Antimicrobial Activity against f. sp. dianthi of TiO/ZnO Thin Films under UV Irradiation: Experimental and Theoretical Study.

We deposited bare TiO and TiO/ZnO thin films to study their antimicrobial capacity against f. sp. dianthi. The deposit of TiO was performed by spin coating and the ZnO thin films were deposited onto the TiO surface by plasma-assisted reactive evaporation technique. The characterization of the compounds was carried out by scanning electron microscopy (SEM) and powder X-ray diffraction techniques. Furthermore, density functional theory (DFT) and time-dependent DFT (TDDFT) calculations were performed to support the observed experimental results. Thus, the removal of methylene blue (MB) by adsorption and posterior photocatalytic degradation was studied. Adsorption kinetic results showed that TiO/ZnO thin films were more efficient in MB removal than bare TiO thin films, and the pseudo-second-order model was suitable to describe the experimental results for TiO/ZnO ( = 12.9 mg/g; = 0.14 g/mg/min) and TiO thin films ( = 12.0 mg/g; = 0.13 g/mg/min). Photocatalytic results under UV irradiation showed that TiO thin films reached 10.9% of MB photodegradation ( = 1.0 × 10 min), whereas TiO/ZnO thin films reached 20.6% of MB photodegradation ( = 3.9 × 10 min). Both thin films reduced the photocatalytic efficiency by less than 3% after 4 photocatalytic tests. DFT study showed that the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) energy gap decreases for the mixed nanoparticle system, showing its increased reactivity. Furthermore, the chemical hardness shows a lower value for the mixed system, whereas the electrophilicity index shows the biggest value, supporting the larger reactivity for the mixed nanoparticle system. Finally, the antimicrobial activity against f. sp. dianthi showed that bare TiO reached a growth reduction of 68% while TiO/ZnO reached a growth reduction of 90% after 250 min of UV irradiation.