Designed synthesis of titanium organic framework for photocatalyst applycation

Constructing by Secondary Building Units SBUs of metal clusters and organic linkers combination that permits the modification of resultant structural modularity for structure designing e

VIETNAM NATIONAL UNIVERSITY-HOCHIMINH CITY

UNIVERSITY OF TECHNOLOGY-HOCHIMINH CITY

VIETNAM NATIONAL UNIVERSITY-HOCHIMINH CITY

UNIVERSITY OF TECHNOLOGY-HOCHIMINH CITY

HA LAC NGUYEN

DESIGNED SYNTHESIS OF NOVEL METAL–ORGANIC FRAMEWORKS FOR PHOTOCATALYST APPLICATION

Major subject: TECHNOLOGY FOR ORGANIC COMPLEXES

Major subject code: 62527505

Independent Referee 1: ………

Independent Referee 2: ………

Referee 1: ………

Referee 2: ………

Referee 3: ……… SUPERVISORS

1 Prof Dr Nam T S Phan

2 Dr Danh T Tong

PROTESTATION

I would like to protest that the research, which will be reported below, belongs to

me All publications were published based on the author’s research, and the author had done the truthful science and contributed to the development progress of science Any claim and conclusion were cited by the references and documented papers The author recognized that the seriousness and authenticity need to be strongly considered

Author

Ha Lac Nguyen

ABSTRACT

Over the past two decades, the prominent growth of Metal Organic Frameworks (MOFs), a high ordered and porous materials class had been receiving the pay attention by the research community specially Constructing by Secondary Building Units (SBUs) of metal clusters and organic linkers combination that permits the modification of resultant structural modularity for structure designing (e.g., post-synthetic modification, predesigned linker, defects chemistry) which can be tunable the structural features (e.g., pore size, porosity) to make MOFs address the environment problems as well as the targeted applications such as gas uptake, separation, catalyst, drug delivery, water treatment In term of MOFs synthesis, the plenteous chemistry of metal and controllability of organic linkers were exploited to make the uncountable amount of new MOFs material In this case, the simple solvothermal reaction or other methods (e.g., hydrothermal, solvent free, slow dispersion) was usually employed to obtain new MOFs This method for MOFs synthesis can generally predict the obtained structures based on the geometry of the metal clusters and the organic linkers guided by reticular chemistry

Although predicting structures is now commonplace, a robust and modular synthetic approach to designing new MOF materials remains elusive as a result of the trial-and-error nature of crystallization processes, a lack of control over crystallization, and the regular discoveries of multiple crystalline phase products once the reaction is complete In MOF chemistry, the building block method, whereby discrete, preassembled metal oxo clusters are reacted with well-defined organic linkers, has been utilized to achieve a greater degree of control over MOF construction However, the isolation and subsequent usage of many discrete metal oxo clusters remains a significant challenge and the relatively slow kinetics originating from the association and dissociation of ligands, limits the applicability of this method Additionally, it is far from given that the desired MOF structure will be obtained as metal oxo building blocks have been observed to rearrange during the synthesis Means of overcoming this lack of total synthetic control is to take inspiration from molecular synthesis, in which certain conditions have been discovered to achieve specific end products In this

contribution, we articulate a strategy for making discrete metal clusters in situ that are

appropriately functionalized to affect imine condensation reactions, commonly used in the chemistry of covalent organic frameworks (COFs) We find that the cluster formation chemistry and that of COFs, when carried out in sequence, overcome the challenge of synthetic incompatibility The structural features of targeted material, termed MOF-901, was fully characterized powder X-ray diffraction and supplemental analyses As a result of the incorporation of Ti(IV) units, MOF-901 was proven to be photocatalytically active and was applied to the photocatalyzed polymerization of methyl methacrylate (MMA)

For further investigation, the photocatalysis properties of MOF which is isoreticular to MOF-901 structure, MOF-902 was successfully synthesized by enlarging the linking unit, and applied to the application of polymerization reaction with these kinds of monomer: methylmethacrylate (MMA), benzylmethacrylate (BMA), and styrene (St) Interestingly, based on the catalysis effect of MOF-902, the molecular weight of polyMMA is as high as the value of polyMMA which is produced

by 901 catalyst, and the polydispersity index of polyMMA produced by

MOF-902 catalyst is lower than MOF-901 (1.27 compared to 1.60)

Moreover, we have successfully synthesized three novel MOFs termed 903(Fe), MOF-904(Fe), and VNU-18(Cu) based on triangular Iron (III) cluster and extraordinary three discrete Cu(II) building units, respectively These materials were full characterized by the powder X-ray diffraction, single crystal X-ray diffraction analysis, thermogravimetric analysis, gas adsorption study MOF-904 and VNU-18 show the permanent porosity with the internal surface area in calculated of 1200 m2 g-1and 1000 m2 g-1, respectively, which are proven by Nitrogen isotherm at 77 K at low pressure

MOF-ACKNOWLEDGEMENTS

On the way to achieve the professional skills and knowledge in the research, I had turned to different vicissitude Fortunately, I was always received the support and encouragement by many people as well as the great results from my efforts In this context, I would like to give my honest acknowledgements to all

First, the acknowledgement was given to my supervisors, Prof Nam T S Phan and Dr Danh T Tong, who not only supported me from the first time I joined their group, but also lead me to another sight of science Specially, they are probably my examples due to their unexhausted contribution to the science and educational work

At this time, I appreciate all Faculty of Chemistry members, University of Technology, for their strong supports during the time I have worked there I hope talking my appreciation to Prof Nhan T H Le, Dr Dung T Le, and my colleagues in Prof Nam Phan’s group

Second, I am grateful to Prof Omar M Yaghi for giving me the opportunity to work in his laboratory at University of California, Berkeley That is surely a great chance I had received to open mind and build up my research thinking I strongly appreciate our visiting Professor, Dr Hiroyasu Furukawa, who directly mentors me when I turn to Center for Molecular and Nanoarchitecture (MANAR Center) as well as during my visiting time at Prof Yaghi’s group Actually, I always keep in mind trying

to do the research like Dr Hiroyasu Furukawa

I was in the wonderful moment in Prof Yaghi’s group with my friends, colleagues, and another group member (Prof Jerrey R Long), visiting Professors from different groups I would say thank to them due to their friendship as well

Third, I would give my gratitude to Dr Felipe Gándara, senior scientist in Department of New Architectures in Materials Chemistry, Materials Science Institute

of Madrid, Spain I was lucky to be his co-worker when he had been in Prof Yaghi’s group before coming back to Spain In fact, my knowledge and skills in crystallography may be affected from him He did not concern to share his professional skills in crystallography technique to me when I tried to learn how to solve the crystal structure by powder X-ray diffraction as well as single crystal later I strongly appreciate all his help

I also want to thank to Mr Kyle E Cordova in Prof Yaghi’s group due to his support when I was in Berkeley I am happy to work with him when he comes to MANAR Center as Global Coordinator for helping MANAR Vietnam student My gratitude is given to him not only because of his valuable discussion but also his contribution to MANAR members He really changed our mind and lead us to do the research meaningfully

In the site of MANAR Center, I would like to acknowledge Prof Hoang Dzung, Prof Hoang T Nguyen because of their entirely encouragement Their valuable discussion would go along with me during the time

I would say acknowledgement to my colleagues at MANAR Center, who had spent several years to research and collaborate with me I appreciate all their helps and assistances Another person I owe him a great debt of gratitude for his irreplaceable advices, guidance and encouragement when I face the challenge I hope these words will be come to him

My deep gratitude is also offered to my parents and my mother-in-law, who really support and strongly encourage me

Finally, I take my own acknowledgement to my wife In fact, I cannot express

my indebtedness by any words to her I would like to thank to my wife due to her love and entirely encouragement Surely that is the motivation that helps me doing the research and overcoming the challenge

I sincerely thank all!

