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Special Issue "Zinc Oxide Nanostructures: Synthesis and Characterization"

A special issue of Materials (ISSN 1996-1944).

Deadline for manuscript submissions: closed (30 November 2017)

Special Issue Editor

Guest Editor
Prof. Sotirios Baskoutas

Department of Materials Science, University of Patras, Patra, Greece
Website | E-Mail
Interests: theoretical and computational methods for the study of the electronic and optical properties of semiconducting nanomaterials; synthesis with physical methods; characterization of amorphous and nanocrystalline materials

Special Issue Information

Dear Colleagues,

Among various metal oxide materials, ZnO presents itself as a multifunctional material due to its own properties and functionalities. The properties of ZnO include its wide band gap (3.37 eV), high exciton binding energy (60 meV), biocompatibility, ease of fabrication and so on. Due to its excellent properties, ZnO is widely used for various potential applications such as catalysis, solar cells, ultraviolet (UV) lasers, light emitting diodes, photo-detectors, sensors (chemical, bio- and gas), optical and electrical devices and so on. Among various applications, the use of ZnO nanomaterials as a photocatalyst has particular interest due to their large surface area; wide band gap; ease of fabrication and cost effective synthesis; biocompatible and environmentally benign nature.

More specifically, the nanostructured ZnO semiconductor used as photocatalytic degradation material against environmental pollutants has also been extensively studied, because of its advantages of non-toxic nature, low cost and high reactivity. However, such a photocatalytic degradation only proceeds under UV irradiation because this semiconductor can only absorb UV light. Therefore, ZnO-based materials capable of visible-light photocatalysis are required.

Furthermore, the synthesis of large-scale arrayed 1D ZnO nanostructures, including nanowires, nanorods, nanobelts and whiskers, is an important step for the fabrication of functional nano/microdevices. Recently, because of its high-temperature strength and rigidity, as well as excellent chemical stability, small-diameter ZnO whiskers have received great attention for industrial applications as reinforcement phase in composite materials. ZnO whiskers with high aspect ratio have also been successfully used as a probing tip to develop new precise high-resolution imaging techniques for atomic force microscopy and scanning tunneling microscopy.

Finally, Magnetic ion-doped ZnO quantum dots (QDs) have been targeted as promising candidates for the implementation of novel technologies, such as in spintronic and quantum computation.

Assoc. Prof. Sotirios Baskoutas
Guest Editor

Manuscript Submission Information

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Keywords

  • ZnO nanostructures
  • electronic properties
  • synthesis
  • characterization
  • sensors
  • optoelectronics
  • excitons
  • fine structure splitting
  • quantum computation
  • photon entanglement

Published Papers (14 papers)

