Synthesis, characterization and metal-uptake behaviour of pyrazole ligands immobilized on silica

The novel didentate ligand 2-(3,5-dimethyl-1-pyrazolyl)ethylamine (Naed) and the tridentate ligand bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl] amine (ddaH) were immobilized onto silica by two different methods. The first method involves the coupling of the ligand to silica, previously modified with (3-glycidyloxypropyl)trimethoxysilane (GLYMO). The second method involves the coupling of the ligand to the oxirane ring of GLYMO in a homogeneous reaction, followed by grafting onto silica, yielding the highest ligand concentrations on the silica (about 0.3 mmol/g silica). With the first method, only part of the epoxy group reacts with the ligand. With Naed, tertiary amines are also formed through reaction of the primary amine group of the ligand with two epoxy groups. These new ion-exchange materials selectively adsorb Cu2+ (maximum capacity 0.11–0.26 mmol Cu2+ per gram of ion exchange) at pH > 2 from aqueous solutions containing a mixture of the bivalent metal ions, Cu2+, Cd2+, Zn2+, Ni2+ and Co2+. For products containing the didentate ligand Naed as the chelating group, the metal-ion capacity decreases rapidly with decreasing pH, while the Cu2+ -uptake capacity for the product containing the tridentate ligand ddaH is comparatively high at low pH.