ALKALINE HYDROTHERMAL
TREATMENT OF TITANATE
NANOSTRUCTURES

Submitted by

DANA LEE MORGAN
Bachelor of Applied Science (Honours, Chemistry)
Associate Degree of Applied Science

A thesis presented to the Queensland University of Technology,
in fulfillment of the requirements of the degree of
Doctor of Philosophy

August 2010



ABSTRACT
Since its initial proposal in 1998, alkaline hydrothermal processing has rapidly
become an established technology for the production of titanate nanostructures. This
simple, highly reproducible process has gained a strong research following since its
conception. However, complete understanding and elucidation of nanostructure
phase and formation have not yet been achieved. Without fully understanding phase,
formation, and other important competing effects of the synthesis parameters on the
final structure, the maximum potential of these nanostructures cannot be obtained.
Therefore this study examined the influence of synthesis parameters on the formation
of titanate nanostructures produced by alkaline hydrothermal treatment. The
parameters included alkaline concentration, hydrothermal temperature, the precursor
material‘s crystallite size and also the phase of the titanium dioxide precursor (TiO2,
or titania).

The nanostructure‘s phase and morphology was analysed using X-ray diffraction
(XRD), Raman spectroscopy and transmission electron microscopy. X-ray
photoelectron

spectroscopy

(XPS),

dynamic

light

scattering

(non-invasive

backscattering), nitrogen sorption, and Rietveld analysis were used to determine
phase, for particle sizing, surface area determinations, and establishing phase
concentrations, respectively. This project rigorously examined the effect of alkaline
concentration and hydrothermal temperature on three commercially sourced and two
self-prepared TiO2 powders. These precursors consisted of both pure- or mixedphase anatase and rutile polymorphs, and were selected to cover a range of phase
concentrations and crystallite sizes. Typically, these precursors were treated with 5–
10 M sodium hydroxide (NaOH) solutions at temperatures between 100–220 °C.
Both nanotube and nanoribbon morphologies could be produced depending on the
combination of these hydrothermal conditions.
Both titania and titanate phases are comprised of TiO6 units which are assembled in
different combinations. The arrangement of these atoms affects the binding energy
between the Ti–O bonds. Raman spectroscopy and XPS were therefore employed in
a preliminary study of phase determination for these materials. The change in
binding energy from a titania to a titanate binding energy was investigated in this

i


study, and the transformation of titania precursor into nanotubes and titanate
nanoribbons was directly observed by these methods. Evaluation of the Raman and
XPS results indicated a strengthening in the binding energies of both the Ti (2p3/2)
and O (1s) bands which correlated to an increase in strength and decrease in
resolution of the characteristic nanotube doublet observed between 320 and 220 cm–1
in the Raman spectra of these products.
The effect of phase and crystallite size on nanotube formation was examined over a
series of temperatures (100–200 °C in 20 °C increments) at a set alkaline
concentration (7.5 M NaOH). These parameters were investigated by employing both
pure- and mixed- phase precursors of anatase and rutile. This study indicated that
both the crystallite size and phase affect nanotube formation, with rutile requiring a
greater driving force (essentially ―harsher‖ hydrothermal conditions) than anatase to
form nanotubes, where larger crystallites forms of the precursor also appeared to
impede nanotube formation slightly. These parameters were further examined in later
studies.
The influence of alkaline concentration and hydrothermal temperature were
systematically examined for the transformation of Degussa P25 into nanotubes and
nanoribbons, and exact conditions for nanostructure synthesis were determined.
Correlation of these data sets resulted in the construction of a morphological phase
diagram, which is an effective reference for nanostructure formation. This
morphological phase diagram effectively provides a ‗recipe book‘ for the formation
of titanate nanostructures.
Morphological phase diagrams were also constructed for larger, near phase-pure
anatase and rutile precursors, to further investigate the influence of hydrothermal
reaction parameters on the formation of titanate nanotubes and nanoribbons. The
effects of alkaline concentration, hydrothermal temperature, crystallite phase and size
are observed when the three morphological phase diagrams are compared. Through