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Research

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Open AccessArticle Surface Properties of Nanostructured, Porous ZnO Thin Films Prepared by Direct Current Reactive Magnetron Sputtering
Materials 2018, 11(1), 131; doi:10.3390/ma11010131
Received: 11 November 2017 / Revised: 30 December 2017 / Accepted: 8 January 2018 / Published: 14 January 2018
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Abstract
In this paper, the results of detailed X-ray photoelectron spectroscopy (XPS) studies combined with atomic force microscopy (AFM) investigation concerning the local surface chemistry and morphology of nanostructured ZnO thin films are presented. They have been deposited by direct current (DC) reactive magnetron
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In this paper, the results of detailed X-ray photoelectron spectroscopy (XPS) studies combined with atomic force microscopy (AFM) investigation concerning the local surface chemistry and morphology of nanostructured ZnO thin films are presented. They have been deposited by direct current (DC) reactive magnetron sputtering under variable absolute Ar/O2 flows (in sccm): 3:0.3; 8:0.8; 10:1; 15:1.5; 20:2, and 30:3, respectively. The XPS studies allowed us to obtain the information on: (1) the relative concentrations of main elements related to their surface nonstoichiometry; (2) the existence of undesired C surface contaminations; and (3) the various forms of surface bondings. It was found that only for the nanostructured ZnO thin films, deposited under extremely different conditions, i.e., for Ar/O2 flow ratio equal to 3:0.3 and 30:3 (in sccm), respectively, an evident and the most pronounced difference had been observed. The same was for the case of AFM experiments. What is crucial, our experiments allowed us to find the correlation mainly between the lowest level of C contaminations and the local surface morphology of nanostructured ZnO thin films obtained at the highest Ar/O2 ratio (30:3), for which the densely packaged (agglomerated) nanograins were observed, yielding a smaller surface area for undesired C adsorption. The obtained information can help in understanding the reason of still rather poor gas sensor characteristics of ZnO based nanostructures including the undesired ageing effect, being of a serious barrier for their potential application in the development of novel gas sensor devices. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessFeature PaperArticle Structural and Electrochemical Characterization of Zn1−xFexO—Effect of Aliovalent Doping on the Li+ Storage Mechanism
Materials 2018, 11(1), 49; doi:10.3390/ma11010049
Received: 5 December 2017 / Revised: 22 December 2017 / Accepted: 27 December 2017 / Published: 29 December 2017
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Abstract
In order to further improve the energy and power density of state-of-the-art lithium-ion batteries (LIBs), new cell chemistries and, therefore, new active materials with alternative storage mechanisms are needed. Herein, we report on the structural and electrochemical characterization of Fe-doped ZnO samples with
[...] Read more.
In order to further improve the energy and power density of state-of-the-art lithium-ion batteries (LIBs), new cell chemistries and, therefore, new active materials with alternative storage mechanisms are needed. Herein, we report on the structural and electrochemical characterization of Fe-doped ZnO samples with varying dopant concentrations, potentially serving as anode for LIBs (Rechargeable lithium-ion batteries). The wurtzite structure of the Zn1−xFexO samples (with x ranging from 0 to 0.12) has been refined via the Rietveld method. Cell parameters change only slightly with the Fe content, whereas the crystallinity is strongly affected, presumably due to the presence of defects induced by the Fe3+ substitution for Zn2+. XANES (X-ray absorption near edge structure) data recorded ex situ for Zn0.9Fe0.1O electrodes at different states of charge indicated that Fe, dominantly trivalent in the pristine anode, partially reduces to Fe2+ upon discharge. This finding was supported by a detailed galvanostatic and potentiodynamic investigation of Zn1−xFexO-based electrodes, confirming such an initial reduction of Fe3+ to Fe2+ at potentials higher than 1.2 V (vs. Li+/Li) upon the initial lithiation, i.e., discharge. Both structural and electrochemical data strongly suggest the presence of cationic vacancies at the tetrahedral sites, induced by the presence of Fe3+ (i.e., one cationic vacancy for every two Fe3+ present in the sample), allowing for the initial Li+ insertion into the ZnO lattice prior to the subsequent conversion and alloying reaction. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessArticle Study on Zinc Oxide-Based Electrolytes in Low-Temperature Solid Oxide Fuel Cells
Materials 2018, 11(1), 40; doi:10.3390/ma11010040
Received: 29 November 2017 / Revised: 23 December 2017 / Accepted: 26 December 2017 / Published: 28 December 2017
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Abstract
Semiconducting-ionic conductors have been recently described as excellent electrolyte membranes for low-temperature operation solid oxide fuel cells (LT-SOFCs). In the present work, two new functional materials based on zinc oxide (ZnO)—a legacy material in semiconductors but exceptionally novel to solid state ionics—are developed
[...] Read more.
