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Search Results (281)

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Keywords = Plasma Electrolytic Oxidation (PEO)

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21 pages, 14026 KiB  
Article
Development of PEO in Low-Temperature Ternary Nitrate Molten Salt on Ti6Al4V
by Michael Garashchenko, Yuliy Yuferov and Konstantin Borodianskiy
Materials 2025, 18(15), 3603; https://doi.org/10.3390/ma18153603 - 31 Jul 2025
Viewed by 157
Abstract
Titanium alloys are frequently subjected to surface treatments to enhance their biocompatibility and corrosion resistance in biological environments. Plasma electrolytic oxidation (PEO) is an environmentally friendly electrochemical technique capable of forming oxide layers characterized by high corrosion resistance, biocompatibility, and strong adhesion to [...] Read more.
Titanium alloys are frequently subjected to surface treatments to enhance their biocompatibility and corrosion resistance in biological environments. Plasma electrolytic oxidation (PEO) is an environmentally friendly electrochemical technique capable of forming oxide layers characterized by high corrosion resistance, biocompatibility, and strong adhesion to the substrate. In this study, the PEO process was performed using a low-melting-point ternary eutectic electrolyte composed of Ca(NO3)2–NaNO3–KNO3 (41–17–42 wt.%) with the addition of ammonium dihydrogen phosphate (ADP). The use of this electrolyte system enables a reduction in the operating temperature from 280 to 160 °C. The effects of applied voltage from 200 to 400V, current frequency from 50 to 1000 Hz, and ADP concentrations of 0.1, 0.5, 1, 2, and 5 wt.% on the growth of titanium oxide composite coatings on a Ti-6Al-4V substrate were investigated. The incorporation of Ca and P was confirmed by phase and chemical composition analysis, while scanning electron microscopy (SEM) revealed a porous surface morphology typical of PEO coatings. Corrosion resistance in Hank’s solution, evaluated via Tafel plot fitting of potentiodynamic polarization curves, demonstrated a substantial improvement in electrochemical performance of the PEO-treated samples. The corrosion current decreased from 552 to 219 nA/cm2, and the corrosion potential shifted from −102 to 793 mV vs. the Reference Hydrogen Electrode (RHE) compared to the uncoated alloy. These findings indicate optimal PEO processing parameters for producing composite oxide coatings on Ti-6Al-4V alloy surfaces with enhanced corrosion resistance and potential bioactivity, which are attributed to the incorporation of Ca and P into the coating structure. Full article
(This article belongs to the Special Issue Microstructure Engineering of Metals and Alloys, 3rd Edition)
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19 pages, 1343 KiB  
Article
Two-Step Plasma Electrolytic Oxidation of Advanced High-Strength Steel in Aluminate and Silicate Solutions
by Roy Morgenstern, Thomas Mehner and Thomas Lampke
Coatings 2025, 15(7), 850; https://doi.org/10.3390/coatings15070850 - 19 Jul 2025
Viewed by 301
Abstract
This work aims to clarify whether the individual advantages of the two commonly used silicate- and aluminate-based electrolytes for the plasma electrolytic oxidation (PEO) of steel can be combined in a two-step process. The first PEO step was carried out in an aluminate–phosphate [...] Read more.