the analysis of these results it was determined that alkaline concentration and
hydrothermal temperature affect nanotube and nanoribbon formation independently
through a complex relationship, where nanotubes are primarily affected by
temperature, whilst nanoribbons are strongly influenced by alkaline concentration.
Crystallite size and phase also affected the nanostructure formation. Smaller
ii


precursor crystallites formed nanostructures at reduced hydrothermal temperature,
and rutile displayed a slower rate of precursor consumption compared to anatase,
with incomplete conversion observed for most hydrothermal conditions.
The incomplete conversion of rutile into nanotubes was examined in detail in the
final study. This study selectively examined the kinetics of precursor dissolution in
order to understand why rutile incompletely converted. This was achieved by
selecting a single hydrothermal condition (9 M NaOH, 160 °C) where nanotubes are
known to form from both anatase and rutile, where the synthesis was quenched after
2, 4, 8, 16 and 32 hours. The influence of precursor phase on nanostructure formation
was explicitly determined to be due to different dissolution kinetics; where anatase
exhibited zero-order dissolution and rutile second-order. This difference in kinetic
order cannot be simply explained by the variation in crystallite size, as the inherent
surface areas of the two precursors were determined to have first-order relationships
with time. Therefore, the crystallite size (and inherent surface area) does not affect
the overall kinetic order of dissolution; rather, it determines the rate of reaction.
Finally, nanostructure formation was found to be controlled by the availability of
dissolved titanium (Ti4+) species in solution, which is mediated by the dissolution
kinetics of the precursor.

KEYWORDS
Alkaline hydrothermal treatment, Soft-chemical, Morphological phase diagram,
Titanium dioxide, Titania, TiO2, Titanate, Nanoparticle, Nanotube, Nanoribbon,

Nanostructure,

Anatase,

Rutile,

Degussa

P25,

Crystallite

size,

Alkaline

concentration, Hydrothermal temperature, Raman spectroscopy, Transmission
electron

microscopy,

X-ray diffraction,

X-ray

photoelectron

spectroscopy,

Dissolution, Kinetics.


iii


PUBLICATIONS ARISING FROM THIS PROJECT
Morgan, D.L.; Triani, G.; Blackford, M.G.; Raftery, N. A.; Frost, R.L.; Waclawik,
E.R. Submitted to Journal of Materials Science, 30th July 2010.
Morgan, D.L.; Liu, H-W.; Frost, R.L.; Waclawik, E.R. Journal of Physical Chemistry
C 2010, 114, 101–110.
Morgan, D. L.; Zhu, H-Y.; Frost, R.L.; Waclawik, E.R. Chemistry of Materials 2008,
20, 3800–3802.
Morgan, D. L.; Waclawik, E. R.; Frost, R. L. Advanced Materials Research (Zuerich,
Switzerland) 2007, 29–30, 211–214.
Morgan, D. L.; Waclawik, E. R.; Frost, R. L. In International Conference on
Nanoscience and Nanotechnology; Jagadish, C., Lu, G. Q. M., Eds.; IEEE Publishing
Company: Brisbane, 2006, p 60–63.

iv


TABLE OF CONTENTS
ABSTRACT ................................................................................................................. i
KEYWORDS ............................................................................................................. iii
PUBLICATIONS ARISING FROM THIS PROJECT ......................................... iv
TABLE OF CONTENTS........................................................................................... v
LIST OF FIGURES ................................................................................................... x
LIST OF TABLES ................................................................................................. xvii
ABBREVIATIONS ............................................................................................... xviii
STATEMENT OF ORIGINALITY ...................................................................... xix
ACKNOWLEDGEMENTS ..................................................................................... xx

CHAPTER 1
INTRODUCTION ...................................................................................................... 1
1.

Introduction ...................................................................................................... 2

2.

Description of the Scientific Problem Investigated.......................................... 2

3.

Overall Objectives of this Study ...................................................................... 2

4.

Specific Aims of the Study............................................................................... 3

5.

Account of Scientific Progress Linking the Scientific Papers ......................... 4

CHAPTER 2
LITERATURE REVIEW.......................................................................................... 5
1.

