Enhanced photocatalytic performance of NiFe₂O₄/ZnIn₂S₄ p-n heterojunction for efficient degradation of tetracycline

The persistent release of tetracycline into the environment significantly endangers both ecosystems and human health. Zinc indium sulfide (ZnIn₂S₄) capable to degrade tetracycline pollutants under visible light irradiation has attracted extensive attentions and great effort has been devoted to augment its catalytic efficacy. In this work, we synthesized a p-n heterojunction, NiFe₂O₄/ZnIn₂S₄, to enhance the carrier migration rate and explained the intrinsic mechanism by density functional theory. When the heterojunction was formed, carriers traversed from the n-type NiFe₂O₄ to the p-type ZnIn₂S₄, instigating the emergence of a built-in electric field to facilitate the separation of carriers. 2 %-NiFe₂O₄/ZnIn₂S₄ exhibited excellent photocatalytic efficiency in tetracycline (TC) degradation and total organic carbon (TOC) removal. Compared to pure ZnIn₂S₄ and NiFe₂O₄, the TC degradation rates of 2 %-NiFe₂O₄/ZnIn₂S₄ were 2.0 times and 16.9 times higher, respectively. Additionally, 2 %-NiFe₂O₄/ZnIn₂S₄ had a saturation magnetization intensity of 3.05 emu/g, allowing for rapid recovery of the catalyst under a magnetic field. Superoxide radicals ([rad]O₂⁻) and holes (h⁺) were the primary active species driving the degradation process. Furthermore, potential reaction pathways of tetracycline in this photocatalytic process were determined and bioconcentration factor and developmental toxicity of the intermediate products were accessed. This work held great potentials for wastewater treatment and provided a pathway for the development of magnetic recyclable photocatalysts.