NIR-enhanced multi-mode catalytic activity over Pd nanocrystals sandwiched within magnetic polydopamine hollow spheres

With the rapid development of social industrialization, energy crisis and environmental problems are becoming increasingly serious. Therefore, there is an urgent need to synthesize multi-mode nanocatalysts for general application. In this paper, a h-Fe3O4@Pd/PDA nanocatalyst with Pd nanocrystals sandwiched between a h-Fe3O4 hollow sphere and a polydopamine (PDA) shell was prepared by a simple redox-oxidative polymerization method. The catalytic activity of h-Fe3O4@Pd/PDA hollow spheres was evaluated using selective reduction hydrogenation of 4-nitrostyrene, reduction of 4-nitrophenol and oxidation of 3,3 ',5,5 '-tetramethylbenzidine (TMB) as catalytic models. h-Fe3O4@Pd/PDA has reduction kinetics of 4-nitrophenol up to 0.77 min-1 mg-1. Importantly, the rate of 4-nitrophenol reduction catalyzed by h-Fe3O4@Pd/PDA was enhanced by 1.43 times under near infrared light (NIR, 808 nm) irradiation. In addition, NIR laser can induce the selective reduction of 4-nitrostyrene to 4-aminostyrene by h-Fe3O4@Pd/PDA with a selectivity of 84.8%. Under different reaction scenarios, h-Fe3O4@Pd/PDA hollow spheres could be recycled by magnetic recovery, and the catalytic reaction activity was above 70% after six cycles. As a result, owing to the simple fabrication, good magnetic separation and high NIR-enhanced catalytic properties, h-Fe3O4@Pd/PDA exhibited a wide range of potential in nanocatalysis. A multi-mode magnetic nanocatalyst shows typical photothermal enhancing catalytic effect under near-infrared (NIR) light irradiation.