Utilization of Metal-Organic Framework-based Hybrid Material in Adsorption and Sensing Applications

Abstract

Metal-organic frameworks (MOFs) have received a great attention during recent decades. Thanks to their exceptional properties such as possessing a large specific surface area, a large pore volume, abundant active sites and adjustable pore and aperture size, they are readily utilized in many attractive applications such as gas storage, catalysis, sensors, environmental treatment, and electric devices. In addition, hybrid composites of MOF and another functional materials can provide an opportunity to achieve an unprecedented property through synergic effect. In this thesis, three different application researches based on MOF or its hybrid are presented. Firstly, magnetic MOF hybrid was prepared and then used to remove copper(II) ion contaminants in aqueous solution. The hybrid with a core-shell structure was sonochemically synthesized through a compact growth of zeolitic imidazolate framework-8 (ZIF-8) nanoparticles on the surface of magnetic iron oxide (Fe3O4). Fe3O4@ZIF-8 hybrid exhibited a large surface area of 896 m2 g-1 and magnetization of 34 emu g-1. A highly crystalline ZIF-8 shell had a thickness of around 100 nm and its content was measured to be 63 wt%. The thickness and content of ZIF-8 layer were found to be controllable with the variations of reaction time and sonication power. From the adsorption study to copper(II) ions, a large adsorption capacity of 323 mg g-1 and a high removal percentage greater than 90% were confirmed. In addition, a similar surface growth protocol was also applied to prepare ZIF-8 decorated expanded vermiculite. Next, a ZIF-8 layer immobilized on filtration membrane was tested as a solid-phase extraction medium in order to improve a Cu2+ detection sensitivity in the colorimetric paper-based sensors. In this device, Cu2+ ions were promptly adsorbed on the ZIF-8 membrane during the period (< 5min) of passing a sample flow, and then efficiently released by adding a small amount of acidic solution. The combination of paper sensor with the preconcentrating ZIF-8 layer demonstrated a very low limit-of-detection value of 10 µg L-1 corresponding to approximately 50 times enhancement in sensitivity when compared with the conventional paper sensor. Furthermore, a linearly detected concentration range was found to be controllable with using a sample volume: 10 – 150 µg L-1 for 10 mL sample and 50 – 500 µg L-1 for 1 mL. Finally, microporous MOF particles were utilized as a template to synthesize porous conducting polymer. The vapor phase polymerization of Cl-doped polypyrrole was carried out within 3D microporous channels of Cu3(btc)2. The polymerization was used selective adsorption of pyrrole molecules on the Lewis-acidic metal sites and then oxidative polymerization by gaseous oxidant. The product exhibited both electrical conductivity and a micro/mesoporous structure resulting in a high surface area after template removal.