Water contaminated with heavy metals can be hazardous to both human health and aquatic ecosystems. Plant-derived sugar polymers have the capability to eliminate these metals but often need additional compounds to enhance their stability or solubility in water. Researchers have recently introduced a sugar-like polymer that encapsulates heavy metals into insoluble clusters, making them easier to extract. In initial experiments, this polymer successfully eliminated ionic cadmium and lead from river water artificially contaminated with these long-lasting pollutants.
Water contaminated with heavy metals can be hazardous to both humans and wildlife. While sugar-based polymers from plants can help remove these metals, they typically require other chemicals to improve their stability or solubility in water. Researchers in ACS Central Science have now reported a sugar-like polymer that effectively confines heavy metals in insoluble clusters for straightforward extraction. In experimental trials, the polymer successfully removed ionic cadmium and lead from river water that was spiked with these enduring contaminants.
High concentrations of certain heavy metal ions in drinking water can be harmful. Traditional methods for purifying water, such as filtration, can demand significant energy and often depend on metal-capturing membranes that can clog rapidly and need frequent replacement. To enhance the purification process, scientists have begun exploring the use of plants. Plants protect their cells with a layer of polysaccharides, which are large molecules formed from repeated sugar units, capable of capturing metal ions. For instance, a recent study employed adhesive polysaccharide extracts from okra and aloe to extract microplastics from wastewater. However, some polysaccharides dissolve in water, necessitating the addition of other substances to create insoluble gels for effective metal capture. This prompted Cassandra Callmann and her research team at the University of Texas at Austin to create a unified material with sugar-like components and adjustable water solubility for the removal of heavy metals from water.
The team developed various polymers featuring a water-insoluble core with different water-soluble carbohydrates attached like charms on a bracelet. Initial experiments revealed that the carbohydrate “charm” optimized for binding ionic cadmium included a carboxylic acid group. During tests with ionic cadmium-laden water, the polymer with the carboxylic acid formed visible clusters within three minutes, which could be filtered out. These clusters could also dissolve back into water, releasing the cadmium when the acidity of the water was adjusted. After three cycles of binding, clustering, and redissolving, the polymer maintained its efficiency in trapping metals, showcasing its potential as a recyclable material.
As a proof-of-concept, the team evaluated the carbohydrate-containing polymer on Colorado River water spiked with ionic cadmium and lead. The river water naturally contained significantly higher levels of ionic calcium, sodium, and magnesium compared to the added metals. Over a 24-hour duration, the polymer effectively captured up to 20% and 45% of the introduced cadmium and lead, respectively, while only minimal amounts of the other metal ions were absorbed. The researchers believe that their innovative material represents a significant advancement towards more efficient, reusable, and selective options for water purification.
The authors express gratitude for funding from the Welch Foundation, the Cancer Prevention Research Institute of Texas, and the National Institutes of Health.
