Preparation and characterization of SnO2 nanoparticles of enhanced thermal stability: The effect of phosphoric acid treatment on SnO2·nH2O

Modified tin dioxide nanoparticles of enhanced thermal stability were prepared by sol–gel technique. The main point of the procedure is phosphoric acid treatment of the tin oxide hydrate (SnO2·nH2O). During the procedure, the molar ratio of P:Sn was varied in the range of 0.01–3.4. The structure and morphology of the modified SnO2 particles (P-SnO2) and that of two reference samples (SnO2 and SnHPO4/SnP2O7) were studied with various methods. diffraction (XRD) and diffuse reflectance infrared Fourier transform (DRIFT) measurements reveal that there are various tin phosphate compounds on the surface of SnO2 particles, improving the thermal stability of the original particles. The phosphate-containing shell formed on tin oxide hydrate inhibits sintering of the particles during calcination. The amorphous untreated SnO2 particles undergo crystallization at around 300 °C (relatively sharp X-ray (1 1 0), (1 0 1) and (2 1 1) reflection peaks appear), whereas P-SnO2 particles remain amorphous up to 550 °C. At 1000 °C, the untreated SnO2 continue to crystallize into bulk material, while the crystal growth of P-SnO2 is inhibited: the average SnO2 crystallite size at P:Sn = 0.01 molar ratio remains 27.7 nm. Increasing phosphoric acid concentrations resulted in decreasing sintering effect during calcination. The band gap energy of the investigated particles was determined from UV–vis–DR measurements.