ARTICLE IN PRESS

Physica B 404 (2009) 1420–1422

Contents lists available at ScienceDirect

Physica B

0921-45

doi:10.1

� Corr

E-m

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

Synthesis and characterization of TiO2 nanoparticle films coatedwith organic dyes

Rika a, M.Y.A. Rahman a,�, M.M. Salleh b, A.A. Umar b, A. Ahmad c

a College of Engineering, Universiti Tenaga Nasional, 43009, Kajang, Selangor, Malaysiab Pusat Pengajian Fizik Gunaan, Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor, Malaysiac Pusat Pengajian Sains Kimia dan Teknologi Makanan, Fakulti Sains dan Teknologi, Universiti Kebangsaan Malaysia, 43600 UKM, Bangi, Selangor, Malaysia

a r t i c l e i n f o

Article history:

Received 29 August 2008

Accepted 27 December 2008

PACS:

78.20.�e

81.15.Fg

Keywords:

Absorption

Hydrolysis technique

Organic dye

Surface morphology

Titanium dioxide

26/$ - see front matter & 2009 Elsevier B.V. A

016/j.physb.2008.12.035

esponding author. Tel.: +603 89287262; fax:

ail address: yusri@uniten.edu.my (M.Y.A. Rah

a b s t r a c t

The synthesis and characterization of TiO2 nanoparticle coated with organic dyes, coumarin and methyl

orange was reported. The films were deposited onto ITO-covered glass substrate by controlled

hydrolysis technique asssited with spin coating technique. The films were characterized by scanning

electron microscope (SEM), X-ray dispersive (XRD) technique and ultraviolet-visible (UV-Vis) spectro-

photometer. The average grain size of the TiO2 films is about 76 nm. The uncoated TiO2 film is crystalline

with anatase and rutile structure. The coated TiO2 films with dye are also crystalline since the

diffraction peaks have been observed at three angles. The maximum absorption of the film coated with

coumarine dye is at 480 nm.

& 2009 Elsevier B.V. All rights reserved.

1. Introduction

Titanium dioxide is a very promising material and has widelybeen used in photocatalysis, optics, sensors and photovoltaics[1,2]. It has been utilised in photoelectrochemical cell since itsfabrication cost is cheap, preparable in thin film form and non-toxic [3]. It was found that the device performance stronglydepends on the grain size of the TiO2 films. The smaller grain sizeof the films, the higher the short-circuit current density and theopen-circuit voltage of the cells [3]. Nanostructured TiO2 films canbe prepared by various techniques, namely, squeegee printing,electrodeposition, sol-gel and metallo-organic decomposition[4–9]. In this work, nanoparticle titanium dioxide films coatedwith organic dye were prepared onto ITO-covered glass substrateby controlled hydrolysis technique assisted by spin-coatingtechnique. The technique was chosen since it can control theexperimental conditions such as quantity of water, temperatureand capping agent [2]. The aim of this work is to prepare thenanostructured TiO2 films coated with organic dye and character-ize them by mean of SEM, XRD and UV-Vis spectrophotometer to

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+603 89212115.

man).

study their surface morphology, structure and optical absorption,respectively.

2. Materials and methods

Raw materials, titanium (IV) etoxide (Ti(OC2H5)4, potassiumchloride (KCL), ethyl alcohol, coumarin and methyl orange dyewere purchased from Aldrich. Nanoparticle TiO2 were prepared bycontrolled hydrolysis of (Ti(OC2H5)4 in ethyl alcohol [2,10]. About0.0596 gram potassium chloride was mixed into 5 ml deionizedwater. 0.085 ml (Ti(OC2H5)4 ml was added by droplet into 5 mlethyl alcohol using a magnetic stirrer and a transparent solutionwas obtained. Then, a 0.02 ml aqueous solution was added bydroplet into the second solution at ambient temperature and themixed solution was further stirred for 25 minutes. 0.00128 gramof coumarin dye was dissolved into 5 ml ethyl alcohol in order toget a 0.001 M solution. This solution was mixed with the previoussolution and stirred. The TiO2 particles were observed to beformed after a few minutes of stirring and resulted in uniformsuspension of TiO2 beads. The solution containing the TiO2

particles was immediately coated onto indium-tin oxide (ITO)substrate by spin coater at a speed of 2000 rpm. The solution wascoated two times onto the substrate in order to achieve the filmwith a sufficient thickness. 0.00164 gram of methyl orange dye

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Rika et al. / Physica B 404 (2009) 1420–1422 1421

was dissolved into 5 ml ethyl alcohol in order to get a 0.001 Msolution. The above procedure were repeated for preparing TiO2

films coumarin dye. The surface morphology of the films werestudied using scanning electron microscope (SEM). The structureof the films were studied by X-ray dispersive (XRD) technique. Theoptical absorption of the films were studied by ultraviolet-visible(UV-Vis) spectrophotometer.

