Removal of Au and Ag from aqueous media with magnetic nanoparticles functionalized with squaramide derivatives.

New magnetic hybrid nanoparticles of FeO coated with organosulfur-squaramide compounds are prepared. The modified-nanoparticles show a good coordination for Ag and Hg cations in water, and present a high affinity for Au ions. The behaviour of the squaramide-coated nanoparticles differs significantly from that previously reported for nanoparticles used as Au scavengers. In the presence of organosulfur-squaramide, the Au salt is reduced to gold nanoparticles that are deposited upon FeO 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.