Zn K-edge Research Articles

Characterizing Zn Corrosion in Printed Zn-Air Batteries Via Operando Dems, XRD, and XAS

Developing low cost energy storage for integrated electronics depends on the ability to increase energy densities while reducing materials and manufacturing costs. Among the several next generation battery chemistries currently being explored, Zn-air batteries are well suited to tackle these challenges and power a wide variety of electronics applications. Zn-air batteries provide a high theoretical energy density, exhibit high performance at high discharge rates, and use low cost, earth abundant materials. Additionally, Zn-air batteries utilize aqueous, non-flammable electrolytes and can be processed entirely in air, making them an emerging candidate to replace Li-ion batteries. Despite their significant promise, side reactions at the Zn anode limit Zn-air battery performance and reduce practical energy densities. Zn corrosion follows a complex series of intermediate reactions in an alkaline environment and is highly dependent on properties of the electrolyte (OH- concentration and use of additives), properties of the electrode (film porosity and active particle size), and cell operating conditions (temperature, current density, depth of discharge, and cell geometry). Thus, each of these factors can alter the fundamental Zn corrosion mechanism and need to be studied systematically to understand their influence on Zn-air battery stability and performance. Previous studies on Zn corrosion have identified single factors that influence reactions at the anode, but typically rely on ex-situ characterization methods that are not representative of the transient and non-equilibrium nature of electrochemical interfaces. In this work, we investigate corrosion in printed Zn-air batteries through the use of operando characterization techniques including differential electrochemical mass spectroscopy (DEMS), X-ray diffraction (XRD), and X-ray absorption spectroscopy (XAS). This approach couples electrochemical measurements with chemical and structural information to directly probe the reaction products at an electrochemical interface and observe non-equilibrium reactions in real time. Moreover, Zn-air batteries are rapidly processed using additive manufacturing in order to investigate several experimental factors in parallel and determine their impact on Zn corrosion. Using this combined approach, we aim to understand which experimental factors significantly influence Zn corrosion in order to identify methods for mitigating self-discharge and improving Zn utilization in Zn-air batteries. DEMS experiments, coupled with operando pressure decay analysis, are used to quantify hydrogen evolution rates at the Zn anode and are used to compare corrosion rates across various cell designs. Through this technique, we examine the effects of current collector type, electrode mass loading, electrode size, and electrolyte concentration on Zn corrosion rates. Based on our results, electrolyte concentration and current collector material have the greatest influence on corrosion rate among the factors studied, while electrode size and electrode mass loading have little effect on corrosion rates. Through operando XRD, we confirm the formation of a passivating oxide layer at the Zn anode and observe that higher electrolyte concentrations lead to faster passivation of the anode under both discharge and open-circuit conditions. Cell potential is also measured during these experiments and is correlated to the fractional amounts of Zn and oxide species in the anode, suggesting that cell potential can be used as a marker for battery lifetime. In addition, operando XAS experiments show characteristic shifts in the Zn K-edge during the passivation process, corresponding to a change in the Zn valence state during oxidation. These shifts are highly dependent on electrolyte concentration, but show little dependence on electrode geometry or mass loading.

High Energy Resolution-X-ray Absorption Near Edge Structure Spectroscopy Reveals Zn Ligation in Whole Cell Bacteria

Identifying the zinc (Zn) ligation and coordination environment in complex biological and environmental systems is crucial to understand the role of Zn as a biologically essential but sometimes toxic metal. Most studies on Zn coordination in biological or environmental samples rely on the extended X-ray absorption fine structure (EXAFS) region of a Zn K-edge X-ray absorption spectroscopy (XAS) spectrum. However, EXAFS analysis cannot identify unique nearest neighbors with similar atomic number (i.e., O versus N) and provides little information on Zn ligation. Herein, we demonstrate that high energy resolution-X-ray absorption near edge structure (HR-XANES) spectroscopy enables the direct determination of Zn ligation in whole cell bacteria, providing additional insights lost from EXAFS analysis at a fraction of the scan time and Zn concentration. HR-XANES is a relatively new technique that has improved our understanding of trace metals (e.g., Hg, Cu, and Ce) in dilute systems. This study is the first to show that HR-XANES can unambiguously detect Zn coordination to carboxyl, phosphoryl, imidazole, and/or thiol moieties in model microorganisms.

Synthesis and Structural Characterization of a Pure ZnAl4(OH)12(SO4)·2.6H2O Layered Double Hydroxide.

