Oxidation Of Zn Research Articles

Influence of Salt Concentration on Electrochemical Stability Window in Aqueous Electrolytes

The thermodynamic limit of water electrolysis restricts the output voltage of aqueous metal ion batteries (MIBs) due to the low electrochemical stability window of water (1.23 V) in dilute electrolytes. It occurs due to the electrolysis of free water molecules into O2 or H2. Such value is unfortunately too low for many applications. For effective utilization of this technology, the ESW needs to be expanded to at least 2 V to achieve high energy density in metal batteries. Interestingly, water electrolysis can be suppressed by binding free water content with high concentrations of salts in highly concentrated water-in-salt electrolytes.In this work, low-cost non-flammable aqueous Zn(ClO4)2 electrolytes have been studied for their electrochemical behaviour at different concentrations. The electrolytes have been evaluated via Raman spectroscopic analysis to examine the modification in local water structures associated with increasing salt concentration. We also used linear sweep voltammetry on a glassy carbon electrode to determine the electrochemical stability window of the electrolytes. Electrochemical results indicate the existence of two distinct regions in the concentration behavior of the onset potential for oxygen evolution reaction (OER) at a cut-off current density of 0.1 mA cm-2. In dilute electrolytes, the overpotential in OER increases with a low slope with increasing concentration, while there is a sharper overpotential increase at higher salt concentrations in the water-in-salt electrolytes. Raman spectroscopic analysis provides evidence of this electrochemical stability expansion as being a result of the disruption of the hydrogen bonding network present in pure water. A more compact and strongly coordinated ion hydration structure occurs in the water-in-salt electrolytes. In this way, a significant increase in oxidative stability and a decline in the Zn oxidation overpotential has been achieved in the highly concentrated water-in-salt electrolytes. Our results indicate that the Zn(ClO4)2 water-in-salt electrolytes offer more efficient Zn redox reactions and a higher electrochemical stability window than the diluted aqueous electrolytes, which is particularly beneficial for the development of high-voltage aqueous Zn ion batteries [1].

ZnO seed-mediated hydrothermal growth of advanced 1-D ZnO and 2-D CuO nanostructured oxide ceramics for gas sensing applications

ZnO and CuO nanostructured oxide ceramics were synthesized on ZnO-seeded micro-glass substrates (denoted as ZOZO and ZOCO, respectively), and their surface and gas-sensing characteristics were explored. The thin film seed layers were deposited using dip-coating and both ZnO and CuO nanostructures were produced through hydrothermal reactions under similar circumstances. X-ray diffraction patterns showed high crystallinity and texturization of ZOZO (in ZnO hexagonal wurtzite system) compared to ZOCO (in CuO monoclinic system). X-ray photoelectron measurements demonstrated the proper oxidation of Zn into Zn2+ in ZOZO and Cu into Cu2+ in ZOCO. Scanning electron microscope images revealed one-dimensional bundled nanorod-like structures in ZOZO and two-dimensional nano-coffee bean-like structures in ZOCO. The different morphologies induced different wettability features as indicated by water contact angles where the hydrophilic surface nature of ZOZO was more advantageous for NH3 detection compared to ZOCO. Gas sensing measurements in 100 ppm NH3 medium showed initially better results by the ZOCO sensor at a low operating temperature (70 °C, S = 9%) compared to the ZOZO sensor which did not show any credible sensitivity below 90 °C. However, as temperature increased, the ZOZO sensor exhibited an ultra-sensitivity of S = 275% at an optimal operating temperature of 150 °C with a limit of detection of 7 ppb whereas the ZOCO sensor recorded a maximum sensitivity of S = 19% at an operating temperature of 170 °C with a limit of detection of 40 ppb. Both sensors showed good repeatability, long-term stability, and selectivity towards ammonia gas. The variation in the properties of the produced films was discussed based on a seed-mediated approach that is consequently suggested to control the growth and alignment of nanoscale structures and their efficiency in subsequent device applications.