This work aims to clarify whether the individual advantages of the two commonly used silicate- and aluminate-based electrolytes for the plasma electrolytic oxidation (PEO) of steel can be combined in a two-step process. The first PEO step was carried out in an aluminate–phosphate electrolyte with pulsed voltage and anodic amplitudes between 150 V and 200 V. The second PEO step was carried out at an increased anodic voltage amplitude of 400 V in a silicate–phosphate electrolyte. As a reference, PEO was conducted in a single step in the same silicate–phosphate electrolyte at an increased anodic voltage amplitude of up to 400 V. The microstructural layer analysis was carried out using SEM and EDX analyses, Raman spectroscopy and XRD analysis. Heterogeneous layers containing iron oxide and iron phosphate form in the silicate–phosphate electrolyte at anodic voltage amplitudes up to 300 V by electrochemical reactions. Further increasing the anodic voltage amplitude up to 400 V results in heterogeneous layers, too. PEO in the aluminate–phosphate electrolyte at 150 V causes the formation of thin, amorphous layers mainly consisting of aluminum and iron oxides. At 200 V amplitude, a PEO layer with pronounced open porosity is formed, which primarily consists of the crystalline phases corundum and hercynite. During subsequent PEO in the silicate–phosphate electrolyte, the previously formed layers were replaced by a macroscopically homogeneous layer that is mostly nanocrystalline and may contain amorphous iron(-aluminum) phosphates and oxides as well as silicon oxide. It can be concluded that the two-step PEO process is suitable for the production of more homogeneous PEO layers. Full article
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14 pages, 5535 KiB  
Article
Studies on the Coating Formation and Structure Property for Plasma Electrolytic Oxidation of AZ31 Magnesium Alloy
by Yingting Ye, Lishi Wang, Xinbin Hu and Zhixiang Bu
Coatings 2025, 15(7), 846; https://doi.org/10.3390/coatings15070846 - 19 Jul 2025
Viewed by 330
Abstract
Plasma electrolytic oxidation (PEO) is an advanced electrochemical surface treatment technology. It can effectively improve the corrosion resistance of magnesium and its alloys. This paper aims to form protective PEO coatings on an AZ31 substrate with different electrolytes, while monitoring the micro-discharge evolution [...] Read more.
Plasma electrolytic oxidation (PEO) is an advanced electrochemical surface treatment technology. It can effectively improve the corrosion resistance of magnesium and its alloys. This paper aims to form protective PEO coatings on an AZ31 substrate with different electrolytes, while monitoring the micro-discharge evolution by noise intensity and morphology analysis. By setting the PEO parameters and monitoring process characteristics, such as current density, spark appearance, and noise intensity, it was deduced that the PEO process consists of the following three stages: anodic oxidation, spark discharge, and micro-arc discharge. The PEO oxide coating formed on the AZ31 alloy exhibits various irregular volcano-like structures. Oxygen species are uniformly distributed along the coating cross-section. Phosphorus species tend to be enriched inwards to the coating/magnesium substrate interface, while aluminum piles up towards the surface region. Surface roughness of the PEO coating formed in the silicate-based electrolyte was the lowest in an arithmetic average height (Sa) of 0.76 μm. Electrochemical analysis indicated that the corrosion current density of the PEO coating decreased by about two orders of magnitude compared to that of untreated blank AZ31 substrate, while, at the same time, the open-circuit potential shifted significantly to the positive direction. The corrosion current density of the 10 min/400 V coating was 1.415 × 10−6 A/cm2, approximately 17% lower than that of the 2 min/400 V coating (1.738 × 10−6 A/cm2). For a fixed 10 min treatment, the longer the PEO duration time, the lower the corrosion current density. Finally, the tested potentiodynamic polarization curve reveals the impact of different types of PEO electrolytes and different durations of PEO treatment on the corrosion resistance of the oxide coating surface. Full article
(This article belongs to the Section Plasma Coatings, Surfaces & Interfaces)
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21 pages, 13173 KiB  
Article
Surface Modification by Plasma Electrolytic Oxidation of Friction Surfacing 4043 Aluminum-Based Alloys Deposited onto Structural S235 Steel Substrate
by Roxana Muntean and Ion-Dragoș Uțu
Materials 2025, 18(14), 3302; https://doi.org/10.3390/ma18143302 - 13 Jul 2025
Viewed by 460
Abstract
The friction surfacing (FS) process has emerged over the past few years as a method for joining both similar and dissimilar materials, for volume damage repair of defective components, and for corrosion protection. The possibility to produce a metallic coating by FS, without [...] Read more.
