Reduction Of Zn Research Articles

Tailoring the Whole Deposition Process from Hydrated Zn2+ to Zn0 for Stable and Reversible Zn Anode

The practical application of aqueous zinc‐ion batteries (ZIBs) indeed faces challenges primarily attributed to the inherent side reactions and dendrite growth associated with the Zn anode. In the present work, N‐Methylmethanesulfonamide (NMS) is introduced to optimize the transfer, desolvation, and reduction of Zn2+, achieving highly stable and reversible Zn plating/stripping. The NMS molecule can substitute one H2O molecule in the solvation structure of hydrated Zn2+ and be preferentially chemisorbed on the Zn surface to protect Zn anode against corrosion and hydrogen evolution reaction (HER), thereby suppressing byproducts formation. Additionally, a robust N‐rich organic and inorganic (ZnS and ZnCO3) hybrid solid electrolyte interphase is in situ generated on Zn anode due to the decomposition of NMS, resulting in enhanced Zn2+ transport kinetics and uniform Zn2+ deposition. Consequently, aqueous cells with the NMS achieve a long lifespan of 2300 h at 1 mA cm−2 and 1 mAh cm−2, high cumulative plated capacity of 3.25 Ah cm−2, and excellent reversibility with an average coulombic efficiency (CE) of 99.7% over 800 cycles.

Tailoring the Whole Deposition Process from Hydrated Zn2+ to Zn0 for Stable and Reversible Zn Anode.

The practical application of aqueous zinc-ion batteries (ZIBs) indeed faces challenges primarily attributed to the inherent side reactions and dendrite growth associated with the Zn anode. In the present work, N-Methylmethanesulfonamide (NMS) is introduced to optimize the transfer, desolvation, and reduction of Zn2+, achieving highly stable and reversible Zn plating/stripping. The NMS molecule can substitute one H2O molecule in the solvation structure of hydrated Zn2+ and be preferentially chemisorbed on the Zn surface to protect Zn anode against corrosion and hydrogen evolution reaction (HER), thereby suppressing byproducts formation. Additionally, a robust N-rich organic and inorganic (ZnS and ZnCO3) hybrid solid electrolyte interphase is in situ generated on Zn anode due to the decomposition of NMS, resulting in enhanced Zn2+ transport kinetics and uniform Zn2+ deposition. Consequently, aqueous cells with the NMS achieve a long lifespan of 2300 h at 1 mA cm-2 and 1 mAh cm-2, high cumulative plated capacity of 3.25 Ah cm-2, and excellent reversibility with an average coulombic efficiency (CE) of 99.7 % over 800 cycles.

Reduced Zn2+ promotes retinal ganglion cells survival and optic nerve regeneration after injury through inhibiting autophagy mediated by ROS/Nrf2

The molecular mechanism of how reduced mobile zinc (Zn2+) affected retinal ganglion cell (RGC) survival and optic nerve regeneration after optic nerve crush (ONC) injury remains unclear. Here, we used conditionally knocked out ZnT-3 in the amacrine cells (ACs) of mice (CKO) in order to explore the role of reactive oxygen species (ROS), nuclear factor erythroid 2-related factor 2 (NFE2L2, Nrf2) and autophagy in the protection of RGCs and axon regeneration after ONC injury. We found that reduced Zn2+ can promote RGC survival and axonal regeneration by decreasing ROS, activating Nrf2, and inhibiting autophagy. Additionally, autophagy after ONC is regulated by ROS and Nrf2. Visual function in mice after ONC injury was partially recovered through the reduction of Zn2+, achieved by using a Zn2+ specific chelator N,N,Nʹ,Nʹ-tetrakis-(2-Pyridylmethyl) ethylenediamine (TPEN) or through CKO mice. Overall, our data reveal the crosstalk between Zn2+, ROS, Nrf2 and autophagy following ONC injury. This study verified that TPEN or knocking out ZnT-3 in ACs is a promising therapeutic option for the treatment of optic nerve damage and elucidated the postsynaptic molecular mechanism of Zn2+-triggered damage to RGCs after ONC injury.

Mordenite-Supported Ag+-Cu2+-Zn2+ Trimetallic System: A Variety of Nanospecies Obtained via Thermal Reduction in Hydrogen Followed by Cooling in an Air or Hydrogen Atmosphere.

