Galvanic Process Research Articles

Insights into oxidation of pentachlorophenol (PCP) by low-dose ferrate(VI) catalyzed with α-Fe2O3 nanoparticles

In this study, the catalytic performance of α-Fe2O3 nanoparticles (nα-Fe2O3) in the low-dose ferrate (Fe(VI)) system was systematically studied through the degradation of pentachlorophenol (PCP). Based on the established quadratic functions between nα-Fe2O3 amount and observed pseudo first-order rate constant (kobs), two linear correlation equations were offered to predict the optimum catalyst dosage and the maximum kobs at an applied Fe(VI) amount. Moreover, characterization and cycling experiments showed that nα-Fe2O3 has good stability and recyclability. According to the results of reactive species identification and quenching experiment and galvanic oxidation process, the catalytic mechanism was proposed that Fe(III) on the surface of nα-Fe2O3 may react with Fe(VI) to enhance the generation of highly reactive Fe(IV)/Fe(V) species, which rapidly extracted a single electron from PCP molecule for its further reaction. Besides, two possible PCP degradation pathways, i.e., single oxygen transfer mediated hydroxylation and single electron transfer initiated polymerization were proposed. The formation of coupling products that are prone to precipition and separation was largely improved. This study proved that nα-Fe2O3 can effectively catalyze PCP removal at low-dose Fe(VI), which provides some support for the application of Fe(VI) oxidation technology in water treatment in the context of low-carbon emissions.

Oxygen reduction reaction on AgPd nanocatalysts prepared by galvanic exchange

In this work galvanic exchange was employed as bimetallic catalyst preparation method to obtain AgPd nanocatalysts. Ag nanoparticles synthesized by the citrate method and commercial silver nanowires (AgNWs) were used for Pd spontaneous deposition. From transmission electron microscopy images, the particle sizes were determined between 10 and 20 nm and AgPd particles with the Ag/Pd molar ratio of 18:82 obtained using MP-AES were larger compared to those of 89:11 ratio. The galvanic exchange process resulted in porous and half-moon shaped particles. Pd distribution for AgPd/C_1 (18:82) and AgPd/C_2 (56:44) catalysts was rather uniform. Decreasing the amount of Pd salt in the galvanic exchange bath led to only surface decoration of Ag particles as can be seen in the case of AgPd/C_3 (79:21) and AgPd/C_4 (89:11). AgPd120NW and AgPd80NW samples showed the Ag/Pd ratio of 82:18 and 94:6, respectively. The electrocatalysts were studied for oxygen reduction reaction (ORR) in alkaline media using the rotating disk electrode technique. Higher specific activity values for ORR were obtained on larger particles, however galvanic exchange process was not limited to surface layers, thus increasing Pd content resulted in lower mass activities. For all the AgPd catalysts a typical Tafel slope value of ∼−60 mV was observed.

Three-phase-boundary Pt in a self-supported MoPt2-MoNi4/Mo2C heterojunction electrocatalyst for highly efficient pH-universal hydrogen evolution reaction

Design of high-performance Pt-based electrocatalysts is significant for hydrogen production through water splitting at pH-universal conditions but still challenging. Herein, the MoPt2-MoNi4/Mo2C three-phase heterojunction is fabricated via simply pyrolyzing hydrothermally resultant Mo-Ni precursor with subsequent galvanic Pt replacement process. It exhibits remarkable and stable hydrogen evolution reaction (HER) performance with impressive mass activity and low overpotential of 53, 77 and 46 mV at the current density of 100 mA cm−2 in alkaline, neutral and acidic media, respectively. Density functional theory calculations illustrate that there are multiple types of Pt sites in the phase of MoPt2 in such three-phase heterojunction, while only the Pt atoms located in the three-phase boundary not only process optimal electronic structure modulated by MoNi4/Mo2C, but also act as highly-active sites for HER. Moreover, downshifted d-band center of Pt triggered by the construction of three-phase MoPt2-MoNi4/Mo2C heterojunction, which regulating the free energy of reactive intermediates sorption and thereby accelerating the entire HER process. This work provides some constructive suggestions to design highly efficient Pt-based heterostructured electrocatalysts towards HER.