The phase purity of a series of ZnAl4(OH)12SO4· nH2O layered double hydroxides (ZnAl4-LDH) obtained from a reaction of bayerite (Al(OH)3) with an excess of zinc(II) sulfate under hydrothermal conditions was investigated as a function of the reaction temperature, the duration of the hydrothermal treatment, and the zinc(II) concentration. The product quality, i.e., crystalline impurities, Al impurities, and bulk Zn:Al ratio, were assessed by powder X-ray diffraction (PXRD), 27Al MAS NMR, and elemental analysis. Structural characterization of a stoichiometric ZnAl4-LDH (120 °C, 9 days, and 2.8 M Zn(II)) showed a well-defined structure of the metal ion layer as evidenced by a single, well-defined Zn environment: i.e., no Zn substitution on the Al sites according to Zn k-edge EXAFS and PXRD. Furthermore, nearly all of the 12 different 1H atoms in the -OH groups and 4 27Al resonances could be assigned using 1H,27Al NMR correlation experiments recorded with ultrafast MAS. The interlayer water content is variable on the basis of thermogravimetric analysis and changes in the 1H MAS NMR spectra with temperature. A composition of ZnAl4(OH)12(SO4)·2.6H2O was obtained from a combination of these techniques and confirmed that ZnAl4-LDH is isostructural with the mineral nickelalumite (NiAl4(OH)12SO4·3H2O).

Polarization-dependent XEOL: Comparison of peculiar near-band-edge emission of non-polar a-plane GaN and ZnO wafers

Polarization-dependent hard X-ray excited optical luminescence (XEOL) spectroscopy was used to study the properties of near-band-edge (NBE) emission of non-polar a-GaN and a-ZnO wafers. We found similar behaviors of a-GaN with a-ZnO that include the positive intensity jump and the blue shift of the NBE emission peak in the XEOL spectrum following the polarization-dependent X-ray absorption near-edge structure (XANES) as the X-ray energy is tuned across the Ga or Zn K-edge. Furthermore, as the X-ray energy is set above the K-edges, different oscillations of XEOL, also following the XANES, were observed depending upon the directions of the excitation X-ray electric field. However, the blue shift of a-ZnO is about two times larger than that of a-GaN that results from the larger polar field in a-ZnO than that in a-GaN. For both a-GaN and a-ZnO, the above K-edge excited oscillations in XANES and XEOL spectra, where the polarization is set parallel to the c-axis, are attributed to simultaneous excitations of the π-bond along the c-axis and in-plane σ-bonds, whereas only the in-plane σ-bonds are excited for the polarization perpendicular to the c-axis. Therefore, these polarization dependent oscillation features of XEOL yields that follow the fluorescence yields can be used as an alternative way to determine the crystallographic orientations.Polarization-dependent hard X-ray excited optical luminescence (XEOL) spectroscopy was used to study the properties of near-band-edge (NBE) emission of non-polar a-GaN and a-ZnO wafers. We found similar behaviors of a-GaN with a-ZnO that include the positive intensity jump and the blue shift of the NBE emission peak in the XEOL spectrum following the polarization-dependent X-ray absorption near-edge structure (XANES) as the X-ray energy is tuned across the Ga or Zn K-edge. Furthermore, as the X-ray energy is set above the K-edges, different oscillations of XEOL, also following the XANES, were observed depending upon the directions of the excitation X-ray electric field. However, the blue shift of a-ZnO is about two times larger than that of a-GaN that results from the larger polar field in a-ZnO than that in a-GaN. For both a-GaN and a-ZnO, the above K-edge excited oscillations in XANES and XEOL spectra, where the polarization is set parallel to the c-axis, are attributed to simultaneous excitations of th...

Synthesis of a Cu/ZnO Nanocomposite by Electroless Plating for the Catalytic Conversion of CO2 to Methanol

The process of methanol synthesis based on the hydrogenation of CO2 was investigated over binary Cu/ZnO catalyst materials, prepared by applying a novel electroless plating fabrication method. The activity of the produced catalytic samples was determined at temperature range between 200 and 300 °C and the feedstock conversion data were supplemented with a detailed microstructure analysis using high-resolution transmission electron microscopy (HRTEM), X-ray powder diffraction (XRD) and Cu and Zn K-edge, X-ray absorption near-edge structure (XANES) measurements and extended X-ray absorption fine-structure (EXAFS) measurements. It was confirmed that the disorder in the Cu crystallites created unique geometrical situations, which acted as the additional reactive centres for the adsorption of the reactant molecule species. Copper and zinc structural synergy (spill-over) was also demonstrated as being crucial for the carbon dioxide’s activation. EXAFS and XANES results provide strong evidence for surface alloying between copper and zinc and thus the present results demonstrate new approach applicable for explaining metal–support interactions.

