Review of Optical Properties of TiO2 Nanoparticles

1. Presentedby:-SubhankarPatra
NitishGajendraMahapatra
BSc.3rd yearphysics
Review of Optical
Properties of TiO2
Nanoparticles

2. Content
1. Introduction
2. Crystal Structure
3. Synthesis of TiO2 coatings
4. Optical Properties of TiO2
5. Applications of TiO2
6. Conclusion

3. INTRODUCTION

4. TiO2 as Nanomaterial
•Titanium dioxide (TiO2) is a well-known nanomaterial which has wide applications ranging
from common products, such as sunscreens to advanced devices, like photovoltaic cells and
a series of environmental and biomedical applications.
• Due to the high bandgap, high resistance to chemical corrosion and photo corrosion, TiO2
remains the most researched semiconductor, despite the multitude of photocatalytic materials
developed so far.
•Titanium dioxide occurs in three crystalline polymorphs: rutile (tetragonal) , anatase
(tetragonal) , and brookite (orthorhombic).
• Rutile is known to be the most stable phase. Due to its scientific and practical importance,
TiO2 rutile has been the subject of many experimental and theoretical investigations.

5. Crystal Structure

6. 2. Crystal Structure
•TiO2 primarily exist in three forms including, the brookite phase (orthorhombic), anatase
phase (tetragonal), and rutile phase (tetragonal), with energy gap
equal to 2.96 eV, 3.2 eV, and 3.02 eV, respectively.
•In addition, the over declared three phases of crystal, there be a present added phase TiO2
(monoclinic) .
• Among these varied phases of crystal, the greatest steady main phase is rutile . The phase of
anatase and brookite are usually more stable than the rutile phase because the surface energy
of them is less than thatof the rutile.

7. Crystal Structure
a) Rutile
b) Anatase
c) Brookite
d) TiO2 (B)
(Red sphere represent
Titanium atoms and grey
sphere represent oxygen
atom)

8. Method of Synthesis of
TiO2

9. synthesis
Sol-Gel Method
Sol Method
Hydrothermal
Method
Using jasmine
flower extract
Method of synthesis

10. Synthesis of TiO2 coatings
•TiO2 can be prepared in the form of powder, crystals, or thin films.
• Liquid-phase processing is one of the most convenient and utilized methods of synthesis.
• It has the advantage of allowing control over the stoichiometry, production of homogeneous
materials, formation of complex shapes, and preparation of composite materials.
•However, there may be some disadvantages such as expensive precursors, long processing
times, and the presence of carbon as an impurity.
•The most used solution routes in the synthesis of TiO2 is Sol gel method.

11. Sol-Gel Method
• In the Sol-gel process, liquid solution (Sol) is
converted into a solid gel phase (Gel) .
•In a typical sol-gel process, TiO2 nanoparticles
are formed by hydrolysis and polycondensation
(de-hydration and de-alcoholation) reactions of
Titanium alkoxide, to form oxo polymers,
which are then transformed into an oxide network.
•The structure and properties of metal oxides is
strongly dependent on the rate of hydrolysis and
poly-condensation
Sol Gel Method

12. Optical Properties of TiO2

13. Optical Properties of TiO2
•The x-ray diffraction pattern confirms tetragonal anatase phase with average crystallite size
of 16–41 nm. TiO2 is one of the most optically active substance and used in many optical
instrument and has many optical Properties such as absorption coefficient ,photoconductivity
spectra , refractive index ,etc.
•The absorption coefficient above the threshold of fundamental absorption follows the (E-Eg)2
energy dependence characteristic of indirect allowed transitions, as illustrated by the α1/2
versus photon energy (E) plot .
•The extrapolated optical absorption gaps of anatase and rutile films are found to be 3.2 and
3.0 eV, respectively, at room temperature
•the absorption coefficient of rutile and anatase has been calculated by using the Formula,
(𝛼ℎ𝜈)1/2 = ( E− Eg)

14. (Room temperature optical absorption spectra of anatase and rutile films
plotted as α1/2 vs photon energy (E) graphs.)

15. Figure shows the photoconductivity spectra of anatase and rutile films. Again, the
photoconductivity threshold energy of the anatase film is higher than that of the rutile
film. The threshold energies approximately agree with the optical band gap energie
s derived from optical absorption, as indicated by the arrows .
(Photoconductivity spectra of anatase and rutile films. The excitation threshold
energies approximately coincide with the optical absorption edges, as indicated by the
arrows.)

16. •Electrical and optical spectroscopic studies of anatase and rutile thin films show that anatase has
properties different from those of rutile.
•At high doping concentrations, a Mott transition to metallic behavior of the donor-band conduction is
observed in anatase films, but not in rutile films.
•This indicates a comparatively large radius of donor electron wave function in anatase and a very
small one in rutile.
Difference between Anatase and
Rutile

17. (Experimental values of the ordinary (no) and extraordinary (ne) refractive index of rutile
TiO2 crystals as a function of wavelength at temperature T = 300C.)
•The rutile has positive birefringence, meaning that its extraordinary refractive index is larger than
its ordinary index. Birefringence is the phenomenon exhibited by certain materials in which an
incident ray of light is split into two rays, called an ordinary ray and an extraordinary ray.

18. Applications of TiO2

19. Applications of TiO2
•Titanium dioxide (TiO2) nanostructures are one of the most plentiful compounds that have
emerged in various fields of technology such as medicine, energy and biosensing.
TiO2 for Cancer Therapy
•TiO2 based nanostructures are potent systems for both targeted delivery and controlled
release of cytotoxic anticancer agents.
TiO2 -Based Antibacterial Devices for Prevention
•Various studies have explained that the photocatalytic activity of TiO2 in water is efficient
against broad range of organisms, such as bacteria, fungi, viruses, algae, protozoa and
bacterial toxins .

20. TiO2 Based Antibacterial application in orthopedic Implants
• A study suggested that Ag-doped TiO2 Nano tubes to reveal that surface modification of Ti-
based implants provides antibacterial properties for TiO2.
TiO2 in Cosmetic industry
TiO2 as Food Additive
•Titanium dioxide is a white metal oxide used in many food categories as food additives
to provide a whitening effect.
•Titanium dioxide has been used in various industrial and cosmetic applications due to its
unique elemental properties. It has been used in the cosmetics industry for “whitening”
and “thickening” in multiple make-up brands

21. CONCLUSION

22. •Rutile is the most widely investigated form of titanium dioxide, a wide-gap semiconductor of
great interest for fundamental research as well as for applications in electronic and optical
devices.
•The increasing interest in anatase is demonstrated by the recent successful application of
colloidal anatase in a novel photochemical solar cell.
• By the discovery of some of its properties, namely, high mobility n-type charge carriers, visible
luminescence due to self-trapped excitons, and a nonmetal-metal transition in the impurity band
of heavily reduced anatase thin films .