A Redox-Mediated Zinc-Air Fuel Cell

As one of the most promising power sources in converting and storing chemical energy, aqueous zinc-air batteries (ZABs) stand out because of their high theoretical energy density, low cost, high safety of aqueous electrolyte, and environmental friendliness. Three main types of ZABs including primary ZABs, mechanically rechargeable ZABs, and electrically rechargeable ZABs have been developed up to now.[1] Primary ZABs for single use are usually discarded after the Zn anode is consumed or passivated although other parts of battery remain intact, leading to enormous waste. To address it, the depleted anode and failure electrolyte can be physically replaced to recover the capacity in mechanically rechargeable ZABs. But the cumbersome disassembly/reassembly process and the performance deterioration after every recharge process limit its practical application. In addition, it is not feasible to replace zinc in some integrated systems, such as the large-scale ZAB stack. Electrically rechargeable ZABs with bifunctional oxygen reduction reaction (ORR)/oxygen evolution reaction (OER) catalysts could be returned to the original state by electrochemical charging process, but also face some formidable challenges, such as dendritic zinc deposition, electrode deformation, and hydrogen evolution, limiting the long-term cycling performance. Besides, sluggish kinetics of ORR/OER and Zn passivation result in low energy efficiency, limited depth of discharge and power density. Especially in the resource-constrained and off-grid region, there isn’t external electricity source to charge the electrically rechargeable ZABs which limits their applications. Moreover, the reactions inherently take place on the surface of Zn anode and air cathode, in which the storage and conversion capability of the cell would be essentially constrained by the surface area of electrode and the volume of electrode compartment.The concept of redox targeting (RT) of battery materials offers a feasible solution to address these issues by employing redox mediators (RMs). To tackle the above challenges, here we demonstrate a redox-mediated Zn-air fuel cell (RM-ZAFC) based on the RT reactions of cobalt triisopropanolamine complex (CoTiPA) with O2 and 7,8-dihydroxy-2-phenazinesulfonic acid (DHPS) with Zn metal in the catholyte and anolyte, respectively. Both the 4-electron (4 e-) ORR and Zn oxidation reactions are liberated from the electrode surface and occur inside separate reactor tanks resorting to the RT processes. Upon operation, Co(III)TiPA in the catholyte is electrochemically reduced to Co(II)TiPA on the cathode and chemically oxidized back through ORR in the gas diffusion tank (GDT) into which O2 is fed. In conventional ZABs, ORR takes place on the triple-phase reaction interface of the heterogeneous electrocatalyst, and the catalytic performance is closely related to the density of exposed active site, electrical conductivity and reaction energy barrier. As compared, the redox-mediated ORR in GDT occurs homogeneously in the catholyte in which the dissolved RM could provide a large quantity of rection sites with tunable reaction energy barrier. For the negative side, DHPS-2H is firstly oxidized to DHPS on the anode and circulated into anodic tank, where it is regenerated by oxidizing Zn to ZnO. The discharge product ZnO is formed and deposited on the Zn granules loaded in the tank. After fully discharged, the cell can be feasibly refueled by replacing the Zn granules in the tank instead of disassembling and reassembling the whole cell. In this RM-ZAFC, the energy storage unit is decoupled from the power generation unit, thus offering greater operation flexibility and system scalability with modular design than the conventional ZABs. Compared with the commercial hydrogen tank used in hydrogen fuel cells, Zn granules loaded in the anodic tank present much higher volumetric capacity, greater safety and ease for storage and transportation. Therefore, as an energy conversion and storage device, RM-ZAFC would have great promise for automotive, backup, and stationary power applications.[2] In addition, we also propose an efficient and zinc regeneration method by RT reaction between RM and the product ZnO in RM-ZAFC to avoid the waste of ZnO and reduce the cost.

Corrosion protection behaviour of electrogalvanised steel sheet by tetravalent vanadium ion

ABSTRACT The corrosion protection behaviour of electrogalvanised steel sheets (EG) by the tetravalent vanadium ion was investigated. Immersion of the bare EG in a NaCl solution revealed that the addition of vanadium(IV) oxide sulphate to the solution led to a transition of the open circuit potential to less noble and the formation of vanadium oxides on the EG surface. The oxide layer included not only vanadium(III) oxides but also a small amount of ZnO, indicating that Zn on the EG surface was oxidised while the vanadium(IV) species was reduced to the vanadium(III) species. The corrosion current density of the EG with the adhering vanadium(III) species was one order of magnitude smaller than that of the bare EG, clearly suggesting that zinc corrosion was reduced by suppressing the reduction reaction of dissolved oxygen. The vanadium(IV) species could be a candidate as a self-healing inhibitor for chromate-free coating technologies by controlling the coupling of Zn oxidation and vanadium(IV) reduction.

