Photocatalytic reduction of nitrate ions in water over metal-modified TiO2

TiO2 and TiO2 doped with Zn2+, Cu2+ and Cr3+ were used as photocatalysts to reduce nitrate and to oxidize formic acid. The metals were added to the TiO2 support by photodeposition and this method did not affect the form of the original crystalline semiconductor (100% anatase). The data obtained in the structural characterization and in the nitrate photoreduction experiments showed that 1.0 g L−1 4.4% Zn–TiO2 photocatalyst had the highest photocatalytic activity and selectivity toward nitrogen. The selectivity and conversion were higher than 95 and 91%, respectively, using a CHOOH:nitrate molar ratio of 16:1, which is twice the theoretical demand in the absence of dissolved oxygen.

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► TiO2 and M–TiO2 (M = Zn2+, Cu2+ or Cr3+) were used to photoreduce nitrate.
► Characterization and photoreduction data showed Zn–TiO2 as the best catalyst.
► Selectivity and conversion reached values higher than 95 and 91%, respectively.