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Zinc Oxide Nanomaterials and Based Devices

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A special issue of Crystals (ISSN 2073-4352). This special issue belongs to the section "Inorganic Crystalline Materials".

Deadline for manuscript submissions: closed (30 June 2020) | Viewed by 63150

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Prof. Dr. Nikolaos Bouropoulos

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Department of Materials Science, University of Patras, Greece and Institute of Chemical Engineering Sciences (FORTH/ICE-HT), Patras, Greece
Interests: biological mineralization; calcium phosphates; calcium phosphate bone cements; crystal growth; controlled drug delivery systems based on biopolymers; synthesis and characterization of ZnO
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Prof. Dr. Ahmad Umar

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Department of Chemistry, Faculty of Science and Arts and Promising Centre for Sensors and Electronic Devices, Najran University, Najran, Saudi Arabia
Interests: semiconductor nanotechnology; functional nanomaterials; sensors; electronic and energy devices; environmental remediation; bio-applications of functional nanomaterials
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Prof. Dr. Sotirios Baskoutas

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Department of Materials Science, University of Patras, 265 04 Patras, Greece
Interests: semiconductor nanostructures; optical properties; energy transfer; sensors; carbon dots from biowaste
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Special Issue Information

Dear Colleagues,

Zinc oxide (ZnO), a II-VI semiconductor, is considered to be one of the most important and multifunctional materials due to its own properties and, hence, wide applications. The tetrahedral coordinated bonding geometry of ZnO crystallizes in the form of a zinc blende type structure or, most commonly, in the hexagonal wurtzite structure. Because of their multifunctional properties, various ZnO nanomaterials such as nanotubes, nanorods, nanowires, nanobelts, nanonails, nanoflowers, hierarchical nanostructures, and so on were synthesized using several synthetic techniques—to name a few, the vapor–liquid–solid thermal sublimation method, hydrothermal growth, electrochemical deposition, molecular beam epitaxy, decomposition of zinc precursor compounds, colloidal or solution based synthesis, etc.

Including various other properties, such as wide band gap and high exciton binding energy, ZnO possesses noncentrosymmetric structures which enable it to be used for the fabrication of various piezoelectric devices and systems. ZnO also possesses interesting biocompatible and environmental benign properties and is thus efficiently used for various chemicals, gases, and biosensors and various other environmental remediation applications. Further, due to their excellent optical, piezoelectric, pyroelectric, and photoconducting properties, ZnO nanostructures are used in a wide range of modern technological applications, including electronic and optoelectronic devices, such as light emitting diodes, sensors and actuators, field emitters, dye-sensitized solar cells, piezoelectric nanogenerators, and so on. Moreover, due to its high isoelectric point, ZnO has the ability to bind biological molecules, making this material suitable for the development of biosensors and other bioanalytical devices.

This Special Issue is a timely approach to surveying recent progress in the area of ZnO nanomaterials and their applications. The articles presented in this Special Issue will cover various topics, ranging from materials preparation, engineering, functionalization, and their various applications, such as sensors (chemical, biological, gas, and so on), environmental remediation, biological labeling, fuel cell, electrocatalysis, catalysis, photocatalysis, electronic devices, bio-applications of nanomaterials, and so on. Certainly, the coverage is not complete, but it is our intention that this Special Issue will offer a unique glimpse of what has been achieved and what remains to be explored in ZnO nanomaterials.

The Special Issue will cover (but not be limited to) the following topics:

Synthesis and characterizations of zinc oxide nanomaterials;
ZnO-based Sensors (bio, chemical, gas, optical, etc.) ;
ZnO-based catalysis and photocatalysis;
Environmental remediation using ZnO nanomaterials;
Electronic devices based on ZnO nanomaterials;
Energy devices based on ZnO nanomaterials;
Bio applications based on ZnO nanomaterials;
Theoretical studies;
Etc.

It is our pleasure to invite you to submit review articles, original papers, and communications for this Special Issue, "Zinc Oxide Nanomaterials and Based Devices".

