Materials Letters 65 (2011) 2224–2227

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Materials Letters

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Hydrothermal synthesis of alpha Fe2O3 nanoparticles capped by Tween-80

Yaqoob Khan a, S.K. Durrani b,⁎, M. Siddique c, Mazhar Mehmood a

a Department of Chemical and materials Engineering, Pakistan Institute of Engineering and Applied Sciences P. O. Nilore, Islamabad, 45650, Pakistanb Materials Division, PINSTECH, P. O. Nilore, Islamabad, Pakistanc Physics division, PINSTECH, P. O. Nilore, Islamabad, Pakistan

⁎ Corresponding author: Tel.: +92 51 2208064; fax:E-mail address: durranisk@gmail.com (S.K. Durrani)

0167-577X/$ – see front matter © 2011 Elsevier B.V. Adoi:10.1016/j.matlet.2011.04.068

a b s t r a c t

a r t i c l e i n f o

Article history:Received 24 February 2011Accepted 20 April 2011Available online 28 April 2011

Keywords:HematiteNanoparticlesFunctional surfacesCrystal growth

Surface modified α-Fe2O3 nanoparticles capped by Tween-80 were prepared by the hydrothermal treatmentof Fe(NO3)2.9H2O at 200 °C. The spherical nanoparticles possessed good crystallinity with an averagecrystallite size of 21 nm. The presence of Tween-80 on the surface of α-Fe2O3 was confirmed by FTIR andMössbauer analysis. The surfactant was effective in controlling the particle shape and restricted the particlegrowth to a narrow range around 40–60 nm as observed by scanning electron microscopy. The α-Fe2O3

nanoparticles obtained without Tween-80 were irregular in shape with a wide size distribution in the range of150–300 nm.

+92 51 9248808..

Fig. 1. XRD patternsthe presence of Twepeak shift. Solid bars

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© 2011 Elsevier B.V. All rights reserved.

1. Introduction

Surface capping of inorganic nanoparticles with organic moleculeshas been the subject of considerable research interest over the pastseveral years because, the application of nanoparticles largely dependon their surface properties. The physical and chemical interactions of alarge variety of organic functional groups with the surface ofnanoparticles often result in remarkable properties along with theirstability and better dispersibility. The surface modification of iron oxidenanoparticles has recently expanded rapidly because of their increasinguse in drug delivery and biological imaging [1,2]. Hematite (α-Fe2O3),being the most stable of all iron oxides is widely used in catalysis [3],gas sensors [4], electrode material for lithium ion batteries [5], and inwater treatment [6]. A variety of surfactants and organic moleculessuch as SDBS [7], CTAB [8], lauric acid [9], n-decanoic acid andn-decylamine [10] have been used to control and modify the size,shape, and surface environment of α-Fe2O3 nanoparticles. Polyox-yethylene sorbitanmonooleate, commercially known as Tween-80, is apopular non-ionic surfactant used widely in cosmetics, foods, andpharmaceutical products. Its use for the synthesis of metallicnanoparticles of silver [11] , nickel [12], copper [13] and gold [14] hasalready been established.

Herein, we report a single step hydrothermal synthesis of sphericalα-Fe2O3 nanoparticles in the presence of Tween-80. For comparison,α-Fe2O3 nanoparticles without surfactant were also prepared underthe same conditions. FTIR and Mössbauer analysis revealed the self

assembly of Tween-80 on the surface of α-Fe2O3 nanoparticles.Scanning Electron Microscopy was used to monitor the effect ofTween-80 on the size and morphology of unmodified and surfacemodified α-Fe2O3 nanoparticles.

of α-Fe2O3 nanoparticles synthesized (a) in the absence and (b) inen-80. Inset shows a magnified section of the patterns to indicaterefer to JCPDS No. 84–0306.

Fig. 2. FTIR spectra of α-Fe2O3 nanoparticles synthesized (a) in the absence and (b) inthe presence and of Tween-80. FTIR spectrum of pure Tween-80 is shown at (c).

2225Y. Khan et al. / Materials Letters 65 (2011) 2224–2227

2. Experimental section

Iron nitrate (Fe(NO3)2.9H2O), sodium hydroxide (NaOH), andTween-80 were used as the starting materials. To the 100 ml of0.25 M aqueous solution of Fe(NO3)2.9H2O were added 5 ml of Tween-80 and stirred for 20 minutes. While stirring, 50 ml of 1 M NaOH weredrop wise added to the mixture containing Fe(NO3)2.9H2O and Tween-80 to form a suspension. The suspension was stirred vigorously foranother 1 h and then poured into a Teflon lined stainless steelautoclave. Hydrothermal reaction was carried out at 200 °C for 5 h.After cooling the autoclave to room temperature naturally, the

Fig. 3. Low and high magnification SEM images of α-Fe2O3 nanoparticles sy

precipitates were collected by centrifugation and washed with distilledwater and absolute ethanol to remove the excessive Tween-80 and anyresidual ions left. Same procedure was used to prepare α-Fe2O3 underthe same conditions without the use of Tween-80 for comparison. Thereddish brown powders collected were dried in air at 90 °C.

