7.4 Mechanisms of the Photocatalytic Disinfection
of Bacteria
In general, the photocatalytic bacterial disinfection involves (1) the generation of
electron/hole pairs by the excitation of the semiconductor, (2) the reaction of the
pathogenic microbes with the photogenerated reactive oxygen species generated at
the surface of the photocatalyst, and (3) the penetration of toxic ions inside the
bacterial cells leading to the disturbance of their enzymatic and replication machinery. At this level, it is crucial to understand the mechanisms involved in the
disinfection process when operating any nanostructured photocatalytic material
(Wang et al. 2011b, 2015b). Wang et al. (2015a, b) developed a mechanism for
the generation of reactive oxygen species and their contributions for the disinfection
of bacterial cells and the degradation of organic pollutants by integrating semipermeable membrane (preventing the direct contact between bacterial cells and semiconductor photocatalytic material) using appropriate scavengers under visible light.
They showed that high degradation of the organic pollutants and disinfection of the
bacterial cells were due to the toxic property of scavengers. Besides, they claimed
that more research must be carried out in the future to optimize the concentration of
scavengers during the disinfection process to prevent the toxicity of the bacteria
cells. Recent publications have provided evidence for other antioxidant enzymes like
superoxide dismutase and catalase (Leung et al. 2008), which are essential for
bacteria cells to face the toxicity. However, recent research by Sun et al. (2014)
reported that the disinfection of the bacterial cell is due to H 2 O 2 generated by the
photolytic material rather than the antioxidant enzyme. This research shows that the
different photocatalytic systems differed in their reactive species generated during
the disinfection process and depend upon the gene of the bacterial cell.
In general, the role of reactive species is to make oxidative stress on the cell
membrane by attacking its integrity. The genetic material of the microorganisms
such as DNA and nucleic acids will also be targeted leading to cell death. Some
studies showed that photocatalytic disinfection mechanisms differ with the used
semiconductor producing different reactive oxygen species (An et al. 2017; Xia et al.
2015b).
Currently, recent research carried out on the genetic technology of the bacterial
cells and its single-gene knockout mutants for a better understanding of the disinfection process using advanced molecular technologies. For example, Sun et al.
(2017) in their resaerch to study investigated the photoelectrocatalytic inactivation
mechanism of bacteria using parental E. coli BW25113 and its isogenic mutants
deficient in catalase HPI (katG-1, JW3914-1) as well as uing deficient superoxide
dismutase Mn-SOD (sodA-1, JW3879-1). shows that the mutants experienced
damages earlier and at higher levels, confirming the essential roles of catalase and
superoxide dismutase (SOD) in the bacterial photoelectrocatalytic resistance. Similar
results were also reported by An et al. (2016) and Huang et al. (2015), who claimed
that due to the complexity of the organism, the disinfection of different pathogenic
microbe favors disforest photocatalytic materials and mechanisms. Moreover, the
7 Photocatalytic Nanomaterials for Bacterial Disinfection
227
of Bacteria
In general, the photocatalytic bacterial disinfection involves (1) the generation of
electron/hole pairs by the excitation of the semiconductor, (2) the reaction of the
pathogenic microbes with the photogenerated reactive oxygen species generated at
the surface of the photocatalyst, and (3) the penetration of toxic ions inside the
bacterial cells leading to the disturbance of their enzymatic and replication machinery. At this level, it is crucial to understand the mechanisms involved in the
disinfection process when operating any nanostructured photocatalytic material
(Wang et al. 2011b, 2015b). Wang et al. (2015a, b) developed a mechanism for
the generation of reactive oxygen species and their contributions for the disinfection
of bacterial cells and the degradation of organic pollutants by integrating semipermeable membrane (preventing the direct contact between bacterial cells and semiconductor photocatalytic material) using appropriate scavengers under visible light.
They showed that high degradation of the organic pollutants and disinfection of the
bacterial cells were due to the toxic property of scavengers. Besides, they claimed
that more research must be carried out in the future to optimize the concentration of
scavengers during the disinfection process to prevent the toxicity of the bacteria
cells. Recent publications have provided evidence for other antioxidant enzymes like
superoxide dismutase and catalase (Leung et al. 2008), which are essential for
bacteria cells to face the toxicity. However, recent research by Sun et al. (2014)
reported that the disinfection of the bacterial cell is due to H 2 O 2 generated by the
photolytic material rather than the antioxidant enzyme. This research shows that the
different photocatalytic systems differed in their reactive species generated during
the disinfection process and depend upon the gene of the bacterial cell.
In general, the role of reactive species is to make oxidative stress on the cell
membrane by attacking its integrity. The genetic material of the microorganisms
such as DNA and nucleic acids will also be targeted leading to cell death. Some
studies showed that photocatalytic disinfection mechanisms differ with the used
semiconductor producing different reactive oxygen species (An et al. 2017; Xia et al.
2015b).
Currently, recent research carried out on the genetic technology of the bacterial
cells and its single-gene knockout mutants for a better understanding of the disinfection process using advanced molecular technologies. For example, Sun et al.
(2017) in their resaerch to study investigated the photoelectrocatalytic inactivation
mechanism of bacteria using parental E. coli BW25113 and its isogenic mutants
deficient in catalase HPI (katG-1, JW3914-1) as well as uing deficient superoxide
dismutase Mn-SOD (sodA-1, JW3879-1). shows that the mutants experienced
damages earlier and at higher levels, confirming the essential roles of catalase and
superoxide dismutase (SOD) in the bacterial photoelectrocatalytic resistance. Similar
results were also reported by An et al. (2016) and Huang et al. (2015), who claimed
that due to the complexity of the organism, the disinfection of different pathogenic
microbe favors disforest photocatalytic materials and mechanisms. Moreover, the
7 Photocatalytic Nanomaterials for Bacterial Disinfection
227