Research on the Mechanism of the Photocatalytic Oxidation Reaction of HCH2OH with Nanoscale TiO2

Nanoscale TiO2 was used as the photocatalyst in the oxidization process of methanol, formaldehyde, and formic acid with the 0.1 mol/L aqueous solution respectively. 60 mL of HCH2OH, HCHO and HCOOH with 0.1 mol/L was put in a glass tube reactor respectively with 0.2 g nanoscale TiO2 oxygen flowed into the reactor with the 60 mL/min from the bottom. An Hg lamp with 364 nm as the main wavelength generated UV light at 25~28℃. And the irradiation lasted 10 h. The final product CO2 and the decreasing reactant were detected by the thermal conductivity detector (TCD) and the hydrogen flame ionization detector (FID) of gas chromatograph respectively. From the change of the concentration of the reactant and CO2, the reaction order of the group was zero order respectively. And the Langmuir-Hinshelwood Equation also confirmed the conclusion. Formic acid was the easiest one to be oxidized and methanol was the most difficult one to be oxidized. TiO2 was characterized by TEM, XRD, SSA and XPS respectively. The micro crystal of TiO2 is mainly anatase characterized by X-ray diffraction (XRD) and its average particle size is about 15 nm from the TEM image. The specific surface area of TiO2 has some reduction after irradiation. Formaldehyde and formic acid were found on the surface of TiO2 after the reaction, which showed that formaldehyde and formic acid were the intermediates of methanol during the photocatalytic reaction. The XPS of TiO2 after reactions showed that the mechanism of oxidization methanol should be: methanol was oxidized to be formaldehyde firstly, then through formic acid, until CO2 and H2O appeared.