The facilitated transport of copper(II), zinc(II), cobalt(II), and nickel(II) ions across polymer inclusion membranes (PIMs), which consist of cellulose triacetate as polymeric support, o-nitrophenyl pentyl ether as plasticizer and 1-alkylimidazole as ion carrier was reported. PIM was characterized by using atomic force microscopy (AFM) technique. The results show that Cu²⁺ can be separated very effectively from others heavy and transition metal cations as Zn²⁺, Co²⁺, and Ni²⁺ (at concentration of 10- 3 M each). Alkyl substituents in position 1 of imidazole ring have an effect on hydrophobic properties and the initial flux of the transported metal ions. Also, the influence of the chloride ions concentration on the separation process was investigated. To explain the mechanism of membrane transport the diffusion of metal ions complexes with 1-alkylimidazole was also measured.