Ternary Biocidal-Photocatalytic-Upconverting Nanocomposites for Enhanced Antibacterial Activity

Active antibacterial food packaging represents one of the most rapidly developing techniques in the food industry. The ability to inhibit, inactivate, kill, or maintain a low level of microbials in food products or food packages is crucial to reducing global foodborne diseases. Notably, metallic silver (Ag) and semiconducting titanium dioxide (TiO₂) nanomaterials as well as their nanocomposites have been widely studied for food packaging because of their intrinsic biocidal and photocatalytic properties, respectively. However, they have inherent limitations associated with potential nanotoxicity of Ag nanoparticles and the need for ultraviolet (UV) irradiation for wide-bandgap TiO₂nanomaterials to invoke photocatalytic oxidation of microbials. In this context, upconverting nanocrystals (UCNCs) convert near infrared photons into visible and UV photons that could excite TiO₂without the use of a UV source. Herein, we designed ternary multifunctional nanocomposites composed of plasmonic Ag, photocatalytic TiO₂, and upconverting NaYF₄@Yb:Tm NPs as highly efficient biocidal nanomaterials under ambient light. The incorporation of UCNCs into the nanocomposites is found to be the key to enhanced antibacterial performance. Compared to Ag NP and Ag/TiO₂nanocomposite counterparts, the ternary Ag/TiO₂/NaYF₄@Yb:Tm nanocomposites yield superior antibacterial performance against Escherichia coli under both ambient light and solar simulator irradiation with UV photons filtered, when either applied alone or mixed with cellulose nanofibrils and then processed into films. Such multicomponent nanocomposites have great potential for use in food packaging as they reduce the amount of potentially toxic Ag used and are able to function without UV.