One-step synthesis of noble metal–titanium dioxide nanocomposites in a flame aerosol reactor

摘要

Noble metal–titanium dioxide nanocomposites (Pt/TiO2, Pd/TiO2 and bimetallic Pt-Pd/TiO2) were synthesized in one step using a flame aerosol reactor (FLAR). The specific surface area, crystal phase and morphology of the nanocomposites were controlled by adjusting the reactant concentration and the temperature–time history in the reactor. The synthesized nanomaterials were characterized using transmission electron microscopy (TEM), electron diffraction, X-ray diffraction (XRD) and nitrogen adsorption (BET). Nanocomposites with 0.5–3.0% (wt%) noble metal loading were synthesized. Nanosized noble metal particles (2–4 nm) were dispersed on the 30–40 nm TiO2 surface with an overall specific surface area in the range of 40–60 m2/g. The specific surface area increased with increasing noble metal loading. For the chosen flame conditions, a mixture of anatase and rutile phase was obtained without noble metal addition. On incorporation of the noble metal, the formation of the rutile phase of titanium dioxide was suppressed. The synthesized nanocomposites were tested for the photocatalytic oxidation of methyl orange dye in an aqueous phase. Platinum particles dispersed on the TiO2 surface enhanced the photocatalytic activity compared to pristine TiO2. The existence of an optimum platinum loading for the highest photocatalytic activity was confirmed, and was approximately 0.5–1.0% Pt. Palladium addition had a detrimental effect on the photocatalytic activity of titanium dioxide. Bimetallic noble metal catalysts (Pt-Pd/TiO2) showed enhanced photocatalytic activity compared to pristine titanium dioxide, but lower than platinum (only)–titanium dioxide nanocomposites.