Preparation of conducting ultrafiltration membranes from redispersable, nanoscaled, crystalline SNO2:Sb particles

Abstract

Inorganic membranes prepared by the sol gel method are promising for use as filter in separation processes. Unsupported and supported conducting membranes have been produced from redispersable nanoscaled crystalline Sb-doped SnO2 powders with a Sb content up to 5 mole % (with respect to Sn). The crystalline particles are monosized (~4 nm) and fully redispersable in aqueous solution at pH >= 8 with a solid content up to 36.8 vol%. By thermal treatment at different temperatures and times, the pore size diameter of the material can be adjusted from 4 to 20 nm with a very narrow pore size distribution (~ +-1 nm) and a total porosity of 63%, practically independent of the sintering parameters. Uniaxial compacted unsupported membranes present similar characteristics with however larger pore size distribution (+-5 nm) and 80% total porosity. Their electrical resistance decreases with sintering temperature and time down to 4 Omega (800°C, 8 h). Fully dispersed aqueous solutions of the powder (7,8 vol%) were used to prepare transparent conducting porous coatings on glass or ceramics by spin-coating. AFter thermal treatment (1 hour at 550°C) single layers 200 nm thick have a typical specific electrical resistance p=2.5-10-² Omega cm and an optical transmission in the visible range measured against air of 90%.