Ammonia-nitrogen removal from water with gCN-rGO-TiO Z-scheme system via photocatalytic nitrification-denitrification process.

Photocatalytic removal of NH-N is expected to be an alternative to the biological method that accompanied with high energy consumption and secondary pollution. However, NH-N is always oxidized into nitrate and nitrite during the photocatalytic processes, which also need to be removed from the water. Herein, the g-CN/rGO/TiO Z-scheme photocatalytic system was prepared and used for the NH-N removal. The results showed the rate constant of NH-N conversion on it was 0.705 h, 1.7 times as high as that on g-CN/TiO, and most of the NH-N were converted into gaseous products. And the experiment result indicated NH-N and NO in water could enhance the removal of each other. According to the results, the main reaction mechanism is speculated as: ·OH radicals and ·O radicals were generated on TiO and oxidized the NH-N into NO, and the latter was reduced into non-toxic N on the conduction band of g-CN. Finally, NH-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.