Easy preparation of porous polyurea through copolymerization of toluene diisocyanate with ethylenediamine and its use as absorbent for copper ions

Abstract

Porous and functional polyurea (PPU) is prepared through a very simple one-step precipitation copolymerization of toluene diisocyanate and ethylenediamine in acetonitrile, and is shown to have high adsorption for Cu2+ ions with high selectivity among 5 ions tested. Effects of pH, adsorption time and initial ion concentration on the adsorption are studied. Compared with a group of reported porous adsorbents, this PPU is of high performance. Based on X-ray photoelectron spectroscopy on PPU before and after the adsorption, the high adsorption of Cu2+ ions is interpreted by the formation of multifunctional complexations of the ions not only with the terminal amines of PPU, but also with oxygen and nitrogen atoms of its carbamido units. Adsorption kinetics simulations by pseudo-first and pseudo-second-order models show that this adsorption follows the latter one; The adsorption analysis using isothermal adsorption equations shows that Freundlich equation is well fitted. All these results are in good agreement with the proposed mechanism for the adsorption process. Selective adsorption tests for different metal ions, i.e. Cu2+, Ni2+, Pb2+, Cd2+ and Cr3+, demonstrate that PPU is highly selective towards Cu2+. Reusability of PPU is also tested, which reveals that 82.5% of the initial adsorption capacity is retained at the fifth recycled use for Cu2+ adsorption.