Formation of silver iodide nanoparticles on silk fiber by means of ultrasonic irradiation

Ultrasonics Sonochemistry 17 (2010) 704–710

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Formation of silver iodide nanoparticles on silk fiber by means of ultrasonic irradiation Amir Reza Abbasi, Ali Morsali * Department of Chemistry, Faculty of Sciences, Tarbiat Modares University, P.O. Box 14155-4838, Tehran, Islamic Republic of Iran

a r t i c l e

i n f o

Article history: Received 12 June 2009 Received in revised form 28 November 2009 Accepted 3 January 2010 Available online 7 January 2010 Keywords: Silver iodide Nanoparticle Silk fiber Ultrasound

a b s t r a c t The growth of silver iodide nanoparticles on silk fiber was achieved by sequential dipping in an alternating bath of potassium iodide and silver nitrate under ultrasound irradiation. Some parameters such as effect of pH, concentration and numerous sequential dipping in growth of the nanocrystal have been studied. The samples were characterized with powder X-ray diffraction (XRD), scanning electron microscopy (SEM), ICP, TGA and solid state UV–vis spectroscopy. Ó 2010 Elsevier B.V. All rights reserved.

1. Introduction In the recent years the preparation and application of nanometer sized materials have been of major interest since they exhibit special industrial properties [1]. Inorganic materials have broad application in materials chemistry and it is well documented that the properties of inorganic nano-materials depend strongly on their size and morphologies. The design and controlled synthesis of nanostructures with different size and morphologies is very important from the viewpoint of both basic science and technology [2–5]. Silver iodide is an important material used in photography, medicine [6], electronic, magnetic, optical, catalytic properties [7] for a variety of metals and semiconductors. Another application of silver iodide nanoparticles is its potential antibacterial effect. Silk fibroin is one of a number of materials that are possible candidates for biomedical applications, because it has good biocompatibility and minimal inflammatory reaction. Many technologies have been explored to fabricate silver halides nanostructures. These technical approaches can be grouped in several ways such as the electrospinning method [8], template synthesis [9], the microemulsion method [10,11], reverse micelles [12], laser-based synthesis [7], host–guest nanocomposite material [13] and ultrasonic spray pyrolysis [14]. Sonochemistry is the research area in which molecules undergo a chemical reaction due to the application of powerful ultra-

* Corresponding author. Tel.: +98 21 82884416; fax: +98 21 88009730. E-mail address: [email protected] (A. Morsali). 1350-4177/$ - see front matter Ó 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.ultsonch.2010.01.002

sound radiation. Sonochemical reactions vary in size, shape, structure and in their solid phase (amorphous or crystalline), but they always produce products of nanometer size [15,16]. The effect of ultrasonic irradiation on chemical reactions is to accelerate them and to initiate new reactions that are difficult to carry about under normal conditions [17,18]. The effects of ultrasound radiation on chemical reactions have been reported in the recent work, and it has been shown that there are two regions of sonochemical activity [19–21], the inside of the collapsing bubble, and the interface between the bubble and the liquid. If the reaction takes place inside the collapsing bubble and water is used as the solvent, the product obtained in this case will be amorphous as a result of the high cooling rates (>1010 K s 1) reached during collapse [21,22]. On the other hand, if the reaction takes place at the interface, one expects to get nanocrystalline products. If the solute is ionic, and hence has a low vapor pressure, then during sonication the amount of the ionic species will be very low inside the bubble and little product is expected to occur inside the bubbles [23,24]. In this paper, we have developed a simple sonochemical method to prepare nanoparticles of AgI on silk fiber. Some parameters such as the effect of pH, concentration of raw materials and numerous sequential dipping in growth of the AgI nanoparticles have been studied. Compared with non-sonochemical methods [25], the advantage of using ultrasound radiation is that it doesn’t need high temperatures during reaction, the use of surfactants is not necessary, increased density of nanoparticles on silk fibers occurs and it yields smaller particles [26,27].

