Synthesis of MIL-53(Fe), TiO2 and BiVO4 and Their Photocatalytic Activity under Visible Light Irradiation
- Abstract
- In this thesis, three types of photocatalysts: TiO2, BiVO4 and metal-organic frameworks (MOF) were studied. For the study of MOF, iron-based MIL-53 crystals with uniform size were successfully synthesized using a microwave-assisted solvothermal method and characterized by XRD, FE-SEM and DRS. We also investigated the photocatalytic activity of MIL-53(Fe) for the decomposition of (methylene blue) MB using H2O2 as an electron acceptor. From XRD and SEM results, the fully crystallized MIL-53(Fe) materials were obtained regardless of preparation method. From DRS results, MIL-53(Fe) samples prepared using microwave-assisted process (MW) displayed the absorption spectrum up to the visible region and then they showed the high photocatalytic activity under visible light irradiation. The MIL-53(Fe) catalyst prepared by two times microwave irradiation showed the highest activity.
For the study of TiO2, TiO2 elongated rhombic was successfully synthesized by solvothermal reaction of titanium butoxide precursor in the presence of oleic acid, oleylamine and vapor water. The sample was doped with transition metal ions (Ce, Cr and Fe) and characterized by XRD, Raman, PL, TEM and DRS. We also investigated the photocatalytic activity of these oxides for the decomposition of rhodamine B (RhB). From XRD and Raman results, metal replacement with the metal ion in the crystal lattice does not change the high crystallinity of the TiO2 structure, and all the metal ions were incorporated into the structures of titania as well as replaced titanium ion or located at interstitial site. In the result of UV-Vis DRS analysis, all the catalysts displayed the similar absorption spectrum up to the visible region, and the absorption band shifted to a higher wavelength on the metal-doped TiO2 samples when compared to the pure TiO2 sample. From PL results, the relative intensity of the 1.0% Ce doped-TiO2 sample is the lowest meaning that its photocatalytic activity is the best in the photocatalytic decomposition of RhB.
For the study of BiVO4, a solvothermal method assisted by microwave technique has been developed for the synthesis of highly crystalline and monoclinic BiVO4 powders with ellipsoidal structure, using Bi(NO3)3.5H2O and Na3VO4.12H2O as raw materials, and oleic acid as surfactant. The phase structure and morphology of as-prepared BiVO4 samples were characterized by XRD, SEM and DRS. We have also investigated the photocatalytic activity of these materials for the decomposition of Rhodamine B under visible light irradiation. From DRS results, BiVO4 samples showed the absorption spectrum up to the visible region and then their photocatalytic activity was shown higher than commercial P-25 TiO2 materials. BiVO4 prepared by the microwave-assisted solvothermal method showed the highest photocatalytic activity due to a small particle-size effect.
Monoclinic-tetragonal heterostructured BiVO4 was successfully synthesized by an ethylene glycol monomethyl ether-water (EGME-H2O) mixed solvothermal method and characterized by XRD, Raman, FE-SEM, TEM and UV-vis DRS. The results show that the presence of EGME play an important factor not only in the control of crystal morphology but also in the formation of crystal phase of BiVO4. BiVO4 crystals with monoclinic-tetragonal heterophase structure could promote the separation of photogenerated electron-hole pairs, which shows higher photocatalytic activity towards RhB photodecomposition under visible light irradiation, much better than single-phase monoclinic scheelite BiVO4. Moreover, the surface morphology, crystalline phase, optical properties and photocatalytic activity of BiVO4 also can be controlled by the different EGME/H2O volume ratio.
