chap 1-5 (reference, appendix n cv).docx

8/10/2019 chap 1-5 (reference, appendix n cv).docx

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CHAPTER 1

INTRODUCTION

1.1 Background of study

Metal oxide nanoparticles are getting more attention by many researchers in recent

years due to their special electronic and chemical properties. Among the metal oxide

semiconductors, TiO 2 and ZnO have been studied extensively due to their chemical

stability and efficient photocatalytic properties (Stoyanova et al . 2013). Both of these

metal oxides are photoactive, photocatalytically active, and antibacterial. Hence they

are typically used in self-cleaning surfaces, water and air purification, and

bactericidal coatings against microbes.

Titanium dioxide (TiO 2) is an oxide of titanium that occur naturally

(Karunaratne 2010). TiO 2 is a cheap, harmless, white and non-biodegradable material

(substance that unable to breakdown naturally by the environment or need a long

period of time to breakdown). It is also has a high refractive index, high dielectric

constant, semiconductor properties and chemical stability (El-Nahass et al. 2012).

TiO 2 is widely produced as a thin film in the form of nanoparticles to the substrate.

The TiO 2 thin film has been studied many years due to their suitability in many

applications.


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It is used in photocatalytic activity, photovoltaic cell, and electrochromic

devices. This is due to their biocompatibility, thermal stability, strong oxidized

stability, non-toxicity and long term photostability (Senthil et al . 2010). It is also

used in non electronic devices such as optical brightener in paint, self-cleaning,

ingredient in sun cream, and bone implant. There are three natural phases of TiO 2,

which are anatase, rutile, and brookite. The anatase of TiO 2 often shows better

photocatalytic activity than rutile form. This has been agreed to the slightly higher

Fermi level of anatase. It has a lower capacity to absorb oxygen and a higher degree

of surface hydroxylation. In the photo-degradation process hydroxyl group on the

surface is very important. This is because in order to produce the very reactive OH

radicals, they directly trap photo-generated holes. Hence oxidize the organic

pollutant. The other indirect role of hydroxyl radical is in producing oxygen radicals

and hindering the electron hole recombination. This hydroxyl radical has a high

oxidization power that is well enough to oxidize and decompose viruses, organic

materials, odour and bacteria.

For most of the photocatalytic decomposition processes in TiO 2, photonic

efficiency is relatively low. Furthermore, photocatalytic reactions on TiO 2

nanoparticles can usually be induced only by ultraviolet light, which limits the

application of TiO 2 as a photocatalyst with visible light It is expected that the

composites of ZnO and TiO 2 would exhibit useful applications in photocatalysis. As

to this, recently, several papers that concerned in improving TiO 2 photocatalytic

activity have been reported. The nanoparticles of ZnO/TiO 2 film would show higher

photocatalytic efficiency than the efficiency of pure nano- ZnO film and nano- TiO 2

film.(Benkara et al . 2010)


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Various technique are used to synthesis thin film of TiO 2 and ZnO, including

vacuum evaporation, sputtering, molecular-beam epitaxy, laser-assisted vacuum

evaporation, chemical-bath deposition, electrodeposition, liquid phase deposition, dip

coating and sol gel process (Wang et al . 2013). However, out of these techniques, the

sol gel is considered as the best. This is because, the sol gel process is a liquid

deposit process using soft chemistry that giving homogenous deposit. This process

provides better prospect to deposit film with large surface area (El-Nahass et al .

2012). Beside that, this method is one of the simplest and economical in term of

equipment.

The sol gel process involves spin coating or dip coating of the oxide sol on

substrate. But in this study, we were focuses more on spin coating. Spin coating is

commonly used in the synthesis of TiO 2 thin film due to rapid growth rates, capacity

of handling large sample sizes, mass production capability, and high yield rates.

1.2 Problem Statement

In this modern day, there is a problem related to air contamination in our house,

workplace and building. This means, there is pollutant inside the building due to

present of viruses, organic materials, odour and bacteria. Furthermore, the

organisation that uses a lot of space for their building such as university, school,

hospital, and large company must used a lot of expenses for their cleaning equipment

and material.

Therefore, from the previous study TiO 2 and ZnO have a lot application such

as photocatalytic activity and self cleaning that is useful to overcome those problems.


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In addition, TiO 2 is a cheap, harmless, white and non-biodegradable material.

Moreover, in this study, we were synthesis the thin film of TiO 2 and ZnO

nanoparticles by sol gel spin coating. Where are more economical and lead to

improved performance of the films.

1.3 Significance of Study

The findings obtained at end of this study are significant to other researchers and

industrial practitioners. This is because we use cheaper substance such as TiO 2 and

ZnO. Furthermore, we also used sol gel process to synthesis TiO 2 and ZnO that is

simple and economical. Hence, would give the chance to produce large surface area

of the coating. Also provide great application in destruction and elimination of

pollutant in air.

1.4 Objectives of the Study

a) To prepare TiO 2 particles in solution from hydrolysis Titanium (IV)

Butoxide and prepare ZnO particles in solution from Zinc Nitrate

Hexahydrate by sol gel method.

b) To synthesize thin film of TiO 2 sol gel spin coating technique and ZnO

particles by solution-immersion technique.

c) To annealed thin film of TiO 2 at temperature 350 C, 400 C, 450 C, 500 C

and 550 C.

d) Characterization of TiO 2/ZnO particles by using UV-Vis (Ultraviolet-

visible Spectroscopy) and Photoluminescence Spectroscopy ( PL) and

Field Fourier Transform Infrared Spectroscopy ( FT-IR)


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CHAPTER 2

LITERATURE REVIEW

2.1 Overview

2.1.1 TiO2

Titanium dioxide (TiO 2) have been attracted many researchers due to its suitability in

many application. Such as, semiconductors, separation, catalysis and chemical

protection (Wang et al . 2013). Titanium dioxide has a wide band gap semiconductor

that exhibits high transparency to visible and near infra red (NIR) light (Hinczewski

et al . 2005). It has three crystalline phases: anatase (tetragonal), rutile (tetragonal),

and brookite. Brookite is a naturally occurring phase, and is extremely difficult to

synthesize. Anatase and rutile also occur naturally, but can be synthesized in the

laboratory easily.

