Metal-Organic Frameworks with Tunable Hydrophilicity for Water Adsorption Appliations

Technology

Therefore, the inventors have investigated the water adsorption behaviors of a novel set of MOFs containing pyrazolate­­-based organic ligands and other N-containing heterocyclic end groups reported to have exceptional water stability for applications in water adsorption-based heat pumping. Specifically, they have developed a new set of water stable Zn2+–pyrazolate MOFs, then post-synthetically oxidized the material with dimethyldioxirane to render the hydrophobic channel interiors more hydrophilic. The increased hydrophilicity of the chemically treated MOF materials results in changes in the water adsorption profile of the modified versus parent materials. Such tunability of the water adsorption characteristics of these new adsorbents is potentially desirable in water adsorption applications such as heat transfer, pumping and storage. Hydrophobic materials have low regeneration temperatures that can allow for the use of low-temperature waste heat or solar collectors as energy sources. Alternatively, more hydrophilic materials might function under more extreme conditions (i.e. provide lower cooling temperature and/or adsorb water at higher external temperatures) and/or achieve large water exchange capacities over a desired working pressure or temperature range.  

Problem Addressed      

Metal organic frameworks are of interest as adsorbents in water adsorption-based heat pumps due to their increased water loading capacities compared to traditionally used materials such as silicas and zeolites. MOFs also allow for unprecedented control over their structural and chemical functionality. The water adsorption behaviors of the few water-stable MOFs containing carboxylate-based ligands, such as MIL-101 (Cr) and MIL-100 (Fe), have been studied in some detail. While they have evidenced characteristics desirable in heat pump adsorbents, they appear to be hydrolytically unstable in the long term.

Advantages      

• MOFs are energetically efficient and environmentally friendly
• MOF materials can be accessed in large scale via a modular synthetic approach
• Tunable hydrophobicity of MOFS allows for wide range of water adsorption applications  

Publications

"Postsynthetic Tuning of Hydrophilicity in Pyrazolate MOFs to Modulate Water Adsorption Properties." Energy & Environmental Science, 2013.