The friction surfacing (FS) process has emerged over the past few years as a method for joining both similar and dissimilar materials, for volume damage repair of defective components, and for corrosion protection. The possibility to produce a metallic coating by FS, without melting the material, classifies this technique as distinct from other standard methods. This unconventional deposition method is based on the severe plastic deformation that appears on a rotating metallic rod (consumable material) pressed against the substrate under an axial load. The present study aims to investigate the tribological properties and corrosion resistance provided by the aluminum-based FS coatings deposited onto a structural S235 steel substrate and further modified by plasma electrolytic oxidation (PEO). During the PEO treatment, the formation of a ceramic film is enabled, while the hardness, chemical stability, corrosion, and wear resistance of the modified surfaces are considerably increased. The morpho-structural characteristics and chemical composition of the PEO-modified FS coatings are further investigated using scanning electron microscopy combined with energy dispersive spectroscopy analysis and X-ray diffraction. Dry sliding wear testing of the PEO-modified aluminum-based coatings was carried out using a ball-on-disc configuration, while the corrosion resistance was electrochemically evaluated in a 3.5 wt.% NaCl solution. The corrosion rates of the aluminum-based coatings decreased significantly when the PEO treatment was applied, while the wear rate was substantially reduced compared to the untreated aluminum-based coating and steel substrate, respectively. Full article
(This article belongs to the Section Metals and Alloys)
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24 pages, 8205 KiB  
Article
Preparation and Characterization of Magnesium Implants with Functionalized Surface with Enhanced Biological Activity Obtained via PEO Process
by Julia Radwan-Pragłowska, Julita Śmietana, Łukasz Janus, Aleksandra Sierakowska-Byczek, Karol Łysiak and Klaudia Kuźmiak
Processes 2025, 13(7), 2144; https://doi.org/10.3390/pr13072144 - 5 Jul 2025
Viewed by 350
Abstract
This study presents the development and comprehensive evaluation of magnesium-based implants with surface modifications using selected polymers and bioactive compounds. The implants were fabricated via plasma electrolytic oxidation (PEO), followed by the application of chitosan, polydopamine (PDA), and gold nanoparticles as bioactive surface [...] Read more.
This study presents the development and comprehensive evaluation of magnesium-based implants with surface modifications using selected polymers and bioactive compounds. The implants were fabricated via plasma electrolytic oxidation (PEO), followed by the application of chitosan, polydopamine (PDA), and gold nanoparticles as bioactive surface coatings. In vitro experiments, including FT-IR spectroscopy, scanning electron microscopy (SEM), wettability tests, biodegradation assays in simulated body fluid (SBF), electrochemical corrosion analysis, and cytotoxicity tests using MG-63 osteoblast-like cells, were employed to assess the physicochemical and biological properties of the materials. The PEO + PDA-modified samples demonstrated the highest corrosion resistance (−1.15 V corrosion potential), enhanced cell viability (~95%), and favorable surface wettability (contact angle ~12.5°), outperforming other tested configurations. These findings suggest that PEO combined with PDA offers a synergistic effect, leading to superior biocompatibility and degradation control compared to unmodified magnesium or single-coating strategies. The developed implants hold promise for orthopedic applications requiring biodegradable, bioactive, and cytocompatible materials. Full article
(This article belongs to the Special Issue Biochemical Processes for Sustainability, 2nd Edition)
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13 pages, 2517 KiB  
Article
Study on the Wear Resistance of 6061 Aluminum Alloy Bipolar Plasma Electrolytic Oxidation Ceramic Coating by the Addition of K2ZrF6
by Rui Tong, Shiquan Zhou, Hongtao Li, Xiang Tao and Jian Chen
Materials 2025, 18(13), 2962; https://doi.org/10.3390/ma18132962 - 23 Jun 2025
Viewed by 357
Abstract
A plasma electrolytic oxidation (PEO) coating was produced on 6061 aluminum alloy within a silicate-containing electrolyte using a bipolar pulsed power supply. The impact of K2ZrF6 addition on the wear resistance of the coating was investigated. The phase composition, surface [...] Read more.
A plasma electrolytic oxidation (PEO) coating was produced on 6061 aluminum alloy within a silicate-containing electrolyte using a bipolar pulsed power supply. The impact of K2ZrF6 addition on the wear resistance of the coating was investigated. The phase composition, surface morphology, and elemental distribution of the coatings were assessed by means of X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), and scanning electron microscopy (SEM). Experimental data revealed that the growth rate of the coating increased by 37.3% compared to that without K2ZrF6; the addition of K2ZrF6 favored the formation of mullite and enhanced the coating densification; it also improved the breakdown voltage of the coating, which increased by 46.0% compared to that without K2ZrF6; and it also demonstrated excellent abrasion resistance, with a reduction of 41.8% in the weight of the abrasion. Full article
(This article belongs to the Special Issue Surface Technology and Coatings Materials)
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20 pages, 12096 KiB  
Article
Effect on the Electrochemical Properties of PEO Films Produced on Commercially Pure Titanium Using Multicomponent Oxide Coatings
by Lauri Ruberti, Heloisa Andréa Acciari, Diego Rafael Nespeque Correa, Yasmin Bastos Pissolitto, Elidiane Cipriano Rangel, Francisco Trivinho-Strixino and Nilson Cristino da Cruz
Metals 2025, 15(6), 658; https://doi.org/10.3390/met15060658 - 13 Jun 2025
Viewed by 765
Abstract
Titanium has specific uses due to its cost, which is counterbalanced by its extraordinary chemical and physical properties. Submarine hulls and nuclear power plant pipes have been made of titanium since the last century due to its high corrosion resistance, and the aircraft [...] Read more.
