Aptamer-functionalized and silver-coated polydopamine-copper hybrid nanoflower adsorbent embedded with magnetic nanoparticles for efficient mercury removal

Mercury (Hg) emissions are increasing annually owing to rapid global industrialization. Hg poisoning can severely affect the human body owing to its persistence and bioaccumulation. In this study, hybrid nanoflowers (NFs) were synthesized by promoting the formation of primary copper-phosphate crystals coordinated with polydopamine (PDA) and Fe3O4 magnetic nanoparticles (MNPs), followed by coating with silver nanoparticles on the surface of the NFs (Ag-MNP-PDA-Cu NFs). The results suggest that the hierarchical structure of the NFs enabled a large surface area with nanosized pores, which were exploited for Hg adsorption. The adsorbed Hg ions could be further eliminated from the solution based on the magnetic characteristics of the NFs. Additionally, hybrid NFs functionalized with Hg2+-binding aptamers (Apt-Ag-MNP-PDA-Cu NFs) were prepared based on the silver-sulfur interactions between the Ag-MNP-PDA-Cu NFs and thiol-modified aptamers. The performance of both adsorbents demonstrated that the immobilization of Hg2+-binding aptamers significantly improved the elimination of Hg from solution. The Hg2+ adsorption isotherm of the Apt-Ag-MNP-PDA-Cu NFs followed the Dubinin-Radushkevich model, with a maximum adsorption capacity of 1073.19 mg/g. The Apt-Ag-MNP-PDA-Cu NFs adsorbed greater amounts of Hg2+ than the non-functionalized NFs at the same concentrations, which confirmed that the functionalization of Hg2+-binding aptamers on the NFs improved the Hg2+ removal performance. The results suggest that Apt-Ag-MNP-PDA-Cu NFs could serve as an efficient Hg-removing adsorbent, possibly by providing binding sites for the formation of T-Hg2+-T complexes.