Hollow Ag@Pd Core–Shell Nanoparticles as Photocatalysts for the Plasmon-Mediated Activation of Oxygen and Oxidation of Benzyl Alcohol

In this work, we propose a plasmon-mediated method to activate oxygen for oxidizing benzyl alcohols to aldehydes. First, hollow Ag@Pd core–shell nanoparticles were prepared and characterized and afterward explored for selective oxidation of benzyl alcohols under visible light illumination. Then, electron paramagnetic resonance analysis and spectroscopic measurements suggested that the main active species responsible for the selective oxidation was 1O2, which was subsequently proved to be generated from the transformation of superoxide radicals •O2–. The light illumination and the presence of a Pd shell were the prerequisites for the successful generation of •O2– and 1O2. Furthermore, the wavelength-dependent performance of Ag@Pd verified the plasmon-mediated nature of these core–shell-type nanocatalysts. Finally, a plausible mechanism of plasmonic activation of oxygen and selective oxidation of benzyl alcohols on Ag@Pd was proposed. Our research opens a green and sustainable way to activate molecular O2 into 1O2 for selective oxidation.