Highly reactive ZnFe2O4/TiO2 p-n heterojunction photocatalyst accelerates interfacial charge transfer for boosted photodegradation of ammonia nitrogen

Excessive ammonia nitrogen (NH₄⁺-N) in wastewater worsens the living conditions of aquatic organisms and causes chronic poisoning of humans. In this work, the ZnFe₂O₄/TiO₂ p-n heterojunction photocatalyst was prepared to remove NH₄⁺-N. ZT-10 (the molar ratio of ZnFe₂O₄ to TiO₂ was 1:10) removed 98.52 % of NH₄⁺-N (50 mg/L) at pH 10 in 90 min with a stabilized crystal structure maintained over four cycles. The experiment results demonstrated universal adaptability to various representative contaminants in actual waters. The meaningful roles of superoxide radical (∙O₂⁻), hydroxyl radical (∙OH), and holes (h⁺) in NH₄⁺-N photoreduction were confirmed by radical trapping experiments. The photocatalytic mechanism revealed that the improvement of photodegradation activity was primarily due to the internal electric field (IEF) generated at the p-n heterojunction interface, which facilitated the precise migration and aggregation of photoinduced electrons (e^-) and holes to space reaction sites, realizing the highly efficient surface catalysis of ZnFe₂O₄/TiO₂ photocatalysts.