CONTENT

Chapter 1: INTRODUCTION 1

1.1 Metal Organic Frameworks (MOFs) 1

1.2 MOFs composites 2

1.3 Interesting features from MOFs material 6

1.3.1 Ultrahigh porosity 7

1.3.2 Reticular synthesis 9

1.3.3 High stability 10

1.3.4 Postsynthetic modification (PSM) 11

1.3.5 Catalytic transformation 13

1.3.6 Gas adsorption 15

1.3.6.1 Hydrogen storage 15

1.3.6.2 Methane storage 16

1.3.6.3 Carbon dioxide uptake and separation 18

1.3.6.4 Proton Conductivity 19

1.3.7 Prospective 20

Chapter 2: THE NOVEL METAL–ORGANIC FRAMEWORKS: SYNTHESIS AND CHARACTERIZATION 21

2.1 Introduction 21

2.1.1 Quest for design the novel MOFs material 21

2.1.2 The aim of the synthesis 21

2.2 Titanium–Organic Framework-901 synthesis 22

2.2.1 New approach to design Ti-MOFs 22

2.2.2 Scope of the work 24

2.2.3 Experimental 26

2.2.3.1 Materials and General Methods 26

2.2.3.1.1 Chemicals 26

2.2.3.1.2 Analytical techniques 27

2.2.3.2 Synthesis and Characterization of [Ti6O6(OiPr)6(AB)6] 29

2.2.3.3 Synthesis of MOF-901 29

2.2.3.4 Synthesis of MOF-902 30

2.2.3.5 Photocatalysis investigation based on MOF-901 30

2.2.3.6 Photocatalysis experiment expansion based on MOF-902 32

2.3 MOFs based on Open Iron (III) sites 33

2.3.1 Motivation and designed linkers 33

2.3.2 Crystal structure design and prediction 33

2.3.2.1 Crystal structure design 33

2.3.2.2 Crystal structure prediction and modelling 34

2.3.3 Experimental 35

2.3.3.1 Materials 35

2.3.3.2 Linker synthesis 36

2.3.3.2.1 4,4',4''-benzene-1,3,5-triyl-tribenzoic acid (H3BTB) synthesis 36

2.3.3.2.1.1 Synthesis of 1,3,5-Tri(4',4',4''-acetylphenyl)benzene 36

2.3.3.2.1.2 Synthesis of H3BTB 37

2.3.3.2.1.3 Azobenzene-4,4’-dicarboxylic acid (H2-AzoBDC) synthesis 37

2.3.3.3 Fe-MOFs synthesis 38

2.3.3.3.1 Fe-MOF based on H2-AzoBDC linker: MOF-903 38

2.3.3.3.2 MOF-903 characterization 39

2.3.3.3.2.1 Crystal structure of MOF-903 39

2.3.3.3.2.2 Powder X-ray diffraction analysis of MOF-903 41

2.3.3.3.2.3 FT-IR analysis of activated MOF-903 42

2.3.3.3.2.4 Thermogravimetric Analysis (TGA) of MOF-903 43

2.3.3.3.3 Fe-MOF based H3BTB linker: MOF-904 44

2.3.3.3.4 MOF-904 characterization 44

2.3.3.3.4.1 Crystal structure of MOF-904 44

2.3.3.3.4.2 Powder X-ray diffraction analysis of MOF-904 47

2.3.3.3.4.3 FT-IR analysis of activated MOF-904 48

2.3.3.3.4.4 Thermogravimetric Analysis (TGA) of MOF-904 49

2.3.3.3.4.5 Nitrogen adsorption at low pressure of MOF-904 50

2.4 Unprecedented Cu(II) cluster-based MOF: VNU-18 50

2.4.1 VNU-18 synthesis 50

2.4.2 VNU-18 characterization 51

2.4.2.1 Crystal structure of VNU-18 51

2.4.2.2 Topological analysis 54

2.4.2.3 Powder X-ray diffraction data collection 55

2.4.2.4 Thermal Gravimetric Analysis of VNU-18 55

2.4.2.5 Gas Adsorption 56

Chapter 3: PHOTOCATALYTIC APPLICATION 58

3.1 Introduction to photocatalysis 58

3.1.1 Photocatalysis based MOFs 58

3.1.2 Tuning light harvesting properties 59

3.1.3 Active site engineering 62

3.2 Titanium Organic Frameworks 64

3.3 Photocatalytic application of MOF-901, and MOF-902 65

3.3.1 Structural analysis of MOF-901 65

3.3.2 Photocatalysis performance of MOF-901 75

3.3.3 Structural analysis of MOF-902 87

3.3.4 Photocatalysis properties and application of MOF-902 96

3.4 Summary 106

Chapter 4: CONCLUSION AND SCIENTIFIC CONTRIBUTION 108

APPENDIX 111

PUBLICATIONS 126

REFERENCES 127

LIST OF FIGURES AND SCHEMES Figure 1 Crystal structure deconstruction for MOF-5 exhibiting clearly 3D extended

framework and topological elucidation 3

Figure 2 Illustration of isoreticular chemistry of MOF-5 (IRMOF-1) in which the

various length or functionality of ditopic linkers were used to construct MOFs with underlying topology unchanged 4

Figure 3 Schematic presentation for synthesis and formation of SURMOF-2

Reproducing based on the reference [25] 5

Figure 4 The formation scheme for UiO-66, -67, -68 system 6 Figure 5 Statistic for surface area of MOFs comparing to conventional porous

material Reproducing based on the reference [11] 7

Figure 6 Schematic demonstration for MOF-177, -180, -200 based tritopic linkers and

Zn4O(CO2)6 octahedral building units Reproducing based on the reference [11] 8

Figure 7 A generic scheme for the postsynthetic modification (PSM) of MOFs (top)

A specific example of PSM on IRMOF-3 with benzoic anhydride (bottom) Reproducing based on the reference [64] 12

Scheme 1 Synthetic scheme depicting the generalized formation of a iscrete

hexameric Titanium Cluster, which can be appropriately functionalized with amine groups to affect imine Condensation reactions Atom colors: Ti, blue; C, black; O, red;

R groups, pink; H atoms and capping isopropoxide units are omitted for clarity 25

Figure 8 MOF-901 was synthesized by exploiting the robust conditions used to form

the discrete hexameric Ti(IV) oxo cluster In forming MOF-901, 4-aminobenzoic acid was judiciously chosen to generate in situ amine-functionalized hexameric clusters, which were, in turn, stitched together through imine-condensation reactions involving benzene-1,4-dialdehyde (a) The crystal structure of MOF-901 is projected along the c-axis (b) and a-axis (c) The discrete hexameric cluster, now incorporated into an extended, crystalline structure, is presented in the inset of (b) Atom colors: Ti, blue;

C, black; O, red; N, green; H, pink; and second layer, orange Capping methoxide moieties are removed for clarity 26

Figure 9 1H-NMR spectrum of polyMMA produced by MOF-901 catalyst 31

Figure 10 13C-NMR spectrum of polyMMA produced by MOF-901 catalyst 32

Scheme 2 Synthesis strategy of 4,4',4''-benzene-1,3,5-triyl-tribenzoic acid (H3BTB) 36

Scheme 3 Synthesis strategy of Azobenzene-4,4’-dicarboxylic acid (H2-AzoBDC) 38

Scheme 4 Synthetic scheme for MOF-903 formation 39 Figure 11 Crystal structure of MOF-903 depicting the interpenetrated acs topology,

in which the light blue is highlighted for the second framework Color code: orange polyhedral, Fe; red, O; black, C; green, N; Hydrogen atoms are omitted for clarify 39

Figure 12 As-symmetric unit of MOF-903 dwaw by ORTEP diagram with 50%

probability 40

Figure 13 The calculated PXRD pattern of MOF-903 from single crystal data (red)

compared with the experimental pattern from the as-synthesized sample (blue) 42

Figure 14 FT-IR spectroscopy of activated MOF-903 43 Figure 15 Thermogravimetric analysis curve of activated MOF-903 under air flow 43 Scheme 5 Synthetic scheme for MOF-904 formation 44 Figure 16 Crystal structure of MOF-904 displaying the interpenetrated sit topology,

in which the light blue is highlighted for the second framework Color code: orange polyhedral, Fe; red, O; black, C; green, N; Hydrogen atoms are omitted for clarify 45

Figure 17 As-symmetric unit of MOF-904 dwaw by ORTEP diagram with 50%

probability Hydrogen atoms’ label is omitted for clarify 46

Figure 18 The calculated PXRD pattern of MOF-904 from single crystal data (red)

compared with the experimental pattern from the as-synthesized sample (blue) 48

Figure 19 FT-IR spectroscopy of activated MOF-904 49 Figure 20 Thermogravimetric analysis curve of activated MOF-904 under air flow 49 Figure 21 Nitrogen isotherm at low pressure measured at 77 K to show the permanent

