2.1 Introduction
Pathogens and microbes can spread diseases in human beings through air, water and
contaminated surfaces. Disinfection processes of these contaminated surfaces are
gaining high importance in order to maintain hygienic work practice and day to day
life activities. The case is more severe in health care centers where the contaminated
surfaces are frequently handled and have a proximity and interaction with patients.
There are different disinfections strategies adopted to prevent the contamination
such as sterilization, adsorption, antibiotics, biocides etc. Pathogens such as
S. aureus, Escherichia Coli and Pseudomonas aeruginosa can contaminate the dry
surfaces and can survive for several weeks to months (Kramer et al. 2006). To
prevent pathogenic infections from contaminated surfaces, generally antimicrobial
agents are coated on the medical devices or incorporated into coating which also
includes metals such as silver and copper. There is a need for alternative approaches
due to the following reasons
(a) Development of microbial resistance to metal ion coating with time
(b) Lack of enough efficacy in complete disinfection as the metals can kill the
bacteria but cannot destruct the endotoxins
(c) High cost of the coatings and related products
Among various alternative approaches, semiconductor based photocatalytic sterilization is found to be an effective approach for disinfection. This is because, the
photogenerated holes, the hydroxyl radicals and the superoxide radicals in the
semiconductor can exhaustively destruct biological molecules such as proteins,
lipids, enzymes and nucleic acids through a series of oxidative chain reactions.
The oxidative power of these photogenerated radicals possess oxidation energy of
120 Kcal mol
À1 , which is sufficient to break the chemical bonds in the above
mentioned organic compounds (Dunlop et al. 2010). Moreover, the nonspecific
nature of reactive oxygen species attack the cell structures of the outer layer of the
pathogens makes it unlikely for the emergence of resistance towards photocatalytic
disinfection (Goulhen-Chollet et al. 2009). Further, the utilization of earth abundant
semiconducting materials and sunlight, the cost effectiveness, and the viability for
commercialization makes the photocatalytic material-based disinfection, an effective
strategy.
The most common semiconductors investigated for photocatalytic disinfection
are TiO 2 , ZnO, CdS, CuO etc. TiO 2 is one of the most widely explored semiconducting materials in the field of photocatalytic disinfection. Appropriate band alignment, low cost and abundant availability makes it a suitable candidate for the same.
Commercially available form of TiO 2 , known as Degussa P25 is the most explored
one in this aspect. ZnO is another wide band gap semiconducting material having
wurtzite crystal structure and have similar properties like TiO 2 . Hence, it also finds
wide applications in the field of photocatalytic water splitting, hydrogen generation,
sensors, antibacterial activity and photo assisted organic destruction.
30
R. P. Antony et al.
Pathogens and microbes can spread diseases in human beings through air, water and
contaminated surfaces. Disinfection processes of these contaminated surfaces are
gaining high importance in order to maintain hygienic work practice and day to day
life activities. The case is more severe in health care centers where the contaminated
surfaces are frequently handled and have a proximity and interaction with patients.
There are different disinfections strategies adopted to prevent the contamination
such as sterilization, adsorption, antibiotics, biocides etc. Pathogens such as
S. aureus, Escherichia Coli and Pseudomonas aeruginosa can contaminate the dry
surfaces and can survive for several weeks to months (Kramer et al. 2006). To
prevent pathogenic infections from contaminated surfaces, generally antimicrobial
agents are coated on the medical devices or incorporated into coating which also
includes metals such as silver and copper. There is a need for alternative approaches
due to the following reasons
(a) Development of microbial resistance to metal ion coating with time
(b) Lack of enough efficacy in complete disinfection as the metals can kill the
bacteria but cannot destruct the endotoxins
(c) High cost of the coatings and related products
Among various alternative approaches, semiconductor based photocatalytic sterilization is found to be an effective approach for disinfection. This is because, the
photogenerated holes, the hydroxyl radicals and the superoxide radicals in the
semiconductor can exhaustively destruct biological molecules such as proteins,
lipids, enzymes and nucleic acids through a series of oxidative chain reactions.
The oxidative power of these photogenerated radicals possess oxidation energy of
120 Kcal mol
À1 , which is sufficient to break the chemical bonds in the above
mentioned organic compounds (Dunlop et al. 2010). Moreover, the nonspecific
nature of reactive oxygen species attack the cell structures of the outer layer of the
pathogens makes it unlikely for the emergence of resistance towards photocatalytic
disinfection (Goulhen-Chollet et al. 2009). Further, the utilization of earth abundant
semiconducting materials and sunlight, the cost effectiveness, and the viability for
commercialization makes the photocatalytic material-based disinfection, an effective
strategy.
The most common semiconductors investigated for photocatalytic disinfection
are TiO 2 , ZnO, CdS, CuO etc. TiO 2 is one of the most widely explored semiconducting materials in the field of photocatalytic disinfection. Appropriate band alignment, low cost and abundant availability makes it a suitable candidate for the same.
Commercially available form of TiO 2 , known as Degussa P25 is the most explored
one in this aspect. ZnO is another wide band gap semiconducting material having
wurtzite crystal structure and have similar properties like TiO 2 . Hence, it also finds
wide applications in the field of photocatalytic water splitting, hydrogen generation,
sensors, antibacterial activity and photo assisted organic destruction.
30
R. P. Antony et al.