Improving Nanosized -Anatase Photocatase photocatalytic Activity for Dental Bleaching Application Omnia Mahmoud Abdel Ghaney

Supervisor: Mostafa El Ashry

Thesis (M.A.)—Nile University, Egypt, 2015 .

"Includes bibliographical references"

Contents:
CHAPTER II: Background and Literature Review ....................................................... 5
1. Teeth discoloration.............................................................................................. 5
1.1 Intrinsic discoloration .................................................................................. 5
1.2 Internalized discoloration ............................................................................ 5
1.3 Extrinsic discoloration ................................................................................. 5
1.3.1 Direct stains ............................................................................................. 6
1.3.2 Indirect stains ........................................................................................... 6
2. Historical background ......................................................................................... 6
3. Mechanisms of peroxide dental bleaching .......................................................... 8
4. Types of dental bleaching ................................................................................. 12
5. In-Office dental bleaching ................................................................................ 12
Efficacy ................................................................................................................ 13
Side effects ........................................................................................................... 14
6. Assisted dental bleaching .................................................................................. 15
6.1 Heat-activated ............................................................................................ 15
6.2 Light-activated ........................................................................................... 16
6.3 Photo-catalyst activated ................................................................................. 17
7. Titania as a photo-catalyst ................................................................................ 18
7.1 Methods of synthesis ................................................................................. 20
7.2 Mechanism of Titania photo-catalysis ....................................................... 21
8. Modifications of Titania ................................................................................... 24
8.1 Non-metal Modification of Titania............................................................ 24
8.2 Heterojunctions .......................................................................................... 26
8.3 Metallic modification of Titania ................................................................ 26
8.4 Modification with Noble metal nano-particles .......................................... 27
8.4.1 Silver addition ........................................................................................ 29
8.4.2 Gold addition ......................................................................................... 31
CHAPTER III: METHODOLOGY ............................................................................. 33
1. Preparation ........................................................................................................ 34
1.1 Fabrication ................................................................................................. 34
ix
The Chemicals ..................................................................................................... 35
1.1.1. Nanosized-anatase preparation (T) ........................................................ 35
1.1.2. Method 1 (M1) noble metal addition (TS, TG preparation) .................. 36
1.1.3. Method 2 (M2) noble metal addition (TSnp, TGnp Preparation) .......... 36
Silver nano-particles preparation (Snp) ............................................................... 37
Gold nano-particles preparation (Gnp) ................................................................ 37
1.2. Characterization ......................................................................................... 37
1.2.1. X-Ray Diffraction (XRD) ...................................................................... 38
1.2.2. Transmission Electron Microscope (TEM) ........................................... 39
1.2.3. UV-Vis Spectrophotometer ................................................................... 40
2. Testing............................................................................................................... 41
2.1. Experimental Solutions preparation .......................................................... 42
2.2. Glassware................................................................................................... 43
2.3. Equipment .................................................................................................. 44
2.3.1. Activating light ...................................................................................... 44
2.3.2. Vis-NIR Spectrophotometer .................................................................. 45
2.4. Experimental set-up ................................................................................... 46
2.5. The experiment .......................................................................................... 47
CHAPTER IV: RESULTS AND DISCUSSION ........................................................ 48
1. Results of the preparation phase ....................................................................... 48
1.1. Titania ........................................................................................................ 48
Transmission electron microscope (TEM)........................................................... 48
UV-Vis spectrophotometer .................................................................................. 49
X-ray diffraction (XRD) ...................................................................................... 50
1.2. Method 1 (M1) noble metal addition ......................................................... 51
1.2.1. Titania silver (TSO) ............................................................................... 51
TEM ..................................................................................................................... 51
UV-Vis spectrophotometer .................................................................................. 52
XRD ..................................................................................................................... 52
1.2.2. Titania gold (TG) ................................................................................... 53
TEM ..................................................................................................................... 53
UV-Vis spectrophotometer .................................................................................. 53
XRD ..................................................................................................................... 54
1.3. Method 2 noble metal addition .................................................................. 55
Silver nano-particles (Snp) .................................................................................. 55
Gold nano-particles (Gnp) ................................................................................... 55
1.3.1. Titania + Silver nano-particles (TSnp) .................................................. 56
TEM ..................................................................................................................... 56
UV-Vis spectroscope ........................................................................................... 57
1.3.2. Titania + gold nano-particles (TGnp) .................................................... 57
TEM ..................................................................................................................... 57
UV-Vis spectroscope ........................................................................................... 58
2. Results of the testing phase ............................................................................... 59
2.1. Pilot study: Effect of Titania photocatalyst on the bleaching process of MB dye (T vs controls) ............................................................................................... 59
UV group ............................................................................................................. 60
Vis light group ..................................................................................................... 61
UV vs Vis ............................................................................................................. 63
2.2. Effect of noble metal addition Method 1(T vs M1) ................................... 64
UV group ............................................................................................................. 64
x
Vis group .............................................................................................................. 66
UV vs Vis ............................................................................................................. 67
2.3. Effect of noble metal addition Method 2 (T vs M2) .................................. 68
UV group ............................................................................................................. 68
Vis group .............................................................................................................. 70
UV vs Vis ............................................................................................................. 71
3. Data analysis ..................................................................................................... 72
3.1. Effect of photocatalyst addition ................................................................. 72
3.2. The effect of addition method on the photosensitivity and photocatalytic activity of Titania (M1 vs M2)............................................................................. 73
3.2.1 M1 vs M2 with Silver ............................................................................ 74
3.2.2 M1 vs M2 with Gold .............................................................................. 75
3.3. Best performance ....................................................................................... 76
CHAPTER V: CONCLUSION.................................................................................... 78
REFERENCES ............................................................................................................ 80
Appendix A ..................................................................................................................

Abstract:
In-office dental bleaching is a popular treatment for restoring and improving teeth color. In-office bleaching products contain high concentrations of hydrogen peroxide (up to 40%), which can be damaging to teeth. Nanosized-anatase photocatalysts (T) were used to enhance the activity of bleaching products using lower concentrations of hydrogen peroxide (H). However, T requires activation by ultraviolet (UV) radiation, which can be harmful to patients. In the present study, we aimed to improve the photocatalytic activity and photosensitivity (to Vis light) of T used for dental bleaching by gold and silver addition. Improvement was evaluated via the photo-degradation of methylene blue dye (MB) in H solution of 3.5% under UV radiation and under Vis light source. T was prepared using sol-gel method and a pilot study was done to assess its activity in both UV and Vis light. T modification with gold (G) and silver (S) was done using two methods (M1, and M2). M1: was done by adding gold and silver precursors to T during preparation making (TS, and TG). M2: was done by preparing gold and silver nanoparticles (Gnp, and Snp) separately and mix them with T freshly in the experimental solution forming (TGnp, and TSnp). The experiment was done by exposing the experimental solutions to activating light for 10 min and measuring the photo-degradation\min of MB using Vis-NIR spectrophotometer. The results showed an improvement in photocatalytic activity and photosensitivity of all samples especially with TSnp, which yielded the best performance in Vis light. We concluded that G and S addition did improve both the photocatalytic activity and photosensitivity of T highlighting the TSnp as a strong candidate for Vis light assisted in-office dental bleaching.

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