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Lytic polysaccharide monooxygenases (LPMOs) consist of a class of enzymes that boost the release of oxidised products from plant biomass, in an approach that is more eco-friendly than the traditional ones, employing harsh chemicals. Since LPMOs are redox enzymes, they could possibly be exploited by immobilisation on electrode surfaces. Such an approach requires knowledge of kinetic and thermodynamic information for the interaction of the enzyme with the electrode surface. In this work, a novel methodology is applied for the determination of such parameters for an LPMO from the filamentous fungus Thermothelomyces thermophila, MtLPMO9H.

Electrodeposition of the rare-earth metals La, Sm, Nd, and Dy from solution in the ionic liquids N-butyl-N-methylpyrrolidinium bistriflimide (BMPTFSI) and trimethyl butylammonium bistriflimide (Me3NBuTFSI) was studied in this work. Both ionic liquids are hydrophobic and present a wide electrochemical window as well as satisfactory ionic conductivity, rendering them promising electrolytes for electroreduction of rare-earth elements. Cyclic voltammetry (CV) performed using a Pt electrode in a three-electrode cell revealed that the rare-earth cations could indeed be reduced to the metallic state in the above-mentioned ionic liquids. Furthermore, electrodeposition of the rare earths was realized on copper substrate under potentiostatic conditions of − 3.1 V versus Ag/0.1 M AgNO3 in acetonitrile at 25 °C for 5 h. Analysis of the electrodeposits by scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) revealed that electrodeposition of the rare earths was feasible using these ionic liquids as the electrolytic medium. Finally, with the aim of identifying a sustainable metallurgical process for electrorecovery of rare earths, a two-compartment electrolytic cell was developed and tested for production of neodymium from a Nd(TFSI)3/BMPTFSI electrolyte.

In the present study, various representative models of finite length diffusion impedance were examined, in order to find the optimum description for dissolved oxygen diffusion, during corrosion of scribed coated steel in cyclic salt spray conditions, at 6, 8 and 12-week intervals. Modified restricted diffusion fitted the experimental data after 6 and 8 weeks and modified restricted or modified transmissive could fit the data after 12 weeks, accompanied by a decrease in corrosion resistance. Oxygen would diffuse through the porous corrosion layer and reduce on the magnetite layer, lying on top of the electrode surface.

Micro-nano structured super-hydrophobic coatings were successfully fabricated on biomimetic Au-film surfaces via a cathodic one-step electrodeposition method. The micro-structure of natural, hydrophobic plant surfaces was imprinted on cellulose acetate films and gold sputtered in order to create 70-100 nm thin, biomimetic Au-films. Two solutions for electrodeposition were studied: An ethanolic solution of myristic acid and lanthanum chloride, and an ethanolic solution of myristic acid and manganese chloride. The cathodic electrodeposition was performed in a two-electrode cell, with a biomimetic Au-film serving as the cathode, and a carbon electrode as the anode. After electrodeposition on the biomimetic Au substrates, the static contact angles of the coatings improved and were as high as 156° for the lanthanum myristate depositions, and 140° for the manganese myristate depositions. The sliding contact angles for both myristate coatings on the biomimetic substrates were less than 2°. The results indicate that a biomimetic substrate improves the hydrophobic properties of the surface. Deposition time and applied voltage were studied as variables, focusing on their influence on each coating’s contact angle, adhesion and substrate coverage. It was observed that tunable adhesion can be achieved for the manganese myristate depositions, showing a potential for future biomedical and lab-on-chip applications.

The enzyme MtPerII is a new peroxidase which has been isolated only recently from fungus Myceliophthora thermophila and has significant thermostability and stability at high H2O2 concentrations. In the present work, an electrochemical kinetic study, based on cyclic voltammetry, is performed for the first time for the catalytic decomposition of H2O2 by MtPerII, at 18°C. Leuco methylene blue (LMB) is used as a mediator and the catalytic and Michaelis constants are determined, assuming a Michaelis-Menten mechanism. Experimental evidence suggest the absence of inhibition by H2O2, for concentrations up to 16mM, and increasing catalytic activity for temperatures up to 50°C. Moreover, a modified electrode is constructed, by attempting the entrapment of MtPerII on a dodecanothiol self-assembled monolayer on gold. The modified electrode is studied chronoamperometrically in solutions containing methylene blue mediator and different concentrations of H2O2. It is shown that adsorbed MtPerII retains its activity and the modified electrode exhibits a considerably high linear region for the detection of H2O2. The experimental findings indicate that MtPerII is a new candidate for analytical and industrial applications.

