Photocatalytic Simultaneous Removal of Nitrite and Ammonia via a Zinc Ferrite/Activated Carbon Hybrid Catalyst under UV-Visible Irradiation

Nitrite and ammonia often coexist in waters. Thus, it is very significant to develop a photocatalytic process for the simultaneous removal of nitrite and ammonia. Herein, zinc ferrite/activated carbon (ZnFe2O4/AC) was synthesized and characterized by X-ray diffraction spectroscopy, transmission electron microscopy, Raman spectroscopy, and ultraviolet- visible diffuse reflectance spectroscopy. The valence band level of ZnFe2O4 was measured by X-ray photoelectron spectroscopy-valence band spectroscopy, and first-principles calculation was performed to confirm the band structure of ZnFe2O4 , The as-synthesized ZnFe2O4/AC species functioned as a photocatalyst to simultaneously remove nitrite and ammonia under anaerobic conditions upon UV-visible light irradiation at the first stage. The results indicated that an average removal ratio of 92.7% with +/- 0.2% error for nitrite degradation for three runs was achieved in 50.0 mg/L nitrite + 100.0 mg/L ammonia solution with pH 9.5 under anaerobic conditions for 3 h at this stage; simultaneously, the removal ratio of 64.0% with +/- 0.2% error for ammonia was also achieved. At the second stage, oxygen gas was bubbled in the reactor to photocatalytically eliminate residual ammonia under aerobic conditions upon continuous irradiation. The results demonstrated that the removal ratios for nitrite, ammonia, and total nitrogen reached to 92.0, 90.0, and 90.2% at 12th hour, respectively, and the product released during photocatalysis is N-2 gas, detected by gas chromatography, fulfilling the simultaneous removal of nitrite and ammonia. The reaction mechanism was exploited.