Semiconducting-ionic conductors have been recently described as excellent electrolyte membranes for low-temperature operation solid oxide fuel cells (LT-SOFCs). In the present work, two new functional materials based on zinc oxide (ZnO)—a legacy material in semiconductors but exceptionally novel to solid state ionics—are developed as membranes in SOFCs for the first time. The proposed ZnO and ZnO-LCP (La/Pr doped CeO2) electrolytes are respectively sandwiched between two Ni0.8Co0.15Al0.05Li-oxide (NCAL) electrodes to construct fuel cell devices. The assembled ZnO fuel cell demonstrates encouraging power outputs of 158–482 mW cm−2 and high open circuit voltages (OCVs) of 1–1.06 V at 450–550 °C, while the ZnO-LCP cell delivers significantly enhanced performance with maximum power density of 864 mW cm−2 and OCV of 1.07 V at 550 °C. The conductive properties of the materials are investigated. As a consequence, the ZnO electrolyte and ZnO-LCP composite exhibit extraordinary ionic conductivities of 0.09 and 0.156 S cm−1 at 550 °C, respectively, and the proton conductive behavior of ZnO is verified. Furthermore, performance enhancement of the ZnO-LCP cell is studied by electrochemical impedance spectroscopy (EIS), which is found to be as a result of the significantly reduced grain boundary and electrode polarization resistances. These findings indicate that ZnO is a highly promising alternative semiconducting-ionic membrane to replace the electrolyte materials for advanced LT-SOFCs, which in turn provides a new strategic pathway for the future development of electrolytes. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessArticle NH4OH Treatment for an Optimum Morphological Trade-off to Hydrothermal Ga-Doped n-ZnO/p-Si Heterostructure Characteristics
Materials 2018, 11(1), 37; doi:10.3390/ma11010037
Received: 25 October 2017 / Revised: 14 December 2017 / Accepted: 23 December 2017 / Published: 27 December 2017
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Abstract
Previous studies on Ga-doped ZnO nanorods (GZRs) have failed to address the change in GZR morphology with increased doping concentration. The morphology-change affects the GZR surface-to-volume ratio and the real essence of doping is not exploited for heterostructure optoelectronic characteristics. We present NH
[...] Read more.
Previous studies on Ga-doped ZnO nanorods (GZRs) have failed to address the change in GZR morphology with increased doping concentration. The morphology-change affects the GZR surface-to-volume ratio and the real essence of doping is not exploited for heterostructure optoelectronic characteristics. We present NH4OH treatment to provide an optimum morphological trade-off to n-GZR/p-Si heterostructure characteristics. The GZRs were grown via one of the most eminent and facile hydrothermal method with an increase in Ga concentration from 1% to 5%. The supplementary OH ion concentration was effectively controlled by the addition of an optimum amount of NH4OH to synchronize GZR aspect and surface-to-volume ratio. Hence, the probed results show only the effects of Ga-doping, rather than the changed morphology, on the optoelectronic characteristics of n-GZR/p-Si heterostructures. The doped nanostructures were characterized by scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, photoluminescence, Hall-effect measurement, and Keithley 2410 measurement systems. GZRs had identical morphology and dimensions with a typical wurtzite phase. As the GZR carrier concentration increased, the PL response showed a blue shift because of Burstein-Moss effect. Also, the heterostructure current levels increased linearly with doping concentration. We believe that the presented GZRs with optimized morphology have great potential for field-effect transistors, light-emitting diodes, ultraviolet sensors, and laser diodes. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessFeature PaperArticle Study of Perfluorophosphonic Acid Surface Modifications on Zinc Oxide Nanoparticles
Materials 2017, 10(12), 1363; doi:10.3390/ma10121363
Received: 27 October 2017 / Revised: 17 November 2017 / Accepted: 22 November 2017 / Published: 28 November 2017
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Abstract
In this study, perfluorinated phosphonic acid modifications were utilized to modify zinc oxide (ZnO) nanoparticles because they create a more stable surface due to the electronegativity of the perfluoro head group. Specifically, 12-pentafluorophenoxydodecylphosphonic acid, 2,3,4,5,6-pentafluorobenzylphosphonic acid, and (1H,1H,2H,2H-perfluorododecyl)phosphonic acid have been used to
[...] Read more.
In this study, perfluorinated phosphonic acid modifications were utilized to modify zinc oxide (ZnO) nanoparticles because they create a more stable surface due to the electronegativity of the perfluoro head group. Specifically, 12-pentafluorophenoxydodecylphosphonic acid, 2,3,4,5,6-pentafluorobenzylphosphonic acid, and (1H,1H,2H,2H-perfluorododecyl)phosphonic acid have been used to form thin films on the nanoparticle surfaces. The modified nanoparticles were then characterized using infrared spectroscopy, X-ray photoelectron spectroscopy, and solid-state nuclear magnetic resonance spectroscopy. Dynamic light scattering and scanning electron microscopy-energy dispersive X-ray spectroscopy were utilized to determine the particle size of the nanoparticles before and after modification, and to analyze the film coverage on the ZnO surfaces, respectively. Zeta potential measurements were obtained to determine the stability of the ZnO nanoparticles. It was shown that the surface charge increased as the alkyl chain length increases. This study shows that modifying the ZnO nanoparticles with perfluorinated groups increases the stability of the phosphonic acids adsorbed on the surfaces. Thermogravimetric analysis was used to distinguish between chemically and physically bound films on the modified nanoparticles. The higher weight loss for 12-pentafluorophenoxydodecylphosphonic acid and (1H,1H,2H,2H-perfluorododecyl)phosphonic acid modifications corresponds to a higher surface concentration of the modifications, and, ideally, higher surface coverage. While previous studies have shown how phosphonic acids interact with the surfaces of ZnO, the aim of this study was to understand how the perfluorinated groups can tune the surface properties of the nanoparticles. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessFeature PaperArticle In-Doped ZnO Hexagonal Stepped Nanorods and Nanodisks as Potential Scaffold for Highly-Sensitive Phenyl Hydrazine Chemical Sensors
Materials 2017, 10(11), 1337; doi:10.3390/ma10111337
Received: 26 October 2017 / Revised: 17 November 2017 / Accepted: 18 November 2017 / Published: 21 November 2017
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Abstract