Figure 23 As-symmetric unit of VNU-18 dwaw by ORTEP diagram with 50%

probability Hydrogen atoms’ label is omitted for clarify 53

Figure 24 Topological presentation for VNU-18 Type of Cu-building block (a),

which is represented by square connection in (b) The combination of two square

connections yields the 4, 4, 4, T10 topology (c) 54

Figure 25 PXRD patterns of VNU-18 demonstrated the good agreement between

simulated, as-synthesized and activated samples 55

Figgure 26 Thermal gravimetric analysis trace of activated (guest-free) VNU-18 56 Figure 27 N2 isotherm of VNU-18 at 77 K Filled and open symbols represent adsorption and desorption, respectively The connected lines are inserted as guides for the eyes 56

Figure 28 Normalized diffuse reflectance spectra of: MIL-125(Ti) (grey), NH2125(Ti) (orange) and MR-MIL-125(Ti) (red) Reproducing based on the reference [110] 60

-MIL-Figure 29 FT-IR spectrum of activated MOF-901 showing the presence of imine

formation and cluster information 67

Figure 30 Post-digestion 1H NMR spectrum of MOF-901 displaying the presence of starting reagents hydrolyzed in HF medium 69

Figure 31 PXRD analysis of activated MOF-901 displaying the experimental pattern

(black), refined Pawley fitting (red), and calculated pattern from the staggered structural model (blue) The difference plot (green) and Bragg positions (pink) are also provided 71

Figure 32 Thermogravimetric analysis of activated MOF-901 underairflow 73

Figure 33 SEM image of MOF-901 Noted is the small particle size Scale bar: 200

nm 74

Figure 34 N2 isotherm of activated MOF-901 at 77 K The filled and open circles represent the adsorption and desorption branches, respectively Inset: Plot of the linear region on the N2 isotherm using the BET equation The connecting line is provided in the N2 isotherm as a guide for the eyes 75

Figure 35 Ultraviolet-visible light disffuse reflectance spectrum of activated

MOF-901 Inset: Optical image highlighting the material’s color 76

Figure 36 Tauc plot displaying the band gap of MOF-901 77 Figure 37 Photoluminescence spectrum of activated MOF-901 using 365 nm laser

irradiation 77

Figure 38 Mott-Schottky plot of MOF-901 at 500 Hz 79 Figure 39 Gel permeation chromatography (GPC) profiles of polyMMA product

produced by MOF-901 with reaction time of 16 h 82

Figure 40 Gel permeation chromatography (GPC) profiles of polyMMA product

produced by MOF-901 with reaction time of 20 h 82

Figure 41 Gel permeation chromatography (GPC) profiles of polyMMA product

produced by MOF-901 with reaction time of 24 h 83

Figure 42 Gel permeation chromatography (GPC) profiles of polyMMA product

produced by MOF-901 with optimized amount, 6.0 L of co-initiator (red), 4.5 L of co-initiator (blue), and 3.0 L of co-initiator (green) This is compared with the GPC profile of polyMMA obtained when P-25 TiO2 was used as a catalyst (black) 84

Figure 43 GPC profiles of polyMMA product demonstrated the recyclability of

MOF-901 over three consecutive cycles, in which the first (red), the second (blue), and the third photoreactions (green) are shown 85

Figure 44 PXRD analysis of MOF-901 showed that the crystalline nature was

retained after applying MOF-901 to three consecutive recycles of photoreaction 87

Figure 45 FT-IR spectrum of activated MOF-902 showing the presence of imine

formation and cluster information 88

Figure 46 Digested 1H-NMR spectrum of activated MOF-901 showing the presence

of starting reagents and clear the methoxide moieties of hexameric Ti–oxo cluster 89

Figure 47 PXRD analysis of activated MOF-902 displaying the experimental pattern

(black), refined Pawley fitting (red), and calculated pattern from the staggered structural model (blue) The difference plot (green) and Bragg positions (pink) are also provided 90

Figure 48 The synthetic scheme to expand the structure of MOF-901 for obtaining

902 (a) and the crystal structure of 902 compared to 901 (b)

MOF-902 displayed the larger pore size by enlarging linking unit Color code: black, C; red, O; blue, Ti; green, N; pink, H The second layers of staggered model MOF-901 and MOF-902 are also highlighted for more clarify 92

Figure 49 TGA curve of activated MOF-902 performs the good agreement of residue

to the model of crystal structure 93

Figure 50 The N2 adsorption isotherm at low pressure, and 77 K of activated

MOF-902 exhibited the permanent porosity of 400 m2 g-1 based BET method 94

Figure 51 Ultraviolet-visible light diffuse reflectance spectrum of activated

MOF-902 Inset: microscope image of activated MOF-MOF-902 94

Figure 52 Optical band gap energy of MOF-902 (a) in comparison with MOF-901

(b) The crystal structures for MOF-901, -902 were presented inset to clarify the linking units which could contribute to lower the band gap energy of MOF-902 as well

as its photocatalysis property 95

Figure 53 PXRD analysis of MOF-902 showed that the crystalline nature was

retained after applying MOF-902 to five consecutive recycles of polyMMA photoreaction 101

Figure 54 GPC profiles of polyMMA product produced in DMF and demonstrated

the recyclability of MOF-902 over five consecutive cycles, in which the first (red), the second (blue), the third (green), the fourth (black), and the five photoreactions (pink) are shown 102

Figure 55 PXRD analysis of MOF-902 showed that the crystalline nature was

retained after applying MOF-902 to five consecutive recycles of polyBMA photoreaction in 1,4-dioxane 103

Figure 56 GPC profiles of polyBMA product produced in 1,4-dioxane and

demonstrated the recyclability of MOF-902 over five consecutive cycles, in which the first (red), the second (blue), the third (green), the fourth (black), and the five photoreactions (pink) are shown 104

Figure 57 PXRD analysis of MOF-902 showed that the crystalline nature was

retained after applying MOF-902 to five consecutive recycles of polySt photoreaction

in THF 105

Figure 58 GPC profiles of polySt product produced in THF and demonstrated the

recyclability of MOF-902 over five consecutive cycles, in which the first (red), the second (blue), the third (green), the fourth (black), and the five photoreactions (pink) are shown 106

LIST OF TABLES Table 1 Designed crystal structure of MOF-903, MOF-904 based Iron (III) triangular

cluster and di- or tri-topic organic linker unit 35

Table 2 Crystal structure data and refinement for MOF-903 40

Table 3 Crystal structure data and refinement for MOF-904 46

Table 4 Crystal structure data and refinement for VNU-18 53

Table 5 FT-IR spectrum signals and assignment for MOF-901 67

Table 6 Important crystallographic information for MOF-901 72

Table 7 Summary of surface area calculation for MOF-901 75

Table 8 Summary of Mn and PDI value of polyMMA produced with various of reaction time 80

Table 9 Photocatalyzed polymerization of methyl methacrylate (MMA) under visible light irradiation 81

Table 10 Comparison of photoreaction results catalyzed by MOF-901 with different amount of co-initiator and UiO-66-NH2 and P-25 TiO2 86

Table 11 Important crystallographic information for MOF-902 91

Table 12 Summary for photoabsorption properties of MOF-902 and other related MOFs 95

Table 13 Polymerization reaction of methylmethacrylate under visible light in the presence of diverse photocatalysts 97

Table 14 Studies of MOF-902 catalysis property with various monomers in comparison to MOF-901 99

Table 15 Recycling study of MOF-902 for polymerization reactions 100

ABBREVIATIONS AND NOMENCLATURES

EA: Elemental analysis

FT-IR: Fourier transform infrared spectroscopy

GPC: Gel permeation chromatography

H-AB = 4-aminobenzoic acid

MIL: Materials Institute Lavosier

MMA: Methyl methacrylate

MOFs: Metal Organic Frameworks

NMR: Nuclear magnetic resonance

NU: Northwestern University

OiPr = Isopropoxide

OMS: Open Metal Site

PCNs: Porous Coordination Networks

PCPs: Porous Coordination Polymers

PDI: Polydispersity Index

polyMMA: poly(methyl methacrylate)

