Removal of Au³⁺ and Ag⁺ from aqueous media with magnetic nanoparticles functionalized with squaramide derivatives

New magnetic hybrid nanoparticles of Fe₃O₄ coated with organosulfur-squaramide compounds are prepared. The modified-nanoparticles show a good coordination for Ag⁺ and Hg²⁺ cations in water, and present a high affinity for Au³⁺ ions. The behaviour of the squaramide-coated nanoparticles differs significantly from that previously reported for nanoparticles used as Au³⁺ scavengers. In the presence of organosulfur-squaramide, the Au³⁺ salt is reduced to gold nanoparticles that are deposited upon Fe₃O₄ nanoparticles. For the first time, the coordination capacity of the carbonyl squaramide groups with the gold cation, based on purely electrostatic cation-dipole interactions, is proved.