Enhancement of UV luminescence in Zn/ZnO nanocomposites synthesized by controlled thermal oxidation of Zn nano-octahedrals

Defect-free photoluminescence (PL) emission is always desirable for the practical applications of functional materials. The presence of metal nanostructures near the semiconductor can result in a reduction of defect emission, if present. Here, the enhancement of ultraviolet (UV) PL emission of Zn/ZnO nanocomposites (NCs) has been demonstrated with a corresponding reduction of defect-mediated PL emission. Zn/ZnO NCs have been synthesized by annealing of Zn nano-octahedral in the air (at 500 °C for 5 h). Annealing at 800 °C has been found to result in the complete oxidation of Zn and the formation of ZnO nanoparticles (NPs). UV and visible PL emissions have been observed from Zn nano-octahedral, Zn/ZnO NCs, and ZnO NPs. The observed PL emissions from Zn have been argued as due to transitions of electrons from sp band to the upper states of 3 d band. For ZnO and Zn/ZnO, UV emission is due to near-band-edge emission of ZnO and visible PL emissions are due to the presence of defect states in ZnO. About 2.15-fold enhancement of UV PL emission of Zn/ZnO NCs has been argued as due presence of metallic Zn in the Zn/ZnO NCs. Thus, the present study can open up a new avenue for Zn/ZnO NCs for possible applications in UV regions.

Near-room temperature synthesis of Zn<sup>2+</sup>-doped γ-Ga<sub>2</sub>O<sub>3</sub> nanoparticles via direct oxidation of Zn–Ga alloy by ultrasound

This study used ultrasound irradiation to fabricate Zn2+-doped γ-Ga2O3 nanoparticles (NPs) from Zn–Ga alloy at near-room temperature (60 °C). The Zn2+-doped γ-Ga2O3 NPs were obtained at 60 °C after two steps of ultrasound irradiation (miniaturization and oxidation of Zn–Ga alloy). The specific surface area of Zn2+-doped γ-Ga2O3 NPs with a zinc content of 4 at.% was 90.4 m2/g. The oxidation behavior of Zn–Ga liquid alloy significantly differed from that of liquid Ga. X-ray photoelectron spectroscopy spectrum and lattice constant of Zn2+-doped γ-Ga2O3 confirmed Zn2+-doping into the γ-Ga2O3 crystal structure. By annealing at 900 °C, the obtained Zn2+-doped γ-Ga2O3 did not transform to Zn2+-doped β-Ga2O3 but to the mixed phase of β-Ga2O3 and ZnGa2O4. The results indicate that Zn2+ cations, with larger ionic radii than Ga3+ cations, are more difficult to be introduced into the β-Ga2O3 crystal lattice. Thus, this ultrasound process can potentially synthesize various metal cations-doped γ-Ga2O3 NPs without using high temperatures and pressures.

Nanostructured films formed on Zn during anodic oxidation in different carbonate-based electrolytes

Electrochemical generation of nanowire arrays by one-step anodic oxidation of Zn in carbonate-based electrolytes of different pH values is described. Zn foil was anodized in a mixture containing 5 mM Na2CO3 and 5 mM NaHCO3, as well as in pure Na2CO3 and NaHCO3 (both 10 mM). The morphology of anodic films was verified by FE-SEM. A special emphasis was put on the analysis of the composition of as-received nanomaterials by various techniques including XRD, XPS, UV–Vis, and Raman spectroscopy. Contrary to previous reports, we confirmed that the unknown phase of zinc carbonate with a formula of ZnCO3·H2O or Zn(HCO3)(OH) is formed at the Zn surface during anodization. The formation of ZnO resulting in more evident electrode passivation was also observed in the electrolytes containing sodium carbonates. The changes occurring during the thermal treatment of as-received materials were described based on TG, XPS, XRD, Raman, and nitrogen adsorption-desorption measurements. It was verified that, except for a several-fold increase in the active surface area, no significant changes in the wire-like morphology of the anodically generated product occur during its thermal conversion to ZnO. Finally, no noticeable differences in the photoelectrochemical performance of ZnO nanostructures formed in different electrolytes were observed.

Oxygen Adsorption on Polar and Non-Polar Zn:ZnO Heterostructures from First Principles.

