To have fresh, clean water flowing directly from the tap is a real luxury. In developing countries, people often have no choice but to drink contaminated water. Water filters can help to alleviate this problem by quickly transforming contaminated surface or ground water into safe drinking water. In the journal Angewandte Chemie, researchers have now presented a new, multifunctional composite material that is capable of removing inorganic, organic, radioactive and microbial contaminants from water.
Water treatment systems typically involve a series of filters, each of which is designed to target a specific group of contaminants. The new filter material, however, is an all-round talent. Researchers from the Universities of Ulm and Zaragoza (Spain) have taken up a new approach to material design, in which molecular components are joined to form multifunctional composites called SILP materials (supported ionic liquid phases). An ionic liquid is a salt that is in a liquid state at room temperature without having been dissolved in a solvent. When the ionic liquid is adsorbed onto a solid substrate, it results in a solid composite material with properties that can be selectively adjusted via chemical modifications to each individual component.
Researchers in Scott G Mitchell and Carsten Streb’s team have now produced the first polyoxometalate (POM)-based SILPs. POMs are molecular transition metal-oxygen clusters in which the metal atoms are bridged by oxygen atoms to create a three-dimensional framework. The researchers used polyoxotungstate anions for the filter material. These anions have a bonding site to which heavy metal ions can be attached. Voluminous tetraalkylammonium cations, known for their antimicrobial effect, were selected as counterions. The resulting ionic liquids are hydrophobic, cannot be mixed with water and form stabile, thin layers on surfaces. Using porous silicon dioxide as a support, the researchers were able to obtain dry, free-flowing powders that are easy to transport and handle.
In laboratory tests, the anions of the new composites reliably removed lead, nickel, copper, chromium and cobalt ions. Radioactive uranium in the form of UO22 was trapped directly by the silicon dioxide support. A water-soluble blue trityl dye typically used in the textile industry was also removed, trapped in the ionic liquid due to its lipophilic character. The antimicrobial cations effectively stopped the growth of coli bacteria.
The scientists hope that their new “POM-SILP” filter materials will serve as a springboard for developing chemically designed, contaminant-specific filtration systems that can be used to safely treat water in remote areas and developing countries, or following natural disasters and chemical accidents.
Carsten Streb, Universität Ulm (Deutschland)
Entfernung von organischen, anorganischen und mikrobiellen Schadstoffen aus Wasser durch immobilisierte Polyoxometallat-ionische Flüssigkeiten (POM-SILPs), doi: 10.1002/ange.201611072