Discarded plastic packaging materials, old CDs, and even LEGO bricks can be transformed into materials that capture significant amounts of moisture from the air. Materials chemists Anastasiia Naryshkina, Paul Schweng and Robert Woodward at the University of Vienna have converted several types of plastic waste into water-attracting polymer networks that take up water even in dry climates and release it again under moderate heating, e.g. using sunlight. The study, to be published in Chem Circularity, offers a route to give plastic waste a second life as an adsorbent for atmospheric water harvesting.
Plastic waste and water scarcity are both major environmental challenges. Atmospheric water harvesting captures water vapour directly from air for triggered re-release and collection, offering promise as a decentralised or off-grid supplementary water source. A suitable adsorbent for water harvesting must attract moisture, be able to hold large quantities of it, and withstand repeated capture-and-release cycles. The Vienna team investigated whether discarded plastics could provide the starting material for these molecular sponges.
Certain plastics comprise of aromatic polymers, whose molecular structures contain rings of six carbon molecules. These rings act as suitable sites from which to tie the polymer chains together, forming a porous network with tiny internal spaces. A subsequent treatment with sulfuric acid adds sulfonic acid groups that attract water even from relatively dry air. The researchers successfully produced such water-loving molecular sponges from various polystyrene packaging materials, old CDs made from polycarbonate, and LEGO bricks made of acrylonitrile butadiene styrene as feedstock. They also successfully treated a selected mixture of waste plastics, demonstrates versatility across these feedstocks.
As an example, the sponge made from general purpose polystyrene, the stuff single-use cutlery and CD cases are made from, could adsorb almost 60% of its own weight in water from humid air and even 20% in dry, desert-like conditions. The water can then be re-released for collection using mild heat sources, such as sunlight with most adsorption/desorption occuring within one hour. The sponges withstand the cycling process well, meaning they can be used to generate water over and over again.
The work establishes a way to turn several aromatic waste plastics into effective materials for the generation of water from air, including mixed plastic feedstocks. Further work into assessing the long-term performance and overall resource requirements of the sponges is ongoing.
Summary:
- Various waste plastics, such as packaging materials, CDs, and LEGO bricks can be transformed into materials that capture moisture from air for collection.
- Mixed plastic feedstocks could also be used to produce the water-capturing materials.
- The materials capture water even in dry conditions and release it upon mild heated, allowing for off-grid water supplies.
- Water capture and release experiments showed repeated use is possible, but detailed testing is ongoing.
About the University of Vienna:
For over 650 years the University of Vienna has stood for education, research and innovation. Today, it is ranked among the top 100 and thus the top four per cent of all universities worldwide and is globally connected. With degree programmes covering 188 disciplines, and approximately 11,000 employees, we are one of the largest academic institutions in Europe. Here, people from a broad spectrum of disciplines come together to carry out research at the highest level and develop solutions for current and future challenges. Its students and graduates develop reflected and sustainable solutions to complex challenges using innovative spirit and curiosity.