A newly developed, polyurethane-based, marine antifouling coating, containing 2% immobilized Econea, was examined in terms of its anticorrosion performance. The novelty of the experimental formulation arises from the immobilization of the biocide which minimizes leaching and was accomplished via a newly developed functionalization method, based on reaction of the biocide with highly reactive isocyanate functionality. The painting system was applied on steel specimens, then scribed with a sharp cutter and examined for 12 weeks in cyclic salt spray exposure. Identification of the rust morphologies was performed with XRD, Raman spectroscopy, SEM, and EDS methods. The absence of paint deformation during the experiment led to the formation of compact corrosion products, firmly adherent to the substrate, allowing transformation to more protective forms, such as oxides (hematite, maghemite, magnetite) and the least harmful of the oxyhydroxides (goethite, feroxyhyte), found in the mixture, ensuring sufficient corrosion protection. The unscratched part of the paint served as a barrier to corrosion product expansion beyond the scribed areas. An acrylic-based antifouling system was also examined for reasons of comparison. The experimental formulation exhibited superior anticorrosion performance overall, since the acrylic system presented extended material loss, blistering, checking, and extensive substrate rust coverage beneath the multilayer coat, implying unsatisfactory corrosion protection.

In the present study, hydrophobic surfaces have been fabricated in a one-step electrochemical process by anodic polarization of copper substrates in methanolic myristic acid solutions at relatively high applied potentials. These solutions have also been modified by the addition of tetraethylammonium tetrafluoroborate as a supporting electrolyte to improve their electric characteristics and enable the same fabrication in drastically milder working conditions. To elucidate the mechanism through which this fabrication occurs, various techniques, namely cyclic voltammetry, linear sweep voltammetry, chronoamperometry and electrochemical impedance spectroscopy, have been employed. The processes taking place during anodic oxidation of copper in methanol are electrodissolution and surface species formation depending on the presence of dissolved oxygen. Current oscillations resulting from the presence of these surface species have also been observed.

A newly developed, silicone-based, marine antifouling coating, containing 0.56% immobilized Econea, was examined in terms of its anticorrosion performance. The novelty of the experimental formulation arises from the immobilization of the biocide which minimizes leaching and was accomplished via a newly developed functionalization method, based on reaction of the biocide with highly reactive isocyanate functionality. The painting system was applied on steel specimens, then scribed with a sharp cutter and examined for 12 weeks in cyclic salt spray exposure. Identification of the rust morphologies was done with XRD, Raman spectroscopy, SEM and EDS methods. The observed paint swelling during the experiment caused the formation of large, coarse rust agglomerates without adherence, which detached frequently causing reinitiation of the corrosion process. This procedure was revealed by the oxyhydroxide nature of the corrosion products. The basic corrosion morphology observed was a mixture of akaganeite and goethite. A commercial, silicone-based, foul-release coating served as a reference. The experimental formulation exhibited superior anticorrosion performance overall, since the reference system presented higher enlargement of the scribed areas, increased substrate material loss, a highly inhomogeneous corrosion layer with voids and smaller (stable) goethite amounts in the rust areas containing mainly akaganeite/goethite mixture.

This study investigates the morphology, composition and corrosion resistance of hot dip galvanized (HDG) steel panels treated by immersion in NaCl solution in the presence of six protective compounds: 8-hydroxyquinoline, 2-mercaptobenzothiazole, 5-amino-1,3,4-thiadiazole-2-thiol, calcium phosphate, cerium nitrate and sodium molybdate. The results reveal that upon corrosion new compounds are formed onto the exposed areas of the treated panels. The presence of these compounds on the surface of the HDG steel panels hinders the corrosion process by reducing the rate of the anodic and cathodic reactions. Τhe conducted experiments provide new insights on the corrosion mechanisms of HDG steel.

