Application of ultrasonic irradiation method for preparation of ZnO nanostructures doped with Sb+3 ions as a highly efficient photocatalyst

Applied Surface Science 276 (2013) 468–475

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Application of ultrasonic irradiation method for preparation of ZnO nanostructures doped with Sb+3 ions as a highly efficient photocatalyst Amir Omidi, Aziz Habibi-Yangjeh ∗ , Mahsa Pirhashemi Department of Chemistry, Faculty of Science, University of Mohaghegh Ardabili, P.O. Box 179, Ardabil, Iran

a r t i c l e

i n f o

Article history: Received 19 January 2013 Received in revised form 14 March 2013 Accepted 19 March 2013 Available online 25 March 2013 Keywords: Ultrasonic irradiation Photocatalyst Sb-doped ZnO Nanostructure

a b s t r a c t Ultrasonic irradiation method was applied for preparation of Sb-doped ZnO nanostructures (0 ≤ mol fraction of Sb+3 ions ≤ 0.15) in water at 60 min without using any organic compound and additional post treatment. The nanostructures were characterized by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT-IR) and UV–vis diffuse reflectance spectroscopy (DRS) techniques. The results showed that the doping greatly changed morphology and size of the pure ZnO. Photocatalytic degradation of methylene blue (MB) on the nanostructures under UV irradiation and effects of various operational parameters were investigated. The results reveal that the maximum degradation occurs on the nanostructures with 0.03 mol fraction of Sb+3 ions. The rate constant increases with irradiation time up to 60 min and then decreases. The photocatalyst with 0.4 g/L have highest degradation rate constant. Moreover, the degradation rate constant decreases with calcinations of the nanostructures. The nanostructures have highest photocatalytic activity at pH 5.4. © 2013 Elsevier B.V. All rights reserved.

1. Introduction Organic dyes from industries such as textiles, printing, dyeing, and food are sources of environmental contamination [1,2]. Removal of these dyes from wastewaters is of a great importance nowadays, because the dyes and their degradation products are usually toxic and carcinogenic, posing a serious hazard to aquatic living organisms. Among many techniques applied for treatment of wastewaters (such as adsorption on various adsorbents, ultrafiltration and coagulation), heterogeneous photocatalysis has been considered as an effective method for environmental cleaning and remediation due to its potential to destroy a wide range of pollutants at ambient temperatures and pressures [3,4]. The interaction of light having energy equal to or higher than band gap of a photocatalyst excites electrons from the valence band to the conduction band, producing electron–hole pairs. The photogenerated electron–hole pairs are easy to recombine within a time scale of nanoseconds [5]. Hence, most of the electron–hole pairs recombine and only a small percentage of them migrate to the surface of photocatalyst where they can be captured by adsorbed molecules to start the catalytic reactions [6,7]. Therefore,

∗ Corresponding author. Tel.: +98 0451 5514702; fax: +98 0451 5514701. E-mail address: [email protected] (A. Habibi-Yangjeh). 0169-4332/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.apsusc.2013.03.118

to enhance the photocatalytic efficiency, it is essential to decrease the recombination of the charge carriers. ZnO is known as an important semiconductor that has been studied extensively in the past few years due to its applications in many fields [8,9]. Among various semiconductors applied in photocatalytic degradation of organic pollutants, nanomaterials of ZnO have been extensively used owing to their high photosensitivity, environmentally friendly feature, good stability, nontoxicity and low-cost [10,11]. With doping ZnO nanomaterials by various cations, the dopant can act as trapping sites to decrease the electron–hole recombination rate and then photocatalytic activity increases [12,13]. In recent years, many papers have been published about preparation of Sb-doped ZnO nanomaterials. Fang et al. prepared Sb-doped ZnO nanocolumns in presence of hexamethylenetetramine in aqueous solutions of ethanol at 90 ◦ C for 24 h and their photoluminescence properties were studied [14]. Sb-doped ZnO thin films were prepared by spin coating method and their structural and optical properties studied [15]. Palani et al. prepared Sb-doped ZnO nanostructures using pulsed laser deposition method at about 700 ◦ C using ZnO as target and Sb-coated Si as substrate and their surface and optical properties were investigated [16]. Zang et al. have fabricated ZnO:Sb nanobelt by thermal evaporation method at 680 ◦ C and recombination mechanism of acceptor-related emissions was investigated by temperature dependent photoluminescence spectra [17]. Carbothermal evaporation method was applied for preparation of Sb-doped ZnO

