Search Results (40)

This study presents the development of Cu-doped NiMo/TiO₂ photoelectrocatalysts for simultaneous green hydrogen production and pharmaceutical pollutant removal under simulated solar irradiation. The catalysts were synthesized via wet impregnation (15 wt.% total metal loading with 0.6 wt.% Cu) and thermally treated at 400 °C and 900 °C to investigate structural transformations and catalytic performance. Comprehensive characterization (XRD, BET, SEM, XPS) revealed phase transitions, enhanced crystallinity, and redistribution of redox states upon Cu incorporation, particularly the formation of NiTiO₃ and an increase in oxygen vacancies. Crystallite sizes for anatase, rutile, and brookite ranged from 21 to 47 nm at NiMoCu400, while NiMoCu900 exhibited only the rutile phase with 55 nm crystallites. BET analysis showed a surface area of 44.4 m²·g⁻¹ for NiMoCu400, and electrochemical measurements confirmed its higher electrochemically active surface area (ECSA, 2.4 cm²), indicating enhanced surface accessibility. In contrast, NiMoCu900 exhibited a much lower BET surface area (1.4 m²·g⁻¹) and ECSA (1.4 cm²), consistent with its inferior photoelectrocatalytic performance. Compared to previously reported binary NiMo/TiO₂ systems, the ternary NiMoCu/TiO₂ catalysts demonstrated significantly improved hydrogen production activity and more efficient photoelectrochemical degradation of paracetamol. Specifically, NiMoCu400 showed an anodic peak current of 0.24 mA·cm⁻² for paracetamol oxidation, representing a 60% increase over NiMo400 and a cathodic current of −0.46 mA·cm⁻² at −0.1 V vs. RHE under illumination, nearly six times higher than the undoped counterpart (–0.08 mA·cm⁻²). Mott–Schottky analysis further revealed that NiMoCu400 retained n-type behavior, while NiMoCu900 exhibited an unusual inversion to p-type, likely due to Cu migration and rutile-phase-induced realignment of donor states. Despite its higher photosensitivity, NiMoCu900 showed negligible photocurrent, confirming that structural preservation and surface redox activity are critical for photoelectrochemical performance. This work provides mechanistic insight into Cu-mediated photoelectrocatalysis and identifies NiMoCu/TiO₂ as a promising bifunctional platform for integrated solar-driven water treatment and sustainable hydrogen production. Full article

Duplex stainless steels, known for their excellent corrosion resistance, are employed in a variety of chloride solutions—acidic, neutral, and alkaline—due to a stable passive film that forms on their surfaces. This study involved polarization tests, EIS (Electrochemical Impedance Spectroscopy) measurements, Mott–Schottky plots, and XPS (X-Ray Photoelectron Spectroscopy) analyses in both static and dynamic conditions across acidic (1NaCl + 0.1N HCl, pH 1.0), neutral (1N NaCl, pH 6.7), and alkaline (1N NaCl + 0.1N NaOH, pH 13.2) chloride solutions to confirm that duplex stainless steels exhibit similar passivation behavior (0.79 μA/cm² > i_p > 0.2 μA/cm² and 590 kΩ·cm² < R_p < 651 kΩ·cm²). Regardless of the pH of the solution, p-type and n-type semiconductive properties were observed, but the balance of the semiconductive tendencies was different. Comparing passive films formed under dynamic conditions, through real-time HCl injection into a neutral chloride solution, with those formed under static conditions, revealed that both conditions yield similar structural and property characteristics in the films, as well as comparable electrochemical behaviors. These findings suggest that the passive film on the stainless steel surface adjusts to the environment and can be spontaneously repassivated in response to environmental changes. Full article

