chapter One


1.1 Research background

Population growth and fossil fuel use are driving the need for alternative and sustainable energy development. Therefore, there is a need for energy-saving materials that are affordable and do not endanger the environment. Areas of interest such as fuel cells, batteries, capacitors and solar cells offer many opportunities for improvement and research focus. (Lacy et al., 2014)

Detection of hazardous materials is a major homeland security concern, and wearable sensors may be desirable to avoid the complexity of materials such as explosives. Luminescent metal-organic frameworks (MOFs) are potentially useful as chemoselective sensors. The study of luminescent behavior in organometallic frameworks is an active research area in inorganic chemistry. A number of 3d elements have been used to study the emission of ligands. The most frequently reported organometallic framework structures are based on Zn2+ and Cd2+ ions with filled d orbitals, thus making d–d transitions impossible. Charge transfer effects within the ligand and/or the ligand metal have been observed in these compounds. Photoluminescence studies are important for understanding charge transfer pathways. Studies on the luminescence behavior of MOFs clearly demonstrate the facile energy transfer from the organic ligands to the metal center. Lifetime studies also show that the excited states have considerable stability and can be used in many important applications. (Zhou, X. et al., 2009; Konar et al., 2013)

Metal-organic frameworks (MOFs), also known as metal-organic networks or coordination polymers, are a new class of compounds containing metal ions linked by organic bridging ligands. A metal-organic framework (MOF) can be viewed as a composition of two main components:
A metal ion (or cluster of metal ions) and an organic molecule called a linker (or bridging ligand).

Metal ion + organic linker ⎯ ⎯ → coordination polymer/MOF

An organic ligand or linker is a group that can donate multiple lone pairs (polydentate) to a metal ion, which can then accept these lone pairs from a vacant orbital shell to form an organometallic framework. Configured. Organometallic frameworks are well-defined, tunable, spatially confined, highly porous materials that are often crystalline, air-sensitive, and resistant to structural collapse upon heating. there is. (Zhang et al., 2006)

1.1.1 Organometallic frameworks as functional materials

Early research on MOFs usually focused on the synthesis of various new compounds with new topologies and compositions. Although the design of new structures remains of high relevance, and the majority of research efforts are devoted to discovering unprecedented network topologies, the main motivation in crystal engineering of MOFs is their specific physical properties and supramolecular properties. We are moving towards designing materials with functionality. , such as catalysis, gas storage, luminescence, nonlinear optical properties (NLO), magnetism, etc. Photoluminescence is a form of luminescence. Phosphors are luminescent materials that emit light when excited by radiation, usually microcrystalline powders or thin films designed to emit visible colors. It is the emission of light from any form of matter after absorption of a photon. It is the process by which molecules absorb, store and emit light and is initiated by photoexcitation. (Nide et al., 2013)

1.2 Synthesis of metallic natural framework

Two techniques are adopted, namely:
(i) traditional (ii) unconventional techniques.

1. Conventional synthesis is often completed with the aid of using solvothermal techniques; i.e. heating a aggregate of natural linker and metallic salt in a solvent system. The substances constituted of this technique are thermally risky or reactive to solvent used, and this will result in breaking of bonds or introduction of metallic webweb sites for visitor species which includes gases to advantage get admission to into the framework’s micropores. In a few cases, assisted microwave-solvothermal synthesis may be used, to reveal or adjust the temperature while the response is in progress. Precipitation and crystallization follows right now after heating a aggregate of a delegated metallic ion and natural linker withinside the presence of a solvent. Thereafter, filtration and drying follows. Slow evaporation technique is a traditional technique and is high quality due to the fact the crystals gather themselves aleven though it’s time consuming. (Tella et al., 2012)

2. Unconventional Synthesis is often completed with the aid of using grinding a aggregate of natural linker and metallic salt in an agate mortar and pestle or in a ball mill and withinside the absence of solvent. This technique is called mechanochemical technique. The metallic webweb sites are uncovered while the aggregate is lightly heated, as a consequence permitting gases which includes hydrogen to bind at those webweb sites. The mechanochemically initiated reactions are corresponding to the ones of solvent reactions. The technique is thought to be environmentally pleasant and might probably provide excessive yield of products.
(Alex et al., 2005; Tella et al., 2012)

1.2.2Chemistry of 8-Hydroxyquinoline

8-hydroxyquinoline is an natural compound with the system C9H7NO. It is a spinoff of the heterocyclic quinoline with the aid of using placement of an OH organization on carbon quantity 8. It is a monoprotic bidentate chelating agent. 8-hydroxyquinoline has a hydrogen atom this is replaceable with the aid of using a metallic, and a heterocyclic nitrogen atom, which bureaucracy with those metals a 5 membered ring. It bureaucracy strong complexes with numerous metallic ions.(Sharet al., 2005)

1.2.2 Chemistry of Benzoic acid

Benzoic acid (C6H5COOH) is a colourless crystalline stable and a easy fragrant carboxylic acid. Benzoic acid happens obviously in lots of flora and it serves as an intermediate withinside the biosynthesis of many secondary metabolites. Benzoic acid is an crucial precursor for the commercial synthesis of many different natural substances. Benzoic acid is specially ate up withinside the manufacturing of phenol with the aid of using oxidative decarboxylation at 300-four hundred 0C. It is one of the ligands used on this studies work. (Jarad et al., 2011)



Structure of 8-hydroxyquinoline



Structure of benzoic

1.4 Justification of observe

Metal natural frameworks were visible to have fantastic photoluminescent properties. They are able to sensing ions and detecting explosive molecules. They have vast packages in organic and environmental systems. Conventional solvothermal syntheses are hired to create luminescent steel natural frameworks. In principle, the porous crystalline MOF structure gives benefits over different sensor substances. In the case of explosives, identity may be performed through detecting a byproduct or additive whilst the explosive itself isn’t without problems detectable (e.g., because of low vapor pressure). The recognition of luminescence over different transduction mechanisms is a outcome of numerous key elements, including the manufacturing of a sign this is seen through eye. Fluorescence spectroscopy is nicely established, and detection limits can attain the unmarried molecule level. Another function is the capacity to deal with powdered substances directly, this is, with out the want for movie fabrication or different processing. (Zhao et al., 2010; Yao et al., 2012; Zhou et al., 2013; Biplab et al., 2014)

1.5 The sluggish evaporation approach

The sluggish evaporation approach is a traditional approach to put together MOFs, which on the whole does now no longer want any outside strength supply. Although this approach is every so often desired due to the fact it’s miles a room-temperature technique and the crystals gotten are natural due to the fact they may be self-assembled, its fundamental downside stays that it calls for greater time as compared with different famous traditional methods. In the sluggish evaporation approach, an answer of the beginning substances is focused through sluggish evaporation of the solvent at a set temperature, on the whole at room temperature. Sometimes the technique entails a combination of solvents, which could growth the solubility of the reagents and might make the technique quicker through faster evaporation of low-boiling solvents. (Hu et al., 2005; Ohi et al., 2004; Halper et al., 2006; Yoo et al., 2011).


Leave a Comment