3. Results and discussion

Fig. 1 shows SEM micrograph for uncoated TiO2 film, TiO2 filmcoated with coumarin dye and TiO2 film coated with methylorange dye. All samples are homogeneous since their grain sizeare identical. It was observed that the uncoated TiO2 film is themost homogeneous since all grain are closely packed to each otherwith the uniform grain size. TiO2 film coated with methyl orangedye is more homogenous than TiO2 film coated with coumarin dyesince its grains are uniformly distributed on TiO2 layer. There are alot of spaces between the grains of TiO2 film coated with coumarindye. From Fig. 1, the average grain size of the samples wasestimated using the scale located at the lower left corner of SEMmicrographs. The average grain size was estimated by taking thediameter for five grains. The average grain size for the uncoatedTiO2 films is 76 nm. The average grain size of the TiO2 filmprepared by screen-printing technique reported was 200 nm [3].The films preparation by this technique caused the films withrough surface structure and bigger grain size. These results are ina good agreement with those reported by [4,7]. The average grainsize of the TiO2 film prepared by screen-printing technique was25 nm [4]. The average grain size of the TiO2 film prepared by sol-gel dipping method was 40 nm [7]. Those for TiO2 coated with

Fig. 1. SEM micrograph for (a) uncoated TiO2 film, (b) TiO2 coated w

coumarin dye and TiO2 coated with methyl red dye are 85 and100 nm, respectively.

Fig. 2 shows XRD pattern for uncoated TiO2 film, TiO2 filmcoated with methyl orange dye and TiO2 film coated withcoumarin dye. In the XRD pattern for uncoated TiO2 film asshown Fig. 2(a), it is observed that there are three diffractionpeaks corresponding with anatase and rutile phase structure. Theanatase phase exists at the diffraction angle of 251, while therutile structure exists at 291 and 401. These results are in goodagreement with those reported in [1,5,7,10,11]. From Fig. 2(b) and(c), it is noticeable that the TiO2 film coated with methyl orangedye and TiO2 film coated with coumarin dye are also crystallinesince three diffraction peaks are observed at the commondiffraction angle of 301, 351 and 511. It is believed that thesethree diffraction angles correspond with the phase of methylorange dye and coumarin dye which has separately deposited onthe TiO2 films by spin coater. These angles are not found in theXRD pattern for uncoated TiO2 film.

Fig. 3 shows the optical absorption spectra for uncoated TiO2

film, TiO2 coated with methyl orange dye and TiO2 coated withcoumarin dye. It was found that the uncoated TiO2 film shows thehighest absorption compared with another two samples at300 nm. The absorption decreases with the increasing wavelengthfor all samples until the wavelength of 400 nm. In the visibleregion (l4400 nm), the absorption increases until the wavelengthof 480 nm. This result is in a good agreement with the opticalbehaviour of TiO2 film prepared by plasma and ion beam assistedmethods [11]. From the figure, the absorption peak for uncoatedTiO2 film occurs at the wavelength of 480 nm. The peak was notobserved for TiO2 coated with coumarin dye and TiO2 coated withmethyl orange dye. However, at the wavelength of 480 nm, TiO2

coated with coumarin dye shows the highest absorption and it is

ith coumarin dye and (c) TiO2 coated with methyl orange dye.

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Fig. 2. XRD spectrum for (a) uncoated TiO2 film, (b) TiO2 coated with methyl

orange dye and (c) TiO2 coated with coumarine dye.

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Fig. 3. Optical absorption spectra for uncoated (a) TiO2 film, (b) TiO2 coated with

methyl orange dye and (c) TiO2 coated with coumarin dye.

Rika et al. / Physica B 404 (2009) 1420–14221422

expected to give the best performance when applied in photo-electrochemical cells [3]. From the results shown in Figs. 1–3, itcan be concluded that there is no correlation between the surfacemorphology and structure of the synthesized films and theiroptical properties.

4. Conclusions

We have successfully prepared a TiO2 nanoparticle films coatedwith organic dyes, coumarin and methyl orange dye by controlledhydrolysis technique assisted with spin coating technique. Thefilms were characterized by scanning electron microscope (SEM),X-ray energy dispersive (EDX) technique and ultraviolet-visible(UV-Vis) spectrofotometer. The average grain size of the TiO2 filmsis about 76 nm. The uncoated TiO2 film is crystalline with anataseand rutile structure. The coated TiO2 films with dye are alsocrystalline since the diffraction peaks have been observed at threeangles. The maximum absorption of the film coated withcoumarine dye is at 480 nm.

Acknowledgments

The authors are very thankful to School of Food Technologyand Chemical Sciences, Faculty of Science and Technology, UKMfor the TiO2 nanoparticle synthesis and characterizations. Thiswork was funded by MOSTI under the eScience grant no. 03-02-03-SF0080.

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