Luận văn thạc sĩ fabrication of photocatalytic thin films containing tio2 nanoparticles and poly(l dopa) by layer by layer self assembly

DOCUMENTATION PAGE WITH ABSTRACT Thai Nguyen University of Agriculture and Forestry Degree Program Bachelor in Environmental Science and Abstract: The photocatalytic thin films contain

THAI NGUYEN UNIVERSITY UNIVERSITY OF AGRICULTURE AND FORESTRY

DUONG CUONG THINH

FABRICATION OF PHOTOCATALYTIC THIN FILMS CONTAINING

Batch : 2011-1016

Thai Nguyen, 15/09/2016

DOCUMENTATION PAGE WITH ABSTRACT

Thai Nguyen University of Agriculture and Forestry

Degree Program Bachelor in Environmental Science and

Abstract:

poly(L-Dopa) were fabricated by layer-by-layer self-assembly The thin films were

characterized by dynamic light scattering (DLS), Fourier transform infrared

spectroscopy (FTIR), scanning electron microscopy (SEM), and atomic force

microscopy (AFM) The photocatalytic activity was evaluated through the degradation

of sulforhodamine B (SRB) in aqueous solution Nano-structured thin films under

different conditions and their photocatalytic activities were investigated and studied

Poly(acrylic acid) (PAA) was used to verify the role of poly(L-Dopa).The results show

that layer-by-layer self-assembly was a simple and useful method to fabricate

Nano-structured thin films with low cost and high reusability High transparency films using

Degussa P25 was attributed to suitable particle size and colloidal stability

Poly(L-Dopa) with negatively charge at wide range of pH values made it a good substitute

among commercially available polyelectrolytes P25 and poly(L-Dopa) were recorded

as an optimal charge with high zeta-potential and small particle size, contributing for

high colloidal stability and low sedimentation at pH 3 The obtained multilayer films

retained the band gap of bare P25 at 3.2 eV and the properties of functional groups of

poly(L-Dopa) The optimal number of P25/Poly(L-Dopa) bilayers was 20.5.The

photocatalytic thin films containing P25 and poly(L-Dopa) are promising materials for

ACKNOWLEDGEMENT

To have completed this thesis, in addition to the ongoing efforts of myself, I

would like to thank for teachers in faculty of International Training and Development

as well as teachers in Thai Nguyen University of Agriculture and Forestry, who have

dedicated teaching to me the valuable knowledge during study time in the university

and given me a chance to do my thesis oversea I had a precious opportunity to take

part in the internship in Department of Biomedical Engineering and Environmental Sciences in National Tsing Hua University (NTHU), Taiwan

First of all, I want to thank my supervisors Assoc Prof Wu Chien-Hou from

Biomedical Engineering & Environmental Science Department, National Tsing Hua

University and PhD Nguyen Huu Tho from Thai Nguyen University of Agriculture

and Forestry Their priceless advices are not only valuable to my research in order to

gain successful results, but also contribute to my future career orientation

the laboratory, who facilitated and provided the information and data necessary for my

