458
S. Das et al.
arranged in a hexagonal pattern. The 2:1 configuration type comprises of two silica tetrahedral sheets amidst which lies an octahedral sheet. This includes the most
abundant clay minerals mica and smectite groups. The serpentine and mica group is
further subdivided by the criteria of dioctahedral and trioctahedral type (Weaver and
Pollard 2011).
They possess adsorbing antimicrobial as well as medicinal properties and have
been explored since long. They serve as a mineral remedy for diarrhea, dysentery,
tapeworm, hookworm, wounds, and abscesses (Otto and Haydel 2013). With excellent adsorption ability, they have been employed for mitigating bacteria in wastewater treatment plants (Hrenovic et al. 2009) and also applications in bioremediation
of other different contaminants (Muter 2014). Their general application could be
observed in home-based water purification or purifying systems where they serve
the purpose for an excellent adsorbent for heavy metals, chemical contaminants, and
bacteria. Clay minerals have an added advantage over other adsorbents via their relative abundance in nature, hydro-plasticity, economical aspects, and environmental
affability while usage. Moreover, their large specific surface area, porosity, surface
charge, and functional groups are added advantage toward being a good adsorbent
(Yuan et al. 2015). Few problems associated with them for large-scale disinfection
applications involve their poorer recovery rate from aqueous solution. However, engineering or modifying their surfaces or crystal lattice with metal oxides or NPs does
improve their expediency, particularly in disinfection of water.
PCD process using bare ZnO NPs may illustrate few limiting factors like stubborn aggregation, alteration of the surface characteristics or crystal growth, and
reduced quantum effects that eventually will lessen its catalytic proficiency and can
frontier its commercial utilization. Nonetheless, retrieval of the small-sized nanophotocatalyst subsequently after water treatment would prove as a technical hindrance and henceforth own ambiguity on particle reusability (Chong et al. 2010). To
address such confines, it is proposed to use clay-based matrices for immobilization
of nano-photocatalyst particles (Praneeth and Paria 2017). Among these, Kaolinite
clay has been extensively accepted as a cosmetic material that has antimicrobial and
healing properties, establishing itself as a harmless candidate for treating water.
Misra et al. modified kaolinite with ZnO using a simple coprecipitation method
and successfully employed it for visible light PCD of a MDR Enterobacter sp. which
is a coliform bacterium possessing potential threats of waterborne nosocomial infections. To our astonishment, only 150 mg/L of the designed clay-based photocatalyst
was sufficient enough to cause 7-log reduction of bacteria within 120 min (Misra
et al. 2018). Moreover, when the reusability and recoverability of the catalyst were
measured, it was found to be photocatalytically efficient for three subsequent cycles.
Earlier Chong et al. (2011) reported the PCD performance of the TiO 2 –Kaolinite
catalyst synthesized using simple two-step sol–gel method against a sewage-isolated
Escherichia coli sp. (ATCC 11775). Normal E. coli is a common model organism
to quantify the efficacy of treatment. Thus using environmental or sewage isolates
demonstrate how PCD could behave in case of robust environmental isolates. Under
the illumination of UV-A light, a 5-log bacterial reduction was achieved in 70 min
at the best operation conditions of 6 g/L TiO 2 –K loading, pH 4.0 and 7.5 L/min
S. Das et al.
arranged in a hexagonal pattern. The 2:1 configuration type comprises of two silica tetrahedral sheets amidst which lies an octahedral sheet. This includes the most
abundant clay minerals mica and smectite groups. The serpentine and mica group is
further subdivided by the criteria of dioctahedral and trioctahedral type (Weaver and
Pollard 2011).
They possess adsorbing antimicrobial as well as medicinal properties and have
been explored since long. They serve as a mineral remedy for diarrhea, dysentery,
tapeworm, hookworm, wounds, and abscesses (Otto and Haydel 2013). With excellent adsorption ability, they have been employed for mitigating bacteria in wastewater treatment plants (Hrenovic et al. 2009) and also applications in bioremediation
of other different contaminants (Muter 2014). Their general application could be
observed in home-based water purification or purifying systems where they serve
the purpose for an excellent adsorbent for heavy metals, chemical contaminants, and
bacteria. Clay minerals have an added advantage over other adsorbents via their relative abundance in nature, hydro-plasticity, economical aspects, and environmental
affability while usage. Moreover, their large specific surface area, porosity, surface
charge, and functional groups are added advantage toward being a good adsorbent
(Yuan et al. 2015). Few problems associated with them for large-scale disinfection
applications involve their poorer recovery rate from aqueous solution. However, engineering or modifying their surfaces or crystal lattice with metal oxides or NPs does
improve their expediency, particularly in disinfection of water.
PCD process using bare ZnO NPs may illustrate few limiting factors like stubborn aggregation, alteration of the surface characteristics or crystal growth, and
reduced quantum effects that eventually will lessen its catalytic proficiency and can
frontier its commercial utilization. Nonetheless, retrieval of the small-sized nanophotocatalyst subsequently after water treatment would prove as a technical hindrance and henceforth own ambiguity on particle reusability (Chong et al. 2010). To
address such confines, it is proposed to use clay-based matrices for immobilization
of nano-photocatalyst particles (Praneeth and Paria 2017). Among these, Kaolinite
clay has been extensively accepted as a cosmetic material that has antimicrobial and
healing properties, establishing itself as a harmless candidate for treating water.
Misra et al. modified kaolinite with ZnO using a simple coprecipitation method
and successfully employed it for visible light PCD of a MDR Enterobacter sp. which
is a coliform bacterium possessing potential threats of waterborne nosocomial infections. To our astonishment, only 150 mg/L of the designed clay-based photocatalyst
was sufficient enough to cause 7-log reduction of bacteria within 120 min (Misra
et al. 2018). Moreover, when the reusability and recoverability of the catalyst were
measured, it was found to be photocatalytically efficient for three subsequent cycles.
Earlier Chong et al. (2011) reported the PCD performance of the TiO 2 –Kaolinite
catalyst synthesized using simple two-step sol–gel method against a sewage-isolated
Escherichia coli sp. (ATCC 11775). Normal E. coli is a common model organism
to quantify the efficacy of treatment. Thus using environmental or sewage isolates
demonstrate how PCD could behave in case of robust environmental isolates. Under
the illumination of UV-A light, a 5-log bacterial reduction was achieved in 70 min
at the best operation conditions of 6 g/L TiO 2 –K loading, pH 4.0 and 7.5 L/min