Simultaneous photocatalytic removal of nitrate and oxalic acid over Cu2O/TiO2 and Cu2O/TiO2-AC composites

•Copper promoted the photocatalytic performance of titania for nitrate reduction.•XPS, TPR and FTIR confirm that copper was present as Cu2O.•Addition of activated carbon reduced reaction rates but improved selectivity to N2.•System is stable with no detected loss of copper species.

Cu2O/TiO2 (1-10 wt% Cu2O) and 2.5% Cu2O/TiO2-AC (2.5-20 wt% AC) photocatalyst composites were synthesised by an ethanol reduction method. The materials were characterised by a number of techniques which confirmed the presence of Cu2O in contact with the TiO2. Pure TiO2 alone was not active for the simultaneous photocatalytic removal of nitrate and oxalic acid under conditions employed, however, photocatalytic activity was observed for TiO2 and TiO2/AC in the presence of Cu2O. This may have resulted from suppression of charge recombination via creation of a p-n heterojunction between Cu2O and TiO2. Within the series, 2.5% Cu2O/TiO2 exhibited the best photocatalytic performance with 57.6 and 99.8% removal of nitrate and oxalic acid, respectively, with selectivities of 45.7, 12.4 and 41.9% to NH4+, NO2− and N2, respectively after 3 h. For the carbon containing photocatalysts, 2.5% Cu2O/TiO2-2·5AC displayed the highest activity with 42.5 and 96.6% removal of nitrate and oxalic acid, respectively, with 32.7, 11.6 and 55.7% selectivities to NH4+, NO2− and N2, respectively. The highest AC loading tested resulted in selectivity to NH4+ of 21.6 with no NO2− detected, together with an improved N2 selectivity (78.4%) albeit at lower (12.7%) nitrate conversion. Data suggests that Cu2O/TiO2 can be used in the photocatalytic reduction of nitrate and improved selectivity towards N2 can be attained by influencing factors which control the relative rate of oxalic acid consumption.

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