Amlan Buragohain, Department of Chemistry, Indian Institute of Technology Guwahati was carried out under my supervision and has not been submitted elsewhere for a degree. I would like to express my deepest gratitude to my parents for all the unconditional love and sacrifices they have made for the sake of my upbringing.
Thesis Overview
The effect of activation temperature on the BET surface area of the materials was also examined. The phase purity of the materials is confirmed by a combination of XRPD analysis, DRIFT spectroscopy and thermogravimetric analysis.
Introduction and Brief History of
Functionalized Metal-Organic Frameworks (MOFs)
INTRODUCTION
Based on the size of the pores, these porous solids can be divided into three categories: microporous (pore diameter, < 2 nm), mesoporous (pore diameter, 2 – 50 nm) and macroporous (pore diameter, > 50 nm). Several studies on the chemical and thermal stability of MOFs have shown that the stability of the framework depends on various factors such as the oxidation state of the metal ion, the lability of metal-ligand bonds, etc.37 It has been found that the successful construction of MOFs with high hydrolytic stability is possible.
BASIC DESIGN PRINCIPLES
The availability of various possible combinations of metal centers and organic molecules can lead to the design of a diverse arrangement of metal-organic architectures, ranging from 0D discrete nanostructures to 3D infinite networks (Figure 1.3). It is notable that the nets from Figure 1.3 can also be represented in a comparable manner in the VLPP manner (Figure 1.5).
SYNTHETIC METHODS
- Hydro/Solvothermal Synthesis
- Microwave-Assisted and Sonochemical Synthesis
- Electrochemical and Mechanochemical Synthesis
- Post-Synthetic Modification
Microwave irradiation (MW)-assisted synthesis has been widely applied for the rapid synthesis of MOFs under hydrothermal conditions. Such post-synthetic modifications (PSMs) are emerging as a promising route towards tailored host-guest interactions for more specific and improved properties of MOFs71.
HISTORY
However, the introduction of a functional group for a desired application is sometimes difficult to achieve during synthesis of MOFs due to the high sensitivity and reactivity of the additional functionality during the formation of MOFs. One square face of the square antiprism consists of O atoms from the carboxylate groups, while the O atoms from the μ3-O and μ3-OH groups construct the other side of the square antiprism.
MOFs AS CHEMICAL SENSORS
- MOFs for Sensing of Nitroaromatic Explosives
- MOFs for Sensing of Hydrogen Sulphide
A large number of Zn-based luminescent MOFs have been reported to date for the detection of nitroaromatic explosives. For example, a 3D Zn(II)-based MOF with molecular formula [Zn4O(cpi)2(H2O)3]∙3DMA·3EtOH· 6H2O (H3cpi = 5-(4-carboxyphenylethynyl)isophthalic acid) has been constructed from π-conjugated H3cpi -ligand. Indeed, a large number of Zn(II)- and Cd(II)-based luminescent MOFs have been used for the detection of nitro explosives.
MOFs FOR CO 2 ADSORPTION
However, the affinity of the material for CO2 is also a crucial parameter which controls and optimizes the interaction of CO2 with the material and the energetic penalty of capture. Adsorption of CO2 within the pores of the material depends on various factors including structural effects on surface functionalization.
MOTIVATION AND OBJECTIVES
Improved Synthesis of Zirconium(IV) Muconate MOF: Characterization, Stability
- INTRODUCTION
- EXPERIMENTAL SECTION
- Materials and General Methods
- Synthesis of [Zr 6 O 4 (OH) 4 (C 6 H 4 O 4 ) 6 ]∙1.5DMF∙10H 2 O (1-H 2 O-AS)
- Synthesis of [Zr 6 O 4 (OH) 4 (C 6 H 4 O 4 ) 6 ]∙1.2DMF∙12H 2 O (1-HCl-AS)
- Activation of The Compounds
- RESULTS AND DISCUSSIONS
- Syntheses, Activation and FT-IR Analysis
- Structure Description
- Gas Sorption Properties
- CONCLUSIONS
- REFERENCES
In the second step, the methanol-exchanged forms of the materials were heated under vacuum at 150 ºC for 12 hours. The FT-IR spectra of the thermally activated forms of structurally related 1-H2O and 1-HCl (Figure 2.4) are similar as expected. The N2 sorption isotherms (Figure 2.8) exhibit type I behavior, confirming the microporous nature of the thermally activated Zr(IV) muconate compound.
