# Antimicrobial Effect of Submicron Complex Oxide Particles CsTeMoO\({}_{6}\) under Visible Light
## 4 Discussion
Possible chemical reactions on the surface of CsTeMoO\({}_{6}\) under visible light will be similar to RbTe\({}_{1.5}\)W\({}_{0.5}\)O\({}_{6}\) and they can be written as:  
\[\text{CsTeMoO}_{6}+\text{hv}\rightarrow\text{CsTeMoO}_{6}\left(\text{h}^ {+}+\text{e}^{-}\right) \tag{1}\]  
\[\text{H}_{2}\text{O}+\text{h}^{+}\rightarrow\text{H}^{+}+\bullet\text{OH} \tag{2}\]  
\[\text{O}_{2}+\text{e}^{-}\rightarrow\bullet\text{O}_{2}\text{{}^{-}} \tag{3}\]  
\[\bullet\text{O}_{2}\text{{}^{-}}+\text{H}^{+}\rightarrow\bullet\text{HO}_{2} \tag{4}\]  
\[2\text{HO}_{2}\bullet\rightarrow\text{H}_{2}\text{O}_{2}+\text{O}_{2} \tag{5}\]  
\[\text{biomolecules}+\text{e}^{-}/\text{h}^{+}/\bullet\text{O}_{2}\text{{}^{-} }/\bullet\text{OH}/\text{H}_{2}\text{O}_{2}\rightarrow\text{oxidation}. \tag{6}\]  
Thus, the oxidation of organic compounds can occur both directly through the interaction with the formed electrons and holes (1), and with the help of the formed hydroxyl and superoxide radicals ((2) and (3)). Moreover, secondary reactions between radicals are possible with the formation of hydrogen peroxide according to reaction ((4) and (5)), which also acts as a strong oxidizing agent. According to [37; 38], an active process of recombination of the resulting electron-hole pairs take place on the surface of the RbTe\({}_{1.5}\)W\({}_{0.5}\)O\({}_{6}\) photocatalyst, which reduces its oxidative capacity. However, studies on the mechanism of the photocatalytic process in the case of CsTeMoO\({}_{6}\) have shown an insignificant contribution of recombination; that is, the main part of the formed electrons and holes enters oxidation reactions [35]. Figure 6: Scheme regarding the responsible conduction levels and the edge of the valence band of compounds CsTeMoO\({}_{6}\) and RbTe\({}_{1.5}\)W\({}_{0.5}\)O\({}_{6}\). Comparing the antimicrobial activity of complex oxides CsTeMoO\({}_{6}\) with RbTe\({}_{1.5}\)W\({}_{0.5}\)O\({}_{6}\) under the same conditions (50 W light source; surface flux density 524 W/m\({}^{2}\) and concentration of complex oxides 2 mg/mL) studied earlier, one can note the following: RbTe\({}_{1.5}\)W\({}_{0.5}\)O\({}_{6}\) had a much stronger inhibitory effect on bacteria _E. coli_ and _S. aureus_, as well as on the vegetative mycelium of the fungus _P. chrysogenum_ compared to cesium oxide both in the dark and in the light, despite the similar electronic structure and close particle size. This may be due to the different reactivity of electron-hole pairs and different efficiency of these reactions (2)-(5). In [39], it was shown that the degree of oxidation of various organic bonds depends, among other things, on the nature of active radicals and particles. Thus, according to [35; 38], in dye oxidation processes by complex metal oxides, the main contribution in the case of RbTe\({}_{1.5}\)W\({}_{0.5}\)O\({}_{6}\) to the decomposition reactions is made by hydroxyl radicals, while for CsTeMoO\({}_{6}\), these are superoxide radicals, and \(\bullet\)OH are formed to a lesser extent. Apparently, hydroxyl radicals are most actively involved in the oxidation of bacteria and vegetative mycelium biomolecules compared to \(\bullet\)O\({}_{2}\)\({}^{-}\), which interact more efficiently with simpler organic molecules. In this regard, RbTe\({}_{1.5}\)W\({}_{0.5}\)O\({}_{6}\) powder shows better antimicrobial activity than CsTeMoO\({}_{6}\), which is more suitable for the oxidation of organic dyes. In addition, different types of fungi have different needs for water and nutrients, so adsorbed water and some impurities on the surface of complex oxides could both inhibit and stimulate their growth. As we have already noted, the antimicrobial effect of nano- and submicron-sized metal oxide particles may depend on the nature of the metals. Thus, it can be hypothesized that different metals are capable of inhibiting certain metabolic targets in microorganisms under both light and dark conditions.