Study of the Interaction of Ti–Zn as a Mixed Oxide at Different pH Values Synthesized by the Sol–Gel Method and Its Antibacterial Properties

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Abstract
TiO2, ZnO, and their combination (TiO2–ZnO) at different molar ratios and pH values (Ti–Zn A and B 3:1, 1:1, and 1:3) via the sol–gel method were characterized by SEM, XRD, UV-Vis, and FT-IR. Moreover, antibacterial tests of the nanoparticles were conducted against Escherichia coli (E. coli), Salmonella paratyphi (S. paratyphi), Staphylococcus aureus (S. aureus), and Listeria monocytogenes (L. monocytogenes). The indirect bandgap of the Ti–Zn binary oxide synthesized in the basic process at molar ratios of 3:1, 1:1, and 1:3 exhibited a higher eV (3.31, 3.30, and 3.19 eV, respectively) compared to pure TiO2 (3.2 eV) and synthesized in the acid process (3.22, 3.29, and 3.19 eV at same molar ratio, respectively); in addition, the results of the indirect bandgap were interesting due to a difference found by other authors. Moreover, the sol–gel method promoted the formation of a spherical, semi-sphere, and semi-hexagonal shape (TiO2, Ti–Zn 1:1, and Ti–Zn 1:3) with a size ≤ 150 nm synthesized during the acid process, with a crystallite size of ~71, ~12, ~34, and ~21 nm, respectively, while ZnO NPs developed a hexagonal and large size (200–800 nm) under the same synthesis process (acid). Samples were classified as TiO2 anatase phase (basic synthesis); however, the presented changes developed in the rutile phase (24% rutile phase) at an acid pH during the synthesis process. Moreover, Ti–Zn maintained the anatase phase even with a molar ratio of 1:3. The most interesting assessment was the antibacterial test; the Ti–Zn A (1:3) demonstrated a bacteriostatic effect compared with all treatments except ZnO, which showed a similar effect in dark conditions, and only Gram-positive bacteria were susceptible (Listeria monocytogenes > Staphylococcus aureus). Therefore, the Ti–Zn characteristic suggests that the results have potential in treating wastewater as well as in pharmaceutical (as drug carriers) and medical applications.

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