Hydrothermal Synthesis of Transition Metal Oxides

TABLE OF CONTENTS

ABSTRACT iv

ÖZ vi

TABLE OF CONTENTS viii

LIST OF TABLES x

LIST OF FIGURES xi

CHAPTER 1 1

INTRODUCTION 1

1. 1 Definition of Hydrothermal Synthesis 1

1.2 History 2

1.3 Properties of Hydrothermal Solvents 5

7

8

1.4 Water as a Reaction Medium in Hydrothermal Synthesis 8

1.5 Advantages of Hydrothermal Synthesis 11

1.6 Industrial Applications of Hydrothermal Method 12

1.7 Crystal Growth 13

1.7.1 Solid Growth Techniques 14

1.7.2 Vapor Phase Growth 14

1.7.3 Solution Growth 15

CHAPTER 2 16

EXPERIMENTAL METHOD 16

2.1 Teflon-Lined Acid Digestion Parr Autoclave 16

2.2 Reagents and Solvents 19

2.3 Characterization Techniques 19

2.3.1 X-ray Powder Diffraction 20

2.3.2 Single Crystal X-Ray Diffraction 20

2.3.3 Infrared Spectroscopy 22

2.3.4 Electron Microscopy (SEM/EDX) 22

2.3.5 Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) 23

CHAPTER 3 24

SYNTHESIS AND CHARACTERIZATION of KV3O8 24

3.1 Introduction 24

3.2 Experimental Procedure 29

3.2.1 Synthesis of KV3O8 29

Element Weight % Atomic % 30

3.2.2 X-ray Crystallographic Analyses 32

3.2.3 Bond Valence Calculations 36

3.2.4 Results and Discussion 37

CHAPTER 4 42

SYNTHESIS AND CHARACTERIZATION of PbVO3Cl 42

4.1 Introduction 42

4.2 Experimental Procedure 45

4.2.1 Synthesis of PbVO3Cl 45

4.2.2 X-ray Crystallographic Analyses 46

3.2.3 Results and Discussion 50

CHAPTER 5 62

CONCLUSIONS 62

REFERENCES 64

LIST OF TABLES

Table1.1 Summary of high performance material applications of hydrothermal 13

synthesis. 13

Tablo 3.1 EDX results of orange plate-shaped crystals (KV3O8). 30

Table 3.2 Crystallographic Data for KV3O8 33

Table 3.3 Atomic Coordinates (x104) and Equivalent Isotropic Thermal Parameters of 34

Table 3.4 Anisotropic Displacement Coefficients (Å2x 103) of KV3O8. 34

Table 3.5 All Bond Angles (degrees) of KV3O8. 35

Table 3.6 Bond Lengths (Å) and Bond Valence (italic) in KV3O8. 36

Table 4.1 Crystallographic Data for PbVO3Cl. 47

Table 4.2 Atomic Coordinates (x104) and Equivalent Isotropic Thermal Parameters of 47

Table 4.3 Bond Lengths (Å) and Bond Valence (italic) in PbVO3Cl. 48

Table 4.4 Anisotropic Displacement Coefficients (Å2x 103) of PbVO3CI. 49

Table 4.5 All Bond Angles (degrees) of PbVO3Cl. 49

Table 4.6 EDX results of yellow needle crystals (PbVO3Cl). 58

LIST OF FIGURES

Figure 1.1 Number of publications year-wise. 4

Figure 1.2 Number of papers on hydrothermal research in materials. 5

Figure 1.3 Phase diagram of water. 7

Figure 1.4 Variation of dielectric constant of water with temperature and pressure. 8

Figure 1.5 Presentation of the P-T behavior of water at various degrees of fill. 10

Figure 2.1 (a) Schematic representation of an autoclave, (b) A Parr acid digestion bomb. 18

Figure 2.2 Picture of Carbolite CWF 1100 furnace. 18

Figure 3.1 Coordination polyhedra adopted by V (V)- and V (IV)- oxo species: 25

(a) tetrahedral, (b) “4 + 1” square pyramidal, (c) “3 + 2” trigonal bipyramidal, 25