implementation process and helped me finish this thesis

Last but not least, thanks to my parents and good friends who always encourage

me and offer support and love

Sincerely,

Duong CuongThinh

TABLE OF CONTENT

ACKNOWLEDGEMENT iii

TABLE OF CONTENT iv

LIST OF FIGURES 1

LIST OF TABLES 3

LIST OF ABBREVIATIONS 4

PART I INTRODUCTION 5

1.1 Research rationale 5

1.2 Research’s objectives 7

1.3 Research questions and hypotheses 7

1.4 Limitations 7

PART II LITERATURE REVIEW 8

2.1 Overview of Titanium dioxide 8

2.1.1 Titanium oxidation structures and properties 8

2.1.2 The photocatalytic activity of TiO2 9

2.2 Layer-by-layer self-assembly 10

2.3 Overview of Poly(L-Dopa) 12

PART III METHODS 13

3.1.1 Chemicals 13

3.1.2 Equipment 14

3.2 Methods 14

3.2.1 General principle 14

3.2.2 Fabrication of photocatalytic thin [TiO2/ Polymer]n films by the layer-by-layer self-assembly 15

3.2.2 Characterization 17

3.2.3 Photodegradation performance 19

PART IV RESULT 20

4.1 Optical Photo 20

4.1.1 Optical photos of P25/PDopa films 20

4.1.2 Optical photos of multiple films 20

4.2 Characterization of P25/Pdopa 21

4.2.1 Dynamic Light Scattering (DLS) 21

4.2.2 FTIR 23

4.2.3 SEM images of P25/Pdopa 24

4.2.4 AFM 26

4.3 Photodegradation performance 30

4.3.1 Calibration 30

4.3.2 Photodegradation activities of PDopa films 31

4.3.2 Photodegradation performance of TiO2 34

4.4 P25/PDoPa films band gap 36

PART V DISCUSSION AND CONCLUSION 38

5.1 Discussion 38

5.2 Conclusion 40

REFERENCES 41

LIST OF FIGURES

Figure 1Crystal structures of rutile, anatase and brookite titanium dioxide 9

Figure 2 Schematic diagram illustrating the principle of TiO2 photocatalysis with the presence of water pollutant (RH) 10

Figure 3 The principle of Layer-by-layer self-assembling method 11

Figure 4 Poly(L-DOPA) 12

Figure 5 Chemicals: a) PDopa, b) SRB 10 uM, DIW c) pH=3, d) PAA 13

Figure 6 Equipment: a) UV-Visible Spectrophotometer, b) Photochemical reactor, c) pH adjustment, d) Magnetic stirrer, e) Ultrasonic, f) DLS 14

Figure 7 Experimental process 15

Figure 8 Photos of P25/PDopa film 20

Figure 9 5.5 bilayer thin films' images: a) St-01, b) St-21, c) P25 20

Figure 10 TiO2 size and zeta-potential at (pH=3, concentration = 1g/l) 21

Figure 11 PDopa zeta-potential and P25 zeta-potential varied from pH 22

Figure 12 P25 size varied from pH 22

Figure 13 FT-IR spectra of Degussa P25, L-Dopa, PDopa, P25/PDopa, PAA, P25/PAA 23

Figure 14 SEM images of (a) 0.5 bilayers, (b) 1.5 bilayers, (c) 2.5 bilayers, (d) 5.5 bilayers, (e) 10.5 bilayers, (f) 15.5 bilayers, (g) 20.5 bilayers 26

Figure 15 AFM images of thin films prepared with the coating sequence of

(P25/PDopa)n: a) 0.5 bilayers, b) 2.5 bilayers, c) 5.5 bilayers before photodegradation

in UV light d) 5.5 bilayers after photodegradation in UV light, e) 5.5 bilayers after photodegradation 28

Figure 16 Absorbance of SRB: a) in range from 400nm to 750nm, b) at 562nm 30

Figure 17 (a) SRB photodegradation profiles of (P25/PAA)n thin films at wavelength

562 nm, (b) the first-order kinetic plot of ln(C/C0) and time(minutes) for photodegradation of SRB using (P25/PAA)n thin films at wavelength 562 nm 31

Figure 18 (a) SRB degradation profiles of (P25/PDopa)n thin films at wavelength 562

nm, (b) the first-order kinetic plot of ln(C/C0) and time(minutes) for photodegradation

of SRB using (P25/PDopa)n thin films at wavelength 562 nm, 33

Figure 19 (a) SRB degradation profiles of (TiO2/PDopa)n thin films at wavelength 562

nm, (b) the first-order kinetic plot of ln(C/C0) and time(minutes) for photodegradation

of SRB using diffirent kinds of TiO2 34

Figure 20 (a) Absorbance of P25/PDoPa films, (b) Absorbance at 300 nm of P25/PDoPa, (c) band gap of P25/PDopa 36

LIST OF TABLES

Table 1 Numbers of layers 17

Table 2 Roughness of P25/PDopa films with different numbers of bilayer 29

AFM

Atomic Force Microscopy

PART I INTRODUCTION

1.1 Research rationale

In the context of the current population explosion followed by the excessive

demand of utilization of both natural and artificial resources in order to motivate the

development of agricultural and industrial manufactures, our environment has been dramatically affected by inadequate access to these kinds of resources and the

shortcomings of management Water, soil and air resources have been polluted

seriously, resulting in a sequence of negative consequences to human being and living

organisms Environmental pollution has become one of the most enormous challenges

of the world that humans need to face in the 21st century Up to now, various

processes have been proposed to constantly tackle and step-by-step take actions to

prevent, mitigate environmental degradation in order to adapt the human demand One of a few possible options can be seen in water reuse by wastewater treatment

from agricultural and industrial activities

In view to suppress the worsening of clean water shortage, development of

advanced techniques with low-cost and high efficiency to treat the wastewater is

desirable Due to its more experts than other conventional water treatment methods,

photo-degradation process of nanoparticles has increasingly gotten the attention of scientists these days A method to mitigate low concentrations of organic

contaminants from gaseous effluents by converting them into products that are in

safety to the environment is known as Heterogeneous photocatalytic oxidation

(PCO)(Blount, Kim, & Falconer, 2001) In that case, Nano-TiO2photocatalyst is

well-known for its high efficiency, low cost, physical and chemical stability,

widespread availability, and noncorrosive property(Carp, Huisman, & Reller, 2004;

