Photocatalytic Oxidation of Ammonia via an Activated Carbon-Nickel Ferrite Hybrid Catalyst under Visible Light Irradiation

The nickel atoms in a metal ferrite lattice inhibit photocatalytic activity with hydrogen peroxide. However, activated carbon bonded on nickel ferrite (AC-NiFe2O4) induces photocatalytic activity of nickel ferrite with hydrogen peroxide, enabling photo-Fenton catalytic oxidation of ammonia under visible-light irradiation in the presence of hydrogen peroxide. The AC-NiFe2O4 catalyst was characterized using X-ray diffraction, transmission electron microscopy, Fourier-transform infrared spectroscopy, and a vibrating sample magnetometer at room temperature. The photocatalytic tests showed that the ammonia degradation efficiency approached 91.0% in the presence of the AC-NiFe2O4 catalyst, whereas the efficiency was only 24.0% without the catalyst under similar conditions over 10 h. Another test showed that the single NiFe2O4 catalyst achieved a degradation efficiency of only 30.0% under similar conditions, indicating that activated carbon can accelerate the rate of ammonia oxidation. Exploration of the oxidation mechanism showed that the oxidation pathway involves an HONH2 intermediate, forming nitrite ions. Kinetic studies showed that the oxidation of ammonia follows a pseudo-first order kinetic law, with a rate constant of 3.538x10(-3) min(-1). The catalyst was used in eight runs, and shown to be stable, recoverable, separable, and reusable, suggesting that it has potential applications in the disposal of ammonia.