Synthesis and Characterization of Monolithic ZnO-SiO2 Nanocomposite Xerogels

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Synthesis and Characterization of Monolithic ZnO-SiO2 Nanocomposite Xerogels 1

D. Prasanna1, P. Elangovan1,a, R. Sheelarani1 1 – Dept. of Physics, Pachaiyappa’s College, Chennai, Tamil Nadu, India a – drelangovanphysics@gmail.com DOI 10.2412/mmse.57.4.239 provided by Seo4U.link

Keywords: nano composites xerogel, sol gel method.

ABSTRACT. Synthesis and characterization of ZnO doped SiO2 monolithic nano composite xerogels were prepared by using sol-gel method. In this method prepared samples were observed, that an ageing period of two days is optimum and a very slow controlled evaporation rate is followed for few days. The prepared ZnO-SiO2 monolithic nano composite xerogels for various concentrations are characterized by X-ray diffraction, field-emission scanning electron microscope and Fourier transform-infrared spectroscopy methods.

Introduction: ZnO nano particle embedded into SiO2 composites have attracted extensive research interests. It has been found that these materials have improved luminescence efficiency compared to bulk ZnO material. Excellent non-linear optical properties, saturable absorption and optical bistability have also been reported for these composites various techniques have been employed to prepare nano ZnO-SiO2 composites, including sol-gel impregnation and magnetron sputtering, etc. Wide varieties of glass, glass-ceramic monolithics, nanostructural powders etc., are synthesized through sol-gel technique. In the present work ZnO embedded into SiO2 nanocomposites are synthesized through the sol-gel process. The steps needed for producing monolithic xerogels are carefully followed.

Experimental.

Materials. Zinc acetate dihydrate (Zn (CH3COO)22H2O), Triethanolamine (TEA) and Sodium hydroxide (NaOH), Ethanol(C2H6O), Tetraethyl orthosilicate (TEOS) were purchased from s d finechem. limited in Chennai.

Analyses. The starting solution is prepared by mixing TEOS, ethanol and water in the ratio of 10:10:14 respectively. The starting solution is stirred at 40C for few minutes. One drop of concentrated HCl is diluted in 3 ml of deionized water, is added drop wise in the starting solution.

SAfter 1 hr. of stirring 4 drops of diluted ammonia solution is added to maintain the pH at 4. The second solution is prepared using 200 g of Zn(CH3COO)22H2O dissolved in deionized water. This solution is stirred for 1½ hrs. at 50C. Finally, the starting and second solutions are mixed and stirred for 1½ hrs. The final sol is poured into the plastic mould and covered with aluminium foil. The sols are aged at 40C for 48 hrs.

After 2 days, few holes are made in the aluminium foil and kept at 40C for 2-7 days in drying oven.

The number of holes are gradually increased thereafter, and dried for another 10 or 15 days. The samples are heat treated in PID controlled furnace, with the following scheme of heat treatment.

1

© 2017 The Authors. Published by Magnolithe GmbH. This is an open access article under the CC BY-NC-ND license http://creativecommons.org/licenses/by-nc-nd/4.0/

MMSE Journal. Open Access www.mmse.xyz

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

In the present work, five samples with different weight fraction of ZnO nanoparticles embedded into the SiO2 matrix are synthesized by sol-gel process. The concentrations (in wt%) of the different components zinc acetate dihydrate, ethanol and TEOS for the five samples are present in Table 1.

Table 1. Formulation and proportions of the samples Sample

Tetraethyl orthosilicate

Pure ethanol

Zinc acetate dehydrate

ZS1

10 ml

10 ml

0.200 g

ZS2

10 ml

10 ml

0.400 g

ZS3

10 ml

10 ml

0.600 g

ZS4

10 ml

10 ml

0.800 g

ZS5

10 ml

10 ml

1g

Intensity (a.u.)

500C

300C

120C

10

20

30

40

50

60

70

80

Position [2 Theta]

Fig. 1. XRD patterns of ZS1 xerogel.

