Polyoxometalate-based Catalysts for Toxic Compound Decontamination and Solar Energy Conversion Open Access

Guo, Weiwei (2016)

Permanent URL: https://etd.library.emory.edu/concern/etds/nk322d873?locale=en
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Abstract

Polyoxometalates (POMs) have been attracting interest from researchers in the fields of Inorganic Chemistry, Physical Chemistry, Biomolecular Chemistry, etc. Their unique structures and properties render them versatile and facilitate applications in medicine, magnetism, electrochemistry, photochemistry and catalysis. In particular, toxic compound (chemical warfare agents (CWAs) and toxic industrial compounds (TICs)) decontamination and solar energy conversion by POM-based materials have becoming promising and important research areas that deserve much attention. The focus of this thesis is to explore the structural features of POMs, to develop POM-based materials and to investigate their applications in toxic compound decontamination and solar energy conversion.

The first part of this thesis gives a general introduction on the history, structures, properties and applications of POMs. The second part reports the synthesis, structures, and reactivity of different types of POMs in the destruction of TICs and CWAs. Three tetra-n-butylammonium (TBA) salts of polyvanadotungstates, [n-Bu4N]6[PW9V3O40] (PW9V3), [n-Bu4N]5H2PW8V4O40 (PW8V4), [n-Bu4N]4H5PW6V6O40.20H2O (PW6V6) are discussed in detail. These vanadium-substituted Keggin type POMs show effective activity for the aerobic oxidation of formaldehyde (a major TIC and human-environment carcingen) to formic acid under ambient conditions. Moreover, two types of POMs have also been developed for the removal of CWAs and/or their simulants. Specifically, a layered manganese(IV)-containing heteropolyvanadate with a 1:14 Stoichiometry, K4Li2[MnV14O40].21H2O has been prepared. Its catalytic activity for oxidative removal of 2-chloroethyl ethyl sulfide (a mustard simulant) is discussed. The second type of POM developed for decontamination of CWAs and their simulants is the new one-dimensional polymeric polyniobate (P-PONb), K12[Ti2O2][GeNb12O40].19H2O (KGeNb). The complex has been applied to the decontamination of a wide range of CWAs and their simulants under mild conditions and in the dark. The third part of this dissertation addresses the use of POM-based materials in photocatalytic hydrogen evolution reactions. The structures, characterizations and catalytic hydrogen generation activities of a new tri-nickel-containing Wells-Dawson POM, [Ni3(OH)3(H2O)3P2W16O59]9- and a new hybrid material that combines POMs, Pt nanoparticles (NPs) and MOFs are investigated.

Table of Contents

Table of Contents

Chapter 1 Introduction: Overview of the Structures, Properties and Applications of Polyoxometalates in Toxic Compound Decontamination and Solar Energy Conversion. 1

1.1 General Structures of POMs. 2

1.2 Catalytic Properties of POMs in Toxic Compound Decontamination. 7

1.2.1 Air-based oxidation of organic compounds by POMs. 7

1.2.2 The use of POMs in the decontamination of toxic compounds. 9

1.3 The use of POMs in solar energy conversion. 12

1.4 Goal of this work and outline. 14

References. 16

Chapter 2 Polyvanadotungstates for Aerobic Oxidation of Formaldehyde under ambient conditions. 26

2.1 Introduction. 27

2.2 Experimental 29

2.2.1 General Methods and Materials. 29

2.2.2 Preparation of Catalysts. 30

2.2.3 Preparation of [n-Bu4N]5[W3V3O19], [n-Bu4N]3H3V10O28, [n-Bu4N]7SiW9V3O40, [n-Bu4N]9P2W15V3O62, [n-Bu4N]5PW11CoO39 and [n-Bu4N]4[SiW11CeIVO39] 31