The nanoporous copper (NPC)-copper oxides (Cu₂O/CuO)/reduced graphene oxide (rGO) composite structure was synthesized by combining the dealloying process of Cu₄₈Zr₄₇Al₅ amorphous ribbons with a microwave-assisted hydrothermal technique at a temperature of 200 °C. The main advantage of the microwave-assisted hydrothermal process is the oxidation of nanoporous copper together with the in situ reduction of graphene oxide to form rGO. The integration of rGO with NPC improves electrical conductivity and streamlines the process of electron transfer. This composite exhibit considerable potential in electrochemical catalysis application, due to the combined catalytic activity of NPC and the chemical reactivity of rGO. Our study relates the transition to n-type rGO in microwave-assisted hydrothermal reactions, and also the development of an electrode material suitable for electrochemical applications based on the p-p-n junction NPC-Cu₂O/CuO/rGO heterostructure. To confirm the formation of the composite structure, structural, morphological, and optical techniques as XRD, SEM/EDX, UV-Vis and Raman spectroscopy were used. The composite’s electrochemical properties were measured by EIS and Mott-Schottky analyses, showing a charge transfer resistance (Rp) of 250 Ω and indicating the type of the semiconductor properties. The calculated carrier densities of 4.2 × 10¹⁸ cm⁻³ confirms n-type semiconductor characteristic for rGO, and 7.22 × 10¹⁸ cm⁻³ for Cu₂O/CuO indicating p-type characteristic. Full article

A Z-scheme heterojunction photo(electro)catalyst was fabricated by coupling sulfonic acid-modified graphitic carbon nitride (SA-g-CN) with bismuth oxyiodide (BiOI). The SA-g-CN component was prepared via wet-impregnation, while BiOI was synthesized through a hydrothermal method. Comprehensive characterization elucidated the structural and morphological properties of the resulting composite. The SA-g-CN/BiOI exhibited exceptional performance in both photocatalytic degradation of tartrazine (TTZ) and photoelectrochemical oxygen evolution reaction (OER). Notably, 98.26% TTZ removal was achieved within 60 min of irradiation, while an OER onset potential of 0.94 V (vs. Ag/AgCl) and a high photocurrent density of 6.04 mA were recorded under AM 1.5G illumination. Band energy calculations based on Mott–Schottky measurements confirmed the formation of a Z-scheme heterojunction, which facilitated efficient charge separation and transfer, thereby enhancing catalytic activity. These findings establish the SA-g-CN/BiOI composite as a promising candidate for sustainable energy generation and environmental remediation applications. Full article

This paper reports experimental results concerning the corrosion of 316L austenitic stainless steels produced by ball milling and spark plasma sintering in NaCl electrolyte. Specimens with grain sizes ranging from 0.3 µm to 3 µm, without crystallographic texture, were obtained and compared with a cast that is 110 µm in grain size and an annealed reference. The potentiodynamic experiments showed that the reduction in grain size leads to a degradation of the electrochemical passivation behavior. This detrimental effect can be overcome by appropriate passivation in a HNO₃ concentrated solution before consolidation. The Mott–Schottky measurements showed that the semiconducting properties of the passive layer do not vary significantly on the grain size, especially the donor density, which is responsible for the chemical passivation breakdown by chloride anions. The total electrical resistance of the layer, measured by impedance spectroscopy is always lower than the one of a cast and annealed 316L, but it slightly increases with a reduction in grain size in the ultrafine grain range. This is followed by a slight increase in the thickness of the oxide layer. The effect of chloride ions is very pronounced in terms of passivation breakdown if the powder is not passivated prior to sintering. This leads to the nucleation and growth of subsurface main pits and the formation of secondary satellite pits, especially for the smallest grain sizes. Passivation of the 316L powder before sintering has been found to be an effective way to prevent this phenomenon. Full article

Photocatalytic methods have been popular in energy production and environmental remediation. Designing high-efficiency photocatalysts is still challenging in converting solar energy into chemical fuels. Herein, a series of surfactant-assisted ZnIn₂S₄ (ZIS) photocatalysts were synthesized by utilizing the one-pot hydrothermal method. Photocatalytic methane production from an acetic acid solution was carried out under LED light (450 nm) irradiation, and the evolved gas was analyzed by the GC-FID system. Reaction factors (surfactant amount, catalyst dose, reaction temperature, substrate concentration, and reaction pH) were optimized for photocatalytic production. With the increase in cetyltrimethylammonium bromide (CTAB) amount, CH₄ production gradually increased. The ZIS-3.75 photocatalyst exhibited the highest photocatalytic CH₄ production rate (0.102 µmol g⁻¹·h⁻¹), which was approximately 1.8 times better than that of pure ZIS (0.058 µmol g⁻¹·h⁻¹). The presence of CTAB reduced the charge transfer resistance and improved photocurrent response efficiency. Structure and morphology were characterized by XRD, FTIR, SEM, TEM, and N₂ adsorption–desorption isotherm analysis. Optical properties were investigated by UV-DRS and PL spectroscopic techniques. The electrochemical evaluation was measured through EIS, Mott–Schottky, and transient photocurrent response analysis. The CTAB-modified catalyst showed excellent stability and reusability, even after five irradiation cycles. Methane production was enhanced by lowering the photogenerated charge transfer resistance and boosting the dispersion of ZIS-3.75 under visible light (450 nm) irradiation. Full article