Dong et al., 2015; Herrmann et al., 2007)

However, the practical applications of TiO2 were prohibited due to its difficulty

of separation and recovery from liquid phase (Dong et al., 2015) In view of tackle

the problem, several approaches have been studied One of these approaches is to

immobilize the TiO2 nanoparticles onto various supports Although numerous

techniques were introduced to be able to fabricate thin films having nanostructured

nanoparticle loss by agglomeration during fabrication(Kim & Sohn, 2002) From

previous study, fabrication of thin films containing TiO2 nanoparticles using

layer-by-layer self-assembly is well-known as a promising technique (Dong et al., 2015)

In this study, the different films of various kinds of TiO2 and Poly (L-Dopa) using

the layer-by-layer self-assembly were fabricated The obtained films were tested by

employing Uv-Vis spectrometer, and characterized by several techniques such as

dynamic light scattering (DLS), Fourier transform infrared spectroscopy (FTIR),

scanning electron microscopy (SEM), and atomic force microscopy (AFM) in order to assess efficiency of them in practical application in case of approaches for the

immobilization efficiency of TiO2 particles with low cost and high reusability

Poly(acrylic acid) (PAA) was used to verify the role of Poly(L-Dopa) Sulforhodamine

B (SRB) was used as a model to study the “photocatalytic activity”

1.2 Research’s objectives

The research aims to prepare TiO2 films with high optical transparency through layer-by-layer self-assembly using commercial TiO2 and Poly(L-Dopa)

1.3 Research questions and hypotheses

a) What is the procedure method of [TiO2/Poly(L-Dopa)]n films?

b) What is roles of Poly(L-dopa) (Pdopa) in fabrication of photocatalytic

multilayer thin films?

c) How effective are P25 Degussa, St-01, and St-21 in term of fabrication of the films and their pollutant degradation?

1.4 Limitations

Due to the shortcoming of time frame, the research could be limited and was not

able to be expended into many as other experiments

PART II LITERATURE REVIEW

2.1 Overview of Titanium dioxide

2.1.1 Titanium oxidation structures and properties

Up to now, the n-type semiconductor Titanium dioxide (TiO2) has been widely

utilized as a photocatalyst due to their potential applications in decomposition of environmental pollutants (Dong et al., 2015; Kim & Sohn, 2002; Wisitsmat,

Tuantranont, Comini, Sberveglieri, & Modarski, 2009) The nano-TiO2photocatalyst is

well-known among the metal oxides for its high efficiency, low cost, biological

inertness, physical and chemical stability, widespread availability, noncorrosive

property and no risks for the environment or humans (Carp et al., 2004; Dong et al.,

2015; Herrmann et al., 2007)

There are three different polymorphs that Titanium dioxide (TiO2) exists asanatase, rutile and brookite(Nolan, Seery, & Pillai, 2009; Pelaez et al., 2012;

Woodley & Catlow, 2009) Rutile is the primary source and the most stable form of

photocatalytically active than the other major phases in Titania (Nolan et al., 2009) The band gap of anatase is 3.2 eV while that of rutile is 3.0 eV, and brookite is ∼3.2

eV (Amtout & Leonelli, 1995; Asahi, Taga, Mannstadt, & Freeman, 2000; Koelsch, Cassaignon, Minh, Guillemoles, & Jolivet, 2004; Pelaez et al., 2012) It proves that

Rutile can be excited by both visible and ultraviolet (UV) light (wavelengths smaller

than 390 nanometers, Anatase is only excited by UV light, and Brookite is not excited

by UV light

In all three forms, titanium (Ti4+) atoms are coordinated to six oxygen (O2−)

atoms, forming TiO6 octahedral (Pelaez et al., 2012) The structures of the three phases are shown in the under figure with the titanium atoms are gray and the oxygen atoms

are red Anatase can be transformed into rutile at high temperatures (Floriano, Scalvi,

Saeki, & Sambrano, 2014) Brookite with its orthorhombic crystal system can be

transformed into rutile with the application of heat(Kadam et al., 2015)

