Nanocrystalline Zn Research Articles

A novel biodegradable nanocrystalline Zn alloy with exceptional biocompatible and antibacterial properties

The development of biodegradable Zn alloys with comprehensive performance for biomedical applications is still challenging. Hence, the nanocrystalline Zn–Cu–Sr–Li alloys were prepared by alloying design and multi-pass high-speed hot rolling. The Zn–3Cu-0.2Sr-0.4Li alloy achieved nanoscale microstructures, resulting in high strength and an ideal corrosion rate that is more suitable for tissue repair cycles. Scanning Kelvin probe force microscopy analysis revealed the potential from high to low was ranked as: ε phase > SrZn13 phase > Zn grains > β phase. The nanoscale Zn grains and β particles formed numerous microcells, enhancing the microgalvanic corrosion effect. The Sr ions could be released more efficiently during the degradation in Li-containing alloys, which endowed the alloys with outstanding biocompatibility. Besides, the synergistic release of Zn ions and Cu ions during alloy degradation endowed the alloy with excellent antimicrobial ability against Staphylococcus aureus (inhibition zone diameter ≈ 7.5 mm). The antimicrobial ability of Zn–3Cu–0.2Sr–0.4Li alloy was superior among the reported biodegradable Zn alloys. These results demonstrated nanocrystalline Zn–Cu–Sr–Li alloys have comprehensive performance and broad application prospects in biodegradable bone implants, providing the experimental and theoretical basis for future research in the biomedical field.

Structural engineering of nanocrystalline Zn0.5Ni0.5Fe2O4 synthesized by auto combustion method through the use of different organic reducing compounds and its effect on magnetic and photocatalytic properties

Structural engineering of nanocrystalline Zn0.5Ni0.5Fe2O4 synthesized by auto combustion method through the use of different organic reducing compounds and its effect on magnetic and photocatalytic properties

Significantly enhanced performance of Li-storage via in-situ oxidation of silicon particles by zinc oxide

The synthesis of Si-based composite material can be realized via the reduction of ZnO by excess Si during ball milling. X-ray diffraction, transmission electron microscopy, and X-ray photoelectron spectroscopy analysis confirmed the presence of the reacted products Zn and SiOx (0 <x < 2) in the Si matrix. The composite material was coated with carbon by a high-temperature carburizing process. The carbon-coated composite material shows excellent cycling stability at 0.2 C by demonstrating a capacity retention rate of 78.05 % after 300 cycles with a charging-specific capacity of 697 mA h/g. These results indicate that the nanocrystalline Zn and amorphous SiOx products from the solid-state reaction of cheap Si and ZnO are very effective in improving the cycling stability of Si-based composite material.

Ultrasonic-assisted soldering of sapphire through metallic transition layers of Al and Zn using Sn-xZn-2Al solder alloys

Ultrasonic-assisted soldering has potential in the electrical industry especially for the joining of ceramics. The Al-activated Sn-based alloys are promising ultrasonic solders due to simple preparation, while the current approaches required long ultrasonic action. In order to increase the efficiency and reduce ultrasonic-induced damage, this study investigated the soldering of sapphire (monocrystalline α-Al2O3) performed under an ultrasonic action for 0.5 s by using Sn-xZn-2Al(x = 9, 25, 45) solder alloys. Microstructures of interfacial transition layers between the sapphire and solders were focused on. It has been found that at the interfaces no interfacial reaction phases formed and the interfacial bonding was realized via metallic transition layers. Three kinds of interfacial structures existed, that is, sapphire/Al atomic layer/β-Sn, sapphire/Al atomic layer/(Zn enrichment layer)/β-Sn and sapphire/Al atomic layer/Zn nanocrystalline clusters/β-Sn. The elements of Al and Zn in the solder alloys underwent a selective and asynchronous adsorption process during the ultrasonic action. An Al atomic layer formed on the sapphire surface by the stronger chemical adsorption and acted as a transition layer between sapphire and β-Sn. The Zn enrichment layer was distributed locally along the interface and as the Zn content increased in the solder alloys, more localized Zn nanocrystalline clusters formed. These Zn transition structures strengthened the interfacial bonding by transforming the Al atomic layer/β-Sn interface into the Al atomic layer/Zn transition structures/β-Sn interfaces. The joints possessed a shear strength of up to 28 MPa when soldering with Sn–45Zn–2Al at 350 °C.