Introduction ...................................................................................................... 6

2.


Hydrothermal Processing ................................................................................. 7

3.

Crystallographic Properties of Titanium Oxides .............................................. 9
3.1

Titanium Dioxide .................................................................................... 9

3.2

Titanate ................................................................................................. 13

4.

Synthesis of Titanium Oxide Nanotubes ........................................................ 16

5.

Alkaline Hydrothermal Method ..................................................................... 18

6.

Variations to the Alkaline Hydrothermal Method.......................................... 19

7.

6.1

Hydrothermal Liquor ............................................................................ 19


6.2

Starting Material ................................................................................... 20

6.3

Method of Treatment ............................................................................ 21

Nanostructure Morphology ............................................................................ 22
v


8.

7.1

Nanotubes.............................................................................................. 23

7.2

Nanoribbons .......................................................................................... 24

Nanostructure Functionalisation..................................................................... 25
8.1

Nanostructure Doping ........................................................................... 25

8.2


Decoration (or Adhesion) of Nanoparticles onto the Nanostructure
Surface .................................................................................................. 26

8.3
9.

Nanostructure Composite Materials...................................................... 27

Nanostructure Applications ............................................................................ 28
9.1

Catalysis and Photocatalysis ................................................................. 28

9.2

Hydrogen Sensing and Storage ............................................................. 29

9.3

Lithium Batteries................................................................................... 29

9.4

Biomedical Applications ....................................................................... 30

10. Mechanisms of Nanostructure Formation ...................................................... 30
10.1 Nanotube Formation Mechanisms ........................................................ 30
10.2 Nanoribbon Formation Mechanisms ..................................................... 35
11. Nanostructure Phase and Composition ........................................................... 36
11.1 Nanotubes.............................................................................................. 36

11.2 Nanoribbons .......................................................................................... 40
12. Conclusion ...................................................................................................... 41
13. References ...................................................................................................... 41
CHAPTER 3
RELATIONSHIP OF TITANIA NANOTUBE BINDING ENERGIES AND
RAMAN SPECTRA ................................................................................................. 49
Statement of Contribution ..................................................................................... 50
Synopsis ................................................................................................................. 51
Abstract.................................................................................................................. 52
Keywords ............................................................................................................... 52
Introduction ........................................................................................................... 52
Experimental.......................................................................................................... 55
Reagents and Synthesis .................................................................................. 55
Characterisation .............................................................................................. 55
Results and Discussion .......................................................................................... 56
Conclusions ........................................................................................................... 60
vi


Acknowledgment................................................................................................... 60
References ............................................................................................................. 60
CHAPTER 4
SYNTHESIS AND CHARACTERISATION OF TITANIA NANOTUBES:
EFFECT OF PHASE AND CRYSTALLITE SIZE ON NANOTUBE
FORMATION .......................................................................................................... 63
Statement of Contribution ..................................................................................... 64
Synopsis................................................................................................................. 65
Keywords............................................................................................................... 66
Abstract ................................................................................................................. 66
Introduction ........................................................................................................... 66

Experimental ......................................................................................................... 68
Reagents, Synthesis and Characterisation ...................................................... 68
Results and Discussion .......................................................................................... 68
Conclusions ........................................................................................................... 72
References ............................................................................................................. 73
CHAPTER 5
DETERMINATION OF A MORPHOLOGICAL PHASE DIAGRAM OF
TITANIA/TITANATE NANOSTRUCTURES FROM ALKALINE
HYDROTHERMAL TREATMENT OF DEGUSSA P25 ................................... 74
Statement of Contribution ..................................................................................... 75
Synopsis................................................................................................................. 76
Manuscript Text .................................................................................................... 77
Supporting Information Available......................................................................... 83
References ............................................................................................................. 84
Electronic Supporting Information ........................................................................ 86
CHAPTER 6
IMPLICATIONS OF PRECURSOR CHEMISTRY ON THE ALKALINE
HYDROTHERMAL SYNTHESIS OF TITANIA/TITANATE
NANOSTRUCTURES ............................................................................................. 90
Statement of Contribution ..................................................................................... 91
Synopsis................................................................................................................. 92
vii


Abstract.................................................................................................................. 93
1.

