Enhanced photocatalytic disinfection of indoor air Amit Vohra * , D.Y. Goswami, D.A. Deshpande, S.S. Block Solar Energy and Energy Conversion Laboratory, Department of Mechanical and Aerospace Engineering, University of Florida, Gainesville, FL 32611, USA Received 18 May 2005; received in revised form 19 September 2005; accepted 24 October 2005 Available online 15 December 2005 Abstract A silver ion doped TiO 2 based photocatalyst, with improved destruction of airborne microbes, has been developed. The performance of the silver ion doped photocatalyst is demonstrated using a catalyst coated filter in a recirculating air experimental facility. Bacillus cereus, Staphylococcus aureus, Escherichia coli, Aspergillus niger, and MS2 Bacteriophage have been used as indexes to demonstrate the high disinfection efficiency of the enhanced photocatalysis process. The microbial destruction performance of the enhanced photocatalyst is found to be an order of magnitude higher than that of a conventional TiO 2 photocatalyst. The process of enhanced photocatalysis can thus be used effectively against high concentrations of airborne microorganisms, making it an attractive option as a defense against bio-terrorism. # 2005 Elsevier B.V. All rights reserved. Keywords: Photocatalysis; Disinfection; Indoor air; Airborne microorganisms; Silver ions 1. Introduction Air Filtration and Purification World Markets predicted that the world market for air filters would rise to US $5 billion in 2005. This rise can be attributed to the security efforts to counter chemical and biological terrorism, as well as the increased awareness of the people towards environment and environmental pollution. In 2000, a document published by the World Health Organization (WHO) stressed that it is our human right to breathe healthy indoor air [1]. It further emphasizes that ensuring acceptable indoor air quality is the responsibility of all concerned. A study done by the US Environmental Protection Agency (EPA) in 1987 concluded that indoor air pollution poses a greater risk than outdoor air pollution [2]. This indoor air pollution is estimated to be the cause of several health related issues and reduced work productivity among people. Allergies and diseases such as asthma and sick building syndrome (SBS) have increased considerably over the last few decades. A recently concluded European survey of around 140,000 individuals in 22 countries shows that this increase is dependent on the environment and the lifestyle of the individuals. Because most of the Americans spend a substantial amount of time indoors, indoor air contamination poses a serious threat to them. Microbial agents in indoor air are considered a serious health hazard and therefore microbial contamination of indoor air has been the major topic of attention in recent times [3]. One of the biggest disease outbreaks due to microbial contamination of indoor air was the Legionnaires’ disease outbreak in Philadelphia in 1976 [4]. Also, the recent bio-terrorism threat due to anthrax has fueled huge interest in new technologies for indoor air disinfection. Advanced oxidation technologies, in particular the photo- catalytic technology offers several environmental and practical advantages over conventional biological or physical disinfec- tion processes. The huge interest generated by photocatalysis has motivated several researchers to look into the basic mode of action of TiO 2 . TiO 2 is a semiconductor with a band gap close to 3.2 eV. UV light with wavelengths shorter than 380 nm photoactivates TiO 2 by providing the band gap energy needed by an electron to jump from the valence band to the conduction band. This implies that when photons of UV light are absorbed on TiO 2 , they generate excited pairs of electrons and holes. The photogenerated holes react with the water to produce hydroxyl radicals (  OH), while the photogenerated electrons react with molecular oxygen to give superoxide radical anions (  O 2  ). These radicals so produced are highly reactive and they work together to completely oxidize the organic species. The attack by the  OH radical, in the presence of oxygen, thus initiates a www.elsevier.com/locate/apcatb Applied Catalysis B: Environmental 65 (2006) 57–65 * Corresponding author. Tel.: +1 352 392 2328; fax: +1 352 846 1630. E-mail address: amitvohr@ufl.edu (A. Vohra). 0926-3373/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.apcatb.2005.10.025