Designing Novel Photocatalysts for Disinfection of Multidrug-Resistant …
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decrease the mass transfer phenomena. This further creates more problems in photocatalytic operations due to reduced light penetration and reduced photocatalyst
activation. Integrating photocatalysis with membrane technologies or membrane filtration like TiO 2 /Al 2 O 3 composite, TiO 2 supported on polymeric and metal and
ceramic membranes (Kim et al. 2003) or polymeric membranes containing TiO 2
particles entrapped in the assembly process (Artale et al. 2001) has somewhat solved
the issue of catalyst reusing. Still problems regarding membrane fouling, blockage,
regeneration and backwashing, low photocatalytic potential and time-dependent loss
of photocatalyst layer over time persist. Thus developing photocatalysts with high
settling potential and lesser chances of deterioration under harsh chemical surroundings are the need of this era. The current section technically provides solutions to the
challenges that prevent the application of TiO 2 and ZnO in slurry based photocatalytic
system (Chong et al. 2010).
2.1 Doping of Photocatalysts for PCD of Microbes
Ion doping of TiO 2 and ZnO, both metallic and nonmetallic, has shown immense
potential in achieving visible light photocatalysis. The dopant usually generates
impurity in the semiconductor narrowing their bandgap and broadening their capability to capture the most abundant solar spectrum. With respect to PCD, nitrogen
(N) has been reported as the most potential dopant (Fujishima et al. 2008; Rizzo
et al. 2014) reported the effect of N-doped TiO 2 on the PCD of MDR E. coli
strain obtained from a WWTP showing higher disinfection rates as compared to
undoped TiO 2 . Mesoporous, N-doped TiO 2 thin films exhibited visible light-driven
PCD against both Gram-positive and Gram-negative bacteria like Bacillus amyloliquefaciens and Pseudomonas aeruginosa, respectively (Mamane et al. 2014; Soni
et al. 2013). Other nonmetallic dopants like Sulfur (S) have been reported in few
literature. Sol–gel mediated synthesis of S-Doped TiO 2 has been reported to have
strong visible light disinfection ability against Micrococcus lylaein lesser time in
comparison to its undoped variant (Yu et al. 2005).
Transition metal like iron (Fe) has been effectively used as a dopant for ZnO, for
visible light PCD of MDR E. coli with/without any further reactivation as depicted
in Figs. 3 and 4 (Das et al. 2017). Generally, the effectiveness of the dopant relies on
its electronegativity and the difference between dopant and ionic radius of Zinc (Zn).
Thus, Fe being chemically stable and existing in two possible oxidation states, Fe
2+
(Ionic radii 0.78 Å) and Fe
3+ (ionic radii 0.64 Å) close to Zn
2+ (ionic radii 0.74 Å),
can easily pierce into Zn lattice without distressing the crystal structure of ZnO.
This results in more charge carriers to improve its conductivity and photocatalytic
potency (Kafle et al. 2016). Increasing Fe concentration as dopant showed that the
optical bandgap gradually diminished (Kafle et al. 2016). Also noble metals like
silver (Ag) when used as dopants convert the n-type ZnO semiconductors into ptype, enhancing their optoelectronic potential and photocatalytic ability. Adhikari
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decrease the mass transfer phenomena. This further creates more problems in photocatalytic operations due to reduced light penetration and reduced photocatalyst
activation. Integrating photocatalysis with membrane technologies or membrane filtration like TiO 2 /Al 2 O 3 composite, TiO 2 supported on polymeric and metal and
ceramic membranes (Kim et al. 2003) or polymeric membranes containing TiO 2
particles entrapped in the assembly process (Artale et al. 2001) has somewhat solved
the issue of catalyst reusing. Still problems regarding membrane fouling, blockage,
regeneration and backwashing, low photocatalytic potential and time-dependent loss
of photocatalyst layer over time persist. Thus developing photocatalysts with high
settling potential and lesser chances of deterioration under harsh chemical surroundings are the need of this era. The current section technically provides solutions to the
challenges that prevent the application of TiO 2 and ZnO in slurry based photocatalytic
system (Chong et al. 2010).
2.1 Doping of Photocatalysts for PCD of Microbes
Ion doping of TiO 2 and ZnO, both metallic and nonmetallic, has shown immense
potential in achieving visible light photocatalysis. The dopant usually generates
impurity in the semiconductor narrowing their bandgap and broadening their capability to capture the most abundant solar spectrum. With respect to PCD, nitrogen
(N) has been reported as the most potential dopant (Fujishima et al. 2008; Rizzo
et al. 2014) reported the effect of N-doped TiO 2 on the PCD of MDR E. coli
strain obtained from a WWTP showing higher disinfection rates as compared to
undoped TiO 2 . Mesoporous, N-doped TiO 2 thin films exhibited visible light-driven
PCD against both Gram-positive and Gram-negative bacteria like Bacillus amyloliquefaciens and Pseudomonas aeruginosa, respectively (Mamane et al. 2014; Soni
et al. 2013). Other nonmetallic dopants like Sulfur (S) have been reported in few
literature. Sol–gel mediated synthesis of S-Doped TiO 2 has been reported to have
strong visible light disinfection ability against Micrococcus lylaein lesser time in
comparison to its undoped variant (Yu et al. 2005).
Transition metal like iron (Fe) has been effectively used as a dopant for ZnO, for
visible light PCD of MDR E. coli with/without any further reactivation as depicted
in Figs. 3 and 4 (Das et al. 2017). Generally, the effectiveness of the dopant relies on
its electronegativity and the difference between dopant and ionic radius of Zinc (Zn).
Thus, Fe being chemically stable and existing in two possible oxidation states, Fe
2+
(Ionic radii 0.78 Å) and Fe
3+ (ionic radii 0.64 Å) close to Zn
2+ (ionic radii 0.74 Å),
can easily pierce into Zn lattice without distressing the crystal structure of ZnO.
This results in more charge carriers to improve its conductivity and photocatalytic
potency (Kafle et al. 2016). Increasing Fe concentration as dopant showed that the
optical bandgap gradually diminished (Kafle et al. 2016). Also noble metals like
silver (Ag) when used as dopants convert the n-type ZnO semiconductors into ptype, enhancing their optoelectronic potential and photocatalytic ability. Adhikari