Enhanced antimicrobial efficacy of thermal-reduced silver nanoparticles supported by titanium dioxide

The antimicrobial efficacy of silver nanoparticles (AgNPs) is influenced by many factors, including the particle size, AgNP oxidation state and support materials. In this study, AgNPs are synthesized and supported by two types of TiO₂ powders (P25 and Merck TiO₂) using two heat-treatment temperatures (120 and 200 °C). The formation of well-dispersed AgNPs with diameters ranging from 3.2 to 5.7 nm was confirmed using transmission electron microscopy. X-ray photoelectron spectroscopy and X-ray diffraction indicated that the majority of the AgNPs were reduced from Ag⁺ to Ag⁰ at 200 °C. The AgNP antimicrobial activity was determined by the zone of inhibition against three fungi, A. niger, P. spinulosum and S. chartarum, and two bacteria, E. coli (Gram-negative) and S. epidermidis (Gram-positive). The antimicrobial activity of metallic AgNPs was more pronounced than that of silver nitrate and some antimicrobial drugs. The AgNPs exhibited optimal antimicrobial efficacy when the AgNP dispersion on the surface of TiO₂ was in the region between 0.2 and 0.7 μg-Ag/m². The minimum (critical) AgNP concentrations needed to inhibit the growth of bacteria (E. coli) and fungi (A. niger) were 13.48 and 25.4 μg/mL, respectively. The results indicate that AgNPs/TiO₂ nanocomposites are a promising disinfectant against both bacteria and fungi.