Combined Tween 20-Stabilized Gold Nanoparticles and Reduced Graphite Oxide–Fe₃O₄ Nanoparticle Composites for Rapid and Efficient Removal of Mercury Species from a Complex Matrix

This study describes a simple method for removing mercuric ions (Hg²⁺) from a high-salt matrix based on the use of Tween-20-stabilized gold nanoparticles (Tween 20-Au NPs) as Hg²⁺ adsorbents and composites of reduced graphite oxide and Fe₃O₄ NPs as NP collectors. Citrate ions adsorbed on the surface of the Tween 20-Au NPs reduced Hg²⁺ to Hg⁰, resulting in the deposition of Hg⁰ on the surface of the NPs. To circumvent time-consuming centrifugation and transfer steps, the Hg⁰-containing gold NPs were collected using reduced graphite oxide–Fe₃O₄ NP composites. Compared with the reported NP-based methods for removing Hg²⁺, Tween 20-Au NPs offered the rapid (within 30 min), efficient (>99% elimination efficiency), durable (>10 cycles), and selective removal of Hg²⁺, CH₃Hg⁺, and C₂H₅Hg⁺ in a high-salt matrix without the interference of other metal ions. This was attributed to the fact that the dispersed Tween 20-Au NPs exhibited large surface-area-to-volume ratio to bind Hg²⁺ through Hg²⁺–Au⁺ metallophilic interactions in a high-salt matrix. The formation of graphite oxide sheets and reduced graphite oxide–Fe₃O₄ NP composites was demonstrated using X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy, Fourier transform infrared spectrometry, and transmission electron microscopy. The mechanism of interaction between Tween 20-Au NPs and Hg²⁺ was studied using visible spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy