The research team headed by Professor Cafer T. Yavuz from the Graduate School of Energy, Environment, Water, and Sustainability (EEWS) at KAIST recently developed a method of selectively separating molecular contaminants in water. The innovative process allows for charge-specific, size-dependent separation of soluble molecules through fluorinated nanoporous (of pore diameters under 100 nm) networks. The research paper was published on November 10 on the online version of Nature Communications.

With industrialization continuously on the rise, the abuse and depletion of natural resources continue to pose threats. As more chemicals are used in both agricultural and industrial fields, the urgency of the issue of contamination has been escalating as well. Water is a primary resource easily exposed to these problems, which, if not treated, can bring about severe consequences associated with impotable water.

On a molecular level, water purification methods have been aided by highly crystalline ordered structures such as zeolites, metal organic frameworks, and widely available nanoporous carbons. Other methods include ozone decomposition and reverse osmosis pellicles. These methods, however, are not completely soluble and can only filter larger molecules, as stronger intermolecular forces bind smaller ones. Up to now, size-dependent separation and the related chemistry of the interaction between smaller molecules had not yet been well-studied.

The research team under Professor Yavuz succeeded in separating molecules based on size and charge, allowing more meticulous filtering of sub-nanoscale molecules. Specifically, they used an ultra-microporous polymeric network that featured fluorines as the predominant surface functional groups. Fluorine has been discovered to interact with similarsized molecules of different charges in separate ways, which can be traced back to the lack of a σ-hole for fluorine atoms. Not only does this discovery speed up the selection process, but it also shows a multitude of potential commercial applications.

Accordingly, Professor Yavuz stated, “Fluorine’s unique charge-specific selectivity will be used in the future for desalinization materials and mixed matrix membranes.” With PhD student Jeehye Byun as the first author, this research has been funded by the KAIST High Risk High Return Project (HRHRP), as well as the Ministry of Science, ICT, and Future Planning.