Prof. Bouropoulos Nikolaos
Prof. Ahmad Umar
Prof. Sotirios Baskoutas
Guest Editors

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Crystals is an international peer-reviewed open access monthly journal published by MDPI.

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Keywords

ZnO nanostructures
ZnO quantum dots
ZnO nanowires and nanorods
ZnO nanocomposites
ZnO thin films
ZnO random laser diodes
ZnO based sensors and biosensors
ZnO heterostructure
ZnO based devices

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Published Papers (13 papers)

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13 pages, 3739 KiB

Open AccessArticle

Effect of CeO₂-ZnO Nanocomposite for Photocatalytic and Antibacterial Activities

by Asad Syed, Lakshmi Sagar Reddy Yadav, Ali H. Bahkali, Abdallah M. Elgorban, Deshmukh Abdul Hakeem and Nagaraju Ganganagappa

Crystals 2020, 10(9), 817; https://doi.org/10.3390/cryst10090817 - 16 Sep 2020

Cited by 33 | Viewed by 4605

Abstract

The impact of a CeO₂-ZnO nanocomposite on the photocatalytic and antibacterial properties compared to bare ZnO was investigated. A CeO₂-ZnO nanocomposite was synthesized using Acacia nilotica fruit extract as a novel fuel by a simple solution combustion method. The obtained CeO₂-ZnO nanocomposite was confirmed structurally by XRD, FTIR, Raman and UV-DRS and morphologically by SEM/TEM analysis. The XRD pattern indicates the presence of both hexagonal Wurtzite-structured ZnO (major) and cubic-phase CeO₂ (minor). FTIR shows the presence of a Ce-O-Ce vibration at 468 cm⁻¹ and Zn-O vibration at 445 cm⁻¹. The existence of a band at 460 cm⁻¹ confirmed the F_2g Raman-active mode of the fluorite cubic crystalline structure for CeO₂. Diffused reflectance spectroscopy was used to estimate the bandgap (E_g) from Kubelka–Munk (K–M) theory which was found to be 3.4 eV. TEM analysis shows almost spherical-shaped particles, at a size of about 10–15 nm. The CeO₂-ZnO nanocomposite shows a good BET specific surface area of 30 m²g⁻¹. The surface defects and porosity of the CeO₂-ZnO nanocomposite caused methylene blue (MB) dye to degrade under sunlight (88%) and UV light (92%). The CeO₂-ZnO nanocomposite also exhibited considerable antibacterial activity against a pathogenic bacterial strain. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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18 pages, 6854 KiB

Open AccessArticle

Microwave Irradiation to Produce High Performance Thermoelectric Material Based on Al Doped ZnO Nanostructures

by Neazar Baghdadi, Numan Salah, Ahmed Alshahrie and Kunihito Koumoto

Crystals 2020, 10(7), 610; https://doi.org/10.3390/cryst10070610 - 13 Jul 2020

Cited by 15 | Viewed by 3719

Abstract

Microwave irradiation is found to be effective to provide highly crystalline nanostructured materials. In this work, this technique has been used to produce highly improved thermoelectric (TE) material based on aluminum (Al) doped zinc oxide (ZnO) nanostructures (NSs). The effect of Al dopant at the concentration range 0.5–3 mol % on the structural and TE properties has been investigated in more details. The optimum concentration of Al for better TE performance is found to be 2 mol %, which could significantly increase the electrical conductivity and reduce the thermal conductivity of ZnO NSs and thus enhance the TE performance. This concentration showed almost metallic conductivity behavior for ZnO NSs at low temperatures, e.g., below 500 K. The electrical conductivity reached 400 S/m at room temperature, which is around 200 times greater than the value recorded for the pure ZnO NSs. Remarkably, the measured room temperature thermal conductivity of the microwave synthesized ZnO NSs was very low, which is around 4 W/m·K. This value was further reduced to 0.5 W/m·K by increasing the Al doping to 3 mol %. The figure of merit recorded 0.028 at 675 K, which is 15 times higher than that of the pure ZnO NSs. The output power of a single leg module made of 2 mol % Al doped ZnO NSs was 3.7 µW at 485 K, which is higher by 8 times than that of the pure sample. These results demonstrated the advantage of the microwave irradiation rout as a superior synthetic technique for producing and doping promising TE nanomaterials like ZnO NSs. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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10 pages, 2521 KiB