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COOH

COOH

COOH

COO-

COOH

COO-

OH-

Silk fiber

COO-

COO-

Silk fiber -OOC

-OOC

-OOC

-OOC

COOH

COOH

COOH

COOH

Ag+ I-

I(Ag++ I)-

Ag+ COO-

COO-

n

Ag+

Ag+

COO-

COO-

Ag+

COO-

Ag+

COO-

Ag+ COO-

COO-

ISilk fiber

Silk fiber -OOC

-OOC

-OOC

(Ag++ I)- n

-OOC

Ag+ I-

Ag+

-OOC

Ag+

-OOC

-OOC

Ag+

Ag+

-OOC

Ag+

I-

Fig. 1. Schematic representation of the formation mechanism of AgI nanoparticles upon silk fiber.

2. Experimental All reagents used were supplied by Merck chemical company and used without further purification. Powder X-ray diffraction (XRD) was carried out on a Philips diffractometer of X’pert Company with monochromatized CuKa radiation. The samples were characterized with a scanning electron microscope (SEM) (Philips XL 30) with gold coating. The thermal behavior was measured with a PL-STA 1500 apparatus. TGA and DTA curves were recorded using a PL-STA 1500 device manufacture by Thermal Science. Sonication was carried out on a SONICA-2200 EP. The contents of silver iodide nanoparticles on the prepared silk fibers were measured by Inductive Coupled Plasma (ICP) carried out on a VARIAN, VISTA-PRO and detector: CCD Simultaneous ICP-OES. The solid state UV–Vis was measured with PG Instruments, T80 + UV/vis/ NIR Spectrometer.

The growth of AgI nanocrystals using an ultrasonic method was prepared as described in the literature [6,20]. The number of dipping steps was 10, 20 and 28 and fiber was dipped 5 (cycle 5), 10 (cycle 10) and 14 (cycle 14) times in silver nitrate and in potassium iodide solutions in definite pH. After each dipping, silk fibers were rinsed in distilled water for 1 min. At the end of the deposition process the samples were dried 1–2 h in an oven at 60 °C. 3. Results and discussion The growth of silver iodide nanoparticles on silk fiber was achieved by sequential dipping in an alternating bath of potassium iodide and silver nitrate under ultrasound irradiation. In alkaline pH, the surface of the silk fiber becomes negatively charged due to the deprotonation of the carboxylic group present at the fiber’s surface [26]. When negative silk was immersed in aqueous AgNO3,

Table 1 Experimental conditions, average diameter and contents of AgI nanoparticles on the silk fibers in various cycles and concentrations.

a b c

Sample [AgNO3] (ppm)

[KI] (ppm)

pH Average particle size

Cycle 5a

Average particle size

Cycle 10a

Average diameter (nm)

Cycle 14a

Average particle size (nm)

1a 2a 3a 4a 1b 2b 3b 4b Blankc

1 1 1 1 1 2.5 1 2.5 1

8 9 12 14 9 9 9 9 9

– – – – 0.2976b 0.2162 0.0793 0.0939 –

– – – – 45.56 58.80 91.29 70.80 –

– – – – 0.3464 0.4480 0.2739 0.3047 0.3102

– – – – 99.80 54.90 50.96 44.59 287.35

– – – – 1.011 0.6366 0.8313 0.6406 –

– – – – 71.80 49.60 41.97 42.10 –

1 1 1 1 1 1 2.5 2.5 1

Number of dipping steps, ICP measurement (ppm), Without ultrasound irradiation.

66 69.5 81.46 182.5 – – – – –

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silver ions were impregnated into the silk fibers through the surface. Most of the incorporated Ag+ ions were bound to silk fiber probably via electrostatic interactions, because the electron-rich atoms of the polar carboxylic group and ether groups of silk fiber

are expected to interact with electropositive transition metal cations [25]. Rinsing by doubly-distilled water effectively removed 0.14 0.12

4a

Abs.

