*3.7. Proposed Mechanism of Photocatalytic Disinfection*

The possible disinfection mechanism has been reported in the literature [9,11,15]. In the present case, we expected that the disinfection mechanism is contributed by the action of the photo-induced reactive oxygen species generated during the reaction (Figure 10). The initial site of attack is expected to be the lipopolysaccharide layer present in the external cell walls of the target bacteria [11]. It is assumed that the oxidative stress which is generated due to this process disintegrates the peptidoglycan layer and results in peroxidation of the lipid membrane, eventually causing oxidation of the membrane proteins [9]. This leads to rapid leakage of K+ ions from the bacterial cells hence dysfunction of the potassium channels resulting in deregulation of cell signaling. Additionally the dwindling cell functionality and viability is also attributed by the peroxidation of polyunsaturated phospholipid components of the cell membrane, eventually leading to cell death [11,15].

**Figure 10.** Proposed mechanism of sun-light assisted photocatalytic disinfection of bacteria using Ag@ZnO core-shell nanoparticles

There is an increasing demand regarding the issue of providing safe and potable drinking water to underdeveloped Third World countries. There is an urgent need to develop strategies that follow an alternate route to address this concern [18]. Based on the above statement, the concept of "Advanced Oxidation Process" can be proposed; based on the proven effectivity and superiority as compared to that of other traditional catalysts.

The catalyst that we have proposed, generally works well towards the basic range of pH values. All the real water samples, especially the likes of tap-water, and river water have basic pH. This can also be explain the better effectivity and working efficiency of the proposed catalyst, although further confirmation is required.

It can also be concluded from the MP-AES analysis that the proposed catalyst is completely non-toxic in nature and can be applied for a wide range of applications. It can also be concluded that, since there is no evidence for the proposed catalyst's toxicity to organisms, it can surely be used as a better, safer option than the traditional ones.
