ORI GIN AL PA PER

Synthesis of Monodisperse Lanthanum HydroxideNanoparticles and Nanorods by Sonochemical Method

Masoud Salavati-Niasari • Ghader Hosseinzadeh •

Omid Amiri

Received: 18 January 2012 / Published online: 3 March 2012

� Springer Science+Business Media, LLC 2012

Abstract In this work, monodisperse nanoparticles and nanorods of lanthanum

hydroxide was synthesized from the reaction of lanthanum(III) nitrate and sodium

hydroxide by sonochemical method. The effect of some of the parameters such as

feeding rate of precursors, different solvents of reaction, time of sonication, and

various surfactants on the particle size and morphology of products was studied. The

as-prepared products were characterized by X-ray diffraction, field emission scan-

ning electron microscopy, transmission electron microscopy.

Keywords La(OH)3 � Sonochemical � Nanoparticles � Nanorods �Monodisperse

Introduction

The synthesis, production and manipulation of nanocrystals (crystals with at least

one dimension (1D) between 1 and 100 nm) is currently one of the favorable areas

of research which also attracts the industrialists for designing and fabricating new

functional materials with novel special properties [1, 2]. As the properties of

nanostructures depend to their shape and size, therefore the ability to prepare

nanostructures with various shapes is central to advances in many areas of modern

science and technology. Among the nanostructures with various shape 1D

nanostructures such as wires, rods, belts and tubes have unique properties and

applications and therefore have become focus of intensive research in the field of

nanotechnology [3, 4]. Because of their unique electronic configuration [4f elec-

trons] lanthanides have been applied in various fields; these lanthanide-based

M. Salavati-Niasari (&) � G. Hosseinzadeh � O. Amiri

Institute of Nano Science and Nano Technology, University of Kashan,

P.O. Box. 87317-51167, Kashan, I. R. Iran

e-mail: salavati@kashanu.ac.ir

123

J Clust Sci (2012) 23:459–468

DOI 10.1007/s10876-012-0454-2

materials have also attractive and interesting magnetic [5], optical [6, 7], electrical

and therapeutic [8] properties. Among the lanthanides, lanthanum has been

extensively examined for its unique properties [9–14]. And lanthanum have been

synthesized in various compositions such as La(OH)3 [15], LaF3 [16], La2(CO3)3

[17], LaPO4 [18–20], LaBO3 [21], LaOF [22], La2Sn2O7 [23], La2O3 [24]

nanoparticles.

Although many methods have been developed for the synthesis of lanthanum

nanostructures including hydrothermal [25], solvothermal [26], micro emulsion or

reverse micelles [27], sol gel [28], laser deposition [29] and other chemical and

physical methods; some of these methods are affected by long reaction time, high

temperature, high pressure, expensive surface materials (surfactant) and so on.

In 1999 a simple, effective and novel route, i.e. sonochemical method, was developed

to prepare nanostructures [30]. Recently, Li et al. have successfully prepared ZnO

nanorod/Ag nanoparticle composites via sonochemical process [31]. Zhu and coworkers

[32] have used a sonochemical method for synthesized MnO2 nanoparticles inside the

pore channels of carbon. Nanosized copper aluminate particles were synthesized using a

precursor method with the aid of ultrasound irradiation [33].

In this work monodisperse, lanthanum hydroxide nanoparticles and nanorods were

successfully prepared from the reaction of lanthanum nitrate and NaOH by sonochem-

ical method. In addition, the effect of some of the parameters such as feeding rate of

precursors, different solvents of reaction, time of sonication, and various surfactants on

the particle size and morphology of products were examined. As-prepared products

were characterized by powder X-ray diffraction (XRD), field emission scanning

electron microscopy (FESEM(transmission electron microscopy (TEM).

