karunya full paper

8/7/2019 karunya full paper

http://slidepdf.com/reader/full/karunya-full-paper 1/9

National Conference on Nanomaterials, Dec. 3-4, 2010, Karunya University

FORMATION AND CHARACTERIZATION OF NANO SIZED TIO2

POWDER BY SOL-GEL METHOD

D. Maheswari1, P. Venkatachalam2,*

, R. Elangovan1, K. Manoharan

1

1Department of physics, Bharathiar University, Coimbatore, TamilNadu ± 641046.

2*Department of Physics (DDE), Annamalai University, Annamalainagar,TamilNadu-608 002.

Corresponding author:1E-mail: [email protected]

ABSTRACT

Titanium dioxide (TiO2) has received in the last few years growingattention thanks to its interesting properties that allow its employment in a wide

range of applications, such as pigments, medical devices and gas sensing. Inparticular, the attention has been recently focused on the semiconducting and

photosensitive behaviour, exploited in several applications concerning theenvironmental field, such as purification of air and water from pollutants and

solar cells for low-cost photovoltaic devices. In the present investigation, thepreparation of nano-sized TiO2 by titanium tetraisopropoxide (Ti(OiPr)4) via sol-

gel method using acid as a catalyst is studied and the optimized conditionsconcerning the proportional amount of acid, water, alcohol is established by XRD

and SEM. The effect of calcination temperature on phase transformation of TiO2 (rutile, anatase and brookite) was determined by XRD. The smallest grain size of

TiO2 powder obtained is 20 nm for anatase at 400 ºC by controlling the acidityand the mole ratio of starting materials. SEM, TEM, Raman spectroscopy, UV

absorption spectrum and X-ray diffraction techniques have been used toinvestigate the structure, morphology and optical properties of TiO

2nano

particles. SEM image showed that TiO2 nano particles obtained were ordered anduniform. Raman and XRD measurements confirmed the crystallinity and anatase

phase of the TiO2 nano particles. The optical absorption measurement of TiO2 nano particles exhibits a blue shift with respect to that of the bulk TiO2 owing to

the quantum size effect.

Key words: TiO2, Sol-Gel, XRD, SEM, Raman spectroscopy, UV spectroscopy

1. INTRODUCITON

TiO2 is an ideal photo catalyst in several ways. It is relatively cheap, highly stable from achemical view point and easily available. TiO2 can be extensively used as photo catalystbecause of its high oxidative power, non toxicity, photo stability and water insolubilityunder most conditions [1]. Many processes are there for production of TiO2 nanoparticle

such as flame aerosol synthesis, hydrothermal synthesis, oxidation of titanium, chemical

vapour deposition, ion sputtering, etc. Among these techniques, sol-gel technique appearsto be very interesting because it shows very small and highly effective TiO2 micro




crystals which are uniformly ordered, suitable to be easily supported and show good

electrical properties [5].

2. EXPERIMENT

Materials and apparatus

Titanium iso propoxide procured from Sigma Aldrich chemical company, Banglore was

used as precursor for TiO2 nano particles. The commercially available TiO2 powder with

anatase to rutile ratio 75: 25 was used. De-ionised water was used for the hydrolysis of titanium isopropoxide, Electrolyte (quasi solid state) ethylene carbonate, acetic acid,acetone, propylene carbonate, lithium iodide, iodine, tetra butyl pyridine was purchased.

Methodology

Sol-gel technique

Sol-gel is considered a low temperature synthesis method that gives pure, homogenousnano particles with good size distribution. Chemical reactions can be tailored at the

molecular level to have a better control [7]. Sol-gel method has been used for theproduction of metal, metal oxide and ceramic nano particles with high purity and good

homogeneity. Sol-gel synthesis method can be used for the production of metal oxide andceramic materials. The sol-gel technique has been used for making optical coatings about

50 years ago, in 1846 silica gel were synthesized and aerogels of zirconia, silicate, borateand in the last decade it attracted more field due to its intensive development and low

cost. Moreover, it provides possibility of varying film properties by changing thecomposition of the solution.

Titanium di oxide

Many polycrystalline solids have been used as photo catalyst, but the best one is found to

be TiO2. Brookite, rutile and anatase are the three polymers of TiO2 and anatase is themost effective one by a photocatalytic point of view and in particular to photo degradate

the organic separation in liquid±solid systems. Titanium di oxide is an importantfunctional material with good physical properties, which make it suitable for thin filmapplications. Because of its high dielectric constant, [3] it is used in microelectronic

devices such as capacitors, gate in semiconductor materials. Titanium di oxide thin film

is used in various optical coatings for its good transmittance in visible region and highrefractive index [5]. Recently TiO2 gains increasing attraction on industrial scale becauseof its high efficiency in hydrogen generation and also its high photo stability in aqueous

solution

Three reactions can be generally described as sol-gel process ± hydrolysis, alcohol

condensation and water condensation. The characteristics and properties of sol-gel

network is controlled by many parameters such as pH, temperature, reaction time, reagentconcentration, type of catalyst, drying time [6].

