Antibacterial surfaces based on functionally graded photocatalytic Fe3O4@TiO2 core–shell nanoparticle/epoxy composites

Functionally graded epoxy composites with various concentration profiles of Fe3O4@TiO2 core–shell nanoparticles (NPs) were synthetized and characterized, with focus on their antibacterial properties. The NPs consisted of rutile, anatase, magnetite and hematite. Graded composites were produced starting with homogeneous 2 vol% to 12 vol% NPs suspensions using a magnetophorese process, leading to an enrichment of TiO2 at the surface of the composite up to 16 vol% from an initial 4 vol%. Homogeneous composites were also produced as references. Graded composites with an initial 4 vol% of NPs inactivated E. coli bacteria in less than 2 hours under simulated solar light (50 mW cm ), significantly faster than their homogeneous analogues. During bacterial inactivation the pH decreased from 6.8 to 5.0. Repetitive E. coli inactivation tests on these 4 vol% graded composites were stable up to 8 cycles and 5 min contact between the bacteria and the sample surface was enough to guarantee an adequate bacterial adhesion.