The influence of the ZrCl4/additive molar ratio on the crystallinity of the compounds was systematically studied.
3D Luminescent Amide-Functionalized Cadmium Tetrazolate Framework for
INTRODUCTION
Therefore, the discriminative detection of TNP from other nitroaromatic explosives with a very low detection limit is an essential task to reduce its harmful effects on the environment. Encouraged by the above advantages, various MOF materials have been synthesized and investigated for the detection of a wide range of analytes, including cations, anions, biomolecules, small molecules, volatile organic compounds, and nitroaromatic explosive materials.9-17. Indeed, a large number of MOF-based fluorescent sensor materials9-17 have been investigated to date for the detection of nitroaromatic explosive compounds, but only a few of them18-26 showed fast and selective sensing behavior toward TNP.
The activated form of the compound (hereinafter referred to as 1') shows its potential for highly selective, sensitive and rapid detection of TNP, even in the presence of other potentially interfering nitroaromatic explosive compounds.
EXPERIMENTAL SECTION
- Materials and General Methods
- Synthesis
- Activation of the Compound
- Single-Crystal X-Ray Diffraction
- Fluorescence Quenching Titration Experiments
The thus synthesized form 1 was heated at 120 °C under vacuum for 12 hours to obtain the activated form of the compound (1'). Finally, the six-membered ring was refined using anisotropic parameters, while the FRAG command was used to determine the amide coordinates. The H atoms were left in the refinement in order to correctly formulate the water molecule.
No indication of the presence of counterions was observed in the Fourier difference or from the elemental analysis.
RESULTS AND DISCUSSIONS
- Synthesis
- Structure Description
- X-ray Powder Diffraction and FT-IR Analysis
- Thermal Stability
- Photoluminescence Properties
- Sensing of Nitroaromatic Explosives
- Estimation of Quenching Constant and Detection Limit for TNP
- Response Time of 1′ towards the Detection of TNP
- Mechanisms for the Detection of Nitroaromatic Explosives
The thermally activated 1' retains its crystallinity, as confirmed from the XRPD patterns (Figure 3.4) of the corresponding sample. A successive quenching of the fluorescence intensity of 1' was observed upon stepwise addition of the analytes. The plots of quenching efficiencies versus exposure times (Figure 3.18) reveal that the addition of 400 μL of TNP to the ethanol suspension of 1′ leads to very rapid detection of the former.
This mechanism can also be supported by the red shift of the fluorescence intensity (Figure 3.9) observed during the gradual addition of TNP solution to a 1' suspension.
CONCLUSIONS
The highest quenching efficiency of TNP may also be related to the strong electrostatic interactions between the Lewis basic amide group of H2L ligand and the highly acidic hydroxyl group of TNP.19 The presence of amide group in H2L ligand increases the surface area of interaction of 1' with the acidic hydroxyl group of TNP via hydrogen bonding and ionic interaction. This increase in surface interaction between the host and the analyte leads to a quenching fluorescence response for TNP.59, 60 Other analytes (except DNP and PNP) possess no acidic hydroxyl group in order to interact with the free basic amide sites of the ligand. Thus, the above mentioned electrostatic interactions are absent in the other analytes, leading to significantly lower quenching performances.
Overall, the combined effects of energy and electron transfer mechanisms and electrostatic interactions can be attributed to the high selectivity of 1' for TNP detection.
Cerium Based Azide- and Nitro-Functionalized UiO-66 Frameworks as Fluorescent Turn-On
INTRODUCTION
Recently, fluorescent turn-on probes based on the reduction of hydroxylamide, nitro and azide groups have attracted much more attention for the rapid and selective detection of H2S.27, 31-44. The application of MOF-based fluorescent turn-on probes with increased sensitivity compared to other traditional methods would be a promising strategy for rapid detection and real-time monitoring of H2S. Only a few MOFs with nitro and azide functionalities have been reported to date as fluorescent turn-on probes for the selective detection of H2S under physiological conditions. In fact, cerium is the most abundant of the rare earth elements and has various applications, including catalysis, yet cerium-based MOFs are still rare.
Herein, we present a new azide-functionalized and an existing nitro-functionalized46 Ce(IV)-based MOF as fluorescent turn-on probes for detection of H2S under physiological conditions.