Titanium iso propoxide is a chemical compound with the formula Ti{OC(CH3)2 }4 .

Ti{OC(CH3)2 }4 + 2H20 TiO2 + 4(CH3)2CHOH

The synthesis was done by hydrolysis of titanium (IV) isopropoxide (TPT) (Sigma-

Aldrich) as a precursor in acetic acid. First, the 1- butanol sol solution is prepared by




adding absolutely ultrapure titanium tera isopropoxide (TTIP) (Aldrich) to a 4 ml of

acetic acid (Aldrich) in a beaker. Both chemicals were used in ratio of 1:4 as received.TTIT and acetic acid ( 1ml of TTIP with 4 ml of acetone) are heated until boiling point

of acid was reached. Next ethanol was added for 5 min. The mixture is vigorously stirredfor 1 hr using a magnetic stirrer [4] so as to keep the homogenous mixture of chemical

compounds. Then, distilled water was added approximately 8 ml to this mixture drop by

drop in the ratio of 1:4:8 and it was left for several minutes to let the hydrolysis-polymerization process to take place. The obtained white solution was filtered to get theprecipitate of TiO2 gel powder and dried at 200°C for 1 hour. The dried powder wascalcinated at 400°C for 1 hour to obtain crystalline sol-gel TiO2 powder.

This is the method of sol-gel synthesis of TiO2 based materials. This titanium di oxide issynthesized in nano size whose diameter is 20-30nm and band gap of 3.2eV. These

nanoporous spherical anatase TiO2 particles are coated on ITO glass plate (Indium tin

oxide) with the thickness of 10µm thickness. The methodology is shown in fig .1. This

plate is left dry at ambient temperature followed by heating at 200° C in an oven under clean environment for a minimum of 30 min [4].This ITO polished glass plate is highquality, low defect, transparent and conductive Indium Tin Oxide coated plates with

superior physical properties. This plate produces a resistance of 30�/sqcm.

Fig.1. methodology of preparation if TiO2 particles




3. CHARACTERIZATION OF TIO2 PARTICLES

The effect of calcination temperature on phase transformation of TiO2 (rutile, anatase and

brookite) was determined by XRD. SEM, TEM, Raman spectroscopy, UV absorption

spectrum and X-ray diffraction techniques have been used to investigate the structure,morphology and optical properties of TiO2 nano particles.

3.1. FT-IR spectroscopy of TiO2 particles

Fig.2.The Fourier transform IR spectrum of a sol- gel TiO2.

This spectrum was used for detecting the presence of functional groups in TiO2

compound. Absorption band at 550±650 cmí1 is due to the Ti±O band. Also, two

absorption bands at 436 and 495 cmí1

are representing the Ti±O±Ti band. In addition, theabsorption band at 1008 and 1125 cmí1 is due to the stretching vibration of the O±C±Cbands of the TTIP titanium tetra isopropyl groups. Sharp absorption band at 1600 cmí1

shows the nitrate group and is a result of nitric acid addition. The OH stretching

frequencies of alcohols lead to large absorption peak in the region 3200±3600 cmí1.

3.2. Raman spectroscopy of TiO2 thin films

The results from Raman spectroscopy showed that films consisted of the anatase phase of

titania and increasing the annealing temperature results in the rutile phase of titania. The

Raman spectra are shown in Fig.3. A strong peak characteristic of the Si substrate ispresent at 520 cmí1

in all the films. The film annealed at 500±700 C display peaks at 143cmí1, 396 cmí1 and 638 cmí1. These are attributed to the anatase phase. The film

annealed at 800 C shows an additional strong peak at 196 cmí1, which also belongs tothe anatase phase. As annealing temperature increased to 900 C a weak peak starts to

appear at 439 cmí1

which is a feature resulting from the evolution of the rutile phase. Theanatase phase irreversibly transforms to the rutile phase on heat treatment above 450 C.

The phase transition temperature depends upon the grain size, presence of impurities,dopants, precursor materials and synthesis methods.




Fig.3. Raman spectroscopy

3.3. XRD study of TiO2 film

Fig.4. XRD pattern of TiO2




Figure 4 shows the XRD pattern of the titania film, which is annealed at 500 C.

Peaks are observed at 2 values of 25.28, 37.98, 48.08, 54.14 and 55.07. The orientationsof the peaks were identified as (101), (004), (200), (105) and (211) and all these

corresponds to the anatase structure because of the closeness of their relative intensitiesto the standard data. There is no rutile phase observed, supporting the Raman spectra

results [7]. The crystallite size t was estimated using the peak corresponding to (101) and

the Scherrer formula, which is a generally accepted �� method of estimating the mean crystallite size:

� � �

Here is the X-ray wavelength used (0.1540 nm), is the broadening of the diffractionline measured as half of its maximum intensity (FWHM) and is the corresponding

Bragg angle [7]. The t value calculated was 21 nm and this result is in agreement with the

grain size of 20 nm observed using scanning electron microscopy results describedbelow.

