Novel Anion Exchange Method for Exact Antimony Doping Control of Stannic Oxide Nanocrystal Powder

There are major problems associated with the preparation of nanometer-sized antimony-doped stannic oxide using the current sol–gel processes, such as difficulties in removing chlorine, in accurate doping of antimony, and in the repeatability of doping. This paper presents a novel solution method of doping, which involves a precipitation–condensation process with non-aqueous ion exchange for removal of chlorine. This involved hydrolysis of SnCl4·5H2O and SbCl3 in an ethanol–ammonia anion-exchange resin mixture at pH=6–8. The removal of chlorine ion and the hydrolysis are conducted at the same time. The short duration of hydrolysis prevents the formation of high condensates. The use of ion-exchange resin saves a great deal of solvent and allows all the hydrolysis products to be recovered by distillation. This ensured that the doping is exact. The determination of antimony within the dry hydrolysate on an atomic absorption spectrometer confirmed the doping accuracy and the repeatability of the method. The proportion of Sb to Sn was found to be between 0.0528 and 0.0550 molar fraction at the optimum conductivity of the nanocrystalline SnO2 doped with Sb. TEM pictures and XRD patterns showed that nanocrystallites fired from the powder were small and had a narrow size range of 10±5 nm at 650°C.