**7. Discussion**

*Renewable and Sustainable Composites*

**88**

**Figure 21.**

**Figure 20.**

**Figure 19.**

For each film, multiple shots were taken at different angles and positions within the films. **Figures 20** and **21** present the most typical configurations of the particle dispersion. **Figure 20** A and B shows the surface of the chitosan without NPs. SEM analysis in overall

*SEM images of the films containing 1.0% TiO2 (A, B) and 1.5% TiO2 (D, C).*

*SEM images of the films containing 0.0% TiO2 (A, B) and 0.5% TiO2 (C, D).*

*XRD analysis diffraction of the TiO2 used in the research, compared to pattern of anatase.*

As a whole, the results in Figures 5 through 12 prove clearly that the biocomposite film made of chitosan and TiO2 NPs can be photoactivated. Once the films containing NPs have produced ROS, they are capable of reducing significantly the amount and growth rate of bacteria. Two different tests (viz., the growth curve analysis and the Kirby-Bauer technique) present incontrovertible evidence that when the bacteria are exposed to the photoactivated biocomposites, their growth pattern is affected, and the end amount is lower. We already mentioned that the reviewed literature proved that the main mechanism affecting the bacteria growth is the production of ROS rendered by the TiO2 upon UV light irradiation. However, in order for these ROS to be effective (in sufficient concentration), the correct polymorph of TiO2 is needed, i.e., anatase. For this reason, we selected this dioxide NPs, seeking to obtain more ROS, as mentioned in Section 4 of this chapter. Nonetheless, it is well-known that different processing conditions (involving temperature) of titanium dioxide can lead to a phase change. Thanks to the XRD characterization, we were able to confirm that the crystal structure used throughout this research was anatase and that the synthesis process of the biocomposite films did not change its crystal structure.

During the said process, the mixing methods used to disperse uniformly the TiO2 NPs in the chitosan could have caused clots and agglomeration of the particles. This was the only reason to use a SEM (secondary imaging mode) to acquire the images shown in Section 6.5. The technique allowed scrutinizing the entire film exposed surface from different angles. This extensive survey did not evince any large clots or even lumps of NPs on the surface of the films. These images also proved that the attachment of the NPs onto the chitosan films was efficacious. In effect, as the TiO2 content increased more, film surface was uniformly covered by the NPs, and no detachment occurred.

To reveal the interaction between TiO2 and chitosan before and after UV irradiation, as already presented in Section 6.3, we acquired a set of FTIR spectra. Due to the addition of oxygen atoms from the TiO2 NPs, one can observe a more intense peak from the O-H bond in **Figures 16–18**. Along that line, as the UV light photoactivated the TiO2, the spectral data revealed a smaller intensity from this bond (O▬H) after the UV irradiation. Finally, the bond nigh 3000 cm<sup>−</sup><sup>1</sup> (C▬H) indicates a degradation of the chitosan polymer as this peak decreases. This could result in a more brittle substrate to hold the nanoparticles, which should be taken into consideration in upcoming applications of the composite.

In closing, even with the rise of superbugs and the decline in effectiveness of antibiotics, innovated materials like nanoparticles show a promising future as the next generation of antimicrobial. In this context, our chitosan/TiO2 biocomposite films can represent an economic option when compared to other materials for similar applications, such as activated carbon, capable of reducing the bacteria present in water. The synthesis process is reproducible and very economical, creating a technology with ample potential application.
