Covalent Organic Cage Materials for CO2 Gas Adsorption and Chemosensing Applications

Abstract

The rapid growth of industrial development changes the global economy and human life becomes more comfortable while on the other hand, it is releasing harmful gases into the environment. Traditional energy sources such as coal, natural gas, and oil emits drastic amounts of carbon dioxide (CO2) gas into the air during the burning process. Hence, to address the issue of controlling the CO2 gas in the environment, it is important to develop sustainable, environmentally friendly materials for capturing and storing the CO2 gas from the industrial process and is the main important research area in the present. On the other hand it is crucial to develop effective and cheap chemosensory materials for the detection of explosives (Nitroaromatics: NACs) and metal ions to control the air and water pollution that affecting the health of living organisms. Porous materials, particularly, Zeolites, COFs, activated carbons, MOFs and COCs are found to be potential as well as sustainable materials for CO2 gas adsorption and chemosensory applications. Although excellent studies have been carried out on covalent organic cage (COC) materials, still underlying mechanism of making the relation between structure and properties were least understood. In this thesis, various covalent organic cage materials have been synthesized by following lower temperature conditions (0 - 5 °C), room temperature as well as reflux method. Further, the CO2 gas adsorption and chemosensing applications of these materials are studied. In this thesis, the research work has started with simple dialdehydes like meta and para-phthalaldehyde derivatives and synthesized both imine and amine-linked covalent organic cage materials and understood their role in CO2 gas sorption applications. The unusual enhancement in CO2 gas adsorption capacity almost 40% was observed in imine-linked para-pthalaldehyde derivative (COC-PI) when the temperature was increased from 273 to 298 K at pressure 1 bar. The enhancement in CO2 gas adsorption capacity of COC-PI investigated in the direction of the flexibility of the COC molecules in the crystal supported the easy penetration of CO2 outcomes and lattice enlargement. Later in chapter four, synthesized four triazine-based imine-linked cage materials by changing the amine precursor molecule to obtain COCs with the various morphologies. The cage materials were showed a good amount of CO2 gas adsorption capacity at 273 K and 298 K with 1 bar pressure. After that the research work has extended to the synthesis of luminescent COC molecules for chemosensing applications. In this thesis, mainly focused on triphenylamine linker molecules because they showed excellent luminescent properties. By taking this advantage, synthesized the both imine and amine linked cage materials for sensing applications of explosives, metal ions, and small molecule (Chloroform, DCM, DMF, etc.) by fluorescence method. The fluorescent characteristics of the cage molecules were studied in various solvents like non-polar, polar protic, and polar aprotic. One of our cage materials (F-COC) was showed excellent enhanced emission in polystyrene (PS) doped matrix when exposed to chloroform vapours. Finally in this thesis, synthesized a novel fluorescent organic cage material for the detection of metal ions (Co2+) in the solution state with good selectivity and sensing.