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S.BENKARA*, S.ZERKOUT.Larbi Ben M’Hidi University Oum El Bouaghi, ALGÉRIE.

Ceramics Laboratory, Mentouri University CONSTANTINE 25000, ALGERIE.

*Sali_benkara@yahoo.fr

Preparation and characterization of ZnO nanorods grown into oriented TiO2 nanotube array

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Abstact

Nanocomposites of ZnO nanorods and TiO2 nanotubes were fabricated via two steps: (1) Formation of TiO2 nanotube arrays in HF solution by anodization method, (2) Deposition of ZnO nanorods by hydrothermal process with ammonia and Zinc nitrate as inorganic precursors. The morphological characteristics and structures of TiO2 NTs and ZnO/TiO2 NRs/Ts were examined by scanning electron microscopy (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

Keywords: ZnO nanorods, TiO2 nanotubes, Nanocomposites, Hydrothermal process, Anodic oxidation.

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Introduction

Zinc oxide and Titanium dioxide have attracted considerable attention because of their great potential to solve environmental problems.

The nano ZnO/TiO2 film would show higher photocatalytic efficiency than the efficiency of pure nano- ZnO film and nano- TiO2 film.

various chemical, electrochemical, and physical deposition techniques have been utilized to fabricate ZnO/TiO2 nanotube composite films.

Among these methods, template-assisted approach has been proven to be effective for the growth of ordered nanostructures.

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Our strategy is to construct ZnO nanorod arrays from TiO2 nanotube. Since the widely used high temperature vapor-phase processes are expensive and energy consuming, the developpement of ZnO/TiO2 films via chemical solution routes is widely desired.

In particularly anodic oxidation which is a simple technique to control the structure parameters of TiO2 nanotube arrays as template and hydrothermal process to syntheses ZnO nanorods.

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Experimental

Preparation of TiO2 nanotubes: Anodic oxidation method was adopted to

prepare TiO2 nanotubes TNTs. Prior to anodization, titanium pieces were degreased in an ultrasonic with distilled water for 10 min, followed by eroding in a mixture of HF solution, nitric acid and distilled water for 1 min; then cleaned with acetone, rinsed with distilled water and dried in air. Anodization is performed in 2 w % HF solution and distilled water with voltage of 20 Volts for 5 h. Finally, samples were rinsed and annealed at 450 °C for 1 h.

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Preparation of ZnO nanorods :

ZnO nanorod arrays have been fabricated on TiO2 nanotube substrate via hydrothermal process. The TiO2 nanotube films was suspended in a sealed Teflon-lined autoclave with the volume of 50 ml, in which 40 ml of aqueous solution containing 0.02 M Zn(NO3)2.6H2O and (0.3-0.4)M NH3H2O, followed by heating at 80°C-100 °C-160 °C for 24h. At last the products were thoroughly washed and dried in air.

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Results and discussion

20 40 60 80

0

20

40

60

80

100

120

140

160

180

200

Fig. 1. The XRD patterns of TiO2 NTs before annealing (a) and after annealing (b).

2 Theta (deg)

Intens

ity (a

.u)

a TiO2 nanotubes before annealing

b TiO2 nanotubes aftre annealing

b

aTi (1

03 )

Ti (11

2)

Ti (11

0) Ti (10

2)

Ti (00

2)

Ti (1

01)

Ana

tase

(101

)

Peaks with 2 value of 25,6°

the crystal plan of anatase (101) phase.

Other peaks Titanium substrate.

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The diffraction peaks with 2θ value of: 32,1°, 34,7° and 36,5° show high crystalinity of wurtzite hexagonal structure.(002) peak is the highest in all XRD peaks of ZnO crystal.

20 25 30 35 40 45-20

0

20

40

60

80

100

120

140

160

180

Fig. 2. The XRD patterns of ZnO/TiO2 at differenthydrothermal temperature: at 80 °C (a), at 100 °C (b)and at 160 °C (c).

Ti (0

02)

Ti (1

00)

ZnO

(101

)

ZnO

(002

)

ZnO

(100

)

Ana

tase

(101

)

c

b

a

Inte

nsity

(a.u

)

2 Theta (deg)

a 80 °Cb 100 °Cc 160 °C

Fig.2.b show a disappearance of the peaks corresponding to titanium, this means that the ZnO has cover all the substrate as the temperature increase to 160 °C

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20 25 30 35 40 45

0

50

100

150

200

250

Fig. 3 The XRD patterns of ZnO/TiO2 with 0,3 M (a) and 0,4 M of ammonia (b).

b

a

Ti (0

02 )

Ti (1

00 )Zn

O (1

01 )Zn

O (0

02)

ZnO

(100

)

Ana

tase

(101

)

Inte

nsity

(u.a

)

2 Theta (deg)

a 0,3 M ammoniab 0,4 M ammonia

No remarkable change in orientation of the films as the amount of ammonia was increased shown in Fig.3 but influenced the intensity of the preferred crystalline orientation.

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SEM image of TiO2 naonotubes

Formed on the Ti substrate by anodization method. This figure reveals that high density, well ordered and uniform nanotubes are formed. There diameters are from 60 nm to 95 nm

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SEM image of ZnO/TiO2 nanocomposites This figure shown ZnO deposition by hydrothermal process on the TiO2 NTs. The ZnO grows oriented through the TiO2 NTs inner channels. It can also prove from this image that the epitaxial growths of oriented ZnO nanorods inside the TiO2 nanotube channels are spilled over the TiO2 NTs.

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XPS ANALYSES:(a) XPS survey spectra of ZnO/TiO2 nanocomposite, (b) Ti 2p XPS spectra,

1000 800 600 400 200 0

0

500

1000

1500

2000

2500

3000

(a)

Ti 3p

Ti 2pZn LMM

Zn LMM

O 1s

O KLL

C 1s

XPS Survey

Inte

nsity

(a.u

)

Binding energy (eV) 450 455 460 465 470 4753000

3500

4000

4500

5000

5500(b)

Inte

nsity

(a.u

)

Ti 2

p 3/

2

Ti 2

p 1/

2

Binding energy (eV)

Ti 2p

Fig.a shows the XSP survey spectra of ZnO/TiO2 nanotube composite. The peaks appears in specter are mainly attributed to Ti, O, Zn and C element. The peaks located at 459,6 and 465,4 eV are attributed to Ti 2p components in Fig.b

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(c) O 1s XPS spectra, (d) Zn 2p XPS spectra.

1030 1025 1020 1015

1700

1800

1900

2000

2100

2200

2300

2400

2500 (c)

Inte

nsity

(a.u

)

Binding energy (eV)

Zn 2p

The peak located at 1021,3 eV is attributed to the Zn 2p. In Fig. d the peak of O1 s is deconvoluted by using symmetric Gaussian curves. The peaks located at 529,6 eV relates to the oxygen atoms of TiO2, a peak at 531,1 eV relates to the oxygen atoms of ZnO, the peak of 533,04 eV related to the oxygen atoms of H2O.

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Conclusion

ZnO/titanate nanocomposites were fabricated via two step route. The TiO2 NTs was fabricated by anodization method. The hydrothermal process was employed to form ZnO nanorods into TiO2 nanotubes. The obtained TiO2 nanotubes and ZnO/TNTs nanocomposite are characterized by different techniques: XRD, SEM and XPS. TiO2 nanotubes are mainly anatase structure and well ordered. The diameter of these nanotubes ranges from 60 to 95 nm. The ZnO nanorods have high crystallinity of wurtzite hexagonal structure.

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Thank you for your attention