A. Omidi et al. / Applied Surface Science 276 (2013) 468–475

nanowires at 900 ◦ C [18]. Very recently, Rana et al. have prepared Sb-doped ZnO nanoparticles via direct precipitation method and calcined them at 500 ◦ C for 4 h and their optoelectronic properties were studied [19]. As can be seen, these methodologies employ harmful chemicals, high temperatures and complicate equipments. Therefore, it is highly desirable to prepare ZnO nanostructures doped with Sb+3 ions using green and template-free methods under mild conditions. In addition, photocatalytic degradation of organic pollutants by Sb-doped ZnO nanomaterials very rarely has been studied [20,21]. Ultrasonic irradiation method has proved extremely useful in preparation of various nanomaterials [22–24]. After irradiation of high power ultrasonic waves into a liquid, the solution shows a variety of chemical transformations [25]. The most important effect is acoustic cavitations: the formation, growth, and implosive collapse of bubbles. During the final stages of cavitation, the extreme local conditions caused by this process (5000 K, 20 MPa) followed by cooling with rate can reach 1010 K/s. The thickness of these regions is about 200 nm from the bubbles interface [25,26]. Due to the high temperature and pressure produced during the cavitation, crystallization of semiconductors can be facilitated. To the best of our knowledge, the preparation of Sb-doped ZnO nanostructures using ultrasonic irradiation method and investigation of their photocatalytic activity has not been reported. Hence, in this paper, a series of ZnO nanostructures doped with Sb+3 ions which their contents are ranging from x = 0.00–0.15 was prepared in water by ultrasonic irradiation for 60 min and they characterized with different techniques. Moreover, influence of various operational parameters (such as mole fraction of Sb+3 ions, ultrasonic irradiation time, catalyst weight, calcinations temperature and pH of solution) on photocatalytic activity of the nanostructures toward degradation of methylene blue (MB) was evaluated under UV irradiation. 2. Experimental 2.1. Materials Zinc acetate (Zn (CH3 COO)2 ·2H2 O, extra pure), antimony chloride (SbCl3 , extra pure), sodium hydroxide (NaOH), MB and absolute ethanol were obtained from Merck and employed without further purification. Double distilled water was used for the experiments.

by transferring the particles, which at first were dispersed in the ethanol to glass substrate attached to the SEM stage. After allowing the evaporation of ethanol from the substrate, the particles on the stage were coated with a thin layer of gold and palladium. Also, Fourier transform-infrared (FT-IR) spectra were obtained using Perkin Elmer Spectrum RX I apparatus. The pH of solutions was measured by Metrohm digital pH meter of model 691. 2.3. Preparation of the nanostructures In a typical procedure for preparation of the nanostructures, zinc acetate (4.2581 g) and antimony chloride (0.1368 g) were dissolved in 100 ml of distilled water under stirring at room temperature. Then, aqueous solution of NaOH (5 M) was slowly added dropwise into the solution under stirring at room temperature until pH of the solution reached to 13. The solution subsequently was irradiated in air for 60 min. The formed suspension was centrifuged to get the precipitate out and washed two times with double distilled water and ethanol, respectively to remove the unreacted reagents and dried in an oven at 60 ◦ C for 24 h. The schematic diagram for preparation of Sb-doped ZnO nanostructures has been illustrated in Scheme 1. 2.4. Photocatalysis experiments Photocatalysis experiments were performed in a cylindrical Pyrex reactor with about 400 ml capacity. The reactor provided with water circulation arrangement to maintain the temperature at 25 ◦ C. The solution was magnetically stirred and continuously aerated by a pump to provide oxygen and complete mixing of the reaction solution. A UV Osram lamp with 125 W was used as UV source. The lamp was fitted on the top of the reactor. Prior to illumination, a suspension containing 0.1 g of the nanostructures and 250 ml of MB (2.75 × 10−5 M) was continuously stirred in the dark for 30 min, to attain adsorption equilibrium. Samples were taken from the reactor at regular intervals and centrifuged to remove the photocatalyst before analysis by spectrophotometer at 664 nm corresponding to maximum absorption wavelength of MB. The adsorption capacity, qe (mol/g), of the nanostructures was calculated by a mass–balance relationship, which represents the amount of adsorbed dye per amount of the photocatalyst: qe =