PSM: Postsynthetic modification

PXRD: Powder X-ray diffraction

Pyen2–: methylpyridin-4-ol)

5,5′-((1E,1′E)-(ethane-1,2-diyl-bis(azanylylidene))bis(methanylylidene))bis(3-RCRS: Reticular Chemistry Structure Resource

SBUs: Secondary building units

SEM: Scanning electron microscope

SXRD: Single crystal X-ray diffraction

TGA: Thermal gravimetric analysis

THBTS3–: 2,4,6-trihydroxy-1,3,5-benzenetrisulfonate

Topology: The definition of “topology” can be understood by the convenient way to describe the molecular structure in three dimensional space Topology studies out of the geometry and set theory by introduction of the concepts as space, dimension, and transformation

Chapter 1: INTRODUCTION

1.1 Metal Organic Frameworks (MOFs)

Metal Organic Frameworks (MOFs) are constructed by the rigid coordination bonds between the organic linkers and inorganic metal ions or clusters as the nodes which is widely designated by Secondary Building Units (SBUs) later.1-3 The organic linkers are also termed as SBUs in term of geometrical views as well It is noted that MOFs have been termed as many names from the first time of invention (Porous Coordination Polymers (PCPs), Porous Coordination Networks (PCN), hybrid inorganic-organic materials, Metal Organic Materials (MOMs), etc.) Those names presented to the same general type of porous material which links two components of transition metals and organic linking units to form the extended structure In fact, an early report in 1979 was published the cyanide-bridged mixed-metal open framework,

in which the authors mentioned the similarities between their network and Zeolites.4The outbreak of research in crystalline material based on metal ions and organic bridging ligands was continue in the late 1990’s.5-9 The name of “Metal Organic Frameworks” has been become famous and popular by Omar M Yaghi in 1995.10More than 20,000 structures of MOFs have been reported and studied so far showing the tremendous development process of crystalline and porous materials.11 MOFs have been considered as the new class of microporous materials possessing the promising properties of high porosity, well-defined crystallinity, thermal stability, catalytic activity and so on.11-13 The key point of the structural features of MOFs in many cases

as gas storage, separation, catalyst, drug delivery is determined by ultrahigh porosity and high internal surface area of MOFs However, some certain applications: Proton conduction, magnetic behavior, catalyst, are related strictly to the active sites (metal cluster, linker active sites, exchanged counter ions) or post synthesis modification (PSM) to the structure of the host materials instead of high surface area of MOFs.14-16

In general, MOFs can be designed not only by employing the different metal coordination or diverse linker units but also by embedding a specific environment to the void space inside the structure The challenging in porous materials (Zeolites,

activated carbon, etc.) is controlling the size, shape, functionality of the void space can

be achieved in MOFs Porous materials are classified into three kinds according to their pore size which was recommended by International Union of Pure and Applied Chemistry (IUPAC) The materials could be microporous materials if their pore diameter is less than 2 nm as found in Zeolites, MOFs Mesoporous silica is one example of mesoporous material when they contain the pore diameter in the range of 2

nm to 50 nm The last one for macroporous is used to call the materials possessing the pore diameter greater than 50 nm like ceramics, amorphous silica and aerogels All MOFs had been published so far belong to both of micro- and mesoporous material

1.2 MOFs composites

As mentioned in brief introduction about MOFs in previous section, MOFs are made from organic linkers and most of metals in periodic table from rare earth

elements to d, f-block transition metals creating the various chemistry in crystalline

porous material The component of metal in MOFs is considered as the nodes which can be isolated single point or metal cluster and directly linked together by rigid or flexible organic linker units The organic units (linker or bridging block) which are used to construct MOFs, can be carboxylate commonly or other anions as phosphate, sulfonate, heterocyclic compound rarely As the key function, the targeted applications need to be considered firstly by choosing the structure of the linker units Because during the MOFs conformation, the organic linkers could effect to the deprotonation process as well as the linking interaction with metal ions which cause the geometrical structure of MOFs In addition, the effect of the structure of the coordination environment in MOFs includes the geometry of metal atom used in the synthesis The simple way to express the most influencing to the topological networks of MOFs is paying attention to the geometry of SBUs The building blocks of metal cluster are initially formed by the linkages between multi-topic linker such as, 1,4-benzenedicarboxylate (BDC), 1,3,5-benzentricarboxylate (BTC), biphenyl-3,3’,5,5’-tetracarboxylate (BPTA) or 1′,2′,3′,4′,5′,6′-hexakis(4-carboxyphenyl)-benzene (CPB) and the metal-oxo pieces which are composed in early of reaction process In 1999, Omar M Yaghi and co-workers published two archetypical MOFs, MOF-5

where BTC = 1,3,5-benzenetricarboxylate) which has been reckoned as the benchmark

in MOFs chemistry by the first showing the ultrahigh porosity of porous mateials.17 In crystal structure of MOF-5, Zn4O plays as model SBU presented by many compounds

in MOFs chemistry later (Figure 1)

Figure 1 Crystal structure deconstruction for MOF-5 exhibiting clearly 3D extended

framework and topological elucidation

In detail, Zn4O SBU is simplified by a node with 6-connected created by six carboxylate groups Every single Zn atom has 4 coordinations including three coordinations from three carboxylate groups and one from centered oxo atom Four Zn atoms in Zn4O SBU are located to generate the tetrahedral building block while every single Zn atom also displays tetrahedral shape As proven in many documentations, this type of cluster can be reproduced by changing another metal atom for example nickel, cobalt.18-20 While in MOF-199, the Cu atoms were displayed as paddle wheel with two opposite atoms which linked to organic blocks by four carboxylate group A single Cu atom coordinates with a single oxygen (also called oxo) or guest solvent to show square pyramidal shape The oxygen atom which links to Cu, will be removed under low pressure after solvent exchanging to open two Cu sites named Cu open metal site (OMS) A lot of published materials utilized OMS of Cu, Zn, Co or Mg21-23atoms to study the behavior in gas storage and other related applications

The tailorability is one of the interesting points in MOFs chemistry letting us to adjust the structure of the material based on the linker functionality and metal cluster modification as well The porous material can be easily enlarged by expending the length of the linker The size and shape of the pore can also be modified by functional groups embedding on the components of MOFs (metal clusters or linker units) MOFs are pictured as the house containing a lot of rooms inside which totally are empty or dense depend on how to decorate the wall of the rooms The definition of

“isoreticular” was proposed by Yaghi and co-workers in 2002 when he published the series of MOF-5 analogue for methane uptake (Figure 2).24 In that work, the isoreticular structures of MOF-5 with the difference of pore size from 3.8 to 28.8 Å had been successfully synthesized and proven by XRD

Figure 2 Illustration of isoreticular chemistry of MOF-5 (IRMOF-1) in which the various

length or functionality of ditopic linkers were used to construct MOFs with underlying topology unchanged

Another work utilized the isoreticular of SURMOF-225, which was reported by Christof Wöll research group in 2012 (Figure 3) In that publication, a novel class of MOFs had been synthesized from Cu-acetate and dicarboxylic acids using liquid phase

epitaxy The structures exhibited the P4 symmetry with the longest channel size 3 × 3

nm2 It is interesting to mention that the theory calculation showed the mechanism for the low-temperature epitaxial process The electronic structure calculation also found the stability of packing Cu carboxylate paddle wheels

Figure 3 Schematic presentation for synthesis and formation of SURMOF-2 Reproducing

based on the reference [25]

Another exemplary MOFs, MIL-10126 was reported in 2005 by G Férey group demonstrated the high chemical stability and high surface area (4100 m2 g-1 calculated

by Brunauer–Emmer–Teller (BET) theory) MIL-101 structure are built by the linking between Cr(III) triangular cluster and 1,3,5-benzenetricarboxylic acid (BTC) as 3-connected units MIL-101 is one of mesoporous material showing extremely large unit

cell parameters (Face Centered Cubic, a = 89 Å) with two kinds of pore size in

calculated of 29 and 34 Å In 2008, another representative MOFs named UiO-66, -67, -6827 with extremely water stability (Figure 4), had been reported by Karl P Lillerud research group The UiO type structure was then applied in a large field of gas adsorption, separation, heterocatalyst, photocatalyst by employing the high porous, chemical and thermal stability in harsh condition.28 The SBU in UiO series is