Experimental

Materials and Physical Measurements

All the chemicals reagents used in our experiments were of analytical grade and

were used as received without further purification. A multiwave ultrasonic generator

(Sonicator 3000; Bandeline, MS 72, Germany), equipped with a converter/

transducer and titanium oscillator (horn), 12.5 mm in diameter, operating at

20 kHz with a maximum power output of 60 W, was used for the ultrasonic

irradiation. The ultrasonic generator automatically adjusted the power level. The

wave amplitude in each experiment was adjusted as needed. A Rigaku D-max C III,

XRD using Ni-filtered Cu Ka radiation, recorded XRD patterns. FE-SEM images

were obtained on LEO 1455VP equipped with an energy dispersive X-ray

spectroscopy. TEM images were obtained on a Philips EM208 transmission electron

microscope with an accelerating voltage of 100 kV.

Preparation Procedure

To prepare, lanthanum nitrate solution 130 mg La(NO3)3.6H2O (Aldrich) was

dissolved in 25 ml water and sodium hydroxide solution was prepared by dissolving

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of 72 mg NaOH (Merck) in 25 ml water. NaOH solution was added to the under

sonication lanthanum nitrate solution drop wise at a rate of 2 ml/min. To investigate

the effect of sonication time, solution was sonicated at various times according to

Table 1. We also examined the effects of feeding rate, different solvents, and

various surfactants (Table 1). Note that in investigation of feeding rate effect we

added NaOH solution at various rate to the under sonication lanthanum nitrate

solution and in examination of different solvent effect we dissolved NaOH at

various solvents (methanol, ethanol, and acetone) and then added this solution to the

under sonication lanthanum nitrate solution. In consideration of surfactant effect

various surfactants (CTAB = Cetyl trimethylammonium bromide, SDS = Sodium

dodecyl sulfate, and PVP = Poly(vinylpyrrolidone)) was added to lanthanum nitrate

solution before the sonication. In all of the above condition, the resulted products

were collected by centrifuge, were washed several times with distilled water, and

were dried at 50 �C in oven.

Results and Discussion

Shown in Fig. 1a is the wide-angle XRD pattern of sample no. 2. All of the

diffraction peaks can be indexed to the hexagonal structure of La(OH)3 (space group

P-3m1) which is very close to the values in the literature (JCPDS no. 36-1481 with

cell constant a = 6.5286 A, b = 6.5286 A and c = 3.8588 A). The broadening of

Table 1 Experimental condition for the preparation of La(OH)3 nanoparticles and nanorods

Sample no. Time (min) Feeding rate

(ml/min)

NaOH in 25ml Surfactant Surfactant (mg)

1 20 2 Water PVP 100

2 30 2 Water PVP 100

3 40 2 Water PVP 100

4 50 2 Water PVP 100

5 30 2 water PVP 100

6 30 2 Acetone PVP 100

7 30 2 Ethanol PVP 100

8 30 2 Methanol PVP 100

9 30 1 Water PVP 100

10 30 3 Water PVP 100

11 30 4 Water PVP 100

12 30 5 Water PVP 100

13 30 2 Water CTAB 109

14 30 2 Water CTAB 218

15 30 2 Water SDS 434

16 30 2 Water SDS 868

17 30 2 Water PVP 100

18 – 2 Water PVP 100

Synthesis of Monodisperse Lanthanum Hydroxide 461

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the peaks indicated that the particles were of nanometric scale. The average particle

size of the obtained products was about 15 nm which was estimated from Debeys–

Scherrer equation: Dc = Kk/bcosh; where b is the breadth of the observed diffraction

line at its half-intensity maximum, K is the so-called shape factor, which usually takes

a value of about 0.9, and k is the wavelength of X-ray source used in XRD [34].

Figure 1b shows the XRD pattern of lanthanum hydroxide nanorods, sample no. 12.

From which we concluded that the La(OH)3 with high purity obtained and the pattern

matches with hexagonal structure (space group P-3m1 with cell constant a = 6.5286

A, b = 6.5286 A and c = 3.8588 A, JCPDS no.36-1481), the sharp diffraction peaks

of sample indicated that well crystallized lanthanum hydroxide crystals can be

obtained under current synthetic procedure. The broadening of the peaks indicated that

the particles were of nanometer scale. For lanthanum hydroxide nanorods, the

intensity ratio between the (100) and the (110) diffractions is 0.85, and between the

(100) and the (101) diffractions is 1.19 which is significantly smaller than the

conventional bulk intensity ratios (1.38 and 2.12, respectively) and lanthanum

hydroxide nanoparticles ratios. This trend reveal that there is a direct relation between

XRD patterns and shape of nanostructures because preferential growth of one face

cause formation of specific shape and in the case of La(OH)3 this preferential growth

along the [100] direction forms 1D structure [35–37].