(d) “4 + 1 + 1” octahedral, and (e) “2 + 2 + 2” octahedral. 25

Figure 3.2. Polyhedral representations of the structures of the (a) [V2O7]4− and (b) [V4O12]4− clusters; (c) ball and stick and (d) polyhedral views of the structure of [V10O28]6−. 26

Figure 3.3 Views of the one-dimensional vanadate chains of (a) KVO3 and (b) β-NaVO3. 27

Figure 3.4 The network structure of V2O5. 28

Figure 3.5 Crystal pictures of KV3O8 (Nikon Eclips L150 Optic Microscope, 10 X magnitudes). 29

Figure 3.6 The SEM EDX peaks of KV3O8. 30

Figure 3.7 Unit cell view of KV3O8 running along a axis. 38

Figure 3.8 Representation of V-O bonds running along c axis in KV3O8 structure. 39

Figure 3.9 Polyhedral representations of VO6 octahedras and VO5 square pyramids. 40

Figure 3.10 Representation of KV3O8 showing K atoms 41

Figure 4.1 Pictures of natural minerals (a) kombatite and (b) vanadinite. 44

Figure 4.2 Yellow crystals of PbVO3Cl (Nikon Eclips L150 Optic Microscope, 10 X magnitudes). 45

Figure 4.3 Unit cell view of PbVO3Cl running along b axis. 51

Figure 4.4 Polyhedral projection of the structure of PbVO3Cl along a axis showing the 52

edge-sharing VO5 pyramids with a trans configuration. 52

Figure 4.5 View of VO5 bonds in PbVO3Cl structure running along a axis. 53

Figure 4.6 The distribution of individual bond lengths in (V+5O5) polyhedra in mineral and inorganic crystal structures: (a) [1+4] coordination and (b) [2+3] coordination. 56

Figure 4.7 The distribution of individual vanadyl, equatorial, and trans bonds in (V5+O6) polyhedra in mineral and inorganic crystal structures: (a) [1+4+1] coordination and (b) [2+2+2] coordination 57

Figure 4.8 The SEM EDX peaks of PbVO3Cl. 59

Figure 4.9 Powder patterns of PbCl2 and white product. 59

Figure 4.10 Powder pattern of PbVO3Cl. 60

Figure 4.11 Infrared spectrum of PbVO3Cl. 61

Figure 4.12 TGA and DSC curve of PbVO3Cl. 61

CHAPTER 1

INTRODUCTION

1. 1 Definition of Hydrothermal Synthesis

In spite of the fact that the hydrothermal technique has made great progress, there is no unanimity about its definition. The term hydrothermal usually refers to any heterogeneous reaction in the presence of aqueous solvents or mineralizers under high pressure and temperature conditions to dissolve and recrystallize materials that are relatively insoluble under ordinary conditions.

There are many different definitions for hydrothermal synthesis in the literature. For instance, Rabenau (1985) defined hydrothermal synthesis as the heterogeneous reactions in aqueous media above 100^oC and 1 bar [1]. According to Laudise (1970), hydrothermal growth means growth from aqueous solution at ambient or near-ambient conditions [2]. Lobachev (1973) defined it as a group of methods in which crystallization is carried out from superheated aqueous solutions at high pressures [3].

Roy (1994) declares that hydrothermal synthesis involves water as a catalyst and occasionally as a component of solid phases in the synthesis at elevated temperature (> 100^oC) and pressure (greater than a few atmospheres) [4]. Byrappa (1992) defines hydrothermal synthesis as any heterogeneous reaction in an aqueous media carried out above room temperature and at pressure greater than 1 atm [5]. Yoshimura (1994) defines it as reactions occurring under the conditions of high temperature-high pressure (> 100^oC, > 1 atm) in aqueous solutions in a closed system [6].

All the above definitions are good for material synthesis. However, there is no definite lower limit for the temperature and pressure conditions. The majority of the authors fix the hydrothermal synthesis at above 100^oC and above 1 atm. According to the all definitions, hydrothermal reaction can be described as “any heterogeneous chemical reaction in the presence of a solvent (whether aqueous or nonaqueous) above room temperature and at pressures greater than 1 atm in a closed system” [7].