Solvothermal synthesis and photocatalytic application of porous Au/TiO2 nanocomposites

Porous titania networks embedded with gold nanoparticles have been synthesized and tested in photocatalytic applications. A solvothermal method was adopted for the in situ reduction of the gold precursor to gold nanoparticles within a preformed TiO2 matrix synthesized by combining a templating technique and sol–gel chemistry. The titania materials were crystalline with anatase crystals of 13 ± 2 nm in diameter; XRD peaks of metallic gold were observed when the gold content was over 1 wt% (gold crystal diameters of 18–25 nm for 1–8 wt% Au). The variation in gold particle size for different gold content was observed by transmission electron microscopy, which also confirmed highly porous structures of the final Au/TiO2 composites. The actual gold content generally increased with the Au content used during synthesis; was enhanced when the pH of the gold precursor solution increased from 2 to 10; and remained relatively constant with changes in the solvothermal temperature (120–180 °C). UV-Visible diffuse reflectance spectra of the Au/TiO2 showed strong absorption at ∼550 nm due to the successful addition of gold nanoparticles to the titania. The number of surface hydroxyl groups was influenced by solvothermal treatment temperature, synthesis pH and gold content. The addition of gold nanoparticles to the TiO2 significantly suppressed recombination of the photon-induced electron–hole pairs. The photocatalytic efficiency of the composites was assessed by monitoring the photocatalytic degradation of methylene blue in aqueous solution; maximum efficiency was more than double that of the pure TiO2 control when using 2.0 to 4.0 wt% gold solutions at pH 7 and optimized solvothermal conditions of 180 °C for 14 h. The photocatalytic efficiency was significantly altered with the addition of gold and was greatly influenced by the anatase crystal size and relative XRD peak intensity, the gold content, and the capability of the material to decrease photon-induced electron–hole recombination.