Zr6O4(OH)4 with 12-connected of carboxylate units The inner core of Zr6- cluster is organized to form octahedral block in which every single Zr atom contains 8 coordinations generating forming a square-antiprismatic coordination consisting of eight oxygen atoms Besides several types of Zr cluster, 6-, 8-, 10-connected also become popular in MOFs based Zr-Oxo cluster

Figure 4 The formation scheme for UiO-66, -67, -68 system

1.3 Interesting features from MOFs material

MOFs are commonly synthesized by connecting the organic linkers and the metal salts under solvothermal condition by heating at relatively low temperature (lower than

300 C) The crystal structure of final product, MOFs, can be obtained depend on the characteristics of the linkers such as the geometry, bulkiness, functional groups, rigid

or flexible linkages The role of the MOFs formation is also indicated by the kinds of metal clusters which are used to react with the organic linkers The mixture of reagents

is dissolved in the single solvent or the co-solvent system to adjust the polarity The important parameters for the synthesis by using solvothermal method are temperature, reagent concentration, the solubility and pH environment under presence of additives

or modulators.29 The reticular chemistry is presented by combination of simplification

of linker units and metal cluster representative (point extension) to describe the structural characters of MOFs

1.3.1 Ultrahigh porosity

The high porous material in MOFs chemistry was the first reported in 1999 by Yaghi and co-workers, in which the structure was elucidated by single crystal X-ray diffraction, gas sorption at low temperature and low pressure supported the permanent porosity.17 The forming of the Zn4O(CO2)6 octahedral building units which made the

chelation to carboxylate linker leads to fcu cube topology The void fraction

calculation was found to be 61% with BET surface area >2300 m2 g-1 The first time one porous material was totally elucidated the crystal structure and other characterizations showing the high porosity compared to traditional porous materials such as activated carbon or zeolites (Figure 5)

Figure 5 Statistic for surface area of MOFs comparing to conventional porous material

Reproducing based on the reference [11]

To increase the surface area of the MOF, the longer linkers can be used to extend the framework without changing the topological structure Although, the longer linkers provide larger space within the material, it is easy to be prone to form interpenetrated framework with two- or multi-fold of intertwined frameworks The way to prevent interpenetration is making the MOFs in the presence of template reagents as well as controlling the geometry of the linkers by bulky functional groups.1,24 However, the

interpenetrated structures are fruitful to enhance the gas storage or separation30 due to the smaller pore size and high stacking interaction of the backbone within the MOFs as well In 2004, the highest surface area of MOFs material at that time was reported termed MOF-177.31 Constructing from similar Zn4O(CO2)6 cluster of MOF-5 and

1,3,5-benzenetribenzoate (BTB) linker, MOF-177 belongs to qom topology (Figure 6)

with the optimized pore diameter of microporous size (<2 nm) leading to 83% void space and BET surface area in calculated of 3780 m2 g-1 In 2010, the combination of

Zn4O(CO2)6 cluster and analogue of BTB linker building two ultrahigh porosity MOFs,32 MOF-200 and MOF-210 [Zn4O(BBC)2 and (Zn4O)3(BTE)4(BPDC)3, respectively; BBC = 4,4′,4′′-(benzene-1,3,5-triyl-tris(benzene-4,1-diyl))tribenzoate; BTE = 4,4′,4′′-(benzene-1,3,5-triyl-tris(ethyne-2,1-diyl)) tribenzoate; BPDC = biphenyl-4,4′-dicarboxylate] were doubled the value of BET surface area to 4530 m2 g-

1 and 6240 m2 g-1, respectively

Figure 6 Schematic demonstration for MOF-177, -180, -200 based tritopic linkers and

Zn4O(CO2)6 octahedral building units Reproducing based on the reference [11]

The multi-topic of the rigid organic linker could lead to the diversibility of topological structure in MOFs due to the variable coordination system from the carboxylate linker to metal cluster The hexa- and octa-topic linkers were used to connect with paddle wheel cluster formulated by Cu2(CO2)4 to increase the number of adsorption site.33 The introduction of hexatopic linker into MOFs to make a series of

unprecedented structure of ntt topology Cu-MOF was reported in 2012 by O Farha

NU-110 [Cu3(BHEHPI); BHEHPI = diyl))tris(ethyne-2,1-diyl))-tris(benzene-4,1-diyl))tris(ethyne-2,1-diyl))triisophthalate], whose organic linker is fully functionalized with the alkyne units rather than benzene rings, displayed a surface area of 7140 m2 g-1 This material is observed the highest BET surface area until now

5,5′,5′′-((((benzene-1,3,5-triyltris(benzene-4,1-1.3.2 Reticular synthesis

Two frameworks are based on the same underlying topology classified to be isoreticular One of the technique for enlarging the pore size and porosity space of MOFs is based on the reticular synthesis as regards the flexibility and functionality requirement Introducing the functionalities without topological structure change can adjust the polarity, size and shape of pores, stability enhancement to study further for the applications in gas storage and separation.34,35 A family of MOFs based

Zn4O(CO2)6 cluster was first presented by Yaghi’s group in 2002 to clarify the ability

of reticular network in crystal structure modification That developed the systematic variation of pore volume and polarity, in which generates an isoreticular series for evaluation of IRMOF-1 to IRMOF-161,24 (MOF-5, IR = isoreticular)

The isoreticular expansion is widely opened not only for pcu net but also for other networks as demonstrated by qom topology of MOF-177 A family of qom

network is interestingly expanded by the introduction of the longer linkers as BTB and BTE (BTE = 4,4′,4′′-(benzene-1,3,5-triyl-tris(ethyne-2,1-diyl)) tribenzoate) generating the high porous material, which was discussed above without observing the interpenetrated framework (MOF-180, MOF-200)

The binuclear Cu paddle wheel cluster for MOF-19936 exemplary was combined with various lengths of expanded triangular linker for BTC (TATB = [4,4′,4′′-(1,3,5-

triazine-2,4,6-triyl)tribenzoate], TATAB = triyl)tris(azanediyl))tribenzoate], TTCA = [triphenylene-2,6,10-tricarboxylate], HTB = [4,4′,4′′-(1,3,3a1,4,6,7,9-heptaazaphenalene-2,5,8-triyl)tribenzoate], and BBC) to

[4,4′,4′′-((1,3,5-triazine-2,4,6-construct several isoreticular structures (tbo net).37-40

After the report of HKUST-1 (MOF-199) and the system of its isoreticular structures, many kinds of MOF, in which the variety of the organic linker (di-, tri-, poly-topic) and similar geometry of metal building block were utilized for isoreticular structure purpose.41-47

1.3.3 High stability

It is noted that the thermal and chemical stability of MOF is the key factor for designed synthesis and opening the tremendous applications The chemical stability is recently considered to enhance the usefulness of MOFs It is the fact that finding the chemically stable MOF is challenge due to the associated and dissociated bonding when treating MOFs with the solvent The research discovered that MOFs based tetravalence metal cluster of titanium (IV), zirconium (IV), and hafnium (IV) can enhance the stability28,48-51 in harsh medium of acidic, basic or boiling water

The extraordinary development of MOFs chemistry leads to the discovery of a new its subclass in 2006 by Yaghi’s group, Zeolitic Imidazolate Frameworks52-55(ZIFs) whose structural concepts as metal building blocks (or SBUs), linker units, postsynthetic (mention in next) are similar to MOFs material ZIFs is the exemplar of high stable MOFs containing two main components of tetrahedral building block of divalent metal (normally Zn, Cu, and Co) and imidazole or imidazole derivatives as organic linkers For building the 3D porous material, the imidazole linker mimics the geometry coordination of Al or Si ions in Zeolite, in which the angle between the fist nitrogen of imidazole to metal and second nitrogen of another imidazole is around

145 That kind of linkers limit the structural variety and topology of ZIFs Research focuses on how to modify the linker in ZIFs synthetic strategy or change the methodology in the synthesis to overcome the topology limitation55 recently received much consideration due to the interesting features from ZIFs in gas separation under flue gas stream.55-57