TiO 2 has a wide band semiconductor. The band gaps of TiO 2 are 3.2 eV for

the anatase, , 3.02 eV for rutile and 2.96 eV for brookite phases. (Wunderlich W. et

al .2004). The valence band of TiO 2 consists of the 2p orbitals for oxygen hybridized

with the titanium 3d orbitals, while the conduction band is only the 3d orbitals of

titanium. When TiO 2 exposed to near-UV light, there is excitation of electrons in the

valence band to the conduction band. Hence, leaves the holes (h+), as shown in


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Figure 2.1. Then excited electrons (e ) in the conduction band will have purely 3d

state. The transition probability of e to the valence band decreases due to dissimilar

party. This leads to a reduction in the probability of e /h+ recombination.

Anatase TiO 2 is considered to be the active photocatalytic component based

on chemical properties, charge carrier dynamics, and the activity of photocatalytic

degradation of organic compounds. Figure 2.2 shows anatase TiO 2 has inherent

surface band bending that forms spontaneously in a deeper region with a steeper

potential compared with the rutile phase. Thus, surface holes trapping dominates

because spatial charge separation is achieved by the transfer of photogenerated holes

towards the surface of the particle via the strong upward band bending. However, in

the rutile phase, only holes that very close to the surface are trapped and transferred

to the surface when the bulk recombination of electrons and holes occurs.

Figure 2.1 Mechanism of light absorption by TiO 2 (Szaciowski K. et al . 2005)


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Figure 2.2 Surface band bending of the (a) anatase and (b) rutile phases of TiO 2

(Li G. et al . 2007)

2.1.2. ZnO

Zinc oxide (ZnO) is a chemical compound found naturally in the mineral called

zincite. It has concerning by many researchers recently due to its low cost and able to

obtained by simple techniques (Savi et al . 2012). The techniques is sol gel synthesis,

hydrothermal/solvothermal methods, microemulsion method, precipitation,and

physical vapor deposition. In the current study, ZnO nanoparticles was prepared by a

simple and cost effective sol gel method (Streams 2011). Sol-gel method gives high-

purity, homogenous, and high-quality nanopowders. The changes of solvent will

cause the morphology of the nanoparticles changing.

ZnO is a wide band gap semiconductor, where at room temperature it has an

energy gap of 3.37 eV. It has been used significantly for its catalytic, electrical,

optoelectronic, and photochemical properties. Based on large surface area and high

catalytic activity ZnO nanostructures, it will be beneficial to be apply to a catalytic

reaction process.(Kumar et al . 2013)


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2.2 Chemical structure

2.2.1 TiO2

TiO 2 is from the family of transition metal oxides. There are three generally known

polymorphs of TiO 2 found in nature: anatase (tetragonal), brookite (orthorhombic),

and rutile (tetragonal). Other than these polymorphs, there are two additional high-

pressure forms have been synthesized from the rutile phase. These are TiO 2 (II) with

a PbO 2 structure and TiO 2 with a hollandite structure.

Rutile TiO 2 has a tetragonal structure and contains 6 atoms per unit cell

(Figure 2.3). The TiO 6 octahedron is slightly distorted. The rutile phase is stable at

most temperatures and pressures up to 60 kbar, where TiO 2 (II) becomes the

thermodynamically favorable phase. It is found that anatase and brookite structures

transformed to the rutile phase after reaching a certain particle size. Where the rutile

phase becoming more stable than anatase when particle sizes greater than 14 nm

(Zhang et al .2000). Once the rutile phase formed, it grew more rapidly than the

anatase. The photocatalytic activity of the rutile phase is usually very poor. However,

it can be concluded that the rutile phase can be active or inactive, which depend on

its preparation conditions .

Anatase TiO 2 also has a tetragonal structure but the distortion of the TiO 6

octahedron is slightly larger for the anatase phase, as depicted in Figure 2.4. The

anatase phase has been reported to develop at temperature below 800 oC which at

higher temperatures transform to the more stable rutile phase (Mechiakh et al . 2011).

The anatase structure is favourable than the other polymorphs for solar cell

applications. This is because of its low dielectric constant, high electron mobility,


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and lower density. The slightly higher Fermi level that has low capacity to adsorb

oxygen and higher degree of hydroxylation in the anatase phase causes an increased

in photoreactivity. Brookite of TiO 2 belongs to the orthorhombic crystal system. The

unit cell TiO 2 has 8 formula units and is formed by edge-sharing TiO 6 octahedra

(Figure 2.5). It is more complicated, has a larger cell volume and is also the least

dense of the 3 forms and is not often used for experimental investigations (Thompson

et al , 2006).

