doping. Both the processes, lead to the cell wall destruction and decomposition of
cellular materials.
The transition metals like manganese and cobalt can increase the surface defects
and alter the electronic band structures leading to improvement in the visible light
activity of ZnO. Rekha et al. (2010) adopted the strategy of doping different
percentage of manganese in the Zn lattice of ZnO using co precipitation route. The
samples showed a better antibacterial activity compared to the pristine one. Similarly, Co doped ZnO thin films fabricated by sol-gel spin coating route by Poongodi
et al. (2015) displayed efficient bactericidal activity towards E. coli and S. aureus.
Like other studies, the enhanced activity was attributed to the improved charge
separation efficiency and reactive oxygen species generation. Surface modified
metals ions on ZnO type materials can induce an interfacial charge transfer
(IFCT), where photogenerated electrons from dopant levels to the surface dopant
ions play a major role in enhancing microbial destruction efficiency under visible
light activity.
Guo et al. fabricated Tantalum doped ZnO investigated by modified pechini type
method (Guo et al. 2015). It was observed by the group that incorporation of 5% of
Ta
5+ into ZnO improved the visible light bactericidal effect towards P. aeruginosa,
E. coli, and S. aureus. Hameed et al. studied the doping effect of Nd into ZnO
towards the inactivation of E. coli and K. pneumonia (Hameed et al. 2016). Rare
earth element doping is another approach which can improve the visible light
activity and photogenerated charge separation efficiency. Bomila and coworkers
developed La, a rare earth element doped ZnO nanoparticles by wet chemical route
for the visible light photocatalytic applications (Bomila et al. 2018). Er/Nd doped
ZnO was developed by Raza et al. using sol-gel technique (Raza et al. 2016).
Improved visible light activity for doped samples was observed and exhibited
improved anticancer and antimicrobial activity compared to the pristine samples
(Fig. 2.9C).
2.5.2.3 Metal Loaded ZnO
Constructing metal-semiconductor hybrid structures is an effective way to tackle
absorption and recombination problems in semiconductors for better photocatalytic
efficiency. The noble metal loading in metal-semiconductor composite play a crucial
role in extending visible light absorption capabilities of wide band gap semiconductors and increasing lifetime of photogenerated charge carriers by scavenging the
photogenerated electrons thereby making photogenerated holes available for
photocatalytic disinfection process. Also, the noble metals such as Ag and Au
generate photogenerated electron hole pairs by a process called surface plasmon
resonance (SPR).
He and coworkers (2014) fabricated Au-ZnO hybrid nanostructures by a photoreduction method to obtain smaller nanoparticles. S. aureus and E. coli were chosen
as the model microbes to study the antibacterial effect under simulated sunlight
(Fig. 2.10A). The photocatalytic effect of Au nanoparticles alone showed
2 Photo-Assisted Antimicrobial Activity of Transition Metal Oxides
47
cellular materials.
The transition metals like manganese and cobalt can increase the surface defects
and alter the electronic band structures leading to improvement in the visible light
activity of ZnO. Rekha et al. (2010) adopted the strategy of doping different
percentage of manganese in the Zn lattice of ZnO using co precipitation route. The
samples showed a better antibacterial activity compared to the pristine one. Similarly, Co doped ZnO thin films fabricated by sol-gel spin coating route by Poongodi
et al. (2015) displayed efficient bactericidal activity towards E. coli and S. aureus.
Like other studies, the enhanced activity was attributed to the improved charge
separation efficiency and reactive oxygen species generation. Surface modified
metals ions on ZnO type materials can induce an interfacial charge transfer
(IFCT), where photogenerated electrons from dopant levels to the surface dopant
ions play a major role in enhancing microbial destruction efficiency under visible
light activity.
Guo et al. fabricated Tantalum doped ZnO investigated by modified pechini type
method (Guo et al. 2015). It was observed by the group that incorporation of 5% of
Ta
5+ into ZnO improved the visible light bactericidal effect towards P. aeruginosa,
E. coli, and S. aureus. Hameed et al. studied the doping effect of Nd into ZnO
towards the inactivation of E. coli and K. pneumonia (Hameed et al. 2016). Rare
earth element doping is another approach which can improve the visible light
activity and photogenerated charge separation efficiency. Bomila and coworkers
developed La, a rare earth element doped ZnO nanoparticles by wet chemical route
for the visible light photocatalytic applications (Bomila et al. 2018). Er/Nd doped
ZnO was developed by Raza et al. using sol-gel technique (Raza et al. 2016).
Improved visible light activity for doped samples was observed and exhibited
improved anticancer and antimicrobial activity compared to the pristine samples
(Fig. 2.9C).
2.5.2.3 Metal Loaded ZnO
Constructing metal-semiconductor hybrid structures is an effective way to tackle
absorption and recombination problems in semiconductors for better photocatalytic
efficiency. The noble metal loading in metal-semiconductor composite play a crucial
role in extending visible light absorption capabilities of wide band gap semiconductors and increasing lifetime of photogenerated charge carriers by scavenging the
photogenerated electrons thereby making photogenerated holes available for
photocatalytic disinfection process. Also, the noble metals such as Ag and Au
generate photogenerated electron hole pairs by a process called surface plasmon
resonance (SPR).
He and coworkers (2014) fabricated Au-ZnO hybrid nanostructures by a photoreduction method to obtain smaller nanoparticles. S. aureus and E. coli were chosen
as the model microbes to study the antibacterial effect under simulated sunlight
(Fig. 2.10A). The photocatalytic effect of Au nanoparticles alone showed
2 Photo-Assisted Antimicrobial Activity of Transition Metal Oxides
47