Bonding Geometry and Reactivity of Methoxy and Ethoxy Groups Adsorbed on Powdered TiO₂

Abstract

Thermo-and photoreactivities of methoxy (CH 3 O(a)) and ethoxy groups (C 2 H 5 O(a)) bonded, via the oxygen atom, to one Ti ion (monodentate adsorption form) or to two Ti ions (bidentate adsorption form) on TiO 2 have been studied by Fourier transformed infrared spectroscopy. Regardless of the similar thermal stability for the two adsorption geometries of the adsorbed alkoxy groups, difference in photoreactivity is observed by monitoring the change of their integrated IR absorptions as a function of UV irradiation time. The monodentate photooxidation rate is ∼1.5 times that of bidentate for both methoxy and ethoxy groups. CH 3 O(a) on TiO 2 is photooxidized to H 2 O(a) and HCOO(a) in the presence of O 2 . On the other hand, C 2 H 5 O(a) is photooxidized to H 2 O(a), HCOO(a), and CH 3 COO(a). A Russell-like mechanism is invoked to explain the formation of the reaction products. Possible reaction steps that control the photoreactivity of the monodentate and bidentate adsorption forms are discussed in terms of this mechanism.

Adsorption and photo-oxidation of acetaldehyde on TiO2 and sulfate-modified TiO2: Studies by in situ FTIR spectroscopy and micro-kinetic modeling

“…One of the major intermediates is reported to be formic acid, in the form of adsorbed formate [37], which is in good agreement with the results presented in previous sections. Experiments conducted under ultrahigh vacuum conditions on rutile single crystals show that photo-fragmentation of acetaldehyde leads to cleavage of the C-C bond and release of a CH 3 • radical [11].…”

Improving Reversible Capacities of High-Surface Lithium Insertion Materials – The Case of Amorphous TiO2

“…Weak peaks at 2978, 2938, and 2977 cm −1 can be attributed to CHstretching frequencies of chemisorbed ethoxide ions (Jackson and Parfitt, 1972;Graham et al, 1981). In the E-TiO 2 -130 sample, new peaks centered at 1378, 1446, and 1547 cm −1 are observed, which are attributed to surface carboxylate (COO − ) functionality (Graham et al, 1981;Hussein et al, 1991;Wu et al, 2000). This indicates that the chemisorbed ethanol species undergoes oxidation to form a carboxylate containing species, possibly acetate on heating above 100°C under vacuum.…”

“…This indicates that there is very little or no physically adsorbed ethanol remaining on a sample heated to 80°C under vacuum. The remaining peaks are attributed to co-adsorbed chemisorbed ethanol and H 2 O (Wu et al, 2000). Weak peaks at 2978, 2938, and 2977 cm −1 can be attributed to CHstretching frequencies of chemisorbed ethoxide ions (Jackson and Parfitt, 1972;Graham et al, 1981).…”

“…The H 2 O bending peak was present at 1626 cm −1 for the www.frontiersin.org E-TiO 2 -80 sample and shifted to 1622 cm −1 for the E-TiO 2 -100 and E-TiO 2 -130 samples. The characteristic peaks of ethanol physically adsorbed on a TiO 2 surface at 1000-1200 cm −1 (C-O and C-C stretching) and 1300-1500cm −1 (CH 2 and CH 3 bending) are of extremely low intensity while the O-H bending peak that should have appeared at~1264 cm −1 is absent in the E-TiO 2 -80 samples (Hussein et al, 1991;Wu et al, 2000). This indicates that there is very little or no physically adsorbed ethanol remaining on a sample heated to 80°C under vacuum.…”

Solution Processable Semiconducting TiOx Thin Films for Photovoltaic Applications

“…The slow formation of ice on the IR detector is an artifact to be disregarded. The spectrum through the gas phase at each time was ratioed by the spectrum taken before UV irradiation [72] Figure 6-15 shows the infrared spectral developments when the TiO x films are irradiated during an 8 hours at room temperature under 16 [83,84,85,86] . after UV irradiation, 15 minutes; (b) before irradiation [72] .…”