Abstract:
The aim of this research is to study the decolorization of two dyes separated and in a
mixture by physico-chemical processes (adsorption, TiO2 and CA-ZnO) and photocatalytic
processes like: TiO2/UV and CA-ZnO/UV. Another study has been led on the degradation
of Monocloramine in homogeneous phase via direct UV photolysis, H2O2/UV and
NaOCl/UV. Treated separately, both dyes have shown an appreciable adsorption on the
two supports and that this process is well represented by an apparent kinetic of order 2.
Besides, Congo Red and Ethyl Violet are described by isotherms of type L and S
respectively and that process is also well represented by the model of Langmuir for Ethyl
Violet and Redlish-Peterson of Congo Red. On the other hand, the photocatalytic system
led via TiO2/UV has been efficient toward both dyes and this process follows an apparent
rate constant of order 1. In another part, this process is well described by the kinetic model
of Langmuir-Hinshelwood and that oxidation process occurs, mainly, in surface. The
inhibition process has been demonstrated by alcohols proving thereby that radicals •OH are
the main oxidation route. The photoproducts issued from the decolorization of the two dyes
have been identified using masse spectroscopy technic. This has permitted to establish a
mechanism of degradation for the two dyes. Same efficiency is obtained using CAZnO/UV process (CA: activated carbon issued from olive cakes). In another side and in the
mixture, the treatment of the two dyes by both systems has, shown that the efficiency
decreases as the concentration of the other added dye increases. Indeed, the addition of the
second substrate slows down the disappearance speed of the other. The kinitics model
remained unchanged for the two processes (2nd order for adsorption and 1 st order for
photocatalysis) The last part treats the degradation of the Monochloramine which occurs
via direct UV photolysis in presence of two lamps: BP (254 nm) and MP (200-600 nm).
The obtained results have been significant. Furthermore, these results have been greatly
enhanced mainly by H2O2/UV. However, for NaOCl/UV system we could mention that the
disappearance rate slows down because of the formation of photoproducts such as: Mono,
Di and Trichloramines. Moreover, the process is well described by an apparent kinetic of
order 1 and those photoproducts identified in H2O2/UV, NaOCl/UV and direct photolysis
systems are nitrates and nitrites