Multimetallic systems, instead of monometallic systems, have been used to develop materials with diverse supported species to improve their catalytic, antimicrobial activity, etc., properties. The changes in the types of nanospecies obtained through the thermal reduction of ternary Ag+-Cu2+-Zn2+/mordenite systems in hydrogen, followed by their cooling in an air or hydrogen atmosphere, were studied. Such combinations of trimetallic systems with different metal content, variable ratios (between them), and alternating atmosphere types (during the cooling after reducing the samples in hydrogen at 350 °C) lead to diversity in the obtained copper and silver nanospecies. No reduction of Zn2+ was evidenced. A low silver content leads to the formation of reduced silver clusters, while the formation of nanoparticles of a bigger size takes place in the trimetallic samples with high silver content. The cooling of the reduced trimetallic samples in the air causes the oxidation of the obtained metallic clusters and silver and copper nanoparticles. In the case of copper, such conditions lead to the formation of mainly copper (II) oxide, while the silver nanospecies are converted mainly into clusters and nanoparticles. The zinc cations provoked changes in the mordenite matrix, which was associated with the formation of point oxygen defects in the mordenite structure and the formation of surface zinc oxide sub-nanoparticles in the samples cooled in the air.

Electrochemical reduction mechanism of Zn2+ in molten NaCl−KCl eutectic

A process comprising selective chlorination and molten salt electrolysis was proposed to develop an efficient and environmental-friendly technology for zinc recovery from metallurgical dusts. The theoretical feasibility of this technology was firstly estimated based on thermodynamic fundamentals. Subsequently, the electrochemical behavior of Zn2+ on tungsten electrode was investigated in molten NaCl−KCl eutectic at 973 K by many electrochemical transient methods. The results showed that the reduction of Zn2+ on tungsten electrode was found to be a one-step process exchanging two electrons with the initial reduction potential of −0.74 V (vs Ag/AgCl), and the electrode process was considered as quasi-reversible and controlled by diffusion. The diffusion coefficient of Zn2+ ions in the melts was determined in the order of 10−5 cm2/s. Finally, the electrolytic preparation of zinc was carried out by potentiostatic electrolysis in molten NaCl−KCl−ZnCl2 eutectic at −1.6 V (vs Ag/AgCl). Spheroidic granular metal with silver-white luster was attained after electrolysis for 9.5 h, and identified as pure Zn. The present study confirms that it is practically feasible to extract pure zinc metal by direct electrolysis of ZnCl2 in molten NaCl−KCl eutectic, and provides a valuable theoretical reference for the efficient recovery of zinc from metallurgical dusts.

The Electrochemical Reduction Mechanism of ZnFe2O4 in NaCl-CaCl2 Melts

The electrochemical reduction process of ZnFe2O4 in NaCl-CaCl2 melts was studied. Thermodynamic analysis shows that the reduction process of ZnFe2O4 is carried out in multiple steps, and it is difficult to reduce Fe3+ to Fe in one step. Electrochemical tests revealed that the reduction process of ZnFe2O4 includes three steps: First, Fe3+ is reduced to Fe in two steps, then Zn2+ is reduced to Zn in one step. The reduction of Fe3+ on the Mo electrode is a reversible process controlled by diffusion, while the reduction of Zn2+ is an irreversible process controlled by diffusion. The influence of electrolysis voltage and temperature on the process of electric deoxidation has also been studied. It is indicated that properly increasing the temperature is conducive to the diffusion of oxygen ions, thereby increasing the deoxidation rate. With the gradual increase of voltage, the reduction process of ZnFe2O4 is ZnFe2O4 → FeO + ZnO → Fe + ZnO → Fe + Zn.

Tuning material properties of amorphous zinc oxynitride thin films by magnesium addition

The amorphous n-type multi-cation and multi-anion compound zinc magnesium oxynitride was fabricated by reactive long-throw magnetron co-sputtering from a metallic zinc and a metallic magnesium target. We achieved magnesium cation compositions in the thin films between 1 at. % and 7.5 at. % by varying the magnesium target power (variable-power approach) and compared this approach to a continuous composition spread. Both approaches lead to a reduction in Zn2+, an addition of Mg2+ cations, and a correlated increase in the oxygen content. Both these methods have the same effect on the optoelectrical properties: The increased magnesium content leads to a systematic decrease in the free charge carrier concentration regime from 1019 cm−3 to 1015 cm−3, a decrease in Hall mobility from 54 cm2 V−1 s−1 to 9 cm2 V−1 s−1, and a spectral shift of the absorption edge from 1.3 eV to 1.7 eV. The amorphous phase of zinc magnesium oxynitride is maintained until MgO crystallites form at a magnesium content ≥3 at. %. The electrical properties of the zinc magnesium oxynitride thin films show excellent long-term stability for at least 12 months.