Open AccessArticle

Quantum-Sized Zinc Oxide Nanoparticles Synthesised within Mesoporous Silica (SBA-11) by Humid Thermal Decomposition of Zinc Acetate

by Tariq Aqeel and Heather F. Greer

Crystals 2020, 10(6), 549; https://doi.org/10.3390/cryst10060549 - 26 Jun 2020

Cited by 12 | Viewed by 3785

Abstract

A modified facile method is presented to synthesise quantum-sized zinc oxide nanoparticles within the pores of a mesoporous silica host (SBA-11). This method eliminates the 3 h alcohol reflux and the basic solution reaction steps of zinc acetate. The mesoporous structure and the ZnO nanoparticles were analysed by X-ray diffractometry, transmission electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, nitrogen sorption analysis and UV–VIS spectroscopy. These tests confirm the synthesis of ~1 nm sized ZnO within the pores of SBA-11 and that the porous structure remained intact after ZnO synthesis. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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16 pages, 5365 KiB

Open AccessEditor’s ChoiceArticle

Green Synthesis of ZnO Nanostructures Using Salvadora Persica Leaf Extract: Applications for Photocatalytic Degradation of Methylene Blue Dye

by Fahad A. Alharthi, Abdulaziz Ali Alghamdi, Asma A. Alothman, Zainab M. Almarhoon, Munairah F. Alsulaiman and Nabil Al-Zaqri

Crystals 2020, 10(6), 441; https://doi.org/10.3390/cryst10060441 - 30 May 2020

Cited by 48 | Viewed by 5062

Abstract

Various ZnO nanomaterials such as nanorods, nanoparticles, and nanosheets were synthesized using Salvadora persica leaf extract via the sol–gel method. The prepared nanomaterials possess a large number of nanocavities. The synthesized nanomaterials were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FT-IR), UV-visible diffuse reflectance studies (UV-DRS), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HT-TEM), and these nanomaterials were used to test photocatalytic applications for the degradation of highly hazardous methylene blue dye. The degradation efficiency was higher for materials with nanorods and nanosheets with nanocavities; this was due to the presence of the nanocavities, which made the catalyst more sensitive to light absorption. This method offers a green synthesis of different nanomaterials in bulk quantity at low cost. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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24 pages, 7637 KiB

Open AccessEditor’s ChoiceArticle

Enhancement of ZnO Nanorods Properties Using Modified Chemical Bath Deposition Method: Effect of Precursor Concentration

by Ahmed Fattah Abdulrahman, Sabah Mohammed Ahmed, Naser Mahmoud Ahmed and Munirah Abullah Almessiere