2.2.4 Preparation of Internal Standard Acetone-2,4-DNP-Hydrazone Solution. 32

2.2.5 Catalytic Aerobic Oxidative Removal of Formaldehyde. 32

2.3 Results and Discussion. 33

2.3.1 Syntheses and characterization of catalysts. 33

2.3.2 Catalytic Aerobic Oxidative Removal of Formaldehyde. 38

2.3.3 Comparison of supported noble metal and POM catalysts for aerobic formaldehyde oxidation. 45

2.3.4 Catalyst stability and reusability. 48

2.4 Conclusions. 50

References. 51

Chapter 3 A Manganese(IV)-containing Heteropolyvanadate for Oxidative Removal of 2-Chloroethyl Ethyl Sulfide. 58

3.1 Introduction. 59

3.2 Experimental 60

3.2.1 General Methods and Materials. 60

3.2.2 Synthesis of K4Li2[MnV14O40]·21H2O.. 61

3.2.3 X-ray Crystallography. 61

3.2.4 Magnetochemical Characterization. 64

3.2.5 Catalytic Oxidation of 2-Chloroethyl Ethyl Sulfide (CEES) 64

3.3 Results and Discussion. 64

3.3.1 Synthesis and Structure. 64

3.3.2 Characterization. 67

3.3.3 Magnetic Properties. 69

3.3.4 Catalytic Properties. 72

3.4 Conclusions. 74

References. 75

Chapter 4 Heteropolyniobates for Liquid- and Gas-Phase Decontamination of Chemical Warfare Agents. 79

4.1 Introduction. 80

4.2 Experimental 81

4.2.1 General Methods and Materials. 81

4.2.2 Synthesis of a new polymeric polyniobate, KGeNb. 81

4.2.3 X-ray Crystallography. 82

4.2.4 Degradation of DMMP by KSiNb and KGeNb. 84

4.2.5 Degradation of DECP by KSiNb and KGeNb. 84

4.2.6 Degradation of live agent (GD) by KSiNb. 84

4.2.7 Gas Phase Adsorptive Degradation of Live Agents (GB and HD) on KSiNb and KGeNb 85

4.2.8 Computational Studies. 85

4.3 Results and Discussion. 86

4.3.1 Synthesis and structure of KGeNb. 86

4.3.2 Decontamination of chemical warfare agents and simulants by KGeNb. 88

4.3.3 Computational studies. 102

4.4 Conclusions. 103

References. 104

Chapter 5 Di- and Trinickel Polyoxometalates for Photocatalytic Hydrogen Evolution 109

5.1 Introduction. 110

5.2 Experimental 112

5.2.1 General Methods and Materials. 112

5.2.2 Synthesis of Na8Li12[Ni2(P2W15O56)2]·74H2O.. 112

5.2.3 Synthesis of Na4Li5[Ni3(OH)3(H2O)3P2W16O59]·48H2O.. 113

5.2.4 Synthesis of TBANi2 and TBANi3 113

5.2.5 X-ray Crystallography. 116

5.2.6 Photocatalytic experimental processes. 116

5.3 Results and Discussion. 117

5.3.1 Syntheses. 117

5.3.2 Structures and Characterizations. 118

5.3.3 Photocatalytic hydrogen evolution. 125

5.3.4 Correlation between POM structure and hydrogen evolution activity. 129

5.4 Conclusions. 129

References. 130

Chapter 6 A Hybrid Nanocomposite of Polyoxometalates, Pt Nanoparticles and Metal-Organic Frameworks for Synergistic Hydrogen Evolution. 134

6.1 Introduction. 135

6.2 Experimental 136

6.2.1 General Methods and Materials. 136

6.2.2 Synthesis of NH2-MIL-53. 138

6.2.3 Synthesis of POM-Pt NPs@NH2-MIL-53 (PNPMOF). 138

6.2.4 Synthesis of POM-Pt NPs@NH2-silica. 138

6.2.5 Photocatalytic experimental processes. 138

6.2.6 Recycle and Reuse. 139

6.3 Results and Discussion. 139

6.3.1 Synthesis and characterization of PNPMOF.. 139

6.3.2 Photocatalytic hydrogen evolution. 147

6.4 Conclusions. 156

References

Chapter 7 Conclusions and Future Outlook. 163

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