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We synthesized NiFe2O4/carbon composite nanoparticles through a straightforward co-precipitation method, and incorporated these particles into porous polyethersulfone (PES) membranes via casting solution blending and film casting cum phase separation. The resulting photocatalytic membranes were used for the oxidative degradation of tetracycline (TC) in flow–through. We could demonstrate a higher catalytic activity in acidic conditions, a photocatalytic enhancement under visible light irradiation, and a 3x higher TC removal by persulfate (PS) in comparison to H2O2. Moreover, we observed the leaching of all Ni from the incorporated NiFe2O4 after using a membrane for 30 h in the flow-through degradation of 5 ppm TC with PS. This was accompanied by a loss of the total organic carbon removal activity, suggesting that Ni plays an important role as mineralization promoter. However, no Fe leaching occurred and the in situ formed FexOy retained the high TC conversion activity of NiFe2O4 after 30 h contact to acidic conditions, highlighting an exceptional long-term stability. We further identified that substrate desorption, catalyst complexation, and metal leaching can be facilitated by the presence of radical scavengers. This significantly contributed to their inhibitory effects, illustrating that an altered substrate-catalyst interaction may frequently be overlooked during the detection of radical species.
Leichtweis et al. (Tue,) studied this question.