Antimicrobial Colloidal Suspensions of Silver-Titania

Titanium dioxide nanoparticles (TiO2Np) exhibiting properties of photocatalyst under ultraviolet light (UV) exposition related with destruction of some hazardous organic moieties. To enhance the antibacterial characteristics of this material in our works, we developed a new method of TiO2Np doping with silver nanoparticles (Ag 0 Np), whose biocidal properties are well defined. The obtained products, Ag 0 Np/TiO2Np, in the form of suspensions and powders were characterized from chemical, physical and antimicrobial activity point of view. In addition, a mechanism of Ag + ions reduction reaction to Ag 0 Np has been proposed. The developed method of the Ag 0 Np/TiO2Np synthesis consists of the in situ chemical deposition of the Ag 0 Np on the dispersed TiO2Np in the form of anatase, using aqueous solutions of poly(acrylic acid sodium salt) (PAS) and NaBH4. The Ag 0 Np synthesis was carried out both in the presence and absence of TiO2Np. The chemical composition of Ag 0 Np/TiO2Np was assessed by atomic absorption spectrometrical method (AAS). The physical properties were evaluated as follows: crystallite structure and dimensions of nanopowders by X-ray diffraction method (XRD), UV-Vis absorption of colloidal suspensions and UV-Vis reflectance of nanopowders by spectrophotometrical method, grain size distribution of nanoparticles by dynamic light scattering method (DLS), stability of colloidal suspensions by zeta potential measurements, forms and shapes of Ag 0 Np and Ag 0 Np/TiO2Np by transmission electronic microscopy (TEM) and scanning electronic microscopy (SEM) respectively. The antimicrobial activity was tested by standard methods against some broad spectra of fungi and bacteria. In suspensions, the concentration of TiO2Np was 1 wt. % and the concentration of Ag 0 Np varied in the range of 0.005…0.15 wt. %. The Ag 0 Np suspensions and Ag 0 Np/TiO2Np suspensions were stable from the physical and chemical point of view. The physical characterization test results were in accordance, proving the achievement of colloidal solutions containing Ag 0 Np and TiO2Np spherical nanocrystallite with average diameters of 4.1 nm and 7.8 nm, respectively. The results of the biological tests showed the high fungistatic and antibacterial activities of both products in form of colloidal suspensions and powders. The developed "one pot method" is efficient, ecological and easy to be scaled-up. The obtained products have biological activity but it depends on the nature of the tested germs, lowering in the series: Gram negative bacteria, Gram positive bacteria and fungi. Also, a synergistic action was proved at destroying of Trichoderma viride fungus, which was not obtained either for Ag 0 Np or for TiO2Np, independently.