Effect of different organic solvents and annealing temperatures on optical property of TiO2 nanoparticles

Pooja Agarwala1,2, Vijaya Agarwala1, Rajnish Garg2

1Centre of Nanotechnology, Indian Institute of Technology Roorkee, India, 2Centre for Nanotechnology -Materials Engineering, University of Petroleum and Energy Studies, Dehradun, India

ByProf. Vijaya Agarwala

Centre of Nanotechnology,Indian Institute of Technology (IIT)

RoorkeeINDIA

IntroductionCrystal structures of TiO2 nanoparticlesSynthetic routes Applications

ExperimentalSynthetic routesNon-aquous Sol-gel synthesisCharacterization tools used

Results and discussionsInfluence of different organic solventsAnalysis of all characterization data

ConclusionsReferences

Contents

1

Crystal structures of TiO2 nanoparticles

Introduction

•Austin and S.-f. Lim, "The Sackler Colloquium on Pormoses and Perils in Nanotechnology for Medicine," PNAS, vol. 105, no. 45, pp. 17217-17221, 2008.•Woodley and C. Catlow, "Structure prediction of titania phases: Implementation of Darwinian versus Lamarckian concepts in an Evolutionary Algorithm," Computational Materials Science, vol. 45, no. 1, pp. 84-95, 2009.•Wikipedia, "Titanium Dioxide," Widipedia, 11 April 2012. [Online].Available: http://en.wikipedia.org/wiki/Titanium_dioxide. [Accessed 16 April 2012].

2

High refractive index

Hydrophilicity

Biocompatibility

Semiconductivity

Corrosion resistance

Physiochemical stability

And low cost.

Properties of TiO2 nanoparticles

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3

Grain size, morphology and structure play an amicable part in deciding the role of TiO2 nanoparticles for various applications.

Highly desirable in the field of sensors, paint, cosmetics, photocatalytic and photovoltaic applications

Various mechanical, electronic, magnetic, optical and sensing properties are greatly dependent on particle size

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Application

4

Bottom Up ApproachChemical method:Reagents: Metal alkoxides, metal chlorides,

metal nitrates.Procedure : flame synthesis, co-precipitation,

chemical vapour deposition, Hydrothermal, Sol-gel.

Heat Treatment: High temperature furnace, Microwave furnace.

Top Down ApproachMechanical method:

High energy planetary ball mill.

5

Synthesis & Characterization of TiO2 Nanoparticles

XRD, SEM, TEM, DSC, UV-Vis, FTIR, BET

Characterization techniques

Experimental

Among all the techniques, sol-gel is the mostly used one, due to the advantages of being economical, easy and feasible. Sol-gel technique prevents co-precipitation, enables mixing at an atomic level and results in small particles which are easily sintered.

Sol-gel method

Chem. Commun., 2011, 47, 3457–3459

6

Non-aquous Sol-gel synthesis

TiCl4

Ethanol/benzyl alcohol

Yellow solution

Orange solution with white puffs

Milky brown solution on aging

Off white solution after 24 hrs

of aging

white amorphous nanopowder

white dispersion

calcination for 1 hour at 500°C

kept in oven for 80°C for 12 hours. Once powder was dried, it was calcined at 450°C for 5 hours in furnace

Etha

nol

benz

yl a

lcoh

ol

In this study, it has been attempted to synthesize TiO2 nanoparticles by non-aqueous sol-gel method using two different types of alcohols, i.e., ethanol and benzyl alcohol and their effect on nanoparticle size and optical properties has been investigated. The influence of higher boiling point on the mechanism of nucleation and growth of nanoparticles has been addressed.

7

The main focus of present study is to establish the effect of boiling point of solvent on the nucleation and growth of TiO2 nanoparticles which finally affects the particle size and consequently the surface area.

Influence of different organic solventsResults and discussions

Higher boiling point of the organic solvent = less evaporation of the solvent = more time for nucleation and growth = bigger particle size

Low boiling point of the organic solvent = more evaporation of the solvent = higher energy at the surface of the nanoparticle = less nucleation and growth = smaller particle size

8

78.37 C

Parti

cle

size

Time for nucleation & growth

Boili

ng p

oint

200 C

Ethanol/benzyl alcohol

Reaction with ethanol

Reaction with benzyl alco

hol

Influence of different organic solvents

TiO2 NPs powderSize-20-30 nm TiO2 NPs suspension

Size-40-60 nm

9

20 40 60 80

**

* *

***

*

*

Dried TiO2

HT TiO2 at 5000C,1h

Inte

nsity

(a.

u.)

2 degree

TiO2(Anatase)

J CPDS-01-071-1167

*

20 40 60 80

Dried TiO2

HT TiO2 at 4500C,5h

TiO2(Anatase)

J CPDS-00-001-0562

*

**

*

**

* ** **

*

2 degree

Inte

nsi

ty (a.u

.)

*

4000 3500 3000 2500 2000 1500 1000 500

Tra

nsm

itta

nce

(a.

u.)

Wavenumber (cm-1)

PA-1 PA-2

548

5553560

3560

14101310

Phase analysis by X-ray diffraction and FTIR spectroscopy

XRD of PA-1 XRD of PA-2

FTIR spectra of PA-1 & PA-2

Higher purity of anatase phase in PA-2 than that is in PA-1 due to longer annealing duration.

Significant sharpening of absorption bands in the region of 600-400 cm-1 in case of PA-2 and clearly indicates the formation of anatase phase.

The absence of peaks corresponding to asymmetrical and symmetrical vibration of M-O-C groups and alkyl groups (1410 & 1310 cm-1) in case of PA-2 indicates relatively pure TiO2 which could be resulted due to the longer calcination duration.

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Morphological analysis

Particle size of PA-1: 20-30 nmParticle size of PA-1: 40-60 nmThe BET surface area of PA-1: 66.6200 m²/g with the pore size of 107.1184 Å and The BET surface area of PA-2: 40.0879 m²/g with the pore size of 74.1372 Å.

FESEM image of PA-1 FESEM image of PA-2

Films of PA-1 & PA-2

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300 350 400 450

0

1

2

3

4

abs. (

a.u

.)

wavelength (nm)

PA-1,TiO2 film

PA-2,TiO2 film

2.50 2.75 3.00 3.25 3.50 3.75 4.00 4.25

0

50

100

150

(h

h(eV)

PA-1 PA-2

Band gap analysis

The effective coverage of visible region extended from 350 nm in PA-1 to 400 nm in case of PA-2. Calculated band gap energies of both TiO2 nanoparticles is 3.54 eV and 3.37 eV for PA-1 and PA-2, respectively.Increased band gap of PA-1 can be explained on the basis of effective mass model (EMM) of small semiconductor particles which was observed to increase as the particle size decreases.

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•Benzyl alcohol with the boiling point 205 C, when used with TiCl4 as precursor creates the bigger sized nanoparticle than is comparison with ethanol having considerably low boiling point of 78.37 C.

•The nanoparticles were formed in the particle size 20-30 nm and 40-60 nm with ethanol and benzyl alcohol, respectively.

•The BET surface area of the particles synthesized in this study is calculated as 66.6200 m²/g and 40.0879 m²/g with ethanol and benzyl alcohol, respectively. The pore size of 107.1184 Å and 74.1372 Å was observed.

•The threshold of spectra in UV-vis of the bigger particles is shifted towards longer wavelength in comparison with smaller particles from 350 nm to 400 nm.

•The band gap energy of bigger particles is more than smaller particles which is in harmony with previous findings.

Conclusions

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References

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Authors acknowledge UCOST and Department of science and technology (DST) for funding.

Acknowledgement

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