Table 2.1 Crystal structure data for TiO 2 (Gupta and Tripathi 2011)

Properties Anatase Rutile Brookite

Crystal structure Tetragonal Tetragonal Orthorhombic

Lattice constant () a = 4.5936

c =2.9587

a = 3.784

c = 9.515

a = 9.184

b = 5.447

c = 5.154

Molecule 2 2 4

Density (g cm-3

) 4.13 3.79 3.99Ti O bond length

()

1.949

1.980

1.937

1.965

1.87 2.04

O Ti O bond angle 81.2

90.0

77.7

92.6

77.0 105

Figure 2.3 Crystal structure of rutile


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Figure 2.4 Crystal structure of anatase

Figure 2.5 Crystal structure of brookite

2.2.2 ZnO

ZnO crystallizes in the structure of wurtzite. Where each anion is bounded by four

cations at the corners of a tetrahedron, and vice versa ZnO is available as large bulk

single crystals. This tetrahedral coordination is usual of sp3 covalent bonding nature.

The present of substantial ionic character in the material tends to increase the band

gap further than expected from the covalent bonding. ZnO is a II VI compound

semiconductor whose ionicity resides at the borderline between the covalent and

ionic semiconductors. The crystal structures of ZnO are wurtzite (B4), zinc blende


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(B3), and rocksalt (or Rochelle salt) (B1) as schematically shown in Figure

2.6.(Properties 2009)

Figure 2.6 Crystal structures of ZnO

2.3 Properties of TiO2 & ZnO

2.3.1 Physical properties

Solutes will affect the solubility of titanium dioxide. It is soluble in hot concentrated

sulphuric acid, hydrochloric acid, nitric acid, but insoluble in dilute alkali and dilute

acid. Titanium dioxide has the performance of the semiconductor. Increasing

temperature will increase the conductivity rapidly. It is also very sensitive to

hypoxia. The melting and boiling points of the board of rutile and anatase titanium

dioxide in fact does not exist. This is because, when anatase and plate titanium

dioxide are at high temperatures, it can be transformed into rutile. Titanium dioxide

has a good thermal stability, the general amount of 0.01% to 0.12%. Furthermore,

titanium dioxide has not too strong hydroscopicity. Where, the hydrophilic is

connected to surface area. The large the surface area, provide greater moisture


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absorption. The moisture absorption of titanium dioxide is related to the surface

treatment and the nature too.

Zinc oxide crystallizes in two major forms, hexagonal wurtzite and cubic

zincblende. The wurtzite structure is most stable at ambient conditions and thus most

common. The growing of ZnO on substrates with cubic lattice structure able to

stabilized zincblende form. The zinc and oxide centers are tetrahedral in both cases,

the general characteristic geometry for Zn(II). At relatively high pressures about 10

GPa, ZnO converts to the rocksalt motif. Polymorphs of hexagonal and zincblende

do not have inversion symmetry (reflection of a crystal relative to any given point

does not transform it into itself). This and other lattice symmetry properties result in

piezoelectricity of the hexagonal and zincblende ZnO, and pyroelectricity of

hexagonal ZnO.

2.3.2 Chemical properties

Titanium dioxide is non-toxic and has stable chemical properties. Under normal

temperature, it almost has no reaction with other material. There is no reaction with

oxygen, hydrogen sulphide, sulphur dioxide, carbon dioxide and ammonia. It is also

insoluble in water, fatty acids, other organic acid and weak inorganic acid except for

alkali and hot nitric acid. But, in several specific conditions, titanium dioxide is able

to react with some substance.

For example, these reactions as follows:

1) TiO 2 can only totally soluble in the condition of long time boiling in strong

sulphuric acid and hydrofluoric acid. The reaction equation is as follows:


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TiO 2+ 2H 2SO 4 = Ti (SO 4)2 + 2H 2O

TiO 2+ H 2SO 4 = TiOSO 4 + H 2O

TiO 2 + 6HF = H 2TiF 6 + 2H 2O

2) Titanium dioxide can melt in the alkali (sodium hydroxide, potassium

hydroxide) or alkali metal carbonate (sodium carbonate, potassium carbonate).

Any one of which is have stated with titanium dioxide can be transformed into

soluble acid titanate.

For example, Titanium dioxide and sodium hydroxide's reaction equation:

TiO 2 + 4NaOH = Na 4TiO 4 + 2H 2O

3) At high temperature, the present of reductant (carbon, starch, petroleum

coke), results in chlorinationof titanium dioxide into titanium tetrachloride by

chlorine. The response equation is as follows:

TiO 2 +2C +2Cl 2 = TiCl 4 + 2CO

4) Titanium dioxide under high temperature can be restored into Low-valent

titanium compounds by hydrogen, sodium, magnesium, aluminum, zinc,

calcium, and some elements of the constant. Ti 2O3 will be obtained if the dry

hydrogen is put into red titanium dioxide. In 2000 and 15.2 MPa of hydrogen,

it also can get TiO. The injection of rutile titanium dioxide into the plasma

chamber, will be reduced it into titanium metal through hydrogen. Three reaction

equations are as follows:

2TiO 2 + H 2 = Ti 2O3 + H 2O

TiO 2 + H 2 = TiO + H 2O

TiO 2 + 2H 2 = Ti + 2H 2O

Crystalline zinc oxide is thermochromic, changing from white to yellow when

heated and in air reverting to white on cooling.


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Zinc oxide is an amphoteric oxide . It is almost insoluble in water, but it is

soluble in (degraded by) most acids, such as hydrochloric acid:

ZnO + 2 HCl ZnCl 2 + H 2O

ZnO is a considerably stable compound. It has a melting point around 1975

degree celcius in which it decomposes into Zinc Vapor and Oxygen.

2.4 Nanoparticles of titanium dioxide and zinc oxide

Various investigations have recognized that TiO 2 is much more effective as a

photocatalyst in the form of nanoparticles than in bulk powder (Han H, Ba R. 2009).

When the diameter of the crystallites of a semiconductor particle falls below a

critical radius of about 10 nm, each charge carrier appears to behave quantum

mechanically as a simple particle in a box. As a result of this confinement, the band

gap increases and the band edges shift to yield larger redox potentials. However, the

solvent reorganization free energy for charge transfer to a substrate remains

unchanged.