Rapid microwave-assisted combustion route for production of MFe2O4 (M = Zn, Ni, Co) nanoferrites for gas sensors view point

Nanocrystalline ZnFe2O4, NiFe2O4 and CoFe2O4 were prepared using rapid microwave assisted combustion technique. Single phase Nanocrystalline structure of ferrites confirmed by X-ray diffraction and Rietveld refinement. Fine powder of Nanocrystalline Zn, Ni and Co ferrites resulted from rapid synthesis route were used for gas sensor fabrication in the form of thick film by screen printing method. Scanning electron microscopy was used to study surface of the sensing element and to study the surface morphology of the sensor. The gas sensing responses of the indigenously built sensor were analyzed by measuring the resistance of sensing element in presence and in absence of LPG. Amongst the studied sensors, NiFe2O4 thick film sensor showed superior response.

Electrodeposited Zn: A promising alternative to ZnO seed layer for hydrothermal growth of ZnO nanowire array

The seed layer consisting of ZnO nanoparticles has long been recognized as the primary option for hydrothermal growth of high-quality ZnO nanowire arrays (ZnO NWAs). Herein, we provide an additional option, i.e., the electrodeposited Zn nano-grains, which can also grow into ZnO nanowires in hydrothermal environment. Remarkably, the nanocrystalline Zn coating can be facilely deposited on various conductive substrates under ambient conditions, while its minimum temperature required for growing ZnO NWAs is only 50 °C. Therefore, it is an ideal alternative to the cost-intensive and energy-consuming ZnO seed layer for industrial-scale production of ZnO NWAs.

Production of Cr3+ substituted Li–Zn nanocrystalline ferrite by citrate method: Studies on structure, cation occupancy, elastic, optical and magnetic performance

The structural, elastic, optical and magnetic characteristics of Li0.4Zn0.2CrxFe2.4-xO4 (0.0 ≤ x ≤ 0.5; step 0.1) produced using a citrate precursor were studied. X-ray powder diffraction data indicate that all of the generated samples are single-phase spinel structures with no additional phases. The lattice parameter reduces from 8.355 Å to 8.333 Å when the chromium content rises. The crystallite sizes of the compositions were assessed by Scherrer's and Williamson-Hall (W–H) approaches. Infrared (IR) spectroscopy revealed two significant absorption bands generated by vibrations at the tetrahedral and octahedral sites. The elastic moduli (bulk modulus ‘B’, rigidity modulus ‘G’ and Young's modulus ‘E’) as well as the Debye temperature (θD) assessed by IR spectroscopy rise as the Cr3+ ions concentration increases. Chromium addition inhibits grain growth and enhances the mechanical strength of Li–Zn nanoferrites. Diffuse reflectance spectra (DRS) were utilized to evaluate the optical band gap (Eg) of Li–Zn–Cr nanoferrite, which was found to drop from 1.96 to 1.84 eV. The vibrating sample magnetometer (VSM) was used to perform the magnetic analysis, and various magnetic parameters were derived using the M − H curves results. Acceptable values of saturation magnetization (78.6–44.05 emu/g) and coercivity (30.87–44.65 G) were found in this system, making these nanoferrites ideal for high-density recording medium and electromagnets applications. Based on the experimental results of lattice parameters, and magnetization, a quite reasonable cation distribution was postulated for all samples. Theoretically predicted lattice parameters and magnetic moments derived from the suggested cation distribution agree with those determined empirically from XRD and VSM results, respectively. The switching field distribution curves were schemed utilizing the first derivative of magnetization data from M − H loops. The Curie temperature decreases significantly with Cr3+ substitution.

Structure evolution and energy storage mechanism of Zn3V3O8 spinel in aqueous zinc batteries.

