In Situ FTIR Study Of Photocatalytic Degradation Of Gaseous Ethanol On Nano-MO₂ (M-Ti, Si)

Nano photocatalytic materials as catalysts can degrade thousands of chemical toxin substances. This method is a promising way of environmental protection for its mild reacting condition and innocuous to ecosystem and without secondary pollution to environment. Especially, a photocatalyst material has been a widely discussed topic in recent years and increasingly applied to air purification. Fourier transform infrared spectroscopy (FTIR) has constituted a powerful tool in studies concerning the nature of surface complexes at solid-gas interface and has also been employed for in situ surface studies. In this way, a FTIR spectroscopy system is designed as an in situ probe for photocatalytic decomposition of gaseous ethanol over MO₂ (M=Ti, Si).On one hand, TiO₂ nanotube samples are prepared via a hydrothermal treatment of TiO₂ powders (P25) in a 10 M NaOH solution at 100℃ for 25.5 h. Subsequently, gas-phase ethanol photocatalytic oxidation on the as-prepared samples has been studied by the FTIR in situ method under different conditions. Obtained results show that proper calcination temperatures (500℃) could promote the photocatalytic activity for the gaseous ethanol oxidation reaction at room temperature under UV irradiation, In addition, it is observed that the process of oxidation of ethanol is effective for the low initial ethanol concentration. There seems to be a correlation between the accumulation of carbon deposits and catalyst deactivation. And other factors that influence the rate of photocatalysis degradation for gaseous ethanol over the TiO₂ nanotube samples are also investigated.On the other hand, since TiO₂ has been intensively studied and widely applied to environmetal purification, this study focuses on another type of heterogeneous photocatalyst, SiO₂. In particular, the adsorption and reaction of gaseous ethanol on a fumed silica are investigated under photoirradiation by in situ FTIR spectroscopy. It is clearly found that the silica increases its photocatalytic activity for the dehydrogenation of ethanol to acetaldehyde under UV irradiation even at room temperature. Formyl species is observed in the gas phase most likely due to combination of H and CO desorbing from the support under photoirradiation during the surface decomposition of ethanol, which provides evidence that the carbon-carbon bond in ethanol may be dissociated to form CO on the surface. Further reaction of CO with oxygen from the silica surface leads to the production of CO₂ in an air environment. In particular, we state that oxygen exchange between free gas-phase O₂molecule and interstitial oxygen atoms in the silica network may take place during the process of the reaction, with the presence of a triplet to singlet ground state transition.The IR bands at 883 and 908 cm'1 are suggested to be attributed to two sorts of radical sites, NBOHC (=Si-O) and POR (=Si-0-O), respectively. The presence of NBOHC and POR on the sample surface, in turn, account for the photocatalytic activities observed in this study toward dehydrogenation and oxidation, respectively.Through the present investigation, the in situ FTIR has been established for the research of adsorption-photocatalysis.