Introduction .................................................................................................... 94

2.


Experimental Procedure ................................................................................. 96

3.

2.1

Synthesis of Nanostructures .................................................................. 96

2.2

Characterization of Nanostructures ....................................................... 97

Determination of Morphological Phase Diagrams ......................................... 97
3.1

Qualitative X-Ray Diffraction Investigation of Nanostructures ........... 97
3.1.1 Anatase Precursor...................................................................... 99
3.1.2 Rutile Precursor ....................................................................... 101
3.1.3 Degussa P25 Precursor ............................................................ 101

3.2

Identification of Nanostructures by Raman Spectroscopy .................. 102
3.2.1 Anatase Precursor.................................................................... 103
3.2.2 Rutile Precursor ....................................................................... 103
3.2.3 Degussa P25 Precursor ............................................................ 105

4.


Construction of the Morphological Phase Diagrams.................................... 105

5.

Confirmation of the Morphological Phase Diagrams ................................... 106
5.1

Confirmation of Nanostructure Morphologies by Transmission Electron
Microscopy Investigations .................................................................. 106

5.2

Brunauer–Emmet–Teller Surface Area Measurements ...................... 108

6.

Interpretation of the Morphological Phase Diagram .................................... 111

7.

Conclusions .................................................................................................. 113

Acknowledgement ............................................................................................... 114
Supporting Information Available ....................................................................... 114
References ........................................................................................................... 115
Electronic Supporting Information ...................................................................... 117
CHAPTER 7
ALKALINE HYDROTHERMAL KINETICS IN TITANATE
NANOSTRUCTURE FORMATION ................................................................... 123
Statement of Contribution ................................................................................... 124

Synopsis ............................................................................................................... 125
Abstract................................................................................................................ 126
1.

Introduction .................................................................................................. 127

2.

Experimental Procedure ............................................................................... 130

viii


2.1

Synthesis of Nanotubes ....................................................................... 130

2.2

Characterisation of Nanostructures ..................................................... 130

3.

Results and Discussion ................................................................................. 131

4.

Conclusions .................................................................................................. 143

Acknowledgement ............................................................................................... 143

References ........................................................................................................... 144
CHAPTER 8
CONCLUSIONS .................................................................................................... 146

ix


LIST OF FIGURES
CHAPTER 1
Figure 1

Flow chart indicating the interaction and arrangement of the

4

chapters. Dashed arrows indicate indirectly related papers.
CHAPTER 2
Figure 1

An example of a sealed glass tube used by De Senarmont in

8

1851 (left), a schematic of the Teflon-lined stainless steel
autoclave used in this study (centre), and a specialised
electrolytic autoclave (right).
Figure 2

Different schematic representations of TiO6 octahedra.


10

Figure 3

Anatase unit cell (left), anatase JCrystal crystal structure

10

representation (centre), and natural anatase crystals from
Habachtal Valley, HoheTauern Mountains, Salzburg, Austria.
Figure 4

Rutile unit cell (left), rutile JCrystal crystal structure

11

representation (centre), and natural rutile crystals from
unknown origin
Figure 5

Brookite unit cell (left), brookite JCrystal crystal structure

12

representation (centre), and natural brookite crystals from
Kharan, Baluchistan, Pakistan.
Figure 6

Schematic structure of monoclinic TiO2–B.


12

Figure 7

Schematic structure of trititanate (top left), hexatitanate (top

13

right), and nonatitanate (bottom). Green coloured octahedra
represent the related octahedra which give rise to the titanate‘s
order.
Figure 8

Schematic of the condensation of a hydrogen trititanate to a

14

hydrogen hexatitanate through a topotactic dehydration
reaction.
Figure 9
x

Schematic of the lamellar lepidocrocite-type titanate structure.