Spinel-type materials are promising for the cathodes in rechargeable aqueous zinc batteries. Herein, Zn3V3O8 is synthesized via a simple solid-state reaction method. By tuning the Zn(CF3SO3)2 concentration in electrolytes and the cell voltage ranges, improved electrochemical performance of Zn3V3O8 can be achieved. The optimized test conditions give rise to progressive structure evolution from bulk to nano-crystalline spinel, which leads to capacity activation in the first few cycles and stable cycling performance afterward. Furthermore, the energy storage mechanism in this nano-crystalline spinel is interpreted as the co-intercalation of zinc ions and protons with some water. This work provides a new viewpoint of the structure evolution and correlated energy storage mechanism in spinel-type host materials, which would benefit the design and development of next-generation batteries.

Investigation on structural, morphological, optical and electrical features of nanocrystalline Zn1−xGdxO films synthesized by unconventional sol–gel screen-printing process

Nanocrystalline pure and gadolinium (Gd) doped zinc oxide (Zn1−xGdxO) films were synthesized on a glass substrate by unconventional sol–gel screen-printing process. The prepared samples were then fired (sintered) at 500 °C to get the desired stoichiometry. The samples thus prepared were analyzed for their structural, morphological, optical and electrical features by exploiting x-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive x-ray (EDX), UV–visible spectroscopy, photoluminescence (PL) spectroscopy and dark (DC) electrical resistivity appraised by two-probe unit. XRD analysis exposed that all the samples were polycrystalline in character exhibiting single-phase hexagonal wurtzite structure. Fiber-like surface morphology was exhibited by the samples. EDX technique indicates that the samples have the prerequisite constituent elements in stoichiometric ratio. The optical band gap (Eg) showed an increment from 3.24 to 3.45 eV on increasing the doping concentration of gadolinium from x = 0 to x = 0.05 illustrating a band gap tuning of 6.48%. PL spectra of prepared samples displayed a strong near band edge emission along with a weak green emission. Dark (DC) electrical resistivity was found to decrease with the increase in gadolinium doping concentration.

Scalable Synthesis of Microsized, Nanocrystalline Zn0.9 Fe0.1 O-C Secondary Particles and Their Use in Zn0.9 Fe0.1 O-C/LiNi0.5 Mn1.5 O4 Lithium-Ion Full Cells.

Conversion/alloying materials (CAMs) are a potential alternative to graphite as Li‐ion anodes, especially for high‐power performance. The so far most investigated CAM is carbon‐coated Zn0.9Fe0.1O, which provides very high specific capacity of more than 900 mAh g−1 and good rate capability. Especially for the latter the optimal particle size is in the nanometer regime. However, this leads to limited electrode packing densities and safety issues in large‐scale handling and processing. Herein, a new synthesis route including three spray‐drying steps that results in the formation of microsized, spherical secondary particles is reported. The resulting particles with sizes of 10–15 μm are composed of carbon‐coated Zn0.9Fe0.1O nanocrystals with an average diameter of approximately 30–40 nm. The carbon coating ensures fast electron transport in the secondary particles and, thus, high rate capability of the resulting electrodes. Coupling partially prelithiated, carbon‐coated Zn0.9Fe0.1O anodes with LiNi0.5Mn1.5O4 cathodes results in cobalt‐free Li‐ion cells delivering a specific energy of up to 284 Wh kg−1 (at 1 C rate) and power of 1105 W kg−1 (at 3 C) with remarkable energy efficiency (>93 % at 1 C and 91.8 % at 3 C).

Size variation in nanocrystalline Zn0.2Ni0.8Gd0.05Fe1.95O4 ferrites: Exchange bias effect and its correlation with disordered surface spins

The article reports the influence of particle size variation on microstructural, optical and magnetic properties of nanocrystalline Gd doped Ni-Zn ferrites with a generic formula Zn0.2Ni0.8Gd0.05Fe1.95O4. The nanoparticles were synthesized using chemical co-precipitation technique and the average crystallite sizes were found in the range of 4 nm–29 nm as estimated from Scherrer’s relation. Raman spectra confirmed the lowering of symmetry of the octahedral sites of the cubic spinel structure with rare earth doping. A blue shift was observed in the absorption profile of the nanoparticles due to the size effect. The 7 T field cooled M-H plots recorded at 5 K exhibited exchange bias for the sample with the smallest particle size which was attributed to the high anisotropy of the canted surface spins compared to the core spins.

