# Photocatalytic Inactivation as a Method of Elimination of _E. coli_ from Drinking Water
## 3 Inactivation Process by Photocatalysts
### Inactivation of _E. coli_ by Heterojunction Systems
coli_ inactivated with this Z-scheme heterojunction system was 10-fold better than the number inactivated with neat graphitic carbon nitride and graphitic carbon nitride doped with platinum [102]. [PERSON] et al. [103] fabricated a Z-scheme ternary heterojunction system made from Ag doped AgVO\({}_{3}\) and BiVO\({}_{4}\) assisted by polyvinylpyrrolidone. This photocatalyst displayed a good photocatalytic performance for the inactivation of _E. coli_ through the action of peroxide radicals and holes generated under visible light irradiation. The Z-scheme heterojunction system of graphene aerogel, bismuth vanadate, silver chloride and silver which was made by a hydrothermal technique. The formation of Z-scheme heterojunction boosted both the charge transfer and separation of electrons. This photocatalyst displayed total inactivation of all the _E. coli_ in the system in less than 25 min in the presence of visible light irradiation [104]. Finally, one other strategy was adopted to reduce the recombination of holes and electrons and obtain a better activity during photocatalysis is the formation of the p-n heterojunction system [105]. _E. coli_ has also been inactivated by the p-n heterojunction photocatalysts, made from polyaniline and zinc oxide. The improved photocatalytic performance of this photocatalyst was linked to the synergistic effect of the p-n heterojunction as well as the generation of hydroxyl and peroxyl radicals assisted by relatively large surface area of the photocatalysts [106]. Examples of other recent studies on the photocatalytic inactivation of _E. coli_ are shown in Table 1. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Photocatalyst** & **Fabrication Method** & **Performance** & **Light Used** & **Reactive Species** & **Ref.** \\ \hline MXene/ anatase TiO\({}_{2}\) & & & 3.4 lg order better & & \\ loaded in reactor made from polyurethane foam & - & & 2.5 lg order & & \\  & & & obtained with UV & Ultraviolet & \(\epsilon^{-}\), HO- and \(h^{+}\) & [107] \\ Cu\({}_{2}\)O on cotton fibers & In-situ synthesis & & 93.25\% _E. coli_ & & \\  & & inactivation & & & \\ Metallic silver on Pinewood & One-step & & Good _E. coli_ & & \\ biochar support & carbothermal & inactivation & Ultraviolet & \({}^{1}\)O\({}_{2}\), OH, \(\cdot\)O\({}_{2}\)-\(\epsilon^{-}\), \(h^{+}\) & [109] \\  & reduction & efficiency & & \\ Composites made from & & & 40\% _E. coli_ reduction & & \\ zeolite and titania & & & in 1 h & Ultraviolet & \(\text{O}_{2}\)\({}^{-}\) & [110] \\ Fe\({}_{3}\)O\({}_{4}\)@SiO\({}_{2}\)@ZnO- & Hydrothermal & & Visible light & \(\text{-OH},\text{O}_{2}\)-\(\epsilon^{-}\), \(h^{+}\) & [111] \\  & & & & \\ Heterostructure of & & & & & \\ ZnO/CdS heterojunction & Hydrothermal & Better performance & Visible light & OH\({}^{-}\) & [112] \\ Ag/TiO\({}_{2}\)/ZnO composite & & & & & \\  & & & & \\ Heterostructure & Ion-exchange and & & & \\ TiO\({}_{2}\)/Ag\({}_{3}\)PO\({}_{4}\)/graphene & electrostatically- & Good performance & Solar light & \(\text{-OH},h^{+}\) & [114] \\  & oxide & assembly & & & \\ Nanop Composites of & & & & & \\ Ag/Cu-cellulose & Chemical reduction & Active against _E. coli_ & visible light & \(\text{O}_{2}\)\({}^{-}\), \(h^{+}\) and OH\({}^{+}\) & [115] \\ Reduced graphene oxide & Green synthesis & Good _E. coli_ & Visible and UV using & - & [116] \\  & & inactivation & metal halide lamp & - & [117] \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Recent studies on the photocatalytic inactivation of _E. coli_.