Hydrophilic ZnO nanorods arrays were fabricated by Akhavan et al. (2009) by
hydrothermal route and the effect of photoinduced antibacterial activity was
observed towards E.coli. The hydrophilic behavior of the ZnO nanorods arrays is
attributed to the formation of surface hydroxyl groups and is responsible for the
increased antibacterial property.
Amir et al. (Hatamie et al. 2015) have developed a ZnO modified textile by a
hydrothermal route and investigated its photocatalytic and antibacterial activity as a
replacement for commercial silver loaded textiles. An antimicrobial packaging film
was developed by Li et al. (2009) where ZnO nanoparticles were coated on polyvinyl chloride film showed better antibacterial activity towards E.Coli and S. aeurus
with more resistance to S aeurus. A size dependent antibacterial activity for ZnO
nanoparticles towards S. aureus under ambient light conditions was demonstrated by
Raghupathi and coworkers (2011), where the antibacterial efficiency was decreasing
with increase in the particle size. Reactive oxygen species generation and aggregation of nanoparticles in the cytoplasm was claimed as the main reason for the
antibacterial effect of the solvo-thermally fabricated ZnO nanoparticles. Similarly
shape controlled ZnO nanoparticles were fabricated by Sarika and coworkers by a
soft chemical synthesis route (Singh et al. 2013). Cauliflower like ZnO
nanostructures showed an effective light induced antibacterial activity towards
S. aureus in contaminated water under UV irradiation. All these investigations
showed that nanostructuring play an important role in the antibacterial effect of
ZnO nanoparticles by improving the surface area which helps in increasing the
contact area. The improved area also plays an important role in the production of
reactive oxygen species responsible for photocatalytic antibacterial efficiency. Also,
controlling the size and shape of the nanoparticles influences the mode of cell wall
destruction.
2.5.2.2 Doped ZnO
As discussed in the previous section, ZnO can absorb only UV light due to its wide
band gap nature (3.3 eV) which hinders its commercial utility. Doping of ZnO by
cationic and anionic species to alter the band gap is found to be an effective approach
to enhance the light absorption range (Djerdj et al. 2010; Lin et al. 2005). In this
direction, Manjula and coworkers (Nair et al. 2011) developed Cobalt (Co) doped
ZnO for the photocatalytic organic decontamination and microbial destruction. Very
good bacterial destruction efficiency was observed by the group using Co doped
ZnO for all the bacterial strains chosen for investigation (Escherichia coli, Klebsiella
pneumoniae, Shigella dysenteriae, Salmonella typhi, Pseudomonas aeruginosa,
Bacillus subtilis and Staphylococcus aureus). Doping noble metals such as silver,
gold and platinum is an effective approach due to the improvement in the
photogenerated charge separation process by scavenging the photogenerated electron by noble metals. Bechambi et al. (2015) developed Ag doped ZnO
nanostructures for photocatalytic applications and observed 100% destruction of
E.coli in 40 min using 1% Ag doping. The improved microbial destruction efficiency
2 Photo-Assisted Antimicrobial Activity of Transition Metal Oxides
45
hydrothermal route and the effect of photoinduced antibacterial activity was
observed towards E.coli. The hydrophilic behavior of the ZnO nanorods arrays is
attributed to the formation of surface hydroxyl groups and is responsible for the
increased antibacterial property.
Amir et al. (Hatamie et al. 2015) have developed a ZnO modified textile by a
hydrothermal route and investigated its photocatalytic and antibacterial activity as a
replacement for commercial silver loaded textiles. An antimicrobial packaging film
was developed by Li et al. (2009) where ZnO nanoparticles were coated on polyvinyl chloride film showed better antibacterial activity towards E.Coli and S. aeurus
with more resistance to S aeurus. A size dependent antibacterial activity for ZnO
nanoparticles towards S. aureus under ambient light conditions was demonstrated by
Raghupathi and coworkers (2011), where the antibacterial efficiency was decreasing
with increase in the particle size. Reactive oxygen species generation and aggregation of nanoparticles in the cytoplasm was claimed as the main reason for the
antibacterial effect of the solvo-thermally fabricated ZnO nanoparticles. Similarly
shape controlled ZnO nanoparticles were fabricated by Sarika and coworkers by a
soft chemical synthesis route (Singh et al. 2013). Cauliflower like ZnO
nanostructures showed an effective light induced antibacterial activity towards
S. aureus in contaminated water under UV irradiation. All these investigations
showed that nanostructuring play an important role in the antibacterial effect of
ZnO nanoparticles by improving the surface area which helps in increasing the
contact area. The improved area also plays an important role in the production of
reactive oxygen species responsible for photocatalytic antibacterial efficiency. Also,
controlling the size and shape of the nanoparticles influences the mode of cell wall
destruction.
2.5.2.2 Doped ZnO
As discussed in the previous section, ZnO can absorb only UV light due to its wide
band gap nature (3.3 eV) which hinders its commercial utility. Doping of ZnO by
cationic and anionic species to alter the band gap is found to be an effective approach
to enhance the light absorption range (Djerdj et al. 2010; Lin et al. 2005). In this
direction, Manjula and coworkers (Nair et al. 2011) developed Cobalt (Co) doped
ZnO for the photocatalytic organic decontamination and microbial destruction. Very
good bacterial destruction efficiency was observed by the group using Co doped
ZnO for all the bacterial strains chosen for investigation (Escherichia coli, Klebsiella
pneumoniae, Shigella dysenteriae, Salmonella typhi, Pseudomonas aeruginosa,
Bacillus subtilis and Staphylococcus aureus). Doping noble metals such as silver,
gold and platinum is an effective approach due to the improvement in the
photogenerated charge separation process by scavenging the photogenerated electron by noble metals. Bechambi et al. (2015) developed Ag doped ZnO
nanostructures for photocatalytic applications and observed 100% destruction of
E.coli in 40 min using 1% Ag doping. The improved microbial destruction efficiency
2 Photo-Assisted Antimicrobial Activity of Transition Metal Oxides
45