ZnO-Graphene hybrid was fabricated by Kavitha et al. (2012) by an in-situ thermal
decomposition process and exhibited an excellent antibacterial effect towards E.coli.
Lefatshe et al. (2017) and coworkers modified the ZnO with nanocellulose structures
and demonstrated the effective antibacterial effect towards S.aureus and E.coli. A
combination of Ag nanoparticle and g-C 3 N 4 was utilized to modify ZnO
nanoparticles by a one pot hydrothermal route for the purpose of photocatalytic
disinfection towards E. coli (Adhikari et al. 2015). Synergistic effect of Ag and ZnO
nanoparticles anchored on the g-C 3 N 4 sheets was ascribed to the disinfection of
E. coli under light and dark conditions. Carbon quantum dots, a cost effective
material, are another class of carbon material which has a unique property in terms
of up conversion of photoluminescence which makes the material, an efficient
sunlight active photocatalyst (Li and Cao 2011). In-situ sol gel chemistry was
applied for the fabrication of carbon quantum dots modified ZnO nanorods by
Kuang et al. (2019), and the resultant material was able to kill ~96% bacteria
under visible light irradiation even at low concentration (0.1 mgL
À1 ). The carbon
quantum dots s for the carbon quantum dots -ZnO composite, was synthesized by an
electrochemical route. Due to the improved charge separation efficiency of the
carbon quantum dots s and the reactive oxygen species generation, antibacterial
efficiency of carbon quantum dots -ZnO nanorod was three to four times higher than
that of ZnO.
2.5.3 Copper (II) Oxide (CuO)
Copper (II) oxide is a p-type semiconductor with a band gap ranging from 1 to 2 eV
and hence it is a visible light active photocatalyst. Due to this property it can be used
as photocatalysts, photoelectrodes, antimicrobial substrate etc. CuO possess a monoclinic crystal structure, with an indirect band gap and it has a carrier diffusion length
of 200 nm with an absorption depth of 500 nm. (Masudy-Panah et al. 2018).
Considering photocatalytic based the bacterial disinfection property of CuO, it is
cheaper than silver and can be synthesized with high surface area and interesting
surface morphologies. This helps to one to tune the antimicrobial efficacy of the CuO
surface and bring to a commercial scale. However due to high charge carrier
recombination rates of CuO, the efficiency remains low and restricts it commercial
utility.
Yousef and coworkers investigated the photocatalytic pathogenic effect of
CuO/TiO 2 nanostructures fabricated by electrospinning route. The efficient charge
separation in TiO 2 –CuO heterojunction followed by accumulation of
photogenerated electrons and holes in the conduction band and valence band
respectively of CuO leads to the formation of reactive oxygen species (convert
O 2 to O
ÁÀ
2
and OH
À to OH
. ). These reactive oxygen species attack the outer
membrane of K. pneumonia, and partially disintegrate the intact structure of the
membrane. Due to the partial disintegration the surface charge of the bacterial cells
2 Photo-Assisted Antimicrobial Activity of Transition Metal Oxides
51
decomposition process and exhibited an excellent antibacterial effect towards E.coli.
Lefatshe et al. (2017) and coworkers modified the ZnO with nanocellulose structures
and demonstrated the effective antibacterial effect towards S.aureus and E.coli. A
combination of Ag nanoparticle and g-C 3 N 4 was utilized to modify ZnO
nanoparticles by a one pot hydrothermal route for the purpose of photocatalytic
disinfection towards E. coli (Adhikari et al. 2015). Synergistic effect of Ag and ZnO
nanoparticles anchored on the g-C 3 N 4 sheets was ascribed to the disinfection of
E. coli under light and dark conditions. Carbon quantum dots, a cost effective
material, are another class of carbon material which has a unique property in terms
of up conversion of photoluminescence which makes the material, an efficient
sunlight active photocatalyst (Li and Cao 2011). In-situ sol gel chemistry was
applied for the fabrication of carbon quantum dots modified ZnO nanorods by
Kuang et al. (2019), and the resultant material was able to kill ~96% bacteria
under visible light irradiation even at low concentration (0.1 mgL
À1 ). The carbon
quantum dots s for the carbon quantum dots -ZnO composite, was synthesized by an
electrochemical route. Due to the improved charge separation efficiency of the
carbon quantum dots s and the reactive oxygen species generation, antibacterial
efficiency of carbon quantum dots -ZnO nanorod was three to four times higher than
that of ZnO.
2.5.3 Copper (II) Oxide (CuO)
Copper (II) oxide is a p-type semiconductor with a band gap ranging from 1 to 2 eV
and hence it is a visible light active photocatalyst. Due to this property it can be used
as photocatalysts, photoelectrodes, antimicrobial substrate etc. CuO possess a monoclinic crystal structure, with an indirect band gap and it has a carrier diffusion length
of 200 nm with an absorption depth of 500 nm. (Masudy-Panah et al. 2018).
Considering photocatalytic based the bacterial disinfection property of CuO, it is
cheaper than silver and can be synthesized with high surface area and interesting
surface morphologies. This helps to one to tune the antimicrobial efficacy of the CuO
surface and bring to a commercial scale. However due to high charge carrier
recombination rates of CuO, the efficiency remains low and restricts it commercial
utility.
Yousef and coworkers investigated the photocatalytic pathogenic effect of
CuO/TiO 2 nanostructures fabricated by electrospinning route. The efficient charge
separation in TiO 2 –CuO heterojunction followed by accumulation of
photogenerated electrons and holes in the conduction band and valence band
respectively of CuO leads to the formation of reactive oxygen species (convert
O 2 to O
ÁÀ
2
and OH
À to OH
. ). These reactive oxygen species attack the outer
membrane of K. pneumonia, and partially disintegrate the intact structure of the
membrane. Due to the partial disintegration the surface charge of the bacterial cells
2 Photo-Assisted Antimicrobial Activity of Transition Metal Oxides
51