Study of one-step photosynthesis of Ag nanoparticles.

During photosynthesis of metal nanoparticles (NPs) in aromatic ketone systems, the aromatic ketone triplets are explored as hydrogen atom/electron abstractors which yield highly reactive radicals. However, their electron donation ability is sparsely recognized. Here we report the investigations of benzophenone (BP)-initiated one-step photosynthesis of Ag NPs in H donor free system using spectroscopic and theoretical methods. Experimentally, the direct observations of BP cation radical (BP+·) and Ag NPs via transit and steady-state absorption spectroscopy demonstrate the electron donation ability of BP triplets which directly reduce Ag+ to Ag0. In the following reactions, both theoretical calculation and experimental results reveal that the generated BP+· recovers itself to BP by grabbing an electron from NO3- and the generated nitrate radicals (NO3·) then decay to nitrogen oxides. Notably, BP plays a role as photocatalyst in our system. This study details the mechanism of one-step photosynthesis of Ag NPs which provides a new insight of aromatic ketones in photochemistry and may offer a facile approach to photosynthesis of metal NPs.