Regenerable Poly(dopamine)-Mediated\nGold Nanostructure-Decorated\nCore–Shell Nanostructures of Magnetite/Polydopamine for Catalytic\nDye Removal

In this paper, we\npresent a facile yet effective method\nfor the\nfabrication of core–shell nanoparticles (NPs) of magnetite\n(Fe<sub>3</sub>O<sub>4</sub>) and polydopamine (Fe<sub>3</sub>O<sub>4</sub>@PDA) and their decoration with a tunable amount of gold NPs\n(AuNPs). For this, Fe<sub>3</sub>O<sub>4</sub> NPs were fabricated\nthrough the polyol method and AuNPs were deposited onto Fe<sub>3</sub>O<sub>4</sub>@PDA via anchoring of as-prepared citrate-stabilized\nAuNPs or reduction of Au ions. PDA with its numerous catechol groups\nenabled the decoration of AuNPs in a well-controlled manner. The resultant\nFe<sub>3</sub>O<sub>4</sub>@PDA@Au nanosystem exhibited highly efficient\ncatalytic activity in removing crystal violet (CV) and malachite green\n(MG) as dye molecules. It was noticed that the quantity of deposited\nAuNPs was the primary determinant of the resulting catalytic activity\nof the suggested system. Both techniques resulted in NP systems demonstrating\ndistinct catalytic activity with reaction constant values of 0.83\nand 1.54 min<sup>–1</sup> for removing CV and MG dyes, respectively.\nThe complete dye removals were attained only within 4 min. Furthermore,\nthe core–shell nanosystem was easily regenerated by removing\nit from the medium via an external magnet and subsequent washing.\nEven after five cycles, the catalytic system provided satisfying activity\nin both dyes indicating its high reusability capacity. The combination\nof AuNPs with distinct characteristics of PDA and magnetic NPs makes\nthis core–shell nanosystem a viable platform for various catalytic\nand wastewater applications.