Titanium has specific uses due to its cost, which is counterbalanced by its extraordinary chemical and physical properties. Submarine hulls and nuclear power plant pipes have been made of titanium since the last century due to its high corrosion resistance, and the aircraft industry has also exploited its remarkable properties, such as lightness and high melting point. Surface modifications by plasma electrolytic oxidation (PEO) may increase its corrosion resistance, roughness and wettability. Furthermore, greater corrosion resistance is a rather attractive property in nuclear power plant pipes, although the increased roughness and wettability are disadvantageous downsides as they favor the attachment of marine organisms. Nonetheless these new features are particularly interesting for biomedical applications. In this study, PEO films were produced on commercially pure titanium substrates using different electrolytes, one of which contains zirconium dioxide and the other consisting of tantalum pentoxide, in addition to a third one composed of a combination of the former two. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) analyses were performed in addition to contact angle and roughness measurements, and electrochemical tests were carried out to comparatively characterize the different film compositions. The results revealed that excellent corrosion resistance was achieved by mixing oxides in the electrolyte. Full article
(This article belongs to the Special Issue Surface Engineering and Properties of Metallic Biomaterials)
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14 pages, 3417 KiB  
Article
The Influence of Water Content in Ethylene Glycol Electrolyte on Magnesium Plasma Electrolytic Fluorinated Coating
by Yifeng Yang, Hao Wang, Xuchen Lu and Cancan Liu
Coatings 2025, 15(6), 701; https://doi.org/10.3390/coatings15060701 - 11 Jun 2025
Viewed by 372
Abstract
Plasma electrolytic fluorination (PEF) of AZ31 magnesium alloy was carried out by adding different ratios of water to the ethylene glycol-ammonium fluoride electrolyte. The structural composition of the coatings was characterized using SEM, XRD, and EDS, and the effects of water content on [...] Read more.
Plasma electrolytic fluorination (PEF) of AZ31 magnesium alloy was carried out by adding different ratios of water to the ethylene glycol-ammonium fluoride electrolyte. The structural composition of the coatings was characterized using SEM, XRD, and EDS, and the effects of water content on the microstructure and corrosion resistance of the PEF coatings were analyzed. The results showed that the addition of water promoted the ionization of ammonium fluoride and increased the conductivity of the glycol electrolyte, which led to a decrease in the termination voltage. However, the coating thickness was not changed by the addition of water. The O element in water was not enough to compete with the F element in the electrolyte and had a small effect on the PEF coating composition, which was still dominated by MgF2. The addition of water had an effect on the structure of the coating: with an increase in water content, the number of coating penetration holes decreases, and the continuity is enhanced. The pores on the surface of the coating tended to be levelled off and transitioned to the typical coating structure of PEO (plasma electrolytic oxidation). The addition of water to the glycol electrolyte was conducive to improving the corrosion resistance of the coatings. The corrosion resistance of PEF coatings in neutral NaCl corrosive medium firstly increased and then decreased, and the strongest corrosion resistance was obtained when the ratio of glycol and water is 6:4. Full article
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21 pages, 4658 KiB  
Article
Potentiostatic Plasma Electrolytic Oxidation (PEO) of Aluminum Alloy AA6082: Effect of Electrical Input on Coating Microstructure and Corrosion Resistance
by Alberto Berardi, Matteo Gamba, Luca Paterlini, Federica Ceriani and Marco Ormellese
Coatings 2025, 15(6), 653; https://doi.org/10.3390/coatings15060653 - 29 May 2025
Viewed by 540
Abstract
Aluminum alloy AA6082 (Al-Si-Mg) is a lightweight alloy that requires thick barrier coatings to be protected from localized corrosion. Plasma Electrolytic Oxidation (PEO) coating is a common anodic surface treatment used for growing protective oxides; the main process variables of PEO are the [...] Read more.
