Electrically-driven facilitated transport of Cs+ across copper ferrocyanide channels in track etched membrane

Copper ferrocyanide (CFCN) crystals, well known for its selectivity for Cs+ ions, have been synthesized within the pores of a polycarbonate track etched membrane (PTEM) by two compartment permeation method using CuSO4 and K4Fe(CN)6. The synthesized material has been characterized by X-ray Diffraction (XRD), Small Angle X-ray Scattering (SAXS), Energy Dispersive X-ray Fluorescence (EDXRF) and Transmission Electron Microscopy (TEM) techniques. X-ray techniques confirmed the presence of nanosized ferrocyanide particles (radius ∼40 nm) within the pores of the PTEM. It has been observed from TEM analysis that the CFCN crystals are almost uniformly filling the conical shaped pores of the PTEM with the dimension of each conical shaped structure being ∼300 nm diameter at surface and ∼140 nm diameter inside. This CFCN loaded PTEM (CFCNm) has been used to study the selective transport of Cs+ over Na+ in presence of nitric acid. The rate of cation transport has been enhanced (∼300%) by application of electric field across the membrane. A cation exchange membrane (Nafion-1135) has been coupled with the CFCNm to protect the ferrocyanide crystals from early degradation. The transport behavior of the Nafion-CFCNm composite system under different experimental conditions has been studied and explanation has been given for the differential transport of Cs+ over Na+ through this membrane. The Cs+ transport rate of the membrane has been found to be limited by the ion exchange capacity of the CFCNm.