0.1 3a

0.08 0.06

2a

0.04 0.02 0 180

1a

200

220

240

260

280

300

320

Wavelength (nm) Fig. 3. Absorption spectra of 2b-AgI nanoparticles in various pH (1a: pH = 8, 2a: pH = 9, 3a: pH = 12, 4a: pH = 14).

Fig. 2. SEM photographs of the AgI nanoparticles in various pH (a: pH = 8, b: pH = 9, c: pH = 12, d: pH = 14, the scale bar is 1 and 2 lm).

Fig. 4. SEM photographs of the AgI-1b nanoparticles in various cycles (1b: cycle 5, pH = 9; 1b: cycle 10, pH = 9; 1b: cycle 14, pH = 9, the scale bar is 1 lm).

A.R. Abbasi, A. Morsali / Ultrasonics Sonochemistry 17 (2010) 704–710

those Ag+ ions that were not attached to silk fibers. The dipping step in the KI solution allows for the formation of the AgI complex and initiates the formation of new AgI particles, as illustrated in Fig. 1. The alternating dipping steps lead to the growth of AgI particles which were confirmed to be nanometric. At the end of the deposition process the samples were dried for 1h in the oven at 65 °C. Some of parameters such as effect of pH, concentration and numerous sequential dipping in growth of the nanocrystal were studied. Various conditions for preparation of AgI nanoparticles on silk fibers in various cycles and concentrations were summarized in Table 1. 3.1. pH effects

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bance reflects both the high AgI concentration and particle size on the surface of fibers [11,26,28].

3.2. Sequential dipping effect Effect of different sequential dipping in growth of the nanoparticles were studied in pH = 9 (Figs. 4–7). Results suggest that with an increase in the silk fiber dipping steps in the KI and AgNO3 solution causes an increase in reaction time, with the subsequent result that the size of particles is decreased (Figs. 4–7). This decrease in the particle size is captured by the decrease of UV absorption (Fig. 8).

Fig. 2 shows an increase in particle size with an increase in pH at a constant concentration. Higher pH leads to more deprotonation of the carboxylic groups of the fiber’s surface and resulting higher formation of AgI on silk surface. Fig. 3 shows an increase in the absorbance with an increase in pH. The increase of the absor-

3.3. Concentration effects

Fig. 5. SEM photographs of the AgI-2b nanoparticles in various cycles (2b: cycle 5, pH = 9; 2b: cycle 10, pH = 9; 2b: cycle 14, pH = 9, the scale bar is 1 lm).

Fig. 6. SEM photographs of the AgI-3b nanoparticles in various cycles (3b: cycle 5, pH = 9; 3b: cycle 10, pH = 9; 3b: cycle 14, pH = 9, the scale bar is 1 lm).

Fig. 9 shows the solid state absorption spectra of the concentration effect on particles size. The results show a decrease in the absorbance as the moles of raw reagent.are increased. This de-

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0.09 0.08 0.07

Abs.

0.06 0.05 0.04 0.03

1b- C. 14 2b- C. 14 3b- C. 14 4b- C. 14

0.02 0.01 0 180

200

220

240

260

280

300

Wavelength (nm) Fig. 9. Absorption spectra of the AgI nanoparticles for cycle of 14 (1b: cycle 14, pH = 9; 2b: cycle 14, pH = 9; 3b: cycle 14, pH = 9; 4b: cycle 14, pH = 9).

crease in the absorbance reflects the decrease in the particle size [10,29,30], as confirm by SEM photographs (Figs. 4–7).

Fig. 7. SEM photographs of the AgI-4b nanoparticles in various cycles (4b: cycle 5, pH = 9; 4b: cycle 10, pH = 9; 4b: cycle 14, pH = 9, the scale bar is 1 lm).

0.12

3b- C. 5

0.1

3b- C. 10

18 16 14

3b- C. 14

0.06

% Frequency

Abs.

