Synthesis of nanostructured SnO2 dispersed on amorphous alumina by hydrothermal method

Nanostructured SnO2 dispersed on amorphous alumina was synthesised by a simple hydrothermal method using urea as hydrolytic agent and simple inorganic salts [SnCl2.2H2O and Al(NO3)3.9H2O] as precursors. The synthesis was carried out in an autoclave at 180°C with an in situ pressure of 12 atmospheres and the powders were calcined at 600, 1000 and 1200°C. Single aluminium oxide and mixed oxides in the molar ratios 1:2 and 2:1 were also prepared under identical conditions. The oxides were characterised by X-ray diffraction (XRD), magic angle spinning nuclear magnetic resonance spectroscopy (27Al MAS NMR), transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), BET surface area, infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). Quite interestingly, as prepared mixed oxide was formed of nanoSnO2 starting from stannous chloride precursor and of spherical particles in the range of 20–50 nm while Al species was formed as amorphous nanoAlOOH. On calcination, AlOOH was transformed to alumina but in all the calcined mixed oxides, alumina was in amorphous phase. Heat treatment reduced the surface area and increased the crystallite size with temperature. It was shown that the nitrate ion present in the hydrothermal solution acts as the internal oxidising agent, thus oxidising SnO to SnO2 and the presence of excess Al precursor favours the formation of stannic oxide only; on the other hand, excess Sn produces both SnO and SnO2 and the yield of SnO2 was directly proportional to ratio of Al precursor.