15


Figure 10

ABA and AAA stacking order of titanates (left) and the


15

hydrogen-bonding of unshared O2+ atoms in a hydrogen
trititanate.
Figure 11

SEM images of helical nanotubes produced by sol-gel

16

templating of an organogel (top left), nanotubes produced by
sol-gel templating of surfactant (top right), and nanotube arrays
produced by anodic oxidation (bottom left) and sol-gel
electrophoresis into an anodic alumina membrane (bottom
right).
Figure 12

TiO2–SiO2 nanotubes synthesised in 1998 by Kasuga et al.

18

Figure 13

High magnification TEM image of nanotubes (right), and high

21

magnification SEM image of nanotubes (top right); and
schematic of nanotube formation (bottom right).

Figure 14

Typical morphologies of one-dimensional nanostructures:

22

nanowires, nanorods, nanotubes, and nanobelts.
Figure 15

Typical nanotube structure (left), diagrammatic representation

23

of three potential nanotube morphologies (centre); ‗scroll-like‘
nanotube cross-section (top right); and ‗onion-like‘ nanotube
cross-section (bottom right).
Figure 16

Typical nanoribbon structure.

24

Figure 17

Nanotubes decorated with CuO nanoparticles (left) and a capped

27

PbS quantum dot within the nanotube pore (right).
Figure 18


Proposed schematic of nanotube formation.

32

Figure 19

Condensation and growth of anatase.

32

Figure 20

HRTEM image of ‗nanoloops‘ on the starting crystallite (left);

33

mechanism of nanotube formation for TiO2 and Na2Ti3O7
(right).
Figure 21

Schematic for nanotube curling proposed by Bavykin et al.

34

xi


Figure 22


Formation of concentric nanotubes. (I) Swelling of TiO2 particle

34

 (II) Delamination and formation of planar fragments
(dissolved, kinetic product)  (III) Formation of monolayered
nanotube through covalent bonding (thermodynamic product).
Figure 23

Schematic drawings depicting the formation process of H2Ti3O7

35

nanotubes and nanowires proposed by Wu et al.
Figure 24

Comparison of XRD line patterns of titania and titanate species

36

and a typical nanotube pattern.
Figure 25

Trititanate nanotube model proposed by Peng and coworkers.

39

Figure 26

Structural features of titanate (left) and anatase (right). Both


40

contain common ‗zig-zag‘ ribbons of TiO6 octahedra, which are
signified as the areas on dashed-line boxes. As described by
Zhu et al.

CHAPTER 3
Figure 1

TEM Images: (a) Nanotube synthesised at 5 M @ 220 °C,

57

SAED inset; (b) Nanotubes and nanoribbons synthesised at 5 M
@ 220 °C; (c) Nanotubes synthesised at 9 M @ 200 °C, SAED
inset.
Raman spectra of samples.

58

Figure 1

Raman spectra of selected samples.

70

Figure 2

XRD patterns of selected samples.


70

Figure 3

TEM images of nanotubes formed with 7.5 M NaOH @

71

Figure 2

CHAPTER 4

140 °C from self-prepared anatase (A) and commercial
rutile (B). Both samples display well formed nanotubes.

xii


CHAPTER 5
Figure 1

Morphological phase diagram of Degussa P25 indicating

79

regions of nanostructure formation after 20 h of hydrothermal
treatment. Phase boundaries were estimated through relative
concentrations of nanostructures from XRD and Raman studies,
but do not imply contiguous percent morphological phase

between each condition.
Figure 2

(A) XRD and (B) Raman spectra of (a) Degussa P25, (b)

80

nanotube, and (c) nanoribbon. Arrows indicate peaks relating to
nanotube phase.
Figure 3

TEM Images of (A) nanoparticle/nanotube interface, (B)
nanotubes,

(C)

nanotube/nanoribbon

interface,

(D)

81

and

nanoribbons. Conditions: 5 mol dm–3 @ 140 °C, 9 mol dm–3 @
160 °C, 5 mol dm–3 @ 220 °C, and 7.5 mol dm–3 @ 220 °C,
respectively
Figure S1