Crystals 2020, 10(5), 386; https://doi.org/10.3390/cryst10050386 - 9 May 2020

Cited by 42 | Viewed by 4433

Abstract

In this study, the effects of different precursor concentrations on the growth and characteristics properties of the zinc oxide (ZnO) nanorods (NRs) synthesized by using modified and conventional chemical bath deposition (CBD) methods were investigated. The morphologic, structural and optical properties of synthesized ZnO NRs with different precursor concentrations were studied using various characterization techniques. The experimental results show that the varying precursor concentration of the reactants has a remarkable and significant effect on the growth and characteristics properties of ZnO NRs. In addition, the characteristic properties of ZnO NRs grown using the modified method showed significantly improved and enhanced properties. The average length of grown ZnO NRs increased with increased precursor concentration; it can be seen that longer ZnO NRs have been investigated using the modified CBD methods. The ZnO NRs synthesized at 0.05 M using the modified method were grown with high aspect ratios than the ZnO NRs grown using conventional means which were 25 and 11, respectively. The growth rate increased with increased precursor concentration; it can be observed that a higher growth rate was seen using the modification CBD method. Furthermore, XRD results for the two cases reveal that the grown ZnO samples were a nanorod-like in shape and possessed a hexagonal wurtzite structure with high crystal quality. No other phases from the impurity were observed. The diffraction peaks along (002) plane became higher, sharper and narrower as precursor concentration increased, suggesting that the crystalline quality of ZnO NRs grown using the modified method was more enhanced and better than conventional methods. However, optical studies show that the transmittance at each concentration was more than two times higher than the transmittance using the modified CBD method. In addition, optical studies demonstrated that the ZnO NRs grown by using modified and conventional methods had a direct E_g in the range of (3.2–3.26) eV and (3.15–3.19) eV, respectively. It was demonstrated in two methods that ZnO NRs grown at a precursor concentration 0.05 M gave the most favorable result, since the NRs had best characteristic properties. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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9 pages, 1693 KiB

Open AccessArticle

ZnO@TiO₂ Core/Shell Nanowire Arrays with Different Thickness of TiO₂ Shell for Dye-Sensitized Solar Cells

by Liqing Liu, Hui Wang, Dehao Wang, Yongtao Li, Xuemin He, Hongguang Zhang and Jianping Shen

Crystals 2020, 10(4), 325; https://doi.org/10.3390/cryst10040325 - 21 Apr 2020

Cited by 11 | Viewed by 3537

Abstract

The ZnO@TiO₂ core/shell nanowire arrays with different thicknesses of the TiO₂ shell were synthesized, through depositing TiO₂ on the ZnO nanowire arrays using the pulsed laser deposition process. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) images show that these core/shell nanowires were homogeneously coated with TiO₂ nanoparticles with high crystallinity, appearing to be a rather rough surface compared to pure ZnO nanowires. The efficiency of ZnO@TiO₂ core/shell structure-based dye-sensitized solar cells (DSSCs) was improved compared with pure ZnO nanowires. This is mainly attributed to the enlarged internal surface area of the core/shell structures, which increases dye adsorption on the anode to improve the light harvest. In addition, the energy barrier which formed at the interface between ZnO and TiO₂ promoted the charge separation and suppressed the carrier recombination. Furthermore, the efficiency of DSSCs was further improved by increasing the thickness of the TiO₂ shell. This work shows an efficient method to achieve high power conversion efficiency in core/shell nanowire-based DSSCs. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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9 pages, 2885 KiB

Open AccessCommunication

Fabrication of Lettuce-Like ZnO Gas Sensor with Enhanced H₂S Gas Sensitivity

by Ziyang Yu, Jie Gao, Longxiao Xu, Tianyu Liu, Yueying Liu, Xiangyue Wang, Hui Suo and Chun Zhao

Crystals 2020, 10(3), 145; https://doi.org/10.3390/cryst10030145 - 26 Feb 2020

Cited by 33 | Viewed by 3210

Abstract

In this work, a lettuce-like ZnO gas sensor with high sensitivity for H₂S detection was successfully fabricated by a one-step hydrothermal method. Characterization analysis of the phases, crystallinities, morphology, and chemical compositions indicated that lettuce-like ZnO has a lettuce-like microsphere structure composed of wurtzite hexagonal ZnO sheets. A gas sensitivity test of the lettuce-like ZnO showed that the sensor had a high H₂S response (113.04 for 100 ppm H₂S) and H₂S selectivity. The lettuce-like ZnO sensor has fast response characteristics while maintaining high sensitivity, and has a response time as low as 15 seconds and a recovery time of 90 seconds, and the detection limit reaches 1 ppm. The sensitive mechanism of lettuce-like ZnO sensor to H₂S is also discussed. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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12 pages, 4369 KiB