Sol–Gel Silica Coatings for Corrosion Protection of Aluminum Parts Manufactured by Selective Laser Melting (SLM) Technology

Metal additive manufacturing is a rapidly growing field based on the fabrication of complex parts with improved performance. The advantages of using this technology include the production of shapes that cannot be produced by traditional machining technologies, the possibility of using trabecular reinforcing structures, and the ability to make parts with topological optimization that allow for increased performance and decreased mass of the parts produced. Metal parts produced by selective laser melting technology exhibit high surface roughness, which limits their direct implementation. Corrosion protection of these surfaces is difficult, especially for galvanic processes. This paper analyzes the possibility of using sol–gel silica (silicon oxide) coatings to effectively protect various surfaces of aluminum alloys produced by selective laser melting technology. Silicon oxide sol–gel protective coatings have demonstrated excellent chemical stability and corrosion resistance, being able to be applied in very thin layers. These properties make them excellent candidates for protecting additive-manufactured metal parts, especially as-built surfaces with a high surface roughness. Nanostructured silica sol–gel protective coatings have demonstrated excellent corrosion resistance and have the potential to replace the highly toxic chromium-based galvanic treatments. Using nanostructured silica sol–gel coatings, aluminum parts can be seamlessly integrated into circular-economy cycles.

Assessment of Cultivated Soil Contamination by Potentially Toxic Metals as a Result of a Galvanizing Plant Failure

Zinc is one of the more mobile metals in the soil and thus involves the risk of entering the food chain. Zinc compounds are used in the galvanization process, which is assumed to be safe for the environment. However, random events or failures such as unsealing bathtubs with liquid zinc or hydrochloric acid, as well as violent fires in industrial halls, may pose a real threat to the environment, including human health. Therefore, this research was carried out to determine the content of zinc and selected potentially toxic metals in arable soils after a failure in a galvanizing plant located in the village of Dębska Wola (southeastern Poland). In addition, the potential risk associated with excessive accumulation of identified pollutants in the environment was assessed. In order to determine the level of contamination, soil samples were taken, and basic physical and chemical properties were analysed. The concentrations of Zn, Pb, and Cd in the soil were determined using the atomic emission spectrometry technique with inductively coupled plasma (ICP-OES), and pH measurements were performed using the potentiometric method after prior wet mineralisation of the research samples. The analysed samples had a varied pH of the organic–mineral horizon from pHH2O 4.66 to pHH2O 5.33 and from pHKCl 3.89 to pHKCl 5.06. As a result of a failure, toxic metal fumes were released into the atmosphere, causing concentrations of Zn in the soil samples from 0–5 cm in the range of 1201–2007 mg∙kg−1, as well as Pb (109–509 mg∙kg−1) and Cd (4.6–17 mg∙kg−1). High contents of zinc and lead found in several soil samples are of anthropogenic nature and require detailed monitoring in order to eliminate the risk associated with their accumulation. The study area should be re-analysed to determine the rate of reclamation of degraded soils.

Insights into the carbon nanotubes-mediated activation of permanganate for decontamination under high salinity

Radical-based advanced oxidation process (AOPs) has attracted great interests in wastewater treatment field. However, by the traditional radical-based method, the degradation of organic pollution is greatly suppressed when radicals react with the co-existing anions in the solution. Herein, an efficient method for degrading of contaminant under high salinity conditions is discussed through a non-radical pathway. Carbon nanotubes (CNTs) was employed as an electron transfer medium to facilitate the electron conversion from contaminants to potassium permanganate (PM). Based the results of quenching experiments, probe experiments, and galvanic oxidation process experiments, the degradation mechanism of CNTs/PM process was demonstrated to be electron transfer, rather than reactive intermediate Mn species. As a result, typical influencing factors including salt concentration, cations, and humic acid have less of an impact on degradation during CNTs/PM processes. In addition, the CNTs/PM system exhibits superior reusability and universality of pollutants, which has the potential to be applied as a non-radical pathway for the purification of contaminant in the large-scale high salinity wastewater treatment.

