Noble metals decorated hierarchical maghemite magnetic tubes as an efficient recyclable catalyst

The noble metal nanocatalysts on high surface area magnetic material supports have huge technological importance in the field of catalysis. The green synthesis of magnetic-noble metal hybrid material has another technological importance. In this study, we report a novel, efficient, and sustainable synthesis methodology for Au nanoparticles (NPs) deposited hierarchical magnetic maghemite (γ-Fe₂O₃) tubes. In this methodology, the green tea extract was used as a reducing agent for both iron oxide and Au NPs synthesis. The natural cotton fibers were used as a sacrificial template to obtain porous and high surface area (90m²/g) magnetic γ-Fe₂O₃ tubes. Further, the Au NPs (7±2nm) were in situ deposited onto the tubes surface after reduction of Au salt by green tea extract. The XPS spectra was confirmed the presence of negatively charged Au on the iron oxide supports due to charge transfer process and strong metal-support material electronic interaction. The Au NPs decorated γ-Fe₂O₃ tubes were possessed 18emu/g saturation magnetization at room temperature which is large enough for the magnetic separation. The synthesized material was showed very good catalytic activity for the hydrogenation reaction of 4-nitrophenol to aminophenol conversion. As the catalyst has very good magnetic property, the reusability of catalyst was checked after magnetic separation and found only 0.29% reduction in catalytic activity after the sixth cycle. Further, the Ag and Pd NPs decorated γ-Fe₂O₃ tubes were also synthesized and tested for the same catalytic reaction and found the highest activity for Pd.