Zinc-induced stress on cells of Halamphora luciae (Bacillariophyceae)

ABSTRACT The aim of the present paper was to study the effect of zinc on the benthic diatom Halamphora luciae. Bioassays using the metal concentration corresponding to the ICzn50 were terminated in two selected endpoints: day 4 (acute phase) and day 9 (chronic phase). A 1.4- and 2.2-fold reduction in Zn2+ with respect to the initial cation concentration was estimated by atomic absorption at days 4 and 9, respectively and was attributed both to precipitation of insoluble carbonates and oxides at alkaline pH and to biosorption. Carrying capacity of Zn-exposed cultures diminished even when growth rate remained unchanged, suggesting some degree of acclimation of the strain to metal stress. Zn stimulated cell bleaching together with the shift into the lipogenic phase, denoted by total lipid quantification and bigger lipid bodies volumes. Lipid peroxidation and phenolic compounds dosage revealed no major metal-induced oxidative stress. On the other hand, metal exposure had an antagonistic effect on the activation of alkaline phosphatase activity after phosphorus starvation. Superoxide dismutase (SOD) activity, cell motility and mucilage secretion were enhanced only during acute exposure. Soluble extracellular polymeric substances (S-EPS) from Zn-exposed cultures denoted a higher heterogeneity in monosaccharide composition. Frustules from metal-exposed cells presented a reduction in areolae diameter together with a lower area:volume ratio of the cells due to the addition of cingular bands.

Modeling of neotame and fructose thermochemistry: Comparison with mono and divalent metal ions by Computational and experimental approach

The metal complexes can demonstrate various interesting biological activities in the human body. However, the role of certain metal ions for specific cell activities is still subject to debate. This study is aimed at comparing the thermochemical properties of neotame (artificial sweetener) and α, β-fructose in gas phase and water medium. The interaction of α and β-fructose, neotame with monovalent and divalent metal ions was studied and comprehended by density functional theory (DFT) using B3LYP functional, 6–311 + G (d, p) and D3 basis set. Metal ion affinities (MIA) values depicted that ionic radius of metal ions played an important role in the interaction of α, β-fructose and neotame. The ∆G parameter was calculated to predict and understand the interaction of metal ions with α and β-fructose, neotame. The results suggested that the presence of hydroxyl groups and oxygen atoms in sugar molecules acted as preferred sites for the binding and interaction of mono and divalent ions. For the first time computational study has been introduced in the present study to review the progress in the application of metal binding with sugar molecules especially with neotame. Moreover, voltammetric behaviour of neotame-Zn2+ was studied using cyclic and differential pulse voltammetry. The obtained results suggest that the peak at −1.13 V is due to the reduction of Zn2+ in 0.1 M phosphate buffer medium at pH 5.5. Whereas, addition of 6-fold higher concentration of neotame to the ZnCl2.2H2O resulted in a new irreversible cathodic peak at −0.83, due to the reduction of neotame-Zn2+ complex. The Fourier transform infrared spectroscopy (FTIR) results indicates that the β-amino group (-NH) and carboxyl carbonyl (-C = O) groups of neotame is participating in the chelation process, which is further supported by DFT studies. The findings of this study identify the efficient chelation factors as major contributors into metal ion affinities, with promising possibilities to determine important biological processes in cell wall and glucose transmembrane transport.

Antagonistic effect of zinc oxide nanoparticle and surfactant on anaerobic digestion: Focusing on the microbial community changes and interactive mechanism

The objective of this study was to evaluate the antagonistic effect of emerging pollutants of zinc oxide nanoparticles (ZnO NPs) and sodium dodecyl sulfate (SDS) on anaerobic digestion and explore their potential mechanism. The results indicated that at a low inhibitory concentration of ZnO NPs (1.0 mM), the practical co-inhibition was decreased by 24% and 18% in co-existence of 50 mg/L SDS and 300 mg/L SDS, respectively. More importantly, the co-existence of 300 mg/L SDS greatly enhanced methanogenesis of organics in seriously inhibited case (2.0 mM of ZnO NPs). The microbial community analysis showed that co-existed SDS enhanced the growth of Methanothrix, Methanosarcina and Methanobacterium. The antagonistic enhancement could be attributed to the net charge reversal, partially agglomeration of ZnO NPs and/or reduction of Zn2+ release in the presence of SDS. These findings could provide useful information for evaluating the co-inhibition of SDS and ZnO NPs on biological processes.