Herein, we report the growth of In-doped ZnO (IZO) nanomaterials, i.e., stepped hexagonal nanorods and nanodisks by the thermal evaporation process using metallic zinc and indium powders in the presence of oxygen. The as-grown IZO nanomaterials were investigated by several techniques in order
[...] Read more.
Herein, we report the growth of In-doped ZnO (IZO) nanomaterials, i.e., stepped hexagonal nanorods and nanodisks by the thermal evaporation process using metallic zinc and indium powders in the presence of oxygen. The as-grown IZO nanomaterials were investigated by several techniques in order to examine their morphological, structural, compositional and optical properties. The detailed investigations confirmed that the grown nanomaterials, i.e., nanorods and nanodisks possess well-crystallinity with wurtzite hexagonal phase and grown in high density. The room-temperature PL spectra exhibited a suppressed UV emissions with strong green emissions for both In-doped ZnO nanomaterials, i.e., nanorods and nanodisks. From an application point of view, the grown IZO nanomaterials were used as a potential scaffold to fabricate sensitive phenyl hydrazine chemical sensors based on the I–V technique. The observed sensitivities of the fabricated sensors based on IZO nanorods and nanodisks were 70.43 μA·mM−1·cm−2 and 130.18 μA·mM−1·cm−2, respectively. For both the fabricated sensors, the experimental detection limit was 0.5 μM, while the linear range was 0.5 μM–5.0 mM. The observed results revealed that the simply grown IZO nanomaterials could efficiently be used to fabricate highly sensitive chemical sensors. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessFeature PaperArticle Ultra-Fast Microwave Synthesis of ZnO Nanorods on Cellulose Substrates for UV Sensor Applications
Materials 2017, 10(11), 1308; doi:10.3390/ma10111308
Received: 31 October 2017 / Revised: 10 November 2017 / Accepted: 12 November 2017 / Published: 15 November 2017
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Abstract
In the present work, tracing and Whatman papers were used as substrates to grow zinc oxide (ZnO) nanostructures. Cellulose-based substrates are cost-efficient, highly sensitive and environmentally friendly. ZnO nanostructures with hexagonal structure were synthesized by hydrothermal under microwave irradiation using an ultrafast approach,
[...] Read more.
In the present work, tracing and Whatman papers were used as substrates to grow zinc oxide (ZnO) nanostructures. Cellulose-based substrates are cost-efficient, highly sensitive and environmentally friendly. ZnO nanostructures with hexagonal structure were synthesized by hydrothermal under microwave irradiation using an ultrafast approach, that is, a fixed synthesis time of 10 min. The effect of synthesis temperature on ZnO nanostructures was investigated from 70 to 130 °C. An Ultra Violet (UV)/Ozone treatment directly to the ZnO seed layer prior to microwave assisted synthesis revealed expressive differences regarding formation of the ZnO nanostructures. Structural characterization of the microwave synthesized materials was carried out by scanning electron microscopy (SEM) and X-ray diffraction (XRD). The optical characterization has also been performed. The time resolved photocurrent of the devices in response to the UV turn on/off was investigated and it has been observed that the ZnO nanorod arrays grown on Whatman paper substrate present a responsivity 3 times superior than the ones grown on tracing paper. By using ZnO nanorods, the surface area-to-volume ratio will increase and will improve the sensor sensibility, making these types of materials good candidates for low cost and disposable UV sensors. The sensors were exposed to bending tests, proving their high stability, flexibility and adaptability to different surfaces. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessFeature PaperArticle Nanostructured ZnO in a Metglas/ZnO/Hemoglobin Modified Electrode to Detect the Oxidation of the Hemoglobin Simultaneously by Cyclic Voltammetry and Magnetoelastic Resonance
Materials 2017, 10(8), 849; doi:10.3390/ma10080849
Received: 26 June 2017 / Revised: 20 July 2017 / Accepted: 21 July 2017 / Published: 25 July 2017
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Abstract
In the present work, a nanostructured ZnO layer was synthesized onto a Metglas magnetoelastic ribbon to immobilize hemoglobin (Hb) on it and study the Hb’s electrochemical behavior towards hydrogen peroxide. Hb oxidation by H2O2 was monitored simultaneously by two different
[...] Read more.
In the present work, a nanostructured ZnO layer was synthesized onto a Metglas magnetoelastic ribbon to immobilize hemoglobin (Hb) on it and study the Hb’s electrochemical behavior towards hydrogen peroxide. Hb oxidation by H2O2 was monitored simultaneously by two different techniques: Cyclic Voltammetry (CV) and Magnetoelastic Resonance (MR). The Metglas/ZnO/Hb system was simultaneously used as a working electrode for the CV scans and as a magnetoelastic sensor excited by external coils, which drive it to resonance and interrogate it. The ZnO nanoparticles for the ZnO layer were grown hydrothermally and fully characterized by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM) and photoluminescence (PL). Additionally, the ZnO layer’s elastic modulus was measured using a new method, which makes use of the Metglas substrate. For the detection experiments, the electrochemical cell was performed with a glass vial, where the three electrodes (working, counter and reference) were immersed into PBS (Phosphate Buffer Solution) solution and small H2O2 drops were added, one at a time. CV scans were taken every 30 s and 5 min after the addition of each drop and meanwhile a magnetoelastic measurement was taken by the external coils. The CV plots reveal direct electrochemical behavior of Hb and display good electrocatalytic response to the reduction of H2O2. The measured catalysis currents increase linearly with the H2O2 concentration in a wide range of 25–350 μM with a correlation coefficient 0.99. The detection limit is 25–50 μM. Moreover, the Metglas/ZnO/Hb electrode displays rapid response (30 s) to H2O2, and exhibits good stability and reproducibility of the measurements. On the other hand, the magnetoelastic measurements show a small linear mass increase versus the H2O2 concentration with a slope of 152 ng/μM, which is probably due to H2O2 adsorption in ZnO during the electrochemical reaction. No such effects were detected during the control experiment when only PBS solution was present for a long time. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessArticle Fabrication and Characterization of Highly Sensitive Acetone Chemical Sensor Based on ZnO Nanoballs