XRD Patterns of the 5 mol·dm–3 (A), 7.5 mol·dm–3 (B),

87

9 mol·dm–3 (C) and 10 mol·dm–3 NaOH treated Degussa P25
series.
Figure S2

Raman spectra of the 5 mol·dm–3 (A), 7.5 mol·dm–3 (B),

88

9 mol dm–3 (C) and 10 mol·dm–3 NaOH treated Degussa P25
series.
Figure S3

Transition of nanoparticles to nanoribbons observed in the

89

XRD (A) and Raman (B). Indicators for nanotubes (star),
anatase (triangle) and rutile (circle) indicated only on transition
patterns (a

b) for clarity.

xiii



CHAPTER 6
Figure 1

XRD patterns of 9 M NaOH-treated anatase series (A), 9 M

100

NaOH-treated rutile series (B), and 5 M NaOH-treated
Degussa P25 series (C). In (A),

indicates nanotube

reflections at 100 °C, residual anatase and rutile at 140 °C, and
residual nanotubes at 200 °C.
Figure 2

Raman spectra of 9 M NaOH-treated anatase series (A), 9 M

104

NaOH-treated rutile series (B), and 5 M NaOH-treated
Degussa P25 series (C). In (A),

indicates the doublet

feature characteristic of nanotube phase at 100, 120 and
140 °C with varying degrees of intensity.
Figure 3

Morphological phase diagrams of hydrothermally treated


105

anatase, rutile, and Degussa P25. The phase boundaries
indicate the relative percentage of nanostructures formed
within each condition rather than contiguous percentage
between each condition. For example, P25 treated with 5 M
NaOH at 120 °C contains 70:30 wt % NP/NT.
Figure 4

Coexistence of nanoparticles and nanotubes along the phase

107

boundary was confirmed through TEM studies as seen in the
5 M @ 120 °C anatase (A) and 10 M @ 120 °C rutile (B)
samples. Pure phase nanotubes were also confirmed in the
7.5 M @ 160 °C anatase (C) and 9 M @ 160 °C Degussa
P25 (D) samples.
Figure 5

Phase transition between nanotubes to nanoribbons was
observed in the 5 M at 220 °C Degussa P25 (A) and 10M at
200 °C rutile samples (B). Pure, highly crystalline nanoribbons
were observed in the 10 M at 220 °C anatase (C) and 10 M at
220 °C rutile (D) samples.

xiv

108



Figure 6

BET surface areas of nanostructures formed from the reaction of 109
anatase, rutile, and Degussa P25 with 9 M NaOH at 160 °C. As
nanotubes were produced, the surface area increased from the
crystallite precursor, reducing in surface areas once nanoribbons
were produced.

Figure 7

Relative

nanotube

concentration

versus

hydrothermal 112

temperature of all hydrothermally treated samples: anatase (A),
rutile (B), and Degussa P25 (C). At high temperature,
nanoribbon

concentration

is


inverse

to

the

nanotube

concentration.
Figure S1.

XRD (A) and Raman (B) patterns of precursors, anatase, rutile 117
and Degussa P25.

Figure S2

XRD patterns of the 5 M (A), 7.5 M (B), 9 M (C) and 10 M (D) 118
and Raman patterns of the 5 M (E), 7.5 M (F), 9 M (G) and
10 M (H) NaOH treated anatase series.

Figure S3

XRD patterns of the 5 M (A), 7.5 M (B), 9 M (C) and 10 M (D) 119
and Raman patterns of the 5 M (E), 7.5 M (F), 9 M (G) and
10 M (H) NaOH treated rutile series.

Figure S4

XRD patterns of the 5 M (A), 7.5 M (B), 9 M (C) and 10 M (D) 120
and Raman patterns of the 5 M (E), 7.5 M (F), 9 M (G) and

10 M (H) NaOH treated Degussa P25 series.

Figure S5

Selected area electron diffraction (SAED) patterns of the 121
anatase- (A), rutile- (B) and Degussa P25-produced (C)
nanotubes. These nanotubes were produced after hydrothermal
treatment of anatase and rutile with 9 M NaOH @ 160 °C and
Degussa P25 with 5 M NaOH @ 180 °C.

xv


CHAPTER 7
Figure 1

XRD patterns of materials formed after 0 hrs (a); 2 hrs (b);