Powder X-ray diffraction analysis of the samples was performed on aRigaku diffractometer using Cu Kα radiation (λ=1.5406 Å). FTIRtransmittance spectra of the powders were collected in KBr pellets inthe range of 4000–400 cm−1 using Nicolet 6700, FTIR. Particlemorphology of the samples was characterized by Scanning ElectronMicroscopy (JSM-5910, JEOL). The room temperature Mössbauer datawas collected in transmission geometry using a 57Co (Rh-matrix) sourceof initially 25 mCi strength. Mössbauer spectrometer was calibratedusing a thinα-Fe foil and data analysis was performed using a computercode Mos-90, assuming that all peaks were Lorentzian in shape.

3. Results and discussion

3.1. XRD analysis

The XRD patterns of α-Fe2O3 nanoparticles synthesized in thepresence and absence of Tween-80 are shown in Fig. 1. Based on thepeak positions, the diffraction peaks were indexed to the hematitephase of Fe2O3, consistent with JCPDS No. 84–0306. The averagecrystallite size calculated from the (104) and (110) reflections usingScherer Formula [15] were found to be 21 and 34 nm for the surfacemodified and unmodified α-Fe2O3 nanoparticles, respectively. Amagnified section of the XRD patterns shown as inset in Fig. 1 indicatesa slight shift of the peak positions toward lower 2θ values for Tween-80capped nanoparticles. This behavior can be explained by the increase inFe–O bond length upon coating the nanoparticles with a layer ofTween-80. For nanoparticles, it is known that there are present anumber of vacancy defects and dangling bonds on the surface. During

nthesized in the absence (a–b) and in the presence (c–d) of Tween-80.

Fig. 4. Mossbauer spectra of (a) unmodified and (b) Surface modified α-Fe2O3

nanoparticles.

2226 Y. Khan et al. / Materials Letters 65 (2011) 2224–2227

synthesis, the active groups of the surfactant molecules tend to occupythese vacancies and coordinate with dangling bonds [16]. Thisinteraction leads to an extension in Fe–O bond length that decreasesthe 2θ angle in the XRD patterns and a shift in peak positions towardlower angle side is observed [17].

3.2. FTIR analysis

The surface capping of α-Fe2O3 nanoparticles with Tween-80 wasconfirmed by FTIR analysis as shown in Fig. 2. The FTIR spectrum of neatTween-80 is also given for comparison. Characteristic peaks of α-Fe2O3

were observed at 552 and 465 cm−1 for both unmodified and surfacemodified samples. A comparison of Fig. 2a and b shows that thenanoparticles synthesized in the presence of Tween-80 has character-istic peaks of CH2 (2845 cm−1), CH3 (2920 cm−1), C–O–C (1098 cm−1),and a broad band due to OH groups (3360 cm-1). The presence of mostof the peaks from the surfactant in the IR spectrum of α-Fe2O3

nanoparticles prepared in the presence of Tween-80 confirm thepresence of active groups on the surface of α-Fe2O3 nanoparticles. Theabsorption bands due to C=O stretch at 1732 cm−1 in Tween-80 is,however not observed in the surface modified α-Fe2O3 nanoparticleswhich might be due to the chemical interaction of Tween-80 with thesurface of Fe2O3 via the oxygen of C=O group. Instead, a broad bandcentered around 1640 cm-1 due to the C–O–Fe bond formation wasobserved. Though the bending vibrations due to OH groups also appear

Table 1Mössbauer parameters of unmodified and surface modified α-Fe2O3.

Sample Subspectra Heff (kOe) Δ (m

Unmodified α-Fe2O3 Sextet 1 512 −0.2Surface coated Sextet 1 514 −0.2α-Fe2O3 Sextet 2 378 −0.2

in this region which contribute to the broadening, it has been suggestedfor several kinds of dicarboxylic acids, adsorbed onto TiO2, that the C=Oabsorption disappeared with increase in carbon chain length [18].Instead, strong absorption below 1700 cm−1 were observed like in thepresent work, and this occurred due to binding of four oxygen atoms ofthe dicarboxylic acid with metal atoms [18]. The absorption band due toOH groups in the range of 3410–3320 cm−1 is also considerably broadbecause Tween-80 introduces three additional –OH groups permoleculeadsorbed onto the surface of α-Fe2O3 nanoparticles [19].

