(Fig. 2.10B). The increase in activity for Au-ZnO was about 3 times higher compared to that of ZnO nanostructures. Lu et al. (2008) employed a tyrosine assisted
one pot hydrothermal synthesis of Ag-ZnO nanocomposite and demonstrated efficient light induced antibacterial efficacy towards gram positive and gram negative
bacteria. Functionalization of textile fabrics using Ag-ZnO nanocomposites were
carried out by Mariana and coworkers (Ibănescu et al. 2014) for effective
photocatalytic and antimicrobial applications. The composites were coated onto to
the fabrics by a pad-dry-cure process followed by treatment under 130
C for
30 minutes. Antimicrobial disc diffusion tests for Ag-ZnO coated fabrics showed
that the antimicrobial efficiency of the modified fabrics increased with increase in Ag
loading. The results were consistent with the photocatalytic dye degradation trend
for the composites. Hence, the production of reactive oxygen species due to
increased surface area was attributed to improved activity of the modified fabrics.
Jin et al. (2019) developed iodine modified ZnO using reflux method to obtain
higher surface oxygen vacancy and higher charge separation efficiency. Smaller
grain size, cage like structure, increased surface oxygen vacancy in nanostructured
I-ZnO (I-ZnO-n) led to improved charge carrier separation and generate more free
radicals for bacterial disinfection. Recently Lam and coworkers (2018) investigated
the bacterial inactivation ability of Ag loaded ZnO micro and nanoflowers synthesized through a surfactant free co-precipitation method followed by photodeposition
route (Fig. 2.10C). The antibacterial effect of the nanoflowers was studied using E.
coli under visible light irradiation. A complete bacterial destruction was obtained
under 180 min visible light irradiation using 5% Ag loaded ZnO micro/nanoflowers
(Fig. 2.10D). In addition, a long term antibacterial activity suppression and cytoplasmic destruction by Ag-ZnO micro/nanoflowers was confirmed by minimum
inhibitory concentration and optical density studies. The photogenerated reactive
oxygen species were identified to be responsible for the cytoplasmic destruction and
cellular leakage of the bacteria and the mechanism proposed by the group is given in
Fig. 2.10E.
2.5.2.4 Composites of ZnO
Proper band alignment of ZnO with other semiconductors favors the photocatalytic
process by improving the photogenerated charge carriers and thereby ROS. Sin et al.
(2018) fabricated ZnO-magnetic Fe 3 O 4 composites by a surfactant free method for
effective bacterial destruction. The resultant composite showed a flower like structure (Fig. 2.11a) and an effective destruction of E. coli was observed under visible
light irradiation compared to pristine ZnO (Fig. 2.11b). The improved charge carrier
recombination time envisaged by photoluminescence studies was attributed to
enhanced effect of the composite photocatalyst. The magnetic property of the
composite was an additional advantage for the efficient separation of the catalyst
after use, makes it suitable for commercial. Graphene like MoS 2 sheets modified
ZnO nanoflowers were developed by Awasthi and coworkers (2016) by a one pot
hydrothermal route. The composites displayed effective antibacterial efficacy
2 Photo-Assisted Antimicrobial Activity of Transition Metal Oxides
49
one pot hydrothermal synthesis of Ag-ZnO nanocomposite and demonstrated efficient light induced antibacterial efficacy towards gram positive and gram negative
bacteria. Functionalization of textile fabrics using Ag-ZnO nanocomposites were
carried out by Mariana and coworkers (Ibănescu et al. 2014) for effective
photocatalytic and antimicrobial applications. The composites were coated onto to
the fabrics by a pad-dry-cure process followed by treatment under 130
C for
30 minutes. Antimicrobial disc diffusion tests for Ag-ZnO coated fabrics showed
that the antimicrobial efficiency of the modified fabrics increased with increase in Ag
loading. The results were consistent with the photocatalytic dye degradation trend
for the composites. Hence, the production of reactive oxygen species due to
increased surface area was attributed to improved activity of the modified fabrics.
Jin et al. (2019) developed iodine modified ZnO using reflux method to obtain
higher surface oxygen vacancy and higher charge separation efficiency. Smaller
grain size, cage like structure, increased surface oxygen vacancy in nanostructured
I-ZnO (I-ZnO-n) led to improved charge carrier separation and generate more free
radicals for bacterial disinfection. Recently Lam and coworkers (2018) investigated
the bacterial inactivation ability of Ag loaded ZnO micro and nanoflowers synthesized through a surfactant free co-precipitation method followed by photodeposition
route (Fig. 2.10C). The antibacterial effect of the nanoflowers was studied using E.
coli under visible light irradiation. A complete bacterial destruction was obtained
under 180 min visible light irradiation using 5% Ag loaded ZnO micro/nanoflowers
(Fig. 2.10D). In addition, a long term antibacterial activity suppression and cytoplasmic destruction by Ag-ZnO micro/nanoflowers was confirmed by minimum
inhibitory concentration and optical density studies. The photogenerated reactive
oxygen species were identified to be responsible for the cytoplasmic destruction and
cellular leakage of the bacteria and the mechanism proposed by the group is given in
Fig. 2.10E.
2.5.2.4 Composites of ZnO
Proper band alignment of ZnO with other semiconductors favors the photocatalytic
process by improving the photogenerated charge carriers and thereby ROS. Sin et al.
(2018) fabricated ZnO-magnetic Fe 3 O 4 composites by a surfactant free method for
effective bacterial destruction. The resultant composite showed a flower like structure (Fig. 2.11a) and an effective destruction of E. coli was observed under visible
light irradiation compared to pristine ZnO (Fig. 2.11b). The improved charge carrier
recombination time envisaged by photoluminescence studies was attributed to
enhanced effect of the composite photocatalyst. The magnetic property of the
composite was an additional advantage for the efficient separation of the catalyst
after use, makes it suitable for commercial. Graphene like MoS 2 sheets modified
ZnO nanoflowers were developed by Awasthi and coworkers (2016) by a one pot
hydrothermal route. The composites displayed effective antibacterial efficacy
2 Photo-Assisted Antimicrobial Activity of Transition Metal Oxides
49