Photocatalytic Degradation of Tetrachloroethylene in Gas Phase on TiO₂ Films:  A Kinetic Study

Abstract

In this work, the degradation of tetrachloroethylene or perchloroethylene (PCE) in an air stream was studied for different values of PCE feed concentrations, relative humidity levels, and light intensities. The TiO 2 photocatalyst was deposited as a thin film on a borosilicate glass plate by means of a sol-gel technique. The reactor was operated under kinetic control regime. An expression of the intrinsic reaction kinetics was developed. This expression is based on a model of the absorption of radiant energy on the surface of the catalyst, followed by a detailed reaction mechanism based on a reaction scheme that involves Cl • as an active reaction intermediate. Experimental results from a differential photoreactor were used to validate the proposed kinetic model and to determine the kinetic parameters by nonlinear regression of experimental data. The obtained results show: (1) first-order kinetics with respect to the PCE concentration, (2) linear dependence with the photon absorption rate, and (3) site-competitive adsorption between PCE and water, resulting in a dependence of the kinetics on the relative humidity.

Revised Disrupted Langmuir–Adsorption Model of Photocatalysis

“…Recently several research groups [6][7][8][9][10] have used an expression for the rate of the photocatalysed reaction of the form given in eqn (14), where Finally, elsewhere, Passalia et al 10 , in their study of the photocatalysed oxidation of formaldehyde in air over a TiO 2 film, using a Langmuir-type rate expression with the form of eqn (21) to fit their data, report a quantum efficiency of only ca. 1.59%.…”

“…For example, some [7][8][9] have assumed reaction (3) is the key process for the removal of P, so that (3) and (9), it follows that under steady-state conditions:…”

“…[7][8][9] where it is assumed that the only fate of the free holes is to react with P, the use of eqn (13) to provide an explicit dependence of rate upon ρ, as derived using the simple processes (3), (6)- (9), the assumption is flawed.…”

“…Such a process has been proposed previously in another popular mechanism 15 , and so is not without precedent. This additional step may be the oxidation of water or that of a surface saturated with O 2 -, generated via reaction (8).…”

Effect of the radiation flux on the photocatalytic inactivation of spores of Bacillus subtilis

“…Photon absorption in the TiO 2 films is essential to the initial step of photocatalytic reaction sequences, and the kinetics of these processes depends on the local superficial rate of photon absorption (LSRPA or e a,s ) [47]. Since the e a,s values cannot be experimentally measured, a radiation field model was devised, which takes into account the radiation emission from the lamps, its propagation in the irradiation compartment, its attenuation in the borosilicate glass at the top of this compartment, and finally the absorption of photons in the TiO 2 films.…”