Carbon Coated Alumina Nanofiber Membranes for Selective Ion Transport

The authors propose a novel type of ion-selective membranes, which combine the advantages of ceramic nanofibrous media with good electrical conductivity. The membranes are produced from Nafen alumina nanofibers (diameter around 10nm) by filtration of nanofiber suspension through a porous support followed by drying and sintering. Electrical conductivity is achieved by depositing a thin carbon layer on the nanofibers by chemical vapor deposition (CVD). Raman and FTIR spectroscopy, X-ray fluorescence analysis, and TEM are used to confirm the carbon structure formation. The deposition of carbon leads to decreasing porosity (from 75 to 62%) and specific surface area (from 146 to 107m(2) g(-1)) of membranes, while the pore size distribution maximum shifts from 28 to 16nm. Measurements of membrane potential in an electrochemical cell show that the carbon coated membranes acquire high ionic selectivity (transference numbers 0.94 for anion and 0.06 for cation in aqueous KCl). Fitting the membrane potential data by the Teorell-Meyer-Sievers model shows that the fixed membrane charge increases proportionally with increasing electrolyte concentration. The carbon coated membranes are ideally polarizable for applied voltages from -0.5 to +0.8V. The potential applications of produced membranes include nano- and ultrafiltration, separation of charged species, and switchable ion-transport selectivity.