Reviewed by Lexie CornerSep 12 2024
In a study published in ACS Central Science, researchers describe a sugar-like polymer that binds heavy metals in insoluble clumps for simple removal. In proof-of-concept studies, the polymer eliminated ionic cadmium and lead from river water contaminated with these persistent pollutants.
Heavy metal contamination in water poses risks to both aquatic life and humans. While plant-based, sugar-derived polymers have been used to remove these elements, they often require additional ingredients to stabilize or dissolve in water.
This new sugar-like polymer can easily remove heavy metals by forming insoluble clumps, simplifying the removal process. In experiments, the polymer effectively removed lead and ionic cadmium from polluted river water.
High concentrations of certain heavy metal ions in drinking water can be hazardous, and traditional filtration methods are energy-intensive. These methods often rely on metal-capturing membranes, which can clog and require frequent replacement. Researchers have turned to plants for inspiration, as plants protect their cells by encasing metal ions in a polysaccharide barrier made of repeating sugar units.
In a recent study, sticky polysaccharide extracts from plants like aloe and okra were used to filter microplastics from wastewater. However, some polysaccharides dissolve in water, requiring additional components to form insoluble gels that can trap and remove metals.
Cassandra Callmann and her research team at the University of Texas in Austin aimed to develop a single material with sugar-like structures and adjustable water solubility to remove heavy metals from water.
The team designed several polymers featuring water-soluble carbohydrates attached to an insoluble backbone, like charms on a bracelet. Preliminary experiments showed that a carboxylic acid group on one carbohydrate "charm" was particularly effective at attracting and binding ionic cadmium.
In tests with water spiked with ionic cadmium, the polymer containing carboxylic acid formed visible clumps within three minutes, which could be easily removed by filtering the solution.
By adjusting the water's pH, the clumps could be dissolved, releasing the cadmium and making the polymer reusable. The material maintained its metal-trapping effectiveness through three cycles of binding, clumping, and redissolving, showing promise as a reusable solution for water purification.
The researchers tested the carbohydrate-containing polymer on Colorado River water spiked with ionic lead and cadmium as a proof-of-concept. In this sample, ionic calcium, sodium, and magnesium were present at much higher concentrations than the other metals.
Over the course of a day, the polymer absorbed small amounts of the other metal ions and removed up to 20 % of the cadmium and 45 % of the lead. The researchers view this novel material as a promising step toward developing more efficient, reusable, and targeted materials for water purification.
The Welch Foundation, the Cancer Prevention Research Institute of Texas, and the National Institutes of Health funded the study.
Journal Reference:
Jeon, S., et al. (2024) Bioinspired, Carbohydrate-Containing Polymers Efficiently and Reversibly Sequester Heavy Metals. ACS Central Science. doi.org/10.1021/acscentsci.4c01010