Permanganate activation with Mn oxides at different oxidation states: Insight into the surface-promoted electron transfer mechanism

The development of new strategies to improve the removal of organic pollutants with permanganate (KMnO4) is a hot topic in water treatment. While Mn oxides have been extensively used in Advanced Oxidation Processes through an electron transfer mechanism, the field of KMnO4 activation remains relatively unexplored. Interestingly, this study has discovered that Mn oxides with high oxidation states including γ-MnOOH, α-Mn2O3 and α-MnO2, exhibited excellent performance to degrade phenols and antibiotics in the presence of KMnO4. The MnO4- species initially formed stable complexes with the surface Mn(III/IV) species and showed an increased oxidation potential and electron transfer reactivity, caused by the electron-withdrawing capacity of the Mn species acting as Lewis acids. Conversely, for MnO and γ-Mn3O4 with Mn(II) species, they reacted with KMnO4 to produce cMnO2 with very low activity for phenol degradation. The direct electron transfer mechanism in α-MnO2/KMnO4 system was further confirmed through the inhibiting effect of acetonitrile and the galvanic oxidation process. Moreover, the adaptability and reusability of α-MnO2 in complicated waters indicated its potential for application in water treatment. Overall, the findings shed light on the development of Mn-based catalysts for organic pollutants degradation via KMnO4 activation and understanding of the surface-promoted mechanism.

Galvanic corrosion mechanism of Ti-Al coupling: the impact of passive films on the coupling effect

The light metals of titanium and aluminum are often used together, so the risk of galvanic corrosion is inevitable. However, the passive films on both metals will change during the galvanic corrosion process, which affects the coupling effect. Thus, this work aims to investigate the variation of passive films with increasing galvanic corrosion time, and further clarify their impact on galvanic corrosion rate. Motto-Schottky (M-S) curves, electrochemical impedance spectroscope (EIS), zero charge potential and XPS were used to characterize the state of the passive films, potentiodynamic polarization and zero resistance ammeter (ZRA) were utilized to analyze the cathodic and anodic reactions on Ti-Al coupling. The results indicate that during galvanic corrosion process the passive film on cathode titanium alloy is transformed from titanium dioxide to low-valent titanium oxide and titanium hydroxide due to hydrogen adsorption behavior, resulting in the increase of defect density in passive film. The passive film on anode aluminum alloy degrades rapidly in the initial galvanic corrosion stage due to the action of Cl− accumulation by non-electrostatic action, also the cathodic reaction on anode aluminum alloy is relatively high under coupled condition, which plays an important role in the high corrosion rate of anode aluminum alloy.

Ultrastable Gold–Copper Nanoclusters on Nitrogen-Doped Graphene Quantum Dots for Selective Electrochemical and Fluorescence Sensing of Glycine

In this work, we present an ultrastable gold–copper nanocluster on nitrogen-doped graphene quantum dot (AuCuNC@N-GQD), with a stability of ≥1 year, achieved through a galvanic exchange process, which displayed intense solid- and solution-state near-infrared emission. Furthermore, the NC exhibited selective and dual sensing of glycine (GLY) through (nonenzymatic) electrochemical (EC) and fluorescence methods, which is assigned to the unique combination of the strong emission and conducting properties of Au–CuNC and N-GQD, respectively, in the same material and is a first-time report of all the above-mentioned. The limits of detection (LODs) obtained for GLY by EC and fluorescence sensing were 10 nM and 1 μM, respectively and are the lowest LOD values reported hitherto in the respective categories. Compared to the controls, AuCuNC@N-GQDs exhibited a ∼20-fold enhancement with a sensitivity of 0.377 μA μM–1 cm–2. The preferential Au–GLY interaction is considered to be the reason for the selective sensing of GLY by AuCuNC@N-GQD and the improvement in the electronic and conductivity characteristics due to N-GQD to the enhanced sensitivity. The sensing performance was successfully extended to real blood and urine samples spiked with GLY without interference.

