Photocatalytic Oxidation of Aqueous Ammonia over Ni, Pd, Pt-modified Titania Nanotubes
Date Issued
2008
Date
2008
Author(s)
Hong, Jian-Hao
Abstract
The photocatalytic oxidation technology applied on the removal of ammonia in water has been proved to be an effective and economical treatment process. Therefore in this research we chose titania nanotubes (TNTs) which have one-dimensional structure and ion exchangeability as photocatalyst. Meanwhile nickel, palladium and platinum were chose for modifying its surface. The effects of kind of metal, loading amount on degradation efficiency of ammonia and distribution of products were examined. Finally, we discussed the reaction mechanism. When Pd/TNTs and Pt/TNTs were used as photocatalysts, the degradation efficiency of ammonia increased with the increase of loaded amount, indicating palladium and platinum are applicable to modify titania nanotubes surface. Also, there were no shielding effect occurred in this two case. It can be ascribed to the ion exchangeability of titania nanotubes. When Ni/TNTs were used as photocatalyst, the degradation efficiency of ammonia decreased with the increase of loaded amount. We supposed nickel loaded on titania nanotubes could not suppress the recombination of photo-holes and photo-electrons, but occupied active sites of titania nanotubes instead to result in the decrease of ion exchangeability and adsorption capacity. So inhibiting effect dominated the overall reaction in the case of Ni/TNTs. Pd/TNTs prefer the formation of nitrite and nitrate regarding the distribution of products. Moreover, the loaded amount increased to a certain extent would lead to a few yield of nitrogen gas, yet nitrite and nitrate were still their primary products. Pt/TNTs with high loaded amount have good ion exchangeability and adsorption capacity for ammonia in comparison with the other two metal-loaded titania nanotubes. It may be the reason that Pt/TNTs are highly selective to produce nitrogen gas in the photocatalytic oxidation of ammonia. Take 30% Pt/TNTs for example, its yield of nitrogen gas was up to 87.8%. However, the actual reaction mechanism should be confirmed by analyzing surface property of metal-loaded titania nanotubes.
Subjects
ammonia
metal-loaded
photolysis
titania nanotubes
titanium dioxide
Type
thesis
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