# ZnO/Ag Nanocomposites with Enhanced Antimicrobial Activity
## 4 Conclusions  
In summary, a soft chemical route was performed to prepare ZnO/Ag nanocomposites. The XRD patterns indicate the formation of separate phases, namely, a hexagonal wurtzite structure for ZnO and a cubic structure for Ag NPs. The formation of these separate phases can be seen when the atomic percentage of silver exceeds 3%. SEM shows that the presence of these Ag nanoparticles causes the growth of ZnO to vary, which can then affect its bactericidal power. STEM allows the morphology and sizes of the Ag NPs to be nano-spheres (-20 nm) on the wurtzite ZnO surface. The absorption bands from the UV-Vis analysis of the samples increase due to the contribution from the surface plasmon resonance absorption of silver nanoparticles, showing significantly higher visible light absorption compared to the ZnO matrix. Raman spectroscopy showed that spectra  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & **Name of Sample** & **Ctr** & **Zn1** & **Zn2** & **Zn3** & **Zn4** & **Zn5** & **Zn6** \\ \hline Percentage of & _S. aureus_ & 96.5 & 15 & 9 & 9 & 9 & 8 & 9 \\ live bacteria (\%) & _E. coli_ & 91.25 & 12 & 6 & 6.5 & 9.5 & 5.5 & 4.5 \\ \hline \hline \end{tabular}
\end{table}
Table 1: Percentage of live bacteria determined by using the flow-cytometer after being stained with the live/dead kit.  
Figure 8: Cytometry charts showing the percentage of live and dead cells.  
measured in non-resonant conditions displayed a clear difference between the ZnO powder (Zn1) and nanocomposites with different Ag concentrations (Zn2-Zn6). Here, several non-fundamental peaks/bands are activated after adding Ag. In this way, it is clear that the silver is segregated in the form of NP and does not occupy positions within the zinc oxide structure. Some of them can be assigned to the previously observed multiphonon modes. When analyzing the effect of the different concentrations of Ag against both bacteria, we can observe that an increase in the concentration of Ag does not correlate with an increase in its effect against the bacteria. Consequently, when the percentage of dopant increases, the Ag NPs tend to agglomerate, thereby decreasing both their surface area and the area of their surface in contact with the bacteria. Hence, using only 1 at% of Ag reduces the percentage of living cells by more than 90% in most cases, thus increasing their effectiveness in the destruction of bacteria by 5% compared to that of zinc oxide without Ag NPs.  
Conceptualization, J.G.C., D.F. and J.B.C.; methodology, J.G.C., B.V. and L.S.; validation, J.G.C., D.F., B.V., L.S and J.B.C.; formal analysis, J.G.C., B.V. and L.S.; investigation, J.G.C., S.P., B.V. and L.S.; resources, J.B.C.; data curation, J.G.C., B.V., L.S., M.G. and V.I.-R; writing--original draft preparation, J.G.C., B.V. and L.S.; writing--review and editing; J.G.C., D.F., B.V. and J.B.C.; supervision, D.F. and J.B.C.; funding acquisition, J.B.C. All authors have read and agreed to the published version of the manuscript.  
The authors would like to acknowledge the financial support of the Spanish Ministry of Economy and Competitiveness under the program Ministerio de Ciencia e Innovacion <<Proyectos de I+D+i>> de los Programas Estatales de Generacion de Conocimiento y Fortalecimiento Cientifico y Tecnologico del Sistema de I+D+i dye de I+D+i Orientada a los Retos de la Sociedad, en el marco del Plan Estatal de Investigacion Cientifica y Tecnica y de Innovacion 2017-2020. Ref. PID2020-116719 RB-C43.  
We also appreciate the characterization assistance provided by the Central Service for Scientific Instrumentation (SCIC) at the Universitat Jaume I. Arnau Perez Salvador for the help in experimentation during the completion of the final degree project.  
The authors declare no conflict of interest.