Mill and Le Hunter (1997) reported that decreasing particle size resulted in

absorption edge blue shifts, the redox potentials of the photogenerated electrons and

holes in quantized semiconductor particles increased. Means, quantized particles

show higher photoactivity than macrocrystalline semiconductor particles.

Futhermore, TiO 2 has been prepared in the form of powders, crystals, thin films,

nanotubes and nanorods. Liquid phase processing is one of the most suitable and

frequently used methods in chemical synthesis. This method has the advantages of

controlling the stoichiometry, homogeneous products and allowing the formation of

complex shapes and preparation of composite materials.
http://en.wikipedia.org/wiki/Amphoteric_oxidehttp://en.wikipedia.org/wiki/Amphoteric_oxidehttp://en.wikipedia.org/wiki/Solubilityhttp://en.wikipedia.org/wiki/Acidhttp://en.wikipedia.org/wiki/Acidhttp://en.wikipedia.org/wiki/Hydrochlorichttp://en.wikipedia.org/wiki/Hydrochlorichttp://en.wikipedia.org/wiki/Hydrochlorichttp://en.wikipedia.org/wiki/Acidhttp://en.wikipedia.org/wiki/Solubilityhttp://en.wikipedia.org/wiki/Amphoteric_oxide


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2.5 Study of TiO2 and ZnO thin films with the same parameters.

2.5.1 Surface Morphologies and photocatalytic activity of TiO2 thin film

annealed at different temperature by AFM

TiO 2 thin film was synthesis using spin coating technique at different annealing

temperature. The study is to determine the optimal annealing temperature, that able

to produce the most excellent photocatalytic performance. Atomic force microscopy

(AFM) was used to determine the surface roughness. While the thin film optical

properties of were determine by UV-VIS spectroscopy (PerkinElmer). The starting

material in this study is titanium isopropoxide (TIP).

From the AFM images and data, as shown in Table 2.2, it show that for the

crystalline films, increasing annealing temperature causes slightly increased of the

grain size and significantly increased the surface roughness. But the thickness of the

film remained at ~255 nm, regardless of the annealing temperature. All of the films

were highly transparent in the visible region (~80%), the optical indirect band gap

decreased slightly with increasing annealing temperature. For the total range films,

the increased annealing temperature to 400 C show the increased of photocatalytic

performance. But, after increase to higher temperature the performance was observed

to decrease. Thus, it concluded that for an annealing time of 2 hour, 400 C is the

optimal temperature for annealing TiO 2 thin film. (Lin et al . 2013)


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Table 2.2 Analytical data

Parameter Units Annealing temperature ( oC)

300 400 500

Mineralogy - Amorphous Anatase Anatase

Average grain size Nm ~10 ~23 ~29

Arithmetic surface roughness Nm 0.32 0.59 0.96

Film thickness Nm ~260 ~250 ~246

Transmission in visible range % ~80 ~80 ~80

Optical indirect band gap eV 3.49 3.49 3.43

Figure 2.7 Images of AFM with different annealing temperature


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2.5.2 Influence of Annealing Temperature on the Photoluminescence Property

of ZnO thin film covered by TiO2 nanoparticles

Fig. 2.8 shows the photoluminescence spectra of TiO 2 ZnO thin films and the bare

ZnO thin film.For the bare ZnO thin film, it has an ultraviolet emission peak centered

at 384 nm. This originates from the recombination of free exciton. There is also

present of wide and weak green emission band. The emission mechanism of green

emission behaviour of ZnO material is unclear yet although it has been widely

studied. There are suggestions from several researchers where the green emission is

probably related with oxygen vacancy defect in ZnO materials.

The results show the ultraviolet emission of ZnO thin films is greatly

improved after they are covered by TiO 2 nanoparticles, while the green emission is

hidden. At pretty high annealing temperature (more than 500 C), the intensity of

ultraviolet emission will decrease and a violet emission peak along with a blue

emission peak appears. This is probably related with the atomic interdiffusion

between TiO 2 nanoparticles and ZnO thin film. Hence, choosing a suitable

annealing temperature is a main factor to obtain the most efficient ultraviolet

emission from TiO 2 ZnO thin film. (Xu et al . 2010)


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Figure 2.8 Photoluminescence spectra of the bare ZnO thin film and TiO 2 ZnO thin

films.

2.6 Photocatalytic activity

In chemistry, the presence of a catalyst will accelerated the photoreaction of

photocatalysis. The light is absorbed by an adsorbed substrate in catalysed

photolysis. In photogenerated catalysis, the photocatalytic activity (PCA) depends on

the ability of the catalyst to create electron hole pairs, which generate free radicals

(e.g. hydroxyl radicals: OH) that able to undergo secondary reactions.

For photocatalytic oxidation (PCO), it is occurs when UV light rays is join

with a TiO 2 coated filter. Where creating hydroxyl radicals and super-oxide ions, that

are extremely reactive electrons. These extreme reactive electrons will violently

combine with other elements in the air, such as bacteria and volatile organic

compounds (VOCs). Where include unsafe pollutants such as ammonia,

formaldehyde and many other regular contaminates that released by building

materials and household cleaners generally found in the home.


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The chemical reaction is occurred between the super-charged ion and the

pollutant after bound together and efficiently "oxidizing" (or burning) the pollutant.

The pollutant will breaks down into non dangerous carbon dioxide and water

molecules. Hence, makes the air more purified.

Figure 2.9 Principle of Photo-catalytic Oxidation

ZnO are most extensively used semiconductor photocatalysts due to their

high photosensitivity, photochemical stability, large band gap, strong oxidizing

power and non-toxic nature.