0.08

0.04

12 10 8 6 4

0.02

2

0 180

0 100-170

210

240

270

300

330

360

Wavelength (nm) Fig. 8. Absorption spectra of the AgI-3b nanoparticles for various cycles (3b: cycle 5, pH = 9; 3b: cycle 10, pH = 9; 3b: cycle 14, pH = 9).

171-240

241-310

311-380

381-450

451-520

521-590

Diameter (nm)

Fig. 10. SEM photographs and the corresponding particle size distribution histograms of the AgI particles without ultrasound method (the scale bar is 2 and 10 lm).

A.R. Abbasi, A. Morsali / Ultrasonics Sonochemistry 17 (2010) 704–710

3.4. Ultrasound effects In order to investigate the role of ultrasound on the nature of products, one of the reactions was performed without ultrasound irradiation. In this reaction, AgI particles on silk fiber were prepared by sequential dipping without ultrasound irradiation. The SEM results (Fig. 10) show high agglomeration and larger particles size. The average particle size for blank sample is over 287 nm, while, the average particle size using ultrasound processing is

709

55 nm. One advantage of using ultrasound in these reactions is that smaller particle sizes are produced. Fig. 11 shows the powder XRD of samples (1a and 2a) and the characteristic peaks corresponding to the AgI crystals, which was identified as chlrorargyrite. The six major peaks found at 22.32°, 23.70°, 25.35°, 39.20°, 42.63° and 46.31° on the 2 theta scale correspond respectively to the (1 0 0), (0 0 2), (1 0 1), (1 1 0), (1 0 3) and (1 1 2) crystal planes. The result indicated that AgI formed on the silk fibers and the crystalline phase of AgI is hexagonal, space groups Fm3m with the lattice parameters a = 3.1442 Å, c = 4.777 Å, z = 1, which are close to the reported values (JCPDS cards number 44–1482). Estimated from the Sherrer formula, D = 0.891k/b cos h, where D is the average crystallite size, k is the X-ray wavelength (0.15405 nm), and h and b are the diffraction angle and full-width at half maximum of an observed peak, respectively [12,31–33], the average size of the crystals of sample number 1 was 35.6 nm. The first peak at 20° corresponds to the silk substrate [15]. For further demonstration, the EDS analysis was performed for 2b-Cycle 14. It indicated that the elements of Ag and I in the products were homogeneously distributed. The EDS spectrum shows the presence of Ag+ and I as the only components (Fig. 12). The contents of silver iodide nanoparticles on the silk fibers were measured by ICP. The data were summarized in Table 1. Thermal gravimetric (TG) and differential thermal analyses (DTA) of sample 2b (as example) were carried out between 40 and 610 °C in a static atmosphere of nitrogen (Fig. 13). The decomposition occurs between 40 and 600°C that probably due to silk material.

Fig. 11. XRD pattern of the AgI nanoparticles at the surface of the silk fibers.

4. Conclusion Silk fiber container silver iodide nanoparticles were prepared by ultrasound using a sequential dipping method. The effect of some parameter, such as pH, concentration, and the numerous sequential dipping steps in growth of the nanometric AgI were studied. XRD analyses indicated that the prepared AgI nanoparticles on fiber were crystalline in structure. These systems depicted a decrease in the absorption peak accompanying a decrease in the particle size as confirmed by the SEM photographs and the corresponding particle size distribution histograms. In addition to the particle size and concentration, the size and location of the UV absorption peaks and shoulders are function of pH and sequential dipping. The lower average size of AgI on silk fiber is the result of using ultrasound irradiation. Acknowledgement

Fig. 12. Energy-dispersive X-ray analysis of compound 2b–Cycle 14.

Support of this investigation by Tarbiat Modares University is gratefully acknowledged. References

Weight of loss (%)

120

DTA

100 80 60 40 20 0 0

200

400

600

12 10 8 6 4 2 0 -2 -4 -6 -8 800

Temperature (°C) Fig. 13. TG and DTA of the AgI nanoparticles in pH = 9.

Δ t(°C)

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