The second example represented for ultra-stable MOFs was published in 2008 by

P Lillerud and co-workers termed UiO-66, UiO-67, UiO-68 which were composed by

a series of ditopic linkers: 1,4-benzenedicarboxylic acid (BDC), biphenyldicarboxylic acid (BPDC), [1,1’:4’,1’’-tertphenyl]-4,4’-dicarboxylic acid (TPDC), respectively, and 12-connected of cubooctahedral zirconium oxo cluster.27The crystal structure of the UiO series is proposed firstly by powder X-ray diffraction until 2011, when the single crystal X-ray diffraction of UiO-68-NH2 had been fully proven by P Behrens’s research group.58 Recently most of the structures belong to UiO-66 type are reported with the full characterization of single crystal X-ray diffraction.59-61

4,4’-The stability of MOFs can be meliorated by introduction of the hydrophobic functional groups such as CH3, CF3, benzene or alkyle within the structure The hydrophobicity of these functional groups may affect to resist the hydrolysis of reversible linkages in the structure of MOFs during the water treatment.55,62 These groups also control the size and shape of the pore to enhance the gas molecules affinity, which is documented as one of the method for improving the gas storage or separation35,57 applications

1.3.4 Postsynthetic modification (PSM)

There has been interesting in tuning the structure via functionalized modification

in order to alter the physical and chemical properties of MOFs The desired MOFs material was executed by incorporating the functionality into the organic linkers before MOFs synthesis attempt, which had been documented historically This method

is termed “prefunctionalization” resulting the pedant groups lining in the pore of MOFs structure such as –Br, –F, –NH2, –CH3, –NO2 A variety of MOF materials including the IRMOFs (Isoreticular Metal–Organic Framework),1,24 ZIFs (Zeolitic Imidazolate Frameworks),52-55 and MIL-53(Fe) (Materials Institute Lavoisier)63 series

of materials have been successfully synthesized by grafting these types of groups on the linkers Although the introduction of the functional groups on the linker backbone

in MOFs have been successful, the scope of functional groups within the pores of the

MOFs has remained relatively limitation due to the incompatible or unstable of all the functionalities when directly using the solvothermal reaction for MOFs synthesis Another route for obtaining functionalized MOFs is exploiting the post synthetic modification technique, in which the chemical modification of a framework has been grafted on the backbone of the pristine material That method was defined formally by Wang and Cohen (Figure 7).64 Comparing to the synthesis of the functionalized MOFs directly from functionalized linkers, MOFs can be synthesized and modified in a heterogeneous manner after the formation of the solid lattice which has been proven

by generally characterized methods The type and the number of functional groups can

be incorporated into the MOFs structure that controlling via PSM is more advantage than the prefunctionalization approach PSM is the excellent technique to modify the structure by metal cluster modification as well as the liker units without changing the topological features

Figure 7 A generic scheme for the postsynthetic modification (PSM) of MOFs (top) A

specific example of PSM on IRMOF-3 with benzoic anhydride (bottom) Reproducing based

on the reference [64]

The first demonstration of PSM on the organic link of a MOF was reported in

2000 for a homochiral MOF, POST-165 [Zn3( 3-O)(D-PTT)6; D-PTT– = dimethyl-5-(pyridin-4-ylcarbamoyl)-1,3-dioxolane-4-carboxylate] It involved N-alkylation of dangling pyridyl functionalities with iodomethane and 1-iodohexane to produce N-alkylated pyridinium ions, which exposed to the pore cavity In 2007, PSM

(4S,5S)-2,2-was fully studied by modifying the amino group of IRMOF-3 with acetic anhydride in order to generate the MOF containing amide substituents.66 That technique enlarges the library of organic reaction based on the backbones of MOFs material in order to alter the specific features of MOFs

The similar procedure of acetylated reaction to produce dangling amide linkages within the pores had utilized for UMCM-1-NH2 [(Zn4O)3(BDC-NH2)3(BTB)4] Despite the reduction of surface area of functionalized MOFs comparing to the pristine MOFs, both of IRMOF-3 and UMCM-1-NH2 show higher hydrogen uptake capacity relative

to the host MOFs material PSM has also been used to introduce the catalytically active sites which can be capped on the metal cluster building blocks as well as via the covalent bonding to organic linkers An example of this procedure was reported in

2005 by Lin and co-workers using the metal binding group (i.e –OH) to metalate the active catalytic sites within the pores A MOF from Cd2+ and (R)-6,6’-dichloro-2,2’-dihydroxy-1,1’-binaphthyl-4,4’-bipyridine was produced with the free and uncoordinated hydroxyl groups that could be metallated with Ti(OiPr)4 yielding a high active, enantioselective asymmetric Lewis acid catalyst.67 UMCM-1-NH2 was also incorporated salicylate chelating groups to metallate with Fe(III) subsequently, which had been used as a catalyst for Mukaiyama aldol reactions.68 The research demonstrated that PSM can be considered as potential improvement in the application

of gas storage and catalysis Additionally, the studies reckoned that PSM may lead to monitor the organic reactions, develop the materials for biomedicine, or manipulate the physical properties of MOFs material.69

1.3.5 Catalytic transformation

As porous material which had been demonstrated to be useful in catalysis, MOFs offer many advantages to their use in catalytic application due to the high internal surface area, tunable pore metrics, as well as high density of the active sites within the structure MOFs may support for homogeneous catalyst by stabilizing the short-live catalysts, size-and shape-selectivity that depend on the porosity and the presence of catalytic active sites, which are encapsulated within the pores

In 1994, the first example of catalysis using an extended frameworks named Cd(BPy)2(NO3)2 (BPy = 4,4’-bipyridine) was reported, which involved the cyanosilylation of aldehydes in a Cd-based framework.70 This research demonstrated the advantages of MOFs as size-selective catalysts by excluding large substrates from the pores In 2006, HKUST-1 exposes open metal sites when the guest solvents removal are successful leading to act as Lewis acid catalysts.71 The metal cluster units function as the catalytically active site upon ligand removal were also reported in MIL-101 [Cr3X(H2O)2O(BDC)3; X = F, OH] and Mn-BTT {Mn3[(Mn4Cl)3(BTT)8]2; BTT3– = 5,5′,5″-(benzene-1,3,5-triyl)tris(tetrazol-2-ide)} Moreover, the number of alkane oxidation, alkene oxidation, and oxidative coupling reactions have also been studied by exploiting the role of metal sites within the SBUs for catalytic activity.72Methane oxidation reaction study in vanadium-based MOF-48 {VO[BDC-(Me)2]; Me

= methyl} was reported by Yaghi and co-workers with the potential features of the catalytic turnover and yield for this oxidation outperforming those homogeneous catalysts which are used for that purpose.73

MOFs contain the catalytic active sites for heterogeneous catalysis based metalloporphyrin, which was presented in PIZA-3 [Mn2(TpCPP)2Mn3].74 The epoxidation of olefins were promoted due to the capable hydroxylating alkanes activity ino the pores Another approach supports for porphyrin units encapsulating

within the pores of the zeolite like MOF, rho-ZMOF [In(HImDC)2·X; HImDC2– = imidazoledicarboxylate, X– = counter anion] has also reported by Eddaoudi and co-

workers in 2008 The high loading of porphyrin units into the pores of rho-ZMOF

leads subsequently to metallate the MOFs for exploiting the metalloporphyrin activity

to the oxidation of cyclohexane without any leaching out of the catalytic components due to the small window size of the framework.75 Inspire by this work, several other systems had been utilized the same approach to encapsulate the polyoxometalates into MIL-101(Cr) or HKUST-1 applied the oxidation of alkenes and the hydrolysis of esters in excess water.76

Nanoparticle catalytic systems is modified by integration to the MOFs via PSM

to enhance the catalyst activity, particle stability and to perform the uniform size

incorporating the palladium nanoparticles within the pores of MIL-101(Cr).77 More recently, the encapsulating of iridium complex by the covalent linking with the organic linkers to generate the catalytic active sites to transfer an electron to a proton in solution, leading to hydrogen evolution, which was reported with bifunctional catalytic MOF of {Zr6O4(OH)4[Ir(DPBPyDC)(PPy)2·X]6; DPBPyDC2– = 4,4′-([2,2′-bipyridine]-5,5′-diyl)dibenzoate, PPy = 2-phenylpyridine}.78