2.2. Instruments The ultrasound radiation was performed using dr. heilscher high intensity ultrasound processor UP200H Germany (0.7 cm diameter Ti horn, 140 W, 23 kHz). The X-ray diffraction (XRD) patterns were recorded on a Philips Xpert X-ray diffractometer with Cu K␣ radiation ( = 0.15406 nm), employing scanning rate of 0.04◦ /s in the 2 range from 20◦ to 80◦ . Diffuse reflectance spectra (DRS) were recorded by a Scinco 4100 apparatus. Surface morphology and distribution of particles were studied via LEO 1430VP scanning electron microscopy (SEM), using an accelerating voltage of 15 kV. The samples used for SEM observations were prepared

469

(C0 − Ce )V W

(1)

where C0 and Ce are concentrations of the dyes in solution (mol/dm3 ) at t = 0 and time of equilibrium. V is the volume of the solution (dm3 ), and W is the weight of the nanostructures (g). The adsorption experiment was carried out in the dark to prevent photocatalytic degradation of MB. 3. Results and discussion Fig. 1 shows the XRD patterns for Sb-doped ZnO nanostructures, in which their mole fractions of Sb+3 ions are 0.00, 0.03, 0.06, 0.10 and 0.15. For pure ZnO, the diffraction peaks are in agreement with

NaOH Zn(CH3COO)2

pH=13 pH=13

mixing mixture

SbCl3

100 ml H2O

USI Sb(OH)3 + Zn(OH)2

Sb-doped ZnO 60 min

Scheme 1. The diagram for preparation of Sb-doped ZnO nanostructures.

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(e) X = 0.15

Transmittance

(d) X = 0.10

Intensity

X (c) = 0.06

(c)

(b)

X = 0.03

(a)

400

800

1200

1600

2000

2400

2800

3200

3600

4000

-1

Wavenumber (cm )

Fig. 2. The FT-IR spectra for Sb-doped ZnO nanostructures with various mole fractions of Sb+3 ions: (a) X = 0.00, (b) X = 0.03, (c) X = 0.06, (d) X = 0.10, and (e) X = 0.15. X (a) = 0.00

20

25

30

35

40

45

50

55

60

65

70

75

80

2 Theta (deg.)

Fig. 1. The XRD patterns for Sb-doped ZnO nanostructures with various mole fractions of Sb+3 ions: (a) X = 0.00, (b) X = 0.03, (c) X = 0.06, (d) X = 0.10, and (e) X = 0.15.

the JCPDS file of 36-1451, which can be indexed as a wurtzite hexagonal crystalline phase. No peaks attributable to possible impurities such as Zn(OH)2 are observed. The peaks are corresponding to (1 0 0), (0 0 2), (1 0 1), (1 0 2), (1 1 0), (1 0 3), (2 0 0), (1 1 2), (2 0 1), (0 0 4) and (2 0 2) planes of ZnO crystal system [27]. The XRD patterns for Sb-doped ZnO nanostructures are similar to pure ZnO and no peaks attributable to any Sb containing material are observed. Thus, it can be concluded that the doping of Sb+3 ions does not change the structure of ZnO. This confirms that the dopant would have substituted in the ZnO lattice without changing its structure [19]. In addition to identification of the crystalline phase, the XRD data were used to estimate average size of the crystallites by Scherrer’s equation [28]. The average particle sizes, D, were calculated using equation 2: D=



K B cos 



(2)

where  is the wavelength of X-ray radiation (0.15406 nm), K the Scherrer’s constant (K = 0.9),  the characteristic X-ray radiation (2 = 36.35◦ ) and B is the full-width-at-half-maximum of the (1 0 1) plane (in radians). The peak broadening in the higher mole fractions of Sb+3 ions indicates that the nanostructures are small in size. The average particle sizes of the nanostructures for various mole fractions of Sb+3 ions are in Table 1. As can be seen, the average particle sizes decreases with increasing mole fraction of Sb+3 ions. The decrease in the particle size is mainly attributed to the formation of Sb O Zn bonds on the surface of the doped nanostructures,

Table 1 Mean particle size (D), adsorption capacity (qe ) long with adsorption% of MB on Sb-doped ZnO nanostructures. No.

