Simultaneous photocatalytic degradation of nitrate and oxalic acid over gold promoted titania

The photocatalytic degradation of nitrate in aqueous solution has been examined using different Au/TiO2 photocatalysts with oxalic acid as hole scavenger. Although complete elimination of oxalic acid was possible under conditions employed, complete nitrate removal was not achieved and the extent of conversion showed a dependence on hole scavenger concentration. The reacting stoichiometry was greater than predicted from the corresponding redox equations and suggests competitive reaction between protons and nitrate for conduction band electrons. The different photocatalysts exhibited different temperature sensitivities with the Hombikat supported Au showing the highest apparent activation energy, probably reflecting the stronger adsorption of carbon dioxide as reaction product.

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► Au/TiO2 can be used for the simultaneous photocatalytic degradation of nitrate and oxalic acid from aqueous solution.
► Nitrate is reduced in competition with protons for photogenerated electrons at the Au surface.
► At low reaction temperatures, CO2 generated as a product inhibits the reaction and the strength of adsorption depends on the nature of the titania support.