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

X-ray 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.