Zn:ZnO nanostructures have been studied extensively due to their potential use in many applications, such as oxygen scavengers for food packaging applications. Under atmospheric conditions, ZnO grows on the surface of Zn via an oxidation process. The mechanisms governing Zn oxidation are still not fully understood, with classical oxidation models, such as the Cabrera Mott, underestimating the oxide thickness of Zn:ZnO core-shell structures. In this work, Ab initio DFT calculations were performed to assess the adsorption properties of oxygen molecules on Zn:ZnO heterostructures to help elucidate the mechanisms involved in the growth of a ZnO film on a Zn substrate. Results suggest that the charge transfer mechanism from the Zn:ZnO heterostructures to the adsorbed oxygen layer can be promoted by two different processes: the electronic doping of ZnO due to the formation of the Zn:ZnO interface and the excess surface charge due to the presence of dangling bonds on the as cleaved ZnO.

Kinetics of oxidation of metals in the air at room temperature using EDX

The kinetics of oxidation of Zn, Cu, Ni and C. steel were studied using the surface techniques, SEM, EDX and XRD, and electrochemical impedance spectroscopy (EIS) technique. EDX results showed that the variation of weight percent oxygen (Wt% O) on the surface of the four metals with the exposure time gave the same behavior, there is an increase of Wt% O with increasing the exposure time until about 2 h followed by a plateau, then the Wt% O increases again with increasing the time of exposure than 4 h. Fitting the experimental data of the four metals to the kinetic laws of oxidation indicated that the logarithmic law was fitted in short exposure (0.5 – 4 h), however, the parabolic law was fitted in long exposure (6 – 10 h). The values of each logarithmic rate constant (kl) and parabolic rate constant (kp)for the four metals were calculated. The kinetic of oxidation of the metals under study with exposure time is confirmed utilizing XRD technique. The protective action of the air-formed oxide films was investigated by EIS technique. The electrochemical impedance spectroscopy results confirmed the EDX results.

Corrosion behavior of Ni-based coating with Ni-coated TiC-reinforced particles by induction cladding in molten brass

In order to improve the wettability of TiC-reinforced particles with Ni-based alloy and decrease electrical resistivity of TiC-reinforced particles, Ni-coated TiC particles were fabricated by electroless plating method. Further, Ni-based coatings with Ni-coated TiC-reinforced particles on the surface of H13 steel were prepared by induction cladding. The microstructure and phase compositions of the coatings were analyzed by optical microscopy, scanning electron microscopy and X-ray diffraction. The microhardness of the coatings was measured by a microhardness tester. The corrosion behaviors of the H13 substrate and Ni-based coatings with and without Ni-coated TiC-reinforced particles in molten brass were investigated. The results showed that the addition of Ni-P layer of approximately 1.2 μm thickness on TiC particles by electroless plating significantly increased cladding temperature of Ni-based coating reinforced by TiC particles, and reduced coating thickness, defects, size of the precipitated phases and microstructure inhomogeneities. The surface microhardness of the Ni-based coating with Ni-coated TiC-reinforced particles is 168% higher than that of the substrate and 17% higher than that of the Ni-based coating. The zinc in the molten brass intruded into the H13 steel and formed mixed oxides of iron, chromium and zinc in the surface layer of the substrate with the intruded oxygen. Then the mixed oxides peeled off in the mixed oxide zoneⅡof Fe and Zn adjacent to corroded surface, while the corrosive mechanism of the Ni-based coatings involves the rapid dissolution of Ni and Si of the received coatings into the molten brass and the oxidation of Si and Zn at the corrosion interface which then peeled off in the mixed oxide zone Ⅰ of Zn and Si adjacent to the coating. The addition of Ni-coated TiC-reinforced particles refined the size of carbide and boride precipitates, preventing the formation of large corrosion pits formed in the matrix phase, and effectively slowed down uneven corrosion of the Ni-based coating.

Solar charging of a Zn-air battery

Solar-charging of Zn-air batteries has been studied by employing a photoelectrocatalytic or a photovoltaic system. Discharging of a Zn-air battery corresponds to oxidation of Zn and formation of ZnO. Charging is the reverse action, i.e., the reduction of ZnO and deposition of metallic Zn on the Zn electrode. In a typical Zn-air battery, charging also corresponds to water oxidation on the counter electrode and oxygen evolution. Because of the high overpotential for the oxygen evolution reaction, charging of the battery necessitates very high voltages, much higher than the voltage produced by the battery. This problem can be overcome by substituting oxygen evolution reaction by photocatalytic oxidation of an organic substance, which may be a biomass waste. This photoelectrocatalytic charging was presently realized with 100% Faradaic efficiency. More than 2 V of power gain was achieved through photoelectrocatalytic charging, i.e., a small input voltage was then necessary in order to charge the battery. Battery charging was also possible by using a photovoltaic cell as long as the cell provides enough open circuit voltage to overcome battery potential, overpotentials and losses. In the present case charging was possible with a commercial photovoltaic cell generating 2.25 V at an incident light intensity of 100 mW cm−2.

