Designing Novel Photocatalysts for Disinfection of Multidrug-Resistant …
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MDR bacteria. According to the reports by Chaurasia et al., this may serve beneficial in combating biofilm producing bacteria and killing of MDR S. Aureus and
uropathogenic E. coli in less than 30 min (Chaurasia et al. 2016).
However, in spite all the efforts, magnetically separable iron oxide visible light
active photocatalysts find limited application, owing to their lessened photocatalytic
activity and reduced stability at times (Beydoun et al. 2000). Therefore, seeking out
and utilizing the naturally existing magnetic minerals might be a preferred method
to attend this crisis. Studying or mining out the photocatalytic properties of natural
magnetic sphalerite (NMS) is greatly needed for assessing its application in bacterial
disinfection.
Since its discovery from a lead–zinc mine in China, NMS had been directly
utilized for visible light bacterial inactivation (Xia et al. 2013). Xia et al. reported
that with 6 h irradiation of fluorescent light, they could irreversibly inactivate both
Gram-positive S. aureus and Gram-negative E. coli without. The inactivation or cell
damage involves substantial membrane damage and other cellular components as
verified by TEM. Point of contact plays a very crucial role in this inactivation, which
initiates the damage from the cellular membrane. Interestingly, the primary ROS
involved in this study was not like the usual •OH or H 2 O 2 , but with superoxide
radical (•O 2
− ). If we get into more insights of this study, a five cycle repeated run
revealed admirable NMS devoid of a substantial loss in photocatalytic and magnetic
property. Although AAS results confirmed a minute ion of heavy metal leaching into
the system, i.e., Zn
2+ (0.17 ppm) and Fe
2+ (0.032 ppm) when suspended in bacterial
cell solution for 8 h. Fortunately, other metal impurities were untraceable and the
control experiments do not show toxicity toward cells due to metal ion leakage.
In another report by Peng et al., NMS was used as the photocatalyst against E.
coli, which could be separable and reused using magnetic field (Peng et al. 2017).
Results confirmed with irradiation Blue LED light complete disinfection of 1.5 ×
10
5 cfu/mL of E. coli could be achieved within 120 min for the first three cycles.
However, the PCD efficiency started to decline in the fourth run, while in the fifth
run just 3.3-log and 3.5-log reduction could be achieved with blue LED and sunlight
respectively. The stability and run dependent loss in photocatalytic properties of
NMS might be blockage of the photocatalyst active sites due to the adsorption of
the degraded bacterial compounds, reducing the probability of light absorption and
charge separation for ROS generation. Their results also showed validation of the
process with other Gram-positive bacteria like S. aureus, Microbacterium barkeri,
and Bacillus subtilis.
Enthused by the good photocatalytic performance of NMS against bacterial
pathogens, the assortment and improvement of efficient alternative materials more
of this kind are immediately needed for lost-cost environmental or water remediation. However, the problems of ion leaching and narrow activity might restrict their
diverse applications (Xia et al. 2013). Thus, thermally altering them might be a viable
option to address the crisis. Thermal treatment can repair the crystal lattice defects,
improve their degree of crystallinity and size (Luan et al. 2014), alter the mineral
phase (Aramendía et al. 2008), and possibly help in better remediation of waterborne
bacteria.
463
MDR bacteria. According to the reports by Chaurasia et al., this may serve beneficial in combating biofilm producing bacteria and killing of MDR S. Aureus and
uropathogenic E. coli in less than 30 min (Chaurasia et al. 2016).
However, in spite all the efforts, magnetically separable iron oxide visible light
active photocatalysts find limited application, owing to their lessened photocatalytic
activity and reduced stability at times (Beydoun et al. 2000). Therefore, seeking out
and utilizing the naturally existing magnetic minerals might be a preferred method
to attend this crisis. Studying or mining out the photocatalytic properties of natural
magnetic sphalerite (NMS) is greatly needed for assessing its application in bacterial
disinfection.
Since its discovery from a lead–zinc mine in China, NMS had been directly
utilized for visible light bacterial inactivation (Xia et al. 2013). Xia et al. reported
that with 6 h irradiation of fluorescent light, they could irreversibly inactivate both
Gram-positive S. aureus and Gram-negative E. coli without. The inactivation or cell
damage involves substantial membrane damage and other cellular components as
verified by TEM. Point of contact plays a very crucial role in this inactivation, which
initiates the damage from the cellular membrane. Interestingly, the primary ROS
involved in this study was not like the usual •OH or H 2 O 2 , but with superoxide
radical (•O 2
− ). If we get into more insights of this study, a five cycle repeated run
revealed admirable NMS devoid of a substantial loss in photocatalytic and magnetic
property. Although AAS results confirmed a minute ion of heavy metal leaching into
the system, i.e., Zn
2+ (0.17 ppm) and Fe
2+ (0.032 ppm) when suspended in bacterial
cell solution for 8 h. Fortunately, other metal impurities were untraceable and the
control experiments do not show toxicity toward cells due to metal ion leakage.
In another report by Peng et al., NMS was used as the photocatalyst against E.
coli, which could be separable and reused using magnetic field (Peng et al. 2017).
Results confirmed with irradiation Blue LED light complete disinfection of 1.5 ×
10
5 cfu/mL of E. coli could be achieved within 120 min for the first three cycles.
However, the PCD efficiency started to decline in the fourth run, while in the fifth
run just 3.3-log and 3.5-log reduction could be achieved with blue LED and sunlight
respectively. The stability and run dependent loss in photocatalytic properties of
NMS might be blockage of the photocatalyst active sites due to the adsorption of
the degraded bacterial compounds, reducing the probability of light absorption and
charge separation for ROS generation. Their results also showed validation of the
process with other Gram-positive bacteria like S. aureus, Microbacterium barkeri,
and Bacillus subtilis.
Enthused by the good photocatalytic performance of NMS against bacterial
pathogens, the assortment and improvement of efficient alternative materials more
of this kind are immediately needed for lost-cost environmental or water remediation. However, the problems of ion leaching and narrow activity might restrict their
diverse applications (Xia et al. 2013). Thus, thermally altering them might be a viable
option to address the crisis. Thermal treatment can repair the crystal lattice defects,
improve their degree of crystallinity and size (Luan et al. 2014), alter the mineral
phase (Aramendía et al. 2008), and possibly help in better remediation of waterborne
bacteria.