Regenerable Poly(dopamine)-Mediated Gold Nanostructure-Decorated Core–Shell Nanostructures of Magnetite/Polydopamine for Catalytic Dye Removal

In this paper, we present a facile yet effective method for the fabrication of core-shell nanoparticles (NPs) of magnetite (Fe₃O₄) and polydopamine (Fe₃O₄@PDA) and their decoration with a tunable amount of gold NPs (AuNPs). For this, Fe₃O₄ NPs were fabricated through the polyol method and AuNPs were deposited onto Fe₃O₄@PDA via anchoring of as-prepared citrate-stabilized AuNPs or reduction of Au ions. PDA with its numerous catechol groups enabled the decoration of AuNPs in a well-controlled manner. The resultant Fe₃O₄@PDA@Au nanosystem exhibited highly efficient catalytic activity in removing crystal violet (CV) and malachite green (MG) as dye molecules. It was noticed that the quantity of deposited AuNPs was the primary determinant of the resulting catalytic activity of the suggested system. Both techniques resulted in NP systems demonstrating distinct catalytic activity with reaction constant values of 0.83 and 1.54 min^-1 for removing CV and MG dyes, respectively. The complete dye removals were attained only within 4 min. Furthermore, the core-shell nanosystem was easily regenerated by removing it from the medium via an external magnet and subsequent washing. Even after five cycles, the catalytic system provided satisfying activity in both dyes indicating its high reusability capacity. The combination of AuNPs with distinct characteristics of PDA and magnetic NPs makes this core-shell nanosystem a viable platform for various catalytic and wastewater applications.