Structure, dissolution, and plant uptake of ferrous/zinc phosphates

Development of slow release fertilizers by tuning dissolution kinetics can reduce the environmental impact of (micro) nutrients added to crops. Mixed metal compounds may have different dissolution kinetics and plant uptake than single metal compounds. In this study, mixed Fe(II)/Zn(II) phosphates (0–100 at% Zn) were prepared by aqueous precipitation and their structural characteristics and dissolution kinetics in a sand column were measured as model for divalent metal and phosphate release in soil. Three minerals were identified, namely vivianite (Fe3(PO4)2·8H2O) at 0–20 at% Zn, phosphophyllite (Zn2Fe(PO4)2·4H2O) at 20–79 at% Zn, and hopeite (Zn3(PO4)2·4H2O) at 79–100 at% Zn. The Fe-rich materials had high SSA of 42–64 m2 g−1, which decreased to ≤4 m2 g−1 for ≥79 at% Zn. The Fe K-edge and Zn K-edge XANES spectroscopy measurements show that the samples had comparable local structure and contained 13–72% of Fe as Fe(III) due to partial oxidation. In the sand column, Zn(II) and Fe(II) phosphates dissolved near-congruently at steady state (>7 h), whereas mixed Fe(II)/Zn(II) phosphates showed preferential release of Zn over P and Fe, likely due to reprecipitation of Fe. Pot experiments demonstrate that Zn from Fe(II)/Zn(II) phosphates is absorbed by bird's eye chili plants (C. annuum), in agreement with the preferential dissolution of Zn(II). These results may provide insight into the dissolution of other divalent metals, which not only aids in the growth of plants and resulting foodstuff but ultimately leads to reductions in environmental contamination.

XAFS investigation of Co/Zn based ZIFs after I2, Cl2 and Br2 adsorption

This study investigates the impact of iodine, chlorine and bromine adsorption on the structure of bimetallic Co/Zn zeolitic imidazolate frameworks (ZIFs). The experimental Co and Zn K-edges XANES (X-ray Absorption Near Edge Structure) spectra of Zn0.5Co0.5C8H10N4 synthesized by microwave synthesis were measured before and after halogens treatment.

Investigation of Cavity Enhanced XEOL of a Single ZnO Microrod by Using Multifunctional Hard X-ray Nanoprobe

The multifunctional hard X-ray nanoprobe at Taiwan Photon Source (TPS) exhibits the excellent ability to simultaneously characterize the X-ray absorption, X-ray excited optical luminescence (XEOL) as well as the dynamics of XEOL of materials. Combining the scanning electron microscope (SEM) into the TPS 23A end-station, we can easily and quickly measure the optical properties to map out the morphology of a ZnO microrod. A special phenomenon has been observed that the oscillations in the XEOL associated with the confinement of the optical photons in the single ZnO microrod shows dramatical increase while the X-ray excitation energy is set across the Zn K-edge. Besides having the nano-scale spatial resolution, the synchrotron source also gives a good temporal domain measurement to investigate the luminescence dynamic process. The decay lifetimes of different emission wavelengths and can be simultaneously obtained from the streak image. Besides, SEM can provide the cathodoluminescence (CL) to be a complementary method to analyze the emission properties of materials, we anticipate that the X-ray nanoprobe will open new avenues with great characterization ability for developing nano/microsized optoelectronic devices.

Operando XAS and UV-Vis Characterization of the Photodynamic Spiropyran-Zinc Complexes.

Thermal and photoinduced processes accompanying complexation of photochromic spiropyrans (SPP) with Zn ions in acetone solution were characterized by means of UV-vis and X-ray absorption spectroscopies in operando regime. SPP ligands are usually transparent at λ > 350 nm, but after mixing with Zn ions, they produce a stable colored (ε = 32 000-38 000 M-1 cm-1) complex with maximum absorption at 525 nm, which makes them a powerful tool for monitoring metal-ion concentration in solution. The complex revealed fluorescence and photochromic behavior under static irradiation with visible light with constant photoreaction quantum yield across its characteristic absorption band. Zn K-edge X-ray absorption spectra show prominent changes in Zn local atomic structure between free Zn ions and Zn complex. The pump-flow-probe scheme was adapted to measure operando changes in Zn coordination upon light irradiation. Within experimental time resolution, we have determined that 20 μs after light irradiation, Zn ion is released out of the complex. This is the first example of the direct spectroscopic probe of the Zn photorelease from the spiropyran complex.