Tungsten oxide (WO₃) and zinc oxide (ZnO) are n-type semiconductors with numerous applications in photocatalysis. The objective of this study was to synthesize and characterize different types of nanostructures (WO₃, WO₃-Mo, TiO₂, and TiO₂-ZnO) for a comparison of hybrid and pure nanostructures to use them as a photoanodes for photoelectrocatalytic degradation of emerging contaminants. With the aim of comparing the properties of both samples, field emission scanning electron microscopy (FE-SEM) and confocal laser-Raman spectroscopy were used to study the morphology, composition, and crystallinity, respectively. Electrochemical impedances, Mott-Schottky, and water splitting measurements were performed to compare the photoelectrochemical properties of photoanodes. Finally, the photoelectrocatalytic degradation of the pesticide Imazalil was carried out with the best optimized nanostructure (TiO₂-ZnO). Full article

CdS thin films were grown on an FTO substrate at different temperatures, employing the low-cost hydrothermal method. All the fabricated CdS thin films were studied using XRD, Raman spectroscopy, SEM, PL spectroscopy, a UV–Vis spectrophotometer, photocurrent, Electrochemical Impedance Spectroscopy (EIS), and Mott–Schottky measurements. According to the XRD results, all the CdS thin films were formed in a cubic (zinc blende) structure with a favorable (111) orientation at various temperatures. The Scherrer equation was used to determine the crystal size of the CdS thin films, which varied from 25 to 40 nm. The SEM results indicated that the morphology of thin films seems to be dense, uniform, and tightly attached to the substrates. PL measurements showed the typical green and red emission peaks of CdS films at 520 nm and 705 nm, and these are attributable to free-carrier recombination and sulfur vacancies or cadmium vacancies, respectively. The optical absorption edge of the thin films was positioned between 500 and 517 nm which related to the CdS band gap. For the fabricated thin films, the estimated Eg was found to be between 2.50 and 2.39 eV. According to the photocurrent measurements, the CdS thin films grown were n-type semiconductors. As indicated by EIS, resistivity to charge transfer (RCT) decreased with temperature, reaching its lowest level at 250 °C. Flat band potential and donor density were found to fluctuate with temperature, from 0.39 to 0.76 V and 4.41 × 10¹⁸ to 15.86 × 10¹⁸ cm⁻³, respectively, according to Mott–Schottky measurements. Our results indicate that CdS thin films are promising candidates for optoelectronic applications. Full article

The relationship between passive film growth behavior and passivation time for plasma-sprayed Fe₄₈Cr₁₅Mo₁₄C₁₅B₆Y₂ amorphous coating in borate buffer solution has been thoroughly studied. The morphological characteristic and structural feature of as-spayed amorphous coating were estimated by scanning electron spectroscopy (SEM), X-ray diffraction (XRD) and transmission electron spectroscopy (TEM). The influence of passivation time on the film evolution properties was measured by electrochemical impedance spectra (EIS), Mott–Schottky curves, atomic force microscope (AFM) and X-ray photoelectron spectroscopy (XPS). The results revealed that both corrosion resistance and self-repairing capacity of passive film greatly increased with time based on high electric field assumption. Reductions in donor density and flat band potential were accountable for a lower conductivity of passive film. An increment in Cr₂O₃ oxide as the inner barrier layer derived from the dehydration reaction of Cr(OH)₃ contributed to the gradually densified structure of passive film. The extracted passive film thickness d increment with passivation time t conformed to the logarithm law on the basis of effective capacitance hypothesis: $d=0.43ln\left(t+52.06\right)-2.18$ (nm). Passivation mechanism within 600 s was ascribed to the adsorption of mechanical mixtures between metal ions and electrolytes, possibly leading to mechanical stress and rupture of passive film in the later growth procedure. The cation vacancy condensation process at the interface of coating/film was propitious in stabilizing the growth rate of passive film. Full article