Friction stir welding (FSW) is a viable technique for joining aluminium alloys that are difficult to fusion weld. However, the produced friction stir (FS) welded materials need to be improved in terms of their resistance to corrosion. The effect of nanoadditives as reinforcing materials on the corrosion behaviour of dissimilar metal/metal joints and compare with the parent metal alloys is demonstrated in the present study. Dissimilar FS welded materials were produced in plates of aluminium alloy (AA) 6082-T6 and AA5083-H111 using nanoadditives of titanium carbide (TiC) nanoparticles, multi walled carbon nanotubes (MWCNT) and cerium molybdate (CeMo) containers loaded with corrosion inhibitor 2-mercaptobenzothiazole (MBT), as reinforcing materials. The corrosion resistance of the samples with or without nanoadditives was studied by electrochemical methods. The results revealed that the incorporation of CeMo containers loaded with MBT during the FSW, enhances the corrosion resistance of the final material through the adsorption of MoO4−2 ions that come from the container shell onto the surface of both AA, as well as the formation of stable complexes between the thiol groups of MBT and the alloying metals, preventing chloride penetration. Keywords: Aluminium alloy 6082-T6, Aluminium alloy 5083-H111, Friction stir welding, Electrochemical impedance spectroscopy, Potentiodynamic polarization

In the present work, the derivation of the standard rate constant k0, the transfer coefficient a and the standard (or formal) potential E0 of immobilized electroactive species, with the use of large amplitude Fourier transform alternating current cyclic voltammetry (FTacV) is examined. Both the kinetic equation of the coverage and the current integral equation are solved. The kinetic regions of the current response are distinguished, the chief observables in the case of both fast and slow kinetics are showcased and finally based on these, a methodology to extract k0, a and E0 is introduced.

In the present work, a kinetic analysis is made concerning the reaction of an electroactive immobilized enzyme with a free substrate, based on a Michaelis-Menten scheme. The proposed kinetic equations are investigated numerically for conditions describing large amplitude fast Fourier transform alternating current voltammetry (FTacV), under different reaction states (transient or steady state for the reaction intermediate as well as quasi or complete reversibility of the electrochemical step). The dependence of two chief observables that occur from the analysis of the results of the method, that is, the maximum of the harmonics and the potential shift of the corresponding dominant peaks, on substrate concentration is presented. The FTacV method is applied experimentally for an immobilized laccase-like multicopper oxidase from Thermothelomyces thermophila, TtLMCO1, and its reaction with epinephrine. From the experimental findings it is shown that the intrinsic characteristics of the system do not lead to the extraction of the desired kinetic data although indications on the relation between the kinetic constants is revealed. Finally, the response of the third harmonic for the first additions of epinephrine at subnanomolarity range can be exploited for the detection of epinephrine at rather low concentrations.

The use of organic solvents in an electrolytic system for neodymium electrorecovery by electrolysis at low temperatures is studied in the current work. More specifically, an alternative route, that of the system of DMSO (Dimethyl sulfoxide) with dissolved NdCl3 has been researched and has given promising results. The study of this electrolytic system has been divided into two stages. Firstly, the characteristics of the electrolyte, the dissolution of NdCl3 in DMSO, the conductivity and the viscosity of NdCl3 solutions in DMSO at various temperatures, and the Nd complexation in the solution were studied and secondly, the electrolysis parameters and their impact on the Nd electrodeposition process were evaluated. Finally, the deposits were submitted to SEM-EDS (Scanning Electron Microscopy-Energy Dispersive X-Ray Spectroscopy) analysis and metallic Nd was confirmed to be electrodeposited by X-ray Photoelectron Spectroscopy (XPS) spectroscopy.