ZnO Nanoparticles Modified with an Amphipathic Peptide Show Improved Photoprotection in Skin.

ZnO nanoparticles of different sizes were functionalized with an amphipathic peptide, and its effect on nanoparticle stabilization and UV photoprotective activity was studied in this article. The peptide-modified nanoparticles exhibited lower aggregation, significant reduction in Zn2+ leaching in vitro and even inside the cells for smaller particle sizes, reduced photocatalytic activity, and reduced cellular toxicity under UV-B treated conditions. In addition, the peptide-modified 60 nm ZnO nanoparticles showed lower genotoxicity, lower oxidative stress induction levels, less DNA damage responses, and less immunogenic potential than the bare counterparts in the presence of UV-B rays. They localized more in the stratum corneum and epidermis ex vivo, indicating better retention in epidermis, and demonstrated improved UV-B protection and/or skin integrity in SKH-1 mice in vivo compared to unmodified nanoparticles and commercial UV-protective agents tested. To our knowledge, this is the first report on the application of peptide-modified ZnO nanoparticles for improved photoprotection.

Weak ferroelectricity and low-permittivity microwave dielectric properties of Ba2Zn(1+x)Si2O(7+x) ceramics

Ba2Zn(1+x)Si2O(7+x) ceramics were prepared using the conventional solid-state method at 1200°C for 3h in air. Apart from the previously reported Ba2Zn(1+x)Si2O(7+x) (x=0) with a monoclinic structure (C 2/c), the end-member compositions at x=−1 and 1 exhibit single-phase β-BaSiO3 with an orthorhombic structure (P212121) and BaZnSiO4 with a hexagonal structure (P63), and possess a coexistence of weak ferroelectricity and low-permittivity microwave dielectric properties. A reduction in Zn2+ content mainly decreases the intensity of the εr anomaly peak at lower temperature and increases the εr (or frequency) stability against temperature. The Zn2+-rich BaZnSiO4 phase has a τf value of −181ppm/°C, whereas the τf value of Zn2+-free BaSiO3 phase decreases to −35.4ppm/°C. The Zn2+ deficiency in Ba2ZnSi2O7 composition could inhibit the presence of BaZnSiO4 phase and improve the τf value, whereas excessive Zn2+ cations prompt the formation of the BaZnSiO4 phase to deteriorate significantly the τf value.

Synthesis of magnetic hollow carbon nanospheres with superior microporosity for efficient adsorption of hexavalent chromium ions

Microporous hollow carbon nanospheres were prepared through the polymerization of 2,4-dihydroxybenzoic acid and formaldehyde in the presence of ammonia and tactfully using chelating zinc species as dynamic porogens during the carbonization step to create extra micropores. The Cr(VI) maximum adsorption capacity of microporous hollow carbon spheres consequently increase from 139.8 mg g−1 of pristine hollow carbon spheres to 199.2 mg g−1. Owing to the presence of the carboxyl groups in the polymer matrix, Zn2+ ions can be easily introduced into the hollow polymer spheres through complexation process. During carbonization, high temperature treatment results in the reduction of Zn2+ to metallic Zn and subsequent evaporation of Zn, consequently forming nanospaces and nanopaths in the carbon shell. As little as 8.6 wt.% Zn2+ in the polymer matrix can increase the micropore volume by 133% and the specific surface area by 86%. The microporous hollow carbon spheres can be made magnetic by anchoring them to 14.0 wt.% γ-Fe2O3 nanoparticles, thus producing a highly efficient Cr(VI) adsorbent. The maximum adsorption capacity measured was 233.1 mg g−1, which is significantly higher than other reported carbon- based adsorbents. After adsorption, the magnetic microporous hollow carbon spheres can be flexibly separated using an external magnet.