Ball milling treatment of Mn3O4 regulates electron transfer pathway for peroxymonosulfate activation

Heterogeneous metal catalysts have attracted considerable interest in advanced oxidation processes (AOPs) for wastewater treatment by activating peroxymonosulfate (PMS). However, it remains challenging to the rational design of efficient reaction pathway for high-performance contaminants removal by regulating the inherent structure of metal oxides. Herein, a high-energy ball milling method was employed to modulate the electronic structure of hausmannite (denoted as BM Mn3O4), which achieved the switching of singlet oxygen into electron transfer process (ETP)-dominated activation of PMS for efficient removal of bisphenol A - an emerging organic pollutant. The reaction pathway was evidenced through galvanic oxidation process, electrochemical techniques, and in-situ Raman spectroscopy, confirming the electrons transferred from pollutants to metastable PMS* complex with BM Mn3O4 serving as electron shuttle. The ETP mechanism was verified to be closely correlated with decreased eg occupancy of Mn in BM Mn3O4, offering high spatial overlapping with O 2p orbital in PMS for generating PMS* complex. Benefitting from the fine-tuned ETP, BM Mn3O4/PMS system showed enhanced intrinsic activity, higher PMS utilization efficiency, and practical applicability for selective oxidation of electron-rich pollutants. This study provided new insights into rational design of reaction-oriented catalysts for environmental engineering.

Mo and N co-doped iron biochar materials activating peroxymonosulfate for enhanced degradation of bisphenol A: Mechanism discussion and practical application

Mo and N co-doped iron biochar material (Fe/Mox-NC) was prepared through one-pot calcination method with anhydrous iron chloride, ammonium molybdate, and cherry stone powder as precursors. The composite can effectively catalyze activation of peroxymonosulfate (PMS) for organic pollutants degradation, and the removal rate of 20 mg/L bisphenol A (BPA) reaches 99.08% in 30 min in the presence of 0.1 g/L Fe/Mo0.1-NC and 1 g/L PMS. Electrochemical analysis indicates that appropriate doped Mo and N can improve the electron transfer performance of the composite, which enhances the PMS activation property for BPA degradation. Quenching experiments and electron paramagnetic resonance analysis both demonstrated that the Fe/Mo0.1-NC/PMS system generated SO4•−, •OH and 1O2, which involved in BPA degradation. Moreover, a galvanic oxidation process had shown that there existed nonradical pathway which relied on electron transfer. The degradation pathway is proposed by measuring the intermediate products with HPLC-HRMS/MS. Through the exploration of the reaction mechanism, low-valence molybdenum ions can promote the cycle of Fe2+/Fe3+, and the pyridine-N and graphitic-N contained in Fe/Mo0.1-NC can catalyze activation of PMS together with Fe2+. The designed membrane filtration device revealed the feasibility of the composite in dynamic process, which was great significant for actual operation of water treatment. Furthermore, the Fe/Mo0.1-NC/PMS system could effectively decompose organic pollutants in the effluent from sewage treatment plant, achieving 82.6% of total organic carbon removal rate. This study not only prepared a novel heteroatom doped Fe-biochar material for PMS activation to degrade organic pollutants, but also deepened the reaction mechanism and explored its applicability for advanced treatment of real wastewater.

Galvanic corrosion behavior of AZ31 Mg alloy coupled with mild steel: effect of coatings

For Mg alloy, it is important to develop effective protection coatings against galvanic corrosion. In this work, the effects of plasma electrolytic oxidation (PEO) coating with and without a polyurethane (PU) top layer on the corrosion and galvanic corrosion (coupled with mild steel) behavior of AZ31 Mg alloy are investigated. The microstructure and compositions of the coatings were studied by scanning electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffractometer (XRD) and Fourier transform infrared spectroscopy (FT-IR). The corrosion and galvanic corrosion behavior of uncoated, PEO and PEO-PU coated AZ31 Mg alloys were evaluated by electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) tests, respectively. Results showed that the PEO coating is characterized by many micropores in structure and the micropores are sealed by the PU top layer. The OCP, EIS and SECM tests revealed that the single PEO coating only slightly reduces the galvanic corrosion tendency and marginally improved the corrosion resistance, resulting in short-term galvanic corrosion protection for AZ31 Mg alloy. In contrast to the single PEO coating, the PEO-PU coating greatly improves the stability of the AZ31 Mg alloy to galvanic corrosion and provides much better long-term corrosion protection performance, which could effectively protect the substrate from galvanic corrosion. The galvanic corrosion processes of the AZ31 Mg alloy with PEO and PEO-PU coatings are also discussed. These results demonstrate that the sealing of PEO coating is essential to inhibit the galvanic corrosion between Mg alloy and other metals.

