“Molecular Cage” Could Help Remove Drugs and Chemical Pollutants From Water

Researchers have developed a new material that could help to remove unwanted pollutants — including leftover medicines and synthetic chemicals — from our waterways.

The metal-organic cage (MOC) molecules are designed to absorb harmful pollutants and trap them inside their cage-like structures. While MOCs have been used previously for gas and chemical capture in organic solvents, this latest research introduces a rare water-soluble MOC made with an easily adaptable synthesis technique. The research is published in  Cell Reports Physical Sciences .

Removing harmful contaminants from water

Unmetabolized medications and chemicals left over from hygiene and personal care products have become of increasing concern in recent years. Studies suggest that these compounds could pose a danger to animal health and welfare when present as environmental contaminants.

“While domestic wastewater passes through wastewater treatment plants, these plants frequently do not meet the capacity or the level of chemical purification required to completely prevent medicinal and healthcare products reaching our ecosystems,” senior study author Dr. Imogen Riddell, a Royal Society University Research Fellow at the University of Manchester, told  Technology Networks .

“Once introduced into natural waterways, these chemicals bioaccumulate in the fatty tissues of aquatic organisms resulting in toxicity and negative effects on the physiology, development and reproduction of the organisms that consume them.”

In search of better treatment options that can selectively bind to and remove these contaminants, researchers have turned to MOCs. These cage-like molecules have previously been used to encapsulate, store and release pollutants — such as the potent greenhouse gas SF6 — but have rarely been applied to water-based systems.

“A longstanding challenge in the MOC community has been to design useful MOCs which are also water-soluble. This has been difficult because MOCs often include organic linkers which have poor solubility in water,” explained first author Jack Wright, a PhD student in Riddell’s research group at the University of Manchester. “Strategies that allow the introduction of water-solubilizing groups, which might address this challenge, often negatively impact the self-assembly of the MOCs themselves.”

To make their MOC water-soluble, the researchers incorporated sulfonates into their MOC’s structure. Sulfonate-based ligands have good solubility in water, however their poor commercial availability has previously limited their use in water-soluble MOCs. In their new paper, the researchers demonstrate an alternative synthesis technique, based on a simple ring-opening addition reaction, that more easily introduces sulfonate moieties into ligands for water-soluble MOCs.

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Taxonomy

• Contaminant Removal
• Spill Containment