Methanol synthesis over Cu–ZnO aggregates supported on carbon nanotubes

Methanol synthesis was studied with catalysts containing Cu and ZnO in the interior space or on the exterior surface of multi-walled carbon nanotubes (CNTs) and were activated by different procedures – reduction in dilute H2 at 513K with or without subsequent exposure to 10% CO/H2 at 673K for 30min. Characterization of the transition-metal species after these treatments by XRD and XAFS revealed striking differences. After mild reduction, XRD reflections related to Cu were missing or were of weak intensity, which could be assigned to very low primary particle sizes as detected by EXAFS. After treatment in CO/H2, reflections arising from alloy phases were obtained for all samples while non-alloyed Cu, although observed by EXAFS, escaped detection by XRD due to small primary particle sizes. Reduction of Zn2+ to Zn(0) was revealed by ZnK XANES only for some samples, which qualifies Zn(0) as a minority oxidation state for the remaining ones. Based on the XANES evidence, a new feature in ZnK EXAFS developing after CO/H2 treatment was interpreted as arising from either alloying or from an SMSI-type interaction of ZnO1−x entities with Cu nanoparticle surfaces. The catalysts exhibited very different productivities and responses to the CO/H2 treatment. In terms of specific activity (related to m2 Cu), the better samples achieved a multiple of the performance shown by a commercial reference, but suffered from insufficient stability. By contrast, such stability was demonstrated for a catalyst containing Cu/ZnO hosted in SBA-15. A catalyst series based on narrow CNTs previously functionalized by thermal shocks in flowing air stood out due to poor performance for unknown reasons. Due to these uncertainties, the data does not permit clear conclusions on the oxidation state of Zn in the promoting interaction with Cu although the general trends favor Zn2+ over Zn(0).

Removal of Zn2+ and Pb2+ using new isolates of Bacillus spp. PPS03 and Bacillus subtilis PPS04 from Paper mill effluents using indigenously designed Bench-top Bioreactor

Biosorption processes have the potential to decrease environmental hazards through their factors such as initial metal ion concentration, temperature, pH and biomass concentration in the solution. In the present study biosorption process was performed using the strains of Bacillus spp. PPS 03 (KF710041) and Bacillus subtilis PPS 04 (KF710042) isolated from sediment core of Paper mill effluent (PME) for the removal of Zn2+and Pb2+ in an indigenously designed Bench-top Bioreactor. The temperature, initial pH, biomass and incubation period of PME for Zn2+ and Pb2+ reduction was standardized. The strains exhibited significant reduction in Zn2+ and Pb2+ of PME to the extent of 73.29% and 85.64% with PPS 03 and 78.15% and 87.57% respectively with PPS 04 after 120 hrs of aerobic treatment. The reduction in the metals occurred from first day of the treatment, but the maximum reduction in these metals was observed after 120 hrs. at pH (7.0±0.2), temperature (35±1.0°C) and biomass (5% v/ v) of the bacterial strains. The removal of metals with strain PPS 04 was more in comparison to the strain PPS 03. The Freundlich isotherms on the data showed that it was linearly fitted for Zn2+and Pb2+. The values of correlation coefficient (R2) of Freundlich isotherms were greater than 0.812 for Pb2+ and Zn2+. The kinetic study for the rate of removal of Pb2+ and Zn2+ by both species was found to best fit a Pseudo first order reaction. The rate constant was found to be inversely proportional to the concentration of parameters. Thus, the microbial strains were found efficient for the biosorption/removal of Pb2+ and Zn2+.

Electrochemical reduction and consumption of 4-phenyl-3-buten-2-one

When benzylideneacetone (BDA), a commonly used brightener in the zinc plating process, is added to a solution containing Zn2+ ions in aqueous 0.5M KCl and 0.1M H3BO3, the zinc electroreduction potential shifts towards negative values by about 0.24V to -1.28V vs. SCE. Two stages are observed during the reduction of Zn2+ to zinc at -1.28V in the presence of BDA. Besides Zn2+ reduction, the BDA, itself, is reduced in two steps at the mercury electrode. The BDA is reduced at a potential of -1.12V versus saturated calomel electrode (SCE) for the first step, the formation of 4-phenyl-2-butanone and at -1.32V vs. SCE for the second step, the formation of 4-phenyl-2-butanol. It was found that, Zn2+ ions do not form complexes with BDA in the substrate's concentrations used in the present study. The mineralization of the solution, which is the loss of organic compounds from solution, occurs during BDA electrolysis and is due to the rapid decomposition of BDA. The mineralization obtained after 60minutes with current density of 0.015 A per square centimeter results in 16% loss of carbon content.