Aluminum alloy AA6082 (Al-Si-Mg) is a lightweight alloy that requires thick barrier coatings to be protected from localized corrosion. Plasma Electrolytic Oxidation (PEO) coating is a common anodic surface treatment used for growing protective oxides; the main process variables of PEO are the composition of the electrolytic solution and the electrical input. This work focuses on the optimization of the electrical input by comparing different coatings produced by potentiostatic PEO at the effective potential of 350 V, applied by different combinations of voltage ramps with various slopes and maintenance times at the fixed potential. All processes lasted five minutes. The innovative character of this research work is the evaluation of the combined effect of the anodizing voltage and its different trends with time on the coating structure and morphology. The corrosion resistance of coated AA6082 is assessed in contact with chlorides, reproducing seawater. The resulting anodic coatings were compared in terms of structure, composition (thickness, XRD, SEM-EDS) and corrosion resistance (potentiodynamic polarization and electrochemical impedance spectroscopy), finding that longer maintenance at high anodizing potentials promotes localized high-energy plasma discharges, producing larger pores and thicker, but less protective coatings. Results show that the coating thickness increases with the maintenance time (maximum thickness value~17.6 μm). Shorter maintenance periods and longer voltage ramps lead to a lower surface porosity and enhanced corrosion performances of the oxide. The thinnest and least porous coating exhibits the best corrosion behavior (CR~1.1 μm/year). Full article
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31 pages, 2749 KiB  
Review
Modern Innovations and Applications in Plasma Electrolytic Oxidation Coatings on Aluminum, Magnesium, and Titanium
by Angus G. McCarroll and Pradeep L. Menezes
Coatings 2025, 15(5), 592; https://doi.org/10.3390/coatings15050592 - 16 May 2025
Viewed by 756
Abstract
Plasma electrolytic oxidation (PEO) is an electrochemical surface modification technique for producing dense oxide layers on valve metals. This review compiles the various modifications to the PEO process that have been used to improve the produced coatings and make them suitable for specific [...] Read more.
Plasma electrolytic oxidation (PEO) is an electrochemical surface modification technique for producing dense oxide layers on valve metals. This review compiles the various modifications to the PEO process that have been used to improve the produced coatings and make them suitable for specific applications, with a focus on examples of aluminum, magnesium, and titanium substrates. An overview of the PEO process is given, highlighting the various process parameters and their effects on the final surface. The challenges with light metals that motivate the use of surface modifications are summarized, along with some of the other modifications that attempt to overcome them. Two broad categories of modifications to the PEO process are presented: in situ modifications, influencing the properties of the coating during its formation, and ex situ modifications, augmenting the properties of an already-formed coating. Finally, specific examples of applications for modified PEO processes are discussed, including battery, biomedical, water treatment, and energy production applications. Full article
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16 pages, 4742 KiB  
Article
Influence of Zn2⁺ Concentration on Ceramic Coatings for Corrosion Protection of Magnesium-Lithium Alloys
by Yifei Wang, Chunming Liu, Hongzhan Li and Zhen Zhang
Materials 2025, 18(9), 2072; https://doi.org/10.3390/ma18092072 - 30 Apr 2025
Viewed by 476
Abstract
This study investigates the enhancement of corrosion resistance in magnesium-lithium alloys through plasma electrolytic oxidation (PEO) coatings incorporating ZnF2 via in situ synthesis. By adjusting Zn2⁺ concentrations (4–16 g/L) in a zirconium salt-based electrolyte, ceramic coatings with tailored ZnF2 [...] Read more.