In this study, TiO₂ thin films formed by dip-coating on an FTO substrate were obtained and characterized using surface, optical and electrochemical techniques. The impact of the dispersant (polyethylene glycol-PEG) on the surface (morphology, wettability, surface energy), optical (band gap and Urbach energy) and electrochemical (charge-transfer resistance, flat band potential) properties were investigated. When PEG was added to the sol–gel solution, the optical gap energy of the resultant films was reduced from 3.25 to 3.12 eV, and the Urbach energy increased from 646 to 709 meV. The dispersant addition in the sol–gel process influences surface features, as evidenced by lower contact-angle values and higher surface energy achieved for a compact film with a homogenous nanoparticle structure and larger crystallinity size. Electrochemical measurements (cycle voltammetry, electrochemical impedance spectroscopy and the Mott–Schottky technique) revealed improved catalytic properties of the TiO₂ film, due to a higher insertion/extraction rate of protons into the TiO₂ nanostructure, as well as a decrease in charge-transfer resistance from 418 k to 23.4 k and a decrease in flat band potential from 0.055 eV to −0.019 eV. The obtained TiO₂ films are a promising alternative for technological applications, due to their advantageous surface, optical and electrochemical features. Full article

n-type Cu₂O thin films were grown on conductive FTO substrates using a low-cost electrodeposition method. The doping of the n−Cu₂O thin films with K ions was well identified using XRD, Raman, SEM, EDX, UV-vis, PL, photocurrent, Mott–Schottky, and EIS measurements. The results of the XRD show the creation of cubic Cu₂O polycrystalline and monoclinic CuO, with the crystallite sizes ranging from 55 to 25.2 nm. The Raman analysis confirmed the presence of functional groups corresponding to the Cu₂O and CuO in the fabricated samples. Moreover, the samples’ crystallinity and morphology change with the doping concentrations which was confirmed by SEM. The PL results show two characteristic emission peaks at 520 and 690 nm which are due to the interband transitions in the Cu₂O as well as the oxygen vacancies in the CuO, respectively. Moreover, the PL strength was quenched at higher doping concentrations which reveals that the dopant K limits e−/h+ pairs recombination by trapped electrons and holes. The optical results show that the absorption edge is positioned between 425 and 460 nm. The computed Eg for the undoped and K−doped n−Cu₂O was observed to be between 2.39 and 2.21 eV. The photocurrent measurements displayed that the grown thin films have the characteristic behavior of n-type semiconductors. Furthermore, the photocurrent is enhanced by raising the doped concentration, where the maximum value was achieved with 0.1 M of K ions. The Mott–Schottky measurements revealed that the flat band potential and donor density vary with a doping concentration from −0.87 to −0.71 V and 1.3 × 10¹⁷ to 3.2 × 10¹⁷ cm⁻³, respectively. EIS shows that the lowest resistivity to charge transfer (Rct) was attained at a 0.1 M concentration of K ions. The outcomes indicate that doping n−Cu₂O thin films are an excellent candidate for biosensor and photovoltaic applications. Full article

Photoelectrochemical (PEC) water splitting is an eco-friendly method for producing clean and sustainable hydrogen fuels. Compared with the fabrication of solar hydrogen using n-type metal oxide semiconductor photoanodes, that of solar hydrogen using p-type metal oxide semiconductor photocathodes has not been researched as thoroughly. Therefore, this study investigated the effect of drop casting time on the PEC performance of a prepared CuBi₂O₄ photocathode. XPS, HRTEM, UV-DRS, Raman spectroscopy, XRD, and SEM analyses were used to characterize the prepared CuBi₂O₄ photocathode. Owing to the high charge separation and transfer, the photocurrent density of the CuBi₂O₄ photocathode was ~0.6 mA cm⁻² at 0.3 V vs. RHE. The nanoporous CuBi₂O₄ photocathode exhibited a high photocurrent density of up to 1.2 mA cm⁻² at 0.3 V vs. RHE with H₂O₂ as a sacrificial agent. Mott–Schottky and impedance measurements were also performed on the CuBi₂O₄ photocathode to estimate its acceptor density and charge-transfer resistance. Full article