Open AccessArticle

Hydrothermal Synthesis of (001) Facet Highly Exposed ZnO Plates: A New Insight into the Effect of Citrate

by Shirui Luo, Ruosong Chen, Lan Xiang and Jing Wang

Crystals 2019, 9(11), 552; https://doi.org/10.3390/cryst9110552 - 24 Oct 2019

Cited by 15 | Viewed by 4357

Abstract

In this work, two synthesis routes were applied to investigate the effect of citrates on the construction of the ZnO structure. Well-dispersed ZnO plates with (001) facet highly exposed were prepared via one-step hydrothermal route, while ZnO nanoparticles were obtained via two-step route. In one-step route, citrates were added before the formation of Zn(OH)₂ precursor, while citrates were added after the formation of Zn(OH)₂. For the first time, the interaction between citrates and the Zn(OH)₂ precursor was investigated and citrates that participated in the formation of Zn(OH)₂ were the main cause for (001) facet exposed structure construction. A growth mechanism about the formation of ZnO plates in the presence of citrates was proposed. The as-prepared ZnO plates showed enhanced photocatalytic activity for the degradation of methylene blue (MB). Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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13 pages, 3227 KiB

Open AccessEditor’s ChoiceArticle

Direct Growth of Flower-Shaped ZnO Nanostructures on FTO Substrate for Dye-Sensitized Solar Cells

by Ahmad Umar, Mohammad Shaheer Akhtar, Tubia Almas, Ahmed Abdulbaqi Ibrahim, Mohammed Sultan Al-Assiri, Yoshitake Masuda, Qazi Inamur Rahman and Sotirios Baskoutas

Crystals 2019, 9(8), 405; https://doi.org/10.3390/cryst9080405 - 4 Aug 2019

Cited by 19 | Viewed by 5243

Abstract

The proposed work reports that ZnO nanoflowers were grown on fluorine-doped tin oxide (FTO) substrates via a solution process at low temperature. The high purity and well-crystalline behavior of ZnO nanoflowers were established by X-ray diffraction. The morphological characteristics of ZnO nanoflowers were clearly revealed that the grown flower structures were in high density with 3D floral structure comprising of small rods assembled as petals. Using UV absorption and Raman spectroscopy, the optical and structural properties of the ZnO nanoflowers were studied. The photoelectrochemical properties of the ZnO nanoflowers were studied by utilizing as a photoanode for the manufacture of dye-sensitized solar cells (DSSCs). The fabricated DSSC with ZnO nanoflowers photoanode attained reasonable overall conversion efficiency of ~1.40% and a short-circuit current density (J_SC) of ~4.22 mA cm⁻² with an open circuit voltage (V_OC) of 0.615 V and a fill factor (FF) of ~0.54. ZnO nanostructures have given rise to possible utilization as an inexpensive and efficient photoanode materials for DSSCs. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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8 pages, 1865 KiB

Open AccessArticle

Raman Spectra and Microstructure of Zinc Oxide irradiated with Swift Heavy Ion

by Yin Song, Shengxia Zhang, Chonghong Zhang, Yitao Yang and Kangyuan Lv

Crystals 2019, 9(8), 395; https://doi.org/10.3390/cryst9080395 - 31 Jul 2019

Cited by 104 | Viewed by 13931

Abstract

Zinc oxide (ZnO) materials irradiated with 350 MeV ⁵⁶Fe²¹⁺ ions were studied by Raman spectroscopy, Photoluminescence spectra (PL) and Transmission electron microscope (TEM). After ⁵⁶Fe²¹⁺ ion irradiation, a strong oxygen vacancy (V_o) related defect absorption peak at 576 cm⁻¹ and an interstitial zinc (Zn_i) -related defect at 80 cm⁻¹~200 cm⁻¹ formed, and with the increase of dose, the absorption peak was obviously enhanced. Through theoretical calculation, different Raman incident light test methods wereused to determine the oxygen vacancy defect (V_o). There were no significant variation tendencies in the other Raman characteristic lines. Our results demonstrate an energy loss process contributing to the defect structure during irradiation. TEM images showed a lot of fundamental defects. But we see no distinct amorphization in the samples in the electron diffraction images, indicating that the higher energy and irradiation dose hardly affected the structure and performance of zinc oxide. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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9 pages, 2818 KiB