Synchrotron X-ray absorption spectroscopy and cation distribution studies of NiAl2O4, CuAl2O4, and ZnAl2O4 nanoparticles synthesized by sol-gel auto combustion method

An array of modern approaches to X-ray including X-ray diffraction (XRD), X-ray absorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) were employed to examine the local atomic structure, cation distribution, and degree of inversion of nanocrystalline metal aluminate MAl2O4 (M = Ni, Cu, Zn) powders produced using the sol-gel auto combustion technique. All samples were revealed to display single-phase cubic spinel structure with Fd-3m space group, as established by the XRD results. The cation distribution within these aluminate spinel structures were completely unique as suggested by the divergent disparity in comparative intensity between (220), (400), (422), and (440) diffraction plans for each XRD pattern. Rietveld refinement examination of the XRD data validates the ZnAl2O4 samples as having normal spinel structure, while CuAl2O4 and NiAl2O4 samples comprise partially-inverse spinel structures with low and high degree of inversion, respectively. The investigative findings gained from experimental Ni, Cu, Zn, and Al K-edge XANES spectra accommodated with the hypothetical computation of absorption spectra using the FEFF9.7 code reinforce this. Four-fold synchronization with oxygen atoms was demonstrated by all Zn ions discovered in the ZnAl2O4 samples. Conversely, the Ni and Cu ions located in the NiAl2O4 and CuAl2O4 samples tend to be synchronized in both tetrahedral and octahedral fashion by four or six oxygen atoms, respectively. Additionally, M2+ altering from Zn2+ ions to be Cu2+ and Ni2+ ions caused a substantial translocation of divalent metal (M2+) ions from the tetrahedral (A) sites to octahedral (B) sites, as clearly demonstrated by the EXAFS spectra. Specifically, the degree of inversion in these metal aluminates is completely dissimilar and identified as 0.83 for NiAl2O4, 0.42 for CuAl2O4 and 0 for ZnAl2O4, as indicated by the curve-fitting analysis of Ni, Cu, and Zn K-edge EXAFS spectra. These values comprise vital data for comprehension of numerous pertinent properties.

Age hardening response of AA7108A investigated by means of Synchrotron-based X-ray Absorption Spectroscopy (XAS) measurements

Enhanced strengthening achieved during age hardening of 7xxx alloys, necessitated the need to study the age hardening response of Cu-free AA7108A wire, as a potential material for automobile fastener production. Age hardening response was investigated by means of Synchrotron-based X-ray Absorption Spectroscopy (XAS) measurements. Linear combination fitting (LCF), using XANES spectra of Zn K-edge showed the gradual removal of Zn atoms from the aluminum matrix of the T4 condition (where Zn is in solution and in GP zones), when subjected to one-step artificial aging treatment at 130 °C and 200 °C, respectively. The reduction of matrix Zn during aging at 130 °C is mainly due to the precipitation of the semi-coherent η’ phase, whose number density increased with increasing aging time. η’ phase is the major phase responsible for hardness and electrical conductivity increase during aging at 130 °C. Reduction of matrix Zn concentration during aging at 200 °C is due to the formation and coarsening of the incoherent η-MgZn2 phase. This resulted in a dramatic decrease in hardness and an increasing trend in the electrical conductivity during aging at 200 °C. Calorimetric study revealed that natural aging occurred at room temperature after solution treatment, and GP zone solvus is found to be below 130 °C. In addition, precipitation of the η’ phase at 130 °C is retarded, due to reduced concentration of vacancies, attributed to the presence of Zirconium (Zr) in the alloy.