133

4 hrs (c); 8 hrs (d); 16 hrs (e); and 32 hrs (f) hydrothermal
treatment of commercial anatase (A) and commercial
rutile (B).
Figure 2

Raman spectra of materials formed after 0 hrs (a); 2 hrs (b);

134

4 hrs (c); 8 hrs (d); 16 hrs (e); and 32 hrs (f) hydrothermal

treatment of commercial anatase (A) and commercial
rutile (B).
Figure 3

TEM images of nanotubes formed from commercial anatase

135

after 2 hours (A) and 8 hours (B and C) of hydrothermal
treatment and from commercial rutile after 4 hours (E–F) of
hydrothermal treatment.
Figure 4

BET surface areas of materials produced after hydrothermal

136

treatment of commercial anatase and commercial rutile.
Figure 5

Particle sizes of nanostructures formed after 2 hours

138

hydrothermal treatment of commercial rutile after filtering
through 0.45 and 0.1 m filters. Original traces of the three
runs and their average are presented.
Figure 6

Percent compositions of anatase, rutile and unmodeled phases


139

(nanotubes and amorphous) content after hydrothermal
treatment of commercial anatase (A) and commercial
rutile (B); and their respective zero (C) and second order
fittings (D).
Figure 7

First-order relationship of specific surface area to time for
anatase (A) and rutile (B).

xvi

141


LIST OF TABLES
CHAPTER 2
Table 1

Selected crystallographic and physical properties of anatase,

11

rutile and brookite.
Table 2

Selected crystallographic and physical properties of H2Ti3O7,
Na2Ti3O7 and HxTi2–x/4


Table 3

15

x/4O4∙H2O

Proposed nanotube phases derived from Table 1 of Tsai and

38

Teng.

CHAPTER 3
Table 1

Nanostructure binding energies and morphology.

56

Approximate crystallite sizes of starting materials.

69

Approximate crystallite size and weight percent composition

96

CHAPTER 4
Table 1


CHAPTER 6
Table 1

of precursors.
Table 2

Precursor specific and average XRD peak positions of

98

nanotubes.
Table S1

Average Raman peak positions of nanostructures (all values

122

in cm–1).

xvii


ABBREVIATIONS
0D

Zero-dimensional

1D


One-dimensional

2D

Two-dimensional

3D

Three-dimensional

BET

Brunauer-Emmett-Teller

ca.

circa

FT-Raman

Fourier-transform Raman spectroscopy

h or hrs

hour(s)

HR-TEM

High-resolution transmission electron microscopy


ICDD

International Centre for Diffraction Data

JPDF or PDF Powder Diffraction File
NR

Nanoribbon

NT

Nanotube

NP

Nanoparticle

P25

Degussa P25

PTFE

Polytetrafluoroethylene

SAED

Selected area electron diffraction

TEM


Transmission electron microscopy

XRD

X-ray diffraction

XPS

X-ray photoelectron spectroscopy

xviii


STATEMENT OF ORIGINALITY
The work contained in this thesis has not been previously submitted for a degree of
diploma at this or any other educational institution. To the best of my knowledge and
belief, the thesis contains no material previously published or written by another
person except where due reference is made.

Dana Lee Morgan
August 2010

xix


ACKNOWLEDGEMENTS
Firstly, sincere thanks go to my supervisor Dr Eric Waclawik for his support and
guidance throughout my PhD. He has always been there for me at all stages of my
project, even when it has involved communicating interstate.

The co-authors of my papers also deserve gratitude for their input and expertise.
Special thanks to Drs Thor Bostrom, Llew Rintoul, Barry Wood and Mr Tony
Raftery for their technical expertise. Your help and tutelage has been invaluable.
My sincere appreciation goes to Ashley and Matty for being wonderful sounding
boards and remarkable friends—I miss the coffees! Also, to Lisa, Matt, James and
the other members of the Inorganic Materials Research group who have been
incredible friends. Thanks also to Drs Dalius Sagatys and Graham Smith for pushing
me to succeed.
I could not have succeeded without the financial support which enabled me to
undertake this research. Therefore, I gratefully acknowledge QUT, the Inorganic
Materials Research Program, the School of Physical and Chemical Society and the
Australian Institute of Nuclear Science and Engineering.
Heartfelt gratitude goes to the members of the Advanced Porous Materials group at
the University of Melbourne. They have supported, provided guidance and
encouragement throughout the write-up of my thesis.
A special thank you to my fellow postgraduate students for their camaraderie, it has
made my time a memorable one.
Finally, I'd like to take this opportunity to say a very large thank you to my family,
especially to my fiancé Wayde Martens, whom has always been there for me, and
has provided me invaluable support throughout this incredible journey.