Magnetic Properties of Cu2+ Substituted Ni–Zn Nano-Crystalline Ferrites Synthesized in Citrate-Gel Route

The Nano-crystalline divalent copper ion substituted Ni–Zn ferrites having chemical formula Ni0.5Zn0.5−xCuxFe2O4 (where x = 0.05 to 0.25 in steps of 0.05) were prepared by citrate gel auto-combustion method. The X-ray diffraction study confirmed the single phase spinel cubic structure and the crystallographic studies indicate that the lattice parameter was observed to be decreased with increasing of Cu2+ concentration. Scanning Electron Microscopy was conducted to observe surface morphology and grain size/shape. Magnetic measurements were carried out using Vibrating Sample Magnetometer for magnetization and Impedance analyzer for permeability up to 15 MHz. Magnetization studies revealed that the incorporation of copper into the system modified the exchange interactions leading to gradual decrease in saturation magnetization. Highest saturation magnetization was observed for the base composition Ni0.5Zn0.5CuFe2O4 with 61 emu/g. There was an increase in coercivity and remanence with copper concentration. Frequency and temperature variation of inductance measurements were performed to understand the system behaviour at different threshold limits. Enhancement of initial permeability was observed up to the concentration x = 0.15 and its variation is observed to be grain size dependent. Temperature variation of permeability leads to Curie temperature, which was increased with increasing of Cu2+ concentration. All magnetic characteristics of the present system of nano crystalline ferrites displayed interesting deviations and reasons were well justified.

Biosynthesis of mixed nanocrystalline Zn–Mg–Cu oxide nanocomposites and their antimicrobial behavior

In this work we synthesised ZnO, MgO, CuO and its composite mixed oxide nanoparticles via green process using medicinal plant Pisonia grandis R.Br. leaf extract. The synthesised ZnO, MgO, CuO nanoparticles were characterised by using x-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) analyses. The mixed oxide nanocomposite materials were characterised by using UV–vis, Fourier-transform infrared spectroscopy (FTIR), Raman, XRD, SEM-EDX, elemental mapping, transmission electron microscopy (TEM), selected area electron diffraction (SAED) analyses. UV–vis studies confirm the absorption of mixed oxide nanocomposites. The presence of biomolecules and metal oxides was confirmed by FTIR. Furthermore, Gas chromatography–mass spectrometry (GC-MS) result also confirms the presence of phenolic biomolecule momeinositol. Structural analysis revealed that mixture of hexagonal ZnO, cubic MgO and monoclinic CuO particles were formed. Morphology of mixed oxide nanocomposites observed by SEM suggests that most oxides particles were flower shaped. TEM and EDS further confirm the presence of mixed oxide nanocomposites. The successful synthesis of mixed zinc, magnesium and copper oxides proves that, biosynthesis of the mixed oxide particles by a plant extract is an effective processing method. The fraction of MgO was found to be the highest because MgO is one of the most stable oxides. The fraction of various oxides may be controlled by modifying the fraction of initial Cu nitrate, Mg nitrate and Zn nitrate. The biosynthesised oxides show good antimicrobial activity under the laboratory condition.

Nanoclustered Pd decorated nanocrystalline Zn doped SnO2 for ppb NO2 detection at low temperature

Nanoclustered Pd (2 mol%) was used to decorate Zn doped SnO2 (10 mol% Zn) in order to increase its sensing performances. Zn doped SnO2 built from nanoparticles was prepared by a hydrothermal method using a non-ionic surfactant - Brij52 and Tripropylamine (TPA) as co-templates. The presence of well-dispersed Zn2+ ions in the SnO2 matrix leads to a nonstoichiometric surface. Pd was deposited by subsequent wet impregnation using hydrazine as reducing agent. The as obtained powders were deposited as thick layers onto commercial substrates, in order to obtain the sensitive structures. The coexistence of a mixture of valence states (Pd0, Pd2+ and Pd4+) was highlighted on the surface of the as prepared layers. Several aspects have been followed regarding the Zn and Pd dispersion into the SnO2 matrix: the large scale and low scale morphology (SEM and TEM/HRTEM) in relation with the synthesis route, the obtained crystallographic phases (XRD, SAED) and the way in which the Zn2+ ions are inserted into the SnO2 structure (XRD, XPS, EPR), the spatial distribution of the added chemical elements, Zn and Pd (SEM, STEM, EDS). All these morphological and structural aspects, as well as the Pd surface chemistry, have been correlated with the sensing properties of the nanostructured materials under controlled gas atmosphere. Through this study, we could harvest the specific role of the aforementioned loadings towards selective detection of low NO2 concentrations, between 350 ppb to 5 ppm, at low operating temperature of 100 °C, for infield conditions.

