Researchers in Austria have developed a special nanostructure to filter a widespread class of harmful dyes from water.
- A crucial component of this nanostructure is a material that is considered waste: used cellulose, for example in the form of cleaning cloths or paper cups. The cellulose is utilised to coat a fine nano-fabric to create an efficient filter for polluted water.
THE RESEARCH: The project has been conducted at the TU Wien, also known as the Vienna University of Technology. The findings have been published in the journal Small Science.
- The authors of the paper are Qaisar Maqbool, Isabella Cavallini, Niusha Lasemi, Simona Sabbatini,Francesca Tittarelli, and Günther Rupprechte.
THE PROBLEM OF POISON IN THE WATER: Organic dyes represent the largest group of synthetic dyes, including so-called azo compounds. They are widely used in the textiles industry, even in countries where little attention is paid to environmental protection, and the dyes often end up in unfiltered wastewater.
- This is dangerous because such dyes degrade very slowly, they can remain in the water for a long time and pose great danger to humans and nature.
- There are various materials that can bind such dyes. But that alone is not enough. If one simply lets the polluted water flow over a filter film that can bind dyes, the cleaning effect is low.
- The researchers established that it is much better to create a nanofabric out of lots of tiny fibres and let the water seep through. The water then comes into contact with a much larger surface area, and thus many more organic dye molecules can be bound.
CELLULOSE WASTE AS A NANO-FILTER: The researchers are working with semi-crystalline nanocellulose, which can be produced from waste material.
- Metal-containing substances are often used for similar purposes. The new material, on the other hand, is harmless to the environment, and can also be produced by upcycling waste paper.
- This nanocellulose is "spun" together with the plastic polyacrylonitrile into nanostructures. However, this requires a lot of technical skill. The research team was successful with a electrospinning process. In this process, the material is sprayed in liquid form, the droplets are electrically charged and sent through an electric field.
- This ensures that the liquid forms extremely fine threads with a diameter of 180 to 200 nanometres during curing. These threads form a fine tissue with a high surface area—a so-called "nanoweb." A network of threads can be placed on one square centimetre, with a total surface area of more than 10 sq cm.
SUCCESSFUL TESTS: The tests with these cellulose-coated nanostructures were very successful: In three cycles, water contaminated with violet dye was purified, and 95% of the dye was removed. The dyes remain stored in the nanoweb. One can then either dispose of the entire web or regenerate it, dissolve the stored dyes and reuse the filter fabric.
- However, more work needs to be done: evaluating the mechanical properties of the sophisticated nanowebs, conducting biocompatibility tests, assessing sensitivity to more complex pollutants, and achieving scalability to industrial-grade standards.