A highly crystallized monoclinic-scheelite type BiVO4 powders were successfully synthesized by solvothermal method. The as-synthesized BiVO4 powders were characterized by XRD, FE-SEM, Raman spectroscopy, UV-vis DRS spectroscopy and terephthalic acid photoluminescence probing technique (TA-PL). From the XRD data and Raman spectra, the monoclinic scheelite phase BiVO4 sample can be obtained at higher solvothermal synthesis temperature more than 140 ◦C. The preparation conditions such as, the Bi/V molar ratio and synthesis temperature, have significant effects on the morphologies of the BiVO4 samples. BiVO4 sample prepared in the excess bismuth shows the highest PL peak, which has the highest formation rate of OH radicals and the highest photocatalytic activity. This result suggests that the formation rate of OH radicals shows a good correlation with the photocatalytic activity.
- Issued Date
- 2016
- Awarded Date
- 2016. 2
- Type
- Dissertation
- Publisher
- Department of Chemical Engineering, The Graduate School, Pukyong National University
- Affiliation
- Department of Chemical Engineering, The Graduate School, Pukyong National University
- Department
- 대학원 화학공학과
- Advisor
- Seong Soo Hong
- Table Of Contents
- Acknowledgment ii
Content vi
Abstract vii
List of Figures xviii
List of Tables xix
Abbreviation xx
Chapter 1. General introduction 1
1.1 The possibilities and challenges of photocatalysts 1
1.2 Synthesis methods 4
1.3 TiO2 7
1.4 MOFs 9
1.5 BiVO4 14
1.5.1 Structure 14
1.5.2 Electronic properties 16
1.5.3 Optical properties 18
1.6 Objective and and scope of thesis 20
1.7 References 21
Chapter 2. Characterization technique 31
2.1 X-ray diffraction 31
2.2 Raman spectroscopy 32
2.3 Electron microscope 33
2.4 UV-visible absorbance spectroscopy 34
2.5 References 36
Chapter 3. Photocatalytic decomposition of MB over MIL-53(Fe) prepared using MW-assisted process under visible light irradiation 38
3.1 Introduction 38
3.2 Materials and methods 40
3.2.1 Chemicals 40
3.2.2 Synthesis of MIL-53(Fe) photocatalyst 40
3.2.3 Characterization 41
3.2.4 Photocatalytic test 41
3.3 Results and discussion 42
3.4 Conclusions 52
3.5 References 53
Chapter 4. Synthesis and characterization of metal-doped TiO2 elongated rhombic by two-phase method and their photocatalytic activity under visible light irradiation 56
4.1 Introduction 56
4.2 Experimental details 58
4.3 Results and discussion 60
4.4 Conclusion 67
4.5 References and Notes 68
Chapter 5. Synthesis of BiVO4 nanoellipsoilds using microwave process and its photocatalytic activity under visible light irradiation 70
5.1 Introduction 70
5.2 Experimental . 71
5.3 Results and discussion 73
5.4 Conclusion 81
5.5 References 82
Chapter 6. The synthesis of monoclinic-tetragonal heterostructured BiVO4 by solvothermal method using EGME-water as mixed solvents and their photocatalytic activity under visible light irradiation 84
6.1 Introduction 84
6.2 Experimental 86
6.2.1 Preparation of catalysts 86
6.2.2 Characterization of catalysts 87
6.2.3 Photocatalytic test 87
6.3 Result and discussion 88
6.3.1 Effect of solvent on the phase structure and morphology of BiVO4 88
6.3.2 Effects of EGME/water volume ratio 97
6.3.3 Formation mechanism of BiVO4 102
6.3.4 Photocatalytic tests. 105
6.4 Conclusions 111
6.5 References 111
Chapter 7. Synthesis of needle-like BiVO4 with improved photocatalytic activity under visible light irradiation 116
7.1 Introduction 116
7.2 Experimental 117
7.3 Results and discussion 120
7.3.1 Characterization of BiVO4 samples 120
7.3.2 Photocatalytic test 127
7.4 Conclusion 131
7.5 References 131
Chapter 8. Conclusions and Future Works . 134
8.1 Conclusion 134
8.2 Future work 137
Publication and Conference 138
- Degree
- Doctor
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