On the high-temperature oxidation of ZnSb for thermoelectric applications

Thermoelectric ZnSb has a native surface oxide layer of Sb2O5 +ZnO, while HT oxidation in air resulted in selective oxidation to ZnO, with no detectable Sb by STEM-EDS. The ZnO consisted of an inner nano-granular and a more columnar outer layer. Thermogravimetry showed parabolic oxidation kinetics at 200–325 °C with an activation energy of 117 kJ/mol, comparing well with literature for oxidation of Zn. Two-stage 16O2 +18O2 oxidation followed by SIMS suggests growth by mixed Zn and O diffusion through a protective ZnO layer that still cannot prevent considerable high temperature oxidation in air, with formation of insulating electrical contacts, unless metallised.

Die-attach bonding at 230 °C using micron Sn-coated Zn particles for high-temperature applications

The advancement of wide bandgap semiconductors has posed higher requirements for power chip packaging technology. Nanoparticles (Ag, Cu, and Cu@Ag) sintering was regarded as an innovative low-temperature bonding method that can be serviced at a high temperature. Considering the expensive cost of silver nanoparticles, Zn particles have been considered as an alternative. Herein, a novel type of submicron Sn-coated Zn particles was proposed to overcome the easy oxidation and high sintering temperature problem of Zn. The structure of Zn70Sn30 (wt.%) core/shell was determined by Scheil model calculation to meet the requirements of low-temperature bonding and high-temperature applications. Multiple reducing agents and reduction times were tentatively investigated to prepare Zn70Sn30 (wt.%) particles. The solder joints prepared based on Zn@Sn preform achieved bonding at 230 °C and exhibited an average shear strength of 28.13 MPa at 250 °C. Unlike the Zn–30Sn solder alloy, the lower reflow temperature produced only a single layer of Cu5Zn8 at the interface of the solder joint, which ensured that all fractures occurred primarily in the Zn@Sn preforms. The electrical resistivity and thermal expansion coefficients of Zn@Sn preform were 8.1 μΩ cm and 12.7 × 10−6/K, respectively. Therefore, the Zn@Sn particles were a potential die-attach material for high-temperature power device packaging.

Low-Temperature-Crystallized Ga2O3 Thin Films and Their TFT-Type Solar-Blind Photodetectors.

Crystalline Ga2O3 (c-Ga2O3) is a promising candidate for next-generation solar-blind photodetectors (SBPDs) but is suffering from high processing temperatures. Herein, seed-induced engineering is proposed via adopting Zn as an induced metal for crystallizing Ga2O3, lowering the processing temperature by 200 °C. After annealing, the Zn/Ga2O3 consists of an inner Ga2O3 layer of a monoclinic crystalline phase, top ZnO crystals coming from Zn oxidation, and a thin corundum Ga2O3 layer between them, which implies a "seed-induced" crystallization mechanism besides the nonequilibrium chaotic state caused by the traditional electron transfer one. As a result, the tailored c-Ga2O3 thin-film transistor-type SBPD with enhanced packing density and finite oxygen deficiency demonstrates a satisfactory responsivity of 8.6 A/W and also an ultrahigh UVC/visible rejection ratio (R254/R450) of 2 × 105. The seed-induced engineering forecasts its potential application in crystalline Ga2O3 SBPDs under a relatively low processing temperature.