STRUCTURAL AND OPTICAL PROPERTIES OF NANOCRYSTALLINE Zn0.5Cd0.5S/CdS THIN FILMS FOR PHOTOVOLTAIC APPLICATIONS

In the present work, structural and optical properties of nanocrystalline Zn0.5Cd0.5S, CdS and Zn0.5Cd0.5S / CdS thin films have been investigated in order to use as window layer for photovoltaic application. Nanocrystalline Zn0.5Cd0.5S and CdS films have been deposited on glass substrates using chemical bath deposition technique (CBD). The atomic force microscopy (AFM) images showed that the prepared nanocrystalline thin films are homogeneous and have nano size structures. XRD analysis showed that, the films have polycrystalline structure with (002) orientation. From the optical properties results, the films have high transmittance ( 70 %). The band gap is found to be higher as comparison with the bulk of the same films indicating blue shift with respect to the bulk value as a result of quantum size effect. The electrical properties results show that the resistivity of CdS, Zn0.5Cd0.5S and Zn0.5 Cd0.5S / CdS was (3.50×102, 3.43×103 and 3.18×102 Ω cm ) respectively.

Structural and magnetic studies on Co-Zn nanoferrite synthesized via sol-gel and combustion methods

Abstract Co–Zn nanocrystalline ferrites with chemical composition Co0:5Zn0:5Fe2O4 were synthesized by sol-gel and combustion methods. The sol-gel method was carried out in two ways, i.e. based on chelating agents PVA and PEG of high and low molecular weights. In auto-combustion method, the ratio of citric acid to metal nitrate was taken as 1:1, while in sol-gel method the chelating agents were taken based on oxygen balance. All the three samples were studied by thermogravimetric and differential thermal analysis for the identification of phase formation and ferritization temperature. The synthesized samples were characterized by powder X-ray diffraction and FT-IR spectroscopy without any thermal treatment. The measured lattice constants and observed characteristic IR absorption bands of the three samples are in good agreement with the reported values showing the formation of a cubic spinel structure. The crystallite sizes of all samples were determined using high intensity peaks and W-H plot. Size-Strain Plot method was also implemented since two of the samples showed low crystallite sizes. The least crystallite size (5.5 nm) was observed for the sample CZVP while the highest (23.8 nm) was observed for the sample CZCA. Cation distribution was proposed based on calculated and observed intensity ratios of selected planes from X ray diffraction data. All structural parameters were presented using experimental lattice constant and oxygen positional parameter, and they correlated with FT-IR results. Magnetic measurements were carried out using vibrating sample magnetometer at room temperature to obtain the characteristic parameters such as saturation magnetization, coercivity, remanence, squareness ratio and Bohr magnetons. Among all, the sample synthesized via citric acid autocombustion method displayed a remarkably higher magnetization of 53 emu/g and the remaining two samples displayed low magnetization values owing to their smaller crystallite sizes.

Highly selective ozone gas sensor based on nanocrystalline Zn0.95Co0.05O thin film obtained via spray pyrolysis technique

Chemiresistors are highly important for monitoring and detection of harmful gases produced from industrial processes and vehicle emissions. We report herein an experimental investigation of the gas-sensing properties of Zn0.95Co0.05O thin film deposited by spray pyrolysis technique. The X-ray photoelectron spectroscopy indicated the presence of Co2+ ions into de ZnO lattice. The gas-sensing measurements revealed the sensitivity of Zn0.95Co0.05O film towards ozone gas in a wide range of concentrations from 20 to 1040 ppb, exhibiting good repeatability and total reversibility after consecutive exposures. Selectivity for ozone is observed in comparison to NO2, NH3, and CO gases even at low levels. This manuscript reports the effectiveness of spray-pyrolysis method for obtaining nanostructured Zn1-xCoxO thin films for practical applications as an ozone gas sensor.

