zno - sio2 photolityc

7/25/2019 ZnO - SiO2 Photolityc

http://slidepdf.com/reader/full/zno-sio2-photolityc 1/5

Ali et al. Int. J. Res. Chem. Environ. Vol.4 Issue 2 April 2014(161-165)

[161]

International Journal of Research in Chemistry and EnvironmentVol . 4 I ssue 2 Apr i l 2014(161-165)

ISSN 2248-9649

Research Paper

Synthesis and Characterization of ZnO/SiO2 Core-Shell Microparticles and

Photolytic Studies in Methylene Blue

Ali İmran Vaizoğullar, Ahmet Balcı Department of Chemistry, Mugla University, TURKEY

(Received 11th

December 2013, Accepted 19th

March 2014)

Available online at: www.ijrce.org

Abstract: ZnO and ZnO/SiO2 particles were synthesized. ZnO surface coated with SiO2. Thecharacterization of these particles was obtained by Fourier transform infrared spectroscopy (FT-IR), X-

ray diffraction (XRD), Scanning electron microscopy (SEM), and optical microscope. Compared

photoactivity pure ZnO and ZnO/SiO2 particles using Methylene Blue solutions in alkaline conditions, we

observed bare ZnO particles slightly degraded Metylen Blue but ZnO/SiO2 particles showed enhanced

photoactivity at the end of 90 minutes. This result that in the removal of organic pollutants, changing of

surface properties plays an important role.

Keywords: Nano synthesis, Fourier transform infrared spectroscopy, X-ray diffraction (XRD), Scanning electron

microscopy (SEM), optical microscope

Introduction

In recent years the synthesis andcharacterization of semiconductor particles attractedgreat attention because of their usege in many areassuch as biomedicine, luminescence, photocatalysis,

solar cells, display panels, single-electron transistors[1-

2]. The synthesis of such particles and the geometric

consepts more relevant for its applications[3]

. Although

ZnO is very good photocatalyst, there are some problems in practice. ZnO is amphoteric, so it turns

Zn+2

and H2O in acidic medium[4-5]

, and formedzincates in the alkaline medium

[6].

So the photo-activity of ZnO varies dependingon the pH value in aqeous solution. For example

Daneshevar et al.[7]

found that %65 removaling ofdiazinon in neutral medium and they provided that

%49 removaling of diazinon in acidic medium(pH=3).

The coating of nanoparticles to enhance the

surface chemical and physical properties is the key for

the successful applications of nanomaterials[8]

. Forexample, Posthumus et al.

[9], modified various oxidic

particles using 3-methacryloxypropyltrimethoxysilaneand improved that association of modified particles

with organic materials. Min et al.[10]

, stored ZnO rods

on the conformal Al2O3 and provided that Al2O3 cylindrical shells surrounds the ZnO rods. Grasset et

al.[11]

coated commercial ZnO nanoparticles with

aminopropyltriethoxysilane under varying conditions

and found that the coating was controllable. Manystudies on the synthesis of composites, i.e. TiO2

[12],

CaCO3[13]

, Fe2O3[14]

covered with SiO2 have been

reported. SiO2 is a most studied shell candidate due toits relative ease in preparation, good environmentalstability and compatibility with other materials, which

motivated us to prepare the core/shell structuredcomposite of ZnO and SiO2 and expected to achieve

novel properties resulting from the synergic interaction

of these two chemical components[15]

.

In this study we synthesized core/shell

structured ZnO/SiO2 microcomposites via a facilechemical route. The obtained samples were

characterized by transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), scanning electron

microscopy (SEM). The photocatalytic performance ofsamples were also studied with Methylenee blue.

