Attachment of TiO₂ Powders to Hollow Glass Microbeads: Activity of the TiO₂-Coated Beads in the Photoassisted Oxidation of Ethanol to Acetaldehyde

Methods for attaching n-TiO₂ particles to hollow microbeads of 80–100 μm average diam and 0.4-0.7 g cm^-3 density are discussed. The floating photoactive microbeads were designed for use in solar-assisted oxidative dissolution of oil films on water. Photoactive beads caused the oxidation of ethanol molecules by dissolved dioxygen to acetaldehyde when exposed to >3 eV incident photons. Particularly photoactive beads were obtained by attaching Degussa P25 TiO₂ particles to aluminosilicate glass microbeads of ~10 μm wall thickness by physisorbing the TiO₂ particles and bonding thermally at 300°C. The TiO₂ thermally bonded to aluminosilicate beads was stable in water and UV light, producing 0.7 mol of acetaldehyde per einstein. Acetaldehyde was produced at an efficiency of 0.5 mol/einstein in the photoassisted oxidation of ethanol on TiO₂-activated borosilicate microbeads, which were made by a process where triethoxysilane was used as binder and ethanol was eliminated in the reaction with surface OH groups. One week of exposure to water caused the borosilicate glass microbeads to dissolve. The aluminosilicate glass was, however, not water-soluble, and the bound TiO₂ particles did not detach from the bead.