One-Step Synthesis of Sulfate-Modified Titania Nanoparticles with Surface Acidic and Sustained Photocatalytic Properties via Solid-State Thermolysis of Titanyl Sulfate

Titania nanoparticles surface-functionalized with sulfate were prepared by thermal degradation of titanyl sulfate. At 600 degrees C pure anatase phase is obtained. X-ray photoelectron spectroscopy (XPS) showed 1.4 at.% sulfur in the +6 oxidation state. At 700 degrees C anatase was still present, which is attributed to the presence of small amounts of stabilizing sulfate groups only detectable by high-resolution XPS, segregating to the nanoparticle interfaces. Adsorption and photocatalytic degradation of acetaldehyde reactions were studied by in situ diffuse reflectance Fourier transform spectroscopy and 2D correlation spectroscopy, and compared with pure anatase nanoparticles. Aldol condensation of acetaldehyde and subsequent accumulation of crotonaldehyde was lower on sulfate-modified titania. Butanoate was identified as an intermediate, which forms after dimerization and aldol condensation. Much more carboxylates and carbonates accumulated on pure anatase catalysts compared with sulfate-modified anatase during photocatalysis. It is conjectured that surface acidic photocatalysts could be beneficial for achieving sustained activity for photodegradation of organic pollutants.