Preparation and Structural Properties of Tin Oxide−Montmorillonite Nanocomposites

Tin oxide intercalated montmorillonite nanocomposites were prepared by an in situ preadsorption method in aqueous solution in the absence of surfactants and organic solvents. The tin oxide particle size was controlled by adjusting the relative supersaturation ratio, S ( S = ( Q − L )/ L ), where Q is the amount of the dissolved material, the Sn(OH) 4 precipitate, and L is its solubility). Increasing the relative supersaturation results in a progressive increase of the size of the SnO 2 nanoparticles up to a maximum, after which a further increase of S results in a decrease of the size of the nanoparticles, since their growth is inhibited. Calcination of the 2−3 nm diameter SnO 2 /Sn(OH) 4 nanoparticles at 400 °C for 3 h resulted in the formation of an oxide lattice structure from a tin oxide/hydroxide structure. XRD measurements indicated the sizes of tin oxide nanocrystals to be in the 1−2 nm diameter range between the layers of montmorillonite. The specific surface area of montmorillonite significantly changed from 30 to 112.5 m 2 /g upon SnO 2 intercalation, as evidenced by BET. The thermoanalytical investigations revealed the optimal calcination temperature of the nanocomposites (400 °C) and proved the presence of the SnO 2 nanoparticles by the heat effect of their crystallization process. The Mössbauer studies of the samples indicated the particle size dependence on the effective vibrating mass ( M eff ) and the Debye temperature (ϑ M ) of the tin oxide nanocrystals. It was confirmed by all of the measurement methods that smaller particle size can be attained by increasing the relative supersaturation ratio of the Sn(OH) 4 precipitate.