Ceramic granules made of aluminum oxide were coated with a nanometer-thin layer of copper oxide, as shown here at 5,000-fold magnification (electron microscopy, colored).
Sena Yüzbasi / Empa
Water contaminated with pathogens causes hundreds of thousands of deaths each year in places where water treatment is lacking or poorly functioning. To put an end to this, the availability of clean water for all mankind has been included in the United Nations (UN) Global Sustainability Agenda since 2015. In accordance with this goal, Empa researchers, in collaboration with their colleagues at Eawag, are developing new materials and technologies to remove pathogens from drinking water, which until now could hardly be eliminated with conventional measures, or only with expensive and complex processes.
The researchers are aiming at the smallest of germs: Tiny pathogens that – unlike the currently circulating coronavirus Sars-Cov-2 – are spreading via contaminated water and thus cause various water-borne diseases such as polio, diarrhea and hepatitis. Among these pathogens is the rotavirus, which is only about 70 nm in size. "Conventional water filters are ineffective against rotaviruses," explains Empa researcher Thomas Graule from Empa's High Performance Ceramics lab in Dübendorf. However, it is precisely these tiny germs that are among the most common pathogens causing gastrointestinal infections. According to the World Health Organization (WHO), in 2016 around 130,000 children worldwide died from rotavirus infections. The researchers have now developed strategies for filtration technologies based on new materials that cleverly circumvent the problem of minuteness.
Porous nanocoating
In order to develop filter technologies that can capture viruses at the nanometer scale, Graule is focusing on composite materials that are functionalized in such a way that they specifically bind viruses. "In water, the surface of the virus particles is negatively charged. We were able to show how the virus particles attach themselves to positively charged surfaces," he explains. For example, the researcher is working in an international team on ceramic granules made of aluminum oxide, whose fine granules are coated with nanometer-thin layers of copper oxide. "Together with the ceramic, the highly porous copper layer forms a composite material with a positively charged and immensely large specific surface," says Graule. The researchers were also able to coat tiny multi-layer carbon nanotubes with copper oxide, thus enabling virus elimination.