Fig.5. SEM photograph of TiO2 particles before treatment




Fig.6. SEM photograph of TiO2 particles after treatment.

3.4. UV/Vis spectrum of TiO2 thin film

The properties of thin films are known to differ from that of bulk materials. As thediameter of crystallites approaches the exciton Bohr diameter, the quantum size effectwhere splitting of the energy bands into discrete quantized energy levels occurs. Figure 6

gives the UV/ Vis spectra of the transparent TiO2 thin films supported on glass slides. The

spectra transmittance was measured in the wavelength range from 200 to 700 nm with an

identical slide in the reference beam and transmittance changes with increase intemperature. This is possibly due to the dual effect of grain growth and increase inporosity in the film. The maximum transmission varies between 70% to 90%.




Fig.7. UV/Vis spectra of TiO2

4. RESULTS AND DISCUSSION

Nano ± sized particles are well known to exhibit different physical properties andchemical properties compared to larger particles. When these nano particles are

used as catalyst, catalytic activity is enhanced due to the increased surface area.

Fig 2 reveals the absorption bands if Ti-O-Ti and presence of nitrate group. Fig 3explains the exact annealing temperature of anatase particles. Fig 4 depicts the

XRD pattern of the sol-gel films with one major peak at 2 = 25.32° whichcorresponds to reflections of the anatase phase of TiO2 [7]. The anatse phase is

considered to be the most active for the photocatalytic reactions. Films arecalcinated at 500° C temperature which is high enough for the formation of active

anates phase. The crystalline size was determined using Scherrer formula found tobe 20nm (nanosize). Fig 5 and 6 shows the SEM image of surface of sol-gel film

at x2000 magnification. Fig 7 denoted the UV-Vis transmittance spectrum of sol-gel derivatives. The film absorbs UV radiation for catalytic activation with almost

all the visible radiation.




5. CONCLUSION

TiO2 thin films were prepared by sol-gel process from titanium alkoxide. The

results of SEM and XRD analysis shows that the sol-gel technique is an efficientway for the preparation of film of nanocrystalline TiO2.The band gap energy of

indirect transition of the TiO2 thin film is calculated to be about 3.4 eV indicatinga quantum size effect. Our nano structured TiO2 thin film which has a little red-

shift will be more efficient in the development of photoelectrodes for photoelectrochemical cell used in solar hydrogen production.

References

1. Nor Hafiazah and Iis Sopyan, Nano -sized TiO2 Photo catalyst via Sol-Gel

method:Eeffect of hydrolysis degree on powder properties, Internal

Journal of publications, Vol 2009, Article ID 962783, 8 page.

2. Young Ug Ahn, Variation of Structural and Optical properties of Sol-gel

TiO2 thin films with catalyst concentration and calcinations temperature,

Science Materials Letter 57 (2003) 4660-4666.

3. Mansor Abdul Hamid, Preparation of TiO2 thin film by Sol-gel dip coating

method, Malaysian Journal of chemistry,2003,Vol.5,No1, pp-086-091.

4. R C Suciu, TiO2 thin film prepared by Sol-gel method, 2009 J.Phys,:

Conf. Ser.182012080.

5. Puangrat Kajitvichyanukul, Sol-gel preparation and properties study of

TiO2 thin film for photocatalytic reduction of Chromiun (VI) in

photocatalysis process, Science and Technology of Advenced Materials 6

(2005) 352-358.

6. Jatinder Kumar, Sol-gel derived of nano- crystal of TiO2 for photocatalyticdegradatoin of Azorubine Dye,International Journal of Chem Tech

Research,Vol.2,No.3,pp-1547-1552, July ± Sep 2010.

7. Tianfa Wen, Preparaton and characterization of TiO2 thin film by the Sol-

gel process, Journal of Material Science 36 (2001) 5923 ± 5926.

8. M. Hamaudanian, Sol-gel Preparation and Characterization of Co/TiO2

Nanoparticle: Application to the degradation of Methyl Orange, Journal of

the Iranian Chemical Society, Vol.7, Suppl, July 2010, Pp-S52-S58.

9. Marcelo M. Viana, Nanocrystalline Titanium oxide thin films prepared by

Sol-gel process, Brazilian Journal of Physics, Vol.36 No.3B, Sep 2006.

10. Kamal K Gupta, Sol-gel drived titanium di oxide finishing cotton fabricfor self cleaning, Indian Journal of Fibre and Textile Research,Vol.33, Dec

2008,pp-443-450.

karunya full paper

Documents