1.3.6 Gas adsorption

Studying of gas storage application has been conducted on porous traditional material as activated carbon, zeolites, or carbon nanotubes MOFs material recently is being received much attention for gas uptake specially hydrogen, carbon dioxide and methane, due to the ultra-high porosity, well-known structural topology, framework flexibility, tunable pore distribution, leading to the active sites decoration for enhancing the gas affinity

1.3.6.1 Hydrogen storage

MOF-5 was the first study in hydrogen storage reported in 2003, in which the research highlighted the advantages of MOFs for potential hydrogen uptake application Since then, the number of research focuses on enhancing the hydrogen uptake capacity based MOFs material For hydrogen adsorption purpose, there has been mainly key factors as pore volume, surface area, and affinity dominated sites which can be exactly controlled via organic linker design to generate the targeted MOFs structure, in which hydrogen uptake capacity gravimetrically may enhance at low temperature (77 K) and high pressure NU-100 and MOF-210 are high porous MOFs exhibited hydrogen adsorption as high as 7.9 to 9.0 weight percent (wt%) at 56 bar for both MOFs and 15wt% at 80 bar for MOF-210.32 However, not all the cases of increasing of the internal surface area lead to be effective for volumetric hydrogen adsorption, which had been fully investigated by taking the advantages of the adsorption enthalpy of hydrogen increasing The open metal sites in MOFs produced

by guest solvents evacuation during the low pressure activation may be suggested to use to increase the heat of adsorption79 of hydrogen adsorption data (Qst) The higher interaction between hydrogen molecules and unsaturated open metal sites causes the

high hydrogen uptake capacity This characteristic was representative in two MOFs containing the open metal sites of zinc single sites and nicel rod packing sites,

Zn3(BDC)3[Cu(Pyen)] [Pyen2– = bis(azanylylidene))bis(methanylylidene))bis(3-methylpyridin-4-ol)] and Ni-MOF-74 They have the highest recently reported initial Qst values (15.1 kJ/mol, 12.9 kJ/mol for

5,5′-((1E,1′E)-(ethane-1,2-diyl-Zn3(BDC)3[Cu(Pyen)]80 and Ni-MOF-74,81 respectively)

It is noted that MOFs with cage-like polyhedral building units may be supported

to enhance the storage of small molecules due to the remaining of kinetically trapped

of adsorbed guests inside the cages By linking the isophthalate units and copper paddle wheels to generate the close packing motif and open copper site building blocks, Zhou and co-workers reported the polyhedral cages MOFs named PCN-12,82which exhibited 3.05wt% of hydrogen uptake capacity at 77K/1atm Theoretically, the interaction of hydrogen and the framework could be stronger when loading the metal ions into the pores, leading to enhance the hydrogen uptake capacity Although the metal ions doping into the pores of MOFs is challenging because the increasing of added mass could limit the gravimetrical hydrogen adsorption, Hupp and co-workers reported the interpenetrated MOFs, in which lithium ions was successfully doped yielding 75% increase in gravimetric hydrogen uptake.83

Although the DOE target for hydrogen storage has not been reached by pure MOFs system yet, research of hydrogen uptake using MOFs is still being receiving much attention due to the novel properties and well-defined structures

1.3.6.2 Methane storage

Natural gas with methane is predominative >98% recently is used to alternate the fossil fuel source based hydrogencarbon, coat or oil in vehicular application due to its high-combustion heat energy, low price and high abundance To reach the goal of practical applications in methane storage, in which the feasible driving range and cheap in gas cylinder with uncomplicated pressure tools need to be considered, high porosity property of adsorbent is really effective to this purpose As discussed in previous sections, MOFs can be designedly tailored to obtain targeted features

including ultra-high surface area, tunable pores and dangling effective sites which found to be affected to methane storage

The first demonstration of methane uptake for extended framework was studied for CuSiF6(BPy)2 in 2000, which exhibited the gravimetrically capacity of methane uptake around 104 mg g-1 at 36 bar and 298 K The total gravimetric methane uptake capacity in MOFs generally can be proportionally increased to the increasing of the pore volume The calculated total uptake values for MOF-177, MOF-200, and MOF-

210 are 345 mg/g, 446 mg/g, and 476 mg/g, respectively, at 80 bar and 298 K There have few of benchmark MOFs for methane storage recently including various kinds of metal cluster such as open copper sites paddle wheels, aluminum closed 8-member rings, open nickel rod building blocks, etc

Six of MOFs material, which can be listed as potential candidates in methane storage application, are NU-111,84 NU-125,85 USTA-20,86 PCN-14,87 Ni-MOF-74,88and HKUST-1.36,89 They are composed by combining the high conjugated organic linkers and open metal sites units of cooper paddle wheel except for the nickel rod based Ni-MOF-74 These MOFs were chosen due to the representative high surface area, broad range of pore size distribution and exceptionally showing high uptake capacity in methane adsorption Among them, HKUST-1 showed the highest total uptake capacity of methane storage as well as the working capacity concept (difference methane capacity between 35 bar and 5 bar) although its surface area is lowest to the others That result supports the conclusion of methane uptake enhancement application which need to be considered not only by surface area but also the suitable pore size and gas molecules interaction inside the pores In 2014, Yaghi and co-workers reported MOF-519 and MOF-52090 composed from Aluminum closed 8-member rings and tri-topic BTB linkers, which can be comparable to working capacity of methane uptake by HKUST-1

HKUST-1 which is available commercially in gram scale may display the highest volumetric methane uptake capacity at 65 bar and ambient temperature in long time

before Al-soc-MOF-191 which was reported by Eddaoudi and co-workers in 2016 In that communication, the square planar of tetra-topic linker 3,3″,5,5″-tetrakis(4-

carboxyphenyl)-p-terphenyl (H4TCPT) that can act as a rectangular molecular building block (MBB) linking to triangular aluminum cluster to generate the 3D, ultra-porous MOFs reaching >5500 m2 g-1 of BET surface area Interestingly, Al-soc-MOF-1

clearly outperforms other MOFs in the methane uptake application, in which this MOF becomes the only porous material can be satisfied the DOE methane uptake target for both of the gravimetrical and volumetric measurement

1.3.6.3 Carbon dioxide uptake and separation

MOFs are promissing material for selective carbon dioxide capture under ambient and flue gas stream By taking advantages of the high surface area, tailorable pore distribution and PSM, MOFs are widely suggested to use for carbon dioxide adsorption and separation The first example for carbon dioxide uptake study was reported in 1998 by two dimensional MOF-2 [Zn(BDC)].92 More recently, a series of MOF-177’s isoreticular structures was fully studied the properties of carbon dioxide capture at room temperature and 35 bar, in which MOF-177 shows the highest carbon dioxide uptake capacity found to be 1470 mg g-1 This research demonstrated that the outstanding of low capacity in carbon dioxide uptake by traditional porous material has been solved by MOFs material As expected, the best excess carbon dioxide uptake reported to date was observed in a MOF with ultrahigh porosity, MOF-20032(2437 mg g-1 at 50 bar and 298 K)

However, the carbon dioxide adsorption is commonly operated at low pressure,

in which Henry’s law has used to calculate the constant of the heat of adsorption (Qst) for the purpose of carbon dioxide capture selectivity The open metal sites in MOFs can be indicated to have more effective interaction between carbon dioxide to metal clusters region in framework The values of 62 kJ/mol and 47 kJ/mol for MIL-101(Cr) and Mg-MOF-74 are the high initial Qst among the MOFs which have been functionalized to decorate effective sites They offer to enhance the carbon dioxide uptake capacity and the selectivity at low pressure

As mentioned in previous sections, the water stability of MOFs may lead to broaden the scope of MOFs application in gas separation The ideal material for carbon dioxide capture from flue and combustion gases requires high selectivity in the

presence of water It is useful to target MOFs, in which the competition between carbon dioxide and water for adsorption is minimized In 2014, Yaghi and co-workers reported a series of ZIFs based mixture of benzimidazole derivative linkers mixture to

generate hydrophobic CHA-ZIFs,55 which demonstrated to be excellent candidates for

carbon capture from flue gas stream In 200 seconds of breakthrough time, CHA-ZIFs

captures 100% of carbon dioxide from the mixture of carbon dioxide and 80% relative humidity of nitrogen (mimic condition of flue and combustion gas) while nitrogen passed through unencumbered

