Kinetics of heterogeneous photocatalytic decomposition of 2,4-dichlorophenoxyacetic acid over titanium dioxide and zinc oxide in aqueous solution
✍ Scribed by Djebbar, Kamel; Sehili, Tahar
- Publisher
- John Wiley and Sons
- Year
- 1998
- Tongue
- English
- Weight
- 263 KB
- Volume
- 54
- Category
- Article
- ISSN
- 1526-498X
No coin nor oath required. For personal study only.
✦ Synopsis
The photocatalytic transformation of 2,4-D in aqueous solution containing a suspension of titanium dioxide or zinc oxide leads to the formation of intermediates which are totally mineralised to carbon dioxide and hydrogen chloride (2,4-dichlorophenol and chlorohydroquinone are the major intermediates). The products at the initial stage of the reaction were 2,4-dichlorophenol (2,4-DCP), chlorohydroquinone, 4-chloropyrocatechol, 2,4-dichloropyrocatechol and 1,4-chlorobenzoquinone. The initial rate of photodegradation was studied as a function of the initial concentration of reactants by the linearised form of the LangmuirÈHinshelwood equation, by which rate constants k and equilibrium adsorption constants K were evaluated. These constants were calculated at di †erent temperatures between 25 and 60¡C. The photodegradation rate increased with increase of pH. The photocatalytic transformation of 2,4-D over titanium dioxide or zinc oxide in solution containing hydrogen peroxide was studied. The latter accelerated the reaction rate of 2,4-D signiÐcantly.
It was found that chloride or bicarbonate ions slowed down the photodegradation rate of 2,4-D by scavenging hydroxyl radicals. Partial inhibition by ethanol is attributed to scavenging of the OH radicals involved in the Ðrst step of the reaction.