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CHAPTER 3

METHODOLOGY

3.1 Chemical:

TiO 2 solution

1. Titanium (IV) Butoxide, reagent grade, 97% AIDRiCH.

2. Glacial Acetic Acid (GAA), Glacial (CH 3COOH), (J.T. BAKER)

3. Triton-X. (J.T. BAKER)

4. Ethyl alcohol.

ZnO solution

1. Zinc Nitrate Hexahydrate

2. Hexamethylenetetramine (HMTA)

3.2 Apparatus:

1. Glass substrate

2. Measuring cylinder (100 mL)

3.

Beaker (250 mL & 50 mL)

4. Schott bottle (100 mL)

5. Magnetic stirrer

6. Sample container

7. Sample box

8. Tweezer

9. Reaction bottle


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3.3 Preparation of Glass Substrate:

The glass substrate of microscope is cut into 3 pieces using the diamond cutter, with

the size of approximately 2.0 cm 2.0 cm for each piece. Methanol, acetone and DI

water is used to clean the glass substrates (so that no extraneous particles on their

surfaces) by using Ultrasonic bath for 5 minutes at 40 C.

i. Methanol : 2 times

ii. Acetone: 2 times

iii. DI water: 2 times

The wet glass substrates is then dried out using hair dryer and put into a sample

container.

3.4 Preparation of TiO 2 Structures:

22.203 mL Ethanol + 4.254 mL TTiB + 1.250 mL GAA + 1 drop Triton X-100 +

0.090 mL DI water and lastly 22.03 mL ethanol was added again into a 100mL

schott bottle at 60 C with continuous stirring to prepare 0.25 M of TiO 2 solution.

After 2 hours, the heat was turned off and stirring is continued for 22 hours.

3.5 Deposition of TiO2 Structures:

TiO 2 thin films were deposited using sol-gel spin coating method. The deposition of

TiO 2 on the glass substrate required 15 drops of TiO 2 sol gel for each layer. Where in

this study each samples prepared is coated with 7 layer of TiO 2 sol gel. This method

involves three steps, which are:

a. Step 1: time= 10 s, speed= 3000 rpm

b. Step 2: time= 30 s, speed= 6000 rpm

c. Step 3: time= 10 s, speed= 2000 rpm


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For each layer of TiO 2, the film was heated in an oven at 150 C for 10 minutes. The

sample was annealed in annealing chamber at 350 C, 400 C, 450 C, 500 C and

550 C for 2 hours.

3.6 Preparation of ZnO Structures:

1.4875 g of Zinc Nitrate Hexahydrate was dissolved in 100 mL of DI water. 0.7012 g

of Hexamethylenetetramine (HMTA) was dissolved in 100 mL of DI water. Then,

the HMTA solution was added into Zinc Nitrate Hexahydrate solution and was

mixed well. The zinc solution is then transferred into a schott bottle and the beaker

containing solution must carefully rinsed with another 50 mL of DI water to make

sure no solution is left. The ZnO solution was heated at 60 C with continuous stirrer.

After 2 hours, the heat was turned off and stirring is continued for 22 hours.

3.7 Deposition of ZnO Structures:

The glass substrate that has been coated with TiO 2 was placed in the reaction bottle.

Then the glass substrate was immersed in ZnO solution and the reaction bottle is

capped. The reaction bottle is placed in water bath at 90 C for 4 hours. After 4

hours, the ZnO solution is removed and the glass substrate was rinsed with DI water

before heated in the oven at 150 C for 20 minutes. The sample was annealed in the

annealing chamber at 500 C for 1 hour.

3.8 Characterization of TiO 2 Structures:

3.8.1 UV-Vis

Ultraviolet (UV) and visible radiation consist of only a small part of the

electromagnetic spectrum. Electromagnetic radiation can be considered a


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combination of alternating electric and magnetic fields that travel through space with

a wave motion. Because radiation acts as a wave, it can be classified in terms of

either wavelength or frequency. When light passes through or is reflected from a

sample, the amount of light absorbed is the difference between the incident radiation

and the transmitted radiation. The amount of light absorbed is expressed as either

transmittance or absorbance. Ultraviolet-visible spectroscopy is used to determine

the optical properties of the thin film TiO 2/ZnO structures.(Upstone 2000)

3.8.2 Photoluminescence Spectrosccopy (PL)

Photoluminescence spectroscopy is a contactless, non-destructive method of probing

the electronic structure of materials. The absorption of light causes the photo-

excitation process occurs when the light is directed to the sample. In this process, the

material jumps to a higher electronic state and when in relaxes it will release the

energy as photon and then return back to a lower energy level. This emission of light

is called photoluminescence (PL). PL is used to investigate the impurity level and

defects, recombination mechanism and quality of material.(C.Li 2006)

3.8.3 Fourier Transform Infrared (FT-IR)

Infrared spectroscopy is to study the interactions between matter and electromagnetic

fields in the infrared region. In this spectral region, the electromagnetic waves

mainly couple with the molecular vibrations. Which is by absorbing IR radiation, a

molecule are able to excite to higher vibrational state. The probability of a particular

IR frequency being absorbed depends on the actual interaction between this

frequency and the molecule. Generally, a frequency will be strongly absorbed if its

photon energy coincides with the vibrational energy levels of the molecule .The


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resulting spectrum shows the absorption and transmission of molecular. Hence,

creates a molecular fingerprint of the sample. Like a fingerprint no two unique

molecular structures produce the same infrared spectrum. (Nicolet et al. 2001).


