STUDY ON THE IMMOBILIZED TITANIUM DIOXIDE CATALYST OF
CHLORTOLURON HERBICIDE
Laoufi N. A., Bentahar F.
Laboratoire des Phénomènes de Transfert. Département de Génie Chimique et de Cryogénie.
U.S.T.H.B. Faculté de Génie Mécanique et de Génie des Procédés Bp 32, El Alia, 16111 Bab
Ezzouar. Algiers. Algeria
nadialaoufi@gmail.com, fatihabentahar@yahoo.fr
abstract
The advanced oxidation processes (AOPs) represent a promising alternative technology for
destruction of pesticides contained in wastewater. The most important of these AOPs is the
photocatalysis in presence of TiO2 particles. It is based on the formation of electrons and wholes
due to the excitation of the semi-conductors particles by UV irradiation. These charge carriers
either recombine or move to its surface where they react with adsorbed molecules.
In the present work, the study of photodegradation of chlorotoluron herbicide has been done in a
photoreactor containing immobilized layers of TiO2 catalyst. The advantage of this type of
photoreactor comparing to the slurries, is that neither separation nor filtration are needed. For
immobilization of TiO2 particles, we used glass sheet as support and four layers have been
deposited and dried at 475 ºC. Photocatalytic degradation of herbicide chlorotoluron in aqueous
thin film flowing over illuminated particulate layers of titanium dioxide in batch-mode plate
photoreactor was investigated using titanium dioxide P25 (Degussa) under 18W high pressure
mercury lamp irradiation. The effect of the distance of UV irradiation tube from glass plate, the
flowrate, UV light irradiation time, solution pH and inorganic ions such as Ca2+ were studied and
optimized values were obtained.
Results showed that this process with optimal operational parameters may lead to complete
degradation of chlorotoluron. Thus, the photocatalytic degradation efficiency of chlortoluron was
increased by decreasing the herbicide amount, the oxidation was complete after 7, best result for
chlortoluron degradation was obtained in neutral solution (i.e. pH range from 6 to 6,5) whatever,
acidic and alkaline pH were favored. The effect of UV-light irradiation time on the photocatalytic
degradation of the herbicide showed that it was degraded at irradiation time of 7 hours and it is
also evident that the percentage of photodegradation increases with increasing irradiation time.
The position of 4,5 cm is the best one to obtain more than 98 % of degradation. By increasing the
Ca2+ concentration, the photocatalytic degradation of chlortoluron was decreased.
The rate constants for the different parameters were evaluated. Kinetic studies showed that
titanium dioxide photocatalyst P25 was very active in chlortoluron degradation; we observed that
70 % of pollutant was degraded after 7 hours of UV irradiation; furthermore, we observed that
chlortoluron degradation was more effective under acidic conditions (near pH = 6) and free pH.
The kinetics were described by the Langmuir-Hinshelwood (L-H) kinetic model. An overall
pseudo-first order kinetic constant has been calculated for chlortoluron conversion and values
obtained in acidic pH are higher than those calculated for basic pH media.
In this work, we remarked that we used the prepared catalyst during 600 hours without obvious
decrease in catalytic activity.