Elsevier

Physica B: Condensed Matter

Volume 597, 15 November 2020, 412401
Physica B: Condensed Matter

Structural, morphological, optical and mechanical studies of annealed ZnO nano particles

https://doi.org/10.1016/j.physb.2020.412401Get rights and content

Highlights

  • The computed size of nanoparticles from XRD and Tem was approximately 21 nm.

  • The UV–Visible Spectroscopy revealed that the band gap decreased from 3.29 eV to 3.24 eV with the increase in temperature.

  • Photoluminescence(PL) spectrum of ZnO nanoparticles shows oxygen vacancy related defect emissions such as orange and red.

  • The wear resistance of ZnO nanoparticles is found to increase with increase of temperature due to the reduction in the brittle nature of ZnO which is resulted from the generation of oxygen vacancies.

  • The higher friction coefficient is due to the large grain size of ZnO nanoparticles.

Abstract

The structural, morphological, optical and mechanical properties of Zinc oxide (ZnO) nanoparticles annealed at different temperatures from 500 °C to 1000 °C with a step size of 100 °C were synthesized from Sol-Gel method. The X-ray diffraction study revealed that ZnO has hexagonal Wurtzite structure. Scanning Electron Microscope(SEM) images of the studied materials possess spherical morphology with induced porosity due to change in annealing temperature. The computed size of nanoparticles from Transmission Electron Microscopy (TEM) was 21 nm. The UV–Visible Spectroscopy revealed that the band gap decreased with increase of the temperature from 3.05eV to 2.82eV. Photoluminescence (PL) spectrum of ZnO nanoparticles shows that oxygen vacancy related defects increased as the temperature increases from 500 °C to 800 °C and decreased beyond 800 °C. The wear resistance of ZnO nanoparticles is found to increase with increase of temperature owing to the generation of oxygen vacancies. The maximum friction coefficient was assigned to largest grain size.

Introduction

ZnO material is a promising material in the family of metal oxides. It has wide band gap 3.37eV, a large binding energy of 60 meV and high electron mobility of ~2000cm2/(V.s) at 80K with good transparency. Due to these properties ZnO material is a potential candidate in the fields of optoelectronic applications such as solar cells, wave guides, laser diodes, gas sensors, spintronics and in bio imaging [[1], [2], [3], [4], [5]]. It is a single semiconductor material which manifests itself as 1-D nano rods, nano plates and nano needles [[6], [7], [8], [9]]. Different methods have been used for the synthesis of ZnO nano powders namely organo metallic precursor method, micro emulsion synthesis, sol-gel process, PVD (Physical Vapour Deposition), Precipitation, chemical vapour deposition [10], chemical bath deposition, Solvothermal and hydro thermal methods [11,12]. In the present study, ZnO nano powders have been prepared from the chemical route (Sol-Gel method) in view of the following 1. Low processing temperature, 2. Short annealing times, 3. High purity of materials and 4. Good control of the size and shape of the particles at atomic level [13,14]. The influence of annealing temperatures on the synthesized samples play a vital role and it is reported in the literature that ZnO nanostructures prepared at room temperature have good stability at high temperatures too [15,16]. ZnO nano powders annealed at high temperatures bare good photo luminescence with enhanced crystallinity [17]. ZnO nanoparticles photoluminescence behaviour would get deteriorated upon annealing as per the literature survey in the perspective of its applications in the fields of optoelectronics and in bio imaging [18]. Further, high temperature annealing provides scope for Zn atom to accommodate itself in the presence of impurity [19,20]. Many device fabrication processes involve high temperature annealing (dopant activation, ohmic contact formation, implantation repairs), and hence the understanding the effect of temperature on the properties of the ZnO nano structures is crucial for the realization of ZnO based Nano devices [21,22]. It has been found that annealing can improve the field-emission (FE) characteristics of ZnO nano structures [23]. The stability at higher temperatures is a prerequisite for the application of ZnO nano structures as oxygen gas sensor, which usually operates at high temperatures [24].

The optical properties of ZnO nanostructures have been extensively studied in the past two decades. However, the mechanical properties of ZnO nanoparticles have not been investigated in spite of its potential applications in mechanical engineering. Li-Yu Lin et al. have studied the effect of annealing temperature on the tribological behaviour of ZnO films prepared by Sol-Gel method. They have reported that the wear resistance of the ZnO films improved when the annealing temperature was increased above 550 °C [25]. They have also noticed that films annealed at high temperatures had better mechanical and wear resistant properties [26]. Huan-Pu Chang et al. studied the influence of oxygen vacancies on the frictional properties of nano crystalline zinc oxide thin films in ambient conditions. The study of the influence of the defects on mechanical properties such as friction and wear resistance plays prominent role in Nano Electro Mechanical Systems (NEMS) [27,28]. Hence, understanding the role of various types of defects generated during the annealing process of ZnO nanoparticles on wear resistance and friction have to be addressed in detail for its use in NEMS.

In the present work, ZnO nanoparticles were prepared by sol-gel method by using PVA as chelating agent. These ZnO nanoparticles are annealed at various temperatures from 500 °C to 1000oCwith a step size of 100 °C to change the defect concentration in the material. The mechanical properties such as wear resistance and friction coefficient of these samples are measured. It is found that the wear resistance increased with increase in temperature and friction coefficient was also found to vary with temperature. The contribution of defects formed during the annealing process to wear resistance and friction are discussed in detail.