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CHAPTER 4

RESULT AND DISCUSSION

4.1 Characterization of TiO 2/ZnO Structures

4.1.1 UV-Vis Results of TiO2/ZnO Structures

Figure 4.1 shows the optical transmittance for different annealing temperature of

TiO 2/ZnO thin film which is measured in the range of wavelength 200-850 nm. The

transmittance spectra show that all film had average transmittance between 1% to

80% within the visible region (400-850 nm). The transmission decreases sharply near

the ultraviolet region about 380 nm due to the band gap absorption.

It is also found that the as-grown of TiO 2/ZnO thin film has the highest

transmittance compare to the others. As-grown is the thin film that has the layer

coated with TiO 2 which did not undergo any annealing process before being coated

with ZnO. The transmittance for the as-grown is about 80%. While, for all of the film

analyzed it is observed that the increase of annealing temperature would decrease the

optical transmission. To be specific, the thin film that was annealed at 350 C, 400 C

and 450 C has similar pattern of transmittance. All of these films start to transmit at

the wavelength 300 nm.

While, the films annealed at temperature 500 C to 550 C behave differently.

It starts to transmit at the wavelength of 500 nm. Based on this observation, it can be

assume that there are changes in the structure of the thin films when annealed at


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different temperature. As it is obviously seen the thin films annealed at temperature

500 C and above have the transmission differ from the other.

However, overall the increased of annealing temperature has the effect of

lowering the transmittance. It is might be due to the increased of the film surface

roughness and increase light scattering on the surface when annealed at certain

temperature. The increase in surface roughness also means that there is decrease in

the films transparency (Firdaus et al . 2012). The low transmittance in visible range

causes light scattering on rough surface of thin film as the particle is less uniformly

dispersed on the glass substrate due to formation of large agglomerated particle. As

obtained in the result, starting at annealing temperature of 500 C and above the

transmittance of the thin film is very low. Means starting temperature of 500 C the

structures of the compound begin to change and became rough which causing the

light to scattered. Hence, decrease the film transparency.

200 300 400 500 600 700 800

0

20

40

60

80

% T

r a n s m

i t t a n c e

Wavelength / nm

as-grown 350 400 450 500 550

as grown

350 oC

550 oC450 oC

500o

C400 oC

Figure 4.1: Ultraviolet- visible transmittance spectra of TiO 2/ZnO with

different annealing temperature


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27

Figure 4.2 shows that the absorption of TiO 2/ZnO thin film increase with

increase of annealing temperature from 350 C to 550C. All the thin film annealed

starts to absorb light at the wavelength of 300 nm. The absorption for all thin film in

the ultraviolet range is relatively high which is at the intensity of 6 arbitrary unit, but

then decrease gradually in the visible region. Where, the absorption is actually

inversely proportional to the transmittance. This might be related to the increase in

grain size which contributes to the light scattering effect due to the high surface

roughness.

400 600 800

0

2

4

6

A b s o r b a n c e

( a . u . )

Wavelength / nm

as-grown 350 400 450 500 550

500 oC

550 oC

450 oC

400 oC

350 oCas-grown

Figure 4.2: Ultraviolet- visible absorbance spectra of TiO 2/ZnO with

different annealing temperature

4.1.2 Photoluminescence Spectroscopy (PL)

Figure 4.3 shows there are two types of peak emission, which are ultraviolet peak

emission and visible peak emission. The peak of ultraviolet can be seen near the

ultraviolet region about 380 nm. Figure 4.3 also shows that the increase of


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annealing temperature will increase the ultraviolet emission until it reaches 450 C.

However, the ultraviolet emission is reduced when the annealing temperature

increase from 500 0C to 550 0C (Xu et al . 2010).

Figure 4.4 shows the enlargement of Figure 4.3 which focuses on the peak at

the UV region within the wavelength of 350 nm 450 nm. It is observed there is a

red-shift occurred as the temperature increased from 350 C to 450 C. The increase of

annealing temperature from 350 C, 400 C and 450 C shows the peak emission will

shifted at 382 nm, 387 nm and 392 nm respectively. However, at the annealing

temperature 500 C and 550 C there is no shifted occur as it has peak relatively

similar as 350 C. This means the increased of annealing temperature might cause

red-shift. Red-shift is occurs usually due to decrease of the band gap cause by the

increase in particle size. (Epitaxy 2001).

Figure 4.5 and 4.6 is plotted based on information obtained from Figure 4.3

by using temperature versus intensity. It differentiates between the peak emission of

UV region and the peak emission of visible region. From both of this figures, it

shows that the increase of annealing temperature on thin film from 350 C to 450 C

will increase the PL peak for both of UV and visible region. However, further

increase of annealing temperature from 500 C to 550 C will decrease the PL peak for

both of the region.

From the observation obtained, it obviously shows that the increase of

annealing temperature on thin film of TiO 2/ZnO structures will increase the peak

emission until certain temperature. Here, in this study, PL peak emissions increase as


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the temperature increases until 450C. The increase in PL peak emission is deduced

due to quality improvement of crystal after being annealed (Du n.d.).While further

increase of annealing temperature up to 500 C and above shows the decreases of PL

peak emission. The crystalline quality of TiO 2/ZnO decrease when the annealing

temperature increased up to 500 C and above (Xu et al . 2010) Based on this

observation, the optimum annealing temperature for the synthesis of TiO 2/ZnO thin

film nanostructures is 450 C.

300 400 500 600 700 800 9000

50

100

150

200

250

300

350

I n t e n s i t y ( a

. u . )

wavelength / nm

as-grown 350 400 450 500 550

450 o C

400 o C

350 o C

500 o C 550 o C

as-grown

Figure 4.3 PL result of TiO 2/ZnO with different annealing temperature.