Open AccessArticle

Passivation Effect on ZnO Films by SF₆ Plasma Treatment

by Yumeng Xu, Baoxue Bo, Xin Gao and Zhongliang Qiao

Crystals 2019, 9(5), 236; https://doi.org/10.3390/cryst9050236 - 5 May 2019

Cited by 22 | Viewed by 4273

Abstract

The passivation effects of SF₆ plasma on zinc oxide (ZnO) films prepared by magnetron sputtering were researched. After the SF₆ plasma passivation of ZnO films, the grain size increases, there is low surface roughness, and a small amount of Zn-F bonds are formed, resulting in the narrowing of band gap. The photoluminescence (PL) intensity of SF₆-passivated ZnO films has a 120% increase compared to the untreated samples, and the reduction in defects can increase the resistivity and stability of ZnO films. ZnO films are used in the preparation of ZnO/p-Si heterojunction diodes. The results of the measurement of current voltage (J–V) show that the reverse current is reduced after SF₆ plasma passivation, indicating an improvement in the electrical properties of ZnO films. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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9 pages, 1817 KiB

Open AccessArticle

The Decoloration of Anionic and Cationic Dyes Using ZnO and ZnO-Cu₂O

by Jiang Dong Dai, Luo Gan, Hai Yan Zhang and Chun Ming Liu

Crystals 2019, 9(5), 229; https://doi.org/10.3390/cryst9050229 - 28 Apr 2019

Cited by 6 | Viewed by 2963

Abstract

ZnO and ZnO-Cu₂O were grown on aluminum foam using hydrothermal method. Due to the positively charged sites on the surface, both ZnO and ZnO-Cu₂O show higher adsorption capability towards anionic dyes, but poorer adsorption capability towards cationic dyes. The adsorption ability of ZnO-Cu₂O is smaller than that of ZnO since there is a depletion layer at the interface. In order to decolorize cationic dyes, ZnO and ZnO-Cu₂O are used as sono-catalyst with ultrasonic irradiation. The ZnO-Cu₂O is better than ZnO in sono-catalysis decoloration of cationic dyes. This may be due to the enhanced piezoelectricity and electrochemical activity, as the free electrons in ZnO are reduced in the depletion layer. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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7 pages, 1213 KiB

Open AccessArticle

Passivation Mechanism of Nitrogen in ZnO under Different Oxygen Ambience

by Xingyou Chen, Zhenzhong Zhang, Yunyan Zhang, Bin Yao, Binghui Li and Qian Gong

Crystals 2019, 9(4), 204; https://doi.org/10.3390/cryst9040204 - 12 Apr 2019

Cited by 4 | Viewed by 2870

Abstract

Nitrogen-doped ZnO thin films were grown on a-plane Al₂O₃ by plasma-assisted molecular beam epitaxy. Hall-effect measurements indicated that the nitrogen-doped ZnO films showed p-type behavior first, then n-type, with the growth conditions changing from oxygen-radical-rich to oxygen-radical-deficient ambience, accompanied with the increase of the N/O ratio in the plasmas. The increasing green emission in the low temperature photoluminescence spectra, related to single ionized oxygen vacancy in ZnO, was ascribed to the decrease of active oxygen atoms in the precursor plasmas. CN complex, a donor defect with low formation energy, was demonstrated to be easily introduced into ZnO under O-radical-deficient ambience, which compensated the nitrogen-related acceptor, along with the oxygen vacancy. Full article

(This article belongs to the Special Issue Zinc Oxide Nanomaterials and Based Devices)

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