Surfaces, Volume 6, Issue 4 (December 2023) – 12 articles

Corrosion inhibitors are widely used as an important tool for the prevention and remediation of different materials exposed to corrosive industrial processes. Corrosion inhibitors are usually added to acid pickling solutions to reduce the deterioration of metallic materials and particularly, corrosion due to hydrochloric acid. In this work, three bis-Schiff bases (BS2, BS4 and BS8) were synthesized and characterized using spectroscopic methods, and their anti-corrosive effects on AISI 1020 carbon steel in a hydrochloric acid solution were studied using gravimetric and electrochemical techniques and quantum chemical methods. The results showed that all substances act as potential corrosion inhibitors as BS8 exhibited the highest efficiency (98%) of all methods. The compounds adsorbed on the metal surface were as per the El-Awady adsorption isotherm. Morphological aspects of the metal were observed upon applying SEM, and the theoretical results acquired from the quantum chemical calculation for molecular properties and the Fe(110) surface adsorption proved to be compatible with the experimental results. Full article

Non-noble metal electrocatalysts for the oxygen evolution reaction (OER) have recently gained particular attention. In the present work, a facile one-step electrodeposition method is applied in situ to synthesize cobalt sulfide nanostructures on nickel foam (NF) electrodes. For the first time, a systematic study is carried out on the impact of the Co/S molar ratio on the structural, morphological, and electrochemical characteristics of Ni-based OER electrodes by employing Co(NO₃)₂·6 H₂O and CH₄N₂S as Co and S precursors, respectively. The optimum performance was obtained for an equimolar Co:S ratio (1:1), whereas sulfur-rich or Co-rich electrodes resulted in an inferior behavior. In particular, the Co_xS_y@NF electrode with Co/S (1:1) exhibited the lowest overpotential value at 10 mA cm⁻² (0.28 V) and a Tafel slope of 95 mV dec⁻¹, offering, in addition, a high double-layer capacitance (C_DL) of 10.7 mF cm⁻². Electrochemical impedance spectroscopy (EIS) measurements confirmed the crucial effect of the Co/S ratio on the charge-transfer reaction rate, which is maximized for a Co:S molar ratio of 1:1. Moreover, field emission scanning electron microscopy (FE-SEM), X-ray diffraction (XRD) and X-ray fluorescence (XRF) were conducted to gain insights into the impact of the Co/S ratio on the structural and morphological characteristics of the electrodes. Notably, the Co_xS_y@NF electrocatalyst with an equimolar Co:S ratio presented a 3D flower-like nanosheet morphology, offering an increased electrochemically active surface area (ESCA) and improved OER kinetics. Full article

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