350 360 370 380 390 400 410 420 430 440 4500

5

10

15

20

25

30

35

40

45

50


. u . )

wavelength / nm

as-grown 350 400 450 500 550

450 o C

400 o C

350 o C

500 o C550 o C

as-grown

Figure 4.4 PL result of TiO 2/ZnO with different annealing temperature on

UV region


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30

0 50 100 150 200 250 300 350 400 450 500 550

5

10

15

20

25

30

35

40

45

50

I n t e n s i t

y ( a

. u . )

Annealing Temperature ( o C)

Figure 4.5 PL emission of TiO 2/ZnO thin film in UV region at variousannealing temperatures (wavelength 380 nm 400 nm)

0 100 200 300 400 500 600

0

50

100

150

200

250

300

350


. u . )

Annealing Temperature ( o C)

Figure 4.6 PL emission of TiO 2/ZnO thin film in visible region at various

annealing temperatures (wavelength 450 nm 800 nm)


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4.1.3 Fourier Transform Infrared (FT-IR)

Figure 4.7 shows the FT-IR result of TiO 2/ZnO thin film annealed with different

temperatures. All the films are analyzed in the wavenumber range of 400-4000 cm -1.

It is observed there is no absorption band from 1200 cm -1 to 4000 cm -1. Then, the

observation is conducted again by using the wavenumber range at 400 cm -1 to 1050

cm -1 as shown in Figure 4.8. The reduce of the wavenumber range is to analyzed the

absorption band more clearer, as there is no absorption band observed at the range

higher than 1200 cm -1.Figure 4.8 shows the present of strong absorption band for all

thin film of TiO 2/ZnO at 540 cm -1 which assigned for Ti-O-Ti bond.(Sonone 2014)

There is also absorption band observed at 460 cm -1 that assigned as zinc oxide bond.

Based on this observation, it is assumed all the thin film of TiO 2/ZnO that

coated with annealing temperature from 350 C to 550 C does not contain any

organic bonding such as aliphatic, C-C bond, alkyl, C-H bond and hydroxyl bond, C-

OH. The thin films of TiO 2/ZnO will also not have the hydroxyl bond because all of

the film has undergo annealing process.(Merouani 2008). This means during

annealing process the moisture has been lost. However, it is deduce that there is no

interaction between the chemical structures of TiO 2 and ZnO. This might be due to

different layer of coating. As TiO 2 layers is coated first then followed by ZnO layer.

Table 4.1 contain the chemical bond and their wavenumber that related to the

nanocrystalline of TiO 2/ZnO.


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32

400 800 1200 1600 2000 2400 2800 3200 3600 400080

85

90

95

100

105

110

I n t e n s i t y ( a u )

Wavenumber (cm -1 )

as-grown 350 400 450 500 550

400 o C

450 o C

350 o C

500 o C

as-grown

550 o C

Figure 4.7: FT-IR result of TiO 2/ZnO with different annealing temperature

(Wavenumber 350 cm -1-4000 cm -1)

400 500 600 700 800 900 1000

70

80

90

100

110

120

130

140

150


. u . )

Wavenumber (cm -1 )

as-grown 350 400 450

500 550

550 o C

400 o C

500 o C

450 o C

350 o C

as-grown

Figure 4.8: FT-IR result of TiO 2/ZnO with different annealing temperature

(Wavenumber 350 cm -1-1050 cm -1)


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34

CHAPTER 5

CONCLUSION AND RECOMMENDATION

3.8 Conclusion

The structured of TiO 2/ZnO thin film are prepared by sol-gel spin coating technique

on the glass substrate. Firstly,the glass substrate is coated by TiO 2 film and annealed

with different temperature. Only then, ZnO film is coated on the TiO 2 film and

forming TiO 2/ZnO thin film. Here the effect of annealing temperature on optical

properties is studied by using UV-Vis, photoluminescence (PL) and FT-IR

measurement. The variation of annealing temperature contributes a great effect on

the optical properties of TiO 2/ZnO structures.

From the UV-Vis result, it reveals that the increased of annealing temperature

on the thin film of TiO 2/ZnO structures will causes a decrease in the transmittance at

the ultraviolet region and conversely cause an increase in thin film absorbance.

Based on PL result, the increased of annealing temperature will increased the

photoluminescence peak with temperature from 300 0C to 450 0C. As the temperature

increase further the photoluminescence peak will decrease. So, we can conclude that

450 C is the optimum annealing temperature to synthesize thin film of TiO 2/ZnO.

While at the ultraviolet region there is shifted of PL peak from 385 nm to 395

nm at annealing temperature 350 C to 450 C. This indicates the present of red shift.


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35

Hence, the decrease of the optical band gap maybe due to the increase of crystalline

structure.

In the FT-IR measurement, all of the thin film shows a strong adsorption band

near 540 cm -1. This reveals the vibration properties of TiO 2. There is also presence of

absorption band at 460 cm -1 which indicates the vibration properties of ZnO. There is

no absorption band found at the range of 2000 cm -1 to 4500 cm -1. This means there is

no organic compound present in the thin film. The hydroxyl bond also not present,

the moisture has been removed during the annealing process.

3.9 Recommendation

This present work is only focused on the optical properties of TiO 2/ZnO

nanostructures. The better result and understanding might be obtained if focused on

the other properties such as electrical properties, structural properties and surface

morphology. The optimum annealing temperature obtained by this study for

synthesis TiO 2/ZnO nanostructures can also be used in the future


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Du, Guotong. (2003) The Study of Deep -Level Emission Center in ZnO Films. 1 13.

