The works presented in this thesis discuss the red-shift enhanced photocatalysis of TiO2-coated carbon nanotubes by atomic layer deposition. The controllable thickness and uniform TiO¬2 layer is characterized, and the thermal treated composites lead to carbon diffusion into oxygen lattices which results in the efficient photocatalysis at visible light. The recyclable composite filters are also fabricated by atomic layer deposition. The filters are recyclable after the organic degradation without any wastage. The greater photocatalysis of composite filter is attributed to the high specific surface area resulting from the high aspect ratio of CNTs and the interactions between TiO2/CNTs interface.

Chapter 1 introduces the background of carbon nanotube and titanium dioxide, including the structure, physical properties and photocatalysis of TiO2/CNTs composites.

Chapter 2 describes the experimental setups and characterization techniques employed in this thesis.

Chapter 3 discusses the photocatalysis of TiO2/MWCNTs composites including the degradation rate of organic substances and the recyclable composite filter.

Chapter 4 concludes the experimental results.

Abstract-------------------------------------------------------------------------------------------I
摘要(Abstract in Chinese)--------------------------------------------------------------------II
Acknowledgement----------------------------------------------------------------------------III
Contents-----------------------------------------------------------------------------------------IV
Figure Captions-------------------------------------------------------------------------------VI
Table List---------------------------------------------------------------------------------------IX

Chapter 1 Introduction------------------------------------------------------------------------1
1-1 Introduction of carbon nanotube----------------------------------------------------------1
1-1-1 Structure of carbon nanotubes-----------------------------------------------------1
1-1-2 Electrical properties of carbon nanotubes---------------------------------------4
1-1-3 Mechanical properties of carbon nanotubes-------------------------------------6
1-1-4 Surface energy of carbon nanotubes----------------------------------------------7
1-2 Introduction of titanium dioxide-----------------------------------------------------------9
1-2-1 Structure of titanium dioxide------------------------------------------------------9
1-2-2 Photocatalysis of titanium dioxide----------------------------------------------11
1-2-3 Photocatalysis of Titanium dioxide/carbon nanotubes composites---------14
1-3 Introduction of methylene blue----------------------------------------------------------19
1-3-1 Basic properties of methylene blue---------------------------------------------19
1-3-2 Degradation of methylene blue in water---------------------------------------19
1-4 Experimental motives---------------------------------------------------------------------20
Reference----------------------------------------------------------------------------------------22

Chapter 2 Experimental---------------------------------------------------------------------26
2-1 Atomic layer deposition-------------------------------------------------------------------26
2-1-1 Introduction of atomic layer deposition----------------------------------------26
2-1-2 Atomic layer deposition process of TiO2---------------------------------------26
2-2 Growth of MWCNTs----------------------------------------------------------------------27
2-3 Photo degradation calculation------------------------------------------------------------28
2-4 Characterization instruments-------------------------------------------------------------29
2-5 Experimental detail------------------------------------------------------------------------31
2-5-1 Photocatalysis of TiO2/MWCNTs-----------------------------------------------31
2-5-2 Photocatalysis of TiO2/MWCNTs/carbon cloth-------------------------------32
References---------------------------------------------------------------------------------------34
Chapter 3 Results and Discussion----------------------------------------------------------35
3-1 Photocatalysis of TiO2/MWCNTs-------------------------------------------------------35
3-1-1 Morphologies by SEM and TEM------------------------------------------------35
3-1-2 X-ray diffraction profile----------------------------------------------------------39
3-1-3 Photocatalysis examination------------------------------------------------------42
3-2 Photocatalysis of TiO2/MWCNTs/carbon cloth----------------------------------------50
3-2-1 Morphologies by SEM------------------------------------------------------------50
3-2-2 Photocatalysis examination------------------------------------------------------52
References---------------------------------------------------------------------------------------56
Chapter 4 Conclusion------------------------------------------------------------------------58
Future Work------------------------------------------------------------------------------------59
Publication List--------------------------------------------------------------------------------60

