This invention is related to a composition of matter useful for sequestering target metal-ions from an environment, said composition comprising a polymer and derivatized nanoparticles comprising inorganic nanoparticles having an attached metal-ion sequestraint, wherein said inorganic nanoparticles have an average particle size of less than 200 nm and the derivatized nanoparticles have a stability constant greater than 10.sup.10 with iron (III).