El-Nahass, M.M., Ali, M.H., and El-Denglawey, A. (2012) Structural and Optical

Properties of Nano-Spin Coated Sol gel Porous TiO2 Films. Transactions of Nonferrous Metals Society of China 22(12): 3003 11.

Epitaxy, Beam. (2001) Defense Technical Information Center Compilation Part Notice.

Firdaus, C.M., Shah Rizam, M.S.B., Rusop, M. and Rahmatul Hidayah, S. (2012)Characterization of ZnO and ZnO: TiO 2 Thin Films Prepared by Sol-GelSpray- Spin Coating Technique. Procedia Engineering 41(Iris): 1367 73.

Gupta, Mital, S. and Manoj, T. (2011) A Review of TiO 2 Nanoparticles. ChineseScience Bulletin 56(16): 1639 57.

Han, H., and Ba, R. (2009) Buoyant photocatalyst with greatly enhanced visible-light activity prepared through a low temperature hydrothermal method IndEng Chem Res, 48: 2891 2898

Hinczewski, D., Saygn, M. , Hinczewski, F., Tepehan, Z. and Tepehan, G.G. (2005)Optical Filters from SiO 2 and TiO 2 Multi-Layers Using Sol gel Spin CoatingMethod. Solar Energy Materials and Solar Cells 87(1-4): 181 96.

Karunaratne, V. (2010) Photocatalyytic Activity of Nano-TiO2 on Glass in Building

Envelope 1 Introduction 2 Material and Methods. :13 14.

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International Nano Letters 3(1): 30.

Lin, C.-P., Chen, H., Nakaruk, A., Koshy, P. and Sorrell, C.C. (2013) Effect ofAnnealing Temperature on the Photocatalytic Activity of TiO 2 Thin Films.

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Mechiakh, R., Sedrine, N.B., and Chtourou, R. (2011) Sol gel Synthesis,

Characterization and Optical Properties of Mercury-Doped TiO 2 Thin FilmsDeposited on ITO Glass Substrates. Applied Surface Science 257(21): 9103 9.

Merouani, A. (2008) S pectroscopic FT-IR Study of TiO 2 Films Prepared by Sol-GelMethod . 6(62): 151 54.

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Properties, General. (2009) General Properties of ZnO .

Savi, Bruna Martinello, Larissa Rodrigues, and Adriano Michael Bernardin. (2012)Synthesis of ZnO Nanoparticles by Sol- Gel Processing . 1 8.

Senthil, T.S., Muthukumarasamy, N., Agilan, S., Thambidurai, M., andBalasundaraprabhu, R. (2010) Preparation and Characterization of

Nanocrystalline TiO 2 Thin Films. Materials Science and Engineering: B 174(1-3): 102 4.

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Stoyanova, A., Hitkova, H., Iordanova, R., Ivanova, N., and Sredkova, M. (2013)Synthesis and Antibacterial Activity of TiO 2/ ZnO Nanocomposites Preparedvia Nonhydrolytic Route a ) b ). 154 61.

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APPENDICES

1. Figures of ultraviolet-visible transmittance spectra of TiO 2/ZnO with

different annealing temperatures.

200 300 400 500 600 700 800

0

20

40

60

80

% T

r a n s m i t t a n c e

Wavelength / nm

as-grown 350 400 450 500 550

as grown

350 o C

550 o C450 oC500 o C

400 o C

2. Figures of ultraviolet-visible absorbance spectra of TiO2/ZnO with different

annealing temperatures

400 600 800

0

2

4

6

A b s o r b a n c e ( a

. u . )

Wavelength / nm

as-grown 350 400 450 500 550

500 o C

550 o C

450 o C

400 o C

350 o Cas-grown


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3. PL result of TiO 2/ZnO with different annealing temperature

300 400 500 600 700 800 9000

50

100

150

200

250

300

350

I n t e

n s

i t y

( a

. u . )

wavelength / nm

as-grown 350 400

450 500 550

450 oC

400 oC

350 oC

500 oC 550 oC

as-grown

4. FT-IR results of TiO 2/ZnO with different annealing temperature.

400 800 1200 1600 2000 2400 2800 3200 3600 400080

85

90

95

100

105

110

I n t e n s i

t y ( a u

)

Wavenumber (cm -1)

as-grown 350 400 450 500 550

400 oC

450 oC

350 oC

500 oC

as-grown

550 oC


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41

CURRICULUM VITAE

A. Personal profile

Full name Siti Rahayu Binti Shahri

National IC number 910618-14-6478

Birth date 18 t June 1991

Citizenship Malaysian

Place of birth Kuala Lumpur, Malaysia

Gender Females

Correspondence address Batu 2 Kampung Bukit

Badong, 45600 Btg Berjuntai,

Selangor.

Telephone number (HP) 013-2848236

Email address [email protected]

B. Hobbies and interests

I enjoying reading, travelling and exploring places. I like to listen to music and I

enjoying making friend with people. I am fluent in Bahasa Malaysia, good in English

and basic in Mandarin.


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C. Education background

1. Sept 2011- July 2014 : University Technology Mara, Shah Alam

Bachelor of Science (Hons) of Applied Chemistry

2. 2009-2011 : Matriculation College of Negeri Sembilan

Life Science

3. 2007-2008 : Sekolah Menengah Kebangsaan Raja Muda Musa,

Selangor Sijil Pelajaran Malaysia (SPM)

D. Work experiences

Post Place Year

Industrial training Department of Chemistry

Malaysia, Petaling Jaya

2013

E. Related experiences

Post Club Year

Member Outward Bound Kesatria

(Uitm Shah Alam)

2011-2013

Member Applied Chemistry

Society (ACES)

2011-2014

chap 1-5 (reference, appendix n cv).docx

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