Ammonia-nitrogen removal from water with gC3N4-rGO-TiO2 Z-scheme system via photocatalytic nitrification-denitrification process

Abstract

Photocatalytic removal of NH3–N is expected to be an alternative to the biological method that accompanied with high energy consumption and secondary pollution. However, NH3–N is always oxidized into nitrate and nitrite during the photocatalytic processes, which also need to be removed from the water. Herein, the g-C3N4/rGO/TiO2 Z-scheme photocatalytic system was prepared and used for the NH3–N removal. The results showed the rate constant of NH3–N conversion on it was 0.705 h−1, 1.7 times as high as that on g-C3N4/TiO2, and most of the NH3–N were converted into gaseous products. And the experiment result indicated NH3–N and NO3− in water could enhance the removal of each other. According to the results, the main reaction mechanism is speculated as: ·OH radicals and ·O2− radicals were generated on TiO2 and oxidized the NH3–N into NO3−, and the latter was reduced into non-toxic N2 on the conduction band of g-C3N4. Finally, NH3–N removal performance for actual coking wastewater was investigated, and the stability of the photocatalyst was tested. This work provides some theoretical basis for the two-step degradation of pollutants by Z-scheme photocatalytic system.