Figure 1 Crystal structures of rutile, anatase and brookite titanium dioxide

(Shannon, 2012; Woodley & Catlow, 2009)

P25 (Degussa, Japan Aerosil) is made from titanium chloride at relatively high

temperature while ST-01 and ST-21 (Ishihara Sangyo Co Ltd.) is anatase powder that

is made from titanium sulfonate P25 Degussa contains 80% anatase and 20% rutile

Meanwhile ST-01, and ST-21 contain 100% anatase (Zarei, Khataee,

Ordikhani-Seyedlar, & Fathinia, 2010)

2.1.2 The photocatalytic activity of TiO 2

When nano-TiO2 is irradiated with ultraviolet (UV) light, electrons are

promoted from the valence band to the conduction band, resulting in the generation of energized “holes” in the former Free electrons react with the oxygen to generate

superoxide radical anions (O2 −), while energized holes react with water (H2O) or

hydroxyl ion (OH−) to generate hydroxyl radicals ( OH)(Dong et al., 2015) The

photogenerated holes and the hydroxyl radicals oxidize decompose organic contaminants (Dong et al., 2015; Kim & Sohn, 2002)

Figure 2 Schematic diagram illustrating the principle of TiO2 photocatalysis

with the presence of water pollutant (RH)(Dong et al., 2015)

Besides the inefficient exploration of visible light, the practical applications of

TiO2 were prohibited by several limitations: Firstly, the absorption capacity to

hydrophobic contaminants is low; secondly, TiO2 particles occupy the high

aggregation tendency; thirdly, It is difficult too separate and recover TiO2 particles

from liquid phase (Dong et al., 2015)

2.2 Layer-by-layer self-assembly

Layer-by-layer self-assembly (LBL-SA) is a versatile bottom-up method

offering superior structure control for fabrication of multilayer films(Zhang, Xu, Sun,

Li, & Pan, 2011) With a simple process based on spontaneous ionic adsorption of

oppositely charged materials from their aqueous solution, LBL-SA can be promising method to carried out with ultrathin (∼1 nm) layers of polymer and inorganic TiO2

(∼3 nm) molecules by the stepwise construction of molecular-level ordered

TiO2/polymer nanocomposite films without costly equipment(Kim & Sohn, 2002;

Kotov, Dekany, & Fendler, 1995; Y J Liu, Wang, & Claus, 1997; Xiang, Lu, & Jiang, 2012) For photocatalytic coatings, TiO2 nanoparticles with ionic charges on their

surface can be effectively incorporated into thin films without severe agglomeration by

the LBL-SA method (Kim & Sohn, 2002)

Figure 3 The principle of Layer-by-layer self-assembling method(Kim & Sohn,

2002; Kotov et al., 1995; Y J Liu et al., 1997; Xiang et al., 2012)

In the case, nano-TiO2 particles with positive charge and Poly(L-Dopa) with

negative charge were employed to fabrication the multilayer films Piranha solution

was used to get the first negative charged layer

2.3 Overview of Poly(L-Dopa)

Figure 4.Poly(L-DOPA)(Gu, Fu, Wu, & Zhang, 2016; Yu, Liu, Yuan, Brown, &

Wang, 2015)

3, 4-dihydroxy-L-phenylalanine (L-DOPA) is an antiparkinsonian agent It is a

natural isomer of the immediate precursor to dopamine phenylalanine) L-DOPA is not only a critical, functional element in mussel adhesive

(3,4-Dihydroxy-L-proteins, but also is known to bind strongly to various natural or synthetic materials(La

et al., 2012).The actions of L-DOPA are the same as dopamine, since dopamine is the

product of the decarboxylation of L-DOPA It can be easily deposited on virtually all

types of inorganic and inorganic substrates, including super hydrophobic surface, with

controllable film thickness and durable stability (Y Liu, Ai, & Lu, 2014)

Poly(Dopa) is obtained via Dopa self-polymerization, which remains the properties of Dopa(Yu et al., 2015)

L-PART III METHODS

3.1 Material

3.1.1 Chemicals

Figure 5 Chemicals: a) PDopa, b) SRB 10 uM, c) DIW pH=3, d) PAA

Degussa P25 was used as provided St-01 and St-21 were bought from Ishihara

Sangyo Co Ltd Poly(L-Dopa) was produced from L-Dopa(>= 98%) PAA, SRB

(C27H30N2O7S2), hydrogen peroxide solution (30% H2O2) were obtained from

Sigma-Aldrich Sulfuric acid (95.0-98.0 %) was bought from J.T.Baken chemicals Doubly

de-ionized water was prepared with Milli-Q system (Millipore, Bedford, MA, USA)

(18.2 M-cm)

- Zetasizer Nano ZS instrument (ZEN 3600, Malvern Instruments Ltd.)