1.3.6.4 Proton Conductivity

The new research has been applied MOFs as inexpensive proton-conducting membranes for fuel cell application The first study of proton conductivity based extended frameworks was performed with Cu(DTOA)(HOC2H4)2 although the reported value of conductivity is quite low.93 It is now clearly that the conductivity of MOFs in water-mediated proton conduction can be improved by the contribution of the acid moieties adding such as carboxylic, phosphonic, or sulfonic acid which were represented in functionalized version of MIL-53 [Fe(OH)(BDC-X); X=H, NH2, OH, (COOH)2] The high proton conductivity of MOFs with high acidic pores [PCMOF-5, La(H5DTP)(H2O)3; DTP8– = 1,2,4,5-tetrakisphosphonomethylbenzene] was found to

be 2.5 × 10−3 S/cm at 98% relative humidity and 60°C further supported for the role of acidic functionality in the framework The high proton conductivity in one-dimensional (1D) Metal–Organic structures lacking any acidic functionality, as in Fe(oxalate)(H2O)2 is observed, in which 1D arrangement of water molecules coordinated to the framework facilitate the proton transfer.94 The sulfate or dimethyl ammonium ions are indicated by the similar role for promoting the proton transport inside the framework which may enhance the conducted activity of MOFs The finding in research of Furukawa and co-workers in 2016 demonstrated the role of those ions in the utra-high proton conductivity of VNU-15 [Fe4(BDC)2(NDC)(SO4)4(DMA)4; Fe(II)/Fe(III); DMA = 1,4-dimethylammonium] at 60% relative humidity and high temperature (90°C), which is higher than traditional Nafion material.95 The similar research of Yaghi and co-workers based high conjugation catecholate linker linking to single point of Fe, or Ti, or V metal cluster in

order to form 3D porous Me-CAT (metal catecholate) supported to the significantly proton transfer ability of DMA ions.96

The practical application of proton conducting requires high temperature of operating condition from 120° to 180°C in anhydrous medium The impregnation of MOFs with amphoteric molecules like imidazole is the simple technique to satisfy the practical consideration, which was presented in 1H-1,2,4-triazole–loaded PCMOF-2 [Na3(THBTS); THBTS3– = 2,4,6-trihydroxy-1,3,5-benzenetrisulfonate].97 Similar results were also obtained for imidazole-doped Al(OH)(NDC) (NDC = 1,4-naphthalenedicarboxylate) which displayed the higher proton conductivity comparing

to the pristine material without loading imidazole molecules

Chapter 2: THE NOVEL METAL–ORGANIC FRAMEWORKS: SYNTHESIS AND CHARACTERIZATION

2.1 Introduction

2.1.1 Quest for design the novel MOFs material

The exemplary structural versatility and permanent porosity of Metal–Organic Frameworks (MOFs) and their consequent potential for breakthroughs in diverse applications have caused these hybrid materials to become the focus of vigorous investigation These properties also hold significance for applications beyond those traditionally envisioned for microporous materials The aspects of MOF structure that make them so attractive for the various purposes are their crystalline structure, and the tailorability of their organic and inorganic components, which allow the geometric structure to be systematically varied

The project aims to provide a rational design for the synthesis of novel tunable MOFs, to study their porous properties, and to prove their efficiency in applications, such as catalysis, gas storage, separations, etc New families of di- and tri-topic organic linker will be utilized for synthesizing MOFs with desired network topologies

A variety of organic linkers based carboxylate functionality and heteroatoms backbone were employed, special attention being given to longer organic linkers to obtain MOFs material that can be used as interpenetrated MOFs system The sorption of various gases (H2, CO2, CH4) and the catalytic properties of the synthesized MOFs will be investigated in the further research Moreover, the ability of the new obtained MOFs to act as adsorbents for gaseous pollutants and molecules resulted from degradation of pharmaceutical and pesticides compounds will be potentially tested

2.1.2 The aim of the synthesis

The general objective of the project is to provide a rational design for the synthesis of novel tunable MOFs, to study their porous properties, and to prove their efficiency in applications, such as catalysis, gas storage, separations, sensing, luminescence, magnetism, etc

The main goals derived from the general objective are:

i) Design, synthesis and characterization of new families of MOFs with desired network topologies

ii) Optimization of MOFs architectures based on the design improvement of new spacers and nodes

iii) Testing the synthesized MOFs for emerging applications, such as: selective sorption capacity, gas storage, catalysis, etc

2.2 Titanium–Organic Framework-901 synthesis

2.2.1 New approach to design Ti-MOFs

The development of the kinetically tuned dimensional augmentation (KTDA) method provides us with the opportunity to target MOFs from designed inorganic building blocks and with a chosen topology.98 Especially using the metal-oxo cluster

as the objective building block for MOFs synthesis was fully studied before by Zhou and co-worker.98 In this context, inorganic building blocks [Fe2M( 3-O)(CH3COO)6] (M = Fe2+,3+, Co2+, Ni2+, Mn2+, Zn2+) were utilized to act as targeted clusters for a kinetically tuned dimensional augmentation synthetic route for the preparation of high crystalline and extremely robust Metal–Organic Frameworks Overall, the synthesis of large single crystals of 34 different Fe-MOFs with thirty different ligands and mixed ligands by rationally tuning the synthetic conditions had been reported and full characterized Moreover, a series of mesoporous metalloporphyrin Fe-MOFs, which named PCN-600(M) (M = Mn, Fe, Co, Ni, Cu), has been also presented by Zhou in

2014 by using the preassembled [Fe3O(OOCCH3)6] building block.99

More recently, according to the research of Eddaoudi’s group, the potential of the molecular building block (MBB) approach for the assembly and development of functional solid-state porous materials has already been recognized and exploited to produce many of porous MOFs based unprecedented high connected rare-earth (RE) clusters.12,13,100 Markedly, his research has been succeeded in controlling the directionality of RE based inorganic molecular building block (MBB) by pioneering the use of fluorinated ligands and/or a modulators such as 2-fluorobenzoic acid (2-

FBA) Accordingly, by implementing MBB approach the isolation of unprecedented high connected porous RE-MOFs, based on high coordinated hexanuclear and

nonanuclear carboxylate based clusters leads to (i) isoreticular fcu-MOFs when linear

ligands are bridging the resultant 12-c cuboctahedron (cuo) secondary building units (SBUs), and (ii) isoreticular ftw-MOFs when the 12-c cuo SBUs were linked by 4-c

square shaped ligands.13

In term of MOFs synthesis, the plenteous chemistry of metal and controllability

of organic linker were exploited to make the uncountable amount of new MOFs material In this case, the simple solvothermal reaction or other methods (e.g., hydrothermal, solvent free, slow dispersion) was usually employed to synthesize MOFs.101,102 This method for MOFs synthesis can generally predict the obtained structures based on the geometry of the metal clusters and the organic linkers guided

by reticular chemistry.1,103 For example, a stable ftw MOF-525 based on porphyrin

units was previous reported in 2012,104 in which square planar – D4h 4-connected node

of tetracarboxyphenylporphyrin (H4TCPP) organic linkers were utilized to connect to

Oh symmetric 12-connected nodes of Zr clusters However, the limitation of this synthetic method also applies to the copious geometry of components generated to MOFs material in term of lack of control of final structure With the different functional groups on triangular 1,3,5-benzentribenzoate (BTB) linker, the reaction between functioned triangular BTB linker with Zn4O(CO2)6 octahedral building lock

leads to three kinds of MOFs based qom 177), pyr 155) and rtl

(MOF-156) topology.105

In order to circumvent the limitation from reticular chemistry method, the building block approach, in which the inorganic clusters were defined and reformed before connecting to the organic linkers via linker exchange, was applied as alternative methodology in MOFs synthesis The crystallization of final product was controlled through dynamic covalent chemistry.106 The synthetic scheme from building block approach is utilized to synthesize MOFs from the tetravalent transition metal ion (e.g.,

Ti4+, Zr4+, Hf4+) whose metal-oxo clusters were surrounded by terminal carboxylate ligands This method is useful for synthetic of MOFs that are composed of strong covalent bonds, which are difficult to associate and dissociate during synthesis process