Materials 2017, 10(7), 799; doi:10.3390/ma10070799
Received: 2 June 2017 / Revised: 4 July 2017 / Accepted: 7 July 2017 / Published: 14 July 2017
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Abstract
Highly sensitive acetone chemical sensor was fabricated using ZnO nanoballs modified silver electrode. A low temperature, facile, template-free hydrothermal technique was adopted to synthesize the ZnO nanoballs with an average diameter of 80 ± 10 nm. The XRD and UV-Vis. studies confirmed the
[...] Read more.
Highly sensitive acetone chemical sensor was fabricated using ZnO nanoballs modified silver electrode. A low temperature, facile, template-free hydrothermal technique was adopted to synthesize the ZnO nanoballs with an average diameter of 80 ± 10 nm. The XRD and UV-Vis. studies confirmed the excellent crystallinity and optical properties of the synthesized ZnO nanoballs. The electrochemical sensing performance of the ZnO nanoballs modified AgE towards the detection of acetone was executed by simple current–voltage (IV) characteristics. The sensitivity value of ∼472.33 μA·mM−1·cm−2 and linear dynamic range (LDR) of 0.5 mM–3.0 mM with a correlation coefficient (R2) of 0.97064 were obtained from the calibration graph. Experimental limit of detection (LOD) for ZnO nanoballs modified AgE was found to be 0.5 mM. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessArticle A Highly-Sensitive Picric Acid Chemical Sensor Based on ZnO Nanopeanuts
Materials 2017, 10(7), 795; doi:10.3390/ma10070795
Received: 2 June 2017 / Revised: 26 June 2017 / Accepted: 8 July 2017 / Published: 13 July 2017
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Abstract
Herein, we report a facile synthesis, characterization, and electrochemical sensing application of ZnO nanopeanuts synthesized by a simple aqueous solution process and characterized by various techniques in order to confirm the compositional, morphological, structural, crystalline phase, and optical properties of the synthesized material.
[...] Read more.
Herein, we report a facile synthesis, characterization, and electrochemical sensing application of ZnO nanopeanuts synthesized by a simple aqueous solution process and characterized by various techniques in order to confirm the compositional, morphological, structural, crystalline phase, and optical properties of the synthesized material. The detailed characterizations revealed that the synthesized material possesses a peanut-shaped morphology, dense growth, and a wurtzite hexagonal phase along with good crystal and optical properties. Further, to ascertain the useful properties of the synthesized ZnO nanopeanut as an excellent electron mediator, electrochemical sensors were fabricated based on the form of a screen printed electrode (SPE). Electrochemical and current-voltage characteristics were studied for the determination of picric acid sensing characteristics. The electrochemical sensor fabricated based on the SPE technique exhibited a reproducible and reliable sensitivity of ~1.2 μA/mM (9.23 μA·mM−1·cm−2), a lower limit of detection at 7.8 µM, a regression coefficient (R2) of 0.94, and good linearity over the 0.0078 mM to 10.0 mM concentration range. In addition, the sensor response was also tested using simple I-V techniques, wherein a sensitivity of 493.64 μA·mM−1·cm−2, an experimental Limit of detection (LOD) of 0.125 mM, and a linear dynamic range (LDR) of 1.0 mM–5.0 mM were observed for the fabricated picric acid sensor. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessFeature PaperArticle Flower-Like CuO/ZnO Hybrid Hierarchical Nanostructures Grown on Copper Substrate: Glycothermal Synthesis, Characterization, Hydrophobic and Anticorrosion Properties
Materials 2017, 10(7), 697; doi:10.3390/ma10070697
Received: 12 May 2017 / Revised: 28 May 2017 / Accepted: 21 June 2017 / Published: 25 June 2017
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Abstract
In this work we have demonstrated a facile formation of CuO nanostructures on copper substrates by the oxidation of copper foil in ethylene glycol (EG) at 80 °C. On immersing a prepared CuO film into a solution containing 0.1 g Zn(acac)2 in
[...] Read more.
In this work we have demonstrated a facile formation of CuO nanostructures on copper substrates by the oxidation of copper foil in ethylene glycol (EG) at 80 °C. On immersing a prepared CuO film into a solution containing 0.1 g Zn(acac)2 in 20 mL EG for 8 h, ZnO flower-like microstructures composed of hierarchical three-dimensional (3D) aggregated nanoparticles and spherical architectures were spontaneously formed at 100 °C. The as-synthesized thin films and 3D microstructures were characterized using XRD, SEM, and EDS techniques. The effects of sodium dodecyl sulphate (SDS), cetyltrimethylammonium bromide (CTAB), and polyethylene glycol (PEG) 6000 as surfactants and stabilizers on the morphology of the CuO and ZnO structures were discussed. Possible growth mechanisms for the controlled organization of primary building units into CuO nanostructures and 3D flower-like ZnO architectures were proposed. The hydrophobic property of the products was characterized by means of water contact angle measurement. After simple surface modification with stearic acid and PDMS, the resulting films showed hydrophobic and even superhydrophobic characteristics due to their special surface energy and nano-microstructure morphology. Importantly, stable superhydrophobicity with a contact angle of 153.5° was successfully observed for CuO-ZnO microflowers after modification with PDMS. The electrochemical impedance measurements proved that the anticorrosion efficiency for the CuO/ZnO/PDMS sample was about 99%. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Review

