Synthesis and Gas Adsorption Property of Conductive SnO2 Porous Gels

Conductive tin oxide porous gels were synthesized by controlled gelation of hydrous tin oxide sols prepared by precipitation from homogeneous solution with heat treatment from 400° to 1100°C. Measurements of density, pore-size distribution, and apparent crystallite size by XRD indicated characteristic evolution of a pore structure during heating: pores interconnected each other through a bulky sample having a narrow size distribution character grew progressively without any substantial porosity change as gelation temperature was raised. Variations in the resistance of the porous samples with introduction of different gas molecules (mostly N2↔O2) were examined in detail. The samples formed by gelation at 400°C showed a high sensitivity in the resistivity-gas adsorption relation, which might be due to an incomplete surface structure of microcrystalline particles. Decreases in the specific surface area and also in the contribution of surface conductivity with increasing temperature of gelation, on the other hand, resulted in the rapid lowering of the gas-sensitivity for the samples obtaind at elevated temperatures.