Results and discussion. Fig.1 shows the XRD patterns of ZS1 xerogel heat treated at different temperatures 120, 300 and 500C. In the XRD patterns of ZS1 xerogel, the absence of any sharp peak, clearly indicates the amorphous nature of the synthesized nanocomposite at all temperatures.

FE-SEM images. The FE-SEM images of ZS1 and ZS4xerogels are provided in Fig. 2 and 4. respectively. The EDS spectrum of the ZS1 and ZS4 xerogels are presented in Figs. 3 and 5. Fig. 2 shows ZnO nanoparticles are embedded in the SiO2 matrix at only few places due to less (0.200 g) ZnO in the nanocomposite. When the amount of ZnO is increased, more interstitial gaps are occupied by ZnO nanoparticles which is clearly evident from the FE-SEM image Fig.4. This fact is supported by the EDS images 3 and 5 respectively.

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Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

Fig. 2. FE-SEM of the ZS1.

Fig. 3. The EDS spectrum of the ZS1.

Fig. 4. FE-SEM of the ZS4.

Fig. 5. The EDS spectrum of the ZS4.

FT-IR spectrum. Fig.6 shows the FT-IR spectrum of ZS1 xerogel samples calcined at 120C, 300C and 500C. In the FT-IR spectrum the broad bands at 3456 and 1633 cm-1 can be attributed to the stretching and bending vibrational modes of OH in molecular water and the SiOH stretching of surface silanols hydrogen-bonded to molecular water respectively [8], [9]. A broad and strong band is observed at 1086 cm-1 that is assigned to asymmetric stretching vibration of siloxane group SiOSi. In addition, weak band located at 962 cm -1 is due to ZnOSi stretching vibration [10]. A medium intensity band is noticed at 801 cm-1 that is due to deformation of SiOSi bond.

A strong peak at 464 cm-1 is caused by the OSiO bending vibration [11].

TG-DTA curves. The TG-DTA curves of ZS1 xerogel recorded in the range of 100 to 1100C are illustrated in Fig. 7.The TGA curve can be roughly divided into four stages. In stage 1 there is a sharp decrease in the weight of the sample when it is heated from room temperature up to about 160C and a weight loss of 17% which corresponds to the loss of physical water. In stage 2 very low weight loss 0.75% is observed between 160 and 360C. Stage 3 occurs between 360 and 600C with weight a loss of nearly 2%. Stage 4 occurs from 600C up to 1020C and corresponds to a very small weight loss of about 1.50%. The weight loss of stages 2, 3 and 4 are associated both with the removal of the organic groups and with evaporation of water formed from polycondensation reactions [12]. The DTA analysis shows a sharp exothermic peak around 530C is the result of progressive MMSE Journal. Open Access www.mmse.xyz

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

decomposition of organic matter [13]. The sharp endothermic peak around 170C is primarily due to the removal of physically bound water. The small exothermic peak about 950C can be attributed to further removal of residual organic matters.

500C

%Transmitt ance

300C

120C

4000

3500

3000

2500

2000

1500

1000

500

Wave number (cm-1)

Fig. 6. FT-IR spectrum of ZS1 xerogel samples.

Fig. 7. TG-DTA curves of ZS1 xerogel.

Summary. ZnO doped SiO2 monolithic nanocomposite xerogels are synthesized successfully via solgel method. It has been observed that an ageing period of 2 days are optimum and a very slow controlled rate of evaporation for the first 7-10 days are the most essential factors in producing crackfree monolithic xerogels. The amorphous natures of the xerogel are confirmed by XRD patterns. The FE-SEM images clearly show the ZnO nanoparticles embedded into the SiO2 matrix. The FT-IR spectrum yields necessary information about the presence of the expected functional groups belonging to the ZnOSiO2nanocomposites. The TGA and DTA analysis provide the details of various stages MMSE Journal. Open Access www.mmse.xyz

Mechanics, Materials Science & Engineering, July 2017 – ISSN 2412-5954

of internal changes happening in the xerogels during heat treatment like removal of bound water, removal of organic matter etc.

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