Effects of phosphate modification on the structure and surface properties of ordered mesoporous SnO2

A series of ordered mesoporous phosphate-modified SnO ₂ samples (mP-SnO ₂) with varying P content were synthesized in a template-assisted sol–gel process, with the use of hexadecylpyridinium chloride as structure-directing agent. In order to enhance the thermal stability, sol–gel derived SnO ₂ × nH ₂O was treated with H ₃PO ₄ at room temperature. The bulk and surface compositions of mP-SnO ₂ were studied by means of inductively coupled plasma atomic emission spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy, and X-ray photoelectron spectroscopy. Elemental analysis revealed that the mesostructured hybrid network adsorbed a significant amount of phosphate during the H ₃PO ₄ treatment. The measured atomic ratio P:Sn of the powder samples varied between 0.08 and 0.45. After calcination at 600 °C, both the unmodified mesoporous SnO ₂ (mSnO ₂) and mP-SnO ₂ with low P content (P:Sn < 0.275) exhibited a disordered porous structure. However, samples with higher phosphate contents preserved their ordered structures even after calcination at 600 °C. The specific surface areas of these mP-SnO ₂ samples were in the range 310–350 m ² g ⁻¹, whereas that of the mSnO ₂ was 30 m ² g ⁻¹.