XAFS Investigation of Nanoparticle Formation in 64Zn+ Ion Implanted and Thermo Oxidized Si

The single crystal CZ n-Si(100) substrates with electron concentration no = 5 × 1016 cm−3 were implanted by 64Zn+ ions with dose of 5 × 1016 cm−2 and energy of 50 keV. During implantation the ion beam current density was less than 0.5 μA/cm2 to avoid the substrate magnetically heating. After implantation, the plates were subjected to isochronous for one hour heat treatment in oxygen atmosphere at temperatures from 400 up to 1000oC with a step of 100oC. Zn K-edge EXAFS spectra were measured in fluorescent mode. Si(111) channel-cut monochromator was used for energy scanning; energy resolution ΔE/E = 2 × 10–4. According to Zn K-edge EXAFS data, all Zn implanted in Si at 900oC is fully oxidized: an absolute maximum of EXAFS Fourier transform at R ~ 1.6 A corresponds to Zn–O distance. Based on XANES data, we suggest an interaction between implanted Zn atoms and Si support.

Nanostructured ZnS:Cu phosphor: Correlation between photoluminescence properties and local structure

Zinc sulfide (ZnS) is a II–VI inorganic semiconductor material and has received remarkable attention because of fundamental physical properties, versatility, nontoxicity, chemical stability and has been widely applied to make numerous optical devices as phosphor material. As a wide band gap semiconductor, ZnS can easily host different metal ions as luminescent center to improve or modify its structural and optical performances such as Cu atoms. In this paper, ZnS:Cu nanoparticles were synthesized by solvothermal method and the photoluminescence and the structural at long- and local-range properties were characterized. According to X-ray diffraction results, ZnS sample crystallizes with the cubic zinc blende structure (F-43m space group) without spurious phases. Images from transmission electron microscope depict the morphology of ZnS particles as round shape and average size value lower than 5 nm. Theoretical and experimental X-ray absorption near edge structure (XANES) spectra at Zn K-edge suggest the incorporation of Cu atoms into the ZnS host and indicate the occurrence of Zn and S vacancies, which are confirmed by extended X-ray absorption fine structure (EXAFS) fit results. These native defects are related to a red-shift observed in the peak emission of photoluminescence (PL) spectrum for ZnS sample, which is centered at ~ 504 nm. An emission in orange-red region is observed as Cu is incorporated in the ZnS host matrix that is attributed to the transition from the 4T1 level to the 6A1 level. Moreover, the intensity of the emissions due to zinc vacancies and interstitial zinc in the deconvoluted PL spectrum is in accordance with results determined in X-ray absorption spectroscopy characterization.

Zn1-xMgxO nanoparticles prepared by the polymeric precursor method: Correlation between photoluminescence and local structure

ZnO is an n-type semiconductor having a wide band gap which has been studied as green phosphors because of its luminescence properties, although the centers and mechanisms responsible for its luminescence are still a matter of controversy. Band gap engineering of ZnO can be achieved by the incorporation of Mg atoms, resulting in the modification of the deep level emission in the visible region. In this study, nanostructured Zn1-xMgxO samples were prepared through the polymeric precursor method and their structural and photoluminescent properties were characterized. FE-SEM images reveal a polygonal morphology of ZnO nanoparticles and a uniform particle size ranging from 35 to for 91 nm depending on the annealing temperature. XRD results show that Zn1-xMgxO samples crystallized completely without the presence of secondary phases (up to 20 at. %) and the diffraction patterns correspond to the hexagonal wurtzite structure with P63mc space. Theoretical and experimental XANES spectra at Zn K-edge along FTIR measurements suggest occurrence of O vacancies. These vacancies are related to the green emission of photoluminescence spectra for ZnO samples, which is centered at ∼529 nm. As the Mg content increases, an enhancement of this emission is observed, which is associated with the recombination of electrons in Mg interstitials donor states and holes at Zn vacancies.

Electronic Structure and Ferromagnetism in Zincblende Zn1−xCoxS Nanoparticles

We have prepared Zn1−xCoxS nanoparticles (NPs) and studied their local-geometric, electronic, and magnetic properties. X-ray diffraction analyses have indicated that NPs with average crystallite sizes of 2.2 ∼ 2.9 nm are single phase and crystallize in the zincblende-type structure. Cobalt ions with oxidation state + 2 (Co2+) replaced for Zn2+ and almost unchanged the zincblende-type structure of the ZnS host lattice. Interestingly, all samples show room-temperature ferromagnetism and ferromagnetic order increases with increasing Co content (x) in Zn1−xCoxS NPs. With the results obtained from analyzing the local-geometric structures at Zn and Co K-edges and photoluminescence spectra, we believe that ferromagnetism in Zn1−xCoxS NPs is related to intrinsic defects and exchange interactions between Co2+ ions. We have also reviewed the recent studies on ZnS-based dilute-magnetic materials.