3.3. Particle size and morphologies

The low and highmagnification SEM images of the unmodified andsurface modified α-Fe2O3 nanoparticles are shown in Fig. 3. For theunmodified samples, irregular particles with a large size distributionfrom 150 to 300 nm can be observed in Fig. 2(a–b). The Tween-80capped α-Fe2O3 nanoparticles however show a nearly sphericalmorphologywith a narrow size distribution in the range of 40–60 nm.The SEM images indicate the effectiveness of Tween-80 in confiningthe growth ofα-Fe2O3 nanoparticles to a smaller size compared to theuncapped nanoparticles.

3.4. Mossbauer analysis

Mossbauer spectra of α-Fe2O3 nanoparticles are shown in Fig. 4.The Mössbauer spectrum of unmodified sample is a magnetic sextetand its parameters correspond to typical hematite [20]. The internalmagnetic field (Heff) is however, less than that of the bulk materialwhich is ranging 520–528 kOe, indicating the nanoparticulate natureof the sample. The modified α-Fe2O3 constituted two magneticsextets. The parameters of sextet 1 were similar to that of uncoatedsample, whereas the sextet 2 might be originating from the change insurface environment of α-Fe2O3 nanoparticles. The internal magne-tization decreased sharply while other Mössbauer parameters likequadruple splitting (Δ), isomer shift (δ) and line width (Г) werealmost same as in the case of pure α-Fe2O3 (Table 1). The presence ofsextet 2 indicates the successful capping of α-Fe2O3 with Tween-80.Mossbauer results also complement the XRD and FTIR analysis.

4. Conclusions

Crystalline α-Fe2O3 nanoparticles were prepared via single step,surfactant assisted hydrothermal route, in which Tween-80 waschemically bound to the surface of nanoparticles. Tween-80 was alsoeffective in restricting the particle growth to narrow range of 40–60 nm, compared to unmodified nanoparticles where particle sizeswere in the range of 150–300 nm. The surface modified α-Fe2O3

nanoparticles are expected to have improved gas sensing and catalyticproperties.

Acknowledgments

Financial support for PhD studies (Y.K) from HEC, Pakistan ishighly acknowledged. Authors are also thankful to Mr. M. Shafi forMossbauer data collection.

m/s) δ (mm/s) Γ (mm/s) Relative Area (%)

2 0.37 0.38 1002 0.36 0.40 785 0.37 0.46 22

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References

[1] Kim DK, Zhang Y, Voit W, Kao KV, Kehr J, Bjelke B, et al. Scr Mater 2001;44:1713–7.[2] Leary SP, Liu CY, Apuzzo MLI. Neurosurgery 2006;58:1009–25.[3] Zhang W, Chen J, Wang X, Qi HL, Peng KS. Appl Organomet Chem 2009;23:200–3.[4] Sun B, Horvat J, Kim HS, Kim WS, Ahn J, Wang GX. J Phys Chem C 2010;114:

18753–61.[5] Wu CZ, Yin P, Zhu X, OuYang CZ, Xie Y. J Phys Chem B 2006;110:17806–12.[6] Li J, Lai XY, Xing CJ, Wang D. J Nanosci Nanotechnol 2010;10:7707–10.[7] Wang H, Geng W-C. Res Chem Intermed 2011:1–7.[8] Jing ZH, Wu SH. Mater Lett 2004;58:3637–40.[9] Moore RGC, Evans SD, Shen T, Hodson CEC. Physica E 2001;9:253–61.[10] Takami S, Sato T, Mousavand T, Ohara S, UmetsuM, Adschiri T. Mater Lett 2007;61:

4769–72.

[11] Kvitek L, Vanickova M, Panacek A, Soukupova J, Dittrich M, Valentova E, et al.J Phys Chem C 2009;113:4296–300.

[12] Wang AL, Yin HB, Ren M, Lu HH, Xue JJ, Jiang TS. New J Chem 2010;34:708–13.[13] Zhang XF, Yin HB, Cheng XN, HuHF, Yu Q,Wang AL. Mater Res Bull 2006;41:2041–8.[14] Premkumar T, Kim D, Lee K, Geckeler KE. Macromol Rapid Commun 2007;28:

888–93.[15] Langford JI, Wilson AJC. J Appl Crystallogr 1978;11:102–13.[16] Guo L, Wu ZH, Liu T, Yang SH. Physica E 2000;8:199–203.[17] Kim JS, Lee SB, Sue SH, Kang HI, Lee M, Bahng JH, et al. J Mater Sci Lett 2001;20:

2211–2.[18] Hug SJ, Bahnemann D. J Electron Spectrosc Relat Phenom 2006;150:208–19.[19] Khan Y, Durrani SK, Mehmood M, Ahmad J, Khan MR, Firdous S. Appl Surf Sci

2010;257:1756–61.[20] Siddique M, Riaz M. Physica B 2010;405:2238–40.