic solutions is investigated, which allows a reduction of the evaporation temperature of the components of working mixtures. The need for such studies is associated with the development of a new direction in the technology of vapor–gas deposition of polymer coatings. Methods have been developed for monitoring the chemical composition of working solutions in evaporators using optical spectroscopy, which makes it possible to calculate the partial pressures of vapor-phase components. Based on these studies, compositions of working solutions are proposed that allow the equalization of the partial pressures of the components of working mixtures with a large difference in the boiling point. With the aid of vapor–gas deposition, siloxane coatings on low-carbon steel were obtained, the protective properties of which exceeded the treatment with volatile inhibitors of the adsorption type by two to three orders of magnitude. A new method of vapor–gas deposition of non-volatile powder inhibitors on metals is proposed. Chemical compositions of siloxane coatings were determined using XPS, and mechanisms of interaction of VS with the polymerization promoters ethylene glycol and 1-hydroxy ethylidene-1,1-diphosphonic acid (HEDP) were proposed. Full article

Triboelectric nanogenerators (TENGs) based on sliding metal–semiconductor junctions are an emerging technology that can efficiently convert mechanical into electrical energy. These miniature autonomous power sources can output large direct current (DC) densities, but often suffer from limited durability; hence, their practical scope remains uncertain. Herein, through a combination of conductive atomic force microscopy (C-AFM) and photocurrent decay (PCM) experiments, we explored the underlying cause of surface wear during the operation of DC-TENGs. Using monolayer-functionalized Si(211) surfaces as the model system, we demonstrate the extent to which surface damage develops during TENG operation. We reveal that the introduction of surface defects (oxide growth) during TENG operation is not caused by the passage of the rather large current densities (average output of ~2 × 10⁶ A/m²); it is instead mainly caused by the large pressure (~GPa) required for the sliding Schottky diode to output a measurable zero-bias current. We also discovered that the drop in output during operation occurs with a delay in the friction/pressure event, which partially explains why such deterioration of DC-TENG performance is often underestimated or not reported. Full article

The development of biodegradable Zn-based alloys for implants that effectively mimic the functionality of native bone throughout the healing process is a multifaceted challenge; this is particularly evident in the task of achieving appropriate corrosion rates. This work explores the incorporation of 0.5wt.%Mn into a Zn−1wt.%Mg alloy, with focus on the relationship between corrosion behavior and microstructure. Electrochemical corrosion tests were carried out in a 0.06 M NaCl solution using as-solidified samples with two distinct microstructural length scales. Mn addition was found to induce significant electrochemical active behavior. Localized corrosion was predominant in interdendritic regions, with the ternary alloy exhibiting a higher susceptibility. For both alloys, the coarsening of the microstructure promoted a slight inclination to accelerate the corrosion rates in both biodegradable Zn alloys. The corrosion rate showed an increase of about nine-times with Mn addition for coarser eutectic spacings, while for finer ones, the increase was by about 22 times. Full article

We measured spectra of low energy electrons emitted in the interaction of singly charged Ne⁺ ions with the Mg surface at incident ion energies ranging from 50 eV to 4 keV. The study examines issues related to the excitation of both the surface and the bulk plasmons of the target. We will also focus on the dynamics of the production of the singlet Ne2p⁴(¹D)3s² and triplet Ne2p⁴(³P)3s² autoionizing states of projectiles scattered in a vacuum. The threshold behavior of the autoionization lines show that double excitation occurs simultaneously in a single scattering. The predominant excitation of the triplet state indicates the importance of charge rearrangement and the electron correlation effects during the collisional excitation. Full article

A flexible chitin nanofiber (ChNF) film with a thin fiber morphology, named, scaled-down (SD)-ChNF film, was previously found to be formed via successive partial deacetylation of the parent self-assembled ChNFs, cationization/dispersion via electrostatic repulsion in aqueous acetic acid, and suction filtration/drying. In this study, acetylation of a SD-ChNF film using acetic anhydride in pyridine was carried out to improve the mechanical properties. The FT-IR spectra of the acetylated SD-ChNF films suggested that acetylation progressed from the surface to the interior of the films with the increasing amounts of pyridine and elevating temperatures. The degrees of acetylation (DA) strongly affected the chitin crystallinity and surface morphology of the acetylated SD-ChNF films. Tensile testing of the acetylated SD-ChNF films indicated that the mechanical properties were improved by adjusting the DA values of the films. For example, the acetylated SD-ChNF film with an 1.84 DA value on surface showed values of 44.1 MPa and 24.9% for tensile strength and elongation at break, respectively. Full article

Flexible and binderless electrodes have become a promising candidate for the next generation of flexible power storage devices. However, developing high-performance electrode materials with high energy density and a long cycle life remains a serious challenge for sodium-ion batteries (SIBs). The main issue is the large volume change in electrode materials during the cycling processes, leading to rapid capacity decay for SIBs. In this study, flexible electrodes for a SnSb alloy–carbon nanofiber (SnSb@NC) membrane were successfully synthesized with the aid of hydrothermal, electrospinning and annealing processes. The as-prepared binderless SnSb@NC flexible anodes were investigated for the storage properties of SIBs at 500 °C, 600 °C and 700 °C (SnSb@NC-500, SnSb@NC-600 and SnSb@NC-700), respectively. And the flexible SnSb@NC-700 electrode displayed the preferable SIB performances, achieving 240 mAh/g after 100 cycles at 0.1 A g⁻¹. In degree-dependent I-V curve measurements, the SnSb@NC-700 membrane exhibited almost the same current at different bending degrees of 0°, 45°, 90°, 120° and 175°, indicating the outstanding mechanical properties of the flexible binderless electrodes. Full article

The search of active, stable and low costs catalysts for the oxygen reduction reaction (ORR) is crucial for the extensive use of fuel cells and metal–air batteries. The development of metal-free catalysts, instead of platinum-based materials, can dramatically reduce the cost and increase the efficiency of these devices. In this work, carbon nanohorns (CNHs) have been covalently functionalized with N-containing heterocycles by the Tour reaction protocol and tested as metal-free ORR catalysts. The insertion of N-functionalities favored the complete reduction of oxygen to hydroxyl ions, while their absence favored the production of hydrogen peroxide. With the aim of determining the N-species responsible for the ORR activity of CNHs, photoemission and electrochemical measurements were combined. Results suggest that protonated N is the main species involved in the ORR process, facilitating the adsorption of oxygen, with their consequent reduction to neutral hydrogenated N species. Full article

Features of the nanosecond discharge development in a non-uniform electric field are studied experimentally. High spatial resolution imaging showed that thin luminous tracks of great length with a cross-section of a few microns are observed against the background of discharge glow in air and argon. It has been established that the detected tracks are adjacent to brightly luminous white spots on the electrodes or in the vicinity of these spots, and are associated with the flight of small particles. It is shown that the tracks have various shapes and change from pulse to pulse. The particle tracks may look like curvy or straight lines. In some photos, they can change their direction of movement to the opposite. It was found that the particle’s track abruptly breaks and a bright flash is visible at the break point. The color of the tracks differs from that of the spark leaders, while the bands of the second positive nitrogen system dominate in the plasma emission spectra during the existence of a diffuse discharge. Areas of blue light are visible near the electrodes as well. The development of glow and thin luminous tracks in the gap during its breakdown is revealed using an ICCD camera. Physical reasons for the observed phenomena are discussed. Full article