Section snippets

Materials and methods

The ZnO nanoparticles were obtained from Sol – Gel method. The materials used in the preparation of ZnO nanoparticles were obtained from HI-Media with 99% purity, and are utilized without any further purification. The deionised water was utilized as a solvent for the preparation of ZnO nanoparticles. The preparation procedure is schematically represented in Fig. 1. For the preparation of ZnO nanoparticles, analytical grade Zn(NO3)26H2O (Zinc Nitrate Hexa hydrate) was mixed with little amount of

Results and discussion

X-ray diffraction patterns of the ZnO nanoparticles are shown in Fig. 2(a). The prominent reflection planes (100) (002) (101) (102) (110) (103) (112) (201) (004) (202) (104) observed from the XRD confirmed the hexagonal wurtzite structure of ZnO. The intensity of these reflection peaks decreased as the temperature increased from 500 °C to 800 °C and there is slight enhancement in the intensity beyond 800 °C as shown in Fig. 2(b). Debye Scherrer formula has been used to estimate the size of the

Conclusion

Nano particles of ZnO have been synthesized from Sol-Gel method, a chemical route using PVA as chelating agent. The nanoparticles were annealed at different temperatures (500°C-100°C–1000 °C). XRD studies have unravelled the formation of hexagonal wurtzite phase in ZnO. TEM results on ZnO nanoparticles annealed at 900 °C, yielded an average particle size of 21 nm, the particles are observed to possess hexagonal geometry. A slight variation in lattice parameters and cell volume has been observed

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

References (56)

  • N.L. Tarwal et al.

    Enhanced photoelectrochemical performance of Ag–ZnO thin films synthesized by spray pyrolysis

    techniqueElectrochimicaActa

    (2011)
  • H. Ren et al.

    Enhancement of ferromagnetism of ZnO:Co nanocrystals by post-annealing treatment: the role of oxygen interstitials and zinc vacancies

    Mater. Lett.

    (2014)
  • S. Zandi et al.

    Microstructure and optical properties of ZnO nanoparticles prepared by a simple method

    Physica B

    (2011)
  • A.F. Jaramillo et al.

    Estimation of the surface interaction mechanism of ZnO nanoparticles modified with organosilane groups by Raman Spectroscopy

    Ceram. Int.

    (2017)
  • M.H. Habibi et al.

    Effect of annealing temperature on optical properties of binary zinc tin oxide nano-composite prepared by sol–gel route using simple precursors: structural and optical studies by DRS, FT-IR, XRD, FESEM investigations

    Spectrochim. Acta Mol. Biomol. Spectrosc.

    (2015)
  • Varsha Srivastava et al.

    Synthesis, characterization and application of zinc oxide nanoparticles(n-ZnO)

    Ceram. Int.

    (2013)
  • Jitao Li et al.

    Surface nanosheets evolution and enhanced photoluminescence properties of Al-doped ZnO films induced by excessive doping concentration

    Ceramic Internatiomal

    (2019)
  • S. Saipriya et al.

    Effect of environment and heat treatment on the optical properties of RF-sputtered SnO2 thin films

    Phys. B

    (2011)
  • R. Kumar et al.

    Ce-doped ZnO nanoparticles for efficient photocatalytic degradation of direct red-23 dye

    Ceram. Int.

    (2015)
  • R. Kumar et al.

    Sono photocatalytic degradation of methyl orange using ZnOnano-aggregates

    J. Alloys Compd.

    (2015)
  • J. Lv et al.

    Effect of annealing temperature on photocatalytic activity of ZnO thin films prepared by sol–gel method

    Superlattice. Microst.

    (2011)
  • H. Wahab et al.

    Optical, structural and morphological studies of (ZnO) nano-rod thin films for biosensor applications using sol gel technique

    Results Phys

    (2013)
  • K. Sowri Babu et al.

    Annealing effects on photoluminescence of ZnO nanoparticles

    Mater. Lett.

    (2013)
  • k Ueda et al.

    Magnetic and electric properties of transition metal-doped ZnO films

    Appl. Phys. Lett.

    (2001)
  • R.F. Service

    Will UV lasers beat the blues?

    Science

    (1997)
  • Y.L. Wu et al.

    Surface modifications of ZnO quantum dots for bio-imaging

    Nanotechnology

    (2007)
  • V. Srikant et al.

    On the optical band gap of Zinc Oxide

    J. Appl. Phys.

    (1998)
  • E. Pyne et al.

    Cerium oxide (CeO2): synthesis, properties and applications

    Spectrochim. Acta, Part A

    (2012)
  • Cited by (6)

    • Treatment of petroleum wastewater using solar power-based photocatalysis

      2022, Petroleum Industry Wastewater: Advanced and Sustainable Treatment Methods
    • H<inf>2</inf> and H<inf>2</inf>S separation by adsorption using graphene and zinc oxide sheets: Molecular dynamic simulations

      2021, Physica B: Condensed Matter
      Citation Excerpt :

      These nanoparticles are commonly used in the oil, gas, and petrochemical industries due to their environmental friendliness. One of the characteristics of this semiconductor oxide is its high thermal resistance and its electrical and piezoelectric properties [19,20]. Zinc oxide is efficient for desulfurization in the temperature range of 351–551 °C due to its optimal thermodynamics [21].

    View full text