Title Page

Contents

Abstract 8

1. Introduction 9

2. Literature survey 11

2.1. Semiconductor materials 11

2.2. Metal oxide semiconductors (MOS) 15

2.3. Tin oxide 15

2.3.1. Crystal structure 15

2.3.2. SnO₂ surface defects 20

2.3.3. SnO₂ band gap 22

2.3.4. SnO₂ nanostructures 22

2.4. Characterizations principles 24

2.4.1. X-ray diffraction (XRD) 24

2.4.2. Field emission scanning electron microscopy (FESEM) 27

2.4.3. Transmission electron microscopy (TEM) 29

2.4.4. Raman spectroscopy 30

2.4.5. X-ray photoelectron spectroscopy (XPS) 32

2.4.6. Textural analysis 34

2.4.7. UV-Visible spectroscopy 37

2.4.8. Photoelectrochemical tests 40

2.4.9. Photoluminescence (PL) spectrometry 44

3. Experimental 46

3.1. Synthesis of small size (SS) and large size (LS) SnO₂ NPs 46

3.2. Characterizations 46

3.2.1. Characterization of the SnO₂ NPs 46

3.2.2. Photoelectrochemical and photocatalytic activity 47

4. Results and discussion 51

4.1. Formation of oxygen vacancies 51

4.2. Crystallinity 51

4.3. Surface feature and microstructure 51

4.4. Surface defects 52

4.5. Textural properties 53

4.6. Direct band gap 60

4.7. Photoelectrochemical (PEC) activity 60

4.8. Photoluminescence (PL) properties 61

4.9. Photocatalytic activity 62

5. Conclusion 68

6. References 70

요약 77

Table 1. Summary of some physical properties of SnO₂ Adapted from Ref. 20. 18

Fig. 1. Electronic structure of different semiconductors. 13

Fig. 2. Band gaps of some semiconductors in an aqueous electrolyte at... 14

Fig. 3. Sn-O phase diagram in atmospheric pressure, showing the formation of... 17

Fig. 4. Unit cell of SnO₂ with rutile structure. Purple and red spheres represent... 19

Fig. 5. Formation energy of intrinsic point defects in SnO₂. Filled circles... 21

Fig. 6. SnO₂ nanostructure: (a) spherical nanoparticles, (b) nanoribbons,... 23

Fig. 7. Schematic presentation illustrating the Bragg's law of X-ray... 26

Fig. 8. Schematic diagram of focusing and deflection of primary electrons. 28

Fig. 9. Energy level diagram showing Stokes and anti-Stokes... 31

Fig. 10. An incoming electron causes the ejection of photoelectron. 33

Fig. 11. Schematic demonstration of the BET plot. 36

Fig. 12. Possible electronic transitions in a molecule. 39

Fig. 13. A typical stepped potential vs. time, and (b) its response as current vs. time curve. 42

Fig. 14. Typical Nyquist graph with impedance vector. 43

Fig. 15. Jablonski energy level diagram showing luminescence processes. 45

Fig. 16. Schematic illustration of set-up used for photoelectrochemical test. 49

Fig. 17. Frequent measurements of photocatalytic test suspension... 50

Fig. 18. XRD patterns of the SS and LS SnO₂. 55

Fig. 19. FESEM images of the LS (a) and SS (b) samples. TEM images (c,d), and... 56

Fig. 20. Raman spectra of the SS and LS samples. inset shows the magnified part of... 57

Fig. 21. XPS data for the binding energies of (a) O 1s for the SS sample, (b) O1s for... 58

Fig. 22. Multipoint BET nitrogen adsorption-desorption isotherms of (a) SS and (c)... 59

Fig. 23. UV-Vis absorption spectra measured by the diffuse reflectance method.... 64

Fig. 24. Photoelectrochemical properties of the SS and LS SnO₂ samples:... 65

Fig. 25. (a) Photoluminescence (PL) emission spectra of the SS and LS samples,... 66

Fig. 26. (a) Photocatalytic degradation of aqueous solutions of the dye methyl... 67