壓電材料在乾淨能源和環境廢水處理的應用中都已展現了充分的催化能力。本研究中，我們使用溶膠-凝膠法合成各種尺寸的菱形晶系 R3c 無鉛鈦酸鉍鈉 (BNT) 顆粒。當我們將BNT用作水分解產氫的壓電催化劑時，BNT 材料能夠達到相當高的產氫效率（高達 506.70 µmol g–1 h–1）；這些壓電催化劑也能有效地降解亞甲藍有機汙染物（MB， k = 0.039 min-1），這表明了它們在污染水處理的應用上具有相當的潛力。
接著，我們摻雜了鐵酸鉍 (BiFeO3) 磁性材料在BNT 基材中，並利用其多鐵特性進一步增益 BNT 基壓電催化劑的壓電催化活性。而BFO的摻雜並不會影響BNT基材本身的結構。其中，BNT-BF 0.4在所有的BNT-BF組成中表現出了最高的產率（高達 1451.74 µmol g-1h-1）。

最後，我們發現壓電場會導致半導體中的能帶傾斜並輔助電荷的轉移，進而抑制載子複合以增加產氫效率。因此，材料的氧空缺、顆粒尺寸和促使電子-電洞對分離的內部電場在壓電催化效率的增益機制上都扮演了重要的角色。

Piezoelectric materials have demonstrated applicability in clean energy production and environmental wastewater remediation through their ability to initiate a number of catalytic reactions. In this study, we used a sol–gel method to synthesize lead-free rhombohedral R3c bismuth sodium titanate (BNT) particles with different sizes. When used as a piezocatalyst to generate H2 through water splitting, the BNT samples provided high production rates of up to 506.70 µmol g–1 h–1； These piezocatalysts also degraded the organic pollutant, methylene blue (MB) with high efficiency (up to k = 0.039 min–1), suggesting their potential to treat polluted water.
Next, we introduced bismuth ferrite (BiFeO3, BFO), the magnetic material, into BNT matrix to further enhance the piezocatalytic activities of the BNT-based piezocatalyst by the assistance of multiferroic nature of the catalyst. The 0.4 BFO-BNT provided highest H2 production rate of up to 1451.74 µmol g-1h-1 among the BFO-BNT with other doping concentrations. Importantly, we found that the piezopotential causes band bending in the semiconductor and aids charge transfer, such that recombination of carriers is suppressed and the rate of H2 production increases. The mechanism of piezoelectric catalysis involved oxygen vacancies, the size of the catalyst, and the internal electric field playing important roles to enhance electron–hole separation which further enhanced the catalysis reactions.

摘要 i
Abstract ii
Table of Contents iii
List of Figures v
List of Tables xi
Acknowledgements xii
Chapter 1 1
Introduction and Literature review 1
1.1 Background 2
1.2 Piezoelectricity 3
1.3 Piezocatalysis 4
1.4 Types of Mechanical Energy in Piezocatalysis: 7
1.4.1 Ultrasonic Cavitation 9
1.4.2 Vortex-induced Shearing force 10
1.4.3 Physical bending 12
1.5 Ferroelectricity 13
1.5.1 Origin of Ferroelectricity 14
1.5.2 Crystallographic Consideration of Ferroelectrics 15
1.5.3 Some Important Ferroelectric Materials 16
1.5.4 Barium Titanate 17
1.5.5 Lead Zirconate Titanate 17
1.5.6 Bismuth layer Structured Ferroelectrics 18
1.6 Relaxor ferroelectrics 18
1.7 Relaxor versus normal ferroelectric 19
1.8 Literature Review 19
Chapter 2 44
Motivation & Objective 44
2.1 (Bi1/2Na1/2)TiO3 System 45
2.2 The objective of proposed work 48
2.3 Synopsis of thesis 49
Chapter-3 50
Experimental Methods, Characterizations Tools and their Principles 50
3.1 Synthesis of Piezoelectric Catalyst 51
3.1.1 Sol-Gel Synthesis of Bi1/2Na1/2TiO3 51
3.1.2 Sol-Gel Synthesis of Bi1/2Na1/2TiO3-BiFeO3 52
3.2 Characterization of Piezoelectric Catalyst 53
3.2.1 Structural and morphology characterization 53
3.2.1.1 X-Ray Diffractometer (XRD) 53
3.2.1.2 Scanning Electron Microscopy (SEM) 54
3.2.1.3 Raman Spectroscopy 55
3.2.1.5 X-ray Photoelectron Spectroscopy 57
3.2.1.6 Transmission Electron Microscopy 58
3.2.1.7 The Brunauer-Emmett-Teller Measurement 59
3.2.1.8 UV-Visible Spectroscopy 60
3.2.1.9 Fluorescence Spectroscopy 61
3.2.1.10 Gas Chromatography 62
3.2.1.11 EPR Spectroscopy 63
3.3 Hydrogen Production Experiments 64
3.3.1 Piezo-catalytic Hydrogen Production of Bi1/2Na1/2TiO3 64
3.3.2 Piezo-catalytic Dye Degradation of Methylene Blue 64
3.4 Theoretical Simulation using Finite Element Method 64
Chapter 4 68
Enhanced Piezocatalytic Activity in Bi1/2Na1/2TiO3 for Water Splitting by Oxygen Vacancy Engineering 68
4.1 Introduction 69
4.2 Results and Discussion 71
4.3 Conclusions 90
Chapter 5 91
Enhancement of Piezocatalytic activity in lead-free multiferroic multicatalytic BNT perovskite for water splitting by bismuth ferrite doping 91
5.1 Introduction 92
5.2 Results and Discussion: 94
5.3 Conclusion 110
Chapter 6 111
Future Perspective 111
Chapter 7 114
References 114
Publications 125
Publications in Progress 126
International Conferences 127

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