Thesis
Adsorption and destruction of methylene blue and acid orange 7 on Ti0₂
- Creator
- Awarding institution
- University of Strathclyde
- Date of award
- 2011
- Thesis identifier
- T13041
- Qualification Level
- Qualification Name
- Department, School or Faculty
- Abstract
- The observed adsorption of methylene blue, MB⁺, and acid orange 7, AO7⁻, on P-25 titania over a range of pH values, pH 2 - 11 and pH 2 - 8 respectively, is reported and the results fitted to a charge distribution, multisite complexation, i.e. CDMUSIC, model, modified for both monomer and aggregated dye adsorption and (for aggregates) co-adsorption of hydroxyl ions. For the MB⁺ system the model predicts that both the apparent dark Langmuir adsorption constant, KL, and the number of adsorption sites, no, increase with increasing pH, and are negligible below pH 6 - 7. For the AO7- system the model predicts that both, KL, and, no, increase with decreasing pH, and are negligible above pH 6. An adsorption study of AO7- using paste films where, KL, and, no, were experimentally determined generated similar trends to those calculated for P-25 powder. The rate of bleaching of MB⁺, photocatalysed by titania using UV light, increases over the pH range 4 - 11 in much the same way the amount of adsorbed MB⁺, [MB⁺]ads, increases, indicating that the rate-determining step involves direct hole oxidation of adsorbed MB⁺. In contrast, at pH 2, the rate of UVA dye photobleaching appears unduly high but is due to an additional reductive, as well as the usual oxidative, bleaching processes. The initial rate of bleaching of MB⁺ via a visible light-driven, dye sensitised process, measured at different pHs correlates with the associated CD-MUSIC-calculated values of [MB⁺]ads, indicating that only dye molecules that are in direct contact with the surface can undergo photodegradation via a dye-sensitised route. Although AO7⁻ adsorption on P-25 titania and paste films is insignificant above pH 6 and increases almost linearly and markedly below this pH, the measured initial rate of bleaching of AO7⁻, photocatalysed by titania using UV appears to only increase modestly (< factor of 2) over the pH range 2 - 10 studied. In contrast, the rate of bleaching of AO7⁻ via a visible light driven, dye-sensitised process, shows some correlation with the amount of dye adsorbed. Such a correlation follows from the basic assumption that only dye molecules that are in direct contact with the surface can undergo photodegradation via a dye-sensitised route. The relevance of this work to the removal of dyes and testing of the efficiency of photocatalytic films is discussed briefly.
- Resource Type
- DOI
- Date Created
- 2011
- Former identifier
- 941973
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