Methanol Photooxidation on Colloidal Anatase TiO2: A Mechanistic Study

We present a study of the methanol photo-oxidation reaction using anatase as a model reaction for colloidal suspensions of photocatalysts. We perform our reactions with suspended anatase nanoparticles of ca. 20 nm diameter. Our model includes photo-oxidation of methanol to formaldehyde under controlled conditions that minimize the content of water and oxygen. We investigate the reaction products from the photooxidation of methanol under an inert atmosphere (Ar) by analyzing the solution phase. Fourier Transform Infrared (FTIR) and Electrospray Ionization (ESI) techniques are employed to detect methanol oxidation products to provide a comprehensive view of the process. We are using modified procedure to detect formaldehyde in a matrix predominantly composed of methanol by detection of a derivative in ESI. Our observations reveal formaldehyde as the predominant photo-oxidation product for UV-illuminated TiO₂ suspension in methanol. Interestingly, our measurements did not show carbon dioxide as a by-product. Conversion of methanol into formaldehyde is consistent with a two electron oxidation mechanism as the main reaction pathway. Here, report our qualitative and quantitative analysis of the possible methanol by products and its implications for the photoelectrochemical measurements of colloidal NPs.