Fe-Ce/layered double hydroxides (LDHs) were synthesized via a facile route by exploiting the “structural memory” of the LDH when the calcined MgAlLDH and ZnAlLDH were reconstructed in the aqueous solutions of FeSO₄/Ce(SO₄)₂. XRD analysis shows the formation of heterostructured catalysts that entangle the structural characteristics of the LDHs with those of Fe₂O₃ and CeO₂. Furthermore, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, TG/DTG, SEM/EDX and TEM results reveal a complex morphology defined by the large nano/microplates of the reconstructed LDHs that are tightly covered with nanoparticles of Fe₂O₃ and CeO₂. Calcination at 850 °C promoted the formation of highly crystallized mixed oxides of Fe₂O₃/CeO₂/ZnO and spinels. The photo-electrochemical behavior of Fe-Ce/LDHs and their derived oxides was studied in a three-electrode photo-electrochemical cell, using linear sweep voltammetry (LSV), Mott–Schottky (M-S) analysis and photo-electrochemical impedance spectroscopy (PEIS) measurements, in dark or under illumination. When tested as novel catalysts for the degradation of phenol from aqueous solutions, the light-driven catalytic heterojunctions of Fe-Ce/LDH and their derived oxides reveal their capabilities to efficiently remove phenol from water, under both UV and solar irradiation. Full article

Titanium beta alloys represent the new generation of materials for the manufacturing of joint implants. Their Young’s modulus is lower and thus closer to the bone tissue compared to commonly used alloys. The surface tribological properties of these materials should be improved by ion implantation. The influence of this surface treatment on corrosion behaviour is unknown. The surface of Ti-36Nb-6Ta, Ti-36Nb-4Zr, and Ti-39Nb titanium β-alloys was modified using nitrogen ion implantation. X-ray photoelectron spectroscopy was used for surface analysis, which showed the presence of titanium, niobium, and tantalum nitrides in the treated samples and the elimination of less stable oxides. Electrochemical methods, electrochemical impedance spectra, polarisation resistance, and Mott–Schottky plot were measured in a physiological saline solution. The results of the measurements showed that ion implantation does not have a significant negative effect on the corrosion behaviour of the material. The best results of the alloys investigated were achieved by the Ti-36Nb-6Ta alloy. The combination of niobium and tantalum nitrides had a positive effect on the corrosion resistance of this alloy. After surface treatment, the polarization resistance of this alloy increased, 2.3 × 10⁶ Ω·cm², demonstrating higher corrosion resistance of the alloy. These results were also supported by the results of electrochemical impedance spectroscopy. Full article

In this work, WO₃ nanostructures were synthesized with different complexing agents (0.05 M H₂O₂ and 0.1 M citric acid) and annealing conditions (400 °C, 500 °C and 600 °C) to obtain optimal WO₃ nanostructures to use them as a photoanode in the photoelectrochemical (PEC) degradation of an endocrine disruptor chemical. These nanostructures were studied morphologically by a field emission scanning electron microscope. X-ray photoelectron spectroscopy was performed to provide information of the electronic states of the nanostructures. The crystallinity of the samples was observed by a confocal Raman laser microscope and X-ray diffraction. Furthermore, photoelectrochemical measurements (photostability, photoelectrochemical impedance spectroscopy, Mott–Schottky and water-splitting test) were also performed using a solar simulator with AM 1.5 conditions at 100 mW·cm⁻². Once the optimal nanostructure was obtained (citric acid 0.01 M at an annealing temperature of 600 °C), the PEC degradation of methylparaben (C_O 10 ppm) was carried out. It was followed by ultra-high-performance liquid chromatography and mass spectrometry, which allowed to obtain the concentration of the contaminant during degradation and the identification of degradation intermediates. The optimized nanostructure was proved to be an efficient photocatalyst since the degradation of methylparaben was performed in less than 4 h and the kinetic coefficient of degradation was 0.02 min⁻¹. Full article