producing a material with good potential applications as particles in gas sensor technology.
This communication described the synthesis of a nanostructured material with excellent potential for gas sensor applications. Nb 2 O 5 -doped SnO 2 particles with a narrow particle size distribution and an average 8 nm particle size were obtained. A novel approach was used to control particle size during the synthesis of SnO 2 processed by the polymeric precursor method. This new approach is based on the control of particle growth during synthesis through the use of dopants such as Nb 2 O 5 . This work involves important aspects that can be applied to the synthesis of nanostructured materials prepared by the polymeric precursor method. The addition of Nb 2 O 5 can modify the rate of nucleation during the SnO 2 crystallization process, promoting a high rate of nucleation. After nucleation, Nb 2 O 5 can inhibit particle growth, thus preventing the formation of necks between particles and the process of coalescence. The probable surface segregation of Nb 2 O 5 suggested by the lattice parameter measurements can contribute toward the inhibition of particle growth. [5] These factors suggest that the nucleation growth process usually observed in the polymeric precursor method can be controlled by additives. More detailed studies about these factors, as well as the effects of other additives, are currently in progress.
Experimental
Doped and undoped SnO 2 particles were synthesized by the polymeric precursor method using an aqueous tin citrate solution prepared from SnCl 2 ×2H 2 O (Mallinckrodt Baker, USA, purity >99.9 %) and citric acid (E. Merck, Germany, purity >99.9 %) with a citric acid/metal ratio of 3:1 (in mol). For the synthesis of Nb 2 O 5 (5 mol.-%) doped SnO 2 particles, an aqueous solution of niobium citrate was prepared from niobium ammonium oxalate, NH 4 H 2 [NbO(C 2 O 4 ) 3 ] 3 ×H 2 O (CBMM, Brazil), and citric acid with a citric acid/ metal ratio of 3:1 (in mol). The aqueous solution of niobium citrate was added to the aqueous solution of tin citrate and mixed in the appropriate amount. Ethylene glycol was added to the citrate solutions, at a mass ratio of 40:60 in relation to the citric acid in both syntheses, to promote a polymerizing reaction. After polymerization at temperatures of 90 C to 120 C for several hours, the solid resin was treated at 300 C for 6 h. The resulting amorphous precursor was ground in a ball mill and calcined at 600 C for 2 h in air.