(Digital Presentation) High Energy Density Picoliter Zn-Air Batteries for Colloidal Robots and State Machines

The recent interest in microscopic autonomous systems, including microrobots, colloidal state machines and smart dust has created a need for microscale energy storage and harvesting. However, macroscopic materials for energy storage have noted incompatibilities with micro-fabrication techniques, creating significant challenges to realizing microscale energy systems. Herein, we photolithographically pattern a microscale Zn/Pt/SU-8 system to generate the highest energy density microbattery at the picoliter (10-12 L) scale. The device scavenges ambient or solution dissolved oxygen for a Zn oxidation reaction, achieving an energy density ranging from 760 to 1070 Wh L-1 at scales below 100 μm lateral and 2 μm thickness in size. More than 10,000 devices per wafer can be released into solution as functional colloids with energy stored onboard. Within a volume of only 2 pL each, these microbatteries can deliver open circuit voltages of 1.16 V with total energies ranging from 5.5 ± 0.3 to 7.7 ± 1.0 μJ and a maximum power near 2.7 nW. We demonstrate that such systems can reliably power a micron-sized memristor circuit, providing access to non-volatile memory. We also cycle power to drive the reversible bending of microscale bimorph actuators at 0.05 Hz for mechanical functions of colloidal robots. The high energy density, low volume and simple configuration promise the mass fabrication and adoption of such picoliter Zn-air batteries for micron-scale, colloidal robotics with autonomous functions.

Insight into the Nature of the ZnO x Promoter during Methanol Synthesis.

Despite the great commercial relevance of zinc-promoted copper catalysts for methanol synthesis, the nature of the Cu–ZnOx synergy and the nature of the active Zn-based promoter species under industrially relevant conditions are still a topic of vivid debate. Detailed characterization of the chemical speciation of any promoter under high-pressure working conditions is challenging but specifically hampered by the large fraction of Zn spectator species bound to the oxidic catalyst support. We present the use of weakly interacting graphitic carbon supports as a tool to study the active speciation of the Zn promoter phase that is in close contact with the Cu nanoparticles using time-resolved X-ray absorption spectroscopy under working conditions. Without an oxidic support, much fewer Zn species need to be added for maximum catalyst activity. A 5–15 min exposure to 1 bar H2 at 543 K only slightly reduces the Zn(II), but exposure for several hours to 20 bar H2/CO and/or H2/CO/CO2 leads to an average Zn oxidation number of +(0.5–0.6), only slightly increasing to +0.8 in a 20 bar H2/CO2 feed. This means that most of the added Zn is in a zerovalent oxidation state during methanol synthesis conditions. The Zn average coordination number is 8, showing that this phase is not at the surface but surrounded by other metal atoms (whether Zn or Cu), and indicating that the Zn diffuses into the Cu nanoparticles under reaction conditions. The time scale of this process corresponds to that of the generally observed activation period for these catalysts. These results reveal the speciation of the relevant Zn promoter species under methanol synthesis conditions and, more generally, present the use of weakly interacting graphitic supports as an important strategy to avoid excessive spectator species, thereby allowing us to study the nature of relevant promoter species.

Ti(IV)-Exchanged Nano-ZIF-8 and Nano-ZIF-67 for Enhanced Photocatalytic Oxidation of Hydroquinone

The metal centres of nano-zeolitic imidazolate framework-8(Zinc) and 67(Cobalt) [nZIF-8(Zn) and nZIF-67(Co)] were partially exchanged with titanium (Ti) centres to form bimetallic nZIF-8(Zn/Ti) (52% Ti4+) and nZIF-67(Co/Ti) (38% Ti4+) respectively, for enhanced photocatalytic performance. A morphological and structural analysis by scanning electron microscopy, energy dispersive spectroscopy (EDS)-mapping and powder X-ray diffraction showed that the particle size, distribution, and the structural integrity of the Sodalite frameworks of the parent ZIFs were retained during the exchange process to form the new bimetallic Ti-ZIFs. Fourier transform infrared spectroscopy confirmed that no additional chemical bonds were formed during the process. X-ray photoelectron spectroscopy binding energies confirmed the preservation of the Zn(II), Co(II) and Ti(IV) oxidation states, as well as the Ti-content, consistent with inductively coupled plasma-optical emission spectrometry and EDS measurements. The Ti-exchanged ZIFs showed higher activity during the photocatalytic oxidation of hydroquinone in comparison with their parent ZIFs. Their kinetic rates were nearly five times faster than those of the parent ZIFs, with the first-order rate constants k = 0.189 min−1 for nZIF-8(Zn/Ti) and k = 0.139 min−1 for nZIF-67(Co/Ti). These catalysts are efficient, stable, and reusable for three photocatalytic cycles without a significant loss of catalytic activity.

