Synthesis of polyamic hydrazide and its application for removal of heavy metal ions from industrial wastes

Abstract

Terephthaloyl dichloride was synthesized via the reaction of terephthalic acid and thionyl chloride. Then, terephthaloyl dichloride reacted with hydrazine hydrate to obtain terephthaloyl hydrazide (TPH). Finally, a novel polymer, polyamic hydrazide (PAH), was synthesized via the reaction of TPH and pyromellitic dianhydride. The obtained polymer was characterized with scanning electron microscopy, nuclear magnetic resonance spectroscopy, Fourier transform infrared spectroscopy, thermal gravimetric analysis, and elemental analysis. The prepared polymer was successfully used for removal of Pb2+ and Cd2+ ions from industrial wastes and the effects of influencing parameters such as pH, contact time, concentration of Pb2+ and Cd2+ ions, background electrolytes, and temperature were investigated. The maximum adsorption capacities of Pb2+ and Cd2+ were found to be 119.6 and 56.6 mg g−1, respectively. The required times in achieving equilibrium between adsorbent and Pb2+ and Cd2+ ions were 30 and 60 min, respectively. The synthesized PAH adsorbent was reusable and its adsorption capacity remained almost constant at least for four adsorption/desorption cycles. The kinetics and mechanism of the adsorption of Pb2+ and Cd2+ on the surface of the prepared polymer were studied and it was found that complexation reactions between active sites of the polymer surface and metal ions is the possible mechanism for adsorption of Pb2+ and Cd2+.