Effects of nano-confinement on Zn(II) adsorption to nanoporous silica

Nanopores (at least one dimension ≤100 nm and no dimension <1 nm) are commonly observed features of grain coatings and primary silicate minerals and can contribute substantially to the total surface area available for chemical reactions. Despite the ubiquity of nanopores in natural and synthetic porous media, a generalizable framework for evaluating the effects of nanopore confinement on both fluid and sorbate properties across the entire nanoscale has yet to emerge. As a result, we have a poor understanding of the effect of pore size on molecular-scale processes controlling nano-confinement phenomena in systems in which mineral surfaces are in contact with aqueous solutions.To address these knowledge gaps, we carried out batch experiments designed to reveal the molecular-level details of adsorption reaction products and attendant isotope fractionation of aqueous Zn(II) for synthetic, variably porous, amorphous silica (SiO2(am)) particles with average pore diameters ranging from 10 nm to 330 nm. Shell-by-shell fitting of Zn K-edge extended X-ray absorption fine structure (EXAFS) spectra reveals that Zn(II) (1) adsorbs as dominantly monodentate, corner-sharing complexes to silicate tetrahedra of all SiO2(am) particles examined, regardless of pore size, (2) is tetrahedrally coordinated by oxygen atoms in nanoporous silica with small pore sizes (≤10 nm), and (3) is present as a mixture of tetrahedrally and octahedrally coordinated surface complexes in silica with larger pore sizes (>10 nm). In addition, at low Zn(II) surface coverages (<0.9 μmol m−2) on macroporous SiO2(am), Zn(II) forms a mixture of octahedrally and tetrahedrally coordinated surface complexes, whereas tetrahedrally coordinated surface complexes predominate at higher Zn(II) coverages (>0.9 μmol m−2).Although molecular-level differences in Zn(II) adsorption complexes are apparent with respect to SiO2(am) pore size, we observed no quantifiable differences in attendant isotope fractionation or adsorption edge structure for Zn(II) uptake on nanoporous SiO2(am) surfaces. These results suggest that the differences in binding energy of tetrahedrally versus octahedrally coordinated Zn(II) complexes at the same site on SiO2(am) are small. Comparison of EXAFS spectra to the results of surface complexation modeling (SCM) of experimental Zn(II) uptake data indicates that monodentate Zn(II) adsorption on the SiO2(am) surface releases two protons through binding one site and passivating an adjacent site, which accounts for the modification of surface charge and surface complex structure during adsorption of Zn(II) cations.This study shows that adsorption of Zn(II) in variably porous SiO2(am) results in differences in surface complex geometry as pore size decreases and as surface coverage of Zn(II) increases. Although surface complexation modeling of Zn(II) adsorption edges on macroporous and nanoporous SiO2(am) does not independently identify these molecular-level differences, combination of SCM and molecular-level observations reveals unique insight into the overall adsorption reaction and neighboring surface site reactivity.

Zn/Co ZIF family: MW synthesis, characterization and stability upon halogen sorption

The bimetallic Zn/Co-ZIF MOFs with different Zn:Co ratio were produced by microwave-assisted solvothermal synthesis. The morphological, structural and electronic properties of the obtained materials were probed with different experimental techniques (XRD, TEM, TGA, BET, UV−Vis, IR, Co and Zn K-edge XANES). The result of the overall characterization study evidences that: (i) for all Zn:Co ratio Zn/Co-ZIFs are isostructural to ZIF-8; (ii) Zn and Co occupy the same crystallographic site having the same local environment; (iii) increasing Co content results in the decrease of solvent and iodine amount adsorbed on the surface of the crystals, while the amount adsorbed inside the pores is almost constant. The Zn/Co-ZIF MOFs were tested for iodine and chlorine sorption.

