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.