EXPERIMENTAL SECTION
- Materials and General Methods
- Synthesis of Ce-UiO-66-N 3 (1-N 3 )
- Synthesis of Ce-UiO-66-NO 2 (2-NO 2 )
- Activation of the Compounds
- Preparation of the Medium for Fluorescence Studies
- Fluorescence Titration Experiments
For all the fluorescence measurements, the excitation wavelength (λex) was 334 nm and the emission spectra were recorded in the range of 344-650 nm. For the recording of the fluorescent turn-on reactions of 1'-N3 and 2'-NO2 towards H2S, NaHS (10 equivalents with respect to the azide and nitro functionalities in 1'-N3 and 2'-NO2, respectively) at the suspension and fluorescence spectra were recorded at a regular time interval (60 s) until saturation. Furthermore, a comparative fluorescence titration study was performed with Zr-based azide- and nitro-functionalized UiO-66 MOFs for revealing the effect of metal ions on H2S detection.
RESULTS AND DISCUSSIONS
- Synthesis and Characterization
- Thermal and Chemical Stability
- Fluorescence Turn-On Experiments: Sensing of H 2 S
- Recyclability Test
- Gas Adsorption Properties
For 1′-N3, there was an almost 7-fold increase in fluorescence emission intensity (λem = 429 nm) after 60 s and near saturation of fluorescence intensity was observed after 760 s (Figure 4.10). The immediate turn-on of fluorescence intensity upon addition of NaHS makes 1′-N3 and 2′-NO2 potential fluorescent sensor materials for rapid and real-time detection of H2S. To quantify the fluorescence responses of 1′-N3 and 2′-NO2 against H2S, fluorometric titrations with different concentrations of NaHS (0 to 10 equivalents) were performed.
The plots of fluorescence intensity versus concentration of 1′-N3 and 2′-NO2 are shown in the insets of Figures 4.20 and 4.21, respectively.
CONCLUSIONS
- INTRODUCTION
- EXPERIMENTAL SECTION
- Materials and General Methods
- Synthesis
- Activation of the As-Synthesized Al-MIL-101-X-CE Materials
- RESULTS AND DISCUSSIONS
- Synthesis and Activation
- Structure Description
- Infrared Spectroscopy
- Thermal Stability
- CONCLUSIONS
- REFERENCES
The synthesis of the previously reported 26 amino-functionalized Al-MIL-101 materials was accomplished under the presented solvothermal reaction conditions. Unfortunately, the crystallinity of the Al-MIL-101-X-MW materials (Figure 5.1) decreased significantly upon prolonged exposure to atmospheric moisture. Due to the sensitivity of the synthesized Al-MIL-101-X-MW materials to moisture, they were not activated to achieve permanent porosity.
All the Al-MIL-101-X materials showed high thermal stability up to 260–430 °C in an air atmosphere.
Synthesis, Characterization and Sorption Properties of Functionalized Cr-MIL-101-X (X
- INTRODUCTION
- EXPERIMENTAL SECTION
- Materials and General Methods
- Synthesis
- Activation of the As-Synthesized Cr-MIL-101-X Compounds
- RESULTS AND DISCUSSIONS
- Synthesis and Activation
- Structure Description
- DRIFT Analysis
- Thermal Stability
- Sorption Properties
- CONCLUSIONS
- REFERENCES
The structures of Cr-MIL-101-X materials are constructed from trimeric oxo-centered [Cr3(μ3-O)Cl(H2O)2]6+ building units composed of [CrO5Cl] octahedra. The DRIFT spectra of the Cr-MIL-101-X materials (Figure 6.4) show great similarity to each other, as expected. In the DRIFT spectra of the thermally activated Cr-MIL-101-X materials, the strong absorption bands due to the asym.
N2 sorption measurements were performed with thermally activated forms of all Cr-MIL-101-X materials.
CONCLUSIONS AND OUTLOOK
The detection limit of the material for TNP sensing was estimated to be M (42.84 ppb), which is comparable to other MOF-based fluorescence sensors reported to date. The high thermal stability and stability of the lightweight, non-toxic Al-MIL-101-X materials together with the significantly high porosity would make them potential candidates for use in gas storage and separation. All functionalized compounds except Cr-MIL-101-C6H4 were obtained by reaction of a mixture of CrO3, H2BDC-X linkers, conc.
The N2 uptake values of the materials depend on the size of the attached functional groups, while their CO2 and benzene adsorption capacities depend on both the size and nature of the grafted functional groups, resulting in different adsorptive framework interactions.
