A team of scientists led by Professor Jian-Ku Shang from the Institute of Metal Research and the University of Illinois at Urbana-Champaign recently developed a new class of antimicrobial materials. These materials can be activated by solar or visible light. The activation produces a great amount of strong oxidants, hydroxyl radicals, which attack cell membranes and walls, resulting in rapid death of various microorganisms by photodisinfection. The team found that addition of trace amount of palladium oxide nanoparticles can effectively control the photoelectron transfer on the surface of a semiconductor oxide, which not only accelerates the microbial killing greatly, but also induces a catalytic memory effect. Consequently, these materials still demonstrate strong antimicrobial effect up to 20 hours after the light activation is switched off, thus creating a unique “photodisinfection in the dark” feature. The discovery of the catalytic memory effect eliminates a fundamental constraint of all traditional photodisinfection technologies, namely the basic requirement of constant light exposure, thus widening the field of applications for photodisinfection process. It also enables the continuous disinfection, day and night, of water using natural light, with a great potential for significant energy savings in water treatment. Their results were recently published in the Journal of Materials Chemistry. The demonstration of photodisnfection in the dark has drawn attention from a great number of research and news organizations around the world,and the article was one of the ten most downloaded Journal of Materials Chemistry articles for February 2010. (http://www.rsc.org/Publishing/Journals/jm/top10.asp)

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