- UV-Vis (Varian (Cary-50 Bio)) spectrometer

- Scanning Electron Microscopy (SEM) (a HITACHI SU8010 scanning electron

microscopy)

- Fourier Transform Infrared Spectroscopy

- Atomic Force Microscopy: a Dimension ICON model (Bruker Corp.)

3.2 Methods

3.2.1 General principle

The multilayer films were fabricated in the same condition excepted for

different kinds of TiO2, namely Degussa P25, St-01, and St-21 The obtained LBL

TiO2/Poly(L-Dopa) multilayer films were tested by UV-vis spectroscopy, and

characterized by DLS, SEM, FTIR and AFM in order to emphasize the influence of

using TiO2 with different particle size and surface zeta-potential Poly(acrylic acid)

(PAA) was used to verify the role of Poly(L-Dopa) Sulforhodamine B (SRB) was used

as a model to study the “photocatalytic activity”

3.2.2 Fabrication of photocatalytic thin [TiO 2 / Polymer] n films by the layer self-assembly

layer-by-Figure 7 Experimental process

 Preparation of glass slides

After cut into small slides with area of 25x09 mm, Glass substrates were cleaned in

a piranha solution (70/30 v/v of concentrated H2SO4 and 30% H2O2) in order to

generate negatively charged surfaces

 Preparation of polymer solution (pH 3.0 , C = 2g/l)

For each two-film fabrication, After 36 mg polymer was dissolved in 18 ml DIW,

the pH of this solution was adjusted to 3.0 by HNO3 This solution was sonicated for

10 minutes before using

 Preparation of TiO2 solution (pH3.0, C = 1g/l)

Before sonication TiO2 solution for 10 minutes, 18 mg TiO2 was measured and

dispersed in 18 ml DIW, and then adjusted until pH=3.0 by HNO3

 PH adjustments

TiO2 solution and polymer solution were adjusted by Portable pH meter

Firstly, using base [pH4] and [pH7] to create baseline

- Click [Cal] button and then [v] until “Different electrode for pH” occurs in the

screen

- Click one more [v]

- After washed, pH meter was dipped into [pH4] to create baseline, and then

 [TiO2/ Polymer]n film procedures

For each multilayer thin film, after immobilized in petri dish by clip, tongs and

magnet, 2 glass slides were sequentially dipped into a solution for 5 minutes, and washed by deionized water (pH3.0 adjusted by HNO3) By controlling this dipping

sequence, LBL-SA thin films of TiO2/polymer were fabricated with desired

number of layers as the under table The experiment was performed at room

temperature TiO2 solutions were always used for the first and the last dipping

Table 1 Numbers of layers

concentration1g/l) were prepared to measure particle size and zeta-potential

Poly(L-Dopa) solutions and P25 solutions (1g/l concentration) with different

pH from 1 to 5 were prepared in order to measure the variety of zeta-potential with different pH

Dynamic Light Scattering Hydrodynamic size and zeta potential of TiO2

suspension and Poly(L-Dopa) were determined by performing dynamic light scattering

measurement using a Zetasizer Nano ZS instrument (ZEN 3600, Malvern Instruments

Ltd.) equipped with a He-Ne laser at a wavelength of 633 nm and a detection angle of

173°

b) SEM procedure

The thickness and surface morphology of the multilayer P25/Poly(L-Dopa) thin

films were measured by using a HITACHI SU8010 scanning electron microscopy at 5

kV Differed from the films used in photodegradation test, the cores of the films which

were used for SEM are made of quartz

c) Atomic Force Microscopy (AFM)

1 μm × 1 μm AFM scans were done on a Dimension ICON model (Bruker

Corp.) using tapping-mode in air at a scan rate of 0.5 Hz with a silicon nitride tip The scanning probe microscope was controlled by Nano-scope software Root mean

squared (RMS) roughness and surface area of the films were also measured

d) Fourier Transform Infrared Spectroscopy (FTIR)

The dried samples (Degauss P25, L-Dopa, Poly(L-Dopa), PAA, P25/PAA,

P25/Poly(L-Dopa)) were grounded with KBr powder (FT-IR grade, Aldrich) before