Background Lytic polysaccharide monooxygenases (LPMOs) are copper-dependent enzymes that oxidatively cleave recalcitrant lignocellulose in the presence of oxygen or hydrogen peroxide as co-substrate and a reducing agent as electron donor. One of the possible systems that provide electrons to the LPMOs active site and promote the polysaccharide degradation involves the mediation of phenolic agents, such as lignin, low-molecular-weight lignin-derived compounds and other plant phenols. In the present work, the interaction of the bulk insoluble lignin fraction extracted from pretreated biomass with LPMOs and the ability to provide electrons to the active site of the enzymes is studied. Results The catalytic efficiency of three LPMOs, namely MtLPMO9 with C1/C4 regioselectivity, PcLPMO9D which is a C1 active LPMO and NcLPMO9C which is a C4 LPMO, was evaluated in the presence of different lignins. It was correlated with the physicochemical and structural properties of lignins, such as the molecular weight and the composition of aromatic and aliphatic hydroxyl groups. Moreover, the redox potential of lignins was determined with the use of large amplitude Fourier Transform alternating current cyclic voltammetry method and compared to the formal potential of the Cu (II) center in the active site of the LPMOs, providing more information about the lignin-LPMO interaction. The results demonstrated the existence of low-molecular weight lignin-derived compounds that are diffused in the reaction medium, which are able to reduce the enzyme active site and subsequently utilize additional electrons from the insoluble lignin fraction to promote the LPMO oxidative activity. Regarding the bulk lignin fractions, those isolated from the organosolv pretreated materials served as the best candidates in supplying electrons to the soluble compounds and, finally, to the enzymes. This difference, based on biomass pretreatment, was also demonstrated by the activity of LPMOs on natural substrates in the presence and absence of ascorbic acid as additional reducing agent. Conclusions Lignins can support the action of LPMOs and serve indirectly as electron donors through low-molecular-weight soluble compounds. This ability depends on their physicochemical and structural properties and is related to the biomass source and pretreatment method. Electronic supplementary material The online version of this article (10.1186/s13068-018-1294-6) contains supplementary material, which is available to authorized users.

Composite nickel coatings, were produced under direct (DC) and pulse current (PC) from a Watt's type bath, containing 0.5 g/L hybrid MWCNT-Al2O3, in presence and absence of additive Sodium Dodecyl Sulfate - SDS. Surface morphology, crystallographic orientation, wear resistance and corrosion resistance were studied. Micro-Raman measurements revealed that MWCNT-Al2O3 particles are distributed at the whole depth of the cross-section profile analysis. The application of pulse current, favored a random crystallographic orientation of Ni crystallites with reduced grain sizes in comparison with pure Ni. The evaluation of the tribological data demonstrated that the composite coatings produced under pulse conditions in presence of additive, exhibited lower coefficient of friction, higher resistance to dry sliding accompanied by the presence of increased amounts of nickel oxide in wear tracks compared to pure Ni coatings. The behavior of pure and composite coatings in corrosive environment was evaluated by electrochemical impedance spectroscopy. It was found that composite coatings attained their corrosion resistance characteristics for 60 h in 0.6 M NaCl solution. Differences between pure nickel and composite coatings were attributed mainly to morphological differences rather than differences on corrosion performance.

The scope of the current research was to assess the feasibility of encapsulating three commercial antifouling compounds, Irgarol 1051, Econea and Zinc pyrithione, in biodegradable poly(lactic acid) (PLA) nanoparticles. The emulsification–solvent evaporation technique was herein utilized to manufacture nanoparticles with a biocide:polymer ratio of 40%. The loaded nanoparticles were analyzed for their size and size distribution, zeta potential, encapsulation efficiency and thermal properties, while the relevant physicochemical characteristics were correlated to biocide–polymer system. In addition, the encapsulation process was scaled up and the prepared nanoparticles were dispersed in a water-based antifouling paint in order to examine the viability of incorporating nanoparticles in such coatings. Metallic specimens were coated with the nanoparticles-containing paint and examined regarding surface morphology.

In the present work, the chief observables, i.e. peak height, peak width and peak potential of the principal peaks, are determined for the case of large amplitude ac-voltammetry (LA-FTacV) of a reversible reaction of free electroactive species. The values of the chief observables are derived from a semi-analytic solution as well as from the solution of the full initial-boundary value problem. A condition under which the large amplitude ac-voltammogram is independent of scan rate, up to the fifth harmonic, is introduced. The dependence of the chief observables on the parameters of the system is shown.

In this work, composite coatings were fabricated by electrolytic co-deposition of hybrid MWCNT-Al2O3 particles with Ni matrix from a Watts type bath, with and without the use of the sodium dodecyl sulfate additive, under both direct and pulse current conditions. The surface morphology and structural characteristics of the coatings were investigated for the different types of applied current mode, in the absence and presence of the additive. The mechanism of electrochemical co-deposition of Ni and hybrid particles was investigated by linear sweep voltammetry, electrochemical impedance spectroscopy and quartz crystal microbalance measurements in order to elucidate some aspects of the co-deposition mechanism. It was found that the presence of hybrid MWCNT-Al2O3 particles promotes direct proton discharge as well as hydrogen coverage, thus decreasing the deposition efficiency.