Material and MethodsZinc acetate (Zn(CH3COO)2·2H2O), di-

ethylene glycol (C4H10O3), polyethylene glycol (400),

tetraethoxysilane (C8H20O4Si) and anhydrous ethanol(C2H5OH) were all bought from Merck. Methylene

Blue was purchased from Aldrich. All solutions were

prepared with distilled water.

http://www.ijrce.org/







[162]

Preparation of ZnO microparticles: 1.5 g zinc

acetate were dispersed for 30 minutes in 100 ml DEG.0.2 g of PEG and 100 ml ethanol was dispersed in a

separate place, each mixture was rapidly stirred in 500ml beaker and it was stirred for 24 hours at 100

oC.

White precipitates were washed with ethanol for three

times and centrifugation. Finally, the precursors weredried 24 h in oven and then ZnO microparticles were

obtained

Preparation of ZnO/SiO2 core/shell structured

nanoparticles: ZnO nanoparticles (obtained from theabove preparation in Section 2.2) were dispersed into

50 ml of ethanol and then slowly transferred into the

500 ml round bottom flask. An appropriate amount ofTEOS (5 ml) together with 25 ml of ethanol, 100 ml

water and 20 ml NH3·H2O were then added into thereaction flask. The mixture containing the ZnO,

TEOS, solvent, and NH3·H2O was stirred for 20h.

Products washed with ethanol for several times, andthen dried in oven at 120 ◦C for 4h.

Characterization of ZnO/SiO2 core/shell structurednanoparticles: The particles were characterized usingFourier transform infrared spectroscopy (FT-IR,Thermo Scientific Nicolet-İS10-ATR), X-ray

diffraction (XRD, Rikagu-Smart Lab), Scanning

electron microscopy (SEM, JEOL JSM 7600-F) andtransmission electron microscope (JEOL JEM 2100F

HRTEM).

Photocatalytic activity experimentThe photocatalytic degradations of Methylene Bluesolutions using prepared ZnO and ZnO/SiO2 particles

were investigated with the following process:

photocatalysts were added into Methylene bluesolution (0,1gr, for 50ml), and the provided suspension

was kept in a dark environment with stirring for 30min to allow the physical adsorption of MethyleneBlue on photocatalyst particles and then starting

photocatalytic working.

After that, the mixture was taken into the photoreactor for photocatalytic degradation. We

measured the UV – vis absorption of the clarified

solution at the wavelength for 600nm. Finally, the photocatalytic degradation was calculated using C/C0,where C is concentration of Methylene Blue in

sampled solution, C0 is concentration of MethyleneBlue in original solution.

Results and DiscussionFT-IR spectra: Figure 1 shows the FT-IR absorptionspectrum of pure ZnO, and ZnO/SiO2 microparticles,

respectively. The peak at 472cm−1 is the characteristicabsorption of Zn – O bond and the peaks at 3363 and1567cm−1 can be attributed to the absorption of water.It is also found that the ZnO/SiO2 microparticlesexhibit absorptions at 791 – 1046cm−1 as shown in Fig.

1(b) which could be ascribed to the characteristic Si – O – Si asymmetric stretching vibration

[16]. Thus we can

infer that SiO2 shells syntesized from the condensation

of TEOS were nicely covered onto the ZnO surface[17]

.

[a]

Figure 1: FT-IR spectra of pure ZnO particles(a)

and ZnO/SiO2 microparticles(b)

X-ray diffraction: The XRD spectra of pure ZnO,

and ZnO/SiO2 microparticles are shown in Figure 2.From Figure 2(a), a series of characteristic peaks:

2.832 (100), 2.617 (002), 2.488 (101), 1.918 (102),

1.630 (110) and 1.481 (103) are observed, and they arein accordance with the zincite phase of ZnO

(International Center for Diffraction Data, JCPDS).

After covering with SiO2 layer, did not change

the characteristic peaks of ZnO/SiO2 particles with thezincite phase of ZnO Figure 2(b), indicating that the

SiO2 did not affect the crystalline structure. As a

results, the diffraction peaks of amorphous SiO2 werenot observed. Similar to the working aboutCaCO3@SiO2 core – shell nanoparticles reported no

peaks of SiO2 shell in XRD spectra[18]

.