Structural, optical, room-temperature and low-temperature magnetic properties of Mg–Zn nanoferrite ceramics

ABSTRACTMg–Zn nanocrystalline ferrites (Mg1−xZnxFe2O4, where x = 0.0 to 1.0) were synthesized by the citrate gel auto-combustion route. XRD revealed the formation of nano-sized particles with cubic spinel structure. Lattice constant and specific surface area increased with Zn substitution. SEM micrographs revealed inhomogeneous grains with agglomerates; EDS spectra confirmed the stoichiometry. HRTEM images showed agglomerated nanoparticles with average particle sizes of 21 nm and 16 nm for x = 0.6 and 1.0, respectively, and lattice fringe images and SAED patterns showed nanocrystalline characteristics corroborating the XRD results. FTIR and Raman spectra recorded at room temperature confirmed the spinel structure of ferrites. VSM technique at room temperature used to measure magnetic properties. MS and HC were found to decrease with increases in the Zn concentration in Mg–Zn ferrites due to a weakening of the A–B interaction and decrease in the particle size and surface effect. Low-temperature magnetic studies were carried out in the ZFC and FC modes using SQUIDS by applying 100 Oe between temperatures of 5 and 400 K, and magnetic isotherms were recorded at temperatures of 51 and 310 K. The study revealed the superparamagnetic nature of the synthesized samples showing that the blocking temperature (TB) depends on interparticle interactions.

Hydrogen induced changes of optical and magnetic properties of nanocrystalline Zn0.95Gd0.03M0.02O (M=Al,Mg): Experimental and DFT studies

This research work aims to study the effect of co-doping by Al3+ to increase the electronic charge carrier concentration inversely to Mg2+. Zn0.97Gd0.03O, Zn0.95Gd0.03Mg0.02O, and Zn0.95Gd0.03Al0.02O nanopowders were synthesised by simultaneous thermal co-decomposition of a mixture of cadmium and metal complexes, followed by hydrogenation at 350 and 600 °C. This study aimed at establishing the preparation conditions including hydrogenation that were essential for the creation of room temperature ferromagnetic order starting from the paramagnetic Gd-doped ZnO by using structural and electronic consequences of codoping with ions of Al or Mg. X-ray diffraction analysis confirms total doping of (Gd, Mg and Al) impurities into ZnO host lattice as well as the absence of secondary compounds/oxides in the synthesised solid solutions. The reflectance has been found to be significantly affected upon co-doping and hydrogenation, while the energy band gap decreases slightly; i.e. Eg = 3.23–3.00 eV. Magnetic measurements reveal that all the as-synthesised doped ZnO powders gained paramagnetic behaviour defeating the diamagnetic characteristic of ZnO, due to the presence of Gd ions with an effective magnetic moment in the range 8.04–7.12 μB. The hydrogenation in the present work conditions did not change the paramagnetic behaviour except for ZnO:Gd:Al-H, showing a partial a magnetic order overlapping with paramagnetic component, resulting in a coercivity of 170.2 Oe, remanence of 0.550 memu/g, and saturation magnetization of 2.14 memu/g. Therefore, the conditions including hydrogenation that were necessary to create FM ordering were determined.First-principles calculations indicate that the Gd doped ZnO systems own large spin polarized effect due to the interaction between Gd-f and O-p electrons. The Mg and Al dopants can modulate the values of magnetic moments.

Locally oxidized film for photocathodic protection of nanocrystalline Zn–Ni alloy in simulated seawater

Nanocrystalline Zn–Ni alloy is easily to be oxidized after exposed in the air, and the formed locally oxidized film can provide an additionally novel photocathodic protection to the bare grain surface under sunlight illumination in simulated seawater. A much lower corrosion rate of nearly 30% is obtained for locally oxidized nanocrystalline Zn–Ni alloy under sunlight condition compared to the dark condition. The anticorrosion mechanism is achieved by cooperating following two mechanisms: photocathodic protection of photoelectrons on the reaction of zinc oxidation, and shielding effect of the formed new zinc based precipitation under sunlight illumination. This is a simple and economical approach with the promise for large-scale application in enhancing corrosion resistance of Zn–Ni alloys.