Materials Letters 92 (2013) 376–378

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Materials Letters

0167-57

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E-m1 Co

Science

journal homepage: www.elsevier.com/locate/matlet

Shape controllable preparation and characterization of submicron lamellarand rod clusters of zinc oxide via conventional and microwave acceleratedreaction methods

Shafiqul Islam a, Mohammad Rezaul Karim a,n, Md. Badruz Zaman a,b,1

a Center of Excellence for Research in Engineering Materials, College of Engineering, King Saud University, Riyadh 11421, Saudi Arabiab Advanced Medical Research Institute, Health Science North, Sudbury, ON, Canada, P3E 5J1

a r t i c l e i n f o

Article history:

Received 4 June 2012

Accepted 4 September 2012Available online 12 September 2012

Keywords:

Zinc oxide

Nanoparticles

Semiconductors

Conventional reaction

Microwave accelerated reaction

7X/$ - see front matter & 2012 Elsevier B.V.

x.doi.org/10.1016/j.matlet.2012.09.021

esponding author. Tel.: þ966 14678677; fax

ail address: mkarim@ksu.edu.sa (M. Rezaul K

ntact details: The Advanced Medical Researc

s North, Sudbury, Ontario P3E 5J1, Canada.

a b s t r a c t

Zinc Oxide (ZnO) submicron lamellar and rod clusters with well-controlled morphologies have been

synthesized by conventional and microwave accelerated reaction methods. Zinc nitrate hexahydrate

and sodium hydroxide were used as a precursor. The pH of the precursor solution (zinc nitrate

hexahydrate) was increased by �12 via the controlled addition of sodium hydroxide (NaOH). Based on

electron microscopy images and X-ray Diffraction (XRD) patterns, the microwave accelerated reaction

method shows improved shape of controllable lamellar and flower like rod clusters.

& 2012 Elsevier B.V. All rights reserved.

1. Introduction

Zinc Oxide is the II–VI semiconductor with a wide band-gap of3.37 eV, which is a direct band-gap structure at room tempera-ture, and has an excitation binding energy of 60 meV [1–4]. Thecombination of high excitonic and biexcitonic oscillator strengthand high temperature characteristics make ZnO a promisingmaterial for optical applications. It has been used as a visibleand ultraviolet photoconductor and as a fluorescent material.Interests in ZnO have intensified as a result of its crystallographicproperties that could make it a suitable substrate for wide band-gap semiconductor devices for ultraviolet/blue/green lasers anddetectors as well [2,5,6]. Currently, ZnO nanoparticles have drawnenormous attention due to a wide range of applications. In mostof these cases, nanoparticles tend to agglomerate due to largespecific surface area as well as high surface energy [7]. In recentyears, microwaves assisted greatly in synthesis of nanomaterials;this has vast advantages over conventional method [8–10]. In thisarticle, we report the synthesis and characterization of ZnOnanocomposites by conventional and microwave acceleratedreaction methods that might make it an attractive candidate forvarious applications.

All rights reserved.

: þ966 14670199.

arim).

h Institute of Canada, Health

2. Experimental section

All stating materials were of analytic reagent grade and usedwithout further purification; De-ionized water was used as asolvent. Zinc nitrate hexahydrate [Zn(NO3)2 �6H2O] was pur-chased from Sigma-Aldrich and sodium hydroxide (NaOH) fromQualiKems.

Conventional synthesis: Sodium hydroxide (1 M) and Zn(NO3)2 �

6H2O (0.05 M) were dissolved in two 100 ml glass beakers with25 ml de-ionized water. Then NaOH (15 ml) was added whilestirring in Zn(NO3). Add 6H2O (25 ml) was added to a 100 mlround bottom flask. The reaction mixture was heated at 101 1Cover an oil bath for 15 min under constant stirring. Subsequentlythe solution was cooled to 40 1C and filtered through a 0.45 mmpore filter and dried in air.

Microwave synthesis: NaOH (1 M) and Zn(NO3)2 were mixedtogether. 6H2O (0.05 M) were prepared in two 100 ml glassbeakers with 25 ml of de-ionized water. Then NaOH (15 ml) wasadded and Zn(NO3) was stirred in. Add 6H2O (25 ml) in a 100 mlbeaker. The sample was irradiated by microwave energy using themicrowave oven (MARS5, CEM with 400 W power, temp 101 1C,time 8 min, under constant stirring). The solution was cooled to40 1C and filtered through a 0.45 mm pore filter and dried in air.

Characterizations: Several analytical techniques were used tocharacterize the synthesized products. The powder X-raydiffraction (XRD) patterns of the samples (as synthesized) wererecorded with a Japan Shimadzu XRD-700 X-ray diffract meterequipped with graphite monochromatized Cu Ka irradiation

S. Islam et al. / Materials Letters 92 (2013) 376–378 377

(l¼0.154056 nm). This employed a scanning rate of 0.021/s in the2y range of 25–751. Sizes and morphologies of the synthesizedproducts were observed with JEOL JSM-6610F Field-emissionscanning electron microscope (FE-SEM).