Dark nanostructured ZnO films formed by anodic oxidation as photoanodes in photoelectrochemical water splitting

Zinc oxide, due to its unique properties is very often considered as an alternative for titanium dioxide commonly used in photoelectrochemical and photocatalytic applications. In this paper, we present, for the first time, a complex characterization of the photoelectrochemical activity of dark ZnO layers formed by anodic oxidation of metallic Zn in alkaline electrolyte. A special emphasis was put on finding any relations between anodizing duration, morphology of the obtained layers, their defective nature, and photoelectrochemical activity. The research strategy included detailed analysis of morphology of the nanostructured ZnO, their physicochemical characterization (e.g., absorption and luminescence properties), and finally, extensive photoelectrochemical measurements. It was found that dark nanoporous ZnO layers are formed during anodization of Zn at the potential of 2 V in 1 M NaOH. However, if the process is longer than 15 min, the surface of the anodically generated film is gradually covered with a layer of ultra-thin nanowires. The highly defective nature of ZnO films was confirmed using photoluminescence measurements, and the number of defects increases significantly with time of anodization. On the other hand, further thermal treatment in air at 200 °C resulted in the gradual elimination of defects, especially those responsible for visible emission. The best photoelectrochemical performance was achieved for the oxide films with a thickness of c.a. 1.6 µm for both as-anodized and annealed samples. The formation of “lawn” nanowires on the surface of the nanoporous film did not cause any significant improvement in the photoelectrochemical properties of the materials.

Nucleases are upregulated in potato tubers afflicted with zebra chip disease.

The defense response of potato tubers afflicted with zebra chip disease involves oxidatively mediated upregulation of nucleases that likely modulate localized programmed cell death to restrict the phloem-mobile, CLso bacterial pathogen to the vasculature. Zebra chip (ZC) is a bacterial disease of potato (Solanum tuberosum L.) caused by Candidatus Liberibacter solanacearum (CLso). Tubers from infected plants develop characteristic brown discoloration of the vasculature, a result of localized programmed cell death (PCD). We examined the potential contribution of nucleases in the response of tubers to CLso infection. Specific activities of the major isozymes of dsDNase, ssDNase, and RNase were substantially upregulated in tubers from CLso-infected plants, despite their significantly lower soluble protein content. However, ZC disease had no effect on nuclease isozyme profiles. Activities of the predominant nuclease isoforms from healthy and CLso-infected tubers had similar pH optima, thermotolerance, and responses to metallic co-factors. Nuclease activities were heat stable to 60°C and resistant to precipitation with 70% (v/v) isopropanol, which constitute effective techniques for partial purification. DNase and RNase isozyme activities were highest at pH 7.2-8.5 and 6.8-7.2, respectively, and profiles were similar for tubers from CLso-infected and non-infected plants. RNase activities were mostly insensitive to inhibition by EDTA, except at pH 8.5 and above. DNase activities were inhibited by EDTA but less sensitive to inhibition at high pH than the RNases. The EDTA-mediated inhibition of DNase (ds/ss) activities was restored with ZnSO4, but not Ca+2 or Mg+2. By contrast, ZnSO4 inhibited the activities of RNases. DTT and CuSO4 inhibited the activities of all three nucleases. These results suggest that activation of tuber nucleases is dependent on the oxidation of sulfhydryl groups to disulfide and/or oxidation of Zn to Zn+2. In light of previous published results that established extensive CLso-induced upregulation of oxidative stress metabolism in tubers, we propose a model to show how increased nuclease activity could result from a glutathione-mediated oxidation of nuclease sulfhydryl groups in diseased tubers. DNases and RNases are likely an integral part of the hypersensitive response and may modulate PCD to isolate the pathogen to the vascular tissues of tubers.

Asymptotic modeling of electrochemical signaling: Testing Zn in urine for non-invasive bladder cancer diagnosis

A theoretical model on chemical signaling for diagnosis based on the combination of signals for marker and inert and/or interfering metabolites is described. The model yields asymptotic relationships between the intensities of the signals representative of marker and accompanying metabolites compensating concentration fluctuations. The model fits well with voltammetric features associated to the oxidation of different urine metabolites and Zn(II) reduction in the same urine samples after alkaline digestion. As a result, a non-invasive electrochemical detection of urothelial carcinoma (bladder cancer, BC) is reported. Different diagnostic criteria are described all displaying high sensitivity, specificity and positive/negative predictive values. The described methodology was tested by means of an analytical trial with 46 patients with histological and pathologically confirmed BC, 30 healthy controls and 26 patients diagnosed of other urinary pathologies,