Figure Captions
Figure 1.1 (a) The 2D graphene sheet is shown along with the vector which specifies the chiral nanotube. The chiral vector OA or Ch = na1 + ma2 is defined on the honeycomb lattice by unit vectors a1 and a2 and the chiral angle θ is defined with respect to the zigzag axis. Along the zigzag axis θ = 0°. The diagram is constructed for (n,m) = (4,2). (b) The pairs of integers (n,m) in the figure specify chiral vectors Ch for CNTs, including zigzag, armchair, and helical tubes. Below each pair of integers (n,m) is listed the number of distinct caps that can be joined continuously to the cylindrical carbon tube denoted by (n, m). The circled dots denote metallic tubes and the small dots are for semiconducting tubes…………………………………………..2
Figure 1.2 (a) Illustrations show C60 buckyball and other fullerenes. This shows that CNT can be derived from a cut-in-half buckyball by adding belt of carbon atoms. (b)-(d) Armchair, zigzag and helical CNT, respectively. (e) Chiral angle and vector (n,m) determine the diameter and length of the CNT. (f) The CNT bonding corresponds to the σ (sp2-hybridization) and π (2pz) bond…………………………….3
Figure 1.3 The semiconducting CNT…………………………………………………5
Figure 1.4 The metallic CNT………………………………………………………….5
Figure 1.5 Elastic properties of CNTs………………………………………………...7
Figure 1.6 (a) TEM images of a MWCNT prior to (left) and coated a monolayer of gold nanocrystals with lots of nuclei. (b) Transverse section of CNT in (a)………….8
Figure 1.7 TiO2 morphologies and lattice structures………………………………...10
Figure 1.8 Phase diagram of TiO2¬…………………………………………………...11
Figure 1.9 Main photocatalytic process occruing on TiO2…………………………..12
Figure 1.10 Band positions of several semiconductors in contact with aqueous electrolyte at pH 1. The lower edgeof the conduction band and upper edge of the valance are presented along with the band gap in electron volts. The energy scale is indicated in electron volts using either the normal hydrogen electrode (NHE) or the vacuum level as a reference. On the right side the standard potentials of several redox couples are presented against the standard hydrogen electrode potential……………13
Figure 1.11 SEM and TEM images of sol-gel made TiO2…………………………..17
Figure 1.12 The proposed mechanisms for the TiO2/CNT system enhancement of photocatalysis………………………………………………………………………...18
Figure 1.13 Molecular formula of methylene blue…………………………………..19
Figure 2.1 The standard absorption spectrum of MB for our work………………….28
Figure 2.2 Illustration of degradation examination setup in section 2-5-1………..…32
Figure 2.3 Illustration of degradation examination setup in section 2-5-2…………..33
Figure 3.1 SEM images of aligned MWCNTs array………………………………...36
Figure 3.2 SEM images of TiO2-coated MWCNTs array……………………………36
Figure 3.3 HRTEM images of 200 cycles-coated TiO2/MWCNT…………………..38
Figure 3.4 Comparison of HRTEM images of TiO2/MWCNT with different deposition cycles……………………………………………………………………..38
Figure 3.5 XRD profiles of TiO2/MWCNTs composites with different deposition cycles…………………………………………………………………………………40
Figure 3.6 The standard XRD profiles of TiO¬2……………………………………...41
Figure 3.7 Residual MB concentration (C/Co) percentages of P-25 and 800 cycles TiO2/MWCNTs composite vs. irradiation time………….……………………….…..45
Figure 3.8 UV-vis reflectance spectra of P-25 and as-made 800 cycles TiO2/MWCNTs composite…….……………………………………………………..45
Figure 3.9 Auger spectra of as-made 800 cycles TiO2/MWCNTs composite..……...46
Figure 3.10 Electron spectroscopy for chemical analysis (ESCA) profile for as-made 800 cycles TiO2/MWCNTs composite……………………………………….………47
Figure 3.11 Degradation rate of MB (for P-25 and TiO2/MWCNTs under UV or WL irradiation) presents as ln[C/Co] vs. irradiation time. The time period before 0 minute (dash line) corresponds to dark condition……………………………………….…...49
Figure 3.12 SEM images of 800 cycles TiO2/MWCNTs/C cloth sandwich structure.51
Figure 3.13 SEM images of 800 cycles TiO2/C cloth structure …………………….51
Figure 3.14 Filtration test setup……………………………………………………...53
Figure 3.15 Degradation of MB water solution (for C cloth, TiO2/C cloth and TiO2/MWCNTs/C cloth under UV or WL irradiation) by filtration test……………..54
Figure 3.16 SEM image of TiO2/MWCNTs/C cloth (sandwich structure) after filtrating and baking………………………………………………………………….55

Table list
Table 1.1 Basic properties of P-25 TiO2……………………………………………..14
Table 3.1 Distribution of TiO2 grain size with different deposition cycles………….42
Table 3.2 Variation of reaction rate constant (k) at different irradiation times (for P-25 and TiO2/MWCNTs under UV or WL irradiation)…………………………...………49

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