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| Author(s): |
Carlos Eduardo Bonancêa
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2010-08-27 |
| Examining board members: |
Paola Corio;
Silvia Maria Leite Agostinho;
Henrique de Santana;
Celize Maia Tcacenco;
Flavio Maron Vichi
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| Advisor: | Paola Corio |
| Abstract | |
This work focuses on the study of photocatalytic and photoelectrocatalytic degradation processes of dyes over titanium dioxide. The main approach is based on the use of spectroscopic techniques, with special emphasis to methodologies based on surface-enhanced Raman spectroscopy. Within this context, the mechanisms involved in the photodegradation and photoelectrodegradation of dyes are investigated by the identification of degradation intermediates through vibrational and electronic spectroscopies. In the so-called photoelectrocatalytic processes, the combination of electrochemical and photochemical processes is an interesting and promising approach for the degradation of a wide variety of organic pollutants. The first step in the development of the present work was to build a photo reactor that allowed the analysis of samples through Raman spectroscopy and presented a good efficiency for both photocatalytic and photoelectrocatalytic processes. We then investigated the kinetic behavior of the photo(electro)degradation of dyes in order to verify the dependence upon the electrochemical applied potential, the effect of the supporting electrolyte, and the identification of intermediate products formed during the degradation process. We also analyzed aspects related to the adsorption mechanisms of the dyes on the titanium dioxide surface. Such aspects can be relevant to the understanding and to the development of efficient techniques for the remediation of organic pollutants. Our studies focused mainly on two dyes: the azo dye Janus green and the anthraquinonic dye alizarin red S. The results obtained in the kinetic study of the photoelectrocatalytic processes suggest that the effect of the applied electrochemical potential strongly depends on the chemical nature of the investigated dye. We have observed that the decolorization of Janus green is favored for photoelectrocatalytic process as compared to the photocatalytic degradation. Such behavior was not observed for the anthraquinonic dye alizarin red S. This difference was related to the nature of the specific interactions between each dye and the catalyst surface. Our studies regarding the mechanisms of degradation revealed that the first steps of the photocatalytic and photoelectrocatalytic processes of Janus green followed different routes. The obtained results indicate that the degradation of Janus green in aqueous TiO2 suspension involves changes in the azo bond (N=N), resulting in the formation of an intermediate compound a derived from the phenosafranine structure, whereas for the photoelectrocatalytic process there are evidences of a different mechanism that does not involve the cleavage of the azo bond. (AU) | |