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Open AccessFeature PaperReview Molecular Mechanisms of Zinc Oxide Nanoparticle-Induced Genotoxicity Short Running Title: Genotoxicity of ZnO NPs
Materials 2017, 10(12), 1427; doi:10.3390/ma10121427
Received: 16 November 2017 / Revised: 9 December 2017 / Accepted: 9 December 2017 / Published: 14 December 2017
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Abstract
Background: Zinc oxide nanoparticles (ZnO NPs) are among the most frequently applied nanomaterials in consumer products. Evidence exists regarding the cytotoxic effects of ZnO NPs in mammalian cells; however, knowledge about the potential genotoxicity of ZnO NPs is rare, and results presented in
[...] Read more.
Background: Zinc oxide nanoparticles (ZnO NPs) are among the most frequently applied nanomaterials in consumer products. Evidence exists regarding the cytotoxic effects of ZnO NPs in mammalian cells; however, knowledge about the potential genotoxicity of ZnO NPs is rare, and results presented in the current literature are inconsistent. Objectives: The aim of this review is to summarize the existing data regarding the DNA damage that ZnO NPs induce, and focus on the possible molecular mechanisms underlying genotoxic events. Methods: Electronic literature databases were systematically searched for studies that report on the genotoxicity of ZnO NPs. Results: Several methods and different endpoints demonstrate the genotoxic potential of ZnO NPs. Most publications describe in vitro assessments of the oxidative DNA damage triggered by dissoluted Zn2+ ions. Most genotoxicological investigations of ZnO NPs address acute exposure situations. Conclusion: Existing evidence indicates that ZnO NPs possibly have the potential to damage DNA. However, there is a lack of long-term exposure experiments that clarify the intracellular bioaccumulation of ZnO NPs and the possible mechanisms of DNA repair and cell survival. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Open AccessReview Three-Dimensional ZnO Hierarchical Nanostructures: Solution Phase Synthesis and Applications
Materials 2017, 10(11), 1304; doi:10.3390/ma10111304
Received: 17 October 2017 / Revised: 5 November 2017 / Accepted: 10 November 2017 / Published: 13 November 2017
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Abstract
Zinc oxide (ZnO) nanostructures have been studied extensively in the past 20 years due to their novel electronic, photonic, mechanical and electrochemical properties. Recently, more attention has been paid to assemble nanoscale building blocks into three-dimensional (3D) complex hierarchical structures, which not only
[...] Read more.
Zinc oxide (ZnO) nanostructures have been studied extensively in the past 20 years due to their novel electronic, photonic, mechanical and electrochemical properties. Recently, more attention has been paid to assemble nanoscale building blocks into three-dimensional (3D) complex hierarchical structures, which not only inherit the excellent properties of the single building blocks but also provide potential applications in the bottom-up fabrication of functional devices. This review article focuses on 3D ZnO hierarchical nanostructures, and summarizes major advances in the solution phase synthesis, applications in environment, and electrical/electrochemical devices. We present the principles and growth mechanisms of ZnO nanostructures via different solution methods, with an emphasis on rational control of the morphology and assembly. We then discuss the applications of 3D ZnO hierarchical nanostructures in photocatalysis, field emission, electrochemical sensor, and lithium ion batteries. Throughout the discussion, the relationship between the device performance and the microstructures of 3D ZnO hierarchical nanostructures will be highlighted. This review concludes with a personal perspective on the current challenges and future research. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Other