The SEM images of ZnO, ZnO/SiO2 microparticles are shown in Figure 3. Figure 3(a)




[163]

shows that ZnO microparticles are sized of 2-4µm.

Figure 3(b) shows the SEM of the surface modifiedZnO/SiO2 particles.

The average diameter of ZnO nanoparticles is

determined to be 2 – 4 µm and ZnO/SiO2 core shell

particles is about 3-5 µm. With the addition of SiO2

occurred in an increase in particle diameter, thethickness of SiO2 shell increases to 3 – 5 µm as shown

in Fig. 3(c,d).

Figure 2: XRD spectra of pure ZnO(a) and ZnO/SiO2 core shell (b) particles

Figure 3: SEM image of ZnO particles(a) and ZnO/SiO2 core shell microparticles(b,c,d)

a

b

a b

c d




[164]

Figure 4: TEM image of ZnO/SiO2 core shell microparticles (a,b)

PHOTOCATALYTİC REMOVAL OF MM

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100 120

İRRADİATİON TİME

P E R C E N

T A G E

O F

R E M O

V A L İ N G

ZnO

ZnO/SiO2

Figure 5: Photocatalytic Degradation of Methylene Blue for ZnO and ZnO/SiO2 particles

The TEM images of ZnO/SiO2 microparticles

are shown in Figure 4. Figure 4 shows that ZnO particles are in core and SiO2 particles are in surface.

We also that SiO2 particles are distributed on ZnO

surface homogenously.

Photocatalytic Degradation: ZnO, and ZnO/SiO2

microparticles were used as photocatalystsrespectively to degrade Methylene Blue dissolved in

water. Figure 5 shows the relationship between C/C0 and irradiation time for Methylene Blue in basicsolution photocatalyzed by ZnO and ZnO/SiO2

microparticles. Within 90 minutes, the photocatalyticdegradation of Methylene Blue is 13 and 68% in the

presence of ZnO, and ZnO/SiO2 microparticles. Thismeans that the modified ZnO/SiO2 microparticles have

higher photocatalytic activity. Although ZnOnanoparticles is a quite active photocatalyst, ZnOreactions with excessive OH

- in alkaline medium,

threrefore leading to the failure of photocatalytic

degradation of Methylene Blue. After ZnO wasmodified with SiO2, the stability of core/shell

structured ZnO/SiO2 microparticles was improved dueto the reduced contact of ZnO with [OH]

−[15].

ConclusionZnO and ZnO/SiO2 microparticles have been

prepared via a simple chemical method. FT-IR,

analysis showed that the successful covering of SiO2 on ZnO surface. The core/shell structure has beenverified by SEM images. The uncoated ZnO showed

weak photocatalytic activity in basic solution of

Methylene Blue. ZnO/SiO2 microparticles consisted ofZnO core and SiO2 shell showed a better

photocatalytic performance in alkaline solutions of

Methylene blue, because of the improved stabilitymodified by the SiO2 shell. This is thought to be a

candidate particles in removing pollutants.

References1. Liao Min-Hung, Hsu Chih-Hsiung, Chen Dong-Hwang,Preparation and properties of amorphous titania-coated zinc

oxide nanoparticles, Journal of Solid State Chemistry, 179,

2020 – 2026 (2006)

2. Kim S., Fisher B., Eisler H.J., Bawendi M., Type-IIquantum dots: CdTe/CdSe(core/shell) and

CdSe/ZnTe(core/shell) heterostructures, J. Am. Chem. Soc.,

125, 11466 – 11467 (2003)

3.Zhong C.J., Maye M.M., Core-Shell assembled

nanoparticales as catalysts, Adv. Mater., 13(19), 1507 – 1511

(2001)

