Adsorption and Solar Light Decomposition of Acetone on Anatase TiO₂ and Niobium Doped TiO₂ Thin Films

Abstract

Adsorption and solar light decomposition of acetone was studied on nanostructured anatase TiO2 and Nb-doped TiO2 films made by sol-gel methods (10 and 20 mol % NbO2.5). A detailed characterization of the film materials show that films contain only nanoparticles with the anatase modification with pentavalent Nb oxide dissolved into the anatase structure, which is interpreted as formation of substituted Nb=O clusters in the anatase lattice. The Nb-doped films displayed a slight yellow color and an enhanced the visible light absorption with a red-shift of the optical absorption edge from 394 nm for the pure TiO2 film to 411 nm for 20 mol % NbO2.5. In-situ Fourier transform infrared (FTIR) transmission spectroscopy shows that acetone adsorbs associatively with eta1-coordination to the surface cations on all films. On Nb-doped TiO2 films, the carbonyl bonding to the surface is stabilized, which is evidenced by a lowering of the nu(C=O) frequency by about 20 cm(-1) to 1672 cm(-1). Upon solar light illumination acetone is readily decomposed on TiO2, and stable surface coordinated intermediates are formed. The decomposition rate is an order of magnitude smaller on the Nb-doped films despite an enhanced visible light absorption in these materials. The quantum yield is determined to be 0.053, 0.004 and 0.002 for the pure, 10% Nb:TiO2, and 20%Nb:TiO2, respectively. Using an interplay between FTIR and DFT calculations we show that the key surface intermediates are bidentate bridged formate and carbonate, and H-bonded bicarbonate, respectively, whose concentration on the surface can be correlated with their heats of formation and bond strength to coordinatively unsaturated surface Ti and Nb atoms at the surface. The oxidation rate of these intermediates is substantially slower than the initial acetone decomposition rate, and limits the total oxidation rate at t>7 min on TiO2, while no decrease of the rate is observed on the Nb-doped films. The rate of degradation of key surface intermediates is different on pure TiO2 and Nb-doped TiO2, but cannot explain the overall lower total oxidation rate for the Nb-doped films. Instead the inferior photocatalytic activity in Nb-doped TiO2 is attributed to an enhanced electron-hole pair recombination rate due to Nb=O cluster and cation vacancy formation.

Acetaldehyde adsorption and condensation on anatase TiO2: Influence of acetaldehyde dimerization

“…Acetaldehyde adsorption was investigated by in situ Fourier-transform infrared (FTIR) spectroscopy, using a vacuum-pumped FTIR spectrometer (Bruker IFS66v/S, Ettlingen, Germany) equipped with a modified IR transmission reaction cell, as described elsewhere and schematically depicted in Figure 3 [32,33]. The IR reaction cell was connected to a home-made gas flow system with a set of computer-controlled mass flow regulators.…”

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

“…All measurements were carried out in a custommodified transmission reaction gas cell, which allows for in situ reaction studies at controlled sample temperatures with simultaneous FTIR spectroscopy, gas dosing and light illumination in a controlled gas atmosphere as a function of reaction time, as described elsewhere [25]. …”

Characterisation, phase stability and surface chemical properties of photocatalytic active Zr and Y co-doped anatase TiO2 nanoparticles

“…The liquid was heated to 303 K and introduced into a 100 ml min -1 synthetic air flow through a 5.5 mm diameter diffusion tube via a home-built gas-generator [29]. The formic acid dose rate was determined as 67 µg min -1 .…”

“…The reported optimal metal dopant concentration for anatase TiO 2 in photocatalysis applications generally falls between 1% and 10% [21,22,28]. Quite generally the route for cation substitution in TiO 2 appears to be a delicate balance between electronic-and structural modification, which may result in either band gap shifts and phase stabilization or undesirable local band gap states and lattice defects [13,29]. These defects act as recombination centres for hot electrons and cause collapse of structure and phase segregation (as demonstrated here at high dopant concentrations).…”