Synthesis, characterization, luminescent properties and biological activities of zinc complexes with bidentate azomethine Schiff-base ligands

A series of zinc complexes with a bidentate azomethine Schiff base ligands derived from 2-tosylaminobenzaldehyde, 2-hydroxy-, 2-hydroxy-5-methoxybenzaldehydes, 2-hydroxynaphthaldehyde and 3,4-dimethoxyphenylethylamine were synthesized by chemical and electrochemical methods. All compounds were characterized on the basis of C, H, N elemental analysis, FT-IR, 1H NMR, UV-vis and photoluminescence studies. The local atomic structures of complexes were determined from analysis of EXAFS and XANES of Zn K-edges. The molecular structure of bis{2-[(E)-2-(3,4-dimethoxyphenyl)ethyliminomethyl]-4-methoxyphenol}zinc(II) was determined by X-ray single-crystal diffraction. The fluorescence spectra show that these complexes in DMSO solutions at room temperature emit bright blue and green luminescence at 428–497 nm. The assignment and the nature of the bands in experimental UV–Vis spectra of complexes were analyzed using time-dependent (TD) DFT calculations. The azomethines and complexes of zinc have been screened for their antibacterial, protistocidal, and fungistatic activities against Penicillium italicum, Colpoda steinii, Escherichia coli 078 and Staphylococcus aureus P-209, and the results are compared with the activity of sulfadimethoxine, toltrazuril and fundazol.

Effects of Myo-inositol Hexakisphosphate on Zn(II) Sorption on γ-Alumina: A Mechanistic Study

Myo-inositol hexakisphosphate (IHP), a most common organic phosphorus in many soils, can strongly interact with aluminum (Al) oxides and influence the fate of metal ions. In this study, the effects of presorbed IHP on γ-Al2O3 (γ-alumina) surfaces on Zn(II) sorption were investigated in batch experiments using a combination of powder X-ray diffraction (XRD), in situ attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), 31P and 27Al solid-state nuclear magnetic resonance spectroscopies (NMR), and Zn K-edge extended X-ray absorption fine structure spectroscopy (EXAFS). The results of the batch experiments show that the presorption of IHP increases the sorption density of Zn(II) on γ-Al2O3 surfaces. The XRD data indicate that the presorption of IHP hinders the formation of Zn–Al layered double hydroxide (LDH) precipitates by raising the critical concentration of Zn(II) required to precipitate the complex. Solid-state NMR spectra further suggest that the chemical environment and speciation of IHP presorbed change, i.e., from inner-sphere surface complexes to ternary surface complexes and to zinc phytate precipitates (Zn-IHP) with the increase in Zn(II) concentration or pH. Linear combination fittings (LCFs) of the EXAFS spectra indicate that the proportion of Zn(II) in binary or ternary surface complexes decreases and that in Zn–Al LDH increases with increasing concentration of Zn(II) at pH 7. Furthermore, the order at which IHP and Zn are added in the reaction can influence the cosorption mechanism. At pH 7, more binary or ternary Zn surface complexes and Zn-IHP form, and less Zn–Al LDH precipitates form if Zn is added first. These results demonstrate that both the timing and concentration of IHP and divalent metals have sweeping influences on their solubility and speciation and these intricacies need to be taken into consideration toward predicting their fates in the environment.

Cation distribution and magnetic properties of Zn-substituted CoCr2O4 nanoparticles

CoCr2O4 is a normal spinel where Co occupies the tetrahedral (A) site and Cr occupies the octahedral (B) site; it is important to examine the cation distribution and magnetic properties by substituting a non-magnetic ion like Zn. In this context, we have synthesized pure phase ZnxCo1-xCr2O4 (x = 0.05, 0.1) of crystallite size 10 nm through conventional co-precipitation technique. Fourier transform of Co, Zn, and Cr K-edge spectra obtained from extended X-ray absorption fine structure demonstrates that while Co and Zn prefer the A site, Cr strongly occupies the B site. The paramagnetic to long range ferrimagnetic transition, TC, decreases from 97 K in CoCr2O4 (bulk) to 87.4 K at x = 0.1 with an intermediate TC of 90 K at x = 0.05. The decrease in TC is ascribed to decrease in A-B exchange interaction confirming the preferential occupation of Zn2+ ions towards the A site. The spin-spiral transition, TS, decreases from 27 K in bulk (CoCr2O4) to 24 K at x = 0.1 followed by a spin lock-in transition, TL, observed at 10 K which remains unchanged with increase in Zn concentration. The diffuse neutron scattering in both compositions shows the evidence of long range spiral ordering in contrast to the simultaneous formation of long and short range order in single crystals of CoCr2O4. The decrease in maximum magnetization from 9 to 8 emu/g and an increase in coercivity from 3.2 to 5.2 kOe at 2 K with an increasing Zn concentration from 0.05 to 0.1 have been explained by considering the Yafet-Kittel model.