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Open AccessBrief Report Two-Dimensional Fluorescence Difference Spectroscopy of ZnO and Mg Composites in the Detection of Physiological Protein and RNA Interactions
Materials 2017, 10(12), 1430; doi:10.3390/ma10121430
Received: 31 October 2017 / Revised: 7 December 2017 / Accepted: 8 December 2017 / Published: 15 December 2017
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Abstract
Two-dimensional fluorescence difference spectroscopy (2-D FDS) was used to determine the unique spectral signatures of zinc oxide (ZnO), magnesium oxide (MgO), and 5% magnesium zinc oxide nanocomposite (5% Mg/ZnO) and was then used to demonstrate the change in spectral signature that occurs when
[...] Read more.
Two-dimensional fluorescence difference spectroscopy (2-D FDS) was used to determine the unique spectral signatures of zinc oxide (ZnO), magnesium oxide (MgO), and 5% magnesium zinc oxide nanocomposite (5% Mg/ZnO) and was then used to demonstrate the change in spectral signature that occurs when physiologically important proteins, such as angiotensin-converting enzyme (ACE) and ribonuclease A (RNase A), interact with ZnO nanoparticles (NPs). When RNase A is bound to 5% Mg/ZnO, the intensity is quenched, while the intensity is magnified and a significant shift is seen when torula yeast RNA (TYRNA) is bound to RNase A and 5% Mg/ZnO. The intensity of 5% Mg/ZnO is quenched also when thrombin and thrombin aptamer are bound to the nanocomposite. These data indicate that RNA–protein interaction can occur unimpeded on the surface of NPs, which was confirmed by gel electrophoresis, and importantly that the change in fluorescence excitation, emission, and intensity shown by 2-D FDS may indicate specificity of biomolecular interactions. Full article
(This article belongs to the Special Issue Zinc Oxide Nanostructures: Synthesis and Characterization)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Title: Scale-up of the electrodeposition of ZnO/eosin Y hybrid thin films for the fabrication of flexible dye-sensitized solar cell modules
Authors: Florian Bittner, Jan Ellinger, Jiri Rathousky, Torsten Oekermann, and Michael Wark

