Photochemical preparation of polyaminocyclodextrin-capped silver nanocomposites: mechanistic insights

Photoreduction of silver salts in the presence of three polyaminocyclodextrin derivatives (AmCD, Figure 1) constitutes a simple and straightforward route to obtain stable Ag nanoparticles. These systems have been suitably characterized (UV-vis, FT-IR, TEM, Figure 2) and tested for their antimicrobial activity.1 We observed that Ag photoreduction is effectively induced by irradiation with green light (513 nm); however, best performances are achieved with the use of a light source having at the same time a significant emission in the near-infrared (NIR) region. On the grounds of analytical and kinetic evidences, we hypothesized a multi-step mechanism for nanoparticle formation. In particular, green irradiation induces an electron-transfer process producing small Ag0 seeds, while the capping agent functions as sacrificial reductant, affording different species (radicals, iminium ions aldehydes). These, in turn, function as reducing agents in a secondary step stimulated by NIR irradiation, from which the final nanocomposite is ultimately obtained.