Flame-made single phase Zn2TiO4 nanoparticles

doi:10.1016/j.matlet.2011.03.058

Materials Letters

Volume 65, Issue 12, 30 June 2011, Pages 2007-2009

https://doi.org/10.1016/j.matlet.2011.03.058 Get rights and content

Abstract

Using zinc naphthenate and titanium tetra isopropoxide (1:1 mol.%) dissolved in ethanol as precursors, single phase Zn₂TiO₄ nanoparticles were synthesized by the flame spray pyrolysis technique. The Zn₂TiO₄ nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive spectroscopy (EDS). The BET surface area (SSA_BET) of the nanoparticles was measured by nitrogen adsorption. The average diameter of Zn₂TiO₄ spherical particles was in the range of 5 to 10 nm under 5/5 (precursor/oxygen) flame conditions. All peaks can be confirmed to correspond to the cubic structure of Zn₂TiO₄ (JCPDS No. 25–1164). The SEM result showed the presence of agglomerated nanospheres with an average diameter of 10–20 nm. The crystallite sizes of spherical particles were found to be in the range of 5–18 nm from the TEM image. An average BET equivalent particle diameter (d_BET) was calculated using the density of Zn₂TiO₄.

Introduction

ZnO–TiO₂ system has been used in paint pigment, gas sensor and catalytic sorbent [1], [2], [3]. Three compounds are known to exist in the ZnO–TiO₂ system, namely: Zn₂TiO₄ (cubic), ZnTiO₃ (hexagonal) and Zn₂Ti₃O₈ (cubic) [4]. The h-ZnTiO₃ decomposes into rutile TiO₂ and cubic Zn₂TiO₄ when the temperature exceeds 945 °C. Cubic Zn₂Ti₃O₈ has been regarded as a low-temperature phase of h- ZnTiO₃, stabled at ~ 600–800 °C and transformed into h-ZnTiO₃ at ~ 820 °C. Zn₂TiO₄ can be easily prepared by conventional solid state reaction between 2ZnO and 1TiO₂ [5], [6]. Single phase ZnTiO₃ was prepared by sol–gel process but it can only exist in a narrow temperature range [7]. As the temperature exceeded 900 °C, the pure ZnTiO₃ phase would decompose into Zn₂TiO₄ and rutile TiO₂. The polymeric precursor method was used to obtain spinel Zn₂TiO₄ powders [8]. Both normal and inverse Zn₂TiO₄ nanocrystalline were prepared by high-energy ball milling from the powder mixture of ZnO and anatase in 2:1 mol.% [9]. The zinc titanate composite nanofibers were prepared using electrospinning method combining with sol–gel process followed by calcining the precursor PVP/Zn(CH₃COO)₂–Ti(OC₄H₉)₄ fibers under air in the temperature range of 400–700 °C [10]. Zn₂TiO₄ was synthesized using ZnO and TiO₂ nanowires as starting materials [11]. The fabricated Zn₂TiO₄:12% TiO₂ ceramic was suitable for microwave dielectric applications. The synthesized ZnO–TiO₂ ceramic fibers were composed of ZnTiO₃, Zn₂TiO₄ and rutile TiO₂. All the mentioned preparation methods did not yield the stabilised final product of Zn₂TiO₄.

Flame spray pyrolysis (FSP) has previously been used to synthesize undoped ZnO and Nb-doped ZnO [12], [13]. FSP is a very promising technique for synthesis of high purity nano-sized materials with controlled size and high surface area in one step. The aim of this research is to apply this technique to synthesize single phase Zn₂TiO₄ nanoparticles. Characterization of the Zn₂TiO₄ nanoparticles was also performed.

Section snippets

Flame synthesis of nanoparticles

Zinc naphthenate (Aldrich, 8 wt.% Zn) and titanium tetra isopropoxide (Aldrich) were used as precursors. The precursors were dissolved in ethanol (Carlo Erba, 98.5%) to obtain a 0.5 mol/L precursor solution. Scheme 1 shows the experimental setup for the synthesis of the flame-made single phase Zn₂TiO₄ nanoparticles. In a typical run, the precursor was fed into a FSP reactor by a syringe pump with a rate of 5 mL/min while 5 L/min O₂ was being dispersed (5/5 flame). The gas flow rates of methane and O

Particle properties

Fig. 1 shows the XRD patterns of the single phase Zn₂TiO₄ nanoparticles. All peaks can be confirmed to correspond to the cubic structure of Zn₂TiO₄ (JCPDS No. 25–1164).

An average BET equivalent particle diameter (d_BET) was calculated using the density of ZnTiO₄ as shown in Table 1. The accurate particle size and morphology of Zn₂TiO₄ dispersion were confirmed by SEM and TEM images.

Fig. 2 (a) shows the morphology of highly crystalline flame-made (5/5) single phase Zn₂TiO₄ nanoparticles from SEM

Conclusions

In summary, we have shown that FSP is a promising technique for the synthesis of high purity nano-sized materials with controlled size and crystallinity in a single step of the single phase Zn₂TiO₄ under 5/5 (precursor/oxygen) flame conditions. All peaks in the XRD spectrum can be confirmed to correspond to the cubic structure of Zn₂TiO₄ (JCPDS No. 25–1156). The SEM result showed the presence of agglomerated nanospheres with an average diameter of 10–20 nm. However the crystallite sizes of

Acknowledgements

The authors would like to gratefully acknowledge the financial support from the National Research University Project under the Office of the Higher Education Commission, Ministry of Education, Thailand.

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Flame-made single phase Zn2TiO4 nanoparticles

Abstract

Introduction

Section snippets

Flame synthesis of nanoparticles

Particle properties

Conclusions

Acknowledgements

J Cryst Growth

j Alloy Compd

Mater Chem Phys

Ceram Inter

Ceram Inter

Mater Lett

J Solid State Chem

Flame-made single phase Zn₂TiO₄ nanoparticles