This study investigates the enhancement of corrosion resistance in magnesium-lithium alloys through plasma electrolytic oxidation (PEO) coatings incorporating ZnF2 via in situ synthesis. By adjusting Zn2⁺ concentrations (4–16 g/L) in a zirconium salt-based electrolyte, ceramic coatings with tailored ZnF2 content, thickness, and porosity were fabricated. The optimal Zn2⁺ concentration of 12 g/L yielded a ZnF2-rich coating with isolated pores and enhanced densification (inner layer resistance Ri = 3.01 × 104 Ω⋅cm2), achieving a corrosion current density (icorr) of 4.42 × 10−8 A/cm2 and polarization resistance (Rp) of 8.5 × 105 Ω⋅cm2, representing a 354-fold improvement over untreated LA103Z. Higher Zn2⁺ concentrations (16 g/L) induced interconnected pores and ZnO formation, degrading corrosion resistance. Long-term immersion (168 h in 3.5 wt% NaCl) confirmed the durability of Zn12 coatings (mass loss: 0.6 mg), while Zn4 and Zn16 coatings exhibited severe localized corrosion. The study demonstrates that balancing Zn2⁺ concentration optimizes ZnF2 passivation and pore isolation, offering a scalable strategy for Mg-Li alloy protection in corrosive environments. Full article
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18 pages, 21884 KiB  
Article
Ti-Supported Oxide Coatings Based on MWO4 (M = Fe, Co, Ni): Plasma Electrolytic Synthesis, Characterization and Catalytic Properties in S, N-Heterocycles Peroxide Oxidation
by Irina G. Tarkhanova, Vladimir M. Zelikman, Irina V. Lukiyanchuk, Marina S. Vasilyeva, Vladimir V. Tkachev, Vladimir V. Korochentsev and Daria H. Shlyk
Molecules 2025, 30(9), 1998; https://doi.org/10.3390/molecules30091998 - 30 Apr 2025
Viewed by 402
Abstract
In this study, catalytically active coatings on titanium were synthesized by plasma electrolytic oxidation (PEO) in aqueous electrolytes based on sodium tungstate with the addition of sodium phosphate or sodium borate and chelate complexes of iron, cobalt or nickel. Taking into account the [...] Read more.
In this study, catalytically active coatings on titanium were synthesized by plasma electrolytic oxidation (PEO) in aqueous electrolytes based on sodium tungstate with the addition of sodium phosphate or sodium borate and chelate complexes of iron, cobalt or nickel. Taking into account the EDX, XPS and XRD data, the oxide–phosphate coatings (PWFe, PWCo, PWNi) contained crystalline titanium oxide and amorphous tungstates and/or phosphates of iron triad metals. Amorphization was facilitated by high phosphorus concentrations (up to 6 at.%). Replacing phosphate with borate in the electrolyte with Ni(II)-EDTA complexes led to the crystallization of WO3 and NiWO4 in the PEO coatings (BWNi). All formed PEO coatings were active in reactions of the oxidative desulfurization (ODS) of thiophene and dibenzothiophene and oxidative denitrogenation (ODN) of pyridine, as well as in the simultaneous removal of S- and N-containing substrates from their mixture. The stability of samples with MWO4 increased in the following series: PWNi < PWCo < PW < PWFe < BWNi. Replacing phosphate with borate in the electrolyte resulted in the preparation of catalysts with enhanced stability and activity. In contrast to PWM catalysts, the BWNi catalyst had selectivity toward the oxidation of pyridine in its mixture with thiophene. Full article
(This article belongs to the Section Materials Chemistry)
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28 pages, 12427 KiB  
Review
Photocatalytic Degradation of Methyl Orange in Wastewater Using TiO2-Based Coatings Prepared by Plasma Electrolytic Oxidation of Titanium: A Review
by Stevan Stojadinović
Reactions 2025, 6(2), 25; https://doi.org/10.3390/reactions6020025 - 8 Apr 2025
Cited by 1 | Viewed by 1348
Abstract
This review analyzes TiO2-based coatings formed by the plasma electrolytic oxidation (PEO) process of titanium for the photocatalytic degradation of methyl orange (MO) under simulated solar irradiation conditions. PEO is recognized as a useful technique for creating oxide coatings on various [...] Read more.
