Spatially ensemble of polydopamine-protected-Au nanocrystals on Fe₃O₄@SiO₂@γ-AlOOH microflower for improving catalytic performance

Highlights: • Fe₃O₄@SiO₂@γ-AlOOH@Au/PDA with hierarchical nanostructures has been developed. • The loading capacity and dispersity of Au nanocrystals are both improved. • PDA-confined-Au-nanocrystals hybrid shell is achieved by a simple one-step method. • This flower-like catalyst exhibits superior catalytic activity and recyclability. Advanced nanocatalysts integrating with high activity and recyclability is one of the most important issues in heterogeneous catalysis. Magnetic hierarchical nanostructures comprising noble metal nanocrystals confined within a protecting penetrable shell will be favored as an efficient candidate toward robust catalytic reactions. This work reports a proof-of-concept magnetic separable nanocatalyst with the polydopamine (PDA)-confined-Au-nanocrystals assembled on the hierarchical surface of Fe₃O₄@SiO₂@γ-AlOOH microflower (Fe₃O₄@SiO₂@γ-AlOOH@Au/PDA). Because of the high surface area of γ-AlOOH hierarchical nanoarchitectures, the loading capacity and dispersity of Au nanocrystals are both improved. These magnetic microflowers present excellent catalytic efficiency and cycling performance in reduction of 4-nitrophenol to 4-aminophenol, which can be ascribed to the superior structure of catalyst. After 9 cycles, the activity of Fe₃O₄@SiO₂@γ-AlOOH@Au/PDA maintains as high as 97.3% due to the protection of PDA shell. In comparison to the spherical Fe₃O₄@SiO₂@Au/PDA, the as-prepared Fe₃O₄@SiO₂@γ-AlOOH@Au/PDA microflowers exhibit quicker catalytic dynamic. The concept of hierarchical nanostructure and penetrable PDA protective layer will be instructive for fabricating high-performance nanocatalysts.