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

Abstract Cu 2 O/TiO 2 (1–10 wt% Cu 2 O) and 2.5% Cu 2 O/TiO 2 -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 Cu 2 O in contact with the TiO 2 . Pure TiO 2 alone was not active for the simultaneous photocatalytic removal of nitrate and oxalic acid under conditions employed, however, photocatalytic activity was observed for TiO 2 and TiO 2 /AC in the presence of Cu 2 O. This may have resulted from suppression of charge recombination via creation of a p - n heterojunction between Cu 2 O and TiO 2 . Within the series, 2.5% Cu 2 O/TiO 2 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 NH 4 + , NO 2 − and N 2 , respectively after 3 h. For the carbon containing photocatalysts, 2.5% Cu 2 O/TiO 2 -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 NH 4 + , NO 2 − and N 2 , respectively. The highest AC loading tested resulted in selectivity to NH 4 + of 21.6 with no NO 2 − detected, together with an improved N 2 selectivity (78.4%) albeit at lower (12.7%) nitrate conversion. Data suggests that Cu 2 O/TiO 2 can be used in the photocatalytic reduction of nitrate and improved selectivity towards N 2 can be attained by influencing factors which control the relative rate of oxalic acid consumption.