Mole fraction of Sb+3

D (nm)

qe (mol/g) × 10−5

Adsorption%

1 2 3 4 5

0.00 0.03 0.06 0.10 0.15

24.8 14.2 11.0 7.7 7.6

1.10 1.18 1.25 1.53 2.23

15.9 17.2 18.2 22.4 32.3

which hinders the growth of grains [29]. Similar results previously have been reported for Sb-doped ZnO nanomaterials [19]. The FT-IR spectra for the nanostructures with various mole fractions of Sb+3 ions in the range of 400–4000 cm−1 are shown in Fig. 2. The broad absorption bands in the range of 2900–3700 cm−1 are corresponding to the O H stretching vibration of adsorbed water on the nanostructures. The peaks about at 415 and 560 cm−1 are related to Zn O stretching mode [30]. Moreover, the peak at 680 cm−1 is corresponding to Sb O stretching vibration [31]. As can be seen, with increasing mole fraction of Sb+3 ions, the characteristic peaks corresponding to Sb O gradually increases. In order to elucidate the grain size and the morphology of the nanostructures, SEM images were taken and are shown in Fig. 3. It is evident that ZnO nanostructures are mainly plates with different sizes. For Sb-doped ZnO nanostructures, with increasing mole fraction of Sb+3 ions, the morphology and size of the nanostructures are changing. Similar to the XRD results, the decrease in the particle size is mainly attributed to the formation of Sb O Zn bonds on the surface of the doped nanostructures. The DRS of the nanostructures with different Sb+3 ions were obtained and the results shown in Fig. 4. The pure ZnO has an absorption maximum at 362 nm. Then, the nanostructures show blue shift relative to the bulk ZnO with absorption at 384 nm that can be attributed to quantum confinement effect of the nanocrystalline ZnO [32]. It can be seen that doping has a slight influence on the absorption spectrum of the pure ZnO. Decreasing concentration of MB in presence of various nanomaterials can be attributed to adsorption and photodegradation processes [33]. In order to compare ability of the nanostructures for adsorption of MB molecules, adsorption experiments were considered. To prevent photocatalytic degradation of MB, the adsorption experiments were carried out in dark. Plots of absorbance at 664 nm (corresponding to max of MB) for adsorption of MB on the nanostructures versus time are demonstrated in Fig. 5. The adsorption capacity (qe ) of the nanostructures was calculated using Eq. (1) after 120 min and the results tabulated (Table 1). Moreover, in Table 1, percent of MB adsorption on the nanostructures are shown. As can be seen, adsorption of MB on the nanostructures increases with mole fraction of Sb+3 ions. The SEM images demonstrated that size of the nanostructures decreases with the dopant content. Then, increase of MB adsorption on the nanostructures can be attributed to increase the surface area with decreasing grain size. Degradation of MB on the nanostructures with different mole fractions of Sb+3 ions have been demonstrated in Fig. 6. Moreover, photolysis of MB under UV irradiation without using any

A. Omidi et al. / Applied Surface Science 276 (2013) 468–475

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Fig. 3. The SEM images for Sb-doped ZnO nanostructures with various mole fractions of Sb+3 ions: (a) X = 0.00, (b) X = 0.03, (c) X = 0.06, (d) X = 0.10, and (e) X = 0.15.

photocatalyst, is shown in Fig. 6. As can be seen, photolysis of MB under UV irradiation with 125 W is very small. It is clear that Sbdoping resulted in a significant enhancement in the photocatalytic activity compared to the pure ZnO under UV irradiation. For pure ZnO, the degradation reaction is completed after 85 min. But, the complete degradation of MB on the nanostructures with 0.03 mol fraction of Sb+3 ions is occurred only at 40 min which is very less than the corresponding time for the pure ZnO.

Observed first-order rate constant of the degradation reaction (kobs ) can be calculated using Eq. (3) [34]: ln

[MB] = −kobs t [MB]◦

(3)

The rate constants for degradation of MB on Sb-doped ZnO nanostructures with 0.03 mol fraction of Sb+3 ions and pure ZnO are 10.1 × 10−2 and 3.46 × 10−2 min−1 , respectively. Then, doping of

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A. Omidi et al. / Applied Surface Science 276 (2013) 468–475 1.80 (a) X = 0.00 (b) X = 0.03 (c) X = 0.06 (d) X = 0.10 (e) X = 0.15