Figure 2 shows TEM image of lanthanum hydroxide nanorods, sample no. 12,

also shows that the average aspect ratio of rods is about 6 nm and diameter of rods

is 1 nm. According to 1D growth mechanism that was proposed in Cheon et al.

review the surface energy of the crystallographic faces of a seed strongly effects the

anisotropic growth of nanocrystals [38] and in the case of La(OH)3 surface energy

of (100) face in mixed solvents is larger than those of other faces. Since the growth

rate of crystals is exponentially depended to the surface energy, such surface energy

differences causes’ fast growth along the [-100] direction resulting nanorods

elongated along [-100] direction.

According to classical nucleation theory (CNT) [39, 40], in obtaining monodis-

perse structures, saturation ratio must be constant and for this propose continues

Fig. 1 XRD patterns of sample no. 2 (a) and sample no. 12 (b)

462 M. Salavati-Niasari et al.

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Fig. 2 TEM images of sample no. 12

Fig. 3 SEM images of La(OH)3 nanoparticles: a sample no. 1, b sample no. 2, c sample no. 3, andd sample no. 4

Synthesis of Monodisperse Lanthanum Hydroxide 463

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source of precursors has needed. In this work we added NaOH solution drop wise so

that the saturation ratio of La(OH)3 in solution were kept constant and by this way

we obtained monodisperse nanostructures. And according to nucleation and growth

mechanism of LaMer [41, 42] for obtaining ultrafine structures concentration of

La(OH)3 in solution should be above minimum limit of nucleation. In this way the

added precursors will consumed to generate nuclei and more nuclei will produced,

the more the nuclei the low the growth, with adding drop wise we don’t allow the

concentration of La(OH)3 to rich the minimum of nucleation and we obtained

ultrafine structures. In this work, the role of sonication is preventing from secondary

growth (i.e. agglomeration).

In addition, some other conditions were examined to investigate the morphology

of products, if any, and compare them with each other. One of key parameters,

which can be effective on particle size, is sonication time. Figure 3 shows

sonication time effects on the size and morphology of nanoparticles from the image

we concluded that there is an optimum time for sonication because in low sonication

time (Fig. 3a), we have agglomerated particles. Because power of sonication is not

sufficient for separate them. On the other hand, in high sonication times (Fig. 3c, d),

collision of particles occurs and particles stick with together. Therefore we chose

30 min (Fig. 3b) as an optimum time for preparation of La(OH)3 nanoparticles

because resulted particles are monodisperse, and fine.

Fig. 4 SEM images of La(OH)3 nanoparticles: a sample no. 5, b sample no. 6, c sample no. 7, andd sample no. 8

464 M. Salavati-Niasari et al.

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For investigating the effects of feeding rate, we carried out the experiment in

different feeding rats of 1, 2, 3, 4, and 5 ml/min. From Fig. 5a–d we see that with

increasing of feeding rate, size of nanoparticles increase. Figure 5a shows the

lowest feeding rate effect in this condition very fine particles can obtained but this

particles are very unstable and agglomerated with together and ultrasonic power

isn’t sufficient to separate them from one another. Figure 3b shows optimum

feeding rate because we have fine, monodisperse, and separated particles.

The effects of various mixed solvents have been shown in Fig. 4. From this

image we can see that in mixed solvents an obvious shape change occurs and rod

like morphology obtain. With increasing vapor pressure of solvents (Fig. 4 a–d) the

aspect ratio and size of this rods increase because in solvents with high vapor

pressure the formed bubbles are filled with molecules of solvents and when these

bubbles collapse more energy is released. The best morphology obtains in sample

no. 12 [43, 44].

