Anisotropic magnetic mesoporous silica catalyst-stir-bars for one-pot reduction-oxidation reaction

Asymmetric magnetic mesoporous silica (AMMS), consisting of mesoporous silica (mSiO₂) anchored at one end of ferric oxide (Fe₃O₄) nanoparticles (NPs), has emerged as a promising catalyst carrier owing to its magnetic recyclability, high loading capability, and unique spatial separation, which enables enhanced mass transfer and accessibility of catalytic active sites. However, conventional AMMS systems typically suffer from chemical isotropy resulting from complete Fe₃O₄ encapsulation and limited tunability of mSiO₂ morphology, thereby seriously restricting their efficacy in practical catalysis. Herein, we report an ionization-degree-mediated anisotropic assembly strategy to synthesize unconventional AMMS featuring exposed Fe₃O₄ (eFe₃O₄) heads and length-tunable mSiO₂ rods. Upon loading with Au NPs, the resultant asymmetric magnetic mesoporous silica catalyst-stir-bars (AMMCs) exhibit enhanced catalytic performance in both Fenton oxidation of Acid Orange 7 (AO7) and hydrogenation of 4-nitrophenol (4-NP) and 2-nitroaniline (2-NA), achieving ultra-fast reaction rates that are orders higher than previously reported Au-based supported catalysts. Notably, the AMMCs also enable efficient one-pot reduction-oxidation catalysis of tetrabromobisphenol A (TBBPA), a reaction typically hindered by incompatible redox-active sites within traditional catalyst systems. In addition, the anisotropic rod-like architecture imparts magnetic-field-induced self-stirring capability, enhancing reaction kinetics by 1.65-fold. This work provides a robust and versatile synthetic strategy for structurally tunable and multifunctionally anisotropic magnetic catalysts for complex one-pot tandem catalysis reactions.