Fig. 1. FE-SEM images of ZnO samples from lower to higher magnification g

Fig. 2. FE-SEM images of ZnO samples from lower to higher magnification gradually

3. Result and discussion

FE-SEM images of ZnO nanorod from the conventional reactionmethod with different magnifications have been shown in

radually (a followed by b, c and d) synthesized by conventional system.

(a followed by b, c and d) prepared by microwave accelerated reaction methods.

30 40 50 60 70

(201

)

(200

)(1

12)(103

)

(110

)

(102

)

(101

)(0

02)

(100

)

(b)

(a)Inte

nsity

2 Theta (degree)

Fig. 3. XRD patterns showing the growth of ZnO-nanorod array synthesized in

(a) conventional and (b) microwave system.

S. Islam et al. / Materials Letters 92 (2013) 376–378378

Fig. 1(a–d). The ZnO at lower magnification bundles of sheet/cluster like lamellar structures (Fig. 1a). By increasing the magni-fication, the sheet-like lamellar shapes become clear and theaverage diameters of the sheet-like lamellar shapes are 3–4 mm(Fig. 1d).

FE-SEM images for microwave accelerated reactions withdifferent magnifications are displayed in Fig. 2(a–d). Interestingly,the ZnO shapes are different from the conventional reactionsystems (although the formulas are same). At a lower magnifica-tion, ZnO rods and clusters of flower shapes are clearly visible(Fig. 2a). The flower-like structures are more pronounced whenthe magnification is increased (Fig. 2c or d). The averagediameters of the flower-like shapes are 3–4 mm. From the topview, the regular hexagonal shape is clearly revealed and uniformin size of needle-like rods that are attached to the center. Thelength ranges from 400 to 800 nm with a width of approximately150 nm (as shown in Fig. 2d). These are quite different from thereported data [11–13].

In Fig. 3, the XRD pattern of the ZnO-nanorod arrays is shownfor both the conventional and microwave accelerated reactionmethod. The characteristic peaks are assigned to be (1 0 0),(0 0 2), (1 0 1), (1 0 2), (1 1 0), (1 0 3), (2 0 0), (1 1 2), and (2 0 1):this indicates synthesized sample having the typical hexagonal(wurtzite) phase of ZnO reported in JCPDS card (No. 36-1451)[14]. No other diffraction peaks of impurities are detected, whichsuggest that the samples have high phase purity. Synthesized in aconventional procedure, this shows characteristic peaks that

resemble the characteristic peaks of microwave synthesizedprocedure, but with a greater intensity.

The chemical purity and stoichiometry of the sample aretested by EDX. The EDX spectrum shows the presence of Zn andOxygen. The atomic percentage of Oxygen is 83.77 (55.82 wt.%)and Zn is 16.23 (44.18 wt.%) and the percentages of atomic weightof Oxygen and Zn are 80.15 (49.71 wt.%), 19.85 (50.29 wt.%) inconventional and microwave synthesis, respectably.

4. Conclusion

In this experiment, similar reaction parameters, such as feedmolar ratio of precursors, temperature, and reaction time, have beenperformed in two different reaction methodologies: conventionalchemical synthesis and microwave accelerated reactions techniques.We found that in comparison to the conventional chemical synthesismethods, the microwave accelerated reaction method demonstratedsuperior lamellar and rod clusters flower like ZnO morphologies.

Acknowledgment

The authors gratefully acknowledge the financial supportfrom NPST program by King Saud University of project number10-NAN1021-02.

References

[1] Irimpan L, Krishnan B, Deepthy A, Nampoori VPN, Radhakrishnan P. J ApplPhys 2008;103:033105.

[2] Geun-Hyoung L. Mater Lett 2012;73:53.[3] Huang MH, Mao S, Ferick H, Yan HQ, Yu YY, Kind H, et al. Science

2001;292:1897.[4] Cao Y, Liu B, Huang R, Xia Z, Ge S. Mater Lett 2011;65:160.[5] Irimpan L, Deepthy A, Krishnan B, Nampoori VPN, Radhakrishnan P. J Appl

Phys 2007;102:063524.[6] Samanta PK, Patra SK, Ghosh A, Chaudhuri PR. Int J Nanosci Nanotech

2009;1:81.[7] Chieng BW, Lee YY. Mater Lett 2012;73:78.[8] Ma MG, Zhu YJ, Cheng GF, Huang YH. Mater Lett 2008;62:507.[9] Bhatte KD, Sawant DN, Pinjari DV, Pandit AB, Bhanage BM. Mater Lett

2012;77:93.[10] Bhatte KD, Sawant DN, Watile RA, Bhanage BM. Mater Lett 2012;69:66.[11] Zhu J, Zhang J, Zhou H, Qin W, Chai L, Hu Y. Trans Nonferrous Met Soc China

2009;19:1578.[12] Kowsari E, Ghezelbash MR. Mater Lett 2012;68:17.[13] Kajbafvala A, Ghorbani H, Paravar A, Samberg JP, Kajbafvala E, Sadrnezhaad SK.

Superlattices Microstructures 2012;51:512.[14] Joint Committee on Powder Diffraction Standards, Powder Diffraction File No.

36-1451.