Stearate Modified Zinc-Aluminum Layered Double Hydroxides and Acrylonitrile Butadiene Rubber Nanocomposites

The aim of this investigation is to highlight the potentials of layered double hydroxides (LDH) and to serve as a replacement for zinc oxide and stearic acid from the basic rubber formulation. This will eventually result in about a 10× significant reduction of Zn2+ ion concentration in the final compound. The unique advantage of stearate ion-modified LDH is the delivery of zinc ions to accelerate and stearate ions to activate the vulcanization process. Furthermore, it can also reinforce the rubber matrix by virtue of its layered structure as nanofiller.

Optimization of parameters for the growth of defect free ZnO nanorod arrays with intense UV emission capacity by electrochemcial route

We present the fabrication of highly oriented, well faceted and defect free ZnO nanorods by electrodeposition using ZnCl2 and KCl as the electrolyte. The ZnO nanostructures were prepared on high purity Cu foil, commercial Cu foil, ITO coated glass and Cu (100nm)/Ti (30nm)/Si substrates. We have studied in detail the effects of various growth parameters such as bath temperature, deposition time, precursor concentration and applied potential on the morphology, structural and optical properties of ZnO nanorods. A detailed mechanism and the effects of various process parameters on the formation of defect free (with controlled microstructure of) ZnO nanorods are reported. Our studies confirmed that the bath temperature and the deposition time critically influenced the aspect ratio of ZnO nanorods. For instance, the growth of ZnO nanorods along the lateral direction affected marginally, whereas, along the c-axis, the growth affected significantly with bath temperature as well as with the deposition time. At higher deposition time the shape of ZnO nanostructures got distorted because of reduction in the bulk pH value of the solution. Similarly, at bath temperature greater than 80°C, the ZnO nanorods were misoriented with cauliflower-like microstructure mainly because of reduction in Zn2+ ion concentration. The ZnO nanostructures prepared under the optimized growth conditions showed an intense UV emission without spreading in the visible region as confirmed by photoluminescence spectroscopy, thus demonstrating the formation of defect free structure.

Systematic Exploration of Synthesis Pathways to Nanoparticulate ZnPd

Synthesis of the intermetallic compound ZnPd by (i) coreduction of Pd2+ and Zn2+ by Superhydride, (ii) the use of ZnH2 as a reducing agent and simultaneously as a Zn source, as well as (iii) electroless plating of nanoparticulate Zn with Pd2+ is systematically explored. Chemical and differential thermal (DTA/TG) analysis, as well as infrared spectroscopy, confirmed the formation of ZnH2 as isolable intermediate during the reduction of Zn2+ with Superhydride. Powder X-ray diffraction (XRD), transmission electron microscopy (TEM), and fractional sedimentation by disk centrifugation were applied to characterize the nanoparticulate products concerning their phase composition, crystallinity, and particle size distribution, respectively. While all routes lead to nanoparticles of ZnPd, electroless plating additionally allows one to control the crystallite size of ZnPd in a range of 2–5 nm.

Affinity binding via Zinc(II) for controlled orientation and electrochemistry of Histidine-tagged nitrate reductase in self-assembled monolayers

Monolayers of CuII-complexes on electrode surfaces are frequently applied for the immobilization and controlled orientation of His-tagged redox proteins. However, affinity binding is limited to applications that require potentials less negative than the reduction potential of the metal complexes. In order to overcome this limitation, we used Zn2+ cations on nitrilotriacetic acid (NTA) modified carbon electrodes for the coordination of His-tagged nitrate reductase (NaR). The NTA modified electrodes were prepared upon diazotation and electrochemical reduction of an aniline functionalized NTA ligand. After coordination of Zn2+ to the bound NTA ligand, self-assembly of NaR is achieved via coordination of the imidazole groups from the His-tag to the NTA–ZnII complex. The electrochemical investigations of the NaR monolayer on NTA–ZnII films demonstrate the catalytic activity for reduction of nitrate to nitrite in the presence of methyl viologen. The catalytic current density correlates with the one expected for a fully active enzyme monolayer. Moreover, the reduction of Zn2+ is not observed at the potential necessary for the reduction of methyl viologen. Therefore, affinity binding based on Zn2+ may be used for the immobilization and electrochemical applications of His-tagged NaR.