Adsorbent That Can Selectively Remove Water Contaminants

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Figure 1. Diagram conceptualizing the process of charge- and size-specific separation by the fluorine-based porous polymer adsorbent

Professor Cafer T. Yavuz and his team at the Graduate School of Energy, Environment, Water, and Sustainability (EEWS) have developed an adsorbent that can selectively capture soluble organic contaminants in water.

This water treatment adsorbent is a fluorine-based nanoporous polymer that can selectively remove water-soluble micromolecules. It has the added advantage of being cheap and easily synthesized, while also being renewable.

The results of this research have been published online in Nature Communication on November 10, 2016. The research paper is titled “Charge-specific Size-dependent Separation of Water-soluble Organic Molecules by Fluorinated Nanoporous Networks.”

Water pollution is accelerating as a result of global industrial development and warming. As new materials are produced and applied in the agricultural and industrial sectors, the types of contaminants expelled as sewage and waste water are also becoming diverse.

Chemicals such as dyes and pesticides can be especially harmful because they are made up of small and highly soluble organic particles that cannot be completely removed during the water treatment process, ultimately ending up in our drinking water.

The current conventional water treatment systems utilize processes such as activated carbon, ozonolysis, and reverse osmosis membrane. These processes, however, are designed to remove larger organic molecules with lower solubility, thus removal of very small molecules with high solubility is difficult. In addition, these micromolecules tend to be charged, therefore are less easily separated in aqueous form.

The research team aimed to remove these small molecules using a new adsorbent technology.

In order to remove aqueous organic molecular contaminants, the team needed an adsorbent that can adsorb micro-sized molecules. It also needed to introduce a chemical function that would allow it to selectively adsorb molecules, and lastly, the adsorbent needed to be structurally stable as it would be used underwater.

The team subsequently developed an adsorbent of fluorine-based porous organic polymer that met all the conditions listed above. By controlling the size of the pores, this adsorbent is able to selectively adsorb aqueous micromolecules of less than 1-2 nm in size.

In addition, in order to separate specific contaminants, there should be a chemical functionality, such as the ability to strongly interact with the target material. Fluorine, the most electronegative atom, interacts strongly with charged soluble organic molecules.

The research team incorporated fluorine into an adsorbent, enabling it to separate charged organic molecules up to 8 times faster than neutral molecules.

The adsorbent developed by Professor Yavuz’s team has wide industrial applications. It can be used in batch-adsorption tests, as well as in column separation for size- and charge-specific adsorption.

Professor Yavuz stated that “the charge-selective properties displayed by fluorine has the potential to be applied in desalination or water treatment processes using membranes.”

This paper was first-authored by Dr. Jeehye Byun, and the research was funded by KAIST’s High Risk High Return Program and the Ministry of Science, ICT and Future Planning of Korea’s Mid-Career Researcher Program, as well as its Technology Development Program to Solve Climate Change.

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Figure 2. Difference in absorbance before and after using a porous fluorine polymer column to separate organic molecules
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Figure 3. Adsorption properties of a fluorine polymer according to the charge and size of organic molecules