Water Adsorption on MOFs Studied by NMR Relaxometry
The 5th International Simposium om Innovative Materials and Processes in Energy Systems
20-23 Oct 2019
|| Pizzanelli Silvia
, Freni Angelo
, Gordeeva Larisa Gennadievna
, Forte Claudia
Institute of Chemistry of Organometallic Compounds
Boreskov Institute of Catalysis SB RAS
The development of effective and stable Metal-organic frameworks (MOFs) for adsorption heat transformation (AHT) and heat storage is a major trend of research in the field . MOFs are microporous materials made of metal ions and organic linkers that create an open crystalline structure, offering high porosity, large surface area and adjustable ad/desorption behavior . Among various MOFs, NH2-MIL-125, with specific surface area ≈ 1300 m2/g and micro-pore volume ≈ 0.56 cm3/g, is considered one of the most promising MOF materials for heat transformation purposes [3,4]. The water adsorption isotherms demonstrated that this compound offers free openings, can adsorb a large amount of water (up to 0.42 g/g) and exhibits S-shaped isotherms , which is convenient for practical use in AHT cycles .
In the present paper, NH2-MIL-125 was synthesized according to the procedure described in the literature  and its interaction with water was thoroughly investigated by solid state Nuclear Magnetic Resonance (NMR) spectroscopy and Fast Field Cycling (FFC) relaxometry. With this aim, several MOF samples were prepared with different levels of hydration, ranging from 0.04 g/g (corresponding to few water molecules adsorbed on the surface of the pores) to 0.45 g/g (i.e., water filling the pores).