Figure 6 shows the surfactant effect on the morphology and size of lanthanum

hydroxide nanoparticles. In Fig. 6a, b (sample no. 13 and 14) we can see that in

presence of CTAB 1D structures can obtain but at low concentration of surfactant

this rod like particles agglomerate therefore in the case of La(OH)3 CTAB has two

roles firstly induce preferential growth (at low concentration) and secondly doesn’t

allow the particles to agglomerate (at high concentration). In Fig. 6c, d the effect of

SDS as surfactant has been shown in this case the addition of surface capping agents

Fig. 5 SEM images of the La(OH)3 nanorods: a sample no. 9, b sample no. 10, c sample no. 11, andd sample no. 12

Synthesis of Monodisperse Lanthanum Hydroxide 465

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has unfavorable effect because particles has grown and agglomerated. In presence of

PVP, we have very fine particles therefore role of PVP is to stabilizing fine particles

Fig. 6e. In summery we have mastery on size and shape of nanostructures in

sonochemical method via addition of various surfactants. The SEM image of sample

no. 18, which was synthesized without ultrasonic treatment as a reference

experiment, has been shown in Fig. 6f. This image can help us to see the advantage

of using ultrasonic treatment in the synthesis of La(OH)3 nanoparticles. As can be

observed, the successful preparation of nanosized products is indeed due to the

ultrasonic treatments.

Fig. 6 SEM images of the La(OH)3 nanoparticles: a sample no. 13, b sample no. 14, c sample no. 15,d sample no. 16, e sample no. 17, and f sample no. 18

466 M. Salavati-Niasari et al.

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Summary

In summary, La(OH)3 nanoparticles and nanorods with the hexagonal structure type

were synthesized by a sonochemical method. This method brings forward a broad

idea to synthesize other rare-earth compounds with various morphologies and novel

properties. The XRD, TEM, and FESEM were used to characterize the products.

The effect of some of the parameters such as feeding rate of precursors, different

solvents of reaction, time of sonication, and various surfactants on the size and

morphology of obtained products were also investigated.

Acknowledgments Authors are grateful to the council of Iran National Science Foundation and

University of Kashan for their unending effort to provide financial support to undertake this work.

References:

1. X. S. Fang and L. Zhang (2006). J. Mater. Sci. Technol. 22, 1.

2. X. S. Fang, C. H. Ye, L. D. Zhang, Y. H. Wang, and Y. C. Wu (2005). Adv. Funct. Mater. 15, 63.

3. Y. Xia, Y. Xiong, B. Lim, and S. E. Skrabalak (2009). Chem. Int. Ed. 48, 60.

4. Y. Xia, P. Yang, and Y. Sun (2003). Adv. Mater. 15, 353.

5. N. Wang, Q. Zhang, and W. Chen (2007). J. Cryst. Res. Technol. 42, 138.

6. H. X. Mai, Y. W. Zhang, R. Si, Z. G. Yan, L. D. Sun, L. P. You, and C. H. Yan (2006). J. Am. Chem.Soc. 128, 6426.

7. X. Wang, J. Zhuang, Q. Peng, and Y. D. Li (2006). Inorg. Chem. 45, 6661.

8. S. P. Fricker (2006). Chem. Soc. Rev. 35, 524.

9. B. Lai, A. C. Johnson, H. Xiong, and S. Ramanathan (2009). J. Power Sour. 186, 115.

10. Y. C. Liu and Y. W. Chen (2006). Ind. Eng. Chem. Res. 45, 2973–2980.

11. C. L. Kuo, C. L. Wang, T. Y. Chena, G. J. Chen, I. M. Hung, C. J. Shih, and K. Z. Fung (2007).

J. Alloys Compd. 440, 367.

12. H. Wei, Y. Wu, N. Lun, and F. Zhao (2004). J. Mater. Sci. 39, 1305.

13. K. Rajesh, K. V. Baiju, M. Jayasankar, and K. G. Warrierw (2008). J. Am. Ceram. Soc. 91, 2415.

14. J. Sun, X. P. Qiu, and W. T. Zhu (2005). Int. J. Hydrogen Energy 30, 437.

15. X. Wang, Y. D. Li, and Angew (2002). Chem. Int. Ed. 41, 4790.

16. X. Wang, J. Zhuang, Q. Peng, and Y. D. Li (2006). Inorg. Chem. 45, 6661.

17. P. Jeevanandam, Y. Koltypin, O. Palchik, and A. Gedanken (2001). J. Mater. Chem. 11, 869.

18. Y. P. Fang, A. W. Xu, R. Q. Song, H. X. Zhang, L. P. You, J. C. Yu, and H. Q. Liu (2003). J. Am.Chem. Soc. 125, 16025.