Designing an ACS by Applying Galvanic Coatings Based on Solving the Optimization Problem

An automated control system for the technological process of applying galvanic coatings to a variety of cathode parts of various shapes and sizes is considered based on solving the problem of finding the optimal arrangement of the parts in a galvanic bath to obtain coatings with the minimum value of criterion R—the ratio of the number of rejected parts Nreject to the total number of parts N placed on the suspension device. To solve the problem, a calculation-logical system is developed that uses the exhaustive enumeration method, the Gomory algorithm modified by the authors, and the branch-and-bound method. When solving the problem, the Gomory algorithm is found to be the best algorithm among the three methods in terms of performance. A two-level control system for the galvanic process in a bath with a suspension device is developed.

Electrocatalytic Performance of Ethanol Oxidation on Ni and Ni/Pd Surface-Decorated Porous Structures Obtained by Molten Salts Deposition/Dissolution of Al-Ni Alloys.

Ni coatings with high catalytic efficiency were synthesised in this work, obtained by increasing the active surface and modifying Pd as a noble metal. Porous Ni foam electrodes were obtained by electrodeposition of Al on a nickel substrate. Deposition of Al was carried out with potential -1.9 V for a time of 60 min in NaCl-KCl-3.5 mol%AlF3 molten salt mixture at 900 °C, which is connected with the formation of the Al-Ni phase in the solid state. Dissolution of Al and Al-Ni phases was performed by application of the potential -0.5 V, which provided the porous layer formation. The obtained porous material was compared to flat Ni plates in terms of electrocatalytic properties for ethanol oxidation in alkaline solutions. Cyclic voltammetry measurements in the non-Faradaic region revealed the improvement in morphology development for Ni foams, with an active surface area 5.5-times more developed than flat Ni electrodes. The catalytic activity was improved by the galvanic displacement process of Pd(II) ions from dilute chloride solutions (1 mM) at different times. In cyclic voltammetry scans, the highest catalytic activity was registered for porous Ni/Pd decorated at 60 min, where the maximum oxidation peak for 1 M ethanol achieved +393 mA cm-2 compared to the porous unmodified Ni electrode at +152 mA cm-2 and flat Ni at +55 mA cm-2. Chronoamperometric measurements in ethanol oxidation showed that porous electrodes were characterised by higher catalytic activity than flat electrodes. In addition, applying a thin layer of precious metal on the surface of nickel increased the recorded anode current density associated with the electrochemical oxidation process. The highest activity was recorded for porous coatings after modification in a solution containing palladium ions, obtaining a current density value of about 55 mA cm-2, and for a flat unmodified electrode, only 5 mA cm-2 after 1800 s.

Modulating Dominant Facets of Pt through Multistep Selective Anchored on WC for Enhanced Hydrogen Evolution Catalysis.

Facilitating the exposure of the active crystal facets on the surfaces of composite catalysts is a representative route to promote catalytic activity. Based on a tailored galvanic replacement reaction, herein, a self-assembly route is reported to prepare Pt-WC/CNT with Pt (200) preferential orientation and well-dispersed structure, which are capable of substantially boosting electrocatalysis in hydrogen evolution reaction (HER). Formation mechanism reveals that the (200)-dominated Pt-based catalysts form in galvanic replacement reaction through selective anchored on WC, and the multistep galvanic replacement process plays a critical role to realize the Pt (200)-dominated growth in higher Pt loading catalyst. These unique structural features endow the Pt-WC/CNT with a high turnover frequency of 94.18 H2·s-1 at 100 mV overpotential, 7-fold higher than that of commercial Pt/C (13.55 H2·s-1), ranking it among the most active catalysts. In addition, this method, which combines with gas-solid reaction and galvanic replacement reaction, paves the way to scalable synthesis as Pt facets-controllable composite catalysts to challenge commercial Pt/C.

Facet type determination based on combined atomic force microscopy and electron backscatter diffraction.