This review analyzes TiO2-based coatings formed by the plasma electrolytic oxidation (PEO) process of titanium for the photocatalytic degradation of methyl orange (MO) under simulated solar irradiation conditions. PEO is recognized as a useful technique for creating oxide coatings on various metals, particularly titanium, to assist in the degradation of organic pollutants. TiO2-based photocatalysts in the form of coatings are more practical than TiO2-based photocatalysts in the form of powder because the photocatalyst does not need to be recycled and reused after wastewater degradation treatment, which is an expensive and time-consuming process. In addition, the main advantage of PEO in the synthesis of TiO2-based photocatalysts is its short processing time (a few minutes), as it excludes the annealing step needed to convert the amorphous TiO2 into a crystalline phase, a prerequisite for a possible photocatalytic application. Pure TiO2 coatings formed by PEO have a low photocatalytic efficiency in the degradation of MO, which is due to the rapid recombination of the photo-generated electron/hole pairs. In this review, recent advances in the sensitization of TiO2 with narrow band gap semiconductors (WO3, SnO2, CdS, Sb2O3, Bi2O3, and Al2TiO5), doping with rare earth ions (example Eu3+) and transition metals (Mn, Ni, Co, Fe) are summarized as an effective strategy to reduce the recombination of photo-generated electron/hole pairs and to improve the photocatalytic efficiency of TiO2 coatings. Full article
(This article belongs to the Special Issue Feature Papers in Reactions in 2025)
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9 pages, 3094 KiB  
Article
Formation of Alpha-Al2O3 Coatings on Tungsten Substrate by Plasma Electrolytic Oxidation
by Stevan Stojadinović and Pedro Nelson
Ceramics 2025, 8(2), 29; https://doi.org/10.3390/ceramics8020029 - 22 Mar 2025
Cited by 1 | Viewed by 532
Abstract
Oxide coatings formed by plasma electrolytic oxidation (PEO) of tungsten substrate for 10 min in a phosphate alkaline electrolyte (PAE, 2 g/L Na3PO4·12H2O) with an addition of 2 g/L, 3 g/L, and 4 g/L NaAlO2 were [...] Read more.
Oxide coatings formed by plasma electrolytic oxidation (PEO) of tungsten substrate for 10 min in a phosphate alkaline electrolyte (PAE, 2 g/L Na3PO4·12H2O) with an addition of 2 g/L, 3 g/L, and 4 g/L NaAlO2 were investigated by SEM/EDS and XRD. In PAE + 2 g/L NaAlO2, a weakly crystalline coating is formed, consisting of amorphous Al2O3, the triclinic phase of WO3, the cristobalite phase of AlPO4 and the gamma and alpha phases of Al2O3. Strong micro-discharges during PEO in PAE with the addition of 3 g/L and 4 g/L NaAlO2 lead to the crystallization of amorphous Al2O3 into gamma-Al2O3 and alpha-Al2O3 phases. The coating formed in PAE + 4 g/L NaAlO2 is well crystallized and rich in alpha-Al2O3, which makes it suitable for high-temperature applications. To explain the composition of the formed coatings and the transformation of the amorphous Al2O3 into gamma and alpha phases, we followed the change in morphology, thickness, chemical and phase composition of the coatings during PEO in PAE + 4 g/L NaAlO2. Full article
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13 pages, 3662 KiB  
Article
KMnO4-Induced Amorphization of ZIF-67 on Plasma Electrolytic Oxidation Coatings for Enhanced Photocatalytic Performance
by Mohammad Aadil and Mosab Kaseem
Coatings 2025, 15(3), 291; https://doi.org/10.3390/coatings15030291 - 2 Mar 2025
Cited by 2 | Viewed by 814
Abstract
This study explores the enhancement of photocatalytic activity in Zeolitic Imidazolate Framework-67 (ZIF-67), integrated with plasma electrolytic oxidation (PEO) coatings on an AZ31 magnesium alloy through post-treatment with potassium permanganate (KMnO4). The KMnO4 treatment induces the partial amorphization of ZIF-67, [...] Read more.
This study explores the enhancement of photocatalytic activity in Zeolitic Imidazolate Framework-67 (ZIF-67), integrated with plasma electrolytic oxidation (PEO) coatings on an AZ31 magnesium alloy through post-treatment with potassium permanganate (KMnO4). The KMnO4 treatment induces the partial amorphization of ZIF-67, resulting in improved light absorption and the increased availability of catalytic sites. Structural and compositional analyses confirmed the formation of MnOx species and amorphous domains that synergistically contribute to enhanced photocatalytic performance. Under visible light, the treated coatings demonstrated remarkable efficiency, degrading 99.43% of rhodamine B (RhB) dye within just 50 min, an improvement attributed to superior light absorption, enhanced charge separation, and the introduction of additional active sites. These findings establish KMnO4 post-treatment as a transformative approach for optimizing MOF-based coatings, offering a pathway to develop advanced functional coatings with exceptional dye degradation capabilities. Full article
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