Carbon Coated Alumina Nanofiber Membranes for Selective Ion Transport

Abstract

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 10 nm) 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 107 m 2 g À1 ) of membranes, while the pore size distribution maximum shifts from 28 to 16 nm. 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 À0.5 to þ0.8 V. The potential applications of produced membranes include nano-and ultrafiltration, separation of charged species, and switchable ion-transport selectivity.

Coupled thermal analysis of carbon layers deposited on alumina nanofibres

“…The nonlinear decrease of pore volume and surface area is obviously associated with the intrinsic porous structure of the deposited carbon, but in general still correlates with the increase of carbon layers thickness. As it was previously shown [37], the 60 s deposition of carbon on the surface of alumina nanofibers in the selected CVD conditions led to uniform carbon distribution along the entire cross-section of alumina disc. The X-ray fluorescence analysis of carbon coated discs was also used here to confirm the preservation of uniform carbon distribution with increasing time of CVD synthesis.…”

“…previously described results of IR spectroscopy [37]. After deposition of carbon for 60 s of CVD, the peaks characterizing the presence of С=С bond (1580 cm -1 ) and С=O bond (1236 cm -1 ) appeared.…”

“…Raman spectroscopy and measurement of electrical resistance confirm this conclusion. These findings could be employed for further development of conductive nanoporous membranes for switchable ion transport [36,37,40] as well electroconductive ceramics [33,34].…”

“…Recently, we have proposed a novel type of ion-selective membranes based on carboncoated Nafen nanofibers, which combine the advantages of ceramic nanofibrous media with good electrical conductivity [36,37]. These composite membranes demonstrate high ionic selectivity and appear to be very promising for nano-and ultrafiltration, separation of charged species, and switchable ion-transport selectivity [38][39][40].…”

Modelling of Electrochemically Switchable Ion Transport in Nanoporous Membranes with Conductive Surface

“…Recently, a new type of highly porous ceramic membranes with a conductive coating was suggested [14,15]. The membranes were prepared by vacuum filtration of a colloidal solution of Nafen alumina fibers with a diameter of about 10 nm through a porous substrate and subsequent drying and annealing.…”