Title: Facile synthesis and efficient sensing performance of metal nano particles decorated single crystal zinc oxide nanowire arrays
Authors: Fariborz Taghipour et al.

Title: Defect state of oxygen in nanograined ferromagnetic ZnO
Authors: Boris B. Straumal 1,2,3,4, Svetlana G. Protasova 2,3, Andrei A. Mazilkin 1,2, Elena A. Straumal 5, Eberhard Goering 3, Gisela Schütz 3, Petr B. Straumal 4,6, Brigitte Baretzky 1
Affiliation: 1 Karlsruher Institut für Technologie, Institut für Nanotechnologie, Hermann-von-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany
2 Institute of Solid State Physics, Russian Academy of Sciences, Ac. Ossipyan str. 2, 142432 Chernogolovka, Russia
3 Max-Planck-Institut für Intelligente Systeme, Heisenbergstrasse 3, 70569 Stuttgart, Germany
4 National University for Research and Technology “MISiS”, Leninsky prospect 4, 119991 Moscow, Russia
5 Institute of Physiologically Active Compounds, Russian Academy of Sciences, 1 Severnij pr., 142432 Chernogolovka, Russia
6 Institute of Metallurgy and Materials Science, Russian Academy of Sciences, Leninsky prospect 49, 117991 Moscow, Russia
Abstract: Using the X-ray photoelectron spectroscopy (XPS) we measured in this work the metal–oxygen bonding energy in ZnO bulk single crystal, ZnO nanograined films (ferromagnetic and diamagnetic) as well as in ZnO2 powders. The microstructure of ZnO films has been chatracterized with transmission electron microscopy and their magnetization curves were measured. Diamagnetic ZnO films consist of wurtzite nanograins divided by narrow amorphous layers. In ferromagnetic ZnO films the wurtzite nanograins are surrounded by the broad amorphous regions. The asymmetric O1s peak in ZnO samples is close to ~530 eV and typically can be deconvoluted into three characteristic Gaussian peaks OI, OII and OIII. The OI peak on the lower binding energy side of the O1s spectrum corresponds to oxygen surrounded by Zn atoms in the ZnO hexagonal wurtzite lattice. The OII peak corresponds to oxygen-deficient areas and the OIII peak corresponds to loosely bound oxygen due to surface adsorption. The ferromagnetic properties of ZnO films and nanoparticles are usually explained by the oxygen vacancies witnessed by the presence of strong OII peak. In our work the XPS spectra of bulk ZnO and diamagnetic ZnO films contain strong OI peak and weak OII and OIII peaks. The ferromagnetic ZnO film possesses the additional peak called OIV with the energy about 1.5 eV higher than the OI peak. The energy of OI peak is close to the energy of O1s peak in samples of zinc peroxide ZnO2 having cubic pyrite lattice. We suppose that corresponds to the metal–oxygen bonds in the broad amorphous regions between ZnO nanograins in ferromagnetic films. These Zn–O bonds could be similar to those in zinc peroxide ZnO2.
Keywords: Grain boundaries; ferromagnetism; ZnO; oxygen; XPS

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