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Use of TiO2 photocatalytic process for removal of airborne organic pollutants, VOCs appear to be superior to traditional technologies.
Applications of Photocatalytic Disinfection - HindawiJoanne Gamage, and Zhisheng Zhang

Department of Chemical and Biological Engineering, University of Ottawa, 161 Louis Pasteur, Ottawa, ON, K1N6N5, Canada

The photocatalytic process is well recognized for the removal of organic pollutants in the gaseous phase such as volatile organic compounds (VOCs), has great potential applications to contaminant control in indoor environments such as residences, office buildings, factories, aircraft, and spacecraft [4041].

To increase the scope of the photocatalytic process in application to indoor air, the disinfection capabilities of this technique are under investigation [39]. Disinfection is of importance in indoor air applications because of the risk of exposure to harmful airborne contaminants. Bioaerosols are a major contributor to indoor air pollution, and more than 60 bacteria, viruses, and fungi are documented as infectious airborne pathogens. Diseases transmitted via bioaerosols include tuberculosis, Legionaries, influenza, colds, mumps, measles, rubella, smallpox, aspergillosis, pneumonia, meningitis, diphtheria, and scarlet fever [42]. Traditional technologies to clean indoor air include the use of activated charcoal filters, HEPA filters, ozonation, air ionization, and guard filters. None of these technologies is completely effective [20].

In the pioneering work by Goswami et al. [4344] investigating the disinfection of indoor air by photocatalysis, a recirculating duct facility was developed to inactivate biological contaminants in the air with photocatalytic techniques. Experiments using Serratia Marcescens in the air achieved a 100% destruction of microorganisms in a recirculating loop in 600 minutes [43]. This time was reduced to less than 3 minutes in later experiments [45].

Photocatalytic oxidation can also inactivate infectious microorganisms which can be airborne bioterrorism weapons, such as Bacillus anthracis (Anthrax) [4648]. A photocatalytic system was investigated by Knight in 2003 to reduce the spread of severe acute respiratory syndrome (SARS) on flights [49], following the outbreak of the disease. Similarly, in 2007 the avian influenza virus A/H5N2 was shown to be inactivated from the gaseous phase using a photocatalytic prototype system [39].

 Effective Photocatalytic Disinfection of E. coli K-12 Using AgBr−Ag−Bi2WO6Nanojunction System Irradiated by Visible Light: The Role of Diffusing Hydroxyl …
LS Zhang, KH Wong, HY Yip, C Hu, JC Yu… - … science & technology, 2010 - ACS Publications
Urgent development of effective and low-cost disinfecting technologies is needed to address the problems caused by an outbreak of harmful microorganisms. In this work, we report effective photocatalytic disinfection of E. coli K-12 by using an AgBr−Ag−Bi2WO6 nano junction system as a catalyst under visible light (λ ≥ 400 nm) irradiation. The visible-light-driven (VLD) AgBr−Ag−Bi2WO6 nano junction could completely inactivate 5 × 107 CFU mL−1 E. coli K-12 within 15 min, which was superior to other VLD photocatalysts such as Bi2WO6 superstructure, Ag−Bi2WO6, and AgBr−Ag−TiO2 composite. Moreover, the photochemical mechanism of bactericidal action for the AgBr−Ag−Bi2WO6 nano junction was investigated by using different scavengers. It was found that the diffusing hydroxyl radicals generated both by the oxidative pathway and the reductive pathway play an important role in the photocatalytic disinfection. Moreover, direct contact between the AgBr−Ag−Bi2WO6 nano junction and bacterial cells was not necessary for the photocatalytic disinfection of E. coli K-12. Finally, the photocatalytic destruction of the bacterial cells was directly observed by TEM images and further confirmed by the determination of potassium ion (K+) leakage from the killed bacteria. This work provides a potential effective VLD photocatalyst to disinfect the bacterial cells, even to destruct the biofilm that can provide shelter and substratum for microorganisms and resist disinfection.

Due to the superior ability of photocatalysis to inactivate a wide range of harmful microorganisms, it is being examined as a viable alternative to traditional disinfection methods such as chlorination, which can produce harmful byproducts. Photocatalysis is a versatile and effective process that can be adapted for use in many applications for disinfection in both air and water matrices. Additionally, photocatalytic surfaces are being developed and tested for use in the context of “self-disinfecting” materials. Studies on the photocatalytic technique for disinfection demonstrate this process to have the potential for widespread applications in indoor air and environmental health, biological, and medical applications, laboratory and hospital applications, pharmaceutical and food industry, plant protection applications, wastewater, and effluents treatment, and drinking water disinfection. Studies on photocatalytic disinfection using a variety of techniques and test organisms are reviewed, with an emphasis on the end-use application of developed technologies and methods.