“…For removing HMs from aqueous media, the essential MSs include sulfides of transition metals such as zinc [14,15], copper [31,32], cobalt [21,22], iron [33][34][35], and cadmium [14,36,37]. MSs contain localized or migratory sulfide 3d electrons or both, exhibiting hybridization with sulfide 3s and 3p orbitals, stabilizing the closest cation neighbors in the trigonal pyramidal, octahedral, tetrahedral, and other configurations in the anion arrays [30,38].…”