19. K. Rajesh, P. Shajesh, O. Seidel, P. Mukundan, and G. K. Warrier (2007). Adv. Funct. Mater. 17,

1682.

20. W. Bu, L. Zhang, Z. Hua, H. Chen, and J. Shi (2007). Cryst. Growth Des. 7, 2305.

21. J. Lin, Y. Huang, J. Zhang, X. Ding, S. Qi, and C. Tang (2007). Mater. Lett. 61, 1596.

22. J. Lee, Q. Zhang, and F. Saito (2003). J Alloys Compd. 348, 214.

23. S. Wang, G. Zhou, M. Lu, Y. Zhou, S. Wang, and Z. Yang (2006). J. Am. Ceram. Soc. 89, 2956.

24. J. Sheng, S. Zhang, S. Lv, and W. Sun (2007). J. Mater. Sci. 42, 9565.

25. Y. Zhang, K. Han, T. Cheng, and Z. Fang (2007). Inorg. Chem. 46, 4713.

26. B. Tang, J. Ge, C. Wu, L. Zhuo, Z. Chen, Z. Shi, and Y. Dong (2004). Nanotechnology 15, 1273.

27. G. Guo, F. Gu, Z. Wang, and H. Guo (2005). J. Cryst. Growth 277, 631.

28. X. Wang, M. Wang, H. Song, and B. Ding (2006). Mater. Lett. 60, 2261.

29. M. F. Vignolo, S. Duhalde, M. Bormioli, and G. Quintana (2002). Appl. Surf. Sci. 197, 522.

30. K. S. Suslick and G. J. Price (1999). Rev. Mater. Sci. 29, 295.

31. F. Li, X. Liu, Q. Qin, J. Wu, Z. Li, and X. Huang (2009). Cryst. Res. Technol. 44, 1249.

32. S. Zhu, H. Zhou, M. Hibino, I. Honma, and M. Ichihara (2005). Adv. Funct. Mater. 15, 381.

33. W. Lv, B. Liu, Q. Qiu, F. Wang, Z. Luo, P. Zhang, and S. Wei (2009). J. Alloys Compd. 479, 480.

34. R. Jenkins, and R. L Snyder (1996). Introduction to X-ray Powder Diffractometry, Chap. 12. p. 90.

35. F. Kim, S. Connor, H. Song, T. Kuykendall, and P. Yang (2004). Angew. Chem. Int. Ed. 43, 3673.

Synthesis of Monodisperse Lanthanum Hydroxide 467

123

36. Y. Sui, W. Fu, and H. Yang (2010). Cryst. Growth Des. 10, 99.

37. D. Seo, J. H. Park, and H. Song (2009). J. Phys. Chem. C 113, 3449.

38. J. Cheon, Y. W. Jun, and J. S. Choi (2006). Angew. Chem. Int. Ed. 45, 3414.

39. C. Burda, X. Chen, R. Narayanan, and M. A. El-Sayed (2005). Chem. Rev. 105, 1025.

40. M. Volmer and A. Weber (1926). Phys. Chem. 119, 227.

41. V. K. LaMer and R. H. Dinegar (1950). J. Am. Chem. Soc. 72, 484.

42. E. E. Finney and R. G. Finke (2008). J. Colloid Interface Sci. 317, 351.

43. F. Dang, N. Enomoto, J. Hojo, and K. Enpuku (2009). Ultrason. Sonochem. 16, 649.

44. A. Starczewska, R. Wrzalik, and M. Nowak (2009). Ultrason. Sonochem. 16, 537.

468 M. Salavati-Niasari et al.

123