Selective reduction of NO3to N2 using a highly stable Cu0/ Cu2O-PANI-CNTs as a photocatalyst at neutral pH

The selective photoreduction of nitrate (NO3 ) to nitrogen (N2) has emerged as an energy-efficient and environmentally friendly NO3 �removal route under mild conditions. However, NO3 �photoreduction often suffers low NO3 �removal efficiency in the absence of hole scavengers at neutral pH, the generation of undesired side products (nitrite (NO2), ammonium (NH4+), nitrogen oxides (NOx), etc.) and poor photocatalyst stability. In this study, a novel copper/copper(I) oxide-polyaniline-carbon nanotubes (Cu0/Cu2O-PANI-CNTs) photocatalyst was prepared through a combination of in situ polymerization and liquid phase reduction processes and used to reduce NO3 � to N2. In the Cu0/Cu2O-PANI-CNTs/hv system, NO3 � was reduced to NO2 � by photogenerated electrons (ecb �) on the surface of Cu0/Cu2O, and the generated NO2  was further reduced to N2 by PANI, resulting in high N2 selectivity. -NH- in PANI acted as photogenerated hole (hvb+) capture centres, leading to NO3 � photo-reduction without additional hole scavengers. Given the interaction between Cu0, ecb � and PANI, Cu0/Cu2O-PANI-CNTs show excellent repeatability. A 100% NO3 � removal efficiency and 100 % N2 selectivity could be achieved by the Cu0/Cu2O-PANI-CNTs/hv system at neutral pH. With river water, secondary effluent and the fourth reuse of the catalyst, the NO3 � removal efficiencies were as high as 93.0%, 91.2% and 84.4%, respectively, with 100 % N2 selectivity.

Automated summary

A novel photocatalyst Cu0/Cu2O-PANI-CNTs was developed for efficient reduction of nitrate to nitrogen under neutral pH, achieving 100% removal efficiency of nitrate and high N2 selectivity. The interaction between Cu0, ecb, and PANI contributes to the excellent repeatability of the catalyst.