1.50

Absorbance

Absorbance

1.20

0.90

Photolysis

0.60

X = 0.00 X = 0.03 X = 0.06

0.30

X = 0.10 X = 0.15

290

340

390

440

490

540

590

640

0.00

690

-30

Wavelength (nm) Fig. 4. UV–vis DRS for Sb-doped ZnO nanostructures with various mole fractions of Sb+3 ions.

the ZnO nanostructures with Sb+3 ions, increases the reaction rate about three times. A limiting factor that controls the activity of photocatalysts is the rapid recombination of photogenerated electrons and holes [35]. Recombination of electron–hole pairs within a photocatalyst is reduced drastically with decreasing in the particle size [36]. Therefore, enhancing the photocatalytic activity by doping the ZnO nanostructures with a proper mole fraction of Sb+3 ions can be attributed to increasing the electron–hole life time. Hence, more charge carriers can reach to surface of the photocatalyst, where the degradation reaction takes place. Photocatalytic activity of the nanostructures with 0.06 and 0.10 Mol fractions of Sb+3 ions is lower than that of 0.03 (Fig. 6). In fact, excessive Sb+3 ions may act as recombination centers of electrons and holes, which lead to a decrease in the photocatalytic activity [37]. Moreover, the nanostructures with 0.15 Mol fraction of Sb+3 ions have high tendency for adsorption of MB (Table 1), then it is not proper photocatalyst for the degradation reaction. Then, the photocatalyst with 0.03 mol fraction of Sb+3 ions was selected as best one. The ultrasonic irradiation time can affect the extent of crystallization, aggregation and growth of the nanostructures. Hence, there is no straightforward relation between photocatalytic activity and time of the ultrasonic irradiation. In order to study the influence

-10

10

30

50

70

90

110

Irradiation time (min) Fig. 6. Photodegradation of MB under UV irradiation on Sb-doped ZnO nanostructures with various mole fractions of Sb+3 ions.

of irradiation time applied for preparation of the nanostructures with 0.03 mol fraction of Sb+3 ions, four comparative samples were prepared, keeping the reaction parameters constant except that the nanostructures were prepared by irradiations for 15, 30, 60 and 90 min. Photocatalytic degradation of MB on the nanostructures prepared with different irradiation times are demonstrated in Fig. 7. It is clear that the rate constant initially increases with irradiation time up to 60 min and then decreases (Fig. 8). Increasing the photocatalytic activity with irradiation time can be attributed to increasing crystallinity of the nanostructures. Further irradiation can increase size and aggregation of the nanostructures and hence the photocatalytic activity will be decrease. In order to study the effect of calcinations temperature on the degradation reaction rate, the nanostructures with 0.03 mol fraction of Sb+3 ions prepared by 60 min of ultrasonic irradiation calcined at 200, 300, 400 and 500 ◦ C for 2 h and the results were depicted in Fig. 9. Moreover, plot of the rate constant versus calcinations temperature is shown in Fig. 10. As can be seen, the rate constant decreases with calcinations temperature. The photocatalyst loses the surface area at higher temperature, 1.8 15 min 30 min

1.80

60 min

1.5

90 min

1.50 Absorbance

Absorbance

1.2

1.20

0.9

0.90 0.6

0.60 X = 0.00 X = 0.03 X = 0.06 X = 0.10 X = 0.15

0.30

0.3

0

0.00

-30

0

20

40

60

80

100

120

-10

10

30

50

70

90

140

time (min) Fig. 5. Plot of MB adsorption on Sb-doped ZnO nanostructures with various mole fractions of Sb+3 ions.

Irradiation time (min) Fig. 7. Photodegradation of MB on Sb-doped ZnO nanostructures prepared at various times of ultrasonic irradiation.

473

1.80

0.10

1.50

0.08

1.20

Absorbance

0.12

-1

kobs (min )

A. Omidi et al. / Applied Surface Science 276 (2013) 468–475

0.06

0.05 g 0.10 g 0.15 g 0.20 g

0.90

0.60

0.04

0.30

0.02

0.00

0.00

-30

0

20

40

60

80

-20

-10

0

10

Fig. 8. Plot of observed first-order rate constant of the degradation reaction on Sbdoped ZnO nanostructures versus ultrasonic irradiation time.

1.8 Room temp. 200 ºC 300 ºC 400 ºC 500 ºC

Absorbance

1.2

0.9

0.6

0.3

0 -30

-20

-10

0

10

20

30

40

50

60

30

40

50

60

70

Irradiation time (min)

Ultrasonic irradiation time (min)

1.5

20

100

70

80

90

Irradiation time (min) Fig. 9. Photodegradation of MB on Sb-doped ZnO nanostructures calcined at various temperatures.