xx


CHAPTER 1
INTRODUCTION

1



Chapter 1: Introduction

1.

INTRODUCTION

This thesis, ―Alkaline hydrothermal treatment of titanate nanostructures‖,
investigated synthesis parameters on the formation of nanostructures from titanium
dioxide powders through the alkaline hydrothermal method. This chapter details the
scientific problem considered, objectives and aims of the study, and the linkages
between research papers published by the author during the course of study, in order
to place the subsequent chapters, and the thesis as a whole within the proper context.

2.

DESCRIPTION OF THE SCIENTIFIC PROBLEM
INVESTIGATED

Alkaline hydrothermally synthesised nanostructures display strong potential for a
variety of applications due to their inherent ion-exchange capabilities and unique
morphologies. However, to effectively utilise these nanostructures, their phase,
formation mechanism and the effects of synthesis parameters need to be fully
understood in order to maximise their potential. Since their discovery, controversy
has dominated the literature regarding the classification of nanostructure phases
under particular hydrothermal conditions and their mechanism of formation. Without
comprehensive elucidation of these properties in hydrothermally produced metal
oxide nanostructures, their applications will not be fully achieved. This study
examined the effect of synthesis parameters on the formation of nanostructures,
principally focussing on nanotubes and nanoribbons formed through the alkaline
hydrothermal method. This systematic investigation into synthesis parameter effects

was designed and undertaken so as to resolve the debates that have surrounded phase
classification and mechanisms of nanostructure formation, and to also provide new
insights and understanding of the alkaline hydrothermal nanostructures and their
properties.

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OVERALL OBJECTIVES OF THIS STUDY

The overall objective of this fundamental study was to examine the synthesis
parameters of alkaline hydrothermal treatment and to determine their influence on
nanostructure formation. Through analysis of this data it was intended that the phase
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Chapter 1: Introduction

and formation mechanism of the nanostructures could be determined. The majority
of previous studies in this field have opted to investigate a narrow selection of
alkaline hydrothermal synthetic parameters. This project was conceived to rigorously
examine the influence of precursor phase and crystallite size, alkaline concentration
and hydrothermal temperature on the formation of alkaline hydrothermally
synthesised nanostructures. To achieve this, three commercially sourced and two
self-prepared titanium dioxide (TiO2, or titania) powders were employed, which
contained both pure- or mixed-phase anatase and rutile polymorphs. These powders
were then treated with varying alkaline concentrations over a wide range of
temperatures. This project primarily uses the techniques of Raman spectroscopy,
X-ray diffraction and transmission electron microscopy to elucidate nanostructure
phase and morphology.


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SPECIFIC AIMS OF THE STUDY

The specific aims of the research presented in this thesis were to:


Utilise X-ray photoelectron spectroscopy (XPS) to examine variations in Ti–
O binding energies and to determine if phase elucidation can be achieved
through this method;



Analyse the effect of phase, crystallite size, hydrothermal temperature and
alkaline concentration on the formation of alkaline hydrothermally produced
nanostructures;



Create a simple, visual interpretation of nanostructure formation influenced
by hydrothermal temperature and alkaline concentration—to produce,
essentially, a ‗recipe book‘ for the production of nanotubes and nanoribbons;



Visually portray the nanostructures produced by three commercial titanium
dioxide powders containing both anatase and rutile polymorphs with different
crystallite sizes and varying concentrations;




Investigate the apparent latency of rutile transformation into nanotubes
compared to anatase; and, to



Evaluate the formation of nanotubes through the previously proposed
dissolution/recrystallisation reaction mechanism.
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