4. Kislov N., Lahiri J., Verma H., Stefanakos D., Batzill M.,

Photocatalytic degradation of methyl orange over single

crystalline ZnO: orientation dependence of photoactivity and photostability of ZnO, Langmuir , 25, 3310 – 3315 (2009)

5. Daneshvar N., Salari D., Khataee A.R., Photocatalytic

degradation of azo dye acid red 14 in water on ZnO as an

alternative catalyst to TiO2, J. Photochem. Photobiol . A:Chem., 162, 317 – 322 (2004)

6. Pare B., Jonnalagadda S.B., Tomar H., Singh P., Bhagwat

V.W., ZnO assisted photocatalytic degradation of acridine




[165]

orange in aqueous solution using visible irradiation,

Desalination, 232, 80 – 90 (2008)

7. N. Daneshvar, S. Aber, M.S. Dorraji, Photocatalytic

degradation of the insecticide diazinon in the presence of

prepared nanocrystalline ZnO powders under irradiation ofUV-C light, Sep. Purif. Technol. 58, 91 – 98 (2007)

8. Honga Ruoyu, Pan Tingting, Qian Jianzhong, Li

Hongzhong, Synthesis and surface modification of ZnOnanoparticles, Chemical Engineering Journal , 119, 71 – 81

(2006)

9. Posthumus W., Magusin P.C.M.M., Brokken-Zijp J.C.M.,

A.H.A. Tinnemans, R. van der Linde, Surface modification

of oxidic nanoparticles using

3methacryloxypropyltrimethoxysilane, J. Colloid Interface

Sci., 269, 109 – 116 (2004)

10. Min B., Lee J.S., Hwang J.W., Keem K.H., Kang M.I.,

Cho K., Sung M.Y., Kim S., Lee M.-S., Park S.O., Moon

J.T., Al2O3 coating of ZnO nanorods by atomic layerdeposition, J. Cryst. Growth, 252, 565 – 569 (2003)

11. Grasset F., Saito N., Li D., Park D., Sakaguchi I., Ohashi N., Haneda H., Roisnel T., Mornet S., Duguet E., J. Alloys

Compd., 360, 298 (2003)

12. Zhang J., Liu Z., Han B., Li Z., Yang G., Li J., Chen J.,Preparation of silica and TiO2 – SiO2 core – shell nanoparticles

in water-in-oil microemulsion using compressed CO2 as

reactant and antisolvent, J. Supercrit. Fluids, 36, 194 – 201

(2006)

13. Bala H., Zhang Y., Ynag H., Wang C., Li M., Lv X.,

Wang Z., Preparation and characteristics of calcium

carbonate/silica nanoparticles with core – shell structure,Colloids Surf. A, 294, 8 – 13 (2007)

14. Maurice V., Georgelin T., Siaugue J.M., Cabuil V.,

Synthesis and characterization of functionalized core – shellFe2O3 – SiO2 nanoparticles, J. Magn. Magn. Mater., 321,

1408 – 1413 (2009)

15. Zhaia Jing, Taoa Xia, Pua Yuan, Zenga Xiao-Fei, Chenb

Jian-Feng, Core-shell structured ZnO/SiO2 nanoparticles:

Preparation, characterization and photocatalytic property,

Applied Surface Science, 257, 393 – 397 (2010)

16. Liden E., Beergstrom L., Person M., Carlsson R.,

Surface modification and dispersion of silicon nitride and

silicon carbide powders, J. Eur. Ceram. Soc., 7, 361 – 368

(1991)

17. Jaroenworaluck A., Sunsaneeyametha W., Kosachan N.,

Stevens R., Characteristics of silica-coated TiO2 and its UVabsorption for sunscreen cosmetic applications, Surf.

Interface Anal., 38, 473 – 477 (2006)

18. Zhang S., Li X., Synthesis and characterization ofCaCO3@SiO2 Core – shell nanoparticles, Powder Technol.,

141, 75 – 79. (2004).

zno - sio2 photolityc

Documents