The distribution of facet types affects the functionality of the surfaces of polycrystalline films. However, we are not aware of a previously published convenient method to determine their distribution. This work describes and demonstrates a process to determine and map the Miller indexes (hkl) of crystal facets exposed at the surfaces of polycrystalline films. To find facet types in non-trivial cases, one must know the orientation of the crystal and the direction in which the facet is facing. The method presented here combines the crystal orientations obtained with electron backscatter diffraction with the topography of the same sample area measured with atomic force microscopy. A challenging step is to transfer the data from the two instruments into a common coordinate system. The sequence of steps in the data processing is presented, with methods to verify the results. The process is illustrated with the analysis of an etched copper clad laminate (CCL) and an electroless Cu film deposited on the CCL. This example relates to facet selection in electroless and galvanic plating processes in printed circuit board production, where an uncontrolled transition from epitaxial to non-epitaxial growth can lead to surfaces with unacceptable roughness.

Single-Atom iron catalyst activating peroxydisulfate for efficient organic contaminant degradation relying on electron transfer

Single-atom iron catalysts (SACs) have drawn extensive attention in advanced oxidation processes (AOPs) because of their tunable electron feature. Although single-atomic metal activation has been developed to optimize the organic contaminant oxidation and understand the associated mechanism governing persulfate-based AOPs, studies on peroxydisulfate (PDS) are rare. Herein, atomic iron was anchored in Enteromorpha-derived carbon matrices via a novel and cost-effective route in this work. This single atomic catalyst (FeSA-NEPBC) exhibited very high activity in PDS conversion for organic pollutant oxidation. Integrated with radical quenching experiments and electron spin resonance (ESR), the nonradical pathways of pollutant degradation was unveiled to be an electron-transfer process. Electrochemical analysis, masking experiments and theoretical calculations unraveled that FeSA-NEPBC/PDS* complex and Fe-pyridinic N4 moiety were the predominant oxidizing intermediate and active sites, respectively. The innovative application of galvanic oxidation process (GOP) was also employed to probe the mechanism. Bisphenol S (BPS) was degraded only when the catalyst-coating the graphite sheets was applied in the GOP, further confirming the occurrence of electron transfer. Moreover, the FeSA-NEPBC/PDS system exhibited favorable performance in realistic wastewater remediation scenarios. This work offers a better mechanistic understanding of PDS activation by the single-atom catalysts, while providing keen insights into the design of stable atomic metal catalysts for practical use.

Tribological Behavior of Structural Steel with Different Surface Finishing and Treatments for a Novel Seismic Damper

In the context of developing an innovative seismic dissipation system, which aims to compromise on the steadiness of friction and processes costs, this work deals with the tribological characterization of an S355JR structural steel, whose surface has been preliminarily treated by different mechanical and galvanic processes. Tribological tests were performed in a pin-on-disk configuration and in reciprocating motion, using values of 1 Hz and 2 Hz as the motion inversion frequency, a constant normal load of 50 N, and variable test duration, according to the most frequent seismic events. The tribological system was composed of S355JR structural steel pins and disks of the same steel, which were alternatively treated by electrolytic nickel plating, electrolytic zinc plating, and two different shot peening processes. The results highlight that while electrolytic nickel increments the overall steadiness of the coefficient of friction (COF), electrolytic zinc plating guarantees the longest first steady-state stage and a COF lower than the one guaranteed by the coupling of untreated pins and disk.

Galvanic displacement of Co with Rh boosts hydrogen and oxygen evolution reactions in alkaline media

The growing energy crisis put an emphasis on the development of novel efficient energy conversion and storage systems. Here we show that surface modification of cobalt by a fast galvanic displacement with rhodium significantly affects the activity towards hydrogen (HER) and oxygen evolution reactions (OER) in alkaline media. After only 20 s of galvanic displacement, the HER overpotential is reduced by 0.16 V and OER overpotential by 0.06 V. This means that the predicted water splitting voltage is reduced from 2.03 V (clean Co anode and cathode) to 1.81 V at 10 mA cm−2 (Rh-exchanged Co electrode). During the galvanic displacement process, the surface roughness of the Co electrode does not suffer significant changes, which suggests an increase in the intrinsic catalytic activity. Density Functional Theory calculations show that the reactivity of the Rh-modified Co(0001) surface is modified compared to that of the clean Co(0001). In the case of HER, experimentally observed activity improvements are directly correlated to the weakening of the hydrogen-surface bond, confirming the beneficial role of Rh incorporation into the Co surface.Graphical abstract

3D reticulated vitreous carbon as advanced cathode material in galvanic deposition process

3D reticulated vitreous carbon as advanced cathode material in galvanic deposition process