Fig. 11. Photodegradation of MB on Sb-doped ZnO nanostructures (X = 0.03) with various weights.

because of aggregation and crystalline growth, therefore the photocatalytic activity decreases with calcinations temperature [38]. The weight of catalyst loading is one of the important parameters for the photocatalysis processes from economical point of view. For avoiding the use of excess catalyst, it is essential to determine the optimum loading for efficient degradation of MB. The optimum catalyst weight was obtained by changing weight of the nanostructures between 0.05 and 0.20 g. In Fig. 11, photodegradation of MB on the nanostructures with various weights was considered. As can be seen, the degradation increases with weight of the photocatalyst up to 0.10 g and then decreases. Increasing the degradation activity with amount of the photocatalyst may be due to increase in the surface area available for the reaction. However, more photocatalyst would also induce greater aggregation of the photocatalyst and the surface area will be decreased. Moreover, at higher weight of the photocatalyst, the scattering of light increases and reduction in light penetration through the solution occurs [39]. The solution pH plays an important role in the photocatalytic degradation of various pollutants. For this reason, influence of solution pH on the degradation reaction was studied by varying the initial pH from 2 to 13 (Fig. 12). It is clear that the degradation

0.12

1.80 pH = 2.0 pH = 3.5 pH = 5.4 pH = 7.0 pH = 9.0 pH = 11.0 pH = 13.0

0.10

1.50

1.20

Absorbance

-1

kobs (min )

0.08

0.06

0.90

0.04

0.60 0.02

0.30 0.00 0

50

100

150

200

250

300

350

400

450

500

550

o

Calcination temperature ( C)

0.00 -30

-20

-10

0

10

20

30

40

50

60

Irradiation time (min) Fig. 10. Plot of observed first-order rate constant of the degradation reaction on Sb-doped ZnO nanostructures versus calcinations temperature.

Fig. 12. Photodegradation of MB on Sb-doped ZnO nanostructures at various pH.

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References

100

%Degradation

80

60

40

20

0 1

2

3

4

Number of runs Fig. 13. Plot of degradation% of MB on the nanostructures at optimized conditions versus number of runs.

reaction at pH 5.4 is greater than those of the others solutions. The zero point charge pH for the photocatalyst will be about at 9 [40]. In acidic solutions, surface of the photocatalyst is positively charged. In these solutions, repulsive force between the photocatalyst and the cationic dye will lead to decrease in MB adsorption on the catalyst. Moreover, similar our previous findings, the nanostructures can dissolve in acidic solutions [38]. In alkaline solutions, surface of the photocatalyst is negatively charged. Then, adsorption of MB with positive charge on the negatively charged photocatalyst increases. As can be seen in Fig. 12, after 30 min in dark, adsorption of MB on the nanostructures at pH 13 and 11 are higher than those of the other solutions. Therefore, alkaline solutions are not proper for degradation of MB on the nanostructures. In order to know reusability of the photocatalyst, the degradation experiments were carried out in optimized conditions. The solution resulting from the photocatalytic degradation of MB was filtered, washed and the photocatalyst was dried. The dried catalyst was used for the degradation under similar conditions. The photocatalyst exhibited 92% of activity after four successive cycles under UV irradiation Fig. 13.

4. Conclusions Nanostructures of ZnO doped with Sb+3 ions with dopant content ranging from x = 0.00 to 0.15 were prepared in water using 60 min ultrasonic irradiation. The nanostructures were characterized by XRD, FT-IR, SEM and DRS techniques and their photocatalytic activity for degradation of MB under UV irradiation systematically was studied. Doping the ZnO nanostructures with 0.03 Mol fraction of Sb+3 ions increases the reaction rate about three times. Enhancing the photocatalytic activity by doping with a proper mole fraction of Sb+3 ions was attributed to decreasing recombination of charge carriers. The rate constant increases with weight of the photocatalyst up to 0.10 g and then decreases. The photocatalytic activity increases with ultrasonic irradiation up to 60 min and then decreases. The photocatalyst retains 92